Temperature: where is the tipping point?

Emissions are a cumulative game
October 21, 2009
World carbon dioxide output: this map shows the relative size of nations according to how much CO2 they emit. North America accounts for 28 per cent. It illustrates total, rather than per capita, emissions. If a per capita scale were used, Australia would be much larger—and Africa barely visible at all.


In terms of their sheer scale and complexity, people often compare the climate change negotiations to the WTO talks. But subsidies and tariffs will always be under human control; climate change will not. Scientists have agreed that a 2°C average rise in temperature from preindustrial levels is what the world can more or less handle. “A two-degree world” has emerged as the one we should be aiming for. The EU, the G8 and President Obama’s Major Economies Forum on Energy and Climate—a kind of G17 formed outside the UN climate talks—have all agreed on this.

Over the past 100 years, worldwide average temperatures have already risen by about 0.75°C (although to the delight of sceptics they have been steady for the past decade). The heating process takes time to kick in, so even if the world stopped producing greenhouse gas emissions tomorrow, temperatures would rise by another 0.6°C, to a total increase of around 1.4°C. Limiting the concentration of CO2 in the atmosphere to 450 parts per million (ppm) would significantly increase our chances of hitting the 2°C target. But the current concentration is already around 380ppm: 85 per cent of the way there. Moreover, emissions are currently rising fast, at a rate of 2.5 to 3 per cent per year.

The point is that carbon emissions is a cumulative game. It is not so much the final rate of emissions that matters, it is how much we pump into the atmosphere on the way there. We might well be producing only half our current CO2 emissions by the middle of the century but, if we keep reaching new record levels every year between 2010 and 2030, that won’t help us at all. The shape of the curve—when we peak, how steeply we fall—decides everything. This is partly a matter of maths and partly also because the world’s forests, oceans and air are all going to become less efficient at soaking up greenhouse gases as the temperature rises. In sum, time is running out faster than we think. Two researchers from the Tyndall Centre for Climate Change Research, Kevin Anderson and Alice Bows, found that the only way to meet the target of 2°C would be if global emissions peaked between 2015 and 2020 and then fell at a rate of 4 per cent, year on year, until world industry was completely decarbonised. A decline on that scale has only ever happened once in history—following the fall of the Soviet Union—and the authors concluded that isn’t going to happen again.

But whether 2°C is achievable or not, the broader goal of Copenhagen remains: the almighty braking, peaking and falling of our emissions. The political deal agreed at the end of this year will govern the vital years until 2020, and once it is adopted, once it starts to make its way through senates and parliaments around the world, it will not be easy to change. And that’s why, as you get closer to the people making the agreement—most of them anyway—there is the smell of something like fear.