Calculating A Global Carbon Budget
If humanity wants to mitigate climate change, it must calculate a global carbon budget and then allocate that budget among regions or countries. Put aside, for a moment, your (justified) skepticism that governments around the world (especially ours in the US) will ever face up to this fact (because it would inevitably lead to limits that would require, um, sacrifice by the SUV- and meat-worshipping American public, not to mention a complete eradication of all wrong-headed Tea Party beliefs). Because it is a mental exercise that is worth exploring on the off-chance that the effects of climate change start to get bad enough that publics and political leaders wake up.
Calculating how much carbon we can emit before warming the atmosphere beyond the 2 degree Centigrade target that has, rightly or wrongly, become the consensus target is not easy. So many subjective variables. But different scientists and working groups have calculated a range of estimates, and journalist Fred Pearce has an excellent article at Environment 360, explaining those estimates:
The IPCC’s first analysis was included in its fifth scientific assessment of climate change, published in September 2013 and reiterated in the synthesis report released last Sunday. It suggested that a two-thirds chance of keeping warming below two degrees required the world to limit its total carbon emissions since 1860 to no more than a trillion tons of carbon. Of this grand all-time total, 515 billion tons had already been emitted by 2011. So, according to the IPCC, we have just under 500 billion tons of our budget left. Then we have to stop. Totally.
The synthesis report said that fossil-fuel power generation would have to be “phased out almost entirely by 2100″ — unless the largely untried technology of capturing CO2 emissions and burying them out of harm’s way could be deployed on a massive scale. Without a drastic slowdown in emissions within the next decade, the phase-out date could happen much earlier, probably before 2050.
The arithmetic seemed straightforward enough. But carbon budget numbers since quoted by other sources do not all follow this IPCC bottom-line figure. They reveal a bewildering array of different estimates for our remaining budget. Among environmental groups, the World Resources Institute (WRI) sticks with the IPCC estimate that we have 485 billion tons left. But other environment groups quote other numbers. For instance, Greenpeace and WWF say 350 billion tons.
Scientists are even less coordinated. A big study in Nature Climate Changein September by Michael Raupach of the Australian National University in Canberra and others, quotes 381 billion tons. The International Institute for Applied Systems Analysis, a think tank based in Laxenberg, Austria, and the Global Carbon Project says we have 327 billion tons to go. While the International Geosphere-Biosphere Programme, an international research consortium based in Sweden, say 250 billion tons.
To confuse things further, another blue-chip study, published last December by Jim Hansen of the Earth Institute at Columbia University and others, argued that we could emit a further 350 billion tons and still keep below 1.5 degrees of warming.
Simple, right? Okay, not really. But you have to start somewhere. Even more difficult is the question of how yo allocate whatever carbon budget you have left among advanced and developing countries. The fair way to do it would be to include historical emissions, so countries that pumped lots of carbon into the atmosphere while achieving great wealth (like the US), would have to figure out how to sharply curtail emissions while developing countries would have more leeway to emit carbon as they grow their economies further. Or rich, developed countries could buy carbon permits from developing countries who have lots of carbon budget left, which would help those countries reduce poverty and achieve more stable, productive economies. But you can imagine how that idea would play in the US Congress.
I don’t have much faith that the United States and other developed nations will pursue limits that are either sufficient or fair (though I will continue to support and vote for any politician who takes climate change seriously). But I am interested in trying to calculate what an individual carbon budget would look like if we did in fact set global limits that were fair and meaningful. And then exploring what it would take to get my budget down to that level. That would give anyone who wants to stop being part of the problem, who wants to be an Earthist, a target they can aim for. Should be fun, er interesting.