Transcript Presentation

Weather Extremes in a
Changing Climate
Gerald A. Meehl
National Center for Atmospheric Research
Boulder, CO
June 26, 2012, 3:10PM “Flagstaff Fire” behind NCAR burning for about
2 hours, NCAR evacuated
The two days prior to the Boulder Flagstaff fire, Boulder set record
highs for those days of 101°(driest March-June on record)
June 26, 2012, 5:40PM “Flagstaff Fire” burning for about 4.5 hours, reverse 911
call to the Meehl house in south Boulder with “pre-evacuation” notice
(lifted 2 days later; 90% containment of the 300 acre fire by July 1)
Record heat and record wildfires
Three days earlier, the day the Waldo Canyon fire broke out in
Colorado Springs (above, June 23, 2012), that city set it’s all-time
record high of 101°
the most destructive fire in Colorado history
destroyed 346 homes, 2 dead
Record Texas wildfires 2011
Hottest and driest summer in Texas history
Record 2010 Russian
heat wave and wildfires
More than 20 daily temperature
records were broken including
the absolute maximum
temperature in Moscow (101F)
Over 2,000 houses destroyed by
fires and about 4,000 people left
homeless, wildfires burned in 17
Russian regions, and a state of
emergency was declared.
A heavy smog from the wildfires
blanketed Moscow, concentration
of toxic particles reached
dangerous levels.
Estimates put the death toll at
about 55,000
Record heat and record Australian bushfires February 7, 2009
largest natural disaster in Australia’s history 173 dead, over 400 injured, ~1800
houses destroyed, ~200 businesses and other buildings destroyed,
The day of the fires, Melbourne set an all-time record
high temperature of 115.5°
Record-setting heat wave the week before, three days in a
row above 109°
Preceded by 8 years of severe drought in southern
Australia
Fire rages; 10,000 homes evacuated
(July 26, 2016, Los Angeles Times)
Los Angeles—Wind-whipped flames raged overnight in the steep, rugged
mountains of the Santa Clarita Valley, charring more than 33,000 acres and
threatening thousands of homes. The Sand Fire continued to burn Monday in the
hills toward Acton. Decades without a major fire and years of drought left the
valley primed for a fast-moving fire that was fueled by excessive heat, low
humidity and extreme dry fuels.
Heat Waves
Impacts on human health and mortality,
economic impacts, ecosystem and wildlife
impacts
The 2003 European heat wave led to the hottest
summer on record in Europe since at least 1540. France
was hit especially hard. The heat wave led to health
crises in several countries and combined with drought to
create a crop shortfall in parts of Southern Europe. Peerreviewed analysis places the European death toll at
more than 70,000.
Dangerous heat wave to persist in northeastern US much of this week
By Andy Mussoline, AccuWeather.com Senior Meteorologist
July 26, 2016; 3:54 PM ET
A stifling heat wave will remain entrenched across the mid-Atlantic and Northeast
much of this week.
In wake of a stormy Monday across the Northeast, the heat will not budge in areas
from Washington, D.C., to New York City and Boston as AccuWeather heat index
temperatures soar into the upper 90s and lower 100s F through this week.
"The heat wave will continue unabated this week," AccuWeather Senior Meteorologist
Dave Dombek said.
But heat waves occur every summer. Are
they really getting worse?
Heat wave intensity has been increasing over the U.S.
(trend from 1961-1990 in the Karl-Knight heatwave index, which tracks the warmest
average minimum temperature over three consecutive nights in a year)
But sometimes it gets really cold!
Blizzard Paralyzes New York City, Boston
A powerful winter storm slammed the I-95
corridor from Philadelphia to Boston on Sunday. Through
today, the blizzard will bring travel to a standstill along the
coastline of northern New England as well. The storm
unleashed around a foot of snow and howling winds in
cities and towns from Philadelphia through New York City
to Boston as it advanced northward offshore Sunday and
Sunday night.
(Dec 27, 2010)
Nearly a foot of snow piled up in
the Boston area on Sunday,
December 26, 2010.
London Comes to a Standstill During the Holiday Season
Because of Snow and Ice
LONDON, UNITED KINGDOM--(Dec. 29, 2010) - December is expected to go down as
the coldest on record. With reports of 5 inches of snow in London, Gatwick Airport
cancelled all flights and Heathrow cancelled all incoming flights on the weekend but
had a few selected flights depart from the airport instead. This left many passengers
planning on spending the Holidays overseas to find other plans until the snow is
completely cleared.
snow-covered
Britain, January 7,
2010
How global warming affects heat extremes: on any given day,
there is a greater probability of a temperature near average, and a
lower probability of extreme cold or extreme heat
How global warming affects heat extremes: a relatively small increase in the
average temperature produces an increased chance of extreme high
temperatures and record high temperatures, and a decreased chance of
extreme low temperatures and record low temperatures
There can still be extreme cold days and record cold temperatures in a
climate that is warmer on average, but there is a greater chance for
extreme heat and record high temperatures
With global warming, there is a shift to warmer
temperatures, thus increasing the risk of record-setting
extreme heat (and record wildfires in areas already at
risk for wildfires)
Global warming by itself doesn’t cause extreme
conditions, but it makes naturally occurring events
more extreme
So we should be seeing an increase in heat extremes
Global warming shifts the odds towards a better
chance for more daily record high temperatures
compared to record lows
we’ve been observing an increase in record highs
compared to record lows
National Climatic Data Center web site archives observed annual
daily record high maximum and record low minimum
temperatures from weather stations across the U.S.
http://www.ncdc.noaa.gov/oa/climate/research/records/
As of July 26, 2016:
January 1, 2000 to January 1, 2010: 313,799 record daily high maximum
temperatures set, and 154,388 record daily low minimum temperatures, a
ratio of roughly two to one (2.04 : 1).
January 1, 2010 to January 1, 2011: 19,213 record highs and 8,374 record
lows, a ratio of a bit more than two to one (2.3 : 1).
Since January 1, 2016: 13,671 record highs, 2,347 record lows
A ratio of nearly seven to one
The increasing ratio of record highs to record lows is
the signature of global warming
What about extreme rainfall?
Summer 2010 Pakistan floods
More than 15 million across Pakistan were affected by the floods, which submerged
one-fifth of the country and laid waste to infrastructure and crop land; The monsoontriggered floods that began in late July spread from the north to the south of the
country, swelling rivers and submerging hundreds of villages.
Flooding near Multan in Punjab Province, Pakistan, August 15, 2010
January 2011, Australia: 20 towns cut off or flooded
across an area larger than France and Germany
A senior official described the flooding in Queensland, Australia, as a
disaster of "biblical proportions".
The floods, Queensland’s worst in 50 years, were triggered by Australia's
wettest spring on record. At least six river systems across Queensland broke
their banks. The floods affected about 200,000 people, and many were
evacuated.
September 2013 Boulder flood
In a five day period in September, 2013,
usually one of the driest months of the year,
Boulder received nearly 18” of rain, close to
the annual total rainfall for Boulder
Every road in every canyon west of Boulder from
Denver to Ft. Collins washed out isolating thousands
prompting the largest helicopter evacuation (more than 1200
people) since Hurricane Katrina in New Orleans
It’s estimated that half the houses with basements in
Boulder experienced water damage
Mudslides near the mouth of
Boulder Canyon destroyed
structures
BRAN fiber exposed
by Bear Creek
flooding below NCAR
Boulder Creek in downtown Boulder
Small drainages coming off the
Flatirons turned into raging torrents
that rampaged down streets in
neighborhoods far from Boulder Creek
Repairing the BRAN
fiber and gas main
The grounds around the
Millennium flooded
But we’ve always had intense rain and floods.
Is it getting worse?
As the oceans warm from increasing human-produced greenhouse gases,
evaporation increases
Warmer air can hold more moisture
That additional moisture in the air increases the moisture supply for
storms
Precipitation (rain and snow) becomes more intense (i.e. for a given storm
event, more precipitation falls) because of this increased moisture supply
So with the warming climate over the 20th and early 21st century, we
should be seeing an increase in precipitation intensity
There has been an observed increase in precipitation
intensity over the U.S. as the climate has warmed
(1958-2012)
US National Climate Assessment, 2013: two-day precipitation total that is
exceeded on average only once in a 5-year period, also known as the once-infive-year event. Changes are compared to the period 1901-1960, and do not
include Alaska or Hawai‘i
What will extremes do in the future?
We study possible future changes in weather and
climate extremes with climate models
To study weather and climate
extremes, you need to be able to
credibly simulate weather and
climate in a numerical model
simulate this:
with this:
Resolution of climate
models is improving:
1995: about 500 km
2000: about 250 km
2005: about 150 km
2011: about 50 km
2016: about 25 km
¼ degree (grid points every 25 km) simulation representative of present-day
climate (about 2 model years per day; about 300 Gb of data per model year)
Climate models can be used to
provide information on future
changes in extreme events such as
heat waves
Heat wave severity defined as the
mean annual 3-day warmest
nighttime minima event
Observed
Model
Model compares favorably with
present-day heat wave severity
In a future warmer climate, heat
waves become more severe in
southern and western North
America, and in the western
European and Mediterranean region
(Meehl, G.A., and C. Tebaldi, 2004: More intense,
more frequent and longer lasting heat waves in the
21st century. Science, 305, 994--997.)
Future
How can global warming
produce both increasing
hot/dry conditions and
increased precipitation
intensity?
In a warming climate,
precipitation in climate
models is projected to
become more intense
almost everywhere
In many of those same
areas the climate model
projections show an
increase of “dry days”
(number of days between
precipitation events)
(Tebaldi , C., J.M. Arblaster, K. Hayhoe, and G.A. Meehl, 2006: Going to the extremes: An
intercomparison of model-simulated historical and future changes in extreme events. Clim. Change, 79,
doi 10.1007/s10584-006-9051-4.)
What about future
hurricanes?
the indications so
far: fewer total,
but the ones that
form will be more
intense
(Tropical cyclone tracks
from a global 20 km
resolution atmospheric
model)
(Oouchi et al., 2006)
“You can’t attribute any specific weather
extreme to climate change”
2016 report from the National
Academy of Sciences
Now:
“You can say something
quantitative about how human
climate change has increased the risk of
certain extremes (e.g. heat waves,
extreme precipitation)”
e.g. World Weather Attribution
(https://wwa.climatecentral.org/)
2 methods to assess human influence on 2015 European summer
heat wave:
1. With observations: Compare this heat wave with heat waves that occurred in the
early 20th century before human-caused climate change: human-induced climate
change at least quadrupled the chances of seeing a heat wave like the one in 2015
2. With climate models: compare the likelihood of seeing days as hot as this heat
wave in a present-day climate simulation, with those simulated without humaninfluenced climate change. Comparing those two “worlds,” this type of heat wave is
now at least twice as likely due to human-caused climate change
What does the future hold?
Possible futures: With aggressive mitigation, globally averaged surface
temperatures stabilize about 2050 and then slowly decrease to meet
the 2C target (and possibly the new 1.5C target from the recent Paris
negotiation)
Future CO2 emissions required to achieve future
CO2 concentrations
(emissions have to drop for concentrations to stabilize due to
long lifetime of CO2 in the atmosphere)
Emissions required
to attain 2C target
Negative emissions
by about 2080
Concentrations
required to attain
2C target
If someone asks you, “Did humans
cause this [heat wave, flood,
temperature record]?”
If someone asks you, “Did humans
cause this [heat wave, flood,
temperature record]?”
You can answer, “Think about
steroids, baseball, climate change,
and extremes”
Summary
Record heat = record wildfires
A relatively small shift in the average produces a very large change in
extremes—more extreme heat and less extreme cold, and more record high
maximum temperatures and fewer record low minimum temperatures
Global warming by itself doesn’t cause extreme conditions, but it makes
naturally occurring events even more extreme
In a future warmer climate:
Increased heat wave intensity, duration and frequency
Decreased cold spells (extreme cold weather will still occur, but less frequently)
Increased precipitation intensity, but increases in dry days in some locations
Increasing ratio or record highs to record lows projected to increase as the
climate warms: e.g. about 20 to 1 by mid-century, 50 to 1 by late century
A warmer climate produces fewer total hurricanes, but the ones that form are
more intense
Steroids and Climate
Steroids analogy:
http://www2.ucar.edu/atmosnews/attribution/steroids-baseball-climate-change
Global warming affected Superstorm Sandy
in at least two ways:
1. Higher mean sea level = more extreme
storm surge
2. more intense precipitation