Evaluation of climate models,Attribution of climate change
IPCC Chapters 7,8 and 12.
John F B MitchellHadley Centre
• How well do models simulate present climate?• How well do they simulate past climate change?• Can natural factors explain the last 100 years?• Can human factors explain recent changes?
“Simulations of the response to natural forcings alone … do not explain the warming in
the second half of the century” SPM
Global mean temperature from an ensemble of 4 simulations using natural and anthropogenic forcing
Stott et al, Science 2000
“Reconstructions of climate data for the last 1000 years also indicate that this warming was unusual and unlikely to be entirely natural in origin” SPM
Arctic Sea Ice Cover: Observation and Simulation (Vinnikov et al., 1999, Science; Chapter 7)
Glacier mass balance
Cumulative balance of glacier mass in some regions
During the 20th century, glaciers and ice
caps have experienced widespread mass
losses and have contributed to sea level
rise
Decline of mountain glaciers projected
to reduce water availability in many
regions
“The warming over the last hundred years is very unlikely to be due to internal variability alone as
estimated from current models” SPM
Optimal detection• Based on spatial and temporal patterns, not
global means • Different components can be scaled separately
(e.g. greenhouses gases, aerosols)• “..most model estimates that take into account
both greenhouse gases and sulphate aerosols are consistent with observations [over the last 50 years]”
• The observations can be used to “correct” model predictions, with uncertainty limits
Substantial GHG warming with small sulphate cooling
Greenhouse warmingslightly larger thanobservedObservations
Time
Tem
pera
ture
Small sulphatecoolingGreenhouse
warming
Different Computer Models
Key technologies to reduce emissions
Efficient lighting; efficient appliances and aircodition; improved insulation ; solar heating and cooling; alternatives for fluorinated gases in insulation and appliances
Efficiency; fuel switching; renewable (hydropower, solar, wind, geothermal and bioenergy); combined heat and power; nuclear power; early applications of CO2 capture and storage
Energy Supply
Transport More fuel efficient vehicles; hybrid vehicles; biofuels; modal shifts from road transport to rail and public transport systems; cycling, walking; land-use planning
Buildings
Key mitigation technologies and practices currently commercially available
Key policies to reduce emissions Appropriate incentives for
development of technologies
Changes in lifestyle and behavior patterns, especially in building, transport and industrial sectors
Effective carbon price signal to create incentives to invest in low-GHG products, technologies and processes
Appropriate energy infrastructure investment decisions, which have long term effects on emissions
A technological society has two choices. First it can wait until catastrophic failures expose systemic deficiencies, distortion and self-deceptions…Secondly, a culture can provide social checks and balances to correct for systemic distortion prior to catastrophic failures.
