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Download Which of the following are scientific statements?
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The Science of Climate Change Kim M. Cobb [email protected] Which of the following are scientific statements? 1) Reducing CO2 emissions would hurt the economy. 2) Improved technology is the best way to slow global warming. 3) A warming of 1ºC over the next 50yrs is dangerous. 4) Global temperatures were 5ºC colder during the Last Glacial Maximum. 5) Hurricane Katrina was caused by global warming. Which of the following are scientific statements? 1) Reducing CO2 emissions would hurt the economy. 2) Improved technology is the best way to slow global warming. 3) A warming of 1ºC over the next 50yrs is dangerous. 4) Global temperatures were 5ºC colder during the Last Glacial Maximum. 5) Hurricane Katrina was caused by global warming. greenhouse gases in the atmosphere trap heat at the Earth’s surface and prevent it from escaping. These gases include: •Carbon dioxide CO2 •Methane CH4 •Nitrous oxide N2O •Chlorofluorocarbons 4 1 •Water vapor H2O (this is the most important one, by far!) without greenhouse gases average temp of Earth would be -18ºC instead of 15ºC 3 2 greenhouse gases trap heat because they absorb radiation in the infrared range, according to specific bond geometries and vibrational modes (ex CO2 below) ice core CO2 records confirm that the CO2 trend began in the 1800’s -clear land for agriculture -Industrial Revolution Who is responsible for CO2 emissions? Total CO2 emissions (in thousands metric tons/yr) Per capita CO2 emissions (in tons/per capita per yr) The ‘instrumental’ record of climate shows a ~1ºC warming over the last century Source: Hadley Center UK Met Office Jones et al., 1999 A paleo perspective: glacial-interglacial cycles CO2 80 ppm range = 200 to 280ppm 5ºC Temperature range = 5ºC But why doesn’t an 80 ppm change in CO2 correspond to a 5 C change? The climate system does not reach equilibrium instantaneously Other processes can change the equilibrium temperature. Why do 99.999% of climate scientists believe that CO2 is warming the planet? 1. Theory predicts that increasing atmospheric CO2 should warm the planet. 2. Geologic evidence links CO2 and temperature in the past. 3. The warming is unprecedented in the most recent centuries (dwarfs natural variability). 4. Climate models show that rising CO2 is necessary to simulate 20th century temperature trends (solar and volcanic minor players). Ice core climate and CO2 records tiny gas bubbles in the ice trap ancient air samples #2 Atmospheric CO2 and temperature over the past 650 thousand years CO2 and temperature are closely linked on geologic timescales To understand how climate has changed in the past, we need to use records of climate preserved in ice cores, ancient tree rings, coral bands, and other “paleoclimatic” sources: key is to CALIBRATE to temperature records #3 The “Hockey Stick” Key Points: error bars increase as you go back in time natural variability accounts for <0.5ºC over the last millennium late 20th century temperature trend is unprecedented #4 Intergovernmental Panel on Climate Change (IPCC) 2001 Consequences of Global Warming (IPCC SPM-AR4) 1) 2) 3) 4) 5) 6) 7) 8) 9) Reduced uptake of CO2 by land and ocean in warmer climate Rising sea levels (0.3 to 0.6m by 2100)…. at a minimum Ocean pH will decrease by 0.14 to 0.35 (already down 0.1) Snow cover will decrease, permafrost melt, sea ice melt Extreme events (temperature and precipitation) will become more frequent Tropical cyclones will become more intense Storm tracks will move poleward Rainfall will increase in the high latitudes, decrease in the subtropics Meridional overturning of Atlantic ocean will decrease The uncertain climate future Range of CO2 emissions scenarios: Strict international agreements CO2 at 600ppm by 2100 Mid-ground 850ppm by 2100 Business as usual 1550ppm by 2100 *390ppm today 280ppm 1800 Lower limit: 1°C by 2100 Upper limit: 6.5°C by 2100 Projected temperature change: global view Take-homes: -poles warm more -land warms more -ocean warming patchy and complex uneven warming will shift rainfall patterns Regional models use global model output, run at high-resolution (5km) grid Length of heat waves increase (# days/event) Diffenbaugh et al, 2005 Peak temperatures increase US http://www.usgcrp.gov/usgcrp/nacc/se-mega-region.htm Projected precipitation change: global view white = models disagree color = models mostly agree stippled = models agree Projecting precipitation is VERY uncertain business, yet extremely critical to human impacts. Projected precipitation change: regional view change in yearly average precipitation mm/day # heavy rain days days/yr # dry days days/yr Diffenbaugh et al, 2005 IPCC says increase in hurricane intensity “likely” (66%) Arctic Summer Sea Ice reducing over 30 years of record New Radar Data Show ice streams That penetrate Deep into Antarctica Rignot et al., Science 2011 Mass balance estimates (blue/black = traditional; Red = satellite gravity) For Can we detect melting of the polar ice sheets? GREENLAND YES ANTARCTICA BOTH Rignot et al., GRL 2011 CERTAIN Warming of 1-6°C by 2100. Sea levels will rise by 6 to 30 inches by 2100. Precipitation patterns will change. More erratic precipitation. Extreme events will increase, hurricanes more intense. Prospect of abrupt climate change. UNCERTAIN Can we do anything about it? What is a country to do? There are only three (prudent) options: 1)use less energy - drive less, drive smaller (plug-in?) cars - conserve electricity - recycle, reuse 2) make “clean” energy - solar power, wind power, nuclear energy 3) take CO2 out of the sky (much more difficult) …. but how much at what cost? Some clear lessons: 1) efficiency makes $$ 2)gains from cellulosic biofuels likely (not corn ethanol!) 3) taking CO2 out of the sky is more costly than not putting it in the atmosphere to begin with