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Is our climate changing? What does the future hold? JULIA SLINGO NERC Centre for Global Atmospheric Modelling The University of Reading OUTLINE • Observational evidence • Scientific basis for climate change • How we predict the future climate and assess the impacts of climate change • Why we are still uncertain about the magnitude and effects of future climate change • What can we do about climate change? Climate has always changed, so what’s different now? Holocene – period of climate stability – coincides with birth of civilisation Natural causes of climate change Variation’s in the Sun’s output Volcanoes Long term natural climate changes are likely driven by Earth's orbit changes The northern hemisphere is probably the warmest it’s been for at least 1000 years Mann et al., Science 1999 (Northern Hemisphere only) For the past 10 years, the planet has been very warm ... Evidence for Climate Change is stacking up! INCREASE • Length of freeze free season • Length of growing season • More frequent heat waves • Wetter winters/Drier summers • Sea level rise DECREASE • Extent of mountain glaciers • Sea-ice amounts and thickness • Fewer Frosts What is different now is that humans are changing the chemical composition of the atmosphere in unprecedented ways…. The NATURAL Greenhouse Effect ..most escapes to outer space and cools the earth... SUN …but some IR is trapped by some gases, in the air, thus reducing the cooling…. Sunlight passes through the atmosphere.. ..and warms the earth. Infra-red radiation is given off by the earth... Arrhenius 1896 The NATURAL Greenhouse Effect The ENHANCED Greenhouse Effect ..most escapes to outer space and cools the earth... SUN More CO2 traps more IR, thus reducing the cooling further Most sunlight passes through the atmosphere.. ..and warms the earth. CO2 CO2 Infra-red radiation is given off by the earth... Arrhenius 1896 The ENHANCED Greenhouse Effect Major Players in the Greenhouse Effect Water Vapour: The natural greenhouse gas which makes our planet habitable Human influences on the greenhouse effect Climate Change Carbon dioxide Fossil fuels, deforestation 100 years Methane 10 years Agriculture, natural gas Other gases (nitrous oxide, CFCs, ground-level ozone..) Aerosols Power generation, transport Fundamentally a cooling effect 2 weeks Concentrations are now higher than for the past thousand years……… IPCC (2001) And the present trends in CO2 and methane are outside those experienced on earth for at least the last 400,000 years….. Earth’s major systems are changing more rapidly than at any time in the last half million years at least. Many of these changes are pushing the planet into hitherto uncharted territory – we have never been here before and it’s because of us….. So….. What does the future hold? …..To answer that question we must use CLIMATE PREDICTION MODELS Models are our laboratory. We use them to explore forcing and feedbacks in the earth system, to test hypotheses, to understand past changes and to predict the future. Image: BMRC Climate Models are huge computer codes based on fundamental mathematical equations of motion, thermodynamics and radiative transfer These govern: Flow of air and water - winds in the atmosphere, currents in the ocean. Exchange of heat between the atmosphere and the earth’s surface Release of latent heat by condensation during the formation of clouds and raindrops Absorption of sunshine and emission of thermal (infra-red) radiation Climate models are extensions of weather forecast models To solve these equations we represent the earth by a grid of squares, typically of length 150 km or smaller. The atmosphere and oceans are divided into vertical slices of varying depths. This gives us a 3-dimensional picture of the circulation of the atmosphere and oceans. UK in typical climate models Models must contain all the components of the climate system and consider all the possible influences on climate ……..And they must consider human behaviour and our response to climate change. Development of climate models over the last 30 years Climate Modelling and Prediction requires huge supercomputers Inside the Earth Simulator Capable of performing 35x109 sums per second Electric Cables Connecting Cabinets Weather in NUGAM Land snow + ice twin typhoons Precipitation (colour scale) Shallow (warm) clouds Deep (cold) clouds Land snow + ice Sea ice Stages in predicting climate change Scenarios from population, energy, economics models EMISSIONS CONCENTRATIONS Carbon cycle and chemistry models HEATING EFFECT ‘Climate Forcing’. CLIMATE CHANGE feedbacks CO2, methane, etc. Gas properties Temp, rain, sea level, etc. Coupled climate models IMPACTS Impacts models Flooding, food supply, etc. Human influences will continue to change atmospheric composition throughout the 21st century How quickly the climate will change in the future depends on: • How much greenhouse gas emissions grow –depends on population growth, energy use, new technologies, etc • How sensitive the climate system is to emissions –how clouds, ice, oceans etc respond to the extra heating Predicted changes in global mean temperatures IPCC (2001) Far outside anything we have experienced over the last 1000 years And possibly close to those last experienced in the age of the dinosaurs! Land areas are projected to warm more than the oceans with the greatest warming at high latitudes Annual mean temperature change, 2071 to 2100 relative to 1990: Global Average in 2085 = 3.1oC ANNUAL NUMBER OF PEOPLE FLOODED Change from the present day to the 2080s (unmitigated emissions) UK Climate Impacts Programme Change in water stress, due to climate change, in countries using more than 20% of their potential water resources. Water availability will be the major issue in the coming century. Pressure on water supplies comes not only from climate change but also from human use. Percentage change in average crop yields for staple crops: wheat, maize and rice. Yellow, brown and red areas denote lower yields But note increased yields in some northern latitudes due to more favourable climate UK TEMPERATURE RISE Medium-high emissions scenario, 2080s Winter Summer °C CHANGE IN PRECIPITATION Medium-high emissions scenario, 2080s Winter Summer % Changes in Extremes Schematic of probabilities of daily temperatures Caveat: Assumes that statistics of weather stay the same Percentage of years experiencing ‘extreme’ seasonal anomalies across southern UK MEDIUM-HIGH EMISSIONS 2020s 2050s 2080s ‘Hot’ August 1995 1 20 63 ‘Warm’ year 1999 28 73 100 10 Hot summer 2003 ‘Dry’ summer 1995 ‘Wet’ winter 1994/95 10 29 50 1 3 7 CLIMATE ‘TIPPING POINTS’ Delicate thresholds where a slight change in the Earth's temperature can cause a dramatic change in the environment that itself triggers a far greater change in global temperatures. The earth has been capable of abrupt changes in the past Examples of potential ‘Tipping Points’ from global warming • Loss of Arctic sea-ice, major ice sheets – shut-down of thermohaline circulation, massive sea level rise. • Melting of permafrost - release of billions of tonnes of methane, a greenhouse gas 20 times more potent than carbon dioxide. • Loss of tropical rainforests, increasing soil temperatures – terrestrial biosphere becomes carbon source rather than carbon sink • Acidification of the oceans - reduction in carbon sequestration leading to further increases in carbon dioxide levels. • …………………..???? UK emits more than its “fair share” of carbon dioxide HOW CAN WE REDUCE CO2 EMISSIONS? • Use less energy –insulate homes, businesses and factories –less polluting transport; travel less –Combined Heat and Power generation • Generate energy without emissions of CO2 –renewable energy (wind, solar..) –nuclear power Multi-faceted approach to reducing emissions: ‘Wedges’ Emissions (MtCO 2 per year) 90,000 Conservation and Energy Efficiency MiniCAM 80,000 Renewable Energy 70,000 60,000 Nuclear 50,000 40,000 30,000 Coal to Gas Substitution Emissions to the atmosphere 20,000 10,000 CCS 2005 2020 2035 2050 2065 2080 2095 Allowable Emissions for WRE 550 Innovative solutions: CO2 capture and storage systems Fuels Processes Storage options INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE (IPCC) CLIMATE CHANGE IS HAPPENING……. …..AND ITS EFFECTS ARE LIKELY TO BE VERY PROFOUND