Articles on Environment Matters:

Global Warming

Global warming is the observed increase in the average temperature of the Earth's near-surface air and oceans in recent decades and its projected continuation.

Global average air temperature near Earth's surface rose 0.74  0.18 °Celsius (1.3 ± 0.32 °Fahrenheit) in the last century. The Intergovernmental Panel on Climate Change (IPCC) concludes, "most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations," which leads to warming of the surface and lower atmosphere by increasing the greenhouse effect . Other phenomena such as solar variation and volcanoes have had a large impact on climate prior to 1950, but volcanism has probably had cooling effects on global mean temperature since 1950. This conclusion has been endorsed by at least 20 scientific societies and academies of science, including all the national academies of science of the G8+5 states. The membership of these organizations include thousands of climate scientists. There are individual scientists who disagree with parts of this conclusion, as does the American Association of Petroleum Geologists .

Models referenced by the IPCC predict that global temperatures are likely to increase by 1.1 to 6.4 °C (2.0 to 11.5 °F) between 1990 and 2100. The range of values reflects the use of differing scenarios of future greenhouse gas emissions as well as uncertainties regarding climate sensitivity. Although most studies focus on the period up to 2100, warming and sea level rise are expected to continue for more than a millennium even if no further greenhouse gases are released after this date. This reflects the long average atmospheric lifetime of carbon dioxide (CO₂).

An increase in global temperatures can in turn cause other changes , including a rising sea level and changes in the amount and pattern of precipitation. There may also be increases in the frequency and intensity of extreme weather events, though it is difficult to connect specific events to global warming. Other consequences include changes in agricultural yields, glacier retreat, reduced summer streamflows, species extinctions and increases in the ranges of disease vectors.

Remaining scientific uncertainties include the exact degree of climate change expected in the future, and especially how changes will vary from region to region across the globe. A hotly contested political and public debate also has yet to be resolved, regarding whether anything should be done, and what could be cost-effectively done to reduce or reverse future warming , or to deal with the expected consequences. Most national governments have signed and ratified the Kyoto Protocol  aimed at combating greenhouse gas emissions. (See: List of Kyoto Protocol signatories .)

The term global warming is a specific example of the broader term climate change , which can also refer to global cooling. In principle, global warming is neutral as to the period or causes, but in both common and scientific usage the term generally refers to recent warming and implies a human influence. The UNFCCC uses the term "climate change" for human-caused change, and "climate variability" for other changes. The term "anthropogenic climate change" is sometimes used when focusing on human-induced changes.

The term itself is non-controversial, as temperature increases (and declines) have been noted throughout history. There is a controversy over whether present trends are anthropogenic. For a discussion of the controversy, see global warming controversy .

Wikipedia.org
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26 May 2007
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Causes of Global Warming

The climate system varies through natural, internal processes and in response to variations in external "forcing" factors including solar activity, volcanic emissions, variations in the earth's orbit (orbital forcing) and greenhouse gases. The detailed causes of the recent warming  remain an active field of research, but the opinion of the IPCC identifies increased levels of greenhouse gases due to human activity as the main influence. This attribution is clearest for the most recent 50 years, for which the most detailed data are available.

Adding carbon dioxide (CO₂) or methane (CH₄) to Earth's atmosphere, with no other changes, will make the planet's surface warmer. Greenhouse gases create a natural greenhouse effect  without which temperatures on Earth would be an estimated 30 °C (54 °F) lower, so that Earth would be uninhabitable. It is therefore not correct to say that there is a debate between those who "believe in" and "oppose" the greenhouse effect as such. Rather, the debate concerns the net effect of the addition of greenhouse gases when allowing for positive or negative feedback.

Contrasting with the majority or consensus view, other hypotheses have been proposed to explain all or most of the observed increase in global temperatures, including: the warming is within the range of natural variation; the warming is a consequence of coming out of a prior cool period, namely the Little Ice Age; and the warming is primarily a result of variances in solar radiation.

One example of an important feedback process is ice-albedo feedback. The increased CO₂ in the atmosphere warms the Earth's surface and leads to melting of ice near the poles. As the ice melts, land or open water takes its place. Both land and open water are on average less reflective than ice, and thus absorb more solar radiation. This causes more warming, which in turn causes more melting, and this cycle continues.

Due to the thermal inertia of the Earth's oceans and slow responses of other indirect effects, the Earth's current climate is not in equilibrium with the forcing imposed by increased greenhouse gases. Climate commitment studies indicate that, even if greenhouse gases were stabilized at present day levels, a further warming of about 0.5 °C (0.9 °F) would still occur.

Wikipedia.org
The Free Encyclopedia
26 May 2007
www.wikipedia.org

Greenhouse Gases In The Atmosphere

The greenhouse effect was discovered by Joseph Fourier in 1824 and was first investigated quantitatively by Svante Arrhenius in 1896. It is the process by which emission of infrared  radiation by atmospheric gases warms a planet's surface. On Earth, the major natural greenhouse gases are water vapor, which causes about 36-70% of the greenhouse effect (not including clouds); carbon dioxide, which causes 9-26%; methane, which causes 4-9%, and ozone, which causes 3-7%.

The atmospheric concentrations of CO₂ and methane (CH₄) have increased by 31% and 149% respectively above pre-industrial levels since 1750. This is considerably higher than at any time during the last 650,000 years, the period for which reliable data has been extracted from ice cores . From less direct geological evidence it is believed that CO₂ values this high were last attained 20 million years ago. About three-quarters of the anthropogenic (man-made) emissions of CO₂ to the atmosphere during the past 20 years are due to fossil fuel burning. The rest of the anthropogenic emissions are predominantly due to land-use change, especially deforestation .

Future CO₂ levels are expected to rise due to ongoing burning of fossil fuels and land-use change. The rate of rise will depend on uncertain economic, sociological, technological, natural developments, but may be ultimately limited by the availability of fossil fuels. The IPCC Special Report on Emissions Scenarios gives a wide range of future CO₂ scenarios, ranging from 541 to 970 parts per million by the year 2100. Fossil fuel reserves are sufficient to reach this level and continue emissions past 2100, if coal, tar sands or methane clathrates are extensively used.

Carbon dioxide sink ecosystems (forests and oceans) are being degraded by pollutants. Degradation of major carbon sinks results in higher atmospheric CO₂ levels.

Anthropogenic emission of greenhouse gases broken down by sector for the year 2000.

Positive feedback effects such as the expected release of methane from the melting of permafrost peat bogs in Siberia (possibly up to 70,000 million tonnes) may lead to significant additional sources of greenhouse gas emissions not included in IPCC's climate models.

The measure of the temperature response to increased greenhouse gas concentrations and other anthropogenic and natural climate forcings is climate sensitivity. It is found by observational and model studies. This sensitivity is usually expressed in terms of the temperature response expected from a doubling of CO₂ in the atmosphere. The current literature estimates sensitivity in the range of 1.5 to 4.5 °C (2.7 to 8.1 °F).

Wikipedia.org
The Free Encyclopedia
26 May 2007
www.wikipedia.org

Attributed and Expected Effects of Global Warming

Some effects on both the natural environment and human life are, at least in part, already being attributed to global warming. A 2001 report by the IPCC suggests that glacier retreat , ice shelf disruption such as the Larsen Ice Shelf , sea level rise, changes in rainfall patterns, increased intensity and frequency of hurricanes and extreme weather events , are being attributed at least in part to global warming. While changes are expected for overall patterns, intensity, and frequencies, it is difficult or impossible to attribute specific events (such as Hurricane Katrina) to global warming.

Some anticipated effects include sea level rise of 110 to 770 mm (0.36 to 2.5 feet) by 2100, repercussions to agriculture, possible slowing of the thermohaline circulation , reductions in the ozone layer, increased intensity and frequency of hurricanes and extreme weather events , lowering  of ocean pH, and the spread of diseases such as malaria  and dengue fever. One study predicts 18 to 35 percent of a sample of 1,103 animal and plant species would be extinct  by 2050, based on future climate projections. However, few mechanistic studies have documented extinctions due to recent climate change.

Two British scientists supporting the mainstream scientific opinion on global warming criticize what they call the "catastrophism and the 'Hollywoodisation'" of some of the expected effects. They argue the sensationalized claims cannot be justified by the science.

The extent and probability of these consequences has caused controversy , as is a matter of uncertainty. A summary of probable effects and recent understanding can be found in the report of the IPCC  Working Group II; the newer AR4 summary reports, "There is observational evidence for an increase of intense tropical cyclone activity in the North Atlantic since about 1970, correlated with increases of tropical sea surface temperatures. There are also suggestions of increased intense tropical cyclone activity in some other regions where concerns over data quality are greater. Multi-decadal variability and the quality of the tropical cyclone records prior to routine satellite observations in about 1970 complicate the detection of long-term trends in tropical cyclone activity. There is no clear trend in the annual numbers of tropical cyclones."

Mitigation
The broad agreement among climate scientists that global temperatures will continue to increase has led nations, states, corporations and individuals to implement actions to try to curtail global warming. Some of the strategies that have been proposed for mitigation of global warming include development of new technologies; carbon offsets; renewable energy such as wind power , and solar power; nuclear power; electricor plug-in hybrid electric vehicles; non-fossil fuel cells ; energy conservation; carbon taxes; improving natural carbon dioxide sinks; deliberate production of sulfate aerosols, which produce a cooling effect on the Earth; population control; carbon capture and storage ; nanotechnology; and environmental vegetarianism. Many environmental groups encourage individual action against global warming, often aimed at the consumer, and there has been business action on climate change.

Wikipedia.org
The Free Encyclopedia
26 May 2007
www.wikipedia.org