"The Final Countdown" and "100 months (or less) to stop emissions"

The Final Countdown

Time is fast running out to stop irreversible climate change, a group of global warming experts warns today. We have only 100 months to avoid disaster. Andrew Simms explains why we must act now - and where to begin.


by Andrew Simms, The Guardian, August 1, 2008

Excerpt:

If you shout "fire" in a crowded theatre, when there is none, you understand that you might be arrested for irresponsible behaviour and breach of the peace. But from today, I smell smoke, I see flames and I think it is time to shout. I don't want you to panic, but I do think it would be a good idea to form an orderly queue to leave the building.Because in just 100 months' time, if we are lucky, and based on a quite conservative estimate, we could reach a tipping point for the beginnings of runaway climate change.

. . .

So, how exactly do we arrive at the ticking clock of 100 months? It's possible to estimate the length of time it will take to reach a tipping point. To do so you combine current greenhouse gas concentrations with the best estimates for the rates at which emissions are growing, the maximum concentration of greenhouse gases allowable to forestall potentially irreversible changes to the climate system, and the effect of those environmental feedbacks. We followed the latest data and trends for carbon dioxide, then made allowances for all human interferences that influence temperatures, both those with warming and cooling effects. We followed the judgments of the mainstream climate science community, represented by the Intergovernmental Panel on Climate Change (IPCC), on what it will take to retain a good chance of not crossing the critical threshold of the Earth's average surface temperature rising by 2C above pre-industrial levels. We were cautious in several ways, optimistic even, and perhaps too much so. A rise of 2C may mask big problems that begin at a lower level of warming. For example, collapse of the Greenland ice sheet is more than likely to be triggered by a local warming of 2.7C, which could correspond to a global mean temperature increase of 2C or less. The disintegration of the Greenland ice sheet could correspond to a sea-level rise of up to 7 metres.

In arriving at our timescale, we also used the lower end of threats in assessing the impact of vanishing ice cover and other carbon-cycle feedbacks (those wanting more can download a note on method from onehundredmonths.org). But the result is worrying enough.

We found that, given all of the above, 100 months from today we will reach a concentration of greenhouse gases at which it is no longer "likely" that we will stay below the 2C temperature rise threshold. "Likely" in this context refers to the definition of risk used by the IPCC. But, even just before that point, there is still a one third chance of crossing the line. . .

Link to article: http://www.guardian.co.uk/environment/2008/aug/01/climatechange.carbonemissions

'100 months' to stop overheating

by Ian Sample, science correspondent, The Guardian, August 1, 2008

Rising greenhouse gas emissions could pass a critical tipping point and trigger runaway global warming within the next 100 months, according to a report today.

The estimate from the New Economics Foundation is based on when emissions will reach such high levels that it "is no longer likely" the world will be able to avoid a 2 C rise in average temperatures. "We know climate change is a huge problem, but there's a missing ingredient of urgency," said Andrew Simms, policy director at the foundation.

According to the UN's experts, greenhouse gas levels in the atmosphere, which are at around 430 ppm, would have to be stabilised at 450 ppm to avoid a rise of more than 2 C.

Simms and Victoria Johnson made a conservative estimate of future emissions based on six greenhouse gases and other pollutants, such as aerosols, which have a cooling effect. They predict that 100 months from today emissions will rise above the critical 450ppm threshold.

According to the government's 2006 report on climate change by Nicholas Stern, a 2 C rise could release vast quantities of carbon stored in soils and permafrost, see 15%-40% of land species threatened with extinction, and up to 4 billion people experiencing water shortages.

Link: http://www.guardian.co.uk/environment/2008/aug/01/carbonemissions.climatechange