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Effects of global warming

2007 Schools Wikipedia Selection. Related subjects: Climate and the Weather;
Natural Disasters

   Conceptual assessment of the risks and impacts of global warming
   according to the Intergovernmental Panel on Climate Change and how
   those risks increase relative to increasing global temperatures. Bars
   at the left hand side indicate projections and estimated uncertainties
   associated with the range of possible climate scenarios.
   Enlarge
   Conceptual assessment of the risks and impacts of global warming
   according to the Intergovernmental Panel on Climate Change and how
   those risks increase relative to increasing global temperatures. Bars
   at the left hand side indicate projections and estimated uncertainties
   associated with the range of possible climate scenarios.

   The predicted effects of global warming for the environment and for
   human life are numerous and varied. The main effect is an increasing
   global average temperature. From this flow a variety of resulting
   effects, namely, rising sea levels, altered patterns of agriculture,
   increased extreme weather events, and the expansion of the range of
   tropical diseases. In some cases, the effects may already be occurring,
   although it is generally difficult to attribute specific natural
   phenomena to long-term global warming.

   The extent and likelihood of these consequences is a matter of
   considerable political controversy; and in the details, a matter of
   some scientific uncertainty. A summary of possible effects and our
   current understanding can be found in the report of the IPCC Working
   Group II ; a discussion of projected climate changes is found in WG I .

   Proposed responses to the effects of global warming fall into two
   categories: mitigation and adaptation.

Effects of Global Warming

   Projected climate changes due to global warming have the potential to
   lead to future large-scale and possibly irreversible changes in our
   climate resulting in impacts at continental and global scales.

   Examples of projected climate changes include:
     * significant slowing of the ocean circulation that transports warm
       water to the North Atlantic,
     * large reductions in the Greenland and West Antarctic Ice Sheets,
     * accelerated global warming due to carbon cycle feedbacks in the
       terrestrial biosphere, and
     * releases of terrestrial carbon from permafrost regions and methane
       from hydrates in coastal sediments.

   The likelihood of many of these changes is uncertain. However, the
   probability of one or more of these changes occurring is likely to
   increase with the rate, magnitude, and duration of climate change.

   The effects of global warming are not uniformly negative. Global
   warming will lead to climate change which will have positive benefits
   in some regions and negative effects in others. Scientists are unable
   to accurately predict when various effects of global warming will occur
   or what the magnitude of the effect will be.

   For this reason, it is not possible to be certain whether the positive
   benefits will outweigh the negative impacts. What is known is that some
   significant negative impacts are projected and these drive most of the
   concern about global warming and motivates attempts to mitigate or
   adapt to the effects of global warming.

   Most of the consequences of global warming would result from one of
   three physical changes: sea level rise, higher local temperatures, and
   changes in rainfall patterns (Figure 1). Sea level is generally
   expected to rise 50-200 cm in the next century (Dean et al. 1987); such
   a rise would inundate 7,000 square miles of dry land in the United
   States (an area the size of Massachusetts) and a similar amount of
   coastal wetlands; erode recreational beaches 100-200 meters, exacerbate
   coastal flooding; and increase the salinity of aquifers and estuaries
   (Titus 1989).

Effects on weather

   Increasing temperature is likely to lead to increasing precipitation
   but the effects on storms are less clear. Extratropical storms partly
   depend on the temperature gradient, which is predicted to weaken in the
   northern hemisphere as the polar region warms more than the rest of the
   hemisphere .

More extreme weather

   This image shows the conclusions of Knutson and Tuleya (2004) that
   maximum intensity reached by tropical storms is likely to undergo a
   moderate increase in a world affecting by substantial global warming,
   with a significant increase in the number of highly destructive
   category 5 storms.
   Enlarge
   This image shows the conclusions of Knutson and Tuleya (2004) that
   maximum intensity reached by tropical storms is likely to undergo a
   moderate increase in a world affecting by substantial global warming,
   with a significant increase in the number of highly destructive
   category 5 storms.

   The Intergovernmental Panel on Climate Change ( IPCC) Third Assessment
   Report "Climate Change 2001" stated that (at that time) "there is no
   compelling evidence to indicate that the characteristics of tropical
   and extratropical storms have changed." There is, however, limited
   evidence from a relatively short time period that storm strength is
   increasing, such as the Emanuel (2005) "power dissipation index" of
   hurricane intensity . Worldwide, the proportion of hurricanes reaching
   categories 4 or 5 – with wind speeds above 56 metres per second – has
   risen from 20% in the 1970s to 35% in the 1990s. Precipitation hitting
   the US from hurricanes increased by 7% over the twentieth century . See
   also Time Magazine's "Global Warming: The Culprit?" and . (The extent
   to which this is due to global warming as opposed to the Atlantic
   Multidecadal Oscillation is unclear.)

   The World Meteorological Organization has suggested a possible link
   between global warming and increasing extreme weather events, as have
   Hoyos et al. (2006), writing, "the increasing ... number of category 4
   and 5 hurricanes ... is directly linked to" increasing temperatures.
   Hurricane modeling has produced similar results, e.g., "hurricanes,
   simulated under warmer, high-CO[2] conditions, are more intense ...
   than under present-day conditions.... greenhouse gas–induced warming
   may lead to ... increasing ... occurrence of highly destructive
   category-5 storms." A paper by 14 scientists notes that "research shows
   very little evidence to support the claim that the rising costs
   associated with weather ... are associated with changes in [their]
   frequency or intensity." The IPCC TAR, in 2001, made no strong
   statements on the issue.

   A substantially higher risk of extreme weather does not necessarily
   mean a noticeably greater risk of slightly-above-average weather .
   However, the evidence is clear that severe weather and moderate
   rainfall are also increasing.

   Stephen Mwakifwamba, national co-ordinator of the Centre for Energy,
   Environment, Science and Technology - which prepared the Tanzanian
   government's climate change report to the UN - says that change is
   happening in Tanzania right now. "In the past, we had a drought about
   every 10 years", he says. "Now we just don't know when they will come.
   They are more frequent, but then so are floods. The climate is far less
   predictable. We might have floods in May or droughts every three years.
   Upland areas, which were never affected by mosquitoes, now are. Water
   levels are decreasing every day. The rains come at the wrong time for
   farmers and it is leading to many problems" .

   Greg Holland, director of the Mesoscale and Microscale Meteorology
   Division at the National Centre for Atmospheric Research in Boulder,
   Colorado, said on April 24, 2006, "The hurricanes we are seeing are
   indeed a direct result of climate change," and that the wind and warmer
   water conditions that fuel storms that form in the Caribbean are,
   "increasingly due to greenhouse gases. There seems to be no other
   conclusion you can logically draw." Holland said, "The large bulk of
   the scientific community say what we are seeing now is linked directly
   to greenhouse gases." (See also "Global warming?" in tropical cyclone)

Increased evaporation

   Increasing water vapor at Boulder, Colorado.
   Enlarge
   Increasing water vapor at Boulder, Colorado.

   Over the course of the 20th century, evaporation rates have reduced
   worldwide ; this is thought by many to be explained by global dimming.
   As the climate grows warmer and the causes of global dimming are
   reduced, evaporation will increase. This may cause heavier rainfall and
   more erosion, and in more vulnerable tropical areas (especially in
   Africa), desertification due to deforestation. 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" .

Cost of more extreme weather

   The economic impact of extreme weather is rising rapidly both because
   of increases in the frequency and intensity of extreme weather and
   because of changes in human behavior. An example of how human behaviour
   has increased exposure to extreme weather is the movement towards
   greater development along vulnerable seacoasts. The economic impact of
   hurricanes has increased because there is more development along
   seacoasts vulnerable to hurricanes. Similarly, the economic impact of
   floods has increased because there is more development in floodplains.

   Choi and Fisher, writing in Climate Change, vol. 58 (2003) pp. 149,
   predict that each 1% increase in annual precipitation would enlarge the
   cost of catastrophic storms by 2.8%.

   The Association of British Insurers has stated that limiting carbon
   emissions would avoid 80% of the projected additional annual cost of
   tropical cyclones by the 2080s. The cost is also increasing partly
   because of building in exposed areas such as coasts and floodplains.
   The ABI claims that reduction of the vulnerability to some inevitable
   impacts of climate change, for example through more resilient buildings
   and improved ﬂood defences, could also result in considerable
   cost-savings in the longterm.

Destabilization of local climates

   The first recorded South Atlantic hurricane, "Catarina", which hit
   Brazil in 2004
   Enlarge
   The first recorded South Atlantic hurricane, "Catarina", which hit
   Brazil in 2004

   In the northern hemisphere, the southern part of the Arctic region
   (home to 4,000,000 people) has experienced a temperature rise 1° to 3
   °C over the last 50 years. Canada, Alaska and Russia are experiencing
   initial melting of permafrost. This may disrupt ecosystems and by
   increasing bacterial activity in the soil lead to these areas becoming
   carbon sources instead of carbon sinks . A study (published in Science)
   of changes to eastern Siberia's permafrost suggests that it is
   gradually disappearing in the southern regions, leading to the loss of
   nearly 11% of Siberia's nearly 11,000 lakes since 1971 . At the same
   time, western Siberia is at the initial stage where melting permafrost
   is creating new lakes, which will eventually start disappearing as in
   the east. Western Siberia is the world's largest peat bog, and the
   melting of its permafrost is likely to lead to the release, over
   decades, of large quantities of methane—creating an additional source
   of greenhouse gas emissions .

   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 40 m/s (144 km/h) winds; monitoring systems may have to
   be extended 1,600 km (1000 miles) further south .

Oceans

Sea level rise

   Sea level has been rising 0.2 cm/year, based on measurements of sea
   level rise from 23 long tide gauge records in geologically stable
   environments
   Enlarge
   Sea level has been rising 0.2 cm/year, based on measurements of sea
   level rise from 23 long tide gauge records in geologically stable
   environments

   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, for example, the
   Greenland and the Antarctic ice sheets. An increase of 1.5 to 4.5 °C is
   estimated to lead to an increase of 15 to 95 cm (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 to 0.2 mm/yr; since 1900, the
   level has risen at 1–2 mm/yr ; since 1992, satellite altimetry from
   TOPEX/Poseidon indicates a rate of about 3 mm/yr .

Temperature rise

   The temperature of the Antarctic Southern Ocean rose by 0.17 °C (0.31
   °F) 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 CO[2].

   More important for the United States may be the temperature rise in the
   Gulf of Mexico. As hurricanes cross the warm Loop Current coming up
   from South America, they can gain great strength in under a day (as did
   Hurricane Katrina and Hurricane Rita in 2005), with water above 85 °F
   seemingly promoting Category 5 storms. Hurricane season ends in
   November as the waters cool.

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.
   Oceans currently absorb about one metric tonne of CO[2] per person per
   year. It is estimated that the oceans have absorbed around half of all
   CO[2] generated by human activities since 1800 (120,000,000,000 tonnes
   or 120 petagrams of carbon) .

   But in water, carbon dioxide becomes a weak carbonic acid, and the
   increase in the greenhouse gas since the industrial revolution has
   already lowered the average pH (the laboratory measure of acidity) of
   seawater by 0.1 units on the 14-point scale, to 8.2. Predicted
   emissions could lower it by a further 0.5 by 2100, to a level not seen
   for millions of 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 for food .

Shutdown of thermohaline circulation

   There is some speculation that global warming could, via a shutdown or
   slowdown of the thermohaline circulation, trigger localised cooling in
   the North Atlantic and lead to cooling, or lesser warming, in that
   region. This would affect in particular areas like Scandinavia and
   Britain that are warmed by the North Atlantic drift. The chances of
   this occurring are unclear; there is some evidence for the stability of
   the Gulf Stream and possible weakening of the North Atlantic drift.
   There is, however, no evidence for cooling in northern Europe or nearby
   seas; quite the reverse.

Ecosystems

   Rising temperatures are beginning to have a noticeable impact on
   ecosystems. 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
   the 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. Many of the species at risk are arctic fauna such as polar
   bears, emperor penguins, many salt wetland flora and fauna species, and
   any species that inhabit the low land areas near the sea. Species that
   rely on cold weather conditions such as gyrfalcons, and snowy owls that
   prey on lemmings that use the cold winter to their advantage will be
   hit hard.

   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 Britain, spring butterflies are
   appearing an average of 6 days earlier than two decades ago . 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 .

   Two 2002 studies in Nature (vol 421) surveyed the scientific literature
   to find recent changes in range or seasonal behaviour by plant and
   animal species. Of species showing recent change, 4 out of 5 shifted
   their ranges towards the poles or higher altitudes, creating " refugee
   species". Frogs were breeding, flowers blossoming and birds migrating
   an average 2.3 days earlier each decade; butterflies, birds and plants
   moving towards the poles by 6.1 km per decade . A 2005 study concludes
   human activity is the cause of the temperature rise and resultant
   changing species behaviour, and links these effects with the
   predictions of climate models to provide validation for them . Grass
   has become established in Antarctica for the first time.

   Forests in some regions potentially face an increased risk of forest
   fires. The 10-year average of boreal forest burned in North America,
   after several decades of around 10,000 km² (2.5 million acres), has
   increased steadily since 1970 to more than 28,000 km² (7 million acres)
   annually. . This change may be due in part to changes in forest
   management practices.

Ecological productivity

   Increasing average temperature and carbon dioxide may have the effect,
   up to a point, of improving ecosystems' productivity. Atmospheric
   carbon dioxide is rare in comparison to oxygen (less than 1% of air
   compared to 21% of air). This carbon dioxide starvation becomes
   apparent in photorespiration, where there is so little carbon dioxide,
   that oxygen can enter a plant's chloroplasts and takes the place where
   carbon dioxide normally would be in the Calvin Cycle. This causes the
   sugars being made to be destroyed, badly suppressing growth. Satellite
   data shows that the productivity of the northern hemisphere has
   increased since 1982 (although attribution of this increase to a
   specific cause is difficult).

   IPCC models predict that higher CO[2] concentrations would only spur
   growth of flora up to a point, because in many regions the limiting
   factors are water or nutrients, not temperature or CO[2]; after that,
   greenhouse effects and warming would continue but there would be no
   compensatory increase in growth.

   Research done by the Swiss Canopy Crane Project suggests that
   slow-growing trees only are stimulated in growth for a short period
   under higher CO[2] levels, while faster growing plants like liana
   benefit in the long term. In general, but especially in rain forests,
   this means that liana become the prevalent species; and because they
   decompose much faster than trees their carbon content is more quickly
   returned to the atmosphere. Slow growing trees incorporate atmospheric
   carbon for decades.

Glacier Retreat

   A map of the change in thickness of mountain glaciers since 1970.
   Thinning in orange and red, thickening in blue.
   Enlarge
   A map of the change in thickness of mountain glaciers since 1970.
   Thinning in orange and red, thickening in blue.
   Lewis Glacier, North Cascades, WA USA is one of five glaciers in the
   area that melted away
   Enlarge
   Lewis Glacier, North Cascades, WA USA is one of five glaciers in the
   area that melted away

   In historic times, glaciers grew during the Little Ice Age, a cool
   period from about 1550 to 1850. Subsequently, until about 1940,
   glaciers around the world retreated as climate warmed. Glacier retreat
   declined and reversed, in many cases, from 1950 to 1980 as a slight
   global cooling occurred. Since 1980, glacier retreat has become
   increasingly rapid and ubiquitous, so much so that it has threatened
   the existence of many of the glaciers of the world. This process has
   increased markedly since 1995.

   Excepting the ice caps and ice sheets of the Arctic and Antarctic, the
   total surface area of glaciers worldwide has decreased by 50% since the
   end of the 19th century . Currently glacier retreat rates and mass
   balance losses have been increasing in the Andes, Alps, Himalaya's,
   Rocky Mountains and North Cascades. 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 .

   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. Glacier runoff declines in the summer as
   glaciers decrease in size, this decline is already observable in
   several regions . 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 .

   Of particular importance are the Hindu Kush and Himalayan glacial melts
   that comprise the principal dry-season water source of many of the
   major rivers of the South, East and Southeast Asian mainland. Increased
   melting would cause greater flow for several decades, after which "some
   areas of the most populated regions on Earth are likely to 'run out of
   water'" as source glaciers are depleted.

   The recession of mountain glaciers, notably in Western North America,
   Franz-Josef Land, Asia, the Alps, Indonesia and Africa, and tropical
   and sub-tropical regions of South America, has been used to provide
   qualitative support to the rise in global temperatures since the late
   19th century. Many glaciers are being lost to melting further raising
   concerns about future local water resources in these glacierized areas.
   The Lewis Glacier, North Cascades pictured at right after melting away
   in 1990 is one of the 47 North Cascade glaciers observed and all are
   retreating .

   Despite their proximity and importance to human populations, the
   mountain and valley glaciers of temperate latitudes amount to a small
   fraction of glacial ice on the earth. About 99% is in the great ice
   sheets of polar and subpolar Antarctica and Greenland. These continuous
   continental-scale ice sheets, 3 km (1.8 miles) or more in thickness,
   cap the polar and subpolar land masses. Like rivers flowing from an
   enormous lake, numerous outlet glaciers transport ice from the margins
   of the ice sheet to the ocean.

   Glacier retreat has been observed in these outlet glaciers, resulting
   in an increase of the ice flow rate. In Greenland the period since the
   year 2000 has brought retreat to several very large glaciers that had
   long been stable. Three glaciers that have been researched, Helheim,
   Jakobshavns and Kangerdlugssuaq Glaciers, jointly drain more than 16%
   of the Greenland Ice Sheet. Satellite images and aerial photographs
   from the 1950s and 1970s show that the front of the glacier had
   remained in the same place for decades. But in 2001 it began retreating
   rapidly, retreating 7.2 km (4.5 miles) between 2001 and 2005. It has
   also accelerated from 20 m (65 ft)/day to 32 m (104 ft)/day. Jakobshavn
   Isbræ in west Greenland is generally considered the fastest moving
   glacier in the world. It had been moving continuously at speeds of over
   24 m (78 ft)/day with a stable terminus since at least 1950. In 2002,
   the 12 km (7.5 mile) long floating terminus entered a phase of rapid
   retreat. The ice front started to break up and the floating terminus
   disintegrated accelerating to a retreat rate of over 30 m (98 ft)/day.
   The acceleration rate of retreat of Kangerdlugssuaq Glacier is even
   larger. Portions of the main trunk that were flowing at 15 m (49
   ft)/day in 1988-2001 were flowing at 40 m (131 ft)/day in summer 2005.
   The front of the glacier has also retreated and has rapidly thinned by
   more than 100 m (328 ft).

   Glacier retreat and acceleration is also apparent on two important
   outlet glaciers of the West Antarctic Ice Sheet. Pine Island Glacier,
   which flows into the Amundsen Sea thinned 3.5 ± 0.9 m (11.5 ± 3 ft) per
   year and retreated five kilometers (3.1 miles) in 3.8 years. The
   terminus of the glacier is a floating ice shelf and the point at which
   it is afloat is retreating 1.2 km/year. This glacier drains a
   substantial portion of the West Antarctic Ice Sheet and has been
   referred to as the weak underbelly of this ice sheet. This same pattern
   of thinning is evident on the neighboring Thwaites Glacier.

Further global warming ( positive feedback)

   Some effects of global warming themselves contribute directly to
   further global warming.

Methane release from melting permafrost peat bogs

   Climate scientists reported in August 2005 that a one million square
   kilometer region of permafrost peat bogs in western Siberia is starting
   to melt for the first time since it was formed 11,000 years ago at the
   end of the last ice age. This will release methane, an extremely
   effective greenhouse gas, possibly as much as 70,000 million tonnes,
   over the next few decades. An earlier report in May 2005 reported
   similar melting in eastern Siberia .

   This positive feedback was not known about in 2001 when the IPCC issued
   its last major report on climate change. The discovery of permafrost
   peat bogs melting in 2005 implies that warming is likely to happen
   faster than was predicted in 2001.

Methane release from hydrates

   Methane clathrate, also called methane hydrate, is a form of water ice
   that contains a large amount of methane within its crystal structure.
   Extremely large deposits of methane clathrate have been found under
   sediments on the ocean floors of Earth. The sudden release of large
   amounts of natural gas from methane clathrate deposits has been
   hypothesized as a cause of past and possibly future climate changes.
   The release of this trapped methane is a potential major outcome of a
   rise in temperature; it is thought that this might increase the global
   temperature by an additional 5° in itself, as methane is much more
   powerful as a greenhouse gas than carbon dioxide. The theory also
   predicts this will greatly affect available oxygen content of the
   atmophere. This theory has been proposed to explain the first mass
   extinction event on earth known as the Permian-Triassic extinction
   event.

Carbon cycle feedbacks

   There have been predictions, and some evidence, that global warming
   might cause loss of carbon from terrestrial ecosystems, leading to an
   increase of atmospheric CO[2] levels. Several climate models indicate
   that global warming through the 21st century could be accelerated by
   the response of the terrestrial carbon cycle to such warming . All 11
   models in the C4MIP study found that a larger fraction of anthropogenic
   CO2 will stay airborne if climate change is accounted for. By the end
   of the twenty-first century, this additional CO2 varied between 20 and
   200 ppm for the two extreme models, the majority of the models lying
   between 50 and 100 ppm. The higher CO2 levels led to an additional
   climate warming ranging between 0.1° and 1.5 °C. However, there was
   still a large uncertainty on the magnitude of these sensitivities.
   Eight models attributed most of the changes to the land, while three
   attributed it to the ocean . The strongest feedbacks in these cases are
   due to increased respiration of carbon from soils throughout the high
   latitude boreal forests of the Northern Hemisphere. One model in
   particular ( HadCM3) indicates a secondary carbon cycle feedback due to
   the loss of much of the Amazon rainforest in response to significantly
   reduced precipitation over tropical South America . While models
   disagree on the strength of any terrestrial carbon cycle feedback, they
   each suggest any such feedback would accelerate global warming.

   Observations show that soils in England have been losing carbon at the
   rate of four million tonnes a year for the past 25 years according to a
   paper in Nature by Bellamy et al. in September 2005, who note that
   these results are unlikely to be explained by land use changes. Results
   such as this rely on a dense sampling network and thus are not
   available on a global scale. Extrapolating to all of the United
   Kingdom, they estimate annual losses of 13 million tons per year. This
   is as much as the annual reductions in carbon dioxide emissions
   achieved by the UK under the Kyoto Treaty (12.7 million tons of carbon
   per year).

Forest Fires

   Rising Global temperature might cause forest fires to occur on larger
   scale, and more regularly. This releases more stored carbon into the
   atmosphere than the carbon cycle can naturally re-absorb, as well as
   reducing the overall forest area on the planet, creating a positive
   feedback loop. Part of that feedback loop is more rapid growth of
   replacement forests and a northward migration of forests as northern
   latitudes become more suitable climates for sustaining forests. There
   is a question of whether the burning of renewable fuels such as forests
   should be counted as contributing to global warming.

          ( Climate Change and Fire)
          ( Climate Roulette: Loss of Carbon Sinks & Positive Feedbacks)
          ( EPA: Global Warming: Impacts: Forests)
          ( Feedback Cycles linking forests, climate and landuse
          activities)

Retreat of Sea Ice

   The sea absorbs heat from the sun, while the ice largely reflects the
   sun rays back to space. Thus, retreating sea ice will allow the sun to
   warm the now exposed sea water, contributing to further warming. The
   mechanism is the same as when a black car heats up faster in sunlight
   than a white car. This albedo change is also the main reason why IPCC
   predict polar temperatures to rise up to twice as much as those of the
   rest of the world.

Negative feedback effects

   Following Le Chatelier's principle, the chemical equilibrium of the
   Earth's carbon cycle will shift in response to anthropogenic CO[2]
   emissions. The primary driver of this is the ocean, which absorbs
   anthropogenic CO[2] via the so-called solubility pump. At present this
   accounts for only about one third of the current emissions, but
   ultimately most (~75%) of the CO[2] emitted by human activities will
   dissolve in the ocean over a period of centuries (Archer, 2005; "A
   better approximation of the lifetime of fossil fuel CO[2] for public
   discussion might be 300 years, plus 25% that lasts forever"). However,
   the rate at which the ocean will take it up in the future is less
   certain, and will be affected by stratification induced by warming and,
   potentially, changes in the ocean's thermohaline circulation.

   Also, as temperature rises, the Earth's thermal radiation rises.

   The impact of these negative feedback effects in relation to the
   positive feedback effects are part of IPCC's global climate models.

Consequences

Economic

   In commenting overall economic effect of global warming in Copenhagen
   Consensus, Professor Robert O. Mendelsohn of Yale School of Forestry
   and Environmental Studies, stated that

          "A series of studies on the impacts of climate change have
          systematically shown that the older literature overestimated
          climate damages by failing to allow for adaptation and for
          climate benefits (see Fankhauser et al 1997; Mendelsohn and
          Newmann 1999; Tol 1999; Mendelsohn et al 2000; Mendelsohn
          2001;Maddison 2001; Tol 2002; Sohngen et al 2002; Pearce 2003;
          Mendelsohn and Williams 2004). These new studies imply that
          impacts depend heavily upon initial temperatures (latitude).
          Countries in the polar region are likely to receive large
          benefits from warming, countries in the mid-latitudes will at
          first benefit and only begin to be harmed if temperatures rise
          above 2.5C (Mendelsohn et al 2000). Only countries in the
          tropical and subtropical regions are likely to be harmed
          immediately by warming and be subject to the magnitudes of
          impacts first thought likely (Mendelsohn et al 2000). Summing
          these regional impacts across the globe implies that warming
          benefits and damages will likely offset each other until warming
          passes 2.5C and even then it will be far smaller on net than
          originally thought (Mendelsohn and Williams 2004)."

   In an October 29, 2006, Stern Review by the former Chief Economist and
   Senior Vice-President of the World Bank Nicholas Stern, he states that
   climate change could affect growth which could be cut by one-fifth
   unless drastic action is taken. (Report's stark warning on climate)

Decline of agriculture

   For some time it was hoped that a positive effect of global warming
   would be increased agricultural yields, because of the role of carbon
   dioxide in photosynthesis, especially in preventing photorespiration,
   which is responsible for significant destruction of several crops. In
   Iceland, rising temperatures have made possible the widespread sowing
   of barley, which was untenable twenty years ago. Some of the warming is
   due to a local (possibly temporary) effect via ocean currents from the
   Caribbean, which has also affected fish stocks .

   While local benefits may be felt in some regions (such as Siberia),
   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, large-scale experiments have shown" ( The Independent, April
   27, 2005, "Climate change poses threat to food supply, scientists say"
   - report on this event).

   Moreover, the region likely to be worst affected is Africa, both
   because its geography makes it particularly vulnerable, and because
   seventy per cent of the population rely on rain-fed agriculture for
   their livelihoods. Tanzania's official report on climate change
   suggests that the areas that usually get two rainfalls in the year will
   probably get more, and those that get only one rainy season will get
   far less. The net result is expected to be that 33% less maize—the
   country's staple crop—will be grown .

Insurance

   An industry very directly affected by the risks is the insurance
   industry; the number of major natural disasters has trebled since the
   1960s, and insured losses increased fifteen-fold in real terms
   (adjusted for inflation) . 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).

   A June 2004 report by the Association of British Insurers declared
   "Climate change is not a remote issue for future generations to deal
   with. It is, in various forms, here already, impacting on insurers'
   businesses now". It noted that weather risks for households and
   property were already increasing by 2-4 % per year due to changing
   weather, and that claims for storm and flood damages in the UK had
   doubled to over £6 billion over the period 1998–2003, compared to the
   previous five years. The results are rising insurance premiums, and the
   risk that in some areas flood risk insurance will become unaffordable
   for some.

   In the United States, insurance losses have also greatly increased, and
   according to one study those increases are mostly attributed to
   increased population and property values in vulnerable coastal areas,
   though there was also an increase in frequency of weather-related
   events like heavy rainfalls since the 1950s (Science, 284, 1943-1947).

Transport

   Roads, airport runways, railway lines and pipelines, (including oil
   pipelines, sewers, water mains etc) may require increased maintenance
   and renewal as they become subject to greater temperature variation,
   and, in areas with permafrost, subject to subsidence .

Flood defense

   For historical reasons to do with trade, many of the world's largest
   and most prosperous cities are on the coast, and the cost of building
   better coastal defenses (due to the rising sea level) is likely to be
   considerable. Some countries will be more affected than others -
   low-lying countries such as Bangladesh and the Netherlands would be
   worst hit by any sea level rise, in terms of floods or the cost of
   preventing them.

   In developing countries, the poorest often live on flood plains,
   because it is the only available space, or fertile agricultural land.
   These settlements often lack infrastructure such as dykes and early
   warning systems. Poorer communities also tend to lack the insurance,
   savings or access to credit needed to recover from disasters .

Migration

   Some Pacific Ocean island nations, such as Tuvalu, are concerned about
   the possibility of an eventual evacuation, as flood defense may become
   economically inviable 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% of 2050’s
   predicted 10 billion world population.)

Northwest Passage

   Melting Arctic ice may open the Northwest Passage in summer, which
   would cut 5,000 nautical miles (9,000 km) from shipping routes between
   Europe and Asia. This would be of particular relevance for supertankers
   which are too big to fit through the Panama Canal and currently have to
   go around the tip of South America. According the Canadian Ice Service,
   the amount of ice in Canada's eastern Arctic Archipelago decreased by
   15% between 1969 and 2004 .

   While the reduction of summer ice in the Arctic may be a boon to
   shipping, this same phenomenon threatens the Arctic ecosystem, most
   notably polar bears which depend on ice floes. Subsistence hunters such
   as the Inuit peoples will find their livelihoods and cultures
   increasingly threatened as the ecosystem changes due to global warming.

Development

   The combined effects of global warming may impact particularly harshly
   on people and countries without the resources to mitigate those
   effects. This may slow economic development and poverty reduction, and
   make it harder to achieve the Millennium Development Goals , .

   In October 2004 the Working Group on Climate Change and Development, a
   coalition of development and environment NGOs, issued a report Up in
   Smoke on the effects of climate change on development. This report, and
   the July 2005 report Africa - Up in Smoke? predicted increased hunger
   and disease due to decreased rainfall and severe weather events,
   particularly in Africa. These are likely to have severe impacts on
   development for those affected.

Environmental

   Secondary evidence of global warming — reduced 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.

   Increasing carbon dioxide may (up to a point) increase ecosystems'
   productivity; but the interaction with other aspects of climate change,
   means the environmental impact of this is unclear. An increase in the
   total amount of biomass produced is not necessarily all good, since
   biodiversity can still decrease even though a smaller number of species
   are flourishing.

Water scarcity

   Eustatic 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% decrease in annual
   rainfall over the past 30 years.

Health

Direct effects of temperature rise

   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. The distribution
   of these changes obviously differs. Palutikof et al calculate that in
   England and Wales for a 1 °C temperature rise the reduced deaths from
   cold outweigh the increased deaths from heat, resulting in a reduction
   in annual average mortality of 7000.

   The European heat wave of 2003 killed 22,000–35,000 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).

   The 2006 United States heat wave has killed 139 humans in California as
   of 29 July 2006. [Deaths of livestock have not been well-documented.]
   Fresno, in the central California valley, had six consecutive days of
   110 degree-plus Fahrenheit temperatures.

Spread of disease

   Global warming is expected to extend the favourable zones for vectors
   conveying infectious disease such as malaria . 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 .

Impacts of glacier retreat

   The continued retreat of glaciers will have a number of different
   impacts. In areas that are heavily dependent on water runoff from
   glaciers that melt during the warmer summer months, a continuation of
   the current retreat will eventually deplete the glacial ice and
   substantially reduce or eliminate runoff. A reduction in runoff will
   affect the ability to irrigate crops and will reduce summer stream
   flows necessary to keep dams and reservoirs replenished. This situation
   is particularly acute for irrigation in South America, where numerous
   artificial lakes are filled almost exclusively by glacial melt.^
   Central Asian countries have also been historically dependent on the
   seasonal glacier melt water for irrigation and drinking supplies. In
   Norway, the Alps, and the Pacific Northwest of North America, glacier
   runoff is important for hydropower.

   Many species of freshwater and saltwater plants and animals are
   dependent on glacier-fed waters to ensure a cold water habitat that
   they have adapted to. Some species of freshwater fish need cold water
   to survive and to reproduce, and this is especially true with Salmon
   and Cutthroat trout. Reduced glacier runoff can lead to insufficient
   stream flow to allow these species to thrive. Ocean krill, a
   cornerstone species, prefer cold water and are the primary food source
   for aquatic mammals such as the Sperm whale.^ Alterations to the ocean
   currents, due to increased freshwater inputs from glacier melt, and the
   potential alterations to thermohaline circulation of the worlds oceans,
   may impact existing fisheries upon which humans depend as well.

   The potential for major sea level rise is mostly dependent on a
   significant melting of the polar ice caps of Greenland and Antarctica,
   as this is where the vast majority of glacial ice is located. The
   British Antarctic Survey has determined from climate modeling that for
   at least the next 50 years, snowfall on the continent of Antarctica
   should continue to exceed glacial losses from global warming. The
   amount of glacial loss on the continent of Antarctica is not increasing
   significantly, and it is not known if the continent will experience a
   warming or a cooling trend, although the Antarctic Peninsula has warmed
   in recent years, causing glacier retreat in that region.^ If all the
   ice on the polar ice caps were to melt away, the oceans of the world
   would rise an estimated 70 m (229 ft). However, with little major melt
   expected in Antarctica, sea level rise of not more than 0.5 m (1.6 ft)
   is expected through the 21st century, with an average annual rise of
   0.0004 m (0.0013 ft) per year. Thermal expansion of the world's oceans
   will contribute, independent of glacial melt, enough to double those
   figures.^

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