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increased temperatures affect air quality in various ways:

1. pollen season is longer in middle and high latitudes.
2. photochemical smog likes hot weather. this combined with the increased production of the precursors of smog (fossil fuel related) will cause greatly reduced air quality, all else being equal.
3. mold does better.
4. wildfires cause smoke and ash hazards.



fog or haze combined with smoke or other air pollutants.


photochemical smog is

produced when pollutants interact with sunlight at warm temps. to produce ozone and other harmful stuff.


precursors of photochemical smog include:

volatile organic compounds (VOC), sulfur dioxide (SO2), and nitrous oxide (NOx). NOx is formed when fossil fuels are burned in air.


photochemical smog likes

NOx (traffic), high temps., sunlight, and calm winds.


at least 2.4 million people worldwide

die prematurely each year from the effects of air pollution. most of these deaths occur in Asia, with China having 656,000 deaths a year.


In U.S., deaths range from

150,000 to 350,000 people.


EPA says that

each year, more than 125,000 Americans get cancer from breathing soot-laden diesel fumes emitted by buses and trucks.


ozone can cause

the muscles in the airways to constrict, trapping air in the alveoli. leads to wheezing and shortness of breath. also can cause COPD.


ozone enters the stomata

of leaves and damages them. strong oxidant.


in polluted areas,

it is likely that ozone concentrations will increase simply owing to the temp. increase. depends on what we do in other areas though.


hadley cell =

more rising near equator, more sinking in subtropics.



rains on mountains, and upstream side of mountain ranges.


general circulation of atmosphere:

- rains a lot near the equator (10N - 10S), which is the rising branch of the Hadley Cell.
- rains much less in subtropics (15N - 40N, 15S - 40S), which is the sinking branch of the Hadley Cell.
- rains a lot in the middle and high latitudes (40-70 N & S), which is associated with midlatitude storms.
- polar latitudes: gets too cold to precipitate much.


as the atmosphere warms,

water vapor concentrations increase. winds bring even more moisture into the rainy regions.


climate model projections of precipitation change

wet gets wetter, dry regions expand.


wet gets wetter

- more water vapor is brought into the regions that are already rainy.
- specifically, tropical regions, monsoons, storm tracks, and high latitudes are expected to moisten.


dry regions expand

- more evaporation from dry land surfaces at higher temps.
- tendency for midlatitude weather to shift poleward. many subtropical regions (in between tropics and midlatitudes) are expected to dry.


uncertainty about specific regional precipitation responses though

- regional responses could change significantly due to shifts in rising motion. small shifts can make a big difference for rain.
- precipitation is much harder to predict than temp.


southwestern north america predicted to

dry dramatically. as bad as the dust bowl by 2060 in some models.



prolonged period of abnormally low rainfall; a shortage of water resulting from this.


drought moves around from

place to place from year to year. might be related to variations in the temp. of the ocean from place to place. El Nino and similar phenomena.
- probably mostly natural variability, things that would have taken place even i n the absence of GHG increase.
- however, it might be that the dry events are getting worse, as models predict.
- also true that water resources in semi-arid areas are stressed to the limit for human uses, e.g. California.


Los Angeles

settles fued with residents of Owens Lake Region from which the city "stole" the water in 1913 and drained the lake within 10 years. dry lakebed resulted in dust and other air quality issues.


In Texas

the summer of 2011 has been both the hottest and driest on record. the drought has cost billions in economic losses, mainly due to agricultural impacts and from wildfires.


from 1930~36

the prairies of the US and Canada experienced severe dust storms brought about by a drought exacerbated by poor soil use practice.


many all-time temp. records in the US Great Plains were set during

the 1930s. severe drying of the american prairie.


drying out of land led to

more extremes in temp.


the dust bowl

centered near where the states of Colorado, Kansas, Oklahoma, and Texas meet.


the dust bowl drought seems to have been associated with

anomalies SST patterns, most likely colder than normal in the tropical pacific, coupled with warmer than normal in the Atlantic (model results).


collapse of mayan civilization

- were among the most vibrant civilizations in central America 250-900 AD.
- they abandoned their southern cities in 8th and 9th centuries maybe due to drought?
- was the southward shift of the rainband the cause?


sahel region

is between the desert and the region drenched by the african monsoon.


sahel drought

This shift around 1970 (from a wet period to an extended drought now) is believed to be due to the changing sea surface temperature patterns in the tropical Atlantic (possible driven by aerosol forcing)


why the shift?

- Model work shows that tropical precip shifts towards the warmer hemisphere (even if the warming happens at high latitudes)
- Models also indicate that aerosol cooling causes the southward shift of rain in the models (aerosols are mostly in the NH and rain shifts away from the sahel, which is in the northern edge of the african monsoon)


shifts are hard to predict

Shifts in rising motion or mid latitude storms could happen due to:
- Differences in forcings (aerosols cooling the oceans in places)
- Differences in feedbacks (cloud responses)
- Changes in ocean currents (a natural ex that messes with rain patterns is El Nino)


how about the most intense storms?

- The strongest downpours require a lot of water vapor in the atmosphere
- Warmer temps. leads to more water vapor
- Thus heavy rainfall events should become more extreme
- Also heavy snowfall events!
- It is important to note that the observational evidence for greater floods and droughts is so far not much above natural variability level