Download presentation
Presentation is loading. Please wait.
1
Evaluation of climate models, Attribution of climate change IPCC Chpts 7,8 and 12. John F B Mitchell Hadley 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?
2
[Summary for Policymakers, WG1]
„Confidence in the ability of models to project future climates has increased.“ [Summary for Policymakers, WG1]
![[Summary for Policymakers, WG1]](http://slideplayer.com/slide/8392817/26/images/2/%5BSummary+for+Policymakers%2C+WG1%5D.jpg "„Confidence in the ability of models to project future climates has increased. [Summary for Policymakers, WG1]")
3
Prediction and Observation of 1997/98 ENSO
Prediction May 97 Observation May 97 Initialization in December 1996 Prediction for May 1997: Pacific SST good large-scale agreement with observations (Stockdale et al., 1998, Nature)
4
Distribution of atmospheric water vapor
satellite data (May, 5) high-resolution atmospheric model (May, 5) Stocker et al, IPCC 2001
5
Global mean temperature from an ensemble of 4 simulations using natural and anthropogenic forcing
Stott et al, Science 2000
6
Arctic Sea Ice Cover: Observation and Simulation
onset of decrease in ice extent accelerated decrease agreement with GFDL model depends on sea ice thickness criterion Hadley Centre has systematic bias (Vinnikov et al., 1999, Science; Chapter 7)
7
Realism of climate models has improved since SAR:
higher grid resolution more physically based parameterizations more complete coupling major deficiencies require continued attention. They include: representation of clouds and their interactions with radiation and aerosols natural variability, such as NAO and ENSO, esp. frequency of ENSO oceanic flow systsems in narrow boundary currents and over sills representation of mixing in the ocean simulation of sea ice dynamics Yet, models are not perfect!
8
“There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities” SPM
9
“There is a longer and more closely scutinised temperature record” SPM
10
Can Natural factors alone explain the recent temperature record?
11
“The warming over the last hundred years is very unlikely to be due to internal variability alone as estimated from current models” SPM
12
“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
13
“Simulations of the response to natural forcings alone … do not explain the warming in the second half of the century” SPM Stott et al, Science 2000
14
Can anthropogenic factors explain the temperature recent record?
15
“..model estimates that take into account both greenhouse gases and sulphate aerosols are consistent with observations over this*period” SPM Stott et al, Science 2000
16
Temperature trends (C), 1949-1997 Anthropogenic forcing improves agreement with observations
Knutson et al, 2000
17
“..attribution studies .. can now take into uncertainty in the magnitude of the modelled response to external forcing…” SPM
18
Attributed trends depend on observations not model simulated trends
Original model trend Temperature Observations Time
19
Attributed trends depend on observations not model simulated trends
Scaling Original model trend Temperature Observations Attributed trend Time
20
Attributed trends depend on observations not model simulated trends
Original model trend Temperature Observations + internal variability Time
21
Attributed trends depend on observations not model simulated trends
Scaling Original model trend Upper Temperature Lower Observations + internal variability Attributed trend + uncertainty estimate Time
22
Optimal detection Based on spatial and temporal patterns, not global means Different components can be scaled separately (eg 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
23
“The anthropogenic sulphate aerosol forcing, while uncertain, is negative over this period and therefore cannot explain the warming” SPM
24
Substantial GHG warming with small sulphate cooling
Temperature Small sulphate cooling Greenhouse warming Greenhouse warming slightly larger than observed Observations Time
25
More substantial GHG warming with large sulphate cooling
Temperature Large sulphate cooling Greenhouse warming Greenhouse warming much larger than observed Observations Time
26
The response to different forcings may be surprisingly similar
Aerosol forcing The response to different forcings may be surprisingly similar Aerosol response CO2 response Reader and Boer , 1998
27
“Most studies find that, over the last 50 years, the estimated rate and magnitude of warming due to increasing greenhouse gases is comparable with or larger than the observed warming” SPM Estimated 5-95% range in attributable trends
28
Model uncertainty in predictions
Allen and Raper pers com, 2001 based on TAR results
29
Uncertainties Difference in recent surface and free atmosphere trends
Size of internal variability Natural forcing Anthropogenic forcing , especially aerosols Estimate of response (sensitivity)
30
“In the light of new evidence and taking into account the remaining uncertainties, most of the observed warming over the last 50 years is likely to be due to the increases in greenhouse gas concentrations”
Similar presentations
