The Climate Change Clock is Ticking 

The UK is in denial about its real carbon emissions, suggests a report from the Stockholm Environment Institute. The academics conclude that if “outsourced” emissions produced in countries like China on goods which are imported into the UK are included in our total carbon footprint, this country’s total greenhouse gas emissions are 49% higher than currently reported. So we should think twice when blaming the Chinese for emitting the CO2 that is required in the manufacture of our fridges and televisions.

The report illustrates once again – as if we had forgotten – that global warming is a global issue. A tonne of CO2 is a tonne of CO2, wherever it is emitted. How you do the counting is more a matter of politics than mathematics. A much greater concern is that all the politics is in danger of obscuring the increasingly drastic nature of the climate change threat. According to Andrew Simms of the New Economics Foundation, the world has only got 100 months left if we are to have a reasonably high chance of staving off runaway global warming.

This is a pretty dramatic claim, and the associated onehundredmonths.org website has an equally dramatic ticking clock counting down until runaway warming begins. “When the clock stops ticking,” it states ominously, “we’ll be beyond the climate’s tipping point, the point of no return.” Yikes. So how valid is this claim? Luckily, NEF’s website provides a 100 months technical note explaining the calculations behind the new campaign. The first thing I noticed is that there isn’t any new modeling work underlying the claim: it is based on existing science, in particular on an analysis by a researcher called Malte Meinshausen which was published in 2006.

Meinshausen was the first scientist to quantify with percentage figures the probability of exceeding certain climatic thresholds: in his 2006 paper he concluded that only by stabilizing greenhouse gas concentrations in the atmosphere at 400 part per million (ppm) would it be “likely” (defined as 66-90% chance) that the world would stay below an eventual warming of two degrees. The NEF analysis has performed a fairly simple calculation, simply counting the time left before this 400 ppm level is reached. The deadline, it turns out, is 1 December 2016.

There are several complicating factors, however. The 400 ppm figure in question is not for CO2 only, but for a basket of atmosphere-altering gases – some of which have a positive “forcing” effect (like CO2 itself) whereas others have a negative (cooling) effect, like sulphate aerosols released by industry. Add the sum of these forcings together and you can arrive at a “CO2-equivalence” figure, which is the one that both NEF and Meinshausen use. The timescales need to be borne in mind, however: CO2 resides in the atmosphere for a century on average, whereas aerosols are washed out by rain in just a week or so.

There are other caveats too. Meinshausen is not saying that two degrees of warming will be reached with certainty when we cross the 400 ppm threshold, but that the risk of seeing two degrees increases steadily thereafter. (Even at 400 ppm there is still a risk of overshooting 2C, of somewhere between 2% and 57%.) At 450 ppm the risk of crossing the 2C line rises to between 26 and 78%, whereas at 550 ppm the risk of overshooting is between 68 and 99%. Indeed, for 550 ppm the risk of overshooting even 3C ranges from 21% to 69%.

There is the question of timescales. Meinshausen’s two degrees calculations referred to two degrees of warming, not the minute the 400 ppm line is crossed in December 2016, but when the atmosphere reaches “equilibrium” – in other words when all the warming processes have had a chance to feed through the system. Like a boiling kettle, the planet has a substantial thermal timelag – it takes a long time for ice sheets to rebalance themselves and for warmer waters to penetrate to the bottom of the deepest oceans. So even at this “tipping point” we still wouldn’t see the expected two degrees of warming until the end of the century at least, if today’s climate models are to be believed.

Reassuring, perhaps – but no cause for complacency. The earth’s thermal timelag also means that today’s emissions will keep on causing warming for decades to come, and that decisions made today on emissions cuts are essential if we are to rebalance the climate in the second half of the century.

In reality, this is a matter of risk analysis: how much risk of destroying our planetary habitat are we prepared to bear in order to keep on burning fossil fuels? Quite a lot, it would seem.

This article was first published in the Guardian (UK) on August 1, 2008