GLOBAL WARMING: Natural Greenhouse Effect Global Warming Controversy and GW Possible effects of GW Outline
Sun and earth Sunlight warms earth's surface Heat radiates back into atmosphere Some heat reabsorbed in atmosphere Remainder radiates into space
EARTH'S ATMOSPHERIC LAYERS TROPOSPHERE 0 -15 km above surface G.H. Effect occurs here STRATOSPHERE 15 - 50 km above surface Ozone layer MESOSPHERE 50 - 80 km above surface "Middle sphere" IONOSPHERE/THERMOSPHERE 80 km and up
ANSWER: The wavelength of the energy changes, and this is the reason for the difference in entry and exit To help you understand this, let's examine wavelengths in more detail... Wavelength and GH Effect THE QUESTION: But if the energy passed through the atmosphere on the way to the earth's surface, why does it get trapped on the way out?
l WAVELENGTH: Electromagnetic radiation (EMR) travels in waves Wavelength (l): distance from one wave crest to the next Shorter l = more energy Fig. 3.7
Note differences in l in incoming and outgoing radiation Wien’s Law: l = 3 mm/T
MOLECULES THAT TRAP HEAT IN G.H. EFFECT: Water vapor & small droplets account for 97% of the natural GH effect H2O "Normal" levels of CO2 in atmosphere also contribute CO2 Natural Greenhouse gases Gases in atmosphere trap radiation at the long wavelength of outgoing radiation, but not at the short wavelength of incoming radiation
Absorbance by H2O and CO2 is at l of emitted radiation, not incoming Incoming l = 0.1 - 1.5 m
So what's the problem? HUMAN ACTIVITIES AFFECT SYSTEM: Affect system so it traps more heat than it normally would This raises temperatures at the Earth's surface WHAT CAUSES THIS? (1.) Increasing CO2 concentrations in atmosphere, trapping more heat (2.) Adding other gases ("greenhouse gases") to atmosphere that also trap heat
Adding CO2: Human Impacts WHAT ADDS CO2 TO THE ATMOSPHERE? Burning fossil fuels for energy Combustion of coal, oil, and natural gas produces CO2 Overwhelms system's capacity to remove CO2 from atmosphere CO2 builds up, traps more heat, temperatures increase
Oil: 30% more CO2 than nat. gas Coal: 43% more CO2 than nat. gas Natural Gas: Lowest CO2 Adding CO2: Human Impacts COMPARING THE FOSSIL FUELS? Which emits the least CO2 per unit energy produced?
QUESTION: Do increasing CO2 concentrations correlate with higher temps? ANSWER: Yes, historically. This connection is questioned by some though
WHERE'S THE OTHER 40-50% FROM? Other Greenhouse gases besides CO2 that trap heat Chlorofluorocarbons (CFCs) Methane (natural gas) Nitrous Oxide (N2O) Greenhouse gases GLOBAL WARMING: CO2 emissions account for 50-60% of the anthropogenic (human-induced) temperature change
METHANE (Natural Gas): 12-20 % of anthropogenic GW due to methane From natural gas leaks, livestock Concentrations currently stable, but high CHLOROFLUOROCARBONS (CFCs): 15-25 % of anthropogenic GW due to CFCs Used as coolants (freon), formerly as propellants Atmospheric concentrations growing by 5% annually NITROUS OXIDE (N2O): 5 % of anthropogenic GW due to N2O From fertilizer use, burning coal, vehicle exhaust Concentrations growing by 0.2% annually
Greenhouse gases PROBLEM #1: Compared to CO2 molecule, each molecule of these gases traps: CFCs: 1,500 - 7,000 times as much heat Methane: 25 times as much heat Nitrous Oxide: 230 times as much heat PROBLEM #2: Trap heat in a wavelength not trapped by CO2
Recapping NATURAL GREENHOUSE EFFECT: Natural trapping of heat by gases in Earth's atmos. Allows life to persist on earth GLOBAL WARMING: Human activities accelerate heat trapping Average global temperatures rise Due to CO2 from fossil fuels, greenhouse gases Global warming theory is controversial Let's look at the controversy
Controversy #1: Recent temp. change RECORDED DATA: Data only goes back to 1860 Since 1860, temps have risen about 0.9o F (0.5o C) This past year (1999) was warmest on record THE CONTROVERSY: Some claim temp. readings are inaccurate due to "urban heat island effect", and temps. aren't really rising
Controversy #2: Correlation between CO2 and temp. PAST CLIMATE: Reconstruct past climate from air bubbles trapped in glaciers. Finds CO2 levels and temp. to be correlated THE CONTROVERSY: CO2 data solid, but temp. estimates are suspect. Contend there is no relation between CO2 levels and temperatures
Controversy #3: Predicting temperature changes CLIMATE MODELS: Create model of earth's weather, input variables and observe changes in the model. Suggests that average temp. could rise 3.6o F (2.0o C) by 2100 THE CONTROVERSY: Climate models higher speculative. Earth's climate too complex to be modeled.
What's the consensus? HUMAN vs. NATURAL: Are current temp. increases human-induced or natural? Consensus: At least partly caused by human activities HOW MUCH WILL IT INCREASE? Consensus: Who knows? Earth's climate simply too complex to be accurately modeled Assuming temperatures rise as expected, what would be the results?
Possible effects of global warming SEA LEVELS RISE: Rising temps. melt ice caps and cause oceans to expand Together these result in higher sea levels Could rise 19 in (48 cm) by 2100 Highly populated coastal areas become unihabitable Arable land decreases; less food production Wealthy countries build dikes, poor countries flood
American breadbasket becomes Canadian breadbasket Global yields down 10-70% Possible effects of global warming GRAIN BELT SHIFT: Crops (corn, wheat, etc.) grow optimally at temps in Midwest U.S. Midwest becomes warmer, optimal temp. range shifts northward
Possible effects of global warming EXTREME WEATHER: Temperature drives weather patterns Higher average temps. means more extreme weather (floods, drought, high/low temps.) Some are wondering if current weather extremes are due to climate change
Ocean "conveyor belt" - could break down if ocean temperatures elevate too much
What should we do now? THREE SCHOOLS OF THOUGHT: Nothing: Contend GW is a hoax and overstated. No action is necessary Wait and see: Need more definitive research to link human activities with temperature increases. Study now and act later. Precautionary strategy: Act now, while you have the chance. Research will never prove connection, so why wait?
International treaties on GW KYOTO, JAPAN (DEC. 1997) Treaty calls for reductions in CO2, methane, nitrous oxide, and three others that damage ozone 38 industrialized nations required to reduce their emissions from 1990 levels by 2012. E.U. 8%; U.S. 7%, Japan 6% Developing countries, including China and India, would have voluntary limits, no set standards
WHY? Reductions cost money in short-term Economy could suffer short-term Global competitors like China have advantage International treaties on GW KYOTO, JAPAN (DEC. 1997) Bush Administration refuses to sign it. Will it ever pass? Not very likely.