The Climate in Emergency

A weekly blog on science, news, and ideas related to climate change

Two Degrees of Separation


Last week, as sometimes happens, I got curious.

While writing–once again–about how the world must stay under 2° C. of warming, I suddenly realized I didn’t know where this number came from. Climate writers frequently assert that if the Earth warms more than that, we will cross a tipping point beyond which climate catastrophe will likely occur. That’s plausible, since tipping points like that do exist. But I had never encountered any explanation of why the tipping point is there or how we discovered it. So, I went hunting and found a 2010 paper cleverly titled Three Views of Two Degrees.

It turns out that 2° C isn’t a scientific limit at all, because current science gives us not just one number but rather a whole cloud of numbers. 2° C is instead, a convenient shorthand for that cloud and it is a rallying cry. And it probably isn’t enough.

Who Said Two Degrees

The 2° C limit was originally a rough estimate made by an economist in the 1970’s. W.D. Nordhous was interested in climate policy, which he approached from a perspective of cost-benefit analysis. He assumed that getting off fossil fuel would cost something and that climate change would also cost something, therefore we should craft climate policy so as to use fossil fuel right up until the point where continuing to do so costs more money than it saves. At that point, we should stop. Nordhous needed some estimate of where that that point might be, so he took a look at the fairly basic information available at the time and concluded that over the past several hundred thousand years the climate has never been more than 2° C warmer than it was at the start of the industrial revolution. He reasoned that exceeding the normal variation would be bad.

2° C itself was, of course, secondary, simply a plausible example of the kind of target Nordhaus wanted. The main point was the principle of the cost/benefit analysis. The thing is, Nordhous wasn’t the only one who needed a definite number for the sake of discussion. It’s simply easier to talk about policy, and easier to run climate models, if you have a single number to work with instead of what the research itself often presents, which is a whole group of interrelated ranges. And so, the 2° C figure has become popular far beyond Nordhous’s original discussion of costs and benefits.

That 2° C was used during a UNFCCC (United Nations Framing Convention on Climate Change) conference in Germany in 1995 probably has a lot to do with its popularity. Angela Merkel, who was Germany’s Environment Minister at the time, chaired that conference and was apparently very impressed. She was instrumental in writing the 2° C goal into the preliminary agreement signed in Copenhagen in 2010. Also, “2” is a nice, whole number, easy to remember. Note that even in America, no one refers to the limit as 3.6° F.

Is 2° C a Real Limit?

Yes and no.

More recent research has confirmed that a 2° C rise would, indeed, take us into temperature ranges the world hasn’t seen in hundreds of thousands of years. In that, Nordhaus was quite correct. However, the climate system has not one tipping point but several; some kick in above 2° C, others kick in below–and there are some, doubtless, that we don’t know about yet.

More importantly, the premise of the limit is flawed.

First, the average temperature of the planet is not the real problem–the real problem is the speed at which the climate changes. As climate deniers are fond of pointing out, Earth’s climate is always changing and has in the past been radically different than it is today. There have been forests in the Antarctic and there have been glaciers in New England; in either case, Earth had rich, vibrant ecosystems. Human society has also weathered climate changes and can obviously do so again. But adaptation, both human and otherwise, takes time. And right now, we’re not getting it.

Second, even if climate catastrophe itself begins only after 2° C of warming (which is questionable), there is a lot that can go very seriously wrong–and some of it has already happened–short of catastrophe. Sea level rise provides the most clear-cut example, since it is unambiguously caused by global warming and higher seas unambiguously cause more severe coastal flooding. Whole nations are at risk of going out of existence. We are also losing glaciers that provide drinking water to huge human populations, seeing increases in dangerously extreme weather events…arguably, global warming may already be contributing to food insecurity, and hence to social and political tension, in the Middle East. A mass extinction is underway. All this is pretty catastrophic, if you happen to be in the middle of it. Nordhous’s original proposal, that we allow the climate to warm up until the 2° C limit so as to make more money off of fossil fuels until then, is heartless in the face of people who are dying of climate change already.

Is 2° C a Useful Goal?

Of course, 2° C is no longer being considered as the amount of warming to allow before getting off fossil fuel. Instead, it represents the course of immediate, aggressive emissions reductions–the closest thing to stopping greenhouse gas emissions today that anybody considers plausible.

Some are calling even this goal unrealistic, arguing that 2° C be abandoned as pointless an unattainable.

It’s not that cutting emissions is not technically feasible. If humanity collectively turned off the machines today, the post-petroleum age would begin tomorrow (greenhouse gas emissions would not stop quite so fast–natural gas wells would still leak, for example–but these would have minimal effect). We just don’t want to do that.

There are good reasons for not simply turning the machines off–I expect that such a sudden shift would cause widespread panic and economic collapse, for one–but not all the reasons out there are good. The fact of the matter is that some people want power and money and luxury and are willing to delay climate sanity and climate justice to get it.

But the thing is, the atmosphere doesn’t care what is politically or technical feasible–if the planet warms by more than 2° C, then whatever happens will happen, be it climate catastrophe or not. We have the option to let go of a goal, but we do not have the option to decline the consequences of our actions.

The fact we are faced with is that we must, as a planet, get off fossil fuel and address other causes of anthropogenic climate change (cement production, deforestation, etc.) as soon as possible because people are dying and ecosystems are collapsing and will continue to do so as long as we keep warping the sky as we are. If 2° C  works as a rallying point towards that end, a finite shorthand to use instead of the more amorphous “immediately,” then well and good. If some other goal works better, then let’s use that instead.

Because while 2° C is not itself a scientifically based deadline, the urgency that now informs its use does have a basis in science.


Author: Caroline Ailanthus

I am a creative science writer. That is, most of my writing is creative rather than technical, but my topic is usually science. I enjoy explaining things and exploring ideas. I have one published novel and another on the way. I have a master's degree in Conservation Biology and I work full-time as a writer.

3 thoughts on “Two Degrees of Separation

  1. Pingback: They Actually Said It! | The Climate Emergency

  2. Pingback: Calculating Cost Part 1 | The Climate Emergency

  3. Pingback: We Agree Not to Destroy the World | The Climate Emergency

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