ATM S 111, Global Warming:
Understanding the Forecast
DARGAN M. W. FRIERSON
DEPARTMENT OF ATMOSPHERIC SCIENCES
DAY 4: 10/13/2015
Part 2: The Symptoms
Extreme heat
Celsius 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
Celsius and Fahrenheit
 The obligatory Celsius vs Fahrenheit discussion….
Celsius has water
boiling point = 100o
And water freezing
point = 0o
Fahrenheit water freezing
point is 32o
Celsius and Fahrenheit
 Every 5 degrees up the Celsius scale = 9 degrees up
the Fahrenheit scale
15o
C
59o
F
10o C
50o F
5o C
41o F
0o C
32o F
A temperature change of 1
degree Celsius is a little less
than two degrees Fahrenheit
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:
Celsius
Fahrenheit
0o
32o
10o
50o
20o
68o
30o
86o
40o
104o
 OK, back to extreme heat…
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 obvious
with clouds.
Water vapor is just as strong
though!
Dryness and Extreme Heat
 Dry climates tend to have a
Soil moisture
large daily temperature range


Lack of greenhouse effect allows
nights to cool there
Also hotter days though since
there’s no evaporational
cooling
Daily temperature range
Evaporation from trees, lakes, etc
lead to milder daytime temperatures
in 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  higher
Soil moisture
heat index during the day,
and warmer nights (due to
the greenhouse effect)

Often humid heat waves are the
worst
Daily temperature range
Warm nights are key in causing
mortality in heat waves (cool nights
provide relief)
Urban Heat Island Effect
Buildings act like clouds to return
longwave back towards surface
Bedford Sq., London
greenspace keeps it cool
Here
pink=hottest
blue=coolest
http://www.seedgen.com/thermallondon/
Urban Heat Island Effect
 Bigger effect at night, when air is stagnant
 Causes:
 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 inclusion
 Back 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
Warm
Wet
Cold Dry
Warm
Wet
Cold Dry
Cold Dry
Warm Wet
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, record
highs 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
Moscow
 Also 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 temp
71 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 conditioning
Victims of heat waves are often elderly or those with weakened
respiratory systems
Check in on your grandparents!
Histogram or “frequency distribution” of daily
maximum temperature gives the natural range
relative frequency
Let 100° F
be the threshold
for a heat wave
100°F
Temperature
The chance of a
heat wave
occurring is the
area in red
divided by total
area under the
curve
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
Expect much higher
heat index due to this
From Delworth et al 1999
study of average heat index
changes
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 cool
 Drier 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/ 1970-1999
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
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