Transcript Slide 1
SAGES Scottish Alliance for Geoscience, Environment & Society CESD Observing and Modelling Climate Change Prof. Simon Tett, Chair of Earth System Dynamics & Modelling: The University of Edinburgh Outline CESD • • • • Observing Climate Change Modelling Climate Causes of Historical Climate Change Projections of Future Climate Change CESD Observing Climate Change: What is the problem? • Observing system not stable • Climate changes slowly • Examples: CESD Global mean temperatures are rising Warmest 12 years: 1998,2005,2003,2002,2004,2006, 2001,1997,1995,1999,1990,2000 Period Rate 50 0.1280.026 100 0.0740.018 Years /decade From Kevin E. Trenberth, NCAR Sea-ice (its ½ what it was) CESD Is this unexpected? Are we missing something fundamental in our understanding of the Earth system? Climate Modelling CESD • Climate modelling has long history – first attempts made in 1950’s. – Developed from numerical weather prediction • Which is how weather forecasting is done – Take physical laws and apply them to atmosphere and oceans. – But now very complex. Modelling the Climate System CESD Main Message: Lots of things going on! Karl and Trenberth 2003 HadCM3 CESD 19 Atmospheric Levels Atmospheric resolution: 3.75 by 2.5 Ocean resolution :1.25 by 1.25 20 Ocean Levels CESD Many important processes occur on scales below that explicitly modelled. What is there… How we model Uncertainties how to do this lead to uncertainties in prediction of climate change CESD Natural Factors that might effect climate Volcanic Aerosol depth 0.2 0 2000 1850 Volcanoes inject aerosol into the upper atmosphere where it stays for 2-3 years. There it scatters sunlight back to space cooling the planet Sunspot Num ber 200 0 1700 2000 The sun may be a variable star with amount of energy reaching the earth changing over decades Important Human Factors CESD 380 CO2 MMR*106 Mauna Loa Observatory 360 1800 1400 320 1200 300 1000 1900 Year 2000 Flasks 1600 340 280 260Ice cores 1700 1800 CH4 MMR*109 Ice cores 800 600 1700 1800 1900 Greenhouse gas concentrations have changed over the last century. 2000 Year As have emissions of sulphur and other aerosols Attribution CESD • are observed changes consistent with expected responses to forcings inconsistent with alternative explanations All forcing Observations Solar+volcanic CESD Understanding and Attributing Climate Change Continental warming likely shows a significant anthropogenic contribution over the past 50 years Projections of Future Changes in Climate CESD Best estimate for low scenario (B1) is 1.8°C (likely range is 1.1°C to 2.9°C), and for high scenario (A1FI) is 4.0°C (likely range is 2.4°C to 6.4°C). Projections of Future Changes in Climate CESD Projected warming in 21st century expected to be greatest over land and at most high northern latitudes and least over the Southern Ocean and parts of the North Atlantic Ocean Projections of Future Changes in Climate CESD Precipitation increases very likely in high latitudes Decreases likely in most subtropical land regions Extreme events CESD Tewkesbury 2007Photograph: Daniel Berehulak/GettyImages Met Office provisional figures show that May to July in the England and Wales Precipitation is the wettest in a record that began in 1766. We must learn from the events of recent days. These rains were unprecedented, but it would be wrong to suppose that such an event could never happen again…. (Hazel Blears, House of Commons, July 2007) Is it human induced climate change or natural variability?