Structure of this presentation1. Global warming-real or not?2. Climate science, models and predictions the zero dimensional approach3. Unexpected events
Is there evidence for Modern Global Warming?A. Instrumental recordsB. ‘Proxy’ records from the recent pastC. Current Environmental Change (glaciers,floral/faunal shifts)How does MGW fit into the climate history of the recent geological past?
Variations of the Earth’s Surface Temperature* *relative to 1961-1990 average Source: IPCC TAR 2001
Superposed on gradual climate change, there is evidence for very sudden climate change from the record of the past
U.S. Temperature Trends: 1901 to 1998 Crawford Ranch Red circles = warming; Blue circles = cooling All stations/trends displayed regardless of statistical significance. Source: National Climatic Data Center/NESDIS/NOAA
Crumbling of the Killimanjaro summit glacier - an effect of global warming
Collapse of the Larsen Ice Shelf near Antarctica - a piece of ice the size of Rhode Island came adrift
Effects of global warming on water cycle Global warming (temperature increase) Speeds up global water cycle • More extreme weather events • Droughts • Storms • Floods
Increase in frequency and intensity of droughts Source: OSTP
Extreme Precipitation Events in the U.S. Source: Karl, et.al. 1996.
So these are the data:There is global warming, there are more extreme events, ice is melting, glaciers are retreating, rainfall patterns are changing, plants and animal species are “moving”, sea level is rising.The real BIG question is:Natural Variability or the “Human Hand”?
The main “Radiation Law is Planck’s Law. Boltzman’s Law is the ‘integrated version’ of PL
The Human Hand?!
GLOBAL WARMING IS LIKELY RELATED TO THE GREENHOUSE EFFECT - HOW DOES THAT WORK?
Principle of Radiative Balance:The solid earth + atmosphere receive heat from the sun BUTalso radiate the same amount of heat back into space
Principles of terrestrial climate: Incoming solar radiation equals outgoing terrestrial radiation Rsun = Rterr The magnitude of Rterr depends on Ts (apply Boltzman Law). Part of the outgoing terrestrial radiation is blocked by ‘greenhouse gases’, and the earth warms up a bit to restore the radiative equilibrium
Illumination of the earth by the sun:1. More heat received at the equator than at the poles2. Solid earth receives more heat by radiation than it radiates backRESULT: CONVECTIVE HEAT TRANSPORT FROM EQUATOR TO POLES THROUGH AIR AND OCEANS
The earth radiates long wavelength EMR which is absorbed by molecules with an uneven # of atoms, such as H2O, CO2, CH4, CFC’s O3(the “greenhouse” gases)
THE GREENHOUSE EFFECTTHE SUN EMITS SHORT WAVELENGTH RADIATION (‘VISIBLE LIGHT’) WHICH PENETRATES THROUGH THE ATMOSPHERE AND HEATS THE SOLID EARTH.THE SOLID EARTH EMITS LONG WAVE LENGTH RADIATION (‘INFRA RED’) WHICH IS ABSORBED ‘ON ITS WAY OUT’ BY THE GREENHOUSE GASES.A THERMAL BLANKET IS THE RESULT
THE TRACE GASES (H2O, CO2, CH4, N2O, O3) SERVE AS GREENHOUSE GASES AND KEEP THE EARTH LIVABLE
IF THE GREENHOUSE EFFECT IS CHANGING: CAN WE DOCUMENT CHANGES IN THE CHEMICAL COMPOSITION OF THE ATMOSPHERE? COULD THESE BE ANTHROPOGENIC? IS THEIR MAGNITUDE ENOUGH TO EXPLAIN MODERN GLOBAL WARMING?
Burning of fossil fuels Source: OSTP
Deforestation Source: OSTP
Indicators of the Human Influenceon the Atmosphere during the Industrial Era Source: IPCC TAR 2001
CARBON RESIDES IN AND MOVES BETWEEN DIFFERENT RESERVOIRS SUCH AS THE ATMOSPHERE, THE PLANT AND ANIMAL WORLD (BIOSPHERE), DISSOLVED IN THE OCEAN AND IN SOILS. THE CARBON MOVEMENTS BETWEEN THESE RESERVOIRS IS CALLED THE CARBON CYCLE
ANTHROPOGENIC CARBON FLUXES IN THE 1990s: FOSSIL FUEL BURNING: 6 BILLION TONS CARBON/YEAR DEFORESTATION: 1.1 BILLION TONS CARBON/YEAR TOTAL: 7.1 BILLION TONS CARBON/YEAR WHERE IS ALL THAT CO2 GOING??
How do we model future atmospheric CO2 concentrations? • Apply a carbon cycle model to a range of future FFF scenarios • Use ‘economic scenarios’ that depend strongly on • Population growth rates • Economic development • Switch to alternative energy technologies • Sharing of technology with the developing world
Carbon cycle model from E&ES 132/359 at Wesleyan University Symbols: Mx = mass of carbon Kx = rate constant FFF = Fossil Fuel Flux of Carbon Feedbacks: Bf = Bioforcing factor; depends on CO2(atm) K4 = f(temperature)
CO2 and SO2 in the 21st Century Source: IPCC TAR 2001
Clear correlation between atmospheric CO2 and temperature over last 160,000 years • Current level of CO2 is outside bounds of natural variability • Rate of change of CO2 is also unprecedented Source: OSTP
If nothing is done to slow greenhouse gas emissions. . . • CO2 concentrations will likely be more than 700 ppm by 2100 • THIS IS WELL OUTSIDE THE • ‘NATURAL RANGE’ OF THE • LAST 200,000 YEARS 2100 Source: OSTP
To go from atmospheric CO2 concentration change to climate change, we need to know the climate sensitivity parameter, l. The common approach is: DTs = lDForDF/DTs = 1/l where DF is the ‘radiative forcing’ caused by the increased CO2 concentration. The value of DF can be calculated from the increase in CO2 concentration using the deBeers law. DTs is the change in the surface temperature of the earth We can solve for l by taking the first derivative of Boltzman’s Law F = t sTs4 or dF/dTs = 4F/Ts leading to a l value of 0.3 K/Wm-2. This approach is the most fundamental response function and uses zero climate feedbacks! Most climate modellers use 0.5 K/Wm-2, incorporating various positive and negative feedbacks.