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Hothouse Earth

Aug 09,2018 - Last updated at Aug 09,2018

It would be churlish to ask what took them so long. Let us be grateful, instead, that the climate scientists are finally saying out loud what they all knew privately at least ten years ago.

What sixteen of them are now saying, in an article in the “Proceedings of the National Academy of Sciences”, is that if we do not soon get off the highway we are currently travelling on, we will be irrevocably committed to a “Hothouse Earth”. How soon is “soon”? Probably no more than ten to twenty years away. That is the last exit.

The article has the usual low-key scientific title: “Trajectories of the Earth System in the Anthropocene”. The authors never raise their voices, but they do point out that the likeliest of those trajectories, the one we will stay on even if all the promises in the 2015 Paris Accord on climate change are kept, runs right off a cliff.

“Hothouse Earth” is not very hospitable to human life. Hundreds of millions or even a billion or two would probably survive, but the damage to agricultural systems would be so extreme that billions more would die. The authors do not say this, of course. Putting it into words is too “alarmist”, but the people who actually have to think about these contingencies, like the military in the developed countries, know it very well.

What the authors are saying is that “global warming” driven directly by human emissions of carbon dioxide and other greenhouse gases is only part of the problem. In fact, it’s the smaller part. The real threat is the unstoppable natural “feedbacks”, triggered by the warming that we have caused, that will take us up to the killing temperatures of Hothouse Earth.

They list ten of them, the biggest being the loss of Arctic sea-ice, the melting of the permafrost zone, dieback in both the boreal and the Amazon forests and changes driven by warming in the ocean circulation system. Just triggering one or two of these feedbacks could cause enough additional warming to set off others, like a row of toppling dominoes, and take us up to those lethal temperatures within this century.

Now, this is not really news to climate scientists. When I was writing a book about climate change ten years ago, I interviewed scores of them in half a dozen countries, including Dr Hans-Joachim Schellnhuber, one of the lead authors of this paper and then the director of the Potsdam Institute for Climate Impact Research in Germany, and German Chancellor Angela Merkel’s climate advisor.

He already knew all this stuff then. Everybody did, at Potsdam, at the Hadley Centre for Climate Change in England, at the National Centre for Atmospheric Research in Boulder, Colorado and in universities that had a serious climate research programme. It was the point of departure, the underlying assumption of every conversation I had.

Yet, the role of these feedbacks in the system was not discussed in the scientific journals, not included in the predictions of future warming issued every four or five years by the Intergovernmental Panel on Climate Change (IPCC), and definitely not part of the public debate. Why not?

If you spot smoke billowing out of a house, you do not wait to see actual flames, check what substances are burning and calculate the heat of the fire. You call the fire department immediately. But that is not how science works.

When you make a statement in science, you have to be able to prove it, generally with hard numbers and testable predictions. The hard numbers simply were not available yet, and if you go public without that evidence, you will be torn to pieces by your scientific colleagues, who are also your rivals, of course.

So the climate scientists did not make grand assertions, but they did manage to get the threshold of 2ºC higher global temperature adopted as the never-exceed target for the IPCC’s efforts to get the warming under control. Nobody said publicly how the scientists arrived at that number, but it was because they thought that +2ºC was about where the feedbacks would start kicking in.

The scale and trigger-points of the feedbacks have finally been calculated, more or less, and the news is just as bad as the scientists feared. We have already passed the point where a return to the stable climate of the past 14,000 years is possible and we are on course for Hothouse Earth.

The best we can do is try to stabilise the warming at or just below, +2ºC, and that will not be possible without major human interventions in the climate system. The “Stabilised Earth” is not a natural stopping place: Staying there would require “deep cuts in greenhouse gas emissions, protection and enhancement of biosphere carbon sinks, efforts to remove CO2 from the atmosphere [and] possibly solar radiation management.”

You will notice that geo-engineering (“solar radiation management”) is already part of the package, and that it will be down to human beings to manage the entire ecosystem to keep it “stable”. As Jim Lovelock, the creator of Earth System Science (“Gaia”), wrote 39 years ago, we may “wake up one day to find that [we have] the permanent lifelong job of planetary maintenance engineer”.

I have not bothered to ask Jim if we are there yet. Of course we are.

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P.S the +2C target is actually way to high, it was a number picked out the air by an economist called William Nordhaus. Current thinking indicates we should be aiming to get co2 back down to 280ppm, considering we are already at 410ppm and the rate of increase is also accelerating, it is pretty much an impossibility.

It's amazing that given the reality of our dire global situtation, some people are still insisting climate change isn't even real. The next few decades are going to be very painful for everyone.

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