EDITOR'S NOTE 11/18/13: After this blog post was published, the IPCC updated its Summary for Policymakers. The figures in this blog post have been updated to reflect new information.
The Intergovernmental Panel on Climate Change’s (IPCC) Fifth Assessment Report (AR5) has delivered an overwhelming consensus that climate change impacts are accelerating, fueled by human-caused emissions. We may have just about 30 years left until the world’s carbon budget is spent if we want a likely chance of limiting warming to 2 degrees C. Breaching this limit would put the world at increased risk of forest fires, coral bleaching, higher sea level rise, and other dangerous impacts.
When Will Our Carbon Budget Run Out?
The international community has adopted a goal for global warming not to rise above 2°C compared to pre-industrial temperatures. Scientists have devoted considerable effort to understanding what magnitude of emissions reductions are necessary to limit warming to this level, as the world faces increasingly dangerous climate change impacts with every degree of warming (see Box 1).
IPCC AR5 summarizes the scientific literature and estimates that cumulative carbon dioxide emissions related to human activities need to be limited to 1 trillion tonnes C (1000 PgC) since the beginning of the industrial revolution if we are to have a likely chance of limiting warming to 2°C. This is “our carbon budget” – the same concept as a checking account. When we’ve spent it all, there’s no more money (and the planet’s overdraft fees will be much more significant than a bank’s small charges for bounced checks).[^1]