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