1. CLIMATE CHANGE THE GREAT DEBATE Session 10

2. CLIMATE CHANGE? If we have learnt anything from this course, it is that climate is not constant It is, and always has been, changing continuously, either warming or cooling Most of the factors involved are out of our control but today is not the first time that biological factors are having an influence on climate

3. WARMING OR COOLING? If we have a choice would we prefer a warmer or a cooler climate? It is obvious from the historic past that we have experienced both warmer and cooler climates than we are living with today. These changes have not been large but even so they have had a big impact on human populations

4. COOLER CLIMATES In the last 2000 years there have been at least two periods of cooler conditions. The Dark Ages from 530 to 900 AD and the Little Ice Age from 1300 to 1850 AD Agriculture was restricted at high latitudes and high altitudes. Elsewhere, there were periods of drought, famine, war and disease. Throughout Western Europe there were times of population decline during cold extremes

5. WARMER CLIMATES (1) Predictions are that if warming continues: (1)Global precipitation will increase but distribution will also change (2)Increased cloud cover (3)Less snowfall and frost (4)Increased monsoon effects (5)Distribution and intensity of tropical cyclones will increase

6. WARMER CLIMATES (2) (6) Sea levels will rise (7) Rates of plant growth will increase (8) Pests and diseases will proliferate (9) Many crops will grow at higher latitudes and altitudes (10) Reduction in heating but increase in air conditioning (11) Relocation of winter sports

7. CLIMATE MODELS Computer models have are being used extensively to predict future climates They are usually based on a doubling of greenhouse gases Some of the predictions are rather alarming, especially those relating to sea level rise – changes from 0.3 to 1.5 meters have been predicted

8. MODEL SHORTCOMINGS They are extreme simplifications of the real Earth They keep all other factors that may affect climate constant and change only the level of greenhouse gases They are only as good as the data that have been entered into them They ignore possible changes in ocean currents and cloud cover

9. SEA LEVEL CHANGES They are a major concern for those living in low-lying coastal areas Sea level has been rising since 1880 and since 1930 the average rate has been approximately 2.5 mm/year The rise is not only due to melting glacial ice but also to expansion of the volume of ocean water as it warms

11. CARBON DIOXIDE CHANGES Ice cores from Antarctica contain small amounts of air trapped at the time the ice was formed Analysis of air samples enables us to determine how the CO2 content of the atmosphere has changed over time It shows that during glacial times the CO2 content was much lower than during interglacial times, including the Holocene

12. During the last 160,000 years air temperature and the amount of CO2 have been closely related

13. CAUSE OR EFFECT? In recent years it has become possible to sample at much closer time intervals and it appears that temperature rises first followed by a rise in CO2 We presume this happens because when the ocean waters warm their ability to hold CO2 in solution is reduced and some of the gas is passed into the atmosphere where it could cause further warming but is it significant?

14. WATER VAPOUR – THE ULTIMATE GREENHOUSE GAS About 98% of the greenhouse effect is due to water vapour in the atmosphere Because there is a super abundance of water on our planet, its concentration in the atmosphere is controlled by the temperature of the Earth, not the other way round It cannot initiate a rise or fall in temperature but it has the effect of magnifying the change. This is called a positive feedback effect

15. Climate sceptics such as Plimer claim that increases in greenhouse gases so far have been tiny compared with the amount, mostly water vapour, that was already in the atmosphere

16. ARE SCEPTICS RIGHT? If they are right, recent climate changes have been driven by changes in orbital movements and energy output from the Sun but are greatly magnified by water vapour in the atmosphere They believe that the increase in carbon dioxide and other greenhouse gases only plays a minor role and so far has not significantly affected our climate

17. FUTURE TEMPERATURE TRENDS If the Believers are right the planet will continue to warm ever more rapidly in the next few decades If the Sceptics are are right, we can expect to see significant cooling because the current sunspot cycle is particularly weak and this is known to have caused significant cooling in the historical past