1. What is Climate Change? Dan Hodson d.l.r.hodson@reading.ac.uk EC110 Economics of Climate Change

2. What is Climate Change? In this lecture we will discuss:  What is Climate?  Can it Change?  Is the Climate Changing?  Can we predict future changes in climate?  Can we Fix it? 13/1/2015Economics of Climate Change: What is Climate Change?

3. What is Climate?

4.  “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 : Maldives to be Warm Antarctica to be Cold Atacama Desert Dry Bergen Wet 13/1/2015Economics of Climate Change: What is Climate Change?

5. What is the Climate System? Land Ocean Atmosphere Ice Vegetation 13/1/2015Economics of Climate Change: What is Climate Change? Atmosphere

6. Atmospheric Composition The Atmosphere is a mixture of gases: –Nitrogen 78% by volume –Oxygen 21% by volume –Argon 0.9% –The remaining 0.1% Carbon Dioxide (CO 2 ) Methane (CH 4 ) Nitrous Oxide (N 2 0) + other trace gases PLUS Water vapour (variable amounts ~1%) Greenhouse Gases 13/1/2015Economics of Climate Change: What is Climate Change?

7. Can Climate change?

8. Ice Ages  Climate has varied in the past. 13/1/2015Economics of Climate Change: What is Climate Change?

9. 13/1/2015Economics of Climate Change: What is Climate Change? Sun

10. The Greenhouse Effect 13/1/2015Economics of Climate Change: What is Climate Change?

11. Greenhouse Gases  Although small fraction of Atmosphere, large impact.  Greenhouses gases are transparent to Sunlight, but opaque to Infrared light/radiation from the Earth.  Greenhouse gases trap Infrared light/radiation -> Warming.  No Greenhouse gases, the average temperature on Earth would be -19ºC, Actually 14ºC.  If the 0.1% was 0.2% -> A warmer climate Greenhouse Gases The remaining 0.1% Carbon Dioxide (CO 2 ) Methane (CH 4 ) Nitrous Oxide (N 2 O) Water vapour 13/1/2015Economics of Climate Change: What is Climate Change?

12. Greenhouse Gases: Are they increasing?  Carbon Dioxide –Burning of Fossil Fuel –Deforestation –Manufacture of Cement (~5% global)  Methane –Agriculture –Natural Gas –Landfill decomposition  Nitrous Oxide –Artificial fertilizers –Burning of Fossil Fuel 13/1/2015Economics of Climate Change: What is Climate Change?

13. Is the Climate changing?

14. Measuring Climate  To know if Climate is Changing – need to measure climate over time.  Measure e.g.: –Temperature –Rainfall –Sea surface height  Over what time? –Centuries?  And where? –Everywhere! 13/1/2015Economics of Climate Change: What is Climate Change?

15. CET 13/1/2015Economics of Climate Change: What is Climate Change?

16. Global Observing Network 13/1/2015Economics of Climate Change: What is Climate Change? 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

17. Has the Earth Surface Warmed? 13/1/2015 IPCC AR5 ~ 0.8ºC “It is certain that Global Mean Surface Temperature has increased since the late 19th century. …. The globally averaged combined land and ocean surface temperature data …, show a warming of 0.85 [0.65 to 1.06] °C, over the period 1880–2012. “ IPCC AR5 WGI

18. Global Trends  More warming over land than oceans 13/1/2015 IPCC AR5 WGI Temperature trends at each point on the Earth Economics of Climate Change: What is Climate Change?

19. Is it unusual?  Global average temperature rose in the 20 th 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! 13/1/2015Economics of Climate Change: What is Climate Change?

20. 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 past temperature from the width of rings.  ~1000 years. 13/1/2015Economics of Climate Change: What is Climate Change?

21. Estimates of past Northern Hemisphere Temperature 13/1/2015Economics of Climate Change: What is Climate Change? IPCC AR4 Recent warming unprecedented

22. Have other things changed?  Arctic Sea Ice Area  Glaciers  Sea level height 13/1/2015 IPCC AR5 WGI Economics of Climate Change: What is Climate Change?

23. Have other things changed?  Oceans are Warming: 13/1/2015 Estimates of the Amount of heat in the upper ocean. IPCC AR5 WGI Economics of Climate Change: What is Climate Change?

24. Can we predict future changes in climate?

25. Climate System Components Land Ocean Atmosphere Ice Vegetation 13/1/2015Economics of Climate Change: What is Climate Change?

26. Modelling the Climate System  Do experiments to find out how Climate components (e.g. water) behave.  Write down a mathematical description of this behaviour.  Convert this into a form for use in a computer.  Can then use model Earth climate to predict future changes in climate. 13/1/2015Economics of Climate Change: What is Climate Change? Physics

27. Is the model Correct?  If we use our Climate Model to simulate 20 th Century climate we can compare to our past measurements of the real 20 th Century climate. –Model Validation 13/1/2015Economics of Climate Change: What is Climate Change? Real WorldModel Annual Rainfall IPCC AR4

28. Two Experiments  EXPT1: Use our climate models to simulate 20 th 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 20 th Century climate as it might have been –No changes in Greenhouse gases –Known changes in Natural Forcings 13/1/2015Economics of Climate Change: What is Climate Change?

29. Results  EXPT1: Greenhouse gases + Natural Forcings. –Black line: measured 20 th Century Global average Temperature. –Red and Blue: 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. 13/1/2015 IPCC AR5 WG1 Economics of Climate Change: What is Climate Change?

30. Projected global temperatures  RCP – different estimates of future GHG emissions. –RCP 8.5 = High Emissions –RCP 2.6 = Low Emissions 13/1/2015 IPCC AR5 WG1  Large range by end of century  Can reverse warming with sufficient mitigation. Economics of Climate Change: What is Climate Change?

31. Projected regional temperature changes 2090-2099 13/1/2015 IPCC AR4  Northern latitudes warm more. –Melting sea ice – feedbacks  Land warms more than oceans. IPCC AR5 WG1 Economics of Climate Change: What is Climate Change?

32. Projected regional Rainfall Changes 2081-2100 13/1/2015  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.  Dotted regions are where we are confident. Summer Winter Economics of Climate Change: What is Climate Change?

33. Can we Fix it?

34. Geoengineering  Can we control the impact of our CO 2 emissions with a technological fix?  Either: I.Remove CO 2 from the atmosphere (Carbon Dioxide Removal, CDR). Probably expensive Does address root cause of the problem II.Reduce the amount of sunlight reaching the surface of the Earth (Solar Radiation Management, SRM). Probably cheaper than (I) Unwanted side effects 13/1/2015Economics of Climate Change: What is Climate Change?

35. Stratospheric aerosols  Feed reflective particles into the upper atmosphere  Reduces sunlight at the surface –Less heating  But: –Particles fall to Earth, need to keep doing it. –CO 2 still rising, if you stop -> rapid warming. –Governance – who is in charge?. –May change patterns of rainfall – more drought? –Oceans will still become more acidic. –Other Unknown impacts! –Moral Hazard. 13/1/2015Economics of Climate Change: What is Climate Change?

36. Summary In this lecture we have discussed:  What we mean by ‘Climate’.  How climate can change – The Greenhouse effect.  The evidence that Climate is changing.  How Projections of future Climate are made and what they tell us.  Technical fixes and the side effects. 13/1/2015Economics of Climate Change: What is Climate Change? Dan Hodson d.l.r.hodson@reading.ac.uk

37. 13/1/2015Economics of Climate Change: What is Climate Change?

38. The ten warmest years on record 1.1998 2.2005 3.2003 4.2002 5.2009 6.2004 7.2006 8.2007 9.2001 10.1997  Eight of these are from the last decade  All are from the last 13 years (Data taken from the Hadley Centre) 13/1/2015 1.2014 2.2010 3.2005 4.1998 5.2003 6.2009 7.2006 8.2002 9.2013 10.2007  Seven of these are from the last decade  All are from the last 18 years Economics of Climate Change: What is Climate Change?