If we want to contain global warming, then we need to constrain carbon dioxide emissions within an appropriate ecological budget. We now know what that budget is.
According to a paper published by Malte Meinshausen and colleagues in NATURE last week and reported in the Financial Times, the Earth’s cumulative carbon dioxide emissions budget for 2000-2050 is 1,000 gigatons.
This budget would limit global warming to no more than 2 degrees C — the target that scientists and politicians have agreed to work toward in the negotiations for a new global climate change treaty.
Two degrees of warming will have significant consequences for people and nature, but would avoid more catastrophic economic and ecological impacts that would likely accompany further warming (see my recent Cool Green Science post on the specific consequences).
So how are we doing in terms of spending within our budget? Not very well according to Mienshausen’s report. Between 2000 and 2006, cumulative global carbon dioxide emissions were about 234 gigatons, and we continue to emit 36.3 gigatons every year. At this pace, we will exhaust the 1,000 gigaton budget by 2027.
To get back on budget, we have a choice. We can continue emitting carbon dioxide at current rates and then abruptly stop when we hit our 1,000 gigaton limit in 2027. Or we can begin reducing emissions now and continue reducing emissions gradually so that our carbon dioxide budget lasts until 2050. Obviously, the latter would be the smarter course.
But there is temptation to continue our profligate carbon spending and to exceed our 1,000 gigaton budget. Since the start of the Industrial era, we have been drawing liberally from the enormous carbon bank accounts that Mother Nature stashed away in the form of fossil fuels. If we were to burn proven reserves, Meinshausen estimates that we would emit between 2,500 and 3,000 gigatons of carbon dioxide, making global warming of more than 2 degrees C a near certainty.
Mother Nature is not going to tell us what to do. Will we stay within our carbon dioxide budget on our own? Or will we overspend and risk the consequences of more severe climate change?
(Image: Smokestack in Japan. Credit: papadont through a Creative Commons license.)