James Ihaka at NZ Herald reports:
New research from Oxford University shows the rate of global warming has been lower over the past decade than it was previously.
The paper, “Energy budget constraints on climate response”, to be published online by Nature Geoscience, shows the estimated average climate sensitivity – or how much the globe will warm if carbon dioxide concentrations are doubled – is almost the same as the estimates based on data up to the year 2000.
The two estimates of the average are only 0.1C different.
The study, which uses data from the past decade, also shows the most extreme rates of warming simulated by climate models over 50- to 100-year timescales are looking less likely.
The most recent global assessment of scientific understanding on the topic of climate sensitivity was carried out by the UN body charged with producing regular evaluations of the state of climate knowledge, the Intergovernmental Panel on Climate Change, in 2007.
It estimated then that if carbon dioxide concentrations eventually doubled from their pre-industrial levels of around 280 ppm to 560 ppm, the long-term temperature rise, hundreds of years in the future, was likely to be between 2°C and 4.5°C, with a best estimate of about 3°C.
In the short term, over the next 50 to 100 years, it suggested likely rises within a range of 1°C and 3°C.
Dr Otto and his colleagues have come up with similar estimates to the IPCC’s long-term projections, but their short-term figures (for what is technically known as the transient climate response) suggest temperatures might only rise by between 0.9 °C and 2°C in coming decades.
So the worst case scenario is now deemed unlikely. Why?
The difference comes about because the researchers have taken account of the most recent decade of flatter temperature rises – which many scientists believe are due to the oceans’ absorption of heat – and other factors.
This makes sense. Despite what some say, there is no scientific doubt that greenhouse gases in the atmosphere have a warming effect as they keep heat in.
But what we have an imprecise knowledge of is how the rest of the climate ecosystem reacts to the warming generated by greenhouse gases. That is why there is legitimate debate about the extent of any warming (but not over the fact there is warming over the long-term).
The uncertainty makes policy responses more difficult, especially the key issue of whether money is better spent on mitigation or adaptation. The key policy challenge with mitigation is getting the big three emitters to agree. Any mitigation efforts that do not include them are useless in an environmental sense (but may have some use in a political sense).