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