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DARGAN M. W. FRIERSONDEPARTMENT OF ATMOSPHERIC SCIENCES
DAY 4 : 10 /13 /2015
ATM S 111, Global Warming: Understanding the Forecast
Extreme heatCelsius vs Fahrenheit
Humid versus dry heat
Urban heat island
Recent years
Heat waves: Europe 2003, Chicago 1995, Russia 2010, Seattle
2009
The human cost of heat
The future of summer sizzle
Part 2: The Symptoms
Celsius and Fahrenheit
The obligatory Celsius vs Fahrenheit discussion….
Celsius has waterboiling point = 100o
And water freezing point = 0o
Fahrenheit water freezingpoint is 32o
Celsius and Fahrenheit
Every 5 degrees up the Celsius scale = 9 degrees up the Fahrenheit scale
0o C
5o C
10o C
32o F
41o F
50o F
A temperature change of 1 degree Celsius is a little less than two degrees Fahrenheit
15o C 59o F
Don’t Make the Following Mistake!
“The best estimate of temperature change with doubled carbon dioxide concentration is 3o C (37.4o F)” I saw this in a very high profile news article one time
(it was quickly corrected)
What’s wrong here?
Celsius versus Fahrenheit
Problem was mixing up temperature change with temperature Again, a 1o change in C = 1.8o change in F Some temperature values I like to remember:
OK, back to extreme heat…
Celsius Fahrenheit
0o 32o
10o 50o
20o 68o
30o 86o
40o 104o
Extreme Heat Concepts
Evaporation: a really effective way to stay cool Sweat, mist coolers in the desert, fountains, etc If there’s a lot of vegetation around, it takes a while to
heat up during the day Video on 1775 experiment: can we survive
temperatures above the boiling point of water?
Villa d’Este Tivoli, Italy
Extreme Heat Concepts
Humidity: makes it feel a lot hotter Evaporation can’t cool you down as much Heat index: takes into account how humidity makes
it feel hotter Remember: humidity = moisture = water vapor
Extreme Heat Concepts
Greenhouse effect: keeps nights warm Higher water vapor content nights stay warmer Turns out nighttime temperatures are very
important for mortality in heat waves too
On a day-to-day basis, the greenhouse effect is most obviouswith clouds. Water vapor is just as strong though!
Dryness and Extreme Heat
Dry climates tend to have a large daily temperature range Lack of greenhouse effect allows
nights to cool there Also hotter days though since
there’s no evaporational cooling
Soil moisture
Daily temperature range
Evaporation from trees, lakes, etclead to milder daytime temperaturesin non-desert climates
“Dust Bowl” of the 1930s
Many all-time temperature records in the U.S. Great Plains were set during the 1930s Severe drying of
the American prairie
Drying out of the land led to more extremes in temperature
Humidity and Extreme Heat
Humid heat waves higherheat index during the day, and warmer nights (due to the greenhouse effect) Often humid heat waves are the
worst
Soil moisture
Daily temperature range
Warm nights are key in causing mortality in heat waves (cool nights provide relief)
Bedford Sq., Londongreenspace keeps it cool
http://www.seedgen.com/thermallondon/
Buildings act like clouds to return longwave back towards surface
Here pink=hottestblue=coolest
Urban Heat Island Effect
Urban Heat Island Effect
Bigger effect at night, when air is stagnantCauses:
Longwave radiation not able to escape as easily More absorption of solar radiation Less evaporation
Thermometer records strongly affected by the urban heat island effect are not used to calculate global temperature trends And other less affected records are corrected before
inclusionBack to individual heat waves…
Cold winter on the East Coast this year?
Was this global cooling??
Feb 13, 2015
Winter 2014-15’s Temperature Anomalies
Winter 2014-2015 temperatures Very cold temperatures in Eastern US Surrounded by warm regions though
Last Two Winters (2012-14)
Average temperatures from Dec ‘12-Feb ‘13 & Dec
‘13-Feb ‘14 Very warm US east coast, colder Siberia The local warm/cold areas tends to be caused by
movements of the jet stream
Patterns of Climate Variability
Wobbling back and forth between these two patterns is common (called the North Atlantic Oscillation)
Much natural climate variability is just sloshing of heat like this One warm/cold season is not
proof/disproof of global warming
Cold Dry
Warm Wet
Cold Dry
Warm Wet
Warm Wet
Warm Wet
Cold Dry
Cold Dry
Longer Time Periods
Natural climate variability like the North Atlantic Oscillation or other patterns average out after a few years Slower, steadier global warming shows up clearly over a 5
year average
One swallow does not a summer make, neither does one fine day. Aristotle
Cold records can be set in a year that is warm in comparison to the long-term global-mean climate.
Hence,
record heat waves can occur in years in which global-mean temperature is not especially warm.
Record Highs vs Record Lows
Have to look at longer periods of time to see a trend
In the US, recordhighs have been significantly outpacing record lows over the last two decades
From Meehl et al 2010
Recent Extreme Heat Waves
Europe 2003 50,000 people died Length of heat wave was key
Paris had 9 straight days of temps > 35o C Also lack of air conditioning in many of these areas
Chicago 1995 700 died Very high humidity
High heat index and high overnight lows
2010 Russian Heat Wave
Moscow average July: 74o F, August: 68o F Hit 86o F 26 days in a row in 2010 Met or broke previous all-time high (99o F) 5 times!
Belarus, Ukraine, Baltic nations, western Russia all affected
Moscow July temps: +12o F Moscow June-August temps: +8o F
2010 Russian Heat Wave
Widespread wildfires Very poor air quality in
MoscowAlso massive crop loss
20% of their wheat crop
Seattle, July 2009, 4-day heat wave (above 90 F)
July 29 all time records broken at SeaTac:
103 F highest temp71 F highest minimum nighttime temp
(high humidity was key to high overnight low)
Dozens of cooling centers were opened
Why do some cities fare better?
High population density is a benefit because people help each other.
Air conditioning
Social planning
Western Washington is vulnerable due to lack of air conditioningVictims of heat waves are often elderly or those with weakened respiratory systemsCheck in on your grandparents!
Temperature
100°F
Histogram or “frequency distribution” of daily maximum temperature gives the
natural range
Let 100° Fbe the thresholdfor a heat wave
The chance of a heat wave occurring is the area in reddivided by total area under the curve
rela
tive
fre
qu
en
cy
Future of Extreme Heat
Simplest expectation: temperatures shift to warmer We expect more hot extremes & less cold extremes Can be modified by changes in humidity though…
Houghton book
Increases in Heat Index
Also, over the world as a whole, moisture content (humidity) is expected to rise Because warmer air can hold more water vapor
From Delworth et al 1999study of average heat index changes
Expect much higher heat index due to this
Effect of Drying On Temperature Extremes
What about places that become drier with global warming? Many land areas are expected to dry with global
warming (next topic: floods & droughts)Drier locations
No more evaporative cooling during the day: hotter days
Less greenhouse warming at night Smaller increase in heat index
Let’s take a look at model predictions…
Global Warming
Projected temperature change
Soil Moisture Changes
drying -> even higher daytime temperature
moistening -> even higher nighttime temperatures
(dots indicate where models agree, slashes where they don’t agree)
Model Predictions: Europe
Summer of 2003 will become average summer by 2040 And by the end of the century the summer of 2003
would be considered unusually coolDrier summers over Europe lead to more
warming there
Model Predictions of Extreme Heat: US
Days over 90o F
From “Global Climate Change Impacts in the US” (US GCRP Report)
Model Predictions of Extreme Heat: US
Days over 100o F
From “Global Climate Change Impacts in the US” (US GCRP Report)
Model Predictions of Extreme Heat: US
Shifting climate zones
Washington State Predictions
Predictions of 2030-2059 compared w/ 1970-1999Change 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
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 will likely become more susceptible to heat waves
than others
- vegetated land may give way to desert