Climate-Greenhouse Effect

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) –This excludes monoatomic gases as greenhouse gases. (That is why argon, the third most abundant atmospheric constituents is transparent to infrared irradiation) The molecular vibrations must be non- symmetric, i.e. infrared active –Homonuclear diatomic molecules only have symmetric vibrations. That’s why N2, O2 are not greenhouse gases.

What are the major greenhouse gases? H2O CO2 CH4 N2O O3 CFCs SF6

Absorption of terrestrial radiation by H2O and CO2 Atmospheric window: nm

What determines the contribution of a greenhouse gas to global warming? Concentrations –H2O and CO2 are the two biggest contributors to the atmospheric warming because of their higher concentrations. Lifetime –The longer-live a gas is, the higher the contribution. e.g. N2O contribution > CH4 Effectiveness as an infrared absorber –For example, CFC-11 and CFC-12

CFC-11 and CFC-12 are effective infrared absorber The absorption spectra of CFC-11 and CFC-12 coincides with the atmospheric window

Comparison of different greenhouse gases CO2CH4CFC-11CFC-12N2O Concentration Preindustrial (<1800) Current ppm ppm ppt ppt ppb Atmospheric lifetime (yr) Per molecule of radiative forcing relative to CO2 1234,00015,800296

Are human beings causing increases in greenhouse gases?

CO2 Concentrations at Mauna Loa, Hawaii The average atmospheric CO2 concentrations observed at Muana Loa, Hawaii increased approximately 40 ppmv between 1958 and The small fluctuations in the curve are seasonal variations due primarily to the withdrawal and production of carbon dioxide by terrestrial life. Notice that minimum values occur during the northern hemisphere summers (when global photosynthetic activity is greatest) and maximum values occur six months later.

Sources and sinks of CO2 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 CO2 is acidic  The oceans are a vast reservoir of CO2).

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

Sources and sinks of methane Sources –Natural: end-product of the metabolism from an anaerobic bacteria, methanogen. Natural wetlands, enteric fermentation (wild animals), termites, biomass burning, ocean/fresh water –Man-made: rice paddies, gas drilling and transmission, landfills, coal mining, biomass burning, enteric fermentation (domestic animals) Sink: OH+ CH4  CH3. + H2O

Nitrous oxide (N2O) Rate of increase 0.25%/year Use of fertilizer increases both nitrification and denitrification  increase N2O production

Sources and sinks of N2O Sources: –denitrification process for energy production by anaerobic bacteria. –Nitrification process (NH4 +  NO3 - ) –Fertilizer use –Biomass burning –Combustion –Unknown sources Sink:Photolysis in the stratosphere natural Man-made

CFC-11

Sources and sinks of CFCs Sources –No natural sources –Synthetic chemicals Sink: Photolysis in the stratosphere.

Is the earth getting warmer?

Temperature over the past one century The global air temperature at the Earth's surface has increased about 0.5 o C during the past century

Temperature over the past 1000 years

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 –New burdens on water capture, storage and distribution system to be expected. 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 –More droughts  widespread forest fire  worsen air quality –Change in how pollutants are dispersed. 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) –Forest could be devastated if the rate of climate change outpaced the rate at which forest species could migrate. Change in the pattern of ocean current

Is the temperature rise due to human activities? Or is it part of the natural variation?

When greenhouse gases, aerosols, and changes in solar irradiance are used as inputs into general circulation models, predicted temperatures are very close to those observed. When greenhouse gases are the only input, predicted temperature are higher than those observed.

The state of climate change science The Earth’s natural greenhouse effect is required to support life on earth. Aerosol particles are important in formation of clouds. Human activities are contributing to increases in greenhouse gases and aerosol loading. The Earth’s surface has warmed during the last century and is projected to continue warming.