Author: r.d.pancost

Rich grew up on a small farm in Ohio and studied Geology at Case Western Reserve University and Penn State University, where he developed tools based on organic compounds to reconstruct past climate. He worked at the Netherlands Institute of Sea Research and joined the University of Bristol Organic Geochemistry Unit in 2000. He helped found the interdisciplinary Cabot Institute and became its Director in 2013, stepping down in 2018 to become Head of the School of Earth Sciences. With Ujima Radio and BGCP, he co-created the Black and Green Ambassadors. Throughout it all, he has most enjoyed bringing brilliant, diverse people together to stimulate the creation of new ideas.

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

Posted on July 9, 2018 by r.d.pancost

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.

Image result for Pliocene SSTs

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.]

The Origins of the Uncertain World

Posted on July 7, 2018July 7, 2018 by r.d.pancost

In late 2014, the Cabot Institute was in deep consultation with artists, colleagues, businesses and political leaders about our contribution to Bristol EU Green Capital 2015. Given the breadth of Cabot, we were keen to contribute in diverse ways, especially around sustainability solutions and the range of environmental challenges we face, from plastics in the sea to procuring safe, sustainable food. However, 2015 was also a fantastic chance to discuss climate change, its causes and impacts and how Bristol and the wider world would have to adapt – especially given that 2015 would culminate with the COP21 climate negotiations in Paris. At the same time, we wanted to examine climate change through a somewhat different lens than had been done in the past. Uncertainty was that lens. We wrote this at the end of 2014 announcing the Uncertain World as our framework for discussing these issues during 2015 and beyond. It went on to inform Bristol’s strong commitments to climate change and its Resilience Strategy.

Originally posted on the Cabot Institute blog, this was our statement of intent.

Over the next 18 months, in collaboration with Bristol Green Capital 2015 artists, civic leaders and innovative thinkers, the Cabot Institute will be participating in a series of activities in which we examine how human actions are making our planet a much more uncertain place to live.Fifty years ago, between 1962 and 1966, J. G. Ballard wrote a trio of seminal environmental disaster novels: The Drowned World, The Burning World and The Crystal World. These novels remain signposts to our future, the challenges we might face and the way people respond to rapid and unexpected change to their environment. In that spirit and coinciding with the Bristol Green Capital 2015, we introduce The Uncertain World, a world in which profound uncertainty becomes as much of a challenge to society as warming and rising sea levels.

J.G Ballard’s The Drowned World
taken from fantasticalandrewfox.com

For the past twenty years, the University of Bristol has been exploring how to better understand, mitigate and live with environmental uncertainty, with the Cabot Institute serving as the focus for that effort since its founding in 2010. Uncertainty is the oft-forgotten but arguably most challenging aspect of mankind’s centuries-long impact on the environment. We live our lives informed by the power of experience: our own as well as the collective experience of our families, communities and wider society. When my father started dairy farming he sought advice from my mother’s grandfather, our neighbours, and the grizzled veterans at the Middlefield auction house. Experience helps us make intelligent decisions, plan strategically and anticipate challenges.

Similarly, our weather projections, water management and hazard planning are also based on experience: tens to hundreds of years of observation inform our predictions of future floods, drought, hurricanes and heat waves. These records – this experience – can help us make sensible decisions about where to live, build and farm.

Now, however, we are changing our environment and our climate, such that the lessons of the past have less relevance to the planning of our future. In fact, many aspects of environmental change are unprecedented not only in human experience but in Earth history. As we change our climate, the great wealth of knowledge generated from human experience is losing capital every day.

The Uncertain World is not one of which we have no knowledge – we have high confidence that temperatures and sea level will rise, although there is uncertainty in the magnitude and speed of change. Nor should we view The Uncertain World with existential fear – we know that warm worlds have existed in the past. These were not inhospitable and most evidence from the past suggests that a climate ‘apocalypse’ resulting in an uninhabitable planet is unlikely.

Nonetheless, increasing uncertainty arising from human-induced changes to our global environment should cause deep concern. Crucial details of our climate remain difficult to predict, and it undermines our ability to plan for our future. We do not know whether many regions of the world will become wetter or dryer. This uncertainty propagates and multiplies through complex systems: how do we make sensible predictions of coastal flood risk when there is uncertainty in sea level rise estimates, rainfall patterns and the global warming that will impact both? We can make predictions even in such complex systems, but the predictions will inevitably come with a degree of uncertainty, a probabilistic prediction. How do we apply such predictions to decision making? Where can we build new homes, where do we build flood defences to protect existing ones, and where do we abandon land to the sea?

Methane escaping from Arctic
permafrost. Image: Treehugger.com

Perhaps most worrying, the consequences of these rapid changes on biological and chemical systems, and the people dependent upon them, are very poorly understood. For example, the synergistic impact of warmer temperatures, more acidic waters, and more silt-choked coastal waters on coral reefs and other marine ecosystems is very difficult to predict. This is particularly concerning given that more than 2.6 billion people depend on the oceans as their primary source of protein. Similarly, warming of Arctic permafrost could promote the growth of CO2-sequestering plants or the release of warming-accelerating methane – or both. Warm worlds with very high levels of carbon dioxide did exist in the past and these do provide some insight into the response of the Earth system, but we are accelerating into this new world at a rate that is unprecedented in Earth history, creating additional layers of uncertainty.
During late 2014 and 2015, the Cabot Institute will host a variety of events and collaborate with a variety of partners across Bristol and beyond to explore this Uncertain World and how we can live in it. How do we better explain uncertainty and what are the ‘logical’ decisions to make when faced with uncertainty? One of our first events will explore how uncertainty in climate change predictions should motivate us to action: the more uncertain our predictions the more we should employ mitigation rather than adaptation strategies. Future events will explore how past lessons from Earth history help us better understand potential future scenarios; how future scenario planning can inform the decisions we make today; and most importantly, how we build the necessary flexibility into social structures to thrive in this Uncertain World.

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

Posted on June 30, 2018January 1, 2022 by r.d.pancost

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.