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
Katsumi MatsumotoGeology and Geophysics, University of Minnesota
24 March, 2011
The science of global warming: Often confused but actually clear
2011 MinnTS Lecture
Katsumi MatsumotoGeology and Geophysics, University of Minnesota
24 March, 2011
Do you believe that global warming is occurring?
Do you believe that scientists are divided over global warming?
Do you believe that global warming is caused by human activities?
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
Venus Earth MarsMercury
179 ºC 477 ºC 15 ºC -47 ºC(relative sizes are to scale)
Hot House Ice HouseJust Right
What determines the surface temperature?(energy “in” versus energy “out”)
Houghton (2009)
Analogy: bank account balance is determined by income and expense
Charles (2009)
Infrared radiation from a building(depends on temperature)
Infrared radiation from Earth (again depends on temperature)
(Sverdrup, 2006)
Northern hemisphere winter
CO2 in atmosphere will absorb thermal radiation
Houghton (2009)
Human emissions of CO2 increases the greenhouse effect and reduces energy “out”
In > Out, so warms, but when will it stop?
Houghton (2009)Earth’s surface
Global warming is a natural response of the planet to restore radiative balance...something we’ve known for a long time
Earth will stop warming when it is warm enough to radiate out as much energy as before
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
Hansen (2004)2 W/m2
Today’s radiative imbalance: 2 X-mas light bulbs/m2
Physics predicts that there must be global warming!
Detection of global warming
Instrumental records
•1653 - First meteorological network in Italy
•1873 - IMO (later WMO) to standardize temperature data
Figure 1.3, IPCC AR4
550 million temp readings!
Ann
ually
ave
rage
d, g
loba
l sur
face
tem
pera
ture
IPCC TAR(Fig. TS6, IPCC AR4)
2005 - 1979
Satellite data
Historical data
NSIDC
Shrinking arctic sea ice
Northwest Passage
Hansen (2004)
Greenland is melting…
JakobshavnIce Stream
Satellite altimetry data net loss of ice mass
(NASA)
Glacial earthquakes
(Ekström, Tsai, Nettles, 2006)
(Fig 5.4, IPCC AR4)
2003-19612003-1993
Global ocean heat content“The smoking gun” of GW
• About 90% of heat from GW into the ocean...but small temp change
• Reason for delay in climate response
1022 J
Wikipedia – data from Douglas (1997)
~1 mm/yr globally
Period of ice cover in Bayfield, WI
Howk (2009)
Detection – winter in Lake Superior
Last boatFirst boat
Root et al., 2003
Other organisms noticing the change:
(Analysis of ~1500 species on migration, flowering,
reproduction...)
Attribution of global warming
Attribution of global warming
How to show this?Earth science – no control experimentUse global climate models
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
IPCC TARForcings
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
(Ed Wolfe, USGS, 1991)
In 1988 Hansen predicted the radiative effect of a volcanic eruption – later proved correct (-1 W m-2)
(Fig. 9.5 & 9.14, IPCC AR4)
Models correctly predict impacts of volcanic eruptions
obs
obs
model mean
Height of lower atmosphere
Temperature
IPCC TAR(Fig. TS6, IPCC AR4)
2005 - 1979
More NH warming
Other “fingerprinting”of anthropogenic warming: faster night time warming etc.
Acceleration of warming
Paleoclimate perspective
Glaciation and Moraines in Minnesota
(Pictures from www.winona.edu)
Glacial(20,000 yrs ago)
CLIMAP (1981)
Interglacial(today)
G-I cycles
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
Houghton (2009)
Ice age viewed from ice and ocean sediment cores(climate and CO2 are highly correlated)
Houghton (2009)
The last glacial cycle
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
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
Experts read peer-reviewed publications, have informal discussions in the hallways and conferences...usually hard for the public to assess
What is consensus? And how do we know it exists?
What is peer-review?
Climate science consensus – unusually publicIPCC assessment of the state of climate science on the basis of peer-reviewed publications
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
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 draftedthrough a careful process involving many opportunities to comment, criticize, and revise won’t deviate much from membership opinions
Who are the deniers?
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
Fred Singer, electrical engineer
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
Patrick Michaels – fellow of the Cato Institute
Michael Crichton! (invited by Congress to testify)
gets funding from OPEC, $2500/day “consulting” fee
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