Observing and Modeling Climate Change

1. SAGESScottish Alliance for Geoscience, Environment & Society Observing and Modelling Climate Change Prof. Simon Tett, Chair of Earth System Dynamics & Modelling: The University of Edinburgh

2. Outline • Observing Climate Change • Modelling Climate • Causes of Historical Climate Change • Projections of Future Climate Change

3. Observing Climate Change:What is the problem? • Observing system not stable • Climate changes slowly • Examples:

4. Global mean temperatures are rising Warmest 12 years: 1998,2005,2003,2002,2004,2006, 2001,1997,1995,1999,1990,2000 50 0.1280.026 100 0.0740.018 Period Rate Years /decade From Kevin E. Trenberth, NCAR

5. Sea-ice (its ½ what it was) Is this unexpected? Are we missing something fundamental in our understanding of the Earth system?

6. Climate Modelling • 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.

7. Modelling the Climate System Main Message: Lots of things going on! Karl and Trenberth 2003

8. HadCM3 19 Atmospheric Levels Atmospheric resolution: 3.75 by 2.5 Ocean resolution :1.25 by 1.25 20 Ocean Levels

9. Many important processes occur on scales below that explicitly modelled. How we model What is there… Uncertainties how to do this lead to uncertainties in prediction of climate change

10. 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 The sun may be a variable star with amount of energy reaching the earth changing over decades

11. Important Human Factors CO2 MMR*106 CH4 MMR*109 380 1800 Flasks Mauna Loa Observatory 360 1600 1400 340 1200 320 1000 300 Ice cores 280 800 Ice cores 260 600 1700 1800 1900 2000 1700 1800 1900 2000 Year Year Greenhouse gas concentrations have changed over the last century. As have emissions of sulphur and other aerosols

12. Attribution • are observed changes consistent with • expected responses to forcings • inconsistent with alternative explanations All forcing Observations Solar+volcanic

13. Understanding and Attributing Climate Change Continental warming likely shows a significant anthropogenic contribution over the past 50 years

14. Projections of Future Changes in Climate 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).

15. Projections of Future Changes in Climate 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

16. Projections of Future Changes in Climate Precipitation increases very likely in high latitudes Decreases likely in most subtropical land regions

17. Extreme events 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?