“Too late” on climate change?

I was enjoying my lunch in Paresky this afternoon — chicken salad on a kaiser roll while sitting on a stool facing Baxter Hall — when a strategically placed flier caught my eye. I’ll quote it at length:

Some numbers are just too much . . .

350ppm is the number that leading scientists say is the safe, stable upper limit for carbon dioxide in our atmosphere.

We’re past it, and rising. However, with swift action it’s not too late to reduce our collective emissions levels.

The rest of the text invites students to attend a jumping-into-a-pile-of-leaves celebration of International Day of Climate Action on Saturday the 24th, the goal being to “call on world leaders to pass climate policies grounded in the latest science and strong enough to get us back to 350.”

There is no doubt that global climate change is among the most important social issues of our day. There is also no doubt that optimism is much to be preferred over pessimism. These things being said, a dose of realism is always necessary, and realism begs the question “is it truly not too late?”

The UN Development Programme’s Human Development Report 2007/08 is organized around the theme “Fighting climate change: Human solidarity in a divided world”. Relying on climate models developed by the Intergovernmental Panel on Climate Change – THE “leading scientists” on the issue – the UNDP presents six possible scenarios for global temperature and CO₂ levels projected to the year 2100. The most pessimistic scenario, given the catchy title ‘A1FI’, assumes “rapid economic and population growth combined with reliance on fossil fuels”. If this is our collective future, the IPCC says that by the end of the century its best estimate is a CO₂ level of a whopping 1550ppm with a global average temperature change of +4.5°C (relative to the preindustrial era) and possibly as high as +6.9°C. With +2°C defined as the threshold for “dangerous climate change,” this is a pretty scary scenario.

Quite frankly, however, the IPCC doesn’t offer us any non-scary scenarios. The most optimistic, titled ‘B1’ (“some mitigation of emissions through increased resource efficiency and technology improvement” in the absence of “rapid economic and population growth”) projects CO₂ stabilization at century’s end at 600ppm, with a best estimate global average temperature change of +2.3°C over preindustrial levels.

Because future greenhouse gas stocks are determined by past greenhouse gas emissions, even stabilizing emission levels this very moment will still result in a significant rise in future CO₂ levels: +200ppm by 2100 even if we stabilized at year 2000 emission levels. To make a +2°C temperature change “unlikely,” the world’s CO₂ ceiling is 350 ppm — the goal of the folks behind the International Day of Climate Action and, as the flier admits, a level we’ve already breached. To make a +2°C change of “medium likelihood,” the world must limit itself to 400 ppm. If our goal is even more limited — simply to stay away from a “very likely” +2°C — we still are allowed just 450ppm. At 650ppm, +2°C is virtually guaranteed.

The 2007/08 Human Development Report lays out an ambitious CO₂ reduction strategy: a 500ppm peak and stabilization at 450ppm by 2100. This is some ways above the 350ppm goal mentioned above, but even this UNDP plan is extremely ambitious. To achieve the 450ppm goal, the UNDP prescribes CO₂ emission cuts for the developed countries from a base year 1990 of [1] 30% by the year 2030 and [2] of 80% by 2050. According to the Environmental Protection Agency, as of 2007 the US was +20.2% from our 1990 levels. That means that using 2007 as our baseline, the US will have to cut CO₂ emissions a whopping 42% by the time Williams students are my age, and this just to dwell in the “medium likelihood” territory for dangerous climate change.

The world’s only examples of greenhouse gas emission reductions of such an incredible and rapid scale involve catastrophic economic collapse, such as in Ukraine since the fall of communism where emissions fell (-55% from 1990 to 2004) alongside absolute declines in population, life expectancy and real GDP per capita. I’m assuming this is not quite what the organizers of the International Day of Climate Action have in mind. Yet a realistic 350ppm scenario which does not involve a serious and lasting global depression exists only in the pages of a Tom Friedman book.

It’s good to be optimistic, and it’s good to take up a challenge in the face of long odds. At the same time, it is very important for everyone concerned about climate change to put at least as much effort into preparing to alleviate the suffering which will result from inevitable catastrophes as into struggling heroically to prevent them.