ATM S 111, Global Warming: Understanding the Forecast

1. ATM S 111, Global Warming: Understanding the Forecast Dargan M. W. Frierson Department of Atmospheric Sciences Day 6: 04/15/2010

2. Reading Assignment • Should have read “Floods and Droughts” p.58-74 • Next assignment: read “The Big Melt” p.75-105 • HW 2 due Friday 11:59 PM • Quiz #1 is next Tuesday in class • Bring a scantron sheet (available from the bookstore) • Bring a #2 pencil • Material will be similar to HW assignments plus material from this week

3. Finishing Up Extreme Heat • Dry climates heat up faster • Humidity makes it feel hotter though • And nights stay hotter due to the greenhouse effect • Simplest changes with warming: shifting the distribution • Additional expectations: Higher moisture globally will mean higher heat index as well, and hotter nights • If climates dry out, then they will take on more desert-like characteristics • What about really extreme heat?

4. Worldwide Temperature Extremes Highest temperature recorded in the world: 136o F (57.8o C) in El Aziziya, Libya

5. Worldwide Temperature Extremes Highest in USA: 134o F (56.7o C) in Death Valley, Calif. States with lowest record high: Alaska & Hawaii tie at 100o F

6. Highest in Washington: 118o F (48o C) in Grant County The Gorge Amphitheater in Grant County

7. Worldwide Temperature Extremes • All these extremes are in desert climates • Note: these are only where weather stations are located • It almost certainly has reached hotter temperatures elsewhere

8. Heat Index Extremes Remember heat index factors in how humid it is Highest heat index in the world: 176o F (80o C) in Dhahran, Saudi Arabia (on the Persian Gulf) Temperature was 108o F (42o C) .

9. Lowest Recorded Temperatures • Coldest ever: • -129o F (-89.2o C) in Vostok, Antarctica • Coldest in US: • -80o F (-62o C) in Prospect Creek, Alaska • Coldest in lower 48 states: • -70o F (-56.7o C) in Montana • Coldest in Washington: • -48o F (-44.4o C) in Mazama & Winthrop

10. Shifting the Distribution of Temperature • If the temperatures just shift to warmer, we’d expect more hot extremes & less cold extremes • If the soil dries out, we wouldn’t expect just a shift though Houghton textbook

11. Projected Annual Average Surface Temperature Change: “2080-2099” minus “1980-1999” Scenario A1B

12. Drier Wetter Projected Soil Moisture Change: “2080-2099” minus “1980-1999” Scenario A1B drying -> even higher daytime temperature moistening -> even higher nighttime temperatures

13. Model Predictions of Extreme Heat: US Frequency of 20 year heat waves: 1-in-20-year heat waves happen every other year over much of the country by the end of 21st century Next few slides from Global Climate Change Impacts in the US by US Global Change Research Program, 2009

14. Model Predictions of Extreme Heat: US Days over 90o F

15. Model Predictions of Extreme Heat: US Days over 100o F

16. Model Predictions of Extreme Heat: US Shifting climate zones

17. Washington State Predictions Predictions of 2030-2059 compared w/ 1970-1999 Change in number of heat waves (heat wave = 3 straight days w/ heat index over 90o F) Change in number of very warm nights From Climate Impacts Group report. Other model used has less severe predictions

18. The future of summer sizzle - the worst heat waves will be more intense - heat waves of a prescribed intensity will occur more frequently - some regions may become more susceptible to heat waves - shift toward higher daytime summer temperatures - vegetated land may give way to desert.

19. Floods and droughts (RG p. 58-74) Floods and droughts: two sides of a catastrophic coin A wetter world (but not everywhere) Are floods increasing? Defining drought What do the oceans have to do with drought? The drying of southern Australia The plough and its followers: farming and rainfall

20. Outline • Precipitation around the world • Rainy regions and deserts • Monsoons • Changes that are expected in the future • Wetget wetter, dryget drier • Heavy rain events with more heavy rain • Changes that have been observed • Increased rainfall? • Droughts in the Sahel • Droughts in Australia

21. Rainiest and Driest Places on Earth • Again, these are just places that have weather stations • There are likely more extreme places that aren’t being measured

22. Rainiest spot on Earth: Mount Waialeale, Hawaii (pictured): 460 inches/year (11.7 meters) Rainiest spot may actually be Lloro, Colombia: 523.6 inches/year (13.3 meters – this is just an estimated amount though)

23. Rainiest year on record: 905 inches (almost 23 meters) in Cherrapunji, India In the foothills of the Himalayas

24. Rainiest day ever: Reunion Island (500 miles off coast of Madagascar) 72 inches (1.86 m) in 24 hours!!! Also just three years ago, Reunion Island set the record for 72 hour rainfall: 155 inches (3.9 m) during a tropical cyclone

25. Extreme Precipitation • All of the above examples are associated with mountains • More rain on windward side of mountains • When air is lifted up the slope • Rain requires water vapor and a lifting mechanism • These extremes are localized rainy areas • Just like the Olympic Peninsula here in Washington! • Let’s take a look at the average precipitation over the whole globe • There are also large scale patterns of rainy and dry

26. Observed precipitation in January and July January Observed precipitation in mm/yr Rainiest spots are narrow bands near the equator Some of the driest places are over the ocean! Most deserts are around 30 degrees latitude July

27. “Hadley Circulation” Air rises above the warmest ocean surface (hot air rises) The circulation takes water vapor away from the deserts at 30 degrees and brings it into the tropical rainy regions “convergence zone”: where winds come together

28. Monsoon Circulation colder hotter Daily = “Sea Breeze” caused by daily solar cycle Seasonally = Monsoon (a persistent version of the sea breeze) caused by seasonal solar cycle Heating of landis key: again hot air rises, and circulation brings in water vapor

29. January Floods and droughts: two sides of a catastrophic coin Wet regions become wetter while dry regions become drier Observed Precipitation July

30. January Floods and droughts: two sides of a catastrophic coin Wet regions become wetter while dry regions become drier ITCZ ITCZ M M M SPCZ SACZ M=monsoon, CZ=convergence zone: Climate models suggest that these features become stronger as the earth warms. July M M M ITCZ ITCZ SPCZ

31. Climate model projections of precipitation change Wet gets wetter, dry gets drier Stippling: where models agree

32. January Why? As the atmosphere warms, water vapor concentrations increase Winds bring in even more moisture into the rainy regions Also more water vapor taken away from dry regions (and more evaporation there) July W = wind from west T = wind from NE blue = rainbelts

33. Global Warming Rain Responses • Wet get wetter • More water vapor is brought into the regions that are already rainy • Dry get drier • More water vapor taken out of the dry regions • And more evaporation from dry land surfaces • There’s a lot of uncertainty about specific precipitation responses though • Precipitation is much harder to predict than temperature • Regional responses could change significantly from changes in the winds

34. Some Additional Predictions • Southwestern North America predicted to dry dramatically • As bad as the Dust Bowl by 2060 in some models Dust Bowl drought level Seager et al 2007

35. US Predictions US predictions

36. How about the most intense storms? The intensity of downpours is believed to be proportional to water vapor concentration Warmer temperatures  more water vapor Thus, heavy rainfall events should become more extreme

37. 1990-2000, Flood Impacts Nearly 100,000 people were killed 320 million people were displaced by floods Total reported economic damages exceeding a trillion dollars Bradshaw, et al. Global Change Biol.13, 1-17 (2007).

38. http://cgz.e2bn.net/e2bn/leas/c99/schools/cgz/accounts/staff/rchambers/GeoBytes/GCSE/Case%20Studies/Causes_of_Flooding_in_Bangladesh.jpghttp://cgz.e2bn.net/e2bn/leas/c99/schools/cgz/accounts/staff/rchambers/GeoBytes/GCSE/Case%20Studies/Causes_of_Flooding_in_Bangladesh.jpg

39. Do forests prevent flooding? • A recent study says yes: Bradshaw et al., Global Change Biol.13, 1-17 (2007) • Analyzed broader scale data and found deforestation explained 14% of floods • They predict that decreasing forest area by 10% would increase flood frequency 4-28% and duration 4-8%

40. Are heavy rain events increasing? And heavy precipitation events in the US are projected to get worse Very heavy events have been increasing

41. Are heavy rain events increasing? Thus far, the changes are pretty small, but suggestive Examples of observational results in the scientific literature that suggest an increase on the frequency of heavy rain events. Note: places where heavy precipitation isn’t increasing are places where the mean precipitation is decreasing

42. Are floods increasing? Trends in the frequency of flood events are difficult to quantify because River configurations and land use are continually changing Hourly rainfall data are available only over limited regions of the globe the data are expensive and there are restrictions on their use Rare events, especially when considered season-by-season it’s difficult to establish statistical significance when dealing with rare events. The latter two are true for heat waves too

43. Defining drought Months or years with below normal water supply. Usually from below average precipitation. The definition is not quantitative. Specific criteria (e.g., how long, how severe...) need to be specified. Other factors such as population growth can create deficiencies in water supply (ie Lake Chad)

44. Which way will the Sahel go? the Sahel SUDAN Darfur The Sahel is in between desert and the region drenched by the African monsoon

45. The African Monsoon in full swing

46. Which way will the Sahel go? wet period extended drought The shift around 1970 is believed to be due to changing sea surface temperature patterns in the tropical Atlantic (possibly driven by aerosol forcing).

47. The disappearance of Lake Chad

48. Lake Chad 1972 1987

49. The drying of southern Australia 4000 2400 1800 1200 1000 800 600 500 400 300 200 150 100 0 250 Desert Mean Australian Rainfall (mm) 1986 - 1995.

50. The drying of southern Australia The decline in rainfall in south-western Australia since the 1960s. Source:http://www.ioci.org.au/publications/pdf/IOCI_Notes_Series2.pdf.