Climate Change: Theory and Forecasts

1. Climate Change: Theory and Forecasts David Gay National Atmospheric Deposition Program (NADP) dgay@uiuc.edu, (217) 244-0462

2. Two Parts • What exactly is climate change? • Theory • What we know • Forecasts

3. So, what is “Climate Change”?

4. First, what is climate? • Definition Average course or conditions of weather at a place, usually over a period of years, as exhibited by • Temperature • Wind velocity • Precipitation (Webster’s) • Prevailing set of weather conditions (temperature, humidity, etc.)

5. So, can WE change climate? • Thomas Jefferson guessed we could in early 1800’s • Trees in VA • Started making measurements • Urban concrete, no trees • Chemical composition of the atmosphere • Sensible energy vs. latent heating • Albedo changes • Natural changes (ice ages, warm periods) • Changing evaporation/precipitation (trends) • Other patterns (Malenkovitch cycles, el Nino/la Nina) • Cloud cover changes?

6. Definition of Climate Change IPCC usage: • Any change in climate over time, whether due to natural variability or from human activity. Alternate: • Change of climate, attributed directly or indirectly to human activity, that • Alters composition of global atmosphere and • Is in addition to natural climate variability observed over comparable time periods

7. So? More than just temperature • Precipitation (amount and patterns) • Atmospheric pressure • Humidity • Circulation changes • Number of storms, droughts, freezes, etc. • And more….

8. Average Temperatures, in ◦C

9. Type of Ecosystem, w T and P

10. Water Cycle

11. Radiation Balance“The Greenhouse” • Example Your stove top

12. Radiation Balance

14. “Effective” Greenhouse Gases Atmospheric Window

15. So, what do we know? • INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE (World Meteorological Organization; UN Env. Program) • http://www.ipcc.ch/

16. Carbon Dioxide Concentration Over Time

17. Methanealso a Greenhouse Gas

18. Quiz • How much has the earth warmed in the last 150 years?

19. Answer ≈ 0.95°C (1.62 °F) since 1850

21. Historic Thermometer Records

22. “Diurnal Temperature Range”

23. Temperature Trends, ◦C

24. Changes In…..

25. Sea-Level Rise Total Change = +170 mm or +6.7 inches

26. Causes of Sea Level Rise

27. Sep 1979 Sep 2003 Arctic Sea Ice 2007 = 4.3 x106 km2 , record low

28. Glacial Retreat Argentiere Glacier, French Alps

29. Trends in Precipitation

30. IPCC Summary of Observations • Global mean surface temperatures have risen • By 0.74°C ± 0.18°C over the last 100 years (1906–2005) • 2005 was one of two warmest years on record • Land regions have warmed at a faster rate than the oceans. • Changes in extremes of temperature are consistent with warming of climate • Widespread reduction in number of frost days in mid-latitude regions, • Increasing number of warm extremes & reducing number of daily cold extremes observed in 70 to 75% of land regions, and • Most marked changes are for cold (lowest 10%, based on 1961–1990) nights, rarer over 1951 to 2003 period.

31. IPCC Summary (cont.) • Sea-surface temperatures warming at all latitudes over all oceans, • Urban-heat island effects real but local, have not biased large-scale trends, • Average arctic temperatures increased at almost twice global average in past 100 years, • Lower-tropospheric temperatures increases slightly greater than those at surface between 1958 to 2005

32. IPCC Summary (cont.) • Lower stratospheric temperatures cooling since 1979, • Precipitation has generally increased over land north of 30°N between 1900 to 2005, but downward trends dominate tropics since 1970s, • Droughts more common, especially in tropics and subtropics, since 1970s, • Changes in large-scale atmospheric circulation apparent

33. Historical Perspective of Temperatures

35. Human Contribution to Climate Change (in one slide) IPCC, 2007

36. Causes of climate change Volcanic eruptions Changes in atmospheric composition (greenhouse) • Climate change is driven by five causes (forcings) • Internal components of the climate system respond by changing and interacting in many ways

37. Natural Causes of Climate Change( non anthropogenic)

38. Milanchovitch Cycles, Orbital Changes today • Earth orbital changes • Result from cyclic variations in Earth's orbit around the Sun • Alter the amount of solar radiation (insolation) received on Earth by season and by latitude

39. Precession of the equinoxes (23k years) Oval/circular changes Inclination Change

40. Changes in Solar Energy Output

41. The smoothed sunspot curve correlate with temperature Some intervals almost entirely lack sunspots, such as the Maunder sunspot minimum from 1645-1715 AD These sunspot minima occurred during the Little Ice Age when the sun was 0.25% weaker Solar activity was generally high during the Medieval Warm Period

42. Other Natural Causes Mt Pinotubo

43. The Modeled Future

44. CO2 Should Increase

45. Predicting TemperatureGlobal Climate Models (GCMs) • Physical equations • Lots of computing • Divide the globe into little boxes

46. Forecast Temperatures

48. Projections of Surface Temperatures

49. Volcanoes Solar GH gases With GH gases W/out GH gases IPCC, 2007 How Good Are the Models?

50. Further Reading • Intergovernmental Panel on Climate Change (IPCC) • UN organization (Weather Meteorological Office) • http://www.ipcc.ch/ • Summary for the physical science basis • http://ipcc-wg1.ucar.edu/wg1/wg1-report.html