On 26 November, the House of Commons Environmental Audit Committee held a special one-off evidence session on the scientific basis for global carbon reduction targets.1
Giving evidence was leading climate scientist Professor James Hansen of NASA’s Goddard Institute for Space Studies, the government’s chief scientific adviser Professor John Beddington and Environment Department (DEFRA) scientific adviser Professor Robert Watson.
In a two-pronged attack, Professor Hansen told MPs that the EU’s target to cap temperature increases at 2°C was too high to stop dangerous climate change. He also said capping atmospheric carbon dioxide levels at 450 parts per million, thought to correspond to a 2°C limit, would in any case lead to more than 2°C of warming.
"Even the level we are currently at, 385 parts per million, is already getting us into the dangerous range," he said. "We really need to go back to no more than 350ppm."
Committee chair Tim Yeo (Cons: South Suffolk) asked if the 2°C target was a safe aim. Professor Hansen responded that 1°C would have been more appropriate. "2°C is very likely to mean that we would not have any sea ice in the Arctic, that we would not have any mountain glaciers," he said.
Delivering the knockout blow, he concluded that the 2°C target "is too high. This is very bad news to be giving to governments, but you cannot change the laws of physics."
Professor Hansen set out his arguments in more detail in a recent scientific article.2 The paper says increased atmospheric CO2 will bring higher than expected warming because the equilibrium climate sensitivity is about 6°C, rather than the ‘best estimate’ of 3°C from the Intergovernmental Panel on Climate Change (IPPC). Climate sensitivity is the amount of warming expected in a modelling experiment where the concentration of CO2 is instantaneously doubled.
Antarctica first formed 50 million years ago when CO2 levels were 450, plus or minus 100ppm. We must keep long-term atmospheric levels below 350ppm to avoid a catastrophic reversal of Antarctic freezing, the article suggests.
In their evidence, Professors Beddington and Watson were more measured. Committee member Martin Horwood (Lib Dem: Cheltenham) asked what atmospheric concentration of CO2 policymakers should aim for. Professor Watson said: "I think the European target [of 2°C]… is an appropriate target."
Pressed on what this would mean for a target CO2 concentration, Professor Watson said: "It depends on what you think the climate sensitivity factor is. I would say you have a 50:50 shot of stabilising at 2°C above pre-industrial [levels] at somewhere between 400 and 450ppm. If you take Jim Hansen’s new estimate of the climate sensitivity factor, it has to be even lower than that, but within the IPCC, within the Stern Report you have a 50:50 shot somewhere around 400 to 450ppm."
On aviation and shipping, Professor Beddington noted that "it seems sensible that aviation and maritime emissions have got to be a decision which is actually taken at an international level".
Professor Watson said later: "It is quite clear that if we are going to try and limit the greenhouse gas concentrations to anything in the range of 400 to 450ppm we have to bring aviation in."
Continuing the theme, David Chaytor (Lab: Bury North) asked the advisers if an expansion of aviation was compatible with reducing emissions. "The answer is obviously no, unless you can actually turn the fuel to something like a biofuel," said Professor Watson.
Mr Chaytor asked the chief scientific adviser if he shared his predecessor’s views on carbon capture and storage (CCS). Professor Beddington agreed that it is "enormously important" but as to Professor David King’s suggestion that it was "the only hope for mankind" he said that he was agnostic. "There is always prayer and things like that," he added.
Professor Watson said in his view, without CCS "there would be no hope of 450. I doubt there would be a hope of 550ppm".