Talk:Effects of global warming/temp
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[edit] Expected effects
Global warming is expected to influence both the natural environment and human life. Some anticipated effects include sea level rise, repercussions to agriculture, reductions in the ozone layer, increased intensity and frequency of extreme weather events, and the spread of disease. In some cases, the effects may already be manifest, although it is difficult to attribute specific incidents of natural phenomena to long-term global warming. Since the mid-1970s, the total annual power of hurricanes has increased markedly because their average intensity and duration have increased; in addition, there has been a high correlation of hurricane power with tropical sea-surface temperature[1][1]. In spite of such strong evidence, the relationship between global warming and hurricanes is still being debated. [2][3] A draft statement by the World Meteorological Organization acknowledges the differing viewpoints on this issue [4].
The extent and probability of these consequences is a matter of considerable uncertainty. A summary of probable effects and recent understanding can be found in the report of the IPCC Working Group II [5].
[edit] Effects on ecosystems
Both primary and secondary effects of global warming — such as higher temperatures, lessened snow cover, rising sea levels and weather changes — may influence not only human activities, but also ecosystems. Some species may be forced out of their habitats (possibly to extinction) because of changing conditions, while others may flourish. Similarly, changes in timing of life patterns, such as annual migration dates, may alter regional predator-prey balance. The effect of advanced spring arrival dates in Scandinavia on birds that over winter in sub-Saharan Africa has been ascribed to evolutionary adaptation of the species to climatic warming [6].
Ocean pH is lowering as a result of increased carbon dioxide levels. Lowering of ocean pH, along with changing water temperature and ocean depth will have a damaging effect on coral reefs.
Another suggested mechanism whereby a warming trend may be amplified involves the thawing of tundra, which can release significant amounts of the potent greenhouse gas, methane, which is trapped in permafrost and ice clathrate compounds [7].
There are also ecological effects of melting polar ice: for example, polar bears use sea ice to reach their prey and they must swim to another ice floe when one breaks up. Ice is now becoming further separated and dead polar bears have been found in the water, believed to have drowned[8]. More recently, some scientists have suggested that the observed cannibalistic behavior in polar bears may be the result of food shortages brought on by global warming (Amstrup et al. 2006).
[edit] Effect on glaciers
Global warming has led to negative glacier mass balance, causing glacier retreat around the world. Oerlemans (2005) showed a net decline in 142 of the 144 mountain glaciers with records from 1900 to 1980. Since 1980 global glacier retreat has increased significantly. Similarly, Dyurgerov and Meier (2005) averaged glacier data across large-scale regions (e.g. Europe) and found that every region had a net decline from 1960 to 2002, though a few local regions (e.g. Scandinavia) have shown increases. Some glaciers that are in disequilibrium with present climate have already disappeared [9] and increasing temperatures are expected to cause continued retreat in the majority of alpine glaciers around the world. Upwards of 90% of glaciers reported to the World Glacier Monitoring Service have retreated since 1995 [10].
Of particular concern is the potential for failure of the Hindu Kush and Himalayan glacial melts. The melt of these glaciers is a large and reliable source of water for China, India, and much of Asia, and these waters form a principal dry-season water source. Increased melting would cause greater flow for several decades, after which "some areas of the most populated region on Earth are likely to 'run out of water'" (T. P. Barnett, J. C. Adam and D. P. Lettenmaier 2005) [11]
[edit] Miniature rock glaciers
Rock glaciers — caches of ice under boulders — are among other water signs such as drying meadows and warming lakes that scientists are studying in the Sierras in the western United States [12]. Connie Millar searches for the rock glaciers in the Yosemite area of the Sierra crest. She hypothesizes that rock glaciers will be predictors of how ecosystems change with rising temperatures. Millar is leading an effort (the Consortium for Integrated Climate Research in Western Mountains [13]) to co-ordinate the work of many scientists to see how the pieces of the Global Warming puzzle may fit.
[edit] Destabilization of ocean currents
There is also some speculation that global warming could, via a shutdown or slowdown of the thermohaline circulation, trigger localized cooling in the North Atlantic and lead to cooling, or lesser warming, in that region. This would affect in particular areas of northern Europe that are warmed by the North Atlantic drift.
[edit] Sea level rise and environmental refugees
Rising global temperatures will melt glaciers and expand the water of the seas through the mechanism of thermal expansion, leading to sea level rise. Even a relatively small rise in sea level would make some densely settled coastal plains uninhabitable and create a significant refugee problem. If the sea level were to rise in excess of 4 meters (13 ft) almost every coastal city in the world would be severely affected, with the potential for major damage to world-wide trade and economy. Presently, the IPCC predicts sea level rise is most probable to be just short of half a metre, and at least between 9 and 88 cm through 2100 [14] - but they also warn that global warming during that time may lead to irreversible changes in the Earth's glacial system and ultimately melt enough ice to raise sea level many meters over the next millennia. It is estimated that around 200 million people could be affected by sea level rise, especially in archipelagos such as the Caribbean, Macronesia, Micronesia, Polynesia, and in low altitude nations such as Vietnam, Bangladesh, China, India, Thailand, Philippines, Indonesia, Nigeria, and Egypt.
An example of the ambiguity of the concept of environmental refugees is the emigration from the island nation of Tuvalu, which has an average elevation of approximately one meter above sea level. Tuvalu already has an ad hoc agreement with New Zealand to allow phased relocation [15] and many residents have been leaving the islands. However, it is far from clear that rising sea levels from global warming are a substantial factor - best estimates are that sea level has been rising there at approximately 1–2 millimeters per year (~1/16th in/yr), but that shorter timescale factors—ENSO, or tides—have far larger temporary effects [16] [17] [18] [19].
[edit] Spread of disease
One of the largest known outbreaks of Vibrio parahaemolyticus gastroenteritis has been attributed to generally rising ocean temperature where infected oysters were harvested in Prince William Sound, Alaska in 2005. Before this, the northernmost reported risk of such infection was in British Columbia, 1000 km to the south (McLaughlin JB, et al.).
Global warming may extend the range of vectors conveying infectious diseases such as malaria. A warmer environment boosts the reproduction rate of mosquitoes and the number of blood meals they take, prolongs their breeding season, and shortens the maturation period for the microbes they disperse [20]. Global warming has been implicated in the recent spread to the north Mediterranean region of bluetongue disease in domesticated ruminants associated with mite bites (Purse, 2005). Hantavirus infection, Crimean-Congo hemorrhagic fever, tularemia and rabies increased in wide areas of Russia during 2004–2005. This was associated with a population explosion of rodents and their predators but may be partially blamed on breakdowns in governmental vaccination and rodent control programs.[21] Similarly, despite the disappearance of malaria in 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 factors are influential [22].
[edit] Financial effects
Financial institutions, including the world's two largest insurance companies, Munich Re and Swiss Re, warned in a 2002 study (UNEP summary) that "the increasing frequency of severe climatic events, coupled with social trends" could cost almost US$150 billion each year in the next decade. These costs would, through increased costs related to insurance and disaster relief, burden customers, taxpayers, and industry alike.
According to the Association of British Insurers, limiting carbon emissions could avoid 80% of the projected additional annual cost of tropical cyclones by the 2080s. According to Choi and Fisher (2003) each 1% increase in annual precipitation could enlarge catastrophe loss by as much as 2.8%.
The United Nations' Environmental Program recently announced that severe weather around the world has made 2005 the most costly year on record [23]. Although there is "no way to prove that [a given hurricane] either was, or was not, affected by global warming" [24], global warming is thought to increase the probability of hurricanes emerging. Preliminary estimates presented by the German insurance foundation Munich Re put the economic losses at more than US$200 billion, with insured losses running at more than US$70 billion.
Nicholas Stern in the Stern Review has warned that one percent of global GDP is required to be invested in order to mitigate the effects of climate change, and that failure to do so could risk a recession worth up to twenty percent of global GDP [25]. Stern’s report[2] suggests that climate change threatens to be the greatest and widest-ranging market failure ever seen. The report has had significant political effects: Australia reported two days after the report was released that they would allott AU$60 million to projects to help cut greenhouse gas emissions[26]. Tony Blair said the Stern Review showed that scientific evidence of global warming was "overwhelming" and its consequences "disastrous"[27].
[edit] Biomass production
The creation of biomass by plants is influenced by the availability of water, nutrients, and carbon dioxide. Part of this biomass is used (directly or indirectly) as the energy source for nearly all other life forms, including feed-stock for domestic animals, and fruits and grains for human consumption. It also includes timber for construction purposes.
While it's thought that an increase in carbon dioxide levels should speed up plant growth, which would slow down the effects of global warming, a new study has found the opposite to be true. Scientists at Stanford have found that "elevated atmospheric carbon dioxide actually reduces plant growth when combined with other likely consequences of climate change -- namely, higher temperatures, increased precipitation or increased nitrogen deposits in the soil." [28]. A rising temperature can also increase the growing season in colder regions. It is sometimes argued that these effects can create a greener, richer planet, with more available biomass. However, there are many other factors involved, and it is currently unclear if plants really benefit from global warming. Plant growth can be limited by a number of factors, including soil fertility, water, temperature, and carbon dioxide concentration. Ocean plants (phytoplankton) are actually harmed by global warming, presumably with negative impact on ocean ecosystems [29].
IPCC models currently predict a possible modest increase in plant productivity. However, there are several negative ramifications: decreases in productivity may occur at above-optimal temperatures; greater variation in temperature is likely to decrease wheat yields; in experiments, grain and forage quality declines if CO2 and temperature are increased; and the reductions in soil moisture in summer, which are likely to occur, would have a negative effect on productivity. [30]
Satellite data show that the productivity of the northern hemisphere did indeed increase from 1982 to 1991 [31]. However, more recent studies [32][33] found that from 1991 to 2002, widespread droughts had actually caused a decrease in summer photosynthesis in the mid and high latitudes of the northern hemisphere.
[edit] Opening up of the Northwest Passage in summer
Melting Arctic ice may open the Northwest Passage in summer in approximately ten years, which would cut 5,000 nautical miles (9,300 km) from shipping routes between Europe and Asia. This would be of particular relevance for supertankers that are too big to fit through the Suez Canal and currently have to go around the southern tip of Africa. According to the Canadian Ice Service, the amount of ice in Canada's eastern Arctic Archipelago decreased by 15% between 1969 and 2004 [34][35]. A similar opening is possible in the Arctic north of Siberia, allowing much faster East Asian to Europe transport.
[edit] Further global warming (positive feedback)
Some effects of global warming themselves contribute directly to further global warming, in a vicious circle, the nature of which may be difficult to predict in advance.
- Methane clathrates (frozen methane-water deposits on the ocean floor) might thaw and release more methane into the atmosphere (the clathrate gun hypothesis).
- The melting of permafrost and ice caps appears to be causing the release of large amounts of additional carbon dioxide or methane from decaying vegetation trapped beneath [36] [37] [38].
- There have been predictions, and some evidence, that global warming might cause loss of carbon from terrestrial ecosystems, leading to an increase of atmospheric CO2 levels [39] [40]
- Melting could also lead to increased heat absorption because ice reflects more solar radiation (i.e., it has higher albedo) than land or water. Because sea ice and seasonal snow cover are more reflective than the underlying sea, any meltback may lead to further warming.
- Warmer temperatures in the oceans reduce the productivity (growth) of ocean phytoplankton (algae). This is expected to reduce the amount of carbon dioxide taken up by photosynthesis in the ocean [41][42], which would again increase the effects of anthropogenic CO2 releases on the overall amount of CO2 in the atmosphere, and hence increase the greenhouse effect. This is a concern because ocean photosynthesis is as large a part of the planet's overall carbon balance as land photosynthesis.
