Wednesday, June 22, 2011

What path are we on? Emissions update

Between 2003 and 2008, the global economy was tracking above the Intergovernmental Panel on Climate Change's (IPCC) worst case scenario for carbon dioxide emissions. The financial crisis brought a brief respite in 2009, when emissions actually dropped (remember, this still means that greenhouse gas levels rose in 2009, just a little more slowly than they had been). But it was recently announced by the International Energy Agency that 2010 saw the largest jump in emissions in human history, putting us back up close to the IPCC worst case. What does this mean? If we continue on this trajectory, where will we end up? This piece by two climate scientists gives plenty of good context. The bottom line? According to the IPCC's most recent major report (2007), our current trajectory puts us on track for a 2100 temperature rise of 3-4°C above pre-industrial levels with likely associated impacts including:
Hundreds of millions of people exposed to increased water stress.
30–40% of species at risk of extinction around the globe.
About 30% of global coastal wetlands lost.
Increased damage from floods and storms.
Widespread coral mortality.
Terrestrial biosphere tends toward a net carbon source.
Reduction in cereal productions.
Increased morbility and mortality from heat waves, floods and droughts.
Remember that these projections are based on IPCC AR4 (2007), which was a compilation of research up to the middle of last decade. A lot has happened in climate science in the last five or six years, and little of it has made the picture any rosier. Crucially, the above projections do not include a variety of feedback mechanisms that were not well understood at the time of publication. And there have also been advances in modeling likely impacts in some areas, notably, sea level rise, which is now thought to be between 0.5 and 1.5 metres by 2100. Of course, if our emissions are towards the upper end of the scenarios, then rises are also likely to be higher than 50 cm. However, I think that it is reduction in cereal production that could be the most significant effect geopolitically in the next few decades.

For a more up to date assessment of the state of the science, see the recent Australian Climate Commission's publication The Critical Decade, whose three chapters are helpfully summarised by Skeptical Science: one; two; three. Here is the concluding paragraph:
As you’ve read in this report, we know beyond reasonable doubt that the world is warming and that human emissions of greenhouse gases are the primary cause. The impacts of climate change are already being felt in Australia and around the world with less than 1 degree of warming globally. The risks of future climate change – to our economy, society and environment – are serious, and grow rapidly with each degree of further temperature rise. Minimising these risks requires rapid, deep and ongoing reductions to global greenhouse gas emissions. We must begin now if we are to decarbonise our economy and move to clean energy sources by 2050. This decade is the critical decade.
Remember, we are not just talking about less ice or a few more days of sunscreen, the likely geopolitical consequences of our current path are dire. It doesn't have to be this way.


Toby said...

The fine print of the temperature ranges on the graph says it's the 50%-90% range of outcomes. Frankly, that's a misleading range to choose, it should be balanced around 50% (say 10%-90%).

I have seen dubious chart manipulation by the skeptics, but I am disappointed to see manipulation used by those trying to educate about the dangers of climate change.

byron smith said...

Toby, the admission is there on the image, though I agree that it does feel less than entirely straightforward to not include a range balanced around the 50% mark.