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Gobal climate change Reading: Keller chapter 16, p. 490-498 and 513-531 temperature atmospheric CO2 Geol 10, Winter 2003 sea level energy resources 1 Studying Global Change Geologic record: what happened in the past Real-time monitoring: what is happening now Mathematical models: predicting the future (also tested against the geologic record) Geol 10, Winter 2003 energy resources 2 Climate Change Climate = average of weather conditions over seasons, years or decades e.g. Missouri's climate now is "humid continental" Depends on latitude, proximity to ocean, etc. Climate changes over geologic time as continents drift and as Ice Ages come and go Geol 10, Winter 2003 energy resources 3 Geol 10, Winter 2003 energy resources 4 The atmosphere Nitrogen N2 ~ 78 % Oxygen O2 ~ 21 % Argon Ar ~ 0.9 % Carbon dioxide CO2 ~ 0.03 % Others < 0.07 % Water contents vary from ~ 0 to 4% within the troposphere (lowest 10 km of the atmosphere) Water and CO2 contribute to the greenhouse effect Geol 10, Winter 2003 energy resources 5 A planet's climate depends on its mass, distance from the sun and atmospheric composition. Without greenhouse gases, Earth's would be roughly –20°C. Geol 10, Winter 2003 average temperature energy resources 6 Greenhouse gases (i) Naturally occurring: Water H2O ~ 0 to 4 % variable Carbon dioxide CO2 ~ 0.03 % increasing Methane CH4 doubled in 200 years Nitrous oxide N2O Ozone O3 (ii) Other very powerful greenhouse gases include HFC's, PFC's and SF6 (all anthropogenic) Geol 10, Winter 2003 energy resources 7 The greenhouse effect Geol 10, Winter 2003 energy resources 8 Light waves velocity = frequency x wavelength Wavelengths ~ 0.4 to 0.7 µm are visible (most sunlight) 1 µm = 1 millionth of a meter (1 x 10-6 m) Geol 10, Winter 2003 energy resources 9 Geol 10, Winter 2003 energy resources 10 Greenhouse Effect Geol 10, Winter 2003 energy resources 11 Temperatures: last 800,000 y We are in an interglacial period; still have permanent ice caps (for the moment) so technically we are still in an Ice Age. Geol 10, Winter 2003 energy resources 12 Temperatures: last 150,000 y Glacial-interglacial cycle is about 120,000 years Now look at CO2 for the same period Geol 10, Winter 2003 energy resources 13 Atmospheric CO2: last 160,000 y Geol 10, Winter 2003 energy resources 14 Temperatures: last 150,000 y Note high CO2 levels coincide with interglacials Geol 10, Winter 2003 energy resources 15 Temperatures: last 18,000 y Glaciers retreated from upper midwest ~10,000 years ago Last ~8,000 years have had relatively stable temperatures Geol 10, Winter 2003 energy resources 16 Temperatures: last 1,000 y Vikings settled Greenland Geol 10, Winter 2003 Vikings abandoned Greenland energy resources 17 Sea temperature in Medieval times estimated ~4 ˚C warmer than today text Medieval warming period Geol 10, Winter 2003 energy resources 18 Temperatures: last 140 y Not everywhere has the same temperature trend, but on average the planet's surface is heating up Geol 10, Winter 2003 energy resources 19 Atmospheric CO2, 1958 to present Seasonal changes reflect uptake of CO2 by plants (photosynthesis) Geol 10, Winter 2003 energy resources 20 CO2 and climate (Last 160,000 years). Clearly the "Greenhouse Effect" is very real and acts on a short timescale What about other greenhouse gases? Geol 10, Winter 2003 energy resources 21 Geol 10, Winter 2003 energy resources 22 Greenhouse gases Each greenhouse gas differs in its ability to absorb heat in the atmosphere. HFC's and PFC's are most heat-absorbent. Nitrous oxide traps ~ 270 times more heat per molecule than CO2; methane traps ~21 times more. Estimates of greenhouse gas emissions are often given in units of millions of metric tons of carbon equivalents (MMTCE), which weights each gas by its Global Warming Potential (GWP) Geol 10, Winter 2003 energy resources 23 Greenhouse gases Some Global Warming Potentials (100 y timescale) Gas GWP (set at CO2 = 1) Carbon dioxide (CO2) 1 Methane (CH4) 21 Nitrous oxide (N2O) HFC-23 310 11,700 CF4 6,500 C2F6 9,200 SF6 Geol 10, Winter 2003 these four are totally anthropogenic 23,900 energy resources 24 Greenhouse gases a,bRate of change is in parts per billion per year (ppb/y) except SF6 (concentration and rate of change in parts per trillion) Atmospheric Lifetime = residence time in years Atmospheric CO2 will double relative to pre-Industrial levels in the next 100 years or so. Methane already has doubled. Geol 10, Winter 2003 energy resources 25 Greenhouse gases Greenhouse gases are global in their effect upon the atmosphere. The main greenhouse gases have long residence times in the atmosphere, and therefore accumulate over time (unlike many local air pollutants) Greenhouse gases are generally well mixed in the atmosphere, so their impact is mostly independent of where they were emitted. Hence the emission of greenhouse gases should be addressed on a global (i.e., international) scale. Geol 10, Winter 2003 energy resources 26 Recent CO2 emissions The US currently emits ~ 25% of anthropogenic CO2, mostly from burning fossil fuels In 1990 the US emitted 5 billion tons of CO2 (~20 tons per person) Geol 10, Winter 2003 energy resources 27 CO2 emissions by country text Geol 10, Winter 2003 energy resources 28 Future estimates of CO2 emissions Projected 40% increase in next 17 years In 2001 the US backed out of the Kyoto treaty (designed to cut CO2 emissions to below 1990 levels by ~2010) for economic and political reasons Geol 10, Winter 2003 energy resources 29 Future CO2 concentrations Geol 10, Winter 2003 energy resources 30 Some conclusions 1. "Naturally occurring" climate change has occurred in the past on many timescales, and will continue in the future. Several times in the past, Earth has been hotter or colder than today 2. Anthropogenic activities have greatly increased (and continue to increase) the concentration of greenhouse gases in the atmosphere 3. In the past, high levels of CO2 (greenhouse gas) have correlated with high temperatures 4. So we should expect global warming to continue in the future (noticeable on a human timescale) Geol 10, Winter 2003 energy resources 31 Global climate change Reading: Keller chapter 16, p. 490-498 and 513-531 temperature atmospheric CO2 Geol 10, Winter 2003 sea level energy resources 32 Greenhouse gases The most important greenhouse gases are CO2 and CH4. So we need to understand the carbon cycle Geol 10, Winter 2003 energy resources 33 Fossil fuel emissions are small relative to natural fluxes Why do they have so large an effect? Geol 10, Winter 2003 energy resources 34 Title text Geol 10, Winter 2003 energy resources 35 Melting ice increases sea level Sea level rise is occurring today Geol 10, Winter 2003 energy resources 36 Submergent coastlines Melting glaciers and ice caps increases sea level Geol 10, Winter 2003 energy resources 37 Retreating Glaciers Positive feedback relationship between warming and melting There are also negative feedback relationships, e.g. more CO2 encourages more plants which consume CO2 Geol 10, Winter 2003 energy resources 38 Sea level rise text Geol 10, Winter 2003 energy resources 39 What if the remaining ice caps melt? • Over 2% of the world’s water is in glaciers • Antarctic ice sheet – Eighty percent of the world’s ice – Nearly two-thirds of Earth’s fresh water – Covers ~1.5 times area of United States – If melted, sea level would rise ~65 meters (200 ft) (Missouri river is at c. 565 ft above sea level at Boonville) Geol 10, Winter 2003 energy resources 40 What if the ice melts? Sea level rise > 60 meters (would happen over several thousand years) Geol 10, Winter 2003 energy resources 41 Title Note change will be rapid Geol 10, Winter 2003 energy resources 42 Future sea level rise (models) Expect about 0.5 m in the next century. Longer range predictions are less certain. Geol 10, Winter 2003 energy resources 43 Changes in rainfall text Geol 10, Winter 2003 energy resources 44 Oceanic circulation Without the circulation, northern Europe would be much colder. Global warming may shut down the Gulf Stream; this would freeze N. Europe Geol 10, Winter 2003 energy resources 45 Normal conditions Geol 10, Winter 2003 energy resources 46 El Niño conditions Suppressed upwelling changes atmospheric circulation, leads to storms, etc. Geol 10, Winter 2003 energy resources 47 Effects of El Niño, 1997-98 Global warming leads to more and stronger El Niño years: For the US, this means floods and storms near S and E coasts. Geol 10, Winter 2003 energy resources 48 What is a normal Earth Temperature? "Snowball" Earth Geol 10, Winter 2003 energy resources Greenhouse Earth 49 What is a normal Earth temperature? Note we are actually way below average for the last 100 million years. So why worry? 1) we were not around last time it was hot! 2) we are perturbing Earth systems much faster than most natural processes Geol 10, Winter 2003 energy resources 50