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

CESD Outline 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   Warmest 12 years: 1998,2005,2003,2002,2004,2006, 2001,1997,1995,1999,1990,2000 Period Rate Years  /decade From Kevin E. Trenberth, NCAR Global mean temperatures are rising

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

CESD 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.

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

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

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 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

CESD Important Human Factors 2000 Ice cores Flasks Year Mauna Loa Observatory Ice cores Year CO 2 MMR*10 6 CH 4 MMR*10 9 Greenhouse gas concentrations have changed over the last century. As have emissions of sulphur and other aerosols

CESD Attribution are observed changes consistent with  expected responses to forcings  inconsistent with alternative explanations Observations All forcing Solar+volcanic

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

CESD 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).

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

CESD 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 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?