1. 1 Climate Change and Urban Climate Dr Janet Barlow Department of Meteorology, University of Reading j.f.barlow@reading.ac.uk MSc Intelligent Buildings March 2009

2. 2 Structure of today’s session Part 1: Climate Change (the global picture) Key reference: Intergovernmental Panel on Climate Change IPCC 4 th Assessment Report http://www.ipcc.ch/index.htm Part 2: Urban Climate (climate at the scale of buildings)

3. 3 Part 1: Climate change What is climate? Has climate changed in the recent past? What might have caused climate to change? What might happen in the future? What can we do about it?

4. 4 What is climate? “Climate is what we expect, weather is what we actually get” Ed Lorenz A full description of climate includes: global means, geographical, seasonal and day-to-day variations of temperature, precipitation, radiation, clouds, snow cover etc.

5. 5 Temperature changes 1 Global mean temperature has increased by 0.6±0.2  C since 1900 For b) satellite data shown in red, tide gauge in blue For c), snow is Mar/Apr cover All changes shown with respect to 1961-1990 average. Smoothed curves decadal values, dots are yearly values. Shaded area are uncertainty intervals.

6. 6 Although it’s really about global change… some places have seen very large warming, other regions have actually cooled. …although in recent years, warming predominates Linear trends in annual temperature (degC per century) Grey areas – insufficient data Trends significant at 5% level indicated by + marks.

7. 7 The evidence for global warming is mounting! INCREASE Length of freeze free season Length of growing season More frequent heat waves Wetter winters/Drier summers Sea level rise (0.1-0.2m during 20 th century, mostly due to thermal expansion of ocean) DECREASE Extent of mountain glaciers Sea-ice amounts and thickness (NH decreased by 10-15% since 1950s) Snow cover (10% reduction in NH snow cover since 1960s) Fewer Frosts

8. 8 Climate change is not unprecedented The earth has been capable of rapid transitions in the past…

9. 9 Mann et al., Science 1999 (Northern Hemisphere only) However, the northern hemisphere is probably the warmest it’s been for at least 1000 years… Reconstruction using proxy records like tree rings and ice cores

10. 10 … the rise in temperature is strongly correlated with a rise in the emission of certain gases into the atmosphere by human activities….

11. 11 Concentrations are now higher than for the past several thousand years… IPCC (2001) Ice core data – different colours indicate different studies. Atmospheric measurements – red lines

12. 12 … And the present trends in CO 2 and methane are outside those experienced on earth for at least the last 400,000 years…..

13. 13 What might have caused these changes? The balance of evidence suggests that there is a discernible human influence on global climate (IPCC, 1995) There is new and stronger evidence that most of the warming over the past 50 years is attributable to human activities (IPCC 2001) Most of the observed increase in global average temperatures since the mid-20 th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations (IPCC 2007)

14. 14 Fundamental processes – many interacting components

15. 15 For a stable climate, the earth must be in energy balance IPCC 2001 Energy absorbed by surface and atmosphere = Energy radiated from Earth- Atmosphere and ocean to space 30% of incoming radiation is reflected back to space

16. 16 The “natural greenhouse effect” Release of carbon dioxide and other gases from human activities enhances the greenhouse effect and causes the Earth to absorb around 2Wm -2 more radiation than it emits  global warming

17. 17 Natural climate forcing mechanisms Solar variability Volcanic eruptions

18. 18 Solar variability: 1 Changes in the Sun’s strength – 11 year cycle with sunspots –small changes that have little impact compared to greenhouse gas changes

19. 19 Solar variability: 2 Changes in Sun-Earth geometry –Sun-Earth distance, tilt of Earth and ellipse of orbit –act over very long timescales, many thousands of years –possibly play a role in inducing ice ages but not important on past 250 years time scale –at current time provides a cooling influence on climate

20. 20 Volcanoes Large eruptions like Pinatubo (1991) put clouds of sulphur dioxide gas into stratosphere, above the weather.  cloud of sulphuric acid droplets scatter and absorb solar radiation  cooling of surface and warming of stratosphere But, aerosols only last a few years, so generally climate impact only lasts a few years

21. 21 Observed effect on T IPCC 2001 El Chichon Pinatubo

22. 22 Anthropogenic causes Greenhouse gases Ozone changes (stratospheric and tropospheric) Tropospheric aerosols Surface albedo changes Heat pollution

23. 23 Greenhouse gases Water vapour is most important natural greenhouse gas, but we don’t usually change it directly so don’t consider it part of anthropogenic climate change Strength of a greenhouse gas depends on –strength of absorption of infra-red radiation –overlap of absorption with other gases –lifetime in the atmosphere –amount added over given period of time CO 2 (carbon dioxide), CH 4 (methane), N 2 O (nitrous oxide), CFCs/HCFCs/HFCs

24. 24 Strengths of greenhouse gases “Forcing”: measure of perturbation to energy budget “GWP”: Global warming potential (combines forcing with lifetime of gas)

25. 25 Ozone Spatially non- uniform Radiative forcing depends critically on level at which ozone changes: –troposphere: ozone has increased and produces a positive radiative forcing (a pollutant at this level) –stratosphere: ozone has decreased implying less absorption and re-emission of IR radiation producing a negative forcing (also small +ve forcing due to increased solar radiation reaching the surface)

26. 26 Tropospheric aerosols Tiny particles (or droplets) Many different types from both natural and anthropogenic sources: –dust (from land-use change) –sulphates (fossil fuel burning) –soot (fossil fuel and biomass burning) –organic droplets (fossil fuel and biomass burning)

27. 27 Aerosols: Direct solar effect Aerosols scatter and absorb solar radiation No aerosol Scattering aerosol Absorbing aerosol Negative radiative forcing  cooling Positive radiative forcing  warming

28. 28 CO 2 vs aerosol forcing CO 2 Sulphates Cannot be used to cancel out greenhouse gas forcing (patterns are completely different) Response may also be different Indirect effect is very uncertain but potentially large

29. 29 Other anthropogenic effects Land use changes alter the albedo and the amount of solar radiation reflected back to space. Urban and industrial regions output large amounts of local heat. Important regionally and may modify the circulation

30. 30 Relative roles: IPCC 2007

31. 31 The future: Human influences will continue to change atmospheric composition throughout the 21st century How sensitive the climate system is to emissions –how clouds, ice, oceans etc respond to the extra heating How quickly the climate will change in the future depends on: How much greenhouse gas emissions grow –depends on population growth, energy use, new technologies, etc

32. 32 Uncertainty Being uncertain does not mean that we know nothing! Many simplifications and assumptions must be made to make useable models of the climate system There are often different ways of doing this and sometimes there isn’t a “best” method. This variation leads to differences in the feedbacks in models and differences in the future predictions

33. 33 How good are climate models? FAR – 1 st assessment report (1990) SAR – 2 nd (1996) TAR – 3 rd (2001) Shaded areas indicate range of model predictions Dots show annual mean variations Black line is decadal variations obtained by smoothing data

34. 34 Models recreate C20 th warming only WITH anthropogenic influence Temperature anomalies with respect to 1901- 1950 average Dashed black line – less than 50% spatial data cover Shaded areas indicate 5-95% range over many simulations from different climate models

35. 35 The Future: you ain’t seen nothing yet… Temperature anomalies with respect to 1980- 1999 average Shaded colour areas indicate ±1 standard deviation; grey bars indicate range of predictions Emission scenarios: A1B: rapid economic growth, mix of energy sources A2: Fragmented regional economic growth B1: clean technology, global solutions

36. 36 Land areas are projected to warm more than the oceans with the greatest warming at high latitudes Temperature anomalies with respect to 1980-1999 average

37. 37 2100: A Different Climate! Increase in global mean temperature of 1.4°C - 5.8°C. Sea level rise by a further 0.09m – 0.88m. Change in frequency and duration of extreme weather events. Increase in the number of hot days, and decrease in number of cold days. Increase in precipitation over northern hemisphere. BUT there are SERIOUS impacts too…

38. 38 Future impacts

39. 39 Impacts of change in water runoff Percentage change of 2081-2100 with respect to 1981-2000 average A1B (“Rapid”) scenario

40. 40 2050: Millions displaced by sea-level rise >1million 50,000 to 1 million 5,000 to 50,000

41. 41

42. 42 So what can we do about it? Mitigation? (Working Group 3 IPCC) (Energy efficiency, “clean” energy and technology transfer to developing countries) Adaptation? (Working Group 2 IPCC) (Some will be necessary as we are already committed to some change)

43. 43 Kyoto Protocol Reduction of emissions of CO 2, CH 4, N 2 O and “basket of 6 gases” which includes SF 6 and several of the HFCs Ratification (particularly by US)? Role of developing nations? http://unfccc.int/kyoto_protocol/items/2 830.php http://en.wikipedia.org/wiki/Kyoto_Proto col 11 th December 1997, Japan – adopted 16 th February 2005 – enforced

44. 44 Contraction and convergence: an equitable solution? FSU: Former Soviet Union. See Global Commons Institute www.gci.org.uk

45. 45 Even if we act quickly….the climate responds slowly Stabilised emissions Stabilised CO 2 concs in the atmosphere Stabilised surface temperature Stabilised sea level 10s/100s yrs~ 100 years 100s / 1000 yrs

46. 46 What have we found so far? Climate change is unlikely to be solely the result of either natural or anthropogenic effects Complexity is still an issue, especially interaction of biosphere and other components Model predictions quite good for global temperatures – but regional predictions still uncertain

47. 47 Websites on Climate Change Intergovernmental Panel on Climate Change http://www.ipcc.ch/index.htm DEFRA website on climate change: http://www.defra.gov.uk/environment/climatechange/ UK Climate Impacts Programme: http://www.ukcip.org.uk/ climateprediction.net – take part in online climate change experiment: http://www.climateprediction.net/index.php