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Yes, it warms the planet - just not as much as thought
By Andrew Orlowski • Get more from this author
Posted in Science, 22nd April 2013 06:03 GMT
The results of a new approach to calculating the effect of CO[SUB]2[/SUB] - using empirical observations - suggest it has a lower impact on the climate than previously thought, and its effects are being over-estimated by the IPCC. Publishing in the American Meterological Society's Journal of Climate, a new paper called An improved, objective Bayesian, approach for applying optimal fingerprint techniques to estimate climate sensitivity, Nicholas Lewis applies objective Bayesian techniques and uses more up-to-date observational data to derive his conclusions.
Estimates of ECS (Equilibirum Climate Sensitivity, defined by the IPCC here) produce a range of temperatures that we can expect from a doubling of atmospheric CO[SUB]2[/SUB] concentrations over pre-industrial levels. They're derived in three ways: from complex climate models (GCMs) which largely ignore observational evidence, simpler models constrained by observations, and direct observation.
The Lewis paper takes the second approach. Aerosols, both natural and manmade, have a potential negative feedback, with volcanic eruptions proving to have a dramatic short-term effect. Lewis uses more up-to-date estimates of aerosol forcing (from volcanos, for example) drawn from the observational data, rather than other papers, and compares global temperatures over short decadal periods, to remove the effect of volcanic eruptions. He also uses a technique called objective Bayesian analysis. Conventional subjective Bayesian analysis relies on highly subjective uniform priors, aka deliberatively-informative "expert" priors, as parameters.
The results don't diverge completely from the IPCC estimates, but they are significantly lower. Lewis finds mode and median climate sensitivity of 1.6°C, with 90 per cent confidence in a range of 1.2°C to 2.2°C. This compares to the IPCC's 2°C-4.5°C 'likely range'. Lewis also has a crack at updating the Forest 06 study
By Andrew Orlowski • Get more from this author
Posted in Science, 22nd April 2013 06:03 GMT
The results of a new approach to calculating the effect of CO[SUB]2[/SUB] - using empirical observations - suggest it has a lower impact on the climate than previously thought, and its effects are being over-estimated by the IPCC. Publishing in the American Meterological Society's Journal of Climate, a new paper called An improved, objective Bayesian, approach for applying optimal fingerprint techniques to estimate climate sensitivity, Nicholas Lewis applies objective Bayesian techniques and uses more up-to-date observational data to derive his conclusions.
Estimates of ECS (Equilibirum Climate Sensitivity, defined by the IPCC here) produce a range of temperatures that we can expect from a doubling of atmospheric CO[SUB]2[/SUB] concentrations over pre-industrial levels. They're derived in three ways: from complex climate models (GCMs) which largely ignore observational evidence, simpler models constrained by observations, and direct observation.
The Lewis paper takes the second approach. Aerosols, both natural and manmade, have a potential negative feedback, with volcanic eruptions proving to have a dramatic short-term effect. Lewis uses more up-to-date estimates of aerosol forcing (from volcanos, for example) drawn from the observational data, rather than other papers, and compares global temperatures over short decadal periods, to remove the effect of volcanic eruptions. He also uses a technique called objective Bayesian analysis. Conventional subjective Bayesian analysis relies on highly subjective uniform priors, aka deliberatively-informative "expert" priors, as parameters.
The results don't diverge completely from the IPCC estimates, but they are significantly lower. Lewis finds mode and median climate sensitivity of 1.6°C, with 90 per cent confidence in a range of 1.2°C to 2.2°C. This compares to the IPCC's 2°C-4.5°C 'likely range'. Lewis also has a crack at updating the Forest 06 study
