Impacts of global Warming

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IMPAds From The phenomenon known as global warming include environmental, social, and economic effects. Environmental impacts include sea-level rise, melting of the polar ice caps, and an average increase in temperature. These impacts are documented in the reports of the Intergovernmental Panel for Climate Change (IPCC), which commissions reports by scientists worldwide on the issue of climate change. The IPCC Report of 2007 is the first one that reflects scientific consensus that global warming is underway, and that it is primarily human induced. For example, human activities, such as fossil fuel burning, land-use changes, agricultural activity, and the production and use of halocarbons are among the factors causing climate change. The economic report by Nicholas Stern in 2007 highlights that climate change has potentially disastrous consequences for humanity.

temperature variability

Perhaps best known, is that temperature variability, specifically temperature increase, will be one of the effects of climate change. While the range of projections relating to temperature rise varies, the IPCC scenarios, using a range of climate models, predict overall a rise in globally-averaged surface temperature of 2.5-10 degrees F (1.4 to 5.8 degrees C) 19902100. While at local and regional levels this figure will vary, at a global level it is roughly 2-10 times larger than the observed warming of the 20th century, and is unprecedented during at least the last 10,000 years, based on paleoclimatic data.

Changes in temperature and precipitation (rainfall) patterns have increased all around the world. In the

United States, average temperatures have increased by roughly 1 degree F (0.6 degrees C) during the past century, and precipitation has increased by five to 10 percent. Alaska has sustained an average temperature increase of 4-7 degrees F (2-4 degrees C) in just the past 50 years. Temperature increase has also had a number of related effects, such as the increased melting of the summer Arctic sea ice. Since 1979, more than 20 percent of the polar ice cap has melted in response to increased surface and ocean temperatures. The oceans are warming. Global ocean temperature has risen by 0.18 degrees F (0.10 degrees C) from the surface to a depth of (2,297 ft.) 700 m. 1961-2003.

WARMING of WATER masses

Key oceanic water masses are changing. Southern Ocean mode waters and Upper Circumpolar Deep Waters have warmed from the 1960s to about 2000. A similar, but weaker pattern of warming in the Gulf Stream and Kuroshio mode waters in the North Atlantic and North Pacific has been observed. Long-term cooling is observed in the North Atlantic subpolar gyre and in the central North Pacific.

sea-level rise

Another predicted effect of climate change is an increase in sea level. Sea-level rise is caused by thermal expansion of the oceans, melting of glaciers and ice caps, melting of the Greenland and Antarctic ice sheets, and changes in terrestrial storage. Changes in sea level will be felt through increases in intensity and frequency of storm surges and coastal flooding; increased salinity of rivers, bays, and coastal aquifers resulting from saline intrusion; increased coastal erosion; loss of important mangroves and other wetlands (the exact response will depend on the balance between sedimentation and sea-level change); and impact on marine ecosystems such as coral reefs.

Sea-level rise is accelerating worldwide. Globally, 100 million people live within about 3.3 ft. (1 m.) of present day sea level. Eight to 10 million people live within 3.3 ft. (1 m.) of high tide in each of the unprotected river deltas of Bangladesh, Egypt, and Vietnam. IPCC reports estimate that the global average sea level rose at an average rate of .07 in. (1.8 mm.) per year 1961-2003, and within that period, the rate of rise was faster 1993-2003, about 0.12 in. (3.1 mm.) per year. Overall, the IPCC concludes there is high confidence that the rate of observed sea level rise has risen from the 19th to the 20th century. The total 20th century rise is estimated to be 0.55 ft. (0.17 m.) In 2001, IPCC projections were for a sea-level rise of between 3.5-34.6 in. (9-88 cm.) 1990-2100 and a global average surface temperature rise of between 2.5-10.4 degrees F (1.4 and 5.8 degrees C.). In 2007, IPCC projections based on different scenarios predict seal level rise from 0.01 to up to 0.02 in. (.18-.59 mm.) by 2099.

Toward the end of the 21st century, projected sea-level rise will affect low-lying coastal areas with large populations. The cost of adaptation could amount to at least five to 10 percent of Gross Domestic Product. Mangroves and coral reefs are projected to degrade further, with additional consequences for fisheries and tourism. Snowmelt runoff as a result of seal level rise will have major consequences. For example, one change will be a change from spring peak flows to late winter peaks in snowmelt-dominated regions. Many species, both aquatic and riparian (riverine) have evolved to take opportunity of the spring flows

Temperature increase has had a number of related effects, such as the increased melting of the summer Arctic sea ice.

as a result of snowmelt. For example, some fish time their reproduction strategies specifically to avoid the stress of springtime flows. Changes in springtime flow regimes, or high winter flows associated with rain or snow events, can scour streambeds and destroy eggs. Trees that provide riparian habitat along rivers may find it harder to reproduce as they depend on high spring flows. Many species, such as salmon, already under pressure from other environmental impacts, will be further impacted by climate change. For example, higher temperatures and a reduced stream flow in the Columbia River Basin may be increasing the mortality of juvenile coho salmon; in some cases increased temperatures may be creating thermal barriers for the migration of adult salmon.

There are a number of associated events that are a result of climate change and will also have impacts on sea-level rise. For example, the Kangerdlugssuaq Glacier in Greenland is moving much faster, melting at a rate of 8.7 mi. (14 km.) a year in comparison to just 3.2 mi. (5 km.) a year in 1988. This loss will also have serious implications for sea-level rise, with some scientists predicting that within the next 100 years, ice cover in this region will completely disappear over summer and that species living within it, such as polar bears, will be threatened. The complete melting of the Greenland Ice Sheet and the West Antarctic Ice Sheet would lead to a contribution to sea-level rise of up to 23 ft. (7 m.) and about 16 ft. (5 m.), respectively.

INCIDENCE AND SEVERITY OF STORMS

Increased incidence and frequency ofstorms is another predicted effect of climate change. For example, since 1996, the number of named tropical storms in the North Atlantic per year has increased by 40 percent, a figure considered extreme in the 1950s. Some research indicates that there is a link between higher sea-surface temperatures and storm frequency. Researchers have found that 1970-2004, warmer sea-surface temperature has been the major factor in the increase in category 4 and 5 hurricanes globally. Scientists have also shown that there is a strong correlation between sea temperature and annual hurricane power in three different hurricane basins in the North Atlantic, and two in the Pacific. Hurricane Katrina and the tsunami in Southeast Asia are both examples of the increased frequency and intensity of natural events that result from climate change.

ATMOSPHERIC COMPOSITION

Another effect of climate change is changes in atmospheric composition. It is possible to measure these changes, as the composition of air, prior to industrialization, is known from testing air bubbles frozen in ice cores from Antarctica. Since pre-industrial times, the concentration of CO2 within the atmosphere has risen from about 270-280 parts per million by volume (ppm) to over 360 ppm today. Moreover, CH4 has risen from about 700 parts per billion by volume (ppb) to over 1700 ppb, and N2O has increased from about 270 ppb to over 310 ppb. Halocarbons, substances that are not naturally present in the atmosphere, are now present in large amounts.

This is important because changes within the atmosphere have disrupted the total energy budget of the planet. The balance between incoming, solar shortwave radiation, and the outgoing long-wave radiations has upset the normal radiative balance. This change is called radiative forcing. The Earth's response to this phenomenon is to try to restore the balance by warming the lower atmosphere. In so doing, the surface temperature of the planet increases.

ECOLOGICAL SYSTEMS

Ecological systems are changing, upset, and modified as a result of climate change. About 20-30 percent of plant and animal species assessed so far are likely to be at increased risk of extinction if increases in global average temperature exceed 2.7-4.5 degrees F (1.52.5 degrees C). Significant loss of biodiversity is projected to occur by 2020 in some ecologically rich sites, including the Great Barrier Reef and Queensland Wet Tropics. Other sites at risk include the Kakadu wetlands, southwest Australia, sub-Antarctic islands, and the alpine areas of both countries. In Latin America, by mid-century, increases in temperature and associated decreases in ground water are projected to lead to gradual replacement of tropical forest by savanna in eastern Amazonia. Semi-arid vegetation will tend to be replaced by arid-land vegetation. There is a risk of significant biodiversity loss through species extinction in many areas of tropical Latin America.

A typical example of the effect of climate change is the coral reef ecosystem. Coral bleaching, resulting from the breakdown of the symbiotic relationship between corals and unicellular algae (zooxanthellae), is often caused by the warming of sea temperatures.

Reef coral are very sensitive to temperatures outside of their acceptable range; a rise of just 1 degree above long-term averages is enough to cause coral stress and bleaching. If these temperatures exceed average levels for a long period of time, the reef system will collapse. The mass bleaching events reported on the Great Barrier Reef and elsewhere around the world over the last five to 10 years have been triggered primarily by anomalously high water temperatures. Increased levels of CO2 in the sea also affect the acidity of the ocean's surface water, and, hence, reduce the amount of dissolved carbon carbonate for reef-building corals.

The extent of ecological consequences will partly dependent on the extent of temperature change and water availability from precipitation and runoff in any given location, but ultimately, ecological changes will occur across the planet. For example, in North America and Australia, parts of these continents will become wetter and others drier, with variability in precipitation events causing unpredictability in runoff patterns and changes to ecological systems. Many species are dependent on, or live within, specific temperature ranges; thus, a change in temperature, for example, their extremity, duration, and seasonality will have a correlative affect on rates of growth and reproduction. For animals, such as turtles, cassowaries, or salmon, all of which reproduce at certain temperatures (and produce certain sexes within certain temperature ranges), variation in thermal regimes will have significant effects. Some species may be able to adapt and shift the geographic ranges of their distribution, but for many, the effects of temperature change will be catastrophic as the areas they live in become unsuitable and uninhabitable.

Increased air temperatures will also effect wetland, estuarine, and marine species. For example, a warming of water temperatures by 7 degrees F (4 degrees C) in present-day ecosystems would represent a northward latitudinal shift in thermal regimes of about 422 mi. (680 km.), which will have major ramifications for aquatic ecosystems. Moreover, enrichment of soils as by CO2 will alter species composition in some wetlands.

Climate change will also alter the hydrological regimes of rivers and lakes through changes in water flows. Reductions in the frequency or intensity of high flows that normally inundate flood plains may dry out wetlands, and cause ecological changes from wetland to terrestrial-adapted species. Water tables will rise in areas that become wetter and vice versa, changing species composition in many areas. For example, a reduction in the frequency or magnitude of high flows that inundate the floodplain would tend to dry out floodplain wetlands, isolate them from the adjacent stream or river, and replace wetland plant species with more terrestrially adapted species.

SOCIETAL IMPACTS

Climate change will have major effects on humanity. For example, global climate change and sea-level rise can influence coastal fisheries in a number of ways. Approximately 70 percent of the U.S. fisheries' catch is derived from estuarine-dependent species, and their young are dependent on suitable habitat. Rising sea levels that lead to destruction of coastal wetlands can have direct negative consequences for coastal fisheries. More indirect effects could result from wetland loss that leads to shoreline erosion, which, by adding fine sediments to the water column, would reduce water clarity and, thus, interfere with feeding ability. Many shellfish species also use coastal wetlands as an important habitat and are vulnerable to wetland loss caused by sea-level rise.

There will be a diverse range of socioeconomic costs arising from weather damage and vulnerability to climate change. The Stern Report concludes that the economic cost of global warming without action, using conservative scientific estimates for change, will be the equivalent of losing at least 5 percent of global gross domestic product (GDP) per year. Nicholas Stern notes that if little action is taken and a wider range of predictions is considered, then the costs to the global economy will be up to 20 percent of the world's GDP or more.

Socioeconomic systems will be affected by the increase in floods, and droughts. Projections confirm that many countries will experience decreased yields to their crop productivity, especially in areas projected to receive lower rainfall. Climate change will significantly affect those living in the Pacific. In the 1990s, for example, the Pacific Island region sustained costs of up to $1 billion from climate-related incidents.

For many African regions, warmer and drier conditions have led to a reduced length of growing season, with detrimental effects on crops. At lower latitudes, especially in seasonally dry and tropical regions, crop productivity is projected to decrease for even small local temperature increases 1.8-3.6 degrees F (1-2 degrees C), which would increase risk of hunger. In some countries, yields from rain-fed agriculture could be reduced by up to 50 percent by 2020.

Water shortages will put increased pressure on forestry and agriculture. By mid-century, annual average river runoff and water availability are projected to increase by 10-40 percent at high latitudes and in some wet tropical areas, and decrease by 10-30 percent in some dry regions at mid-latitudes and in the dry tropics, some of which are already water-stressed areas. For example, in Africa By 2020, 75-250 million people are projected to experience an increase in water stress from climate change. If coupled with increased demand, this will adversely affect livelihoods and exacerbate water-related problems. In the course of the century, water supplies stored in glaciers and snow cover are projected to decline, reducing water availability in regions supplied by melt water from major mountain ranges, where more than one-sixth of the world population currently lives. Freshwater availability in central, south, east, and southeast Asia, particularly in large river basins, is projected to decrease because of climate changes that, along with population growth and increasing demand arising from higher standards of living, could adversely affect more than a billion people by the 2050s.

Much livestock will find it hard to adapt to the physiological effects associated with climate change, and there are projected increases in pest infestations associated with climate extremes. Projections also show that a warming of the world's temperature by a few degrees will result in a global increase in food prices.

Climate change will also have impacts on human health. For example, people will experience higher heat stress, and loss of life in floods and storms. Heat-related mortality will increase. There will also be a range of direct impacts on disease through increased range of vectors such as mosquitoes. Projected climate change-related exposures are likely to affect the health status of millions of people, particularly those with low adaptive capacity. These indluce increases in malnutrition and consequent disorders, with implications for child growth and development; increased deaths, disease, and injury due to heat waves, floods, storms, fires and droughts; the increased burden of diarrheal disease; the increased frequency of cardio-respiratory diseases due to higher concentrations of ground level ozone related to climate change; and the altered spatial distribution of some infectious disease vectors.

The impacts of climate change will fall disproportionately on developing countries that do not have the economic or social resilience to adapt quickly enough to the effects they will experience. For example, the effects of sea-level rise will affect many Pacific Island nations who will be displaced by coastal flooding and erosion. In Bangladesh, up to 90 percent of the country consists of low-lying land. The effects of climate change on Bangladesh and other countries will be major, displacing millions, and potentially causing a worldwide environmental refugee crisis. Researchers estimate that up to 50 million people worldwide will become environmental refugees by 2010, due to rising sea-level rise, intense and more frequent storms, inundation, and other climate change-induced effects. Ongoing coastal development and population growth in areas such as Cairns and Southeast Queensland (Australia) and Northland to Bay of Plenty (New Zealand) are projected to exacerbate risks from sea-level rise and increases in the severity and frequency of storms and coastal flooding by 2050.

The Working Group 1 Fourth Assessment Report, 2007 has concluded that, of the more than 29,000 observational data series seven, from 75 studies that show significant change in many physical and biological systems, more than 89 percent are consistent with the direction of change expected as a response to warming. Importantly, both past and future anthropogenic CO2 emissions will continue to contribute to warming and sea-level rise for more than a millennium, due to the timescales required for removal of this gas from the atmosphere.

sEE ALso: Diseases; Ecosystems; Floods; Global Warming; Hurricanes and Typhoons; Oceanic Changes; Sea Level, Rising.

BIBLIoGRAPHY. Kevin Baumert, et al., Climate Data: Insight and Observations (Pew Center on Global Climate Change, 2004); Intergovernmental Panel on Climate Change (IPPC), Climate Change 2001: The Third Assessment Report of the Intergovernmental Panel on Climate Change (Cambridge University Press, 2001); IPCC, Working Group II Contribution to the Intergovernmental Panel on Climate Change

Fourth Assessment Report Climate Change 2007: Climate Change Impacts, Adaptation and Vulnerability (IPPC, 2007); W. Mitchell, et al., Sea Level Rise in Australia and the Pacific. Pacific Islands Conference on Climate Change, Climate Variability and Sea Level Change (Rarotonga, Cook Islands, April 2000); S. Solomon, et al., Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Cambridge University Press, 2007); Nicholas Stern, Stern Review on the Economics of Climate Change (HM Treasury, 2007).

Melissa Nursey-Bray Australian Maritime College Rob Palmer Research Strategy Training

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