The Greenhouse Effect Good or Bad Global Climate

The Greenhouse Effect Good or Bad?

Global Climate History Geologic evidence clearly indicates relative long-term climate stability that has allowed liquid H 2 O to exist for most of geologic history.

Earth’s Atmosphere 77% N 2, 21% O 2, 1% Ar, + trace gases (CO 2, CH 4, H 2 O) Absorbs incoming solar radiation and warms the planet. Important component of global climate.

Without atmosphere, average Earth temperatures would be a cool – 17°C!!

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.

Greenhouse Glass, the material that greenhouse is made of, 1) transmits 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. The gases in the atmosphere that act like glass in a greenhouse are called greenhouse gases. • 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.

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 i • An increase in the concentration of greenhouse gases leads to an increase in the magnitude of the greenhouse effect. (Called enhanced greenhouse effect) – This results in global warming

Enhanced greenhouse effect When concentrations of greenhouse gases increase, more infrared radiation is returned towards the Earth. The surface temperature rises.

Climate Change vs. Variability Climate variability is natural. Even in a stable climate regime, there will always be some variation (wet/dry years, warm/cold years) A year with completely “average” or “normal” climate conditions is rare The challenge for scientists is to determine whether any increase/decrease in precipitation, temperature, frequency of storms, sea level, etc. is due to climate variability or climate change.

The Last Ice Age 30% of the land surface was covered by ice (only 10% is covered today) Northern Idaho was covered by ~1 km thick ice sheet

Selected Greenhouse Gases • Carbon Dioxide (CO 2) – Source: Fossil fuel burning, deforestation i Anthropogenic increase: 30% i Average atmospheric residence time: 500 years i Methane (CH 4) – Source: Rice cultivation, cattle & sheep ranching, decay from landfills, mining i Anthropogenic increase: 145% i Average atmospheric residence time: 7 -10 years i Nitrous oxide (N 2 O) – Source: Industry and agriculture (fertilizers) i Anthropogenic increase: 15% i Average atmospheric residence time: 140 -190 years

What determines the contribution of a greenhouse gas to global warming? • Concentrations – H 2 O and CO 2 are the two biggest contributors to the atmospheric warming because of their higher concentrations. • Lifetime – The longer-lived a gas is, the higher the contribution. e. g. N 2 O contribution > CH 4 • Effectiveness as an infrared absorber – For example, CFC-11 and CFC-12

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. 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.

The concentration of greenhouse gases, particularly CO 2, is important global climate regulation What regulates the amount of CO 2? ?

The Earth’s Climate System - very complex!!

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).

Methane Rate of increase: 0. 9% annually 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.

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+ CH 4 CH 3. + H 2 O

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

Short-Term Climate Change • Climate change over short time scales (<1, 000 years) WARM COLD • Related to complex, poorly understand interactions between atmosphere, hydrosphere, and lithosphere Possible Causes 1. Orbital Parameters of the Earth 2. Changes in Atmospheric Composition 3. Changes in Ocean Circulation 4. Sunspot Activity 5. Changes in Reflectivity (albedo)

Recent 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 – 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 O 3 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