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The science of global warming: Often confused
but actually clear
2011 MinnTS Lecture
Katsumi Matsumoto
Geology and Geophysics, University of Minnesota
24 March, 2011
The science of global warming: Often confused
but actually clear
2011 MinnTS Lecture
Do you believe that global warming is occurring?
Do you believe that global warming is caused
by human activities?
Do you believe that scientists are divided
over global warming?
Katsumi Matsumoto
Geology and Geophysics, University of Minnesota
24 March, 2011
Outline
• The big picture: Energy in vs. energy out
• Detection of global warming
• Attribution of global warming
• Paleoclimate perspective
• Scientists on climate change
What determines the temperatures of
the terrestrial planets?
Sun
(relative sizes are to scale)
179 ºC
477 ºC
15 ºC
-47 ºC
Mercury
Venus
Earth
Mars
Hot House
Just Right
Ice House
What determines the surface temperature?
(energy “in” versus energy “out”)
Analogy: bank account
balance is determined
by income and expense
Houghton (2009)
Infrared radiation from a building
(depends on temperature)
Charles (2009)
Infrared radiation from Earth
(again depends on temperature)
Northern hemisphere winter
(Sverdrup, 2006)
CO2 in atmosphere will absorb thermal radiation
In > Out, so
warms, but when
will it stop?
Human emissions of
CO2 increases the
greenhouse effect and
reduces energy “out”
Houghton (2009)
Earth will stop warming when it is warm enough to
radiate out as much energy as before
Earth’s surface
Houghton (2009)
Global warming is a natural response of the planet to restore
radiative balance...something we’ve known for a long time
A long history
• 1681 : greenhouse effect of glass (Mariotte)
• 1824 : greenhouse effect of atmosphere (Fourier)
• 1861 : laboratory confirmation of the greenhouse
properties of CO2 and H2O (Tyndall)
• 1895 : prediction of CO2-induced warming (Arrhenius)
All this history lead to the Keeling Curve
Today’s radiative imbalance: 2 X-mas light bulbs/m2
Physics predicts that there must be global warming!
2 W/m2
Hansen (2004)
Detection of global warming
Annually averaged, global surface temperature
Instrumental records
•1653 - First meteorological
network in Italy
•1873 - IMO (later WMO) to
standardize temperature data
550 million temp readings!
Figure 1.3, IPCC AR4
Satellite data
2005 - 1979
Historical data
(Fig. TS6, IPCC AR4)
IPCC TAR
Shrinking arctic sea ice
NSIDC
Northwest Passage
Greenland is melting…
Jakobshavn
Ice Stream
Hansen (2004)
Satellite altimetry data Æ net loss of ice mass
(NASA)
Glacial earthquakes
(Ekström,
Tsai, Nettles, 2006)
Global ocean heat content
“The smoking gun” of GW
1022 J
2003-1961
2003-1993
• About 90% of heat from GW into
the ocean...but small temp change
• Reason for delay in climate response
(Fig 5.4, IPCC AR4)
~1 mm/yr globally
Wikipedia – data from Douglas (1997)
Detection – winter in
Lake Superior
Period of ice cover
in Bayfield, WI
Howk (2009)
First boat
Last boat
Other organisms noticing
the change:
(Analysis of ~1500 species on
migration, flowering,
reproduction...)
Root et al., 2003
Attribution of global warming
Attribution of global warming
What do we need to show?
(1) Anthropogenic forcings are doing it
(2) Natural forcings are insufficient
• Orbital variations
• Tectonic activity
• Solar variability
• Internal variability
How to show this?
Earth science – no control experiment
Use global climate models
Forcings
IPCC TAR
How reliable are the global climate models?
(show movies)
1) Models based on established physical laws
2) Ability to model key aspects of current climate
large scale temperature, precipitation, radiation, wind, ocean
temperatures, currents, ice cover, seasonality of monsoons and
storm tracks…
3) Examine model predictions of:
past climate, larger warming of nighttime temperatures, larger
NH warming, short-term cooling following volcanic eruptions…
Uncertainties in tropical precipitation, El Nino,
representation of clouds, small scale projections
IPCC AR4 FAQ8.1
1991 Mt Pinatubo
In 1988 Hansen predicted the radiative effect of a
volcanic eruption – later proved correct (-1 W m-2)
(Ed Wolfe, USGS, 1991)
Models correctly predict impacts of volcanic eruptions
Height of lower atmosphere
obs
obs
Temperature
model mean
(Fig. 9.5 & 9.14, IPCC AR4)
2005 - 1979
More NH warming Æ
Other
“fingerprinting”
of anthropogenic
warming: faster
night time
warming etc.
Acceleration of warming Æ
(Fig. TS6, IPCC AR4)
IPCC TAR
Paleoclimate perspective
Glaciation and
Moraines in Minnesota
(Pictures from www.winona.edu)
Interglacial
(today)
G-I cycles
Glacial
(20,000 yrs ago)
CLIMAP (1981)
18,000 YEARS AGO
Note the ice, lakes
and coasts
14,000 YEARS AGO
13,000 YEARS AGO
12,000 YEARS AGO
11,000 YEARS AGO
10,000 YEARS AGO
9,000 YEARS AGO
8,000 YEARS AGO
7,000 YEARS AGO
6,000 YEARS AGO
We can reconstruct past ice by
examining isostatic rebound
Ice age viewed from ice and ocean sediment cores
(climate and CO2 are highly correlated)
Houghton (2009)
The last glacial cycle
Houghton (2009)
Past sea level vs. global temperature
Archer (2007)
Climate change deniers
Scientists on the problem
Jim Hansen in 1988 testified to US
Senate that he was certain that record
warmth was not natural
Æ Got the ball rolling (UNFCCC in ‘92)
An almost complete unanimity among climate
scientists on the reality of global warming
Complete disconnect from public perception...
Scientific consensus
What is consensus? And how do we know it exists?
Experts read peer-reviewed publications, have informal
discussions in the hallways and conferences...usually hard
for the public to assess
What is peer-review?
Careful, highly critical examination of the work being
proposed for publication; very toug
Anyone can say anything, but not everyone can get research
results published in peer-reviewed journals
Climate science consensus – unusually public
IPCC assessment of the state of climate science on the
basis of peer-reviewed publications
Oreskes’ survey of peer-reviewed publications
Searched 8500 journal publications between 1993 and 2003
w/ “global climate change.” Is global warming occurring and
are humans partly responsible?
Who’s arguing that global warming is here?
Intergovernmental Panel on Climate Change
• 1990 – qualitative persuasion of human interference
• 1995 – “discernable human influence on global climate”
• 2001 – “most of the warming over the last 50 yrs is
likely attributable to human activities
• 2007 – “very likely” (>90% probability)
National science academies
Professional societies whose membership expertise
bears on global climate change
Reports and statements by IPCC, academies, and societies drafted
through a careful process involving many opportunities to comment,
criticize, and revise Æ won’t deviate much from membership opinions
Who are the deniers?
Fred Singer, electrical engineer
Works with Exxon, American Petroleum Institute: “proposed a $5
million campaign… to convince the public that the science of global
warming is riddled with controversy and uncertainty”
– Newsweek 2007
Patrick Michaels – fellow of the Cato Institute
Paid at least $100,000 by companies involved in coal-fired power
production to make the public case against climate change
Richard Lindzen, MIT professor in meteorology
gets funding from OPEC, $2500/day “consulting” fee
Michael Crichton! (invited by Congress to testify)
Myths and skepticisms – look these up yourself
1.
Scientists can’t even predict next week’s weather
2.
Climate model predictions have never been tested
3.
Hansen has been wrong before
5.
Global warming + global dimming -> Southern warming
6.
GCMs don’t have clouds
7.
Climate models can’t explain the past
8.
Climate is chaotic and thus not predictable
9.
Regional and local climate predictions are bogus
Summary
• Physics predicts global warming when incoming solar
radiation is greater than outgoing terrestrial radiation
• Detection by observations - warming of atmosphere,
ocean, Arctic sea ice, Greenland melting, sea level rise
• Attribution to humans - use of global climate models,
fingerprinting predictions validated, observed changes
cannot be explained with natural causes alone
• Paleoclimate perspective – CO2 and climate are highly
correlated; so are sea level and global temperature
• Complete unanimity among active climate scientists