1. Global Warming The heat is on!

2. What do you know about global warming? Did you know: Did you know: –the earth on average has warmed up? –some places have got colder in the past 250 years? –Temperature, rainfall, storms, drought, sea level, sea ice and glaciers are all changing due to global warming? –We think that human activities are partly responsible.

3. Proof: The Earth is getting warmer

4. Mann et al., Science 1999 (Northern Hemisphere only) And the northern hemisphere is probably the warmest it’s been for at least 1000 years… Global average temperature is one way of measuring the climate of the Earth

5. What is climate? “Global warming” is a popular term for climate change “Global warming” is a popular term for climate change Climate is the average weather Climate is the average weather –“ Climate is what we expect, weather is what we get” Reading climate? Reading climate? Climate is easier to predict than weather! Climate is easier to predict than weather! To CD!

6. What affects the climate system?

7. What can affect climate? Climate is a balance between the Earth being heated by the Sun, and cooling by sending out heat itself Climate is a balance between the Earth being heated by the Sun, and cooling by sending out heat itself Changing the solar radiation that we get Clouds Particles like dust Changes to snow and ice Volcanoes Changing the infra- red radiation the Earth sends to space “Greenhouse” gases Clouds

8. SUN Sunlight passes through the atmosphere....and warms the earth...most escapes to outer space and cools the earth... Infra-red radiation is given off by the earth... …but some IR is trapped by some gases in the air, thus reducing the cooling…. THE GREENHOUSE EFFECT: identified in 1896! Arrhenius 1896

9. “Human” Global warming Without some natural greenhouse effect the Earth would be at -15 degrees C (Brr….) Without some natural greenhouse effect the Earth would be at -15 degrees C (Brr….) We get this from the natural amounts of water vapour and carbon dioxide in the atmosphere We get this from the natural amounts of water vapour and carbon dioxide in the atmosphere But human activities add carbon dioxide and other greenhouse gases to the atmosphere But human activities add carbon dioxide and other greenhouse gases to the atmosphere More greenhouse effect More greenhouse effect “Global warming” “Global warming”

10. SUN Sunlight passes through the atmosphere....and warms the earth. Infra-red radiation is given off by the earth... More greenhouse gases leads to more trapping of IR and a warmer surface Arrhenius 1896 CO 2 More energy is absorbed by the Earth than it emits

11. Other human effects on climate? Particles (or aerosols) in the atmosphere reflect sunlight back to space and can cause cooling in local areas (and also gives us air quality problems). But small changes compared to greenhouse effect. Particles (or aerosols) in the atmosphere reflect sunlight back to space and can cause cooling in local areas (and also gives us air quality problems). But small changes compared to greenhouse effect. Large scale agriculture changes the Earth’s surface which affects the radiation reflected back Large scale agriculture changes the Earth’s surface which affects the radiation reflected back

12. Climate lucky dip!

13. The future of climate change? By 2100: Increase in global mean temperature of 1.4°C - 5.8°C. Sea level rise by a further 0.09m – 0.88m.

14. IPCC (2001) Climate changes over the next few decades are predicted to be much larger than we have seen so far, but there is quite a range of “uncertainty” in the predictions…

15. Global change Changing the temperature patterns around the globe Changing the temperature patterns around the globe Changing wind and rainfall patterns Changing wind and rainfall patterns Global climate change Global climate change

16. And in the UK? 2080 temperature change (K) 2080 precipitation change (%) Source: Mat Collins, Hadley Centre

17. ANNUAL NUMBER OF PEOPLE FLOODED Change from the present day to the 2080s (unmitigated emissions) Impacts of climate change may be disastrous……. UK Climate Impacts Programme

18. Water Supply Water availability will be the major issue in the coming century. Pressure on water supplies comes not only from climate change but also human use. Countries shown currently use more than 20% of water resources

19. Food supplies Percentage change in average crop yields for staple crops: wheat, maize and rice. Yellow, brown and red areas denote lower yields But note increased yields in some northern latitudes due to more favourable climate

20. How do we predict climate change? We only have one real Earth to experiment with so.. We build artificial ones… inside a computer We only have one real Earth to experiment with so.. We build artificial ones… inside a computer This involves equations that describe things like This involves equations that describe things like How the air moves How the air moves How the ocean currents work How the ocean currents work How water freezes and melts and evaporates and condenses (forming clouds!) How water freezes and melts and evaporates and condenses (forming clouds!) We have to divide the earth up into squares and calculate these things only every few 100kms We have to divide the earth up into squares and calculate these things only every few 100kms

21. 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 The Met Office

22. Probability forecasts? We need to know what is most likely to happen, not just what can theoretically happen! We need to know what is most likely to happen, not just what can theoretically happen! Temperature change Likelihood High Low To CD

23. Summary Climate change is real. Climate change is real. Global warming is most likely to happen, although different parts of the globe will warm by different amounts Global warming is most likely to happen, although different parts of the globe will warm by different amounts At least over the past 50 years, human activities have contributed to climate change At least over the past 50 years, human activities have contributed to climate change Future changes will be larger than those we have seen already Future changes will be larger than those we have seen already To CD