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Climate Change – is it really happening? Kathy Maskell Walker Institute for Climate System Research, University of Reading Overview • • • • Where we are with the science What’s new in IPCC (2007) – focus on WG1 Skeptics – countering their agruments Current challenges for climate science Global mean temperatures are rising faster with time Period Rate 50 0.1280.026 100 0.0740.018 Years /decade IPCC (2007) Evidence of warming…. across the globe, atmosphere, land and ocean since 1979 Surface Atmosphere Evidence of warming…. • Land and ocean surface • Ocean to depths of at least 3000 m • Warmer oceans > thermal expansion and sea level rise IPCC (2007) ‘Warming of the climate system is unequivocal’ – IPCC 2007 • The land, oceans and the air are all warming, sea ice and glaciers are melting Mountain 2004 1941 glaciers are melting Sub-Saharan Africa and Mediterranean are getting drier Northern Europe is getting wetter Recent warming is unusual The northern hemisphere is probably the warmest it’s been for at least 1300 years Temperature can be inferred from tree ring width Mann et al., Science 1999 (Northern Hemisphere only) People are changing the atmosphere in drastic ways Carbon dioxide levels are higher than at any time in last 650,000 years! (IPCC 2007) Greenhouse gases – sources and sinks Carbon dioxide - sources ~2/3 from fossil fuels ~1/3 from deforestation Carbon dioxide – sinks 30% into ocean, 25% uptake by terrestrial biosphere 45% remained in atmosphere – removed slowly Methane – from cows, paddy fields .. Natural sources – e.g., wetlands Nitrous oxide – from agriculture and land-use change Natural sources Other human effects on climate? Aerosols - small particles – From SO2, biomass burning, industrial dust – Typically reflect sunlight back to space – IPCC (2007) better quantified, but still quite uncertain Typically produce a cooling DIRECT EFFECT scatter sunlight back to space INDIRECT EFFECT make clouds brighter and last longer Natural factors …. can they explain the warming? Variation’s in the Sun’s output Volcanoes 11-year sun-spot cycle Effects short-lived 1-2 years BASIC SCIENCE: Effect of human activities since 1750 - positive radiative forcing Radiative Forcing (RF) IPCC (2007) The Climate System Climate models must contain the atmosphere, the oceans, ice and the land surface and consider all the possible influences on climate The physics within climate models Dr u uv tan 1 p uw 2 sin v 2 cos w Su Dt r r cos r Dr v u 2 tan 1 p vw 2 sin u Sv Dt r r r Dr w 1 p Dt r r g Dr Dr r u 0 S Dt Dt u 2 v2 r 2 cos u S w Dr mX S mX Dt p RT Climate models are our laboratory. We use them to understand past changes and to predict the future. The earth is represented by a grid of squares, typically of length 250 km, and by a stack of layers. This gives us a 3-D picture of the circulation of the atmosphere and oceans Human influence seen on every continent New in IPCC (2007) human influence “very likely” (90%) IPCC (2007) How do we forecast climate? Future greenhouse gas/aerosol emissions depend on population, energy use, new technologies, etc Climate forcing Climate system response and feedbacks - clouds, ice, oceans etc Emissions of CO2 through the 21st century Climate change will get worse in the 21st Century By 2100: world could be 2 to 4oC warmer – on top of the 0.7oC we’ve already seen. IPCC (2007) IPCC (2001) Regional temperature changes Warming greatest over land and at most high northern latitudes and least over the Southern Ocean and parts of the North Atlantic Ocean 2020s 2080s low med high IPCC (2007) IPCC (2007): Projections of likely shifts in rainfall patterns % change in rainfall by end of 21st century, where more than 2/3 of the models agree on the sign of the change. White areas denote regions where no consistent signal is predicted e.g. Africa. IPCC (2007) Other projected changes • Sea level rise – Mainly due to thermal expansion of sea water – 0.2 to 0.6m rise by 2100 – Not the same everywhere – regional pattern not well known (could be 2 or 3 times global mean) • Ice sheets • Recent dramatic melting around Antarctic and Greenland • These dynamical effects not included in numbers above IPCC (2007) By: Roger Braithwaite and Jay Zwally. Key areas of uncertainty and challenges for climate research • There’s still a big range in temperature projections – due to differences in model feedbacks (clouds especially) • Carbon cycle feedbacks … • Regional patterns and extremes – especially rainfall • Interactions between climate variability and climate change Modelling climate at higher resolution Improves: El Niño and its effects, hurricanes and other tropical weather, mid-latitude storms CLIMATE CHANGE IS HAPPENING……. Climate change is happening. Climate change is serious. Time for action …. Find out more ……. www.walker-institute.ac.uk www.ipcc.ch ipcc-wg1.ucar.edu …..AND ITS EFFECTS ARE LIKELY TO BE VERY PROFOUND Solar irradiance does not correlate with recent warming Surface Temperature Solar Irradiance Solar forcing over 20th century – positive, but much smaller than greenhouse gases Figure courtesy of Gareth Jones How unusual is the current warmth? Impacts of climate change (IPCC 2007 – WG2) • Human influence evident in observed impacts • • • • (earlier spring, rivers and lakes, heat related deaths, agriculture) 1/3rd of species at increased risk of extinction Millions at risk from coastal flooding Human health – heat, drought, diseases Food – yields likely to increase at higher latitudes (up to 3ºC warming) – yields decrease in developing world • Water – more rainfall at high latitudes – decrease in areas already water stressed – Less water stored in snow and ice – less spring, summer meltwater