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 Years  /decade IPCC (2007)

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) Evidence of warming…. across the globe, atmosphere, land and ocean since 1979 SurfaceAtmosphere

‘Warming of the climate system is unequivocal’ – IPCC 2007 Mountain glaciers are melting Sub-Saharan Africa and Mediterranean are getting drier Northern Europe is getting wetter The land, oceans and the air are all warming, sea ice and glaciers are melting

Recent warming is unusual Mann et al., Science 1999 (Northern Hemisphere only) The northern hemisphere is probably the warmest it’s been for at least 1300 years Temperature can be inferred from tree ring width

People are changing the atmosphere in drastic ways Carbon dioxide levels are higher than at any time in last 650,000 years! (IPCC 2007)

~1/3 from deforestation Greenhouse gases – sources and sinks Carbon dioxide - sources ~2/3 from fossil fuels 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

Aerosols - small particles –From SO 2, biomass burning, industrial dust –Typically reflect sunlight back to space –IPCC (2007) better quantified, but still quite uncertain Other human effects on climate? DIRECT EFFECT scatter sunlight back to space Typically produce a cooling INDIRECT EFFECT make clouds brighter and last longer

Natural factors …. can they explain the warming? Variation’s in the Sun’s output Volcanoes Effects short-lived 1-2 years 11-year sun-spot cycle

BASIC SCIENCE: Effect of human activities since positive radiative forcing Radiative Forcing (RF) IPCC (2007)

Climate models must contain the atmosphere, the oceans, ice and the land surface and consider all the possible influences on climate The Climate System

The physics within climate models

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 IPCC (2007) New in IPCC (2007) human influence “very likely” (90%)

How do we forecast climate? Climate system response and feedbacks - clouds, ice, oceans etc Emissions of CO 2 through the 21 st century Future greenhouse gas/aerosol emissions - depend on population, energy use, new technologies, etc Climate forcing

IPCC (2001) By 2100: world could be 2 to 4 o C warmer – on top of the 0.7 o C we’ve already seen. Climate change will get worse in the 21st Century IPCC (2007)

Warming greatest over land and at most high northern latitudes and least over the Southern Ocean and parts of the North Atlantic Ocean Regional temperature changes 2020s2080s low med high IPCC (2007)

 % change in rainfall by end of 21 st 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): Projections of likely shifts in rainfall patterns 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) By: Roger Braithwaite and Jay Zwally. IPCC (2007) Ice sheets Recent dramatic melting around Antarctic and Greenland These dynamical effects not included in numbers above

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……. …..AND ITS EFFECTS ARE LIKELY TO BE VERY PROFOUND Climate change is happening. Climate change is serious. Time for action …. Find out more ……. ipcc-wg1.ucar.edu

Figure courtesy of Gareth Jones Solar irradiance does not correlate with recent warming Surface Temperature Solar Irradiance Solar forcing over 20 th century – positive, but much smaller than greenhouse gases

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) 1/3 rd 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 melt- water