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
Sun What determines the temperatures of the terrestrial planets? (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 CO 2 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 CO 2 and H 2 O (Tyndall) 1895 : prediction of CO 2 -induced warming (Arrhenius)
All this history lead to the Keeling Curve
Today s radiative imbalance: 2 X-mas light bulbs/m 2 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 net loss of ice mass (NASA)
Glacial earthquakes (Ekström, Tsai, Nettles, 2006)
Global ocean heat content The smoking gun of GW 10 22 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 First boat Last boat Howk (2009)
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
(Ed Wolfe, USGS, 1991) 1991 Mt Pinatubo In 1988 Hansen predicted the radiative effect of a volcanic eruption later proved correct (-1 W m -2 )
Models correctly predict impacts of volcanic eruptions Height of lower atmosphere obs obs Temperature model mean (Fig. 9.5 & 9.14, IPCC AR4)
More NH warming 2005-1979 Other fingerprinting of anthropogenic warming: faster night time warming etc. Acceleration of warming (Fig. TS6, IPCC AR4) IPCC TAR
Paleoclimate perspective
(Pictures from www.winona.edu) Glaciation and Moraines in Minnesota
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
We can reconstruct past ice by examining isostatic rebound 6,000 YEARS AGO
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 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 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 CO 2 and climate are highly correlated; so are sea level and global temperature Complete unanimity among active climate scientists