Transcript Slide 1

26 Jan 2008
The Science of Climate Change:
What have we done?
What can we expect?
What can we do?
Michael J. Prather
Fred Kavli Professor of Earth System Science
UC Irvine
Thanks to the IPCC
Bert Bolin
(d. 30 Dec 2007)
Sir John Houghton
IPCC TAR 2001:
Third Assessment Report
IPCC AR4 2007:
Fourth Assessment Report
The Earth's climate is now clearly out of balance and is warming.
Many components of the climate system—including the temperatures of
the atmosphere, land and ocean, the extent of sea ice and mountain
glaciers, the sea level, the distribution of precipitation, and the length of
seasons—are now changing at rates and in patterns that are not natural
and are best explained by the increased atmospheric abundances of
greenhouse gases and aerosols generated by human activity during the
20th century.
...
Evidence from most oceans and all continents except Antarctica shows
warming attributable to human activities. Recent changes in many
physical and biological systems are linked with this regional climate
change.
...
American Geophysical Union statement re Human Impacts on Climate, adopted Dec 2007
“We have sun, earth, and atmosphere, so we have weather!”
Harris Telemacher (Steve Martin) in LA Story
so, what about climate?
CLIMATE = statistics of atmospheric weather + oceans + ecosystems + ...
Both weather and climate have inherent dynamical variability like El Nino.
This precludes a definitive prediction, and leads naturally to a statistical
approach in forecasts (e.g., 80% chance of rain tomorrow, 84% chance that
global warming over this century will be greater than 2°C).
How has climate varied in the past ?
How are we changing the atmosphere ?
Is climate change a response to human activities ?
What can we expect this century ?
Ice Age Climates: the Pleistocene
Last interglacial
Current warm period
Last Ice Age
Ice Ages: the Pleistocene
measurements from ice cores show correlations between
the greenhouse gases and temperatures and size of glaciers
N2O
CO2
CH4
Temperature proxy
Ice Volume proxy
2007 IPCC AR4
Thousands of Years before 2005
The Holocene
the last 11,000 yr of relatively stable climate
11,000 yr
2007 IPCC AR4
The Anthropocene: the atmosphere
Agriculture, Industry & Land-use change
have dramatically changed change the
global atmosphere: increasing both
greenhouse gases (CO2, CH4, N2O)
and sulfate aerosols.
2001 IPCC TAR
COOLING
WARMING
The Anthropocene: the radiative imbalance
Greenhouse gases trap the Earth’s heat and warm the planet.
Aerosols and their interactions with clouds reflect sunlight and cool.
COOLING
WARMING
The net heat imbalance is called radiative forcing (RF, in W m-2)
2001 IPCC TAR
The Anthropocene: the heat is going into the ocean
The RF imbalance is heating the oceans.
software
bug in floats
2007 IPCC AR4
The Anthropocene: mean surface temperatures warm
2007 IPCC AR4
but not everywhere, and not uniformly
2001 IPCC TAR
ICE-AGE Radiative Forcing
Note: CO2 and CH4 are
the driving forces here.
Note: CO2 and CH4 are
positive feedbacks here.
2007 IPCC AR4
Detection & Attribution: How do we know we caused it?
Global mean surface temperature anomalies (°C) from 1900 to 2005
from observations (black)
from AOGCM* simulations forced with
natural forcings only
(blue, 19 simulations w/ 5 models)
from AOGCM simulations forced with
both anthropogenic and natural forcings
(red, 58 simulations w/ 14 models)
*AOGCM = atmosphere+ocean climate models
2007 IPCC AR4
Greenhouse gas signal seen on every continent except Antarctica
PINK matches BLACK (obs.)
2007 IPCC AR4
What else is happening to the climate?
Global average sea level rose at an average rate
of 1.8 mm per year over 1961 to 2003. The rate was
faster over 1993 to 2003, about 3.1 mm per year.
Whether the faster rate for 1993 to 2003 reflects
decadal variability or an increase in the longer term
trend is unclear.
2007 IPCC AR4
During recent millennia of relatively stable climate, . . . populations
have grown rapidly. In the next 50 years, even the lower limit of
impending climate change (an additional global mean warming of 1°C
above the last decade) is far beyond the range of climate variability
experienced during the past thousand years and poses global
problems in planning for and adapting to it.
Warming greater than 2°C above 19th century levels is projected to be
disruptive, reducing global agricultural productivity, causing widespread
loss of biodiversity, and—if sustained over centuries—melting much of the
Greenland ice sheet with ensuing rise in sea level of several meters.
...
American Geophysical Union statement re Human Impacts on Climate, adopted Dec 2007
The Anthropocene: what about the future?
2001 IPCC TAR
The Anthropocene: what about the future?
2001 IPCC TAR
impacts
2007 IPCC AR4
Climate Prediction: “Climate Normals” are the
daily, monthly & annual 30-year climate averages
1971-2000 U.S. Normals
~8,000 stations
T. Karl, 2007
•
Main Parameters
– Temperature (max, min, mean)
– Heating & Cooling Degree Days
– Spring/Fall Freeze dates; growing season
– Precipitation (usually liquid equivalent;
sometimes snow)
– Occasionally: clouds, sea level pressure, RH,
others
•
WMO Recommendation
– Countries update normals every 10 years
– Current period 1971-2000
– Next scheduled period:
1981-2010 for use in 2010s
but climate is changing:
2001-2006 ACTUALS minus 1971-2000 NORMALS (°C)
• January Min. Temperature
–
–
Most areas in continental U.S are now 3 – 7
degrees warmer during winters nights
Florida , S. Georgia now 2 – 4 degrees cooler
• July Max. Temperature
–
–
Most of Western U.S. now 3 - 7 degrees
warmer during summer days
Some Parts of South U.S. cooler
T. Karl, 2007
-7 °C
to
+7 °C
predicting the next decade from the climate normals
unpredictable
2007 IPCC AR4
Katrina 28 Aug 2005
extreme climate
Rita 25 Sep 2005
+22 more paragraphs + ½-page graphic!
Heat Waves: 2003
October 9, 2003-9
Copyright © 2003 Earth Policy Institute
RECORD HEAT WAVE IN EUROPE TAKES
35,000 LIVES
Far Greater Losses May Lie Ahead
Janet Larsen
A record heat wave scorched Europe in
August 2003, claiming an estimated 35,000
lives. In France alone, 14,802 people died
from the searing temperatures—more than
19 times the death toll from the SARS
epidemic worldwide. In the worst heat spell
in decades, temperatures in France soared to
104 degrees Fahrenheit (40 degrees Celsius)
and remained unusually high for two weeks.
climatology of heat waves
2003 was an extremely rare event in terms of
climate statistics, a 5.4-sigma extreme,
a one-in-a-thousand year event.
2007 IPCC AR4
predicting the next heat waves
without anthropogenic forcing: every 1000 yrs
with anthropogenic forcing: every 250 yrs
2007 IPCC AR4
translating global warming
2 x CO2 = about 3°C global mean warming
= about 10°F warmer summers in Southeastern US
GFDL, 2001
With climate change, as with ozone depletion, the human footprint on
Earth is apparent.
The cause of disruptive climate change, unlike ozone depletion, is
tied to energy use and runs through modern society. Solutions will
necessarily involve all aspects of society.
Mitigation strategies and adaptation responses will call for collaborations
across science, technology, industry, and government. Members of the . . .
scientific community, collectively have special responsibilities:
to pursue research needed to understand it;
to educate the public on the causes, risks, and hazards; and
to communicate clearly and objectively with those who can
implement policies to shape future climate.
American Geophysical Union statement re Human Impacts on Climate, adopted Dec 2007
Greenhouse Gas Emissions
Sector GHG Emissions
2007 IPCC AR4
size of the problem
plus 7 more
Two views of current emissions of the Kyoto Greenhouse Gases
2007 IPCC AR4
A Climate Forecast:
uncertainty in positive climate
feedbacks in a warmer world
2007 IPCC AR4
Our future climate
2007 IPCC AR4
We can do little to alter the next 25 years of climate change.
We can choose the scenario for the next 90 years.
2007 IPCC AR4