So now we know how much carbon we have left. Researchers at Oxford University in the UK and the Potsdam Institute in Germany, with contributions from other renowned academic institutions, have calculated the global “carbon budget” - that is, the amount of greenhouse gas that we can spew out before causing catastrophic and irreversible changes to the climate.
They report on their work in the prestigious peer reviewed journal Nature.
The 2°C limit
Scientists have agreed for several years that raising global temperatures by more than 2 ° Celsius above pre-industrial levels is about the limit of safe change to the climate. More warming than that, and some of the effects of climate change start to become irreversible and catastrophic. Droughts, heatwaves, storms, floods, sea level rises and the spread of hunger and disease. Large swathes of the world become unsuitable for agriculture.
Beyond 2°C, the triggering of various tipping points also becomes likely. Tipping points are reached when warming sets off a feedback mechanism which results in rapidly increasing further warming. For instance, when the permafrost melts in Siberia it releases methane from the underlying swamps, which in turn increases warming because methane is a greenhouse gas twenty times more powerful than carbon dioxide.
Another feedback mechanism will be reached when the Amazon warms so much that instead of being a massive “sink” or absorber of carbon, it becomes a net carbon source.
The carbon budget: How much is left?
So avoiding these outcomes is a good idea. But the research into the carbon budget makes worrying reading. Over the course of time, from pre-industrial levels to the distant future, we can emit about 1 trillion tonnes of carbon before we raise temperatures by 2°, according to the researchers.
The problem is we have already emitted half of that and are on track to emit the rest in the next 20 years at current rates. And we could not burn more than about a quarter of the current proven and economically recoverable fossil fuel reserves, if were to stay within the carbon budgets. Explain that to Saudi Arabia, Russia, Canada, etc.
Copenhagen targets inadequate
The other problem is that these findings mean the emissions goals now being discussed in the run-up to the Copenhagen conference in December, at which a new successor to the Kyoto treaty should be forged, are too puny to meet this carbon budget safely.
The researchers found there was a less than 50 per cent probability that halving emissions by 2050 – the figure that has most traction at the talks – will be sufficient to keep us below a 2° warming.
Developed countries, which are coalescing around a target of cutting their emissions by 80 per cent by 2050, would have to up this to 90-95 per cent, according to the scientific analysis.
So the likelihood is that even if a 50 per cent cut in global emissions by 2050 is reached – which is a very big if indeed – the world will still overshoot the temperature target and end up in worse trouble than we thought.
So what do we do? Stay tuned…
The FT is shortly to begin a series looking at the different possibilities available to complement emissions cuts as a way of reducing the temperature rises.
Climate scientists warn of looming disaster (FT, 29/04/09)