Prof. John Shepherd, NOC, Univ. of Southampton and Tyndall Centre for Climate Change Research

Climate Change: The Factor Forty Problem

Wednesday, 8th November, 2006.

Abstract

The IPCC third assessment projects that global mean temperatures will increase by between 1.4 and 5.8 °C by 2100 and the fourth assessment is likely to say something similar. However, temperatures will continue rising for a very long time (maybe a thousand years) after that, as it is only the projections which stop in 2100. Moreover, comparison with past natural climate changes suggests that current models may under-estimate the sensitivity of our climate to rather small changes. Climate has changed in the past in unexpected and surprising ways, which we do not yet understand, and we should be prepared for a bumpy ride, with further surprises in the future. Ocean acidification provides a further strong motivation for emissions reductions.

In such circumstances we should take precautionary action, and to stabilise temperature anywhere near the bottom end of the IPCC range, and moderate acidification, global CO2 emissions will need to be reduced to the level of the ocean sink (i.e. to about 25% of their current global level) over the next century or so. To achieve this is going to be a massive problem. The Kyoto Protocol was just a very small step in (roughly) the right direction.

The Big Picture is that while emissions need to be reduced by a factor of 4, population growth will worsen the problem by another factor of 2. Increased energy use (per capita) in the developing world (to the EU level only) implies another factor of about 5. So altogether we probably need a factor of 40 in decarbonisation of the global energy supply in this century. Improved energy efficiency and renewables (etc) may be able to deliver a factor of 4. Hydrogen is only a carrier, and has to be generated from a primary source. The only other known options are bio-fuels, nuclear power, and decarbonisation of continued use of fossil fuels by CO2 sequestration. This must be physical or chemical sequestration, because biological sinks are too small, too difficult to quantify, and too uncertain (too easily remobilised). Even so transport, especially aviation, represents the most intractable part of the problem.

CO2 sequestration (CCS) technology represents a possible way forward, though the cost is non-trivial. We should develop this technology urgently, and research other macro-engineering technologies (such as albedo modification) as a precautionary measure. CCS needs to be deployed on a large scale, and it will take a long time, so we should start soon. We need to increase (global) R&D in this area substantially. However, research & education are not enough. Nothing will actually happen unless governments act to create the economic incentives that make it worth-while. Replacement of existing indirect taxes like VAT by a carbon tax to raise the same revenue would be a good start.

So if you are interested in climate change, tune in!