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Although the discussion of global warming often focuses on temperature, global warming or any climate change may cause changes in other geographical elements as well, including changes in sea level, amount and pattern of precipitation, climate patterns and various other forms of climate change. By the end of this century it is likely that greenhouse gases will have doubled and the average global temperature will have risen by at least 2C.
In the worst case scenario it could completely alter the climate in many regions of the world. Such changes can trigger various detrimental effects by causing floods, droughts, heat waves, reduction of agricultural yields which could lead in turn to global food insecurity and the widespread collapse of existing social systems, causing mass migration and conflict over resources as some parts of the world become much less habitable. This won’t result in mass extinction of human race but significant casualties may occur.
Facts
Temperatures in the lower troposphere have increased at somewhere between 0.12 and 0.22 °C per decade since 1979. Over the past 1-2 thousand years before 1850 the temperature has been relatively stable, with various (possibly local) fluctuations, such as the Medieval Warm Period or the Little Ice Age. Over the past century or so the global (land and sea) temperature has increased by approximately 0.6 ± 0.2°C . At the same time, atmospheric carbon dioxide has increased from around 280 parts per million in 1800 to around 315 in 1958 and 367 in 2000. Other greenhouse gas emissions have also increased.
Climate models, driven by estimates of increasing carbon dioxide and to a lesser extent by generally decreasing sulfate aerosols, predict that temperatures will increase (with a range of 1.4°C to 5.8°C for change between 1990 and 2100). Much of this uncertainty results from not knowing future CO2 emissions, but there is also uncertainty about the accuracy of climate models. Climate commitment studies predict that even if levels of greenhouse gases and solar activity were to remain constant, the global climate is committed to 0.5°C of warming over the next one hundred years due to the lag in warming caused by the oceans.
Sudden release of methane clathrate (a greenhouse gas) has been hypothesized as a cause of past global warming. Two events possibly linked in this way are the Permian-Triassic extinction event and the Paleocene-Eocene Thermal Maximum. However, warming at the end of the last ice age is thought to not be due to clathrate release.
Causes
The climate system varies both through natural, "internal" processes as well as in response to variations in external "forcing" from both human and non-human causes, including changes in the Earth's orbit around the Sun (Milankovitch cycles), solar activity, and volcanic emissions as well as greenhouse gases.
The scientific consensus is that a significant proportion of this past rise, particularly in the last 25-50 years, is due to humanity's emission of greenhouse gases such as carbon dioxide (CO2). This consensus is summarized by the findings of the Intergovernmental Panel on Climate Change (IPCC). In the Third Assessment Report, the IPCC concluded that "most of the warming observed over the last 50 years is attributable to human activities".
Although the scientific consensus is clear on the general conclusions - enough to persuade the governments of more than 140 countries to ratify the Kyoto Protocol - there are issues about just how much greenhouse gas emissions warm the planet. The uncertainties have in the past been exploited by politicians, corporations, and others with vested interests in opposing the activities needed to mitigate global warming; however, business opinion is increasingly changing to accept global warming as real and that action is needed. The scientific consensus is otherwise opposed by only a small minority of scientists.
Carbon dioxide during the last 400,000 years and the rapid rise since the Industrial Revolution.
Coal-burning power plants, automobile exhausts, factory smokestacks, and other waste vents of the human environment contribute about 22 billion tons of carbon dioxide and other greenhouse gases into the earth's atmosphere each year. About half of human emissions has remained in the atmosphere.
The atmospheric concentration of CO2 has increased by 31% above pre-industrial levels since 1750. This is considerably higher than at any time during the last 420,000 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 40 million years ago.
About three-quarters of the anthropogenic emissions of CO2 to the atmosphere during the past 20 years is due to fossil fuel burning. The rest is predominantly due to land-use change, especially deforestation. In particular, the change in climate forcing from greenhouse gases since 1750 was estimated to be 8 times larger than the change in forcing due to increasing solar activity over the same period.
Effects
The predicted effects of global warming are many and various, both for the environment and for human life. The primary effect (indeed, the primary symptom) of global warming is increasing carbon dioxide and increasing global average temperature. From this flow a variety of secondary effects, including sea level rise, impacts on agriculture, reductions in the ozone layer (see below), increased extreme weather, and the spread of disease. In some cases, the effects may already be being experienced, although it is generally difficult to attribute specific natural phenomena to long-term global warming.
Oceans
Sea level rise
With increasing average global temperature, the water in the oceans expands in volume, and additional water enters them which had previously been locked up on land in glaciers and the polar ice caps. Although no definite predictions exist as to the exact magnitude, timing and distribution of sea level rise, most estimates foresee that an increase of 1.5-4.5°C will lead to an increase of 15 – 95cm (IPCC 2001).
The sea level has risen more than 120 metres since the peak of the last ice age about 18,000 years ago. The bulk of that occurred before 6000 years ago. From 3000 years ago to the start of the 19th century sea level was almost constant, rising at 0.1-0.2 mm/y; since 1900 the level has risen at 1-3 mm/y ; since 1992 satellite altimetry from TOPEX/Poseidon indicates a rate of about 3 mm/y.. If ice caps in Greenland and Antarctica melt, the Greenland ice sheet would raise sea levels by more than 20ft, the West Antarctic ice sheet by another 15ft.
Some countries will be more affected than others - low-lying countries such as Bangladesh and the Netherlands will be worst hit by any sea level rise, in terms of floods or the cost of preventing them.
Temperature rise
The temperature of the Antarctic Southern Ocean rose by 0.17°C between the 1950s and the 1980s, nearly twice the rate for the world's oceans as a whole. As well as effects on ecosystems (eg by melting sea ice, affecting algae that grow on its underside), warming could reduce the ocean's ability to absorb CO2.
Acidification
The world’s oceans soak up much of the carbon dioxide produced by living organisms, either as dissolved gas, or in the skeletons of tiny marine creatures that fall to the bottom to become chalk or limestone.
But in water, carbon dioxide becomes a weak carbonic acid, and "the increase in the greenhouse gas since the industrial revolution has already altered the average pH - the laboratory measure of acidity - significantly and will go on doing so for at least 100 years."
There are concerns that increasing acidification could have a particularly detrimental effect on corals (16% of the world's coral reefs have died from bleaching since 1998) and other marine organisms with calcium carbonate shells. Increased acidity may also directly affect the growth and reproduction of fish as well as the plankton on which they rely on for food. Scientists warn that the chemistry of the oceans is changing in ways unprecedented for 20 million years. Some predict that the world's coral reefs will die within 35 years.
Destabilization of ocean currents
There is some speculation that global warming could trigger localized cooling in the North Atlantic and lead to cooling, or lesser warming, in that region, affecting in particular areas like Scandinavia and Britain that are warmed by the North Atlantic drift. Professor Mike Schlesinger, of the University of Illinois, reported that the shutdown of the Gulf Stream, once seen as a "low probability event", was now 45 per cent likely this century, and 70 per cent probable by 2200. If it comes sooner rather than later it will be catastrophic for Britain and northern Europe, giving us a climate like Labrador (which shares our latitude) even as the rest of the world heats up: if it comes later it could be beneficial, moderating the worst of the warming.
Heat is transported from the equator polewards mostly by the atmosphere but also by ocean currents, with warm water near the surface and cold water at deeper levels. The best known segment of this Thermohaline circulation (THC) is the Gulf Stream. Warm water from the Carribean is transported to the North Atlantic, where its effect in warming the atmosphere contributes to warming Europe. The evaporation of ocean water in the North Atlantic increases the salinity (relative saltiness) of the water as well as cooling it, both actions increasing the density of water at the surface. The formation of sea ice further increases the salinity. This dense water then sinks and the circulation stream continues in a southerly direction. Global warming could lead to an increase in freshwater in the northern oceans, by melting glaciers in Greenland and by increasing precipitation.
A recent movie describes such a scenario. The Gulf Stream is no longer transporting warm water to Europe, the tropics get hotter and hotter, and the poles colder and colder. In a series of massive thunderstorms, the atmosphere flips over, and increasingly cold stratospheric air is drawn down to the earth's surface, creating a low-pressure system that produces hundreds of feet of snow. Temperatures in Canada drop 100 degrees in an hour. Just about everyone north of Washington, D.C., dies. The following summer, the ice melts and a continental flood ensues. Hurricanes hit Belfast. San Francisco Bay freezes. Hailstones the size of canned hams bomb Tokyo.
More extreme weather
As the climate grows warmer, evaporation will increase. This will cause heavier rainfall and more erosion, and in more vulnerable tropical areas (especially in Africa), desertification. Many scientists think that it could result in more extreme weather as global warming progresses.
The IPCC Third Annual Report says: "...global average water vapour concentration and precipitation are projected to increase during the 21st century. By the second half of the 21st century, it is likely that precipitation will have increased over northern mid- to high latitudes and Antarctica in winter. At low latitudes there are both regional increases and decreases over land areas. Larger year to year variations in precipitation are very likely over most areas where an increase in mean precipitation is projected".
Water scarcity
Sea level rises threaten to contaminate groundwater, affecting drinking water and agriculture in coastal zones. Increased evaporation will reduce the effectiveness of reservoirs. Increased extreme weather means more water falls on hardened ground unable to absorb it - leading to flash floods instead of a replenishment of soil moisture or groundwater levels. In some areas, shrinking glaciers threaten the water supply.
Higher temperatures will also increase the demand for water for cooling purposes.
In the Sahel, there has been on average a 25 per cent decrease in annual rainfall over the past 30 years.
Natural catastrophes
According to one study, 35–40% of the worst catastrophes have been climate change related (ERM, 2002). Over the past three decades, the proportion of the global population affected by weather-related disasters has doubled in linear trend, rising from roughly 2% in 1975 to 4% in 2001.(ERM, 2002).
The total surface area of glaciers worldwide has decreased by 50% since the end of the 19th century. As of March 2005, the snow cap that has covered the top of Mount Kilimanjaro for the past 11,000 years since the last ice age has almost disappeared [18]. The loss of glaciers not only directly causes landslides, flash floods and glacial lake overflow, but also increases annual variation in water flows in rivers. Glaciers retain water on mountains in high precipitation years, since the snow cover accumulating on glaciers protects the ice from melting. In warmer and drier years, glaciers offset the lower precipitation amounts with a higher meltwater input.
Hurricanes were thought to be an entirely north Atlantic phenomenon. In April 2004, the first Atlantic hurricane to form south of the Equator hit Brazil with 90 mph winds; monitoring systems may have to be extended 1000 miles further south. Precipitation hitting the US from hurricanes increased by 7% over the twentieth century. Hurricanes, typhoons and violent storms proliferate, grow even fiercer, and hit new areas. The storms gather their energy from warm seas, and so, as oceans heat up, fiercer ones occur and threaten areas where at present the seas are too cool for such weather
Forests face an increased risk of forest fires which could release vast amounts of carbon dioxide to speed global warming. The 10-year average of boreal forest burned in North America, after several decades of around 2.5 million acres, has increased steadily since 1970 to more than 7 million acres annually. Britain's Met Office predicted in 1999 that much of the Amazon will dry out and die within 50 years, making it ready for sparks - from humans or lightning - to set it ablaze.
Reduced ozone layer
One of the lesser-known effects of global warming is a reduction in the thickness of the ozone layer, which protects life on Earth from harmful radiation. Global warming appears to be partially countering the improvements in the ozone layer caused by the reduction in the use of ozone-destroying chemicals achieved through the Montreal Protocol. "What appears to have caused the further loss of ozone is the increasing number of stratospheric clouds in the winter, 15 miles above the earth. These clouds, in the middle of the ozone layer, provide a platform which makes it easier for rapid chemical reactions which destroy ozone to take place."
The ecological impact may have further knock-on effects, as it reduces photosynthesis in plants (with potential impacts on agriculture) and damages the DNA of plankton, which play a significant role in the world's carbon cycle.
Environmental
Secondary evidence of global warming — lessened snow cover, rising sea levels, weather changes — provides examples of consequences of global warming that may influence not only human activities but also ecosystems. Increasing global temperature means that ecosystems may change; some species may be forced out of their habitats (possibly to extinction) because of changing conditions, while others may flourish. Few of the terrestrial ecoregions on Earth could expect to be unaffected.
Rising temperatures are beginning to impact on ecosystems. Butterflies have shifted their ranges northward by 200 km in Europe and North America. Plants lag behind, and larger animals' migration is slowed down by cities and highways. In the Arctic, the waters of Hudson Bay are ice-free for three weeks longer than they were thirty years ago, affecting polar bears, which do not hunt on land.
For some time it was hoped that a positive effect of global warming would be increased agricultural yields, because of the role of CO2 in photosynthesis.
Whilst local benefits may be felt in some regions (such as Siberia or Iceland), recent evidence is that global yields will be negatively affected. "Rising atmospheric temperatures, longer droughts and side-effects of both, such as higher levels of ground-level ozone gas, are likely to bring about a substantial reduction in crop yields in the coming decades. Moreover, a balmier planet could also assist the spread of infectious disease by providing a more suitable climate for parasites and spreading the range of tropical pathogens. That could include crop diseases which, combined with substantial climate shifts, might cause famine. Effects could be even more dramatic
Migration
Some Pacific Ocean island nations, such as Tuvalu, are concerned about the possibility of an eventual evacuation, as flood defense may become economically unviable for them. Tuvalu already has an ad hoc agreement with New Zealand to allow phased relocation.
In the 1990s a variety of estimates placed the number of environmental refugees at around 25 million. (Environmental refugees are not included in the official definition of refugees, which only includes migrants fleeing persecution.) The Intergovernmental Panel on Climate Change (IPCC), which advises the world’s governments under the auspices of the UN, estimated that 150 million environmental refugees will exist in the year 2050, due mainly to the effects of coastal flooding, shoreline erosion and agricultural disruption. (150 million means 1.5 percent of 2050’s predicted 10 billion world population.
Health
Rising temperatures have two opposing direct effects on mortality: higher temperatures in winter reduce deaths from cold; higher temperatures in summer increase heat-related deaths.
In August 2003 a heatwave in Europe killed 22-35,000 people, based on normal mortality rates (Schär and Jendritzky, 2004). It can be said with 90% confidence that past human influence on climate was responsible for at least half the risk of the 2003 European summer heat-wave (Stott et al 2004).
If average temperatures increase by 1 degree C, there will be an estimated 24,000 additional murders in the US each year (as the additional heat stress leads to more frequent rage). (New Scientist 11/5/02, review of Body Heat by Mark Blumberg.)
It has been claimed that global warming will probably extend the favorable zones for vectors conveying infectious disease such as malaria. However, it has been pointed out that despite the disappearance of infectious disease most temperate regions, the indigenous mosquitoes that transmitted it were never eliminated and remain common in some areas. Thus, although temperature is important in the transmission dynamics of malaria, many other variables are of equal or greater importance.
In poorer countries, this may simply lead to higher incidence of such diseases. In richer countries, where such diseases have been eliminated or kept in check by vaccination, draining swamps and using pesticides, the consequences may be felt more in economic than health terms, if greater spending on preventative measures is required.
A reduced ozone layer has negative impacts on human health - notably skin cancer and eye problems such as cataracts. However, the net effect of the thinning of the ozone layer on human health may be positive. Research by Dr. Edward Giovannucci, a Harvard University professor of medicine and nutrition who gave a keynote lecture at a recent American Association for Cancer Research, suggests that vitamin D might help prevent 30 deaths for each one caused by skin cancer. Vitamin D is nicknamed the "sunshine vitamin" because the skin makes it from ultraviolet rays.
Strategies
Contrarily to other Apocalypse causes, we have the power to slow global warming and amend human activities that release heat-trapping gases and particles into the air. The most important of these activities are the burning of fossil fuels (coal, gas, oil) and deforestation. To reduce the emission of heat-trapping gases such as carbon dioxide, methane, and nitrous oxides, we can curb our consumption of fossil fuels, use technologies that reduce emissions wherever possible, and protect the world’s forests.
The world's primary international agreement on combating climate change is the Kyoto Protocol. Various other strategies include development of new technologies, renewable energy, electric cars (and hybrids), and fuel cells, Energy conservation, carbon taxes and carbon sequestration schemes.
Economists stressed there is little time for delay. If action is put off for a decade, it will need to be twice as radical; if it has to wait 20 years, it will cost between three and seven times as much.
The good news is that it can be done with existing technology, by cutting energy waste, expanding the use of renewable sources, growing trees and crops (which remove carbon dioxide from the air) to turn into fuel, capturing the gas before it is released from power stations.
The better news is that it would not cost much: one estimate suggested the cost would be about 1 per cent of Europe's GNP spread over 20 years; another suggested it meant postponing an expected fivefold increase in world wealth by just two years. Many experts believe combating global warming would increase prosperity, by bringing in new technologies.
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