Presentation on theme: "Greenhouse Effect & Global Warming. Some Evidence The global air temperature at the Earth's surface has increased about 0.5 o C during the past century."— Presentation transcript:
The Greenhouse Greenhouses are used to grow plants, especially in the winter. The glass panels of the greenhouse let in light but keep heat from escaping. This causes the greenhouse to heat up, like the inside of a car parked in sunlight, and keeps the plants warm enough to live in the winter.
Greenhouse Glass, the material that greenhouse is made of, 1) transmit short-wavelength visible light, 2) absorbs and redirects the longer wavelengths of energy. These two aspects make the greenhouse warmer than outside air temperature.
Greenhouse effect of the atmosphere Light from the sun includes the entire visible region and smaller portions of the adjacent UV and infrared regions. Sunlight penetrates the atmosphere and warms the earth’s surface. Longer wavelength infrared radiation is radiated from the earth’s surface. A considerable amount of the outgoing IR radiation is absorbed by gases in the atmosphere and reradiated back to earth. The gases in the atmosphere that act like glass in a greenhouse are called greenhouse gases.
Natural Greenhouse effect The natural greenhouse effect causes the mean temperature of the Earth's surface to be about 33 o C warmer than it would be if natural greenhouse gases were not present.
Enhanced greenhouse effect When concentrations of greenhouse gases increase, more infrared radiation is returned toward the earth and the surface temperature rises.
What makes a gas greenhouse gas? Able to absorb infrared light Must have molecular vibration(s) The molecular vibrations must be non- symmetric, i.e. infrared active –Homonuclear diatomic molecules only have symmetric vibrations. That’s why N 2, O 2 are not greenhouse gases.
What are the major greenhouse gases? H 2 O CO 2 CH 4 N 2 O O 3 CFCs
Are human beings causing increases in greenhouse gases?
CO 2 Concentrations at Mauna Loa, Hawaii The average atmospheric CO 2 concentrations observed at Muana Loa, Hawaii increased approximately 40 ppmv between 1958 and 1995.
Methane Atmospheric methane has increased steadily to present day levels; this increase is highly correlated with human population growth and with related activities, including agricultural practices. Rate of increase: 0.9% annually
Nitrous oxide (N 2 O) Rate of increase 0.25%/year Use of fertilizer increases both nitrification and denitrification increase N2O production
Sources and sinks of CO 2 Sources –Natural: respiration of vegetation and soil detritus –Man-made: Fossil fuel combustion, deforestation Sinks: slow exchange of carbon between surface waters and deep layers of ocean. (Seawater is alkaline while CO 2 is acidic The oceans are a vast reservoir of CO 2 ).
Worldwide Carbon Emissions Carbon (10 9 metric tons) 0 1 2 3 4 5 6 7 8 175018001850190019502000 Year Liquid fuel Total Gas fuel Solid fuel
Future Carbon Dioxide Levels Increasing CO 2 emissions, especially in China and developing countries Likely to double within 150 years: Increased coal usage Increased natural gas usage Decreased petroleum usage (increased cost and decreasing supply)
Status of CO 2 Pre-industrial Amount:280 ppm Present Amount:382 ppm Maximum Allowable ≤450 ppm Rate of Change:+2 ppm/year (and growing)
Kyoto Protocol Adopted in 1997 Cut CO 2 emissions by 5% from 1990 levels for 2008-2012 Symbolic only, since cuts will not significantly impact global warming
170 220 270 320 370 0 0 200000 400000 600000 Time (YBP) CO 2 (ppm) Antarctica 25 26 27 28 29 30 31 SST (°C) Tropical Pacific CO 2 Concentration Vs. Temperature
Greenhouse Effect & Global Warming The “greenhouse effect” & global warming are not the same thing. –Global warming refers to a rise in the temperature of the surface of the earth An increase in the concentration of greenhouse gases leads to an increase in the the magnitude of the greenhouse effect. (Called enhanced greenhouse effect) –This results in global warming
Consequences of global warming Sea level rise –Beach erosion –Coastal wetland loss –Loss of low-lying territories Water resources change –Precipitation pattern shift –Increases instances of heavy precipitation Effects on agriculture –Changes in the length of growing season –Growth of undesirable plant species
Consequences of global warming (Continued) Effects on air quality –Increase in reaction rates and concentrations of certain atmospheric species increase in O3 in urban areas Impacts on human health –Changes in patterns of sickness and death. –Respiratory problems affected by air quality change Biodiversity –Some species may grow too quick and overshoot their reproductive period (e.g. reef corals) Change in the pattern of ocean current