What Occam's razor teaches meabout climate changeAndy Bunn, Huxley College of the EnvironmentWestern Washington UniversityCarbonMasters, Bellingham WAApril, 2009
What Occam's razor teaches meabout climate change• “Law of succinctness”• When multiple competing hypotheses areequal in other respects, choose the hypothesisthat introduces the fewest assumptions
What Occam's razor teaches meabout climate change• The simplest model tends to be the right one• CO 2 is a heat trapping gas• If you put a heat trapping gas in theatmosphere you expect it to trap heat
The basic science of the physicalcauses of the greenhouse effect is verywell understoodIt is physics andphysics is easyIPCC AR4
Ice Cores Preserve the History of Atmospheric CO 2 andclimate over the recent ice ages
Ice Cores Preserve the History of Atmospheric CO 2 andclimate over the recent ice agesHuman change385 ppm
550 ppm, 1000ppm?Ice Cores Preserve the History of Atmospheric CO 2 andclimate over the recent ice agesHuman change385 ppm
Early climate change historyJean Fourier: 1768-1830World-class mathematicianJohn Tyndall 1820-1893Physics giant, polymathSvante Arrhenius 1859-1927Nobel Prize in Chemistry
Jean Fourier: 1768‐1830• Pioneered planetary energybl balance studies• Infrared radiation (“dark heat”)balances incoming solarradiation• Without considering atmosphere, thinks earthshould be much colder than it is• Concludes earth acts as a ‘glass house’, trappingheat. Not sure what causes the effect
John Tyndall 1820‐1893• Connected specific gases to thegreenhouse effect• Earth "held fast in the iron gripof frost“ if not for greenhousegases• Greenhouse gases are “a local dam, by whichthe temperature at the earth's surface isdeepened; the dam, however, finally overflows,and we give to space all that we receive fromthe sun.”
Svante Arrhenius 1859‐1927• Fundamental work in chemicalthermodynamics• Built on Tyndall and made firstestimate of temperaturesensitivity to atmospheric CO 2doubling“By the influence of the increasing percentage of carbonic acid inthe atmosphere, we may hope to enjoy ages with more equableand better climates, especially as regards the colder regions of theearth, ages when the earth will bring forth much more abundantcrops than at present, for the benefit of rapidly propagatingmankind.”
Arrhenius to Revelle to Keeling to Hansen:Where will all this carbon go?“On the Influence ofCarbonic Acid in the Airupon the Temperatureof the Ground,”by Svante Arrhenius(1896)
Arrhenius: naïve assumption• Added carbon will partition itself between the oceanand atmosphere in the same proportions that existsthere now• Atmosphere had something like 600 Pg of C• Ocean had had something like 38,000 Pg of C• I.e. 1.6% of any added CO 2 will stay in theatmosphere and the rest would be “sunk” into theoceans• So Arrhenius didn’t think this warming would everhappen, and neither did most scientists for another60 years. Until…
“Human beings are nowcarrying out a large scalegeophysical experiment ofa kind that could not havehappened in the past norbe reproduced in thefuture.” Roger Revelle(Revelle & Suess, 1957)Roger Revelle, seen here studying seawater chemistry, ca.1936, and as a leading adminstrator as well as scientist, ca.1958. http://www.aip.org/history/climate/
Dissolution of CO 2 in SeawaterCO 2 to carbonic acid: CO 2 +H 2 O ↔H 2 CO 3Carbonic acid to bicarbonate: H CO ↔ H + +HCO‐2 3 3Bicarbonate to carbonate: HCO 3‐ ↔ H + +CO‐23‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐Net: CO 2 +H 2 O+CO‐23 →2HCO 3The ability to dissolve CO 2 depends on the relativeconcentrations of carbonate ions (HCO ‐ ‐2 3 &CO 23 )which are controlled by ocean pH. The net results isthat the factor oceans can absorb CO 2 is reduced bya factor of ~10. This is called the “Revelle factor”.
Keeling’s test of Revelle’s hypothesisAbove: 1961Right: in1990s"Keeling's a peculiar guy," Revelle laterremarked. "He wants to measure CO2 inhis belly... And he wants to measure it withthe greatest precision and the greatestaccuracy he possibly can."
Uptake byland andoceans
The basic science of the physicalcauses of the greenhouse effect is verywell understoodIt is physics……and physics is easyPhysics is easy……compared to chemistryChemistry is easy……compared to biologyBiology is easy……compared to understanding human societies!
• Academia Brasiliera de• Indian National ScienceCiências BrazilAcademy, India• Royal Society of Canada, • Accademia Nazionale deiCanadaLincei, Italy• Chinese Academy of Sciences, • Science Council of Japan,ChinaJapan• Académie des Sciences, • Russian Academy of Sciences,FranceRussia• Deutsche Akademie der• Royal Society, United KingdomNaturforscher Leopoldina, • National Academy of Sciences,GermanyUnited States of America
How science works
Thermometer recordsDiscrete PeriodsAnomalies(degC) from1951-1980
Temperature trends (°F per century) since 1920
World glacier monitoring serviceAnnualhttp://www.geo.unizh.ch/wgms/
World glacier monitoring serviceCumulativehttp://www.geo.unizh.ch/wgms/