JTH14 1 The Modeling of Climate and Climate Change; can we trust model predictions? University of California, Irvine 21 February 2003 by John Houghton

JTH15 2 Outline Introduction Cloud Radiation Feedback Ocean Interactions The Carbon Cycle The Climate of the 20th Century Climate Projections for the 21st Century Regional Climate Modeling Patterns of Climate Response

JTH15 3 The greenhouse effect Long-wave radiation 236 Wm -2 Equivalent T = 255 K (-18ºC) 390 Wm -2 T = 255 K (-15ºC) 236 Wm -2 Solar radiation

JTH15 4 Spectra of outgoing radiation from Earth observed by IRIS on Nimbus 3

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JTH15 6 The Enhanced Greenhouse Effect Solar (S) and longwave (L) radiation in Wm  2 at the top of the atmosphere SL236 T =  18°C SL CO 2 x 2 SL236 CO 2 x 2 SL236 CO 2 x 2 + Feedbacks H 2 O (+60%) Ice/Albedo (+20%) Cloud? Ocean? T S = 15°C  T S ~ 1.2K  T S ~ 2.5K

JTH15 7 The climate system

JTH15 8 The Development of Climate models, Past, Present and Future Atmosphere Land surface Ocean & sea-ice Sulphate aerosol Sulphate aerosol Sulphate aerosol Non-sulphate aerosol Non-sulphate aerosol Carbon cycle Atmospheric chemistry Ocean & sea-ice model Sulphur cycle model Non-sulphate aerosols Carbon cycle model Land carbon cycle model Ocean carbon cycle model Atmospheric chemistry Atmospheric chemistry Off-line model development Strengthening colours denote improvements in models Mid 1970s Mid 1980sEarly 1990sLate 1990sPresent dayEarly 2000s?

JTH15 9 Predicting impacts of climate change Emissions Concentrations CO 2, methane, sulphates, etc. Global climate change Temperature, rainfall, sea level, etc. Regional detail Mountain effects, islands, extreme weather, etc. Impacts Flooding, food supply, etc. Scenarios from population, energy, economics models Carbon cycle and chemistry models Coupled global climate models Regional climate models Impacts models The main stages required to provide climate change scenarios for assessing the impacts of climate change. Hadley Centre - PRECIS brochure

JTH15 10 Coupled atmosphere / ocean climate model Radiation Atmosphere: Density Motion Water Heat Exchange of: Momentum Water Ocean: Density (inc. Salinity) Motion Sea Ice Land

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JTH levels in atmosphere 20 levels in ocean 2.5 lat 3.75 long 1.25 THE HADLEY CENTRE THIRD COUPLED MODEL - HadCM3 30km -5km

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JTH15 14 Physical Feedbacks Water vapour Ice albedo Clouds Oceans Ice sheets

JTH14 15 Cloud Radiation Feedback

JTH15 16 Cloud radiation feedback

Global average change in T /C

JTH15 18 Model Estimates of Cloud Radiative Forcing with CO 2 Doubling

JTH15 19 Effect of cloud feedback formulation on climate prediction Feedback schemeGlobal Av Temp change,C for doubled CO2 –RH5.3 –CW2.8 –CWRP1.9 –after Senior & Mitchell, Hadley Centre

JTH15 20 Net cloud forcing: January to July Hadley Centre

JTH15 21 SHIP TRACKS UNDER CLOUD Washington state

JTH14 22 Ocean Interactions

JTH14 23 IPCC Synthesis Report

JTH15 24 Strength of the thermohaline circulation in the North Atlantic. Hadley Centre

JTH15 25 IPCC Third Assessment Report Modelled transport of water in Atlantic conveyor belt

JTH15 26 Projected changes in annual temperatures for the 2050s The projected change in annual temperatures for the 2050s compared with the present day, when the climate model is driven with an increase in greenhouse gas concentrations equivalent to about 1% increase per year in CO 2 The MetOffice. Hadley Center for Climate Prediction and Research. BW 11

JTH15 27 Changes in surface air temperature, relative to the present day, 20 years after the hypothetical collapse of the thermohaline circulation. Hadley Centre

JTH15 28 Surface Temperature Combined effect of THC collapse ( ) and global warming Cooling over UK: 1-3°C

JTH14 29 The Carbon Cycle

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JTH15 31 IPCC Third Assessment Report

JTH15 32 Human Perturbation of the Carbon Cycle

JTH15 33 Partitioning of CO 2 uptake using O 2 measurements

JTH s 1990s Atmospheric increase 3.3 ± ± 0.1 Emissions (fossil fuel, cement) 5.4 ± ± 0.4 Ocean-atmosphere flux -1.9 ± ± 0.5 Land atmosphere flux -0.2 ± ± 0.7 partitioned as follows: Land-use change 1.7 (0.6 to 2.5) NA Residual terrestrial sink -1.9 (-3.8 to 0.3) NA IPCC Third Assessment Report Global CO 2 budgets in GtC per year

JTH15 35 Carbon cycle feedbacks

JTH15 36 Change in carbon content of soil (top) and vegetation (bottom) between 1860 and predicted by Hadley Centre climate model Hadley Centre

JTH15 37 Simulated changes in the global total soil and vegetation carbon content (Gt C) between 1860 and Hadley Centre

JTH15 38 Influence of ENSO on CO 2 Variability Annual changes in atmospheric CO 2 are dominated by ENSO –after removing anthropogenic rise –rise during El Nino –fall during La Nina  CO 2 - black, Nino3 - red

JTH15 39 Influence of Volcanoes on CO 2 Variability 2 notable exceptions to ENSO correlation CO 2 levels lower than expected Coincide with major volcanic eruptions  CO 2 - black, Nino3 - red El Chichon Pinatubo

JTH15 40 Constraint from ENSO Sensitivity Model with q 10 =2 has realistic sensitivity to ENSO. Reconstructions for range of q 10. Infer q 10 =2.1±0.7.

JTH15 41 Constraint from Sensitivity to Volcanoes Model with q 10 =2 has realistic sensitivity to Pinatubo. Reconstructions for range of q 10. Infer q 10 =1.9±0.4

JTH15 42 ENSO and Pinatubo Variations as a constraint on climate-carbon cycle feedback Model without C cycle Feedback Model with C cycle Feedback (q 10 = 2) Grey region is estimate of uncertainty related to q 10 parameter for soil respiration q 10 = 3 q 10 = 1

JTH15 43 Photo: Tim Hewison

JTH15 44 Estimated carbon uptake if suitable arable land north of 30º N were to be replaced with trees. Hadley Centre The additional effect on climate of the changes in surface reflectivity when trees are planted on suitable arable land north of 30º N, expressed as equivalent carbon emissions. The difference between the two diagrams above. Negative values show where the net effect of planting trees is to warm climate.

JTH15 45 NET EFFECT OF PLANTING TREES expressed as equivalent carbon uptake tonnes of carbon per hectare – Negative values show where the net effect of planting trees is to warm climate Met Office / Hadley Centre

JTH15 46 EMISSIONS AND CONCENTRATIONS OF CO 2 from unmitigated and stabilising emission scenarios Unmitigated emissions 750 ppm stabilisation550 ppm stabilisation Source: IPCC

JTH15 47 The Climate of the 20 th Century

JTH15 48 Global mean surface air temperature anomalies from 1,000 year control simulations with three different climate models, - Hadley, GFDL and Hamburg, compared to the recent instrumental record. No model control simulation shows a trend in surface air temperature as large as the observed trend. If internal variability is correct in these models, the recent warming is likely not due to variability produced within the climate system alone. IPCC Third Assessment Report

JTH15 49 Simulated annual global mean surface temperatures Natural forcing Anthropogenic forcing

JTH15 50 Simulated annual global mean surface temperatures

JTH15 51 IPCC statements on Detection “The balance of evidence suggests a discernible human influence on global climate” 1995 Report “There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities”2001 Report

JTH14 52 Climate Projections for the 21st century

JTH15 53 The solid line shows a GCM prediction of temperature change. Prior to 1990, historical emissions were used. Beyond 1990, the IS92a emissions scenario was used. The dashed line shows the results of scaling the model prediction to give the best fit to the most recent 50 years of observations. The shaded region is the uncertainty estimate. Hadley Centre

JTH15 54 SRES scenario familys More economic More environmental More regional More global B: balanced FI: fossil intensive T: non-fossil A1 A2 B2B1

JTH15 55 IPCC Third Assessment Report Globally averaged tempertaure change for scenario SRES B2

JTH15 56 IPCC Third Assessment Report Globally averaged precipitation change for scenario SRES B2

JTH15 57 Hadley Centre - PRECIS brochure Area averaged changes in summer rainfall for the period over southern Asia as predicted by nine coupled models forced by the A2 emissions scenario (taken from Chapter 10 of the Scientific Basis of the IPCC Third Assessment Report). In other areas predictions can show much greater differences in magnitude and even sign.

JTH15 58 Observed and projected changes in extremes Confidence in observed changes (latter half of the 20th century) Likely Very likely Likely, over many areas Likely, over many Northern Hemisphere mid- to high- latitude land areas Likely, in a few areas Not observed in the few analyses available Insufficient data for assessment Changes in Phenomenon Higher maximum temperatures and more hot days over nearly all land areas Higher minimum temperatures, fewer cold days and frost days over nearly all land areas Reduced diurnal temperature range over most land areas Increase of heat index over land areas More intense precipitation events Increased summer continental drying and associated risk of drought Increase in tropical cyclone peak wind intensities Increase in tropical cyclone mean and peak precipitation intensities Confidence in projected changes (during the 21st century) Very likely Very likely, over most areas Very likely, over many areas Likely, over most mid-latitude continental interiors (Lack of consistent projections in other areas) Likely, over some areas IPCC Third Assessment Report

JTH15 59 Simulated temperature rise and thermal expansion for the 4xCO2 experiment

JTH14 60 Regional Climate Modelling

JTH15 61 Hadley Centre - PRECIS brochure Schematic diagram of the resolution of the Earth’s surface and the atmosphere in the Hadley Centre regional climate model.

JTH15 62 Regional Climate Model High resolution (50km) over limited area (Europe, Indian subcontinent) Embedded in global model, so subject to same uncertainties Takes account of local characteristics, e.g. mountains, coasts Better regional detail, better prediction of extremes in weather (eg flooding) Everybody wants one!

JTH15 63 Hadley Centre - PRECIS brochure The representation of the Philippines in RCMs with resolutions of 400 km (the GCM), 50 km and 25 km.

JTH15 64 Hadley Centre - PRECIS brochure Patterns of present-day winter precipitation over Britain. Left, as simulated with the global model. Middle: as simulated with the 50 km regional model. Right, as observed.

JTH15 65 Hadley Centre - PRECIS brochure The frequency of winter days over the Alps with different daily rainfall thresholds. Purple bars, observed. Dark red bars simulated by the GCM. Green bars simulated by the RCM.

JTH15 66 Hadley Centre - PRECIS brochure A tropical cyclone is evident in the mean sea-level pressure field from the RCM (right) but not in the driving GCM (left) for the corresponding day (from an RCM over southern Africa, developed by the Hadley Centre in collaboration with the university of Cape Town).

JTH15 67 Hadley Centre - PRECIS brochure Predicted changes in summer surface air temperatures between the present day and the end of the 21st century. Left, from the global model. Right, from the regional model.

JTH15 68 Hadley Centre - PRECIS brochure Predicted changes in monsoon precipitation over India, between the present day and the middle of the 21st century from the GCM (left) and the RCM (right).

JTH14 69 Is the Climate Chaotic?