Climate Change: Observations and Projections

1. AP3A90/APMA90 Climate Change and Food Systems Climate Change: Observations and Projections Dan Hodson d.l.r.hodson@reading.ac.uk

2. Climate Change: Observations and Projections In this lecture: • What is Climate? • Observations of a changing Climate. • Climate modelling and Projections of future Climate Change • Uncertainty in Climate modelling and projection. Climate Change: Observations and Projections.

3. What is Climate? Maldives to be Warm Antarctica to be Cold Atacama Desert Dry Bergen Wet “Climate is what you expect, Weather is what you get”. Climate is the statistics of weather, e.g. the average of weather conditions over some period of time. Expect : Climate Change: Observations and Projections.

4. The Climate System Ice Atmosphere Land Ocean Vegetation Climate Change: Observations and Projections.

5. The Atmosphere Climate Change: Observations and Projections.

6. Atmospheric Composition Greenhouse Gases Dry air contains: • Nitrogen 78% by volume • Oxygen 21% by volume • Argon 0.9% • The remaining 0.1% • Carbon Dioxide (CO2) • Methane (CH4) • Nitrous Oxide (N2O) • + other trace gases PLUS Water vapour (variable amounts ~1%) Climate Change: Observations and Projections.

7. The Greenhouse Effect Climate Change: Observations and Projections.

8. Electromagnetic Radiation Fir0002/Flagstaffotos All objects emit Electromagnetic Radiation (Light). Very hot objects emit visible light (Shortwave). Cooler objects emit infrared light (Longwave). This radiation carries Energy away from an object which can then be absorbed by another object. Climate Change: Observations and Projections. http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License

9. Main Greenhouse Gases Water vapour • The remaining 0.1% • Carbon Dioxide (CO2) • Methane (CH4) • Nitrous Oxide (N2O) Greenhouse Gases Although small fraction of Atmosphere, large impact. Greenhouses gases are almost transparent to Shortwave radiation from the Sun, but almost opaque to Longwaveradiation from the Earth. Hence Greenhouse gases trap some outgoing Longwave radiation -> Disequilibrium -> Warming. With no Greenhouse gases, average temperature of the Earth’s surface would be -19ºC rather than 14ºC. Climate Change: Observations and Projections.

10. The Greenhouse Effect Climate Change: Observations and Projections.

11. Observations of Climate Change Climate Change: Observations and Projections.

12. Climate Change • Climate can be defined as the average of weather. • Climate is what we Expect. • A Change in Climate means e.g. a change in the average weather conditions & change in what we expect e.g.: • Warmer summers • Wetter winters • But also can talk about the Climate in terms of other system components e.g. • The height of the sea. • The number of forest fires each summer. Climate Change: Observations and Projections.

13. Observing the Weather • People have always watched and noted the weather, but Objective measurements using scientific instruments began only ‘recently’: • Thermometers around since 1600’s • Early 1700’s Daniel Gabriel Fahrenheit manufactured first reliable mercury thermometers. • The Central England Temperature record is the Oldest instrumental record of temperature in the world. • Monthly measurements back to 1649. Climate Change: Observations and Projections.

14. CET Climate Change: Observations and Projections.

15. Observing the Weather • Observations continued in this uncoordinated way for many years. • Individual Weather diaries • Marine weather logbooks • Once weather forecasting began, it was realised that coordinated, reliable, regular measurements of the weather were required. • World Meteorological Organisation (1950) set up to coordinate this observation across the World. Climate Change: Observations and Projections.

16. Global Observing Network Locations of land, ship and buoy observations across the world at 6am 14 January 2008 Land observations concentrated in inhabited areas and mainly in the Northern Hemisphere 1970 Climate Change: Observations and Projections.

17. Has the Earth Surface Warmed? Different estimates (smoothed) ~ 0.8ºC IPCC AR4 Climate Change: Observations and Projections.

18. Is the rate of warming increasing? IPCC AR4 Climate Change: Observations and Projections.

19. Global Trends Temperature trends at each point on the Earth IPCC AR4 More warming over land than oceans Some regions have cooled. Climate Change: Observations and Projections.

20. The ten warmest years on record • 1998 • 2010 • 2005 • 2003 • 2002 • 2009 • 2004 • 2006 • 2007 • 2001 • Nine of these are from the last decade • All are from the last 15 years • 1998 • 2005 • 2003 • 2002 • 2009 • 2004 • 2006 • 2007 • 2001 • 1997 • Eight of these are from the last decade • All are from the last 13 years 2012 (Data taken from the Hadley Centre) Climate Change: Observations and Projections.

21. Is it unusual? Global average temperature rose in the 20th Century Is this unusual? Have temperatures changed like this in the past? Problem: Very few temperature measurements before 1900. How can we measure temperatures before the invention of the thermometer? Natural Thermometers! Climate Change: Observations and Projections.

22. Tree Rings Trees grow outwards and lay down a new ring of wood every year. More vigorous growth = thicker ring. Growth dependent on temperature, rainfall etc. Can estimate temperature from the width of rings. ~1000 years. Climate Change: Observations and Projections.

23. Estimates of past Northern Hemisphere Temperature Recent warming unprecedented IPCC AR4 Climate Change: Observations and Projections.

24. Have other things changed? Arctic Sea Ice Area Glacier Lengths Sea level height Climate Change: Observations and Projections.

25. Have other things changed? Three Estimates of the Amount of heat in the upper ocean. Oceans are Warming: Climate Change: Observations and Projections.

26. Greenhouse Gases • Carbon Dioxide • Burning of Fossil Fuel • Manufacture of Cement (~5% global) • Deforestation • Methane • Agriculture • Natural Gas • Landfill decomposition • Nitrous Oxide • Artificial fertilizers • Burning of Fossil Fuel • Are these changes unusual? Climate Change: Observations and Projections.

27. Ice Cores Ancient gases trapped in bubbles in Antarctic Ice. Can recover ice & gases that have been stored for 10 000s of years. Can measure levels of Greenhouse gases in Ancient atmosphere. Climate Change: Observations and Projections.

28. Unprecedented? End of Last Ice Age IPCC AR4 Rate of increase of greenhouse gases unprecedented in last 20 000 years. Climate Change: Observations and Projections.

29. Observations of Climate Change: Summary • Many 1000s of measurements form estimate of changing climate. • Global average (mean) surface temperature rose by ~0.8ºC during the 20th Century. • 9/10 of the last 10 years were the warmest on record globally. • These warm temperature are likely highest in the past ~1000 years. • Also • Sea level & Upper ocean heat content rose • Arctic sea ice and Glaciers melted • Concentrations of Major Greenhouse gases risen over 20th Century. • Largest seen in last 20 000 years. Climate Change: Observations and Projections.

30. Modelling the Climate Climate Change: Observations and Projections.

31. Climate System Components Ice Atmosphere Land Ocean Vegetation Climate Change: Observations and Projections.

32. Why? • Why do we need a model of the Climate System? • Most of Experimental Science • Take some part of the World. • Make some change. • Measure any Effect. • The Climate System is the World. • Can’t do real experiments on the Whole Climate System. • Need Climate Models. Climate Change: Observations and Projections.

33. Modelling the Climate System Physics Do experiments to find out how Climate components (e.g. water) behave. Write down a mathematical description of this behaviour. Convert this into a numerical form for use in a computer. Can then use model Earth climate to perform experiments not possible with the real Earth Climate. Climate Change: Observations and Projections.

34. Is the model Correct? Annual Rainfall Real World Model IPCC AR4 • If we use our Climate Model to simulate 20th Century climate we can compare to our past measurements of the real 20th Century climate. • Model Validation Climate Change: Observations and Projections.

35. Is the model Correct? • Models simulate some variables better than others. • Temperature is predicted accurately • Rainfall less so • Climate models reproduce many of the features of the real climate • Global Patterns temperature & rainfall • Seasonal retreat of ice caps • North Atlantic Gulf Stream these are not explicitly built into the model, they emerge from the physics. • More confidence that models are reliable. Climate Change: Observations and Projections.

36. Two Experiments • EXPT1: Use our climate models to simulate 20th Century climate as it was. • Known Increases in Greenhouse gases • Known changes in Natural Forcings • Volcanoes • The slight variations of light from the Sun. • EXPT2: Use our climate models to simulate 20th Century climate as it might have been • No changes in Greenhouse gases • Known changes in Natural Forcings Climate Change: Observations and Projections.

37. Results IPCC AR4 • EXPT1: Greenhouse gases + Natural Forcings. • Black line: measured 20th Century Global average Temperature. • Red Line: Average of same experiment with many different climate models. • EXPT2: Natural Forcings Only. • Implication: Increases in Global average Temperature due to increases in Greenhouse gas emissions. Climate Change: Observations and Projections.

38. Projections of future Climate Change Climate Change: Observations and Projections.

39. Projected global temperatures • A2/A1B/B1 – different estimates of future GHG emissions. • A2 = High Emissions • B1 = Low Emissions • Large range by end of century. • Some warming even if we stopped emitting all GHG today. Climate Change: Observations and Projections.

40. Projected regional temperature changes 2090-2099 B1 (low) A2 (high) IPCC AR4 • Northern latitudes warm more. • Melting sea ice – feedbacks • Land warms more than oceans. Climate Change: Observations and Projections.

41. Projected regional Rainfall Changes 2090-2099 Northern Winter Northern Summer • Different regions show different rainfall changes. • Northern high latitudes: increased rainfall in N. Hemisphere winter. • Wetter, more flooding. • Southern Africa & Mediterranean reduced rainfall in N. Hem. Summer • Drier, more droughts. • Grey shading – regions where we are confident. Climate Change: Observations and Projections.

42. Extremes • 2003 European heatwave • Probably hottest EU summer in last 500 years. • Stott et al (2004) likely to be considered a cool summer in 2100. These are projections of the increase in the average temperatures and rainfall. If the average temperature increases, then the chance of heat waves occurring increases. Climate Change: Observations and Projections.

43. Uncertainty in Climate modelling and projection. Climate Change: Observations and Projections.

44. Climate Projections: Sources of Uncertainty In Science it’s important to understand what you don’t know. Three sources of uncertainty in climate projections: • Uncertainty in future Greenhouse gas levels (Scenario Uncertainty) • Uncertainty in the formulation of the Climate models (Model Uncertainty) • Intrinsic uncertainty in the climate system. (Internal Variability) Climate Change: Observations and Projections.

45. Scenario Uncertainty Emissions Scenarios IPCC,2000 • We don’t know what future Greenhouse gas emissions will be. • Produce ‘Scenarios’ – estimates of future emissions based on estimates of future •  Population Projections • Economic Development • Structural and Technological Change • Vary from High growth (A1) to Low growth (B2). Climate Change: Observations and Projections.

46. Model Uncertainty Climate models are only approximate models of the real world. • They have low resolution • A region of 200km x 200km represented by a single point. • They cannot represent small scale processes directly • Formation of rain represented by statistical rather than physical model. • They cannot include all processes in the Climate System • Ocean biology, Dynamic vegetation, Agriculture, Economics are only just beginning to be included. • There are many Climate models (17 used in last IPCC report) Climate Change: Observations and Projections.

47. Intrinsic Uncertainty (Internal Variability) • Butterfly effect. Sensitivity to the initial conditions. • Because we do not know the exact state of the Climate system now, we cannot predict the exact future state of the climate. If we start our Climate model and watch how the temperature evolves. If we start the model again, but with e.g. slightly cooler initial temperatures. The temperature evolves differently. Climate Change: Observations and Projections.

48. Working with uncertainty • Although these sources of uncertainty exist we can assess and quantify the scale of uncertainty. • This allows us to assign a level of confidence to climate projections. • This allows the IPCC AR4 to say: • “Most of the observed increase in global average temperatures since the mid-20th century is very likelydue to the observed increase in anthropogenic greenhouse gas concentrations”. Climate Change: Observations and Projections.

49. Summary In this lecture we have discussed: • What Climate is. • Observations of a Changing Climate. • Climate Modelling and Projections of future Climate Change • Uncertainty in Climate Modelling and Projection. Climate Change: Observations and Projections.

50. Next Lecture The next lecture: Climate Change and Livestock Les Crompton Jan 15th • Dan Hodson • d.l.r.hodson@reading.ac.uk Climate Change: Observations and Projections.