The Invisibility of the Sea

In 2017, the Cabot Institute and the Brigstow Institute hosted a variety of workshops on ‘Perspectives from the Sea’, bringing together scientists, engineers and humanities scholars to share personal reflections, their experiences and methods, and their understanding of the sea.  This was so inspiring that we commissioned artist Rodney Harris to further explore these topics, The Invisibility of the Sea, displayed in the Earth Sciences Gallery.  He produced a fantastic variety of pieces, including the one below.

As part of this, we assembled a working paper of perspectives.  The following are two of my contributions.

I find Rod’s artwork to be profoundly moving, perhaps arising from my own complicated journey from the landlocked US state of Ohio to living on an island and devoting my life to understanding the nature and history of our mysterious oceans.  I grew up on a dairy farm, about as far from the sea as you can get, physically and culturally. In particular, the daily and inflexible demands of dairy farming meant that vacations were rare, and I only saw the sea once or twice growing up. In those early days, Lake Erie was my analogue for the Invisibility of the Sea.  I grew up with its history, from famous Revolutionary War battles to battles with pollution; I fished on Lake Erie with my Aunt and Uncle, even though we were cautioned not to eat too much of the perch and walleye that we caught; to pay my way through University, I studied invasive zebra mussels; and my family and friends went to ‘North Coast’ beaches for picnics and parties. But it was not the Sea. There was no vastness; there was no depth.

 

Ironically, my first profound relationship with the Sea came from going further inland, during my geology degree and PhD training and research. It was not the Sea of our modern world.  It was the sea explored and imagined via the sedimentary rocks deposited in ancient oceans tens of millions of years ago. I studied and still study times of mass extinction, dramatic climate change or periods of profound chemical transformation, all manifested through the fossils – especially molecular fossils – produced in those ancient seas, buried in sediments and preserved in magnificent sequences of sedimentary rocks. Sometimes it seems that my work borders on the mythical as I study these ancient, secret seas that no longer exist. I study ammonites, belemnites and pleisiosaurs, cyanobacteria and thaumarchaeota, in ancient oceans such as the Western Interior Seaway, the Permian Basin, the Tethyan and Panthalassa Oceans, at locations such as Tarfaya, Zumaia and Lomonosov Ridge, at Kheu River and Waipara and Meishan.

 

This sense of mystery arises from time and space – the vastness of the ocean, its mercurial nature and its inscrutable depths, but also the billions of years of Earth history it records. It is why it is home to so many myths.  Rod’s work captures the mystery and superstition with which ancient seafarers regarded the ocean – a place of ritual and norms, of sea serpents, mermaids and mythical beasts, of Odysseys. All of his ‘Balmoral Barometers’, especially but not only the Barometer of the Superstition of the Sea, capture our fraught relationships with this vast and seemingly unknowable body. And the vastness of the oceans and their invisible depths allow such myths to persist. We no longer believe that dinosaurs will be found in an isolated corner of the Amazon, but some still cling to beliefs that we will discover a buried Atlantis or prehistoric mega-sharks, 20-m long Miocene Megaladons still preying on giant squid or baleen whales in the great dark deep of the ocean.

 

This is the Invisibility that has always fascinated me.  I have now been on research expeditions across our Seas and dived via submersible to the bottom of the Mediterranean. I am fascinated by both the surface and deep ocean and the different relationships we have with each. When we think of the ‘Sea’, I think we emotionally connect differently to its volatile surface and its infinite, mysterious depths. The surface is what we experience in trade, slavery, migration, travel, holiday snorkelling and exploration; this is what provides escape from persecution, threatens us with sea level rise, is the source of most of our fish, where sailors lose their lives; it is the network of ocean roads that support our global economy and sustained a global slave trade. In contrast, the deep ocean is vast, mysterious and constant – a home to krakens, hidden prehistoric sharks and lost cities but also limitless resources and room for waste.

 

More recently, however, it has become clear to me that for most of us all of the ocean remains invisible.  We do not see the plastic or toxins in the ocean – plastics that now form islands of trash and can be found in every part of the ocean.  We do not see the incremental but biologically devastating increases in temperature and decrease in pH due to increasing carbon dioxide in our atmosphere.  We can measure those.  But as a society we do not see them. The sea is invisible. Perhaps even more invisible now, despite our many scientific advances, than in the past when it was so intimately connected to our daily lives. This is where mystery meets apathy. Our assumptions, our view of the sea, are informed from earliest history, when only tens of millions of humans lived on the planet and our impact was small and could be absorbed, when a deep ocean could be a home to sea serpents and krakens and be a repository for our rubbish. On my first research expedition we discovered, half-buried in 2-km deep mud just north of Crete, a magnificent 2-m tall amphora but also plastic bottles: similar waste from separate millennia. Ingrained in us is the belief that the ocean is a great constant, impervious to human action.

 

It is not.  Those sedimentary records tell us otherwise. Its circulation can change; its chemistry can change; its biology can change.  It is evident in Rod’s Brent Knoll, each colour made from a different bit of the sea’s sedimentary history and each representing a profound change in those ancient oceans. Although the oceans have been a constant during humanity’s brief domination of the planet, they can change. And now they are changing at a pace perhaps unprecedented in the history of our planet. Because of us.

 

We have allowed that to happen not because the sea is ‘invisible’ but because we have chosen not to see. But we are no longer allowed the privilege of blindness. Ocean warming is devastating our coral reefs, plummeting fish stocks are causing us to raid the ocean depths to feed our growing population, toxic blooms of algae kill fish and blight our beaches, and plastic… is everywhere. Much of the sea was invisible to our ancestors.  We do not have that excuse.

 

The Invisible and Inconstant Deep Sea

Today, the deep sea is a dark and empty world. It is a world of animals and Bacteria and Archaea – and relatively few of those. Unlike almost every other ecosystem on our planet, it is bereft of light and therefore bereft of plants.  The animals of the deep sea are still almost entirely dependent on photosynthetic energy, but it is energy generated kilometres above in the thin photic zone. Beneath this, both animals and bacteria largely live off the scraps of organic matter energy that somehow escape the vibrant recycling of the surface world and sink to the twilight realm below. In this energy-starved world, the animals live solitary lives in emptiness, darkness and mystery. Exploring the deep sea via submersible is a humbling and quiet experience.  The seafloor rolls on and on and on, with only the occasional shell or amphipod or small fish providing any evidence for life.

And yet life is there.  Vast communities of krill thrive on the slowly sinking marine snow.  Sperm whales dive deep into the ocean and emerge with the scars of fierce battles with giant squid on which they feed.  And when one of those great creatures dies and its carcass plummets to the seafloor, within hours it is set upon by sharks and fish, ravenous and emerging from the darkness for the unexpected feast. Within days the carcass is stripped to the bones but even then new colonizing animals arrive and thrive. Relying on bacteria that slowly tap the more recalcitrant organic matter that is locked away in the whale’s bones, massive colonies of worms spring to life, spawn and eventually die.

But all of these animals, the fish, whales, worms and amphipods, depend on oxygen. And the oceans have been like this for almost all of Earth history, since the advent of multicellular life nearly a billion years ago.  This oxygen-replete ocean is an incredible contrast to a handful of events in Earth history when the deep oceans became anoxic. Then, plesiosaurs, ichthyosaurs and mosasaurs, feeding on magnificent ammonites, would have been confined to the sunlit realm, their maximum depth of descent marked by a layer of bright pink and then green water, pigmented by sulfide consuming bacteria.  And below it, not a realm of animals but a realm only of Bacteria and Archaea, single-celled organisms that can live in the absence of oxygen, a transient revival of the primeval marine ecosystems that existed for billions of years before complex life evolved.

 

Withdrawn – Contemplating Environmental Histories and Futures in Leigh Woods

Withdrawn was one of Bristol Green Capital’s flagship Arts Projects by Luke Jerram.  Among other inspiring Art, Luke is perhaps best known for his Earth, Moon and Mars exhibits, including in the Great Hall of the building my School resides in.  Withdrawn was a similarly contemplative piece and the following are the reflections I brought to the project via my co-curation and collaboration.

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On the 23rd of August, and as part of Bristol 2015 European Green Capital, I have the privilege of participating in a conversation about the future of our coastal seas that has been inspired by Luke Jerram’s ethereal and evocative Withdrawn Project in Leigh Woods.  The conversation will include Luke, but also the esteemed chef, Josh Eggleton who has championed sustainable food provision and is providing a sustainable fish supper for the event, and my University of Bristol Cabot Institute colleague, Dani Schmidt, who is an expert on the past and current impacts of ocean acidification on marine ecosystems.

My engagement with Withdrawn has been inspired on multiple levels, primarily the enthusiasm of Luke but also arising from my role as Cabot Director and my own research on the oceans. Withdrawn inspires reflection on our dependence on the sea and how we have polluted and depleted it, but also on how we obtain our food and the people at the heart of that industry.

All of these issues are particularly acute for our island nation, ringed by nearly 20,000 kilometres of coastline and culturally and economically dependent on the sea. Beyond our own nation, over 2.6 billion people need the oceans for their dietary protein, a point driven home to Cabot in conversations with Sir David Attenborough . He passionately referred to the oceans as one of our most vital natural resources. And of course, as Withdrawn reminds us, the oceans have vast cultural and spiritual value. It also reminds us that those oceans and those resources are at profound risk.

I’ve spent over 25 years studying our planet and its oceans. However, my first ocean research expedition did not occur until 1999, and it was a transformative experience. We were exploring the deep sea communities fuelled by methane extruded from the Mediterranean seafloor.  Isolated from light, the ocean floor is a largely barren world, but in parts of the Mediterranean it is interrupted by explosions of colourful life, including tubeworms, bacterial colonies, fields of molluscs and strange and lonely fish, all thriving in exotic mountains of carbonate crusts cut by saline rivers. These are vibrant ecosystems but so far removed from the surface world and light that they instead depend on chemical energy sourced from deep below the bottom of the ocean. And even here we found human detritus, plastic and cans and bottles.

Those were powerful observations, in large part because of their symbolism: our influence on the oceans is pervasive and quite often in ways that are challenging to fully comprehend and often invisible to the eye. These include, for example:

  • The potentially devastating impact of plastic on marine ecosystems, including plastic nanoparticles that are now, for all intents and purposes, ubiquitous. Of course, pollutants are not limited to plastic – our lab now identifies petroleum-derived hydrocarbons in nearly every ocean sediment we analyse.
  • The decreasing pH of the oceans, due to rising CO2 levels, an acid when dissolved in water. We acidifying the oceans, apparently at a rate faster than at any other time in Earth history, a deeply alarming observation. We are already seeing some consequences of ocean acidification on organisms that make calcium carbonate shells. However, what concerns most scientists is how little we know about the impacts of rapid ocean acidification on marine ecosystems.
  • Ocean warming. A vast amount of the energy that has been trapped in the Earth system by higher greenhouse gas concentrations has been absorbed by the oceans. Its impact on marine life is only beginning to be documented, but it has been invoked, for example, as an explanation for declines in North Sea fisheries.

And these represent only a few of the chemical and environmental changes we are making to the marine realm. They do not even begin to address the numerous issues associated with our over-exploitation and poor management of our marine resources.

Compounded, these factors pose great risk to the oceans but also to all of us dependent on them. As Cabot Institute Director, I engage with an inspiringly diverse range of environmental scientists, social scientist, engineers, doctors and vets.   And in those conversations, of all the human needs at threat due to environmental change, it is water and food that concern me the most.  And of these, our food provision seems the most wildly unpredictable. The synergistic impact of warmer temperatures, more acidic waters, and more silt-choked coastal waters on a single shellfish species, let alone complex ecosystems such as coral reefs or North Sea food webs, is very difficult to predict. This uncertainty becomes even more pronounced if we factor in nutrient runoff from poorly managed land, eutrophication and ocean anoxia leading to more widespread ‘dead zones’. Or the impact of plastic, hydrocarbon, and anti-biofouling pollutants. The ghost ships of Withdrawn quietly tell the story of how our increased demand and poor management have led to overexploitation of fish stocks, causing an industry to face increasing uncertainty. But they also invoke deeper anxieties about how environmental change and pollution of our seas could devastate our food supply.

But Withdrawn, like other Green Capital Arts projects and like all inspiring art, does not telegraph a simple message.  It does not shout to ‘bring back local fisherman’ or ‘save our oceans’.  These messages are present but subtly so, and for that both Luke and the National Trust should be celebrated. The boats themselves are captivating and draw you into the fisherman’s efforts; they acknowledge our dependence on the ocean and that we must continue to exploit it. To others they are suggestive of some past catastrophe, a tsunami that has somehow deposited fishing boats in a wildly unanticipated place. And yet to others, they suggest the changing character of seas, seas that once stood 100 m higher than they do today and which almost certainly will do so again if all of our coal and oil is burned into carbon dioxide.

Withdrawn is about all of those things. And consequently, at its deepest level, I think Withdrawn is about change.

Geologists have a rather philosophical engagement with the concept of change – on long enough timescales, change is not the exception but the defining character of our planet and life. I should clarify that the aforementioned Mediterranean expedition was my first proper research excursion to the modern seas, but it came long after numerous visits to ancient ones.  In 1993, my PhD co-supervisor Mike Arthur took a group of us to Colorado where we collected samples from sedimentary rocks that had been deposited in the Cretaceous Western Interior Seaway 90 million year ago, a Seaway from a hotter, ice-free world, in which higher oceans had invaded a downflexed central North American basin. That might not seem like a proper marine experience but to a geologist you can reconstruct an ocean in startling clarity from the bold clues preserved in the rock: current flows that tell you the shape of the coastline; fossils that reveal the ecosystem, from cyanobacterial mats on the seafloor to inoceramids and ammonites to great marine reptiles in the waters above; and the rocks themselves that reveal a shallow sea in which limestone was deposited across a great platform.

But it was only like this at some times.  The fascinating aspect of these rocks is the complex pattern of sedimentation – from limestones to shales and back again – limestones that were much like the lime cliffs of Lyme Regis, switching in a geological blink of the eye to oil shales similar to those in Kimmeridge Bay, from which, further North and at greater depths and pressures, North Sea oils derive. Limestone. Shale. Limestone. Shale. A pattern repeated hundreds of times.  In the Western Interior Seaway.  Along the Jurassic Coast. Across the globe, from the Tarfaya, Vocontian and Maracaibo basins to the Hatteras Abyss, from Cape Verde to the Levant Platform. Cycles and cycles of astonishingly different rock types – all bundled up in patterns suggesting they were modulated by the ever changing character of Earth’s orbit.  These cycles are change, from a sea with clear waters, little algal growth and ringed with reefs to one fed with nutrients and gorged with algal blooms and stripped of oxygen.

Change is a necessary and inevitable feature of our planet.  And of the human condition.

But we seem incapable of resisting the urge to impose a value judgment for or against change. It is either viewed as a technocratic marvel to be celebrated or a violation against the natural state of the world and to be resisted.  But often, change is conflated with loss.  And there is something of loss in Withdrawn. These are the ‘Ghost Ships’ of Leigh Woods.  Ghosts of a way of life that no longer exists. Ghosts of the animals these boats once hunted.  Ghosts of some past and inexplicable event.

Of course, change will always be about progress vs loss, its value neither solely good nor bad but nonetheless inevitable.  But just because a geologist recognises the inevitability of change does not mean he thinks we should be passive to it. Change will come but should be managed, a significant challenge given its rapid pace over the past 150 years. In fact, one of the main observations of Dani Schmidt’s research is that our current rate of environmental change appears to be essentially unprecedented in Earth history, let alone human experience.

My hope is that Withdrawn has caused people to engage with the concept of change. How do we manage change in the 21st century?  How do we recognise those things that can and should be let go. As one visitor said, ‘We want to resist romanticising the past.’  Conversely, how do we decide what change must be moderated, because its cost is too high?  We can reduce our plastic consumption and waste, and we can enforce more rigorous regulations to stop the pollution of our planet – and we should.  More complicated questions arise from how we manage our dependencies on these precious marine resources, but it is clear that we can eat fish more sustainably and that we must create marine reserves that will not only conserve species but serve as biodiversity hotspots benefitting all of the oceans.

Perhaps most importantly, how do we recognise those things that must be preserved?  When I see the ghost ships of Withdrawn, I feel the poignant loss of our connection with nature and our connection with what it provides. Our food is now produced far away, delivered to sterile supermarkets via ships, trains and lorries; maybe that is necessary on a planet of over 7 billion people but if so, we must strive to preserve our connection to the sea – to our whole planet – understanding what it provides and understanding its limits.

 

 

 

 

 

 

 

 

 

 

 

 

 

The Uncertain World Artwork

Everyone, gather round! I want to tell you how the marvelous @LucasAntics Park Row artwork came to pass!
In 2014, Bristol was preparing to be the European Green Capital in 2015. Many great projects were envisioned, including collaborations with Bristol’s outstanding artists, like @lukejerram who created Withdrawn: lukejerram.com/withdrawn/ and many curated by @FestivalofIdeas
It had been about 50 years since the publication of J.G. Ballard’s iconic disaster novels, The Drowned World, The Burning World and my favourite, the surreal and biologically disturbing The Crystal World. Consequently, ideas were brainstormed around these.
These did not happen. That was probably for the best as no matter how brilliant and perceptive Ballard is, these novels have a very white, male, colonial perspective. Not ideal for our diverse city. 
But it simulated conversations. As @cabotinstitute Director, I was asked: “What will be the nature of our future world, under climate change?” And my answer was ‘An Uncertain World.’ We can predict warming & rainfall, but we are creating a world beyond all human experience. 

This was informed by our work on past climates. It has been about 3 million years since the Earth last had so much carbon dioxide in its atmosphere. And the rate of increase is nearly unprecedented in Earth history.

richpancost.blogs.bristol.ac.uk/2018/08/17/evi…

richpancost.blogs.bristol.ac.uk/2018/08/17/an-…

And hence the Uncertain World.

And to visualise that, we thought it would be fascinating to juxtapose our city – specifically St Werburgh’s – with it’s ancient Mesozoic past. Flooded and thriving with plesiosaurs, ammonites and icthyosaurs. And who better than @LucasAntics?

And so Alex created these! Thanks to @ERC_Research and @NERCscience for helping to fund it!
And we all loved them so much, that we got permission to paint them on the side of the @BristolUni Drama Building!

Learn more about Alex’s great work at her website: Visit. It. Now. And be filled with joy.

lucasantics.com

To read about what we learned about the challenges of living with Uncertainty, more relevant now than ever, go here:

richpancost.blogs.bristol.ac.uk/2020/01/11/the… 

Fun fact: @DrHeatherBuss and I have all of the original artwork in our house! Including these drawings of a soon to be flooded St Werburgh’s. Views toward St Werburgh’s City Farm and Graffiti Tunnel!

AND…. all* of the original drawings of the menagerie of critters, not all of whom made it into the art!

*All but one that we gave away to a young fan of Mary Anning!

Thank you for listening. I thank Alex and others for inspiring me to use some quirkiness, wonder and silliness as a gateway to the very serious conversations we must have about climate change and biodiversity loss. 💚 

Postscript: The Green Capital Year was amazing. I loved it our collaborations with artists, engaged citizen movements and innovators. But it was not as inclusive as it should have been. And from that lesson arose the Green and Black Ambassadors.

richpancost.blogs.bristol.ac.uk/category/green…

Past Climates, Extreme Futures and Communication

Anthropogenic climate change will be devastating.  Devastating.

But I do not think scientists are communicating just how devastating it could be.  Typically, we communicate with an IPCC approach, in which scientists like me provide policy makers and the world our very very best understanding of what is likely to happen. On the other hand, there is a growing group of so-called “doomer messages” in which the worst scenarios are deemed inevitable.

Neither is true.

A few weeks ago, I got this draft for a press release on our paper exploring how Co2 decline caused cooling and growth of the Antarctic ice sheet across the Eocene-Oligocene boundary about 30 million years ago. The news item led with: “Scientists have discovered that a decline in CO2 cooled the Earth’s climate over 30 million years ago. However the Earth’s transition from greenhouse to icehouse could be partially reversed in the next centuries due to the anthropogenic rise in CO2.”

Oh, I thought. The word ‘could’ is doing some damned heavy lifting in that second sentence.

Our future climate forecasting tends to focus on the next 100 years, framed by IPCC, itself framed by timelines thought to be at least somewhat relevant to policy makers and the public.  On those timescales we expect minimal ice sheet melting (about 1 to 1.5 m) even under the most severe global warming scenarios. Moreover, the few studies that have projected the fate of ice sheets beyond 2100 generally show them to be persistent and sea level rise to be modest (2-5 m). There are solid scientific reasons to think this. Ice sheets, once built, are hard to melt, a concept called hysterisis; and ice sheet hysterisis could be particularly strong due to the fact that ice sheets are high (such that temperatures at their surface are lower than they would be at ground level), future projections suggest more snow accumulating at their surface, and the presence of the ice sheet itself cools the region and planet via its high albedo.

But.

They could melt in the coming centuries at very high CO2 levels.

They could.

They could.

At about the same time, I had written a twitter rant that was inspired by the same frustration.

“I’m done fucking about with climate change messaging. Action is going too slowly. Despite heat waves, wildfires, floods and death, our governments are strutting towards #COP26 with proposals that are insultingly incremental.  Not only is this a moral failure in light of what is likely to happen, it is an existential gamble given what *could* happen. The @IPCC_CH  report is imminent and it will outline both likely and extreme possibilities, but the Summary for Policy Makers will emphasise the likely rather than the low probability risks. As scientists, we are doing our best to determine what will likely happen given certain emissions trajectories. But as a communicator, I must become more assertive about what *could* happen. Extreme risks – possible and devastating even if unlikely – must dictate our urgency.

If playing Russian Roulette, you focus on the damned bullet; you don’t ignore it because it is only a 15% probability event.”

It could happen.

It could happen.

Three million years ago, the Earth’s CO2 level was around 400 ppm, levels similar to those of today. And sea level was perhaps 20 m higher, due to significant contraction of the Greenland and West Antarctic Ice Sheets.

Prior to 35 million years ago, CO2 levels were around 800 ppm, levels that we could attain by the end of this century.  And sea level was about 100 m higher than it is today, in part due to the near complete absence of the Greenland and Antarctic ice sheets.

Rarely in Earth history have ice sheets been able to persist under the energy balance of a high greenhouse gas world.  And therefore, our continued injection of fossil carbon into the atmosphere will almost certainly bring about the demise of our current ice sheets and cause catastrophic sea level rise. The only question is when.  We think it will happen in a few thousand years.

It could happen in the coming centuries.

It *could* happen.

And of course that is not the only possible consequence of rapid global warming.  In the same twitter thread, I wrote: “As permafrost thaws, much of the released methane will be oxidised to CO2; much of the carbon will be washed to and buried in the Arctic Ocean. But there is a risk that much of it will be mobilised into the atmosphere ramping up warming not just by a little but by a lot. Polar warming could happen faster than forecast. Droughts and famines could be more widespread. Food security could disappear. Reefs are forecast to die at 2C warming, devastating fisheries.”

In the same week, another paper also drew on the geological record of Earth, exploring how the rate of climate change affected extinction rates.  They concluded that: “A temperature increase of 5.2 °C above the pre-industrial level at present rates of increase would likely result in mass extinction comparable to that of the major Phanerozoic events, even without other, non-climatic anthropogenic impacts.”

5.2 °C at present rates is rather unlikely, given trends in the economy, energy production and increasing costs of extracting fossil fuels.  But it could happen.  We could find ways to access other fossil carbon cheaply.  Climate sensitivity could be higher than we think.  Those permafrost and other carbon cycle feedbacks could be larger than we think. 5.2 °C of warming could happen.

We have not internalised these existential risks yet.

Instead, we are acting like global warming is something best to be avoided due to its catastrophic nature and to which we must prepare to adapt – because that is what the likely scenarios suggest.

We are not acting like this is an existential crisis, not necessarily one that will cause humanity to go extinct but one that is damn near that.  A crisis that will be devastating for our society, our civilization and our planet.

And these are not one in a million risks but one in a hundred or one in ten risks. Again, I say: “If playing Russian Roulette, you focus on the damned bullet; you don’t ignore it because it is only a 15% probability event.”

But that is a bad analogy; because with climate change every chamber has a bullet, just some are worse than others.

We are playing Russian Roulette with our planet.

We are playing Russian Roulette with our children.

With a loaded gun.

Our society must put down the fucking gun.

 

The Uncertain World Project – Engagement to build Action

The ERC-funded Greenhouse Earth System (TGRES) explored the climate, ecology and biogeochemical processes associated with ancient hot climates, potential analogues for our future. Ancient climate research contributes to public dialogue by reinforcing our understanding (or lack thereof) of contemporary processes and change. It is particularly powerful because it conveys such knowledge via narratives of past events that complement forecasts for the future (Pancost, Nature Geoscience 2017). Aspects of TGRES research that are critical to understanding our future include: (i) determining that pCO2 levels have not exceeded 400ppm for ~3 million years; (ii) further evidence that the current rate of climate change is nearly without precedent; and (iii) showing that rapid warming has dramatic but complex hydrological and biogeochemical consequences.

The goal of TGRES public engagement was to use past climate change research to curate a space for dialogue, thereby building public ambition for bolder climate action and more creative approaches to resilience.  Central to our engagement strategy was relocating discussion away from the current policy debate to ancient worlds, thereby creating a place of reflection – what we called the Uncertain World.  We collaboratively explored what we know or do not about our past and future, renewing motivation for climate action. Moreover, by focusing on the uncertainty in the Earth system, we explored the creative forms of resilience that will be required in the coming century.

It gained a large platform when Bristol became the European Green Capital, and TGRES PI Pancost became its Scientific Advisor. We co-curated the Uncertain World by writing Bristol 2015’s opening call for action and hosting one of the flagship Summits – a two-day forum with city, national and international stakeholders, informed by public contributions gathered through the year. The Summit’s conclusions were further explored with the public, including via a discussion with the Mayor. We also collaborated on ~30 other events, including contributions to 3 Festivals, 2 other Summits and the Green Capital Arts Program (with Pancost writing its Introduction, co-hosting talks with the Festival of Ideas, co-curating the Fog Bridge Installation, advising on @Bristol’s Blue Marvel movie and co-sponsoring Withdrawn with the National Trust). The Uncertain World’s images of Mesozoic sea animals swimming through the streets of Bristol are now a fixture of Bristol’s street art.

Collectively, these events reached >100,000 people; combined with the final report (Cabot Institute Report on Living with Environmental Uncertainty.pdf), they were a major part of Bristol’s public dialogue in 2015-2016 to build political action. Pancost attended COP21 with Mayor G Ferguson (the official UK City Delegation) and supported his commitment to be carbon neutral by 2050, a pledge repeated by his successor Marvin Rees and then enshrined in the One City Plan (on which Pancost was an official advisor and which was a 2019 finalist for the EU Capital of Innovation). Bristol’s decarbonisation target was accelerated to 2030, when we became the first UK city to declare a Climate Emergency. The Uncertain World was also central to Bristol’s Resilience Strategy (one of the Rockefeller 100 Resilient Cities); Pancost was invited to join the Resilience Sounding Board where TGRES research created a space of constructive uncertainty, contributing to the co-creation of shared resilience principles. Perhaps most importantly, the Uncertain World program changed scope to refocus on inclusion and equity in the environmental movement, leading to the Green and Black Conversation and Ambassadors Program.

This is adapted from the ERC report (ERC TGRES Engagement Report – Uncertain World and Green & Black) on engagement as part of the TGRES Project.

 

 

An ancient rapid climate change event – still much slower than what we are doing today.

In 2015, I was interviewed by Susan Kucera when she visited Bristol to show her beautiful film on climate change – Breath of Life.  Working with Jeff Bridges, she has created a powerful new film – Living in the Future’s Past – that features those interviews with me and many other scientists, psychologists, politicians and philosophers. My own contributions on climate change reflect on the history of our planet and how that provides perspective for our current unprecedented rate of climate change. To elaborate on that, I am posting some recent press releases on the research that informed my reflections (and yet to be published at the time of interview). In particular, in the movie I discuss our research a carbon dioxide increase (and associated global warming event) that occurred over 100 million years ago. It is an event that we consider fast geologically but happened 100s of times more slowly than the carbon dioxide we are adding today.

Image result for living in the futures past

 

The research was led by Dr David Naafs, a Research Fellow with me in the Organic Geochemistry Unit; it was based on Dutch Rubicon Grant he was awarded in 2012.  But we need to acknowledge three others.  First, our colleague Dani Schmidt has been grappling with the topic of rapid geological carbon release events for years; it was her work with Andy Ridgwell that began to reveal that these geologically rapid events were not at all rapid by modern standards.  Second, the work would not have been possible without a fantastic geological section; the Cau section in Spain had been studied for years prior to this by several colleagues at the University of Jaen, including Jose Manuel Castro and Maria Luisa Quijano.  All of these brilliant scientists – and many others – have helped shape our understanding of the geological past.  And almost all come to the same conclusion: although geology is a vast and powerful force, rarely does it act with the terrible speed and efficiency with which we are extracting fossil fuels from the Earth and transforming our carbon cycle.

From our press release at the time:

University of Bristol Cabot Institute researchers and their colleagues today published research that further documents the unprecedented rate of environmental change occurring today, compared to that which occurred during natural events in Earth’s history.

The research, published online on the 4th of January (2016) in Nature Geosciences (‘Gradual and sustained carbon dioxide release during Aptian Oceanic Anoxic Event 1a’), reconstructs the changes in atmospheric carbon dioxide (pCO2) during a global environmental change event that occurred about 120 Million years ago. New geochemical data provide evidence that pCO2 increased in response to volcanic outgassing and remained high for around 1.5-2 million years, until enhanced organic matter burial in an oxygen-poor ocean caused a return to original levels.

Lead author Dr David Naafs explained: ‘Past records of climate change must be well characterised if we want to understand how it affected or will affect ecosystems. It has been suggested that the event we studied is a suitable analogue to what is happening today due to human activity and that a rapid increase in pCO2 caused ocean acidification and a biological crisis amongst a group of calcifying marine algae. Our work confirms that there was a large increase in pCO2. The change, however, appears to have been far slower than that of today, taking place over hundreds of thousands of years, rather than the centuries over which human activity is increasing atmospheric carbon dioxide levels. So despite earlier claims, our research indicates that it is extremely unlikely that widespread surface ocean acidification occurred during this event.’

The observation that yet another putative ‘rapid’ geological event is occurring perhaps a thousand times slower than today and not associated with widespread surface ocean acidification has been the focus of much recent research at the University of Bristol. Co-author Professor Daniela Schmidt, who was also a Lead Author on the IPCC WGII report on Ocean systems, emphasised that today’s finding builds on one of the IPCC’s key conclusions: that the rate of environmental change occurring today is largely unprecedented in Earth history.  She said, ‘This is another example that the current rate of environmental change has few if any precedents in Earth history, and this has big implications for thinking about both past and future change.’

The research was possible due to the exceptional Spanish section that the team analysed. Co-author Professor José Manuel Castro of the University of Jaen adds, ‘The sediments at Cau accumulated very rapidly resulting in an expanded section. This allowed the high resolution multidisciplinary analysis that are the basis for this important study.’

Senior Author and Director of the University’s Cabot Institute, Professor Rich Pancost, added,  ‘We often use the geological record to help us test or expand our understanding of climate change, for example, determining the sensitivity of Earth’s temperature to higher CO2 levels. But testing the risks associated with the pace of modern environmental change is proving problematic, due to a lack of similar rapid changes in the geological past. Consequently, these risks, in this case to the marine ecosystems on which so many of us depend, remain associated with profound uncertainty. Decreasing CO2 emissions, as recently agreed in Paris, will be necessary to avoid these risks.’

This research was published in Nature Geosciences.

See also the News and Views perspective.

The research was funded by a NWO (Netherlands Funding Council) Rubicon Grant to David Naafs and NERC funding to Rich Pancost.

 

It has been about 3 million years since the Earth’s atmosphere last had 400 ppm of carbon dioxide

In 2015, I was interviewed by Susan Kucera when she visited Bristol to show her beautiful film on climate change – Breath of Life.  Working with Jeff Bridges, she has created a powerful new film – Living in the Future’s Past – that features those interviews with me and many other scientists, psychologists, politicians and philosophers. My own contributions on climate change reflect on the history of our planet and how that provides perspective for our current unprecedented rate of climate change. To elaborate on that, I am posting some recent press releases on the research that informed my reflections (and yet to be published at the time of interview).

Image result for living in the futures past

 

In particular, I discuss work in collaboration with colleagues at Southampton, showing that the Earth’s current pCO2 level of 400 ppm is higher than it has been for nearly 3 million years (this work also refers to our research on the Pliocene, which I have also written about here). 

A multinational research team, led by scientists at the University of Southampton and the University of Bristol Cabot Institute, has developed new records of past CO2 levels.  These reveal that the CO2 content of the Earth’s atmosphere between 2.8 to 3.3 million years ago, were higher than that of the pre-industrial Earth and likely higher than at any other point over the past two million years – but similar to values reached in the past decade.

The new records are based on geochemical analyses of marine sediments. These have been measured using techniques developed at Bristol and Southampton over the past decade. The Bristol team includes Professor Richard Pancost from the University of Bristol, Director of the Cabot Institute and the Primary Investigator of the wider grant under which this research was conducted, as well as Dr Marcus Badger, Professor Dan Lunt and Professor Daniela Schmidt.  Professor Pancost explains: “We cannot directly measure the CO2 levels on Earth prior to about 1 million years ago, and so we instead use proxies.  In the case of our project, funded by the NERC, we used a combination of approaches based on the chemical signatures of organisms preserved in sediments at the bottom of the sea.”

By studying the relationship between CO2 levels and climate change during a warmer period in Earth’s history, the team have been able to estimate how the climate will respond to increasing levels of carbon dioxide, a parameter known as ‘climate sensitivity’.  The findings, which have been published in Nature, fall in line with estimates in the most recent IPCC report.  “Today the Earth is still adjusting to the recent rapid rise of CO2 caused by human activities, whereas the longer-term Pliocene records document the full response of CO2-related warming,” says Southampton’s Dr Gavin Foster, co-lead author of the study.  “Our estimates of climate sensitivity lie well within the range of 1.5 to 4.5°C warming per CO2 doubling summarised in the latest IPCC report. ”

Professor Dan Lunt, also of the University of Bristol and the Cabot Institute adds: “We compared the temperature response to CO2 change in the warm Pliocene to that during colder times, like the glacial cycles of the last 800 thousand years.  The temperature response was around half that of the colder period, but that difference can be largely resolved by considering the growth and retreat of large continental ice sheets during more recent glacial cycles. These ice sheets reflect a lot of sunlight and their growth consequently amplifies the impact of CO2 changes, but they were smaller and less variable during the warm Pliocene.”

“Our new records also reveal an important change at around 2.8 million years ago, when levels dropped to values of about 280 ppm, similar to those seen before the industrial revolution,” says lead author of the study Dr Miguel Martinez-Boti, also from Southampton. “This appears to have caused a dramatic global cooling that initiated the ice-age cycles that have dominated Earth’s climate ever since.”

Professor Pancost added: “When we account for the influence of the ice sheets, we can confirm that the Earth’s climate changed with a similar sensitivity to overall forcing during both warmer and colder climates. During the Pliocene the Earth was warmer by around 2°C than it is today and atmospheric CO2 levels were around 350-400 parts per million (ppm), similar to the levels reached in recent years.  This suggests that in the long term, we have already committed to 2 °C warming, and future CO2 increases will only add to that.”

NOTE: Subsequent to this work, we pushed this methodology further back into Earth history, into the Eocene (30 to 50 million years ago).  This was probably the last time the Earth had pCO2 levels similar to what we might reach by the end of the century (>800 ppm).  

Plio-Pleistocene climate sensitivities evaluated using high-resolution CO2 records by M.A. Martínez-Botí, G.L. Foster, T. B. Chalk, E.J. Rohling, P.F. Sexton, D.J. Lunt, R.D. Pancost, M.P.S. Badger & D.N. Schmidt DOI: 10.1038/nature14145

This work was funded by an NERC grant to Pancost (PI), G Foster, D Schmidt and D Lunt.

Back to the Future ‘Hothouse’

Our current global warming target and the trajectory it places us on, towards a future ‘Hothouse Earth’, has been the subject of much recent discussion, stimulated by a paper by Will Steffen and colleagues.  In many respects, the key contribution of this paper and similar work is to extend the temporal framing of our climate discussions, beyond 2100 for several centuries or more.  Analogously, it is useful to extend our perspective backwards to similar time periods, to reflect on the last time Earth experienced such a Hothouse state and what it means.

The Steffen et al paper allows for a variety of framings, all related to the range of natural physical, biological and chemical feedbacks that will amplify or mitigate the human intervention in climate.  [Note: the authors frame their paper around the concept of a limited number of steady state scenarios/temperatures for the Earth.  They then argue that aiming for 2C, potentially an unstable state, could trigger feedbacks tipping the world towards the 4C warmer Hothouse.  I find that to be somewhat simplistic given the diversity of climate states that have existed, if even transiently, over the past 15 million years, but that is a discussion for another day.] From my perspective, the most useful framing – and one that remains true to the spirit of the paper is this: We have set a global warming limit of 2C by 2100, with an associated carbon budget. What feedback processes will that carbon budget and warming actually unleash over the coming century,  how much additional warming will they add, and when?

That is a challenging set of questions that comes with a host of caveats, most related to the profound uncertainty in the interlinked biogeochemical processes that underpin climate feedbacks. For example, as global warming thaws the permafrost, will it release methane (with a high global warming potential than carbon dioxide)? Will the thawed organic matter oxidise to carbon dioxide or will it be washed and buried in the ocean? And will the increased growth of plants under warmer conditions lead instead to the sequestration of carbon dioxide? The authors refer to previous studies that suggest a permafrost feedback yielding an additional 0.1C warming by the end of the century; but there is great uncertainty in both the magnitude of that impact and its timing.

And timing is the great question at the heart of this perspective piece.  I welcome it, because too often our perspective is fixed on the arbitrary date of 2100, knowing full well that the Earth will continue to warm and ice continue to melt long after that date.  In this sense, Steffen et al is not a contradiction to what has been reported from the IPCC but an expansion on it.

Classically, we discuss these issues in terms of fast and slow feedbacks, but in fact there is a continuum between near instantaneous feedbacks and those that act over hundreds, thousands or even millions of years.  A warmer atmosphere will almost immediately hold more water vapour, providing a rapid positive feedback on warming – and one that is included in all of those IPCC projections.  More slowly, soil carbon, including permafrost, will begin to oxidise, with microbial activity stimulated and accelerated under warmer conditions – a feedback that is only just now being included in Earth system models.  And longer term, all manner of processes will come into play – and eventually, they will include the negative feedbacks that have helped regulate Earth’s climate for the past 4 billion years.

There is enough uncertainty in these processes to express caution in some of the press’s more exuberant reporting of this topic.  But lessons from the past certainly underscore the concerns articulated by Steffen et al.  We think that the last time Earth had 410 ppm CO2, a level similar to what you are breathing right now, was the Pliocene about 3 million years ago.  This was a world that was 1 to 2C warmer than today (i.e. 2 to 3C warmer than the pre-industrial Earth) and with sea levels about 10 m higher.  This suggests that we are already locked into a world that far exceeds the ambitions and targets of the Paris Agreement.  This is not certain as we live on a different planet and one where the great ice sheets of Greenland and Antarctica might not only be victims of climate change but climate stabilisers through ice-sheet hysteresis. And even if a Pliocene future is fixed, it might take centuries for that warming and sea level change to be realised.

But that analogue does suggest caution, as advocated by the Hothouse Earth authors.

It also prompts us to ask what the Earth was like the last time its atmosphere held about 500 ppm CO2, similar to the level needed to achieve the Paris Agreement to limit end-of-century warming below 2C.  A useful analogue for those greenhouse gas levels is the Middle Miocene Climate Optimum, which occurred from 17 to 14.7 million years ago.

d11BAlkCenozoic_CO2_SameScale_AIv1_NoBilj-NoPagani99v2.jpg

Figure showing changes in ocean temperature (based on oxygen isotopic compositions of benthic foraminifera) and pCO2 over the past 60 million years (from Palaeo-CO2).  Solid symbols are from the d11B isotope proxy and muted symbols are from the alkenone-based algal carbon isotope fractional proxy. Note the spike in pCO2 associated with the MMCO at about 15 million years ago.

As one would expect for a world with markedly higher carbon dioxide levels, the Miocene was hotter than the climate of today.  And consistent with many of Steffen et al.’s arguments, it was about 4C hotter rather than a mere 2C, likely due to the range of carbon cycle and ice-albedo feedbacks they describe.  But such warmth was not uniform – globally warmer temperatures of 4C manifest as far hotter temperatures in some parts of the world and only slightly warmer temperatures elsewhere. Pollen and microbial molecular fossils from the North Sea, for example, indicate that Northern Europe experienced sub-tropical climates.

But what were the impacts of this warmth?  What is a 4C warmer world like?  To understand that, we also need to understand the other ways in which the Miocene world differed from ours, not just due to carbon dioxide concentrations but also the ongoing movement of the continents and the continuing evolution of life.  In both respects, the Miocene was broadly similar to today.  The continents were in similar positions, and the geography of the Miocene is one we would recognise. But there were subtle differences, including the ongoing uplift of the Himalayas and the yet-to-be-closed gateway between North and South America, and these subtle differences could have had major impacts on Asian climate and the North Atlantic circulation, respectively.

Similarly, the major animal groups had evolved by this point, and mammals had firmly established their dominance in a world separated by 50 million years from the dinosaurs.  Remnant groups from earlier times (hell pigs!) still terrorised the landscape, but many of the groups were the same or closely related to those we would recognise today.  And although hominins would not appear until the end of the Miocene, the apes had become well established, represented by as many as a 100 species. In the oceans, the differences were perhaps more apparent, the seas thriving with the greatest diversity of cetaceans in the history of our planet and associated with them the gigantic macro-predators such as Charcharadon megalodon (The MegTM).

Image result for Miocene fauna and flora

Smithsonian mural showing Miocene Fauna and landscape.

But it is the plants that exhibit the most pronounced differences between modern and Miocene life. Grasses had only recent proliferated across the planet at the time of the MMCO, and the C4 plants had yet to expand to their current dominance. And in this regard, the long-term evolution of Earth’s climate likely played a crucial role.  There are about 8100 species of C4 plants (although this comprises only 3% of the plant species known to us) and most of these are grasses with other notable species being maize and sugar cane. They are distinguished from the dominant C3 plants, which comprise almost all other species, by virtue of their carbon dioxide assimilation biochemistry (the Hatch-Slack mechanism) and their leaf cellular physiology (the Kranz leaf anatomy).  It is a collective package that is exceptionally well adapted to low carbon dioxide conditions, and their global expansion about 7 million years ago was almost certainly related to the long-term decline in carbon dioxide from the high levels of the Middle Miocene. Although C4 plants only represent a small proportion of modern plant species, the Miocene world, bereft of them, would have looked far different than today – lacking nearly half of our modern grass species and by extension clear analogues to the vast African savannahs.

Aside from these, the most profound differences between the Miocene world and that of today would have been the direct impacts of higher global temperatures.  There is strong evidence that the Greenland ice sheet was far reduced in size compared to that of today, and its extent and even whether or not it was a persistent ice sheet or an ephemeral one remains the subject of debate. Similarly, West Antarctica was likely devoid of permanent ice, and the East Antarctic Ice Sheet was probably smaller – perhaps far smaller – than it is today.  And collectively, these smaller ice sheets were associated with a sea level that was about 40 m higher than that of today.

The hot Miocene world would have been different in other ways, including the hydrological cycle.  Although less studied than for other ancient intervals, it is almost certain that elevated warmth – and markedly smaller equator-to-pole temperature differences – would have impacted the global distribution of water.  More water was evidently exported to the high latitudes, resulting in a warmer and vegetated Antarctica where the ice had retreated. It was also likely associated with far more extreme rainfall events, with the hot air able to hold greater quantities of water.  More work is needed, but it is tempting to imagine the impact of these hot temperatures and extreme rainfall events.  They would have eroded the soil and flushed nutrients to the sea, perhaps bringing about the spread of anoxic dead zones, similar to the Oceanic Anoxic Events of the Mesozoic or the dead zones of modern oceans caused by agricultural run-off. Indeed, the Miocene is characterised by the deposition of some very organic-rich rocks, including the North Pacific Monterey Formation, speaking to the occurrence of reduced oxygen levels in parts of these ancient oceans.

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It is unclear if our ambitions to limit global warming to 2C by the end of this century really have put us on a trajectory for 4C. It is unclear if we are destined to return to the Miocene.

But if so, the Miocene world is one both similar to but markedly distinct from our own – a world of hotter temperatures, extremes of climate, fewer grasslands, Antarctic vegetation, Arctic forests and far higher sea levels. Crucially, it is not the world for which our current society, its roads, cities, power plants, dams, borders, farmlands and treaties, has been designed.

Moreover, the MMCO Earth is a world that slowly evolved from an even warmer one over millions of years*; and that then evolved over further millions of years to the one in which we now inhabit. It is not a world that formed in a hundred or even a thousand years.  And that leaves us three final lessons from the past.  First, we do not know how the life of this planet, from coral reefs to the great savannahs, will respond to such geologically rapid change.  Second, we do not know how we will respond to such rapid change; if we must adapt, we must learn how to do so creatively, flexibly and equitably.  And third, it is probably not too late to prevent such a future from materialising, but even if it is, we still must act to slow down that rate of change to which we must adapt.

And we still must act to ensure that our future world is only 4C hotter and analogous to the Miocene; if we fail to act, the world will be even hotter, and we will have to extend our geological search 10s of millions of years further into the past, back to the Eocene, to find an even hotter and extreme analogue for our future Hothouse World.

 

*The final jump into the MMCO appears to have been somewhat more sudden, but still spanned around two-hundred thousand years.  A fast event geologically but not on the timescales of human history.

The Pliocene – The last time Earth had 400 ppm of Carbon Dioxide

One of the main approaches for better understanding our future Uncertain World, both with respect to minimising that uncertainty but also identifying the limits to our knowledge, is to look to the past.  A few years ago, we passed 400 ppm of CO2 in the atmosphere, a level that we have not experienced for about 3 million years, during the Pliocene epoch.  That coincided with Bristol hosting the 2nd International Conference on the Pliocene, providing an opportunity through this piece, originally published on The Conversation, and its embedded video to discuss how we try to unravel ancient climates to better understand the future.  I have updated some of the text, reflecting some of the changing intellectual landscape.  To provide some immediate context, below is the latest record of current atmospheric carbon dioxide concentrations from the Mauna Loa Observatory (i.e. The Keeling Curve).

How can air bubbles trapped in ice for millions of years, or fossilised fern fronds, or the chemical make-up of rocks that were underwater in the distant past provide us with an inkling of our future?

The answer lies in these clues provided by studying the Pliocene epoch, the span of geological time that stretched from 5.3 to 2.6 million years ago. This period of Earth’s history is interesting for many reasons, but one of the most profound is that the Earth’s atmosphere apparently contained high concentrations of carbon dioxide. Our best estimates suggest concentrations of about 300-400 parts per million (ppm) – much higher than concentrations of 100 years ago, but the same or lower than today after centuries of industrialisation and fossil fuel burning.

So studying the Pliocene could provide valuable insight into the type of planet we are creating via global warming. Our researchers at the Cabot Institute recently released a video on the topic, which has coincided with pronounced flooding across the UK [in Winter and Spring 2014] and renewed attention focused on our weather and climate. There is little doubt that increased carbon dioxide concentrations will cause global warming. The key questions are how much, and with what consequences.

One of the key lessons from Earth history is climate sensitivity. Climate sensitivity can be expressed in various ways, but in its simplest sense it is a measure of how much warmer the Earth becomes for a given doubling of atmospheric carbon dioxide concentrations.

This is well known for the Pleistocene, and especially the past 800,000 years of Earth history, a period for which we have detailed temperature reconstructions and carbon dioxide records derived from bubbles of gas trapped in ancient ice cores.

During that time, across several ice ages, the planet’s climate sensitivity showed warming of about 2.5-3°C for a doubling of carbon dioxide, which falls in the middle of the range of predictions given by models. Ice core records, however, extend back no more than a million years, and this time period is generally characterised by colder climates than those of today.

 

A section of an ice core of from 16,000 years ago. National Ice Core Laboratory

If we want to explore climate sensitivity on a warmer planet, we must look further back into Earth history, to times such as the Pliocene.

Reconstructing atmospheric carbon dioxide concentrations without relying on ice cores is admittedly more challenging. Instead of directly measuring the concentration of carbon dioxide in gas bubbles, we must rely on indirect records. For example, carbon dioxide concentration influences the number of stomata (pores) on plant leaves, and this can be measured on the fossils of ancient leaves. Alternatively, there are a number of geochemical tools based on how carbon dioxide affects the pH of seawater, or how algae take up carbon dioxide as they photosynthesise – these are recorded in the chemical composition of ancient fossils.

[For more info on how we reconstruct atmospheric carbon dioxide, especially in times pre-dating our ice core records, see this fantastic website maintained by Gavin Foster and friends.]

 Atmospheric CO2 from AD 1000 to AD 2018 (right) from a mix of ice core records and measuresments of the astmosphere from Mauna Lao.  On the left is a compilation of ice core CO2 (red) and boron isotope based estimates (blue).  Note the age scales are different but y-axis is the same. See this document for references.

From p-CO2.org.

These means of drawing estimates come with larger margins of error, but they still provide key insights into climate sensitivity on a warmer Earth. Recent research indicates that these various carbon dioxide estimates of Pliocene carbon dioxide levels are converging, giving added confidence from which to derive estimates of climate sensitivity. In particular, it seems an increase of carbon dioxide from about 280ppm (equivalent to that before the industrial revolution) to about 400ppm in the Pliocene resulted in an Earth warmer by 2°C.  The below figure shows the sea surface temperatures reconstructed for the Pliocene using a range of chemical and biological proxy data (a) and the difference (anomaly) between those temperatures and those of the modern pre-industrial world, i.e. before we started adding carbon dioxide to the atmosphere in significant quantities (b); notice how much hotter the oceans were, especially at high latitudes. From the Proceedings of the Royal Society.

 

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This next figure is derived from an ensemble of climate models, which allows an extrapolation between data and therefore a comparison of temperatures on land and the modern pre-industrial world.  Again, note how much higher temperatures were at high latitudes… but also continental interiors.  We are seeing a manifestation of this now, with elevated temperatures occurring all over the globe but some areas experiencing much more dramatic warming.  This work is from the amazing PlioMIP project and this figure is specifically from the PAGES website, adapted from Haywood et al., 2013.

 

Image result for images of pliocene warmth terrestrial

 

Taking into account other factors, this suggests a climate sensitivity of about 3°C, which confirms both the Pleistocene and model-based estimates. It also suggests that we have yet to experience the full consequences of the greenhouse gases already added to the atmosphere, let alone those we are still putting into it.  [And finally, it suggests that there is a risk that we have already surpassed the agreed limits of the Paris Climate Agreement.]

So then, what was this much warmer world like? First of all, it was not an inhospitable planet – plants and animals thrived. This should not be a surprise – in fact, the Earth was much warmer even further back into the past. The changes in the climate we are inducing is a problem for us humans, and for our societies, not the planet we’re on. [And that is particularly evident, as I re-post this blog.  We are experiencing a global heatwave that is causing forest fires (where associated with aridity), but it is also impacting infrastructure and the economy, warping rail lines, disrupting work patterns, driving up electricity usage. It is also causing deaths which raises a particularly acute and challenging question – are we and the ecosystems on which we depend prepared for the speed of this rapid global warming?  Organisms and ecosystems had millions of years to evolve in a manner that allowed them to thrive in the Pliocene and previous greenhouse climates.]

Second, the Pliocene was a rather different world. For example, higher global temperatures were associated with a climate that was also wetter than at present. That provides important corroborating evidence for models that predict a warmer and wetter future.

Perhaps most striking, sea level in the Pliocene appears to have been between 10 to 40 metres higher than today, indicating that both the Greenland Ice Sheet and Antarctic Ice Sheet were markedly smaller. To put that into context, the Met Office has already commented on how flooding in the UK has been affected by sea level rise of 12cm over the last 100 years, and will be exacerbated further by another 5-7cm by 2030.

We must be careful in how we extract climate lessons from the geological record, and that is particularly true when we consider ice sheet behaviour. One widely discussed concept is ice sheet hysteresis. This is a fancy way of saying that due to feedback mechanisms, it could be easier to build an ice sheet on Greenland or Antarctica than it is to melt one. If hysteresis is a force stabilising our current ice sheets, then it may be that a planet with today’s carbon dioxide levels of 400 ppm will not necessarily have a sea level 20 metres higher than that of today – as it was during the Pliocene. On the other hand if hysteresis is rather weak, then the question is not whether we will see such a massive sea level change, but how long it will take to arrive (probably hundreds or even thousands of years).

Most importantly, the collective research into Earth history, including the Pliocene, reveals that Earth’s climate can and has changed. It also reveals that climate does not just change randomly: it changes when forced in ways that are relatively well understood – one of these is the concentration of carbon dioxide in our atmosphere. And consequently, there is little doubt from Earth’s history that transforming fossil carbon underground into carbon dioxide in the air – as we are doing today – will significantly affect the climate we experience for the forseeable future.

[Gerald Haug delivered the keynote for the Pliocene Conference and his outstanding public lecture is available here. With an introduction from the founder of the Organic Geochemistry Unit, Geoff Eglinton.]

[For a more fulsome discussion of how Warm Climates of the Past can hold Lessons for the Future, please check out our Special Royal Society Volume on the topic.  Led by my Bristol colleague Dan Lunt but with lots of friends.]

Ancient ‘Dead Seas’ offer a stark warning for our own future

The oceans are experiencing a devastating combination of stresses. Rising CO2 levels are raising temperatures while acidifying surface waters.  More intense rainfall events, deforestation and intensive farming are causing soils and nutrients to be flushed to coastal seas. And increasingly, the oceans are being stripped of oxygen, with larger than expected dead zones being identified in an ever broadening range of settings. These dead zones appear to be primarily caused by the runoff of nutrients from our farmlands to the sea, but it is a process that could be exacerbated by climate change – as has happened in the past.

Recently, our group published a paper about the environmental conditions of the Zechstein Sea, which reached from Britain to Poland 270 million years ago. Our paper revealed that for tens of thousands of years, some parts – but only parts – of the Zechstein Sea were anoxic (devoid of oxygen). As such, it contributes to a vast body of research, spanning the past 40 years and representing the efforts of hundreds of scientists, which has collectively transformed our understanding of ancient oceans – and by extension future ones.

The types of processes that bring about anoxia are relatively well understood. Oxygen is consumed by animals and bacteria as they digest organic matter and convert it into energy. In areas where a great deal of organic matter has been produced and/or where the water circulation is stagnant such that the consumed oxygen cannot be rapidly replenished, concentrations can become very low. In severe cases, all oxygen can be consumed rendering the waters anoxic and inhospitable to animal life.  This happens today in isolated fjords and basins, like the Black Sea.  And it has happened throughout Earth history, allowing vast amounts of organic matter to escape degradation, yielding the fossil fuel deposits on which our economy is based, and changing the Earth’s climate by sequestering what had once been carbon dioxide in the atmosphere into organic carbon buried in sediments.

Red circles show the location and size of many dead zones. Black dots show Ocean dead zones of unknown size. Image source: Wikimedia Commons/NASA Earth Observatory

In some cases, this anoxia appears to have been widespread; for example, during several transient Cretaceous events, anoxia spanned much of what is now the Atlantic Ocean or maybe even almost all of the ancient oceans. These specific intervals were first identified and named oceanic anoxic events in landmark work by Seymour Schlanger and Hugh Jenkyns.  In the 1970s, during the earliest days of the international Deep Sea Drilling Program (now the International Ocean Discovery Program, arguably the longest-running internationally coordinated scientific endeavor), they were the first to show that organic matter-rich deep sea deposits were the same age as similar deposits in the mountains of Italy. Given the importance of these deposits for our economy and our understanding of Earth and life history, scientists have studied them persistently over the past four decades, mapping them across the planet and interrogating them with all of our geochemical and palaeontological resources.

In my own work, I have used the by-products of certain bacterial pigments to interrogate the extent of that anoxia.  The organisms are green sulfur bacteria (GSB), which require both sunlight and the chemical energy of hydrogen sulfide in order to conduct a rather exotic form of bacterial photosynthesis; crucially, hydrogen sulfide is only formed in the ocean from sulfate after the depletion of oxygen (because the latter yields much more energy when used to consume organic matter). Therefore, GSB can only live in a unique niche, where oxygen poor conditions have extended into the photic zone, the realm of light penetration at the very top of the oceans, typically only the upper 100 m.  However, GSB still must compete for light with algae that live in even shallower and oxygen-rich waters, requiring the biosynthesis of light harvesting pigments distinct from those of plants, the carotenoids isorenieratene, chlorobactene and okenone. For the organism, this is an elegant modification of a molecular template to a specific ecological need. For the geochemist, this is an astonishingly fortuitous and useful synthesis of adaptation and environment – the pigments and their degradation products can be found in ancient rocks, serving as molecular fossil evidence for the presence of these exotic and diagnostic organisms.

And these compounds are common in the black shales that formed during oceanic anoxic events.  And in particular, during the OAE that occurred 90 million years ago, OAE2, they are among the most abundant marker compounds in sediments found throughout the Atlantic Ocean and the Tethyan Ocean, what is now the Mediterranean Sea.  It appears that during some of these events anoxia extended from the seafloor almost all the way to the ocean’s surface.

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Today, the deep sea is a dark and empty world. It is a world of animals and Bacteria and Archaea – and relatively few of those. Unlike almost every other ecosystem on our planet, it is bereft of light and therefore bereft of plants.  The animals of the deep sea are still almost entirely dependent on photosynthetic energy, but it is energy generated kilometres above in the thin photic zone. Beneath this, both animals and bacteria largely live off the scraps of organic matter energy that somehow escape the vibrant recycling of the surface world and sink to the twilight realm below. In this energy-starved world, the animals live solitary lives in emptiness, darkness and mystery. Exploring the deep sea via submersible is a humbling and quiet experience.  The seafloor rolls on and on and on, with only the occasional shell or amphipod or small fish providing any evidence for life.

“Krill swarm” by Jamie Hall – NOAA. Licensed under Public Domain via Wikimedia Commons

And yet life is there.  Vast communities of krill thrive on the slowly sinking marine snow, can appear.  Sperm whales dive deep into the ocean to consume the krill and emerge with the scars of fierce battles with giant squid.  And when one of those great creatures dies and its carcass plummets to the seafloor, within hours it is set upon by sharks and fish, ravenous and emerging from the darkness for the unexpected feast. Within days the carcass is stripped to the bones but even then new colonizing animals arrive and thrive. Relying on bacteria that slowly tap the more recalcitrant organic matter that is locked away in the whale’s bones, massive colonies of tube worms spring to life, spawn and eventually die.

But all of these animals, the fish, whales, tube worms and amphipods, depend on oxygen. And the oceans have been like this for almost all of Earth history, since the advent of multicellular life nearly a billion years ago.

This oxygen-replete ocean is an incredible contrast to the north Atlantic Ocean during at least some of these anoxic events. Then, plesiosaurs, ichthyosaurs and mosasaurs, feeding on magnificent ammonites, would have been confined to the sunlit realm, their maximum depth of descent marked by a layer of surprisingly pink and then green water, pigmented by the sulfide consuming bacteria.  And below it, not a realm of animals but a realm only of Bacteria and Archaea, single-celled organisms that can live in the absence of oxygen, a transient revival of the primeval marine ecosystems that existed for billions of years before more complex life evolved.

We have found evidence for these types of conditions during numerous events in Earth history, often associated with major extinctions, including the largest mass extinction in Earth history – the Permo-Triassic Boundary 252 million years ago.  Stripping the ocean of oxygen and perhaps even pumping toxic hydrogen sulfide gas into the atmosphere is unsurprisingly associated with devastating biological change.   It is alarming to realise that under the right conditions our own oceans could experience this same dramatic change.  Aside from its impact on marine life, it would be devastating for us, so dependent are we on the oceans for our food.

The conventional wisdom has been that such extreme anoxia in the future is unlikely, that Cretaceous anoxia was a consequence of a markedly different geography.  North America was closer to Europe and South America only completely rifted from Africa about 150 million years ago; the ancient Atlantic Ocean was smaller and more restricted, lending itself to these extreme conditions.

And yet questions remain.  What was their trigger?  Was it really a happenstance of geography?  Or was it due to environmental perturbations? And how extensive were they? The geological record preserves only snapshots, limiting the geographical window into ancient oceans, and this is a window that narrows as we push further back in time. In one of our recent papers, we could not simulate such severe anoxia in the Atlantic Ocean without also simulating anoxia throughout the world’s oceans, a truly global oceanic anoxic event.  However, that model can only constrain some aspects of ocean circulation and there are likely alternative mechanisms that confine anoxia to certain areas.

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Over the past twenty years, these questions have intersected one another and been examined again and again via new models, new geochemical tools and new ideas.  And an emerging idea is that the geography of the Mesozoic oceans was not as important as we have thought.

That classical model is that ancient oceans, through a combination of the aforementioned restricted geography and overall high temperatures, were inherently prone to anoxia.  In an isolated Atlantic Ocean, oxygen replenishment of the deep waters would have been much slower.  This would have been exaggerated by the higher temperatures of the Cretaceous, such that oxygen solubility was lower (i.e. for a given amount of oxygen in the atmosphere, less dissolves into seawater) and ocean circulation was more sluggish. Consequently, these OAEs could have been somewhat analogous to the modern Black Sea.  The Black Sea is a restricted basin with a stratified water column, formed by low density fresh water derived from the surrounding rivers sitting stably above salty and dense marine deep water. The freshwater lid prevents mixing and prevents oxygen from penetrating into deeper waters. Concurrently, nutrients from the surrounding rivers keep algal production high, ensuring a constant supply of sinking organic matter, delicious food for microbes to consume using the last vestiges of oxygen.  The ancient oceans of OAEs were not exactly the same but perhaps similar processes were operating. Crucially, the configuration of ancient continents in which major basins were isolated from one another, suggests a parallel between the Black Sea and the ancient North Atlantic Ocean.

But over the past twenty years, that model has proved less and less satisfactory.  First, it does not provide a mechanism for the limited temporal occurrence of the OAEs.  If driven solely by the shape of our oceans and the location of our continents, why were the oceans not anoxic as the norm rather than only during these events? Second, putative OAEs, such as that at the Permo-Triassic Boundary occur at times when the oceans do not appear to have been restricted.  Third, coupled ocean-atmosphere models indicate that although ocean circulation was slower under these warmer conditions, it did not stop.

But also, as we have looked more and more closely at those small windows into the past, we have learned that during some of these events anoxia was more restricted to coastal settings.  And that brings us back to the Zechstein Sea. We mapped the extent of anoxia at an unprecedented scale in cores drilled by the Polish Geological Survey, and we discovered an increasing abundance of GSB molecular fossils in rocks extending from the carbonate platform and down the continental slope, suggesting that anoxia had extended out into the wider sea.  But when we reached the deep central part of the basin, the fossils were absent.  In fact, the sediments contained the fossils of benthic foraminifera, oxygen dependent organisms living at the seafloor, and the sediments had been bioturbated, churned by ancient animals. The green sulfur bacteria and the anoxia were confined to the edge of the basin, completely unlike the Black Sea.  This is not the first such observation and this is consistent with new arguments mandating not only a different schematic but also a different trigger.  And perhaps that trigger was from outside of the oceans.

If the trigger was not solely a restriction of oxygen supply then the alternative is that it was an excess of organic matter, the degradation of which consumed the limited oxygen. A likely source of that organic matter and one that is consistent with restriction of anoxia to ocean margins is a dramatic increase in nutrients that stimulated algal blooms – much like what is occurring today.  And that increase in nutrients, as elegantly summarized by Hugh Jenkyns, could have been caused by an increase in erosion and chemical weathering, driven by higher carbon dioxide concentrations, global warming and/or changes in the hydrological cycle, all of which we now know occurred prior to several OAEs. And again, similar to what is occurring today.

It is likely that today’s coastal dead zones are due not to climate change but to how we use our land and especially to our excess and indiscriminate use of fertilisers, most of which does not help crops grow or enhance our soil quality but is instead washed away to pollute our rivers and coastal seas. And yet that only underscores the lessons of the past.  They suggest that global warming might exacerbate the impacts of our poor land management, adding yet another pressure to an already stressed ecosystem.

Runoff of soil and fertiliser  during a rain storm. Image source: Wikimedia Commons

The Zechstein Sea study is not the key to this new paradigm (and that ‘paradigm’ is far from settled).  There is probably no single study that marked our change in understanding.  Instead, this new model has been gradually emerging over nearly 20 years, as long as I have been studying these events. New geochemical data, such as the distribution of nutrient elements, suggest that many of these anoxic episodes, whether local or global, were associated with algal blooms.  And other geochemical tools, such as the isotopic composition of trace metals, provide direct evidence for changes in the chemical weathering that liberated the bloom-fueling nutrients.

Science can move in monumental leaps forward but more typically it evolves in small steps. Sometimes, after years of small steps, your understanding has fundamentally changed. And sometimes that change means that your perception of the world, the world you love and on which you depend, has also changed.  You realize that it is more dynamic than you thought – as is its vulnerability to human behaviour.
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This was originally posted on the Cabot Institute Blog and is an expanded version of an article on The Conversation.

This blog has also appeared in IFL Science and The Ecologist.