80 percent by 2050 is not enough

"In order to stay below 2 °C, global emissions must peak and decline in the next 10 to 15 years, so there is no time to lose. -- Bali Climate Declaration

Item 1: The U.S. Senate Environment and Public Works Committee has come up with a bill that "calls for a roughly 70 percent cut from 2005 levels by 2050 in the production of carbon dioxide and other climate-altering pollutants." (New York Times, Dec. 6, 2007)

Item 2: The mainstream environmental movement, including the likes of Bill McKibben and the Step it Up gang, has widely agreed on a goal of an 80 percent cut in greenhouse gases by 2050. Democratic presidential contenders Joe Biden, Hillary Clinton, Chris Dodd, John Edwards, Dennis Kucinich and Barack Obama also support the 80 by 2050 target. (NPR)

Item 3. America's premier climate-change campaigner, Al Gore, and Democratic presidential candidate Bill Richardson say we need at least a cut of at least 90 percent by 2050.

Item 4. George Monbiot, Britain's leading climate-change activist-author, says even that might not be enough. In his latest column. he points out that if the whole idea is to limit global warming to 2°C, a threshold many climatologists believe will trigger enormous changes in the biosphere, then we need to think about a 100 percent cut.

So who's target is based on science, rather than politics? (And never mind the different reference years for the cut; although some are using 2005, some 2000 and others 1990, the scale of the problem remains regardless.) Well, for that we turn to

Item 5. Andrew J. Weaver, Kirsten Zickfeld, Alvaro Montenegro and Michael Eby, climatologists with the School of Earth and Ocean Science at, University of Victoria, out on Vancouver Island, recently published the following in Geophysical Research Letters (Vol. 34, L19703. doi:10.1029/2007GL031018, 2007):

All emission targets considered with less than 60% global reduction by 2050 break the 2.0°C threshold warming this century, a number that some have argued represents an upper bound on manageable climate warming. Even when emissions are stabilized at 90% below present levels at 2050, this 2.0°C threshold is eventually broken. Our results suggest that if a 2.0°C warming is to be avoided, direct CO2 capture from the air, together with subsequent sequestration, would eventually have to be introduced in addition to sustained 90% global carbon emissions reductions by 2050.

Monbiot does a little extra math and discovers that even those dire warnings from a peer-reviewed journal might not be giving us the straight dope. He writes

In the new summary published by the Intergovernmental Panel on Climate Change (IPCC), you will find a table which links different cuts to likely temperatures. To prevent global warming from eventually exceeding 2°, it suggests, by 2050 the world needs to cut its emissions to roughly 15% of the volume in 2000.

I looked up the global figures for carbon dioxide production in 2000 and divided it by the current population. This gives a baseline figure of 3.58 tonnes of CO2 per person. An 85% cut means that (if the population remains constant) the global output per head should be reduced to 0.537t by 2050. The UK currently produces 9.6 tonnes per head and the US 23.6t. Reducing these figures to 0.537t means a 94.4% cut in the UK and a 97.7% cut in the US. But the world population will rise in the same period. If we assume a population of 9bn in 2050, the cuts rise to 95.9% in the UK and 98.3% in the US.

Note that each American, on average, produces more than 20 tonnes, but we'll need to get that down to about one third of a tonne over the next 42 years, if we're going to avoid catastrophic climate change. The scale of the problem, it would seem, has not yet sunk in where it's needed.

Oh, and incidentally, the only Republican presidental wannabe with a 2050 GHG emission reduction goal is John McCain, who likes 65 per cent.