CLIMATE CHANGE
http://en.wikipedia.org/wiki/Climate_change
Climate change factors
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Climate changes reflect variations within the Earth's atmosphere, processes in other parts of the Earth such as oceans and ice caps, and the effects of human activity. The external factors that can shape climate are often called climate forcings and include such processes as variations in solar radiation, the Earth's orbit, and greenhouse gas concentrations.
Variations within the Earth's climate
Weather is the day-to-day state of the atmosphere, and is a chaotic non-linear dynamical system. On the other hand, climate — the average state of weather — is fairly stable and predictable. Climate includes the average temperature, amount of precipitation, days of sunlight, and other variables that might be measured at any given site. However, there are also changes within the Earth's environment that can affect the climate.
Glaciation
Percentage of advancing glaciers in the Alps in the last 80 years
Glaciers are recognized as being among the most sensitive indicators of climate change, advancing substantially during climate cooling (e.g. the Little Ice Age) and retreating during climate warming on moderate time scales. Glaciers grow and collapse, both contributing to natural variability and greatly amplifying externally forced changes. For the last century, however, glaciers have been unable to regenerate enough ice during the winters to make up for the ice lost during the summer months (see glacier retreat).
The most significant climate processes of the last several million years are the glacial and interglacial cycles of the present ice age.[citation needed] Though shaped by orbital variations, the internal responses involving continental ice sheets and 130 m sea-level change certainly played a key role in deciding what climate response would be observed in most regions. Other changes, including Heinrich events, Dansgaard–Oeschger events and the Younger Dryas show the potential for glacial variations to influence climate even in the absence of specific orbital changes.
Ocean variability
A schematic of modern thermohaline circulation
On the scale of decades, climate changes can also result from interaction of the atmosphere and oceans. Many climate fluctuations — including not only the El Niño Southern oscillation (the best known) but also the Pacific decadal oscillation, the North Atlantic oscillation, and the Arctic oscillation — owe their existence at least in part to different ways that heat can be stored in the oceans and move between different reservoirs. On longer time scales ocean processes such as thermohaline circulation play a key role in redistributing heat, and can dramatically affect climate.
The memory of climate
More generally, most forms of internal variability in the climate system can be recognized as a form of hysteresis, meaning that the current state of climate reflects not only the inputs, but also the history of how it got there. For example, a decade of dry conditions may cause lakes to shrink, plains to dry up and deserts to expand. In turn, these conditions may lead to less rainfall in the following years. In short, climate change can be a self-perpetuating process because different aspects of the environment respond at different rates and in different ways to the fluctuations that inevitably occur.[citation needed]
Non-climate factors driving climate change
Effects of CO2 on climate change
Main article: Greenhouse gas
Carbon dioxide variations during the last 500 million years
Current studies indicate that radiative forcing by greenhouse gases is the primary cause of global warming. Greenhouse gases are also important in understanding Earth's climate history. According to these studies, the greenhouse effect, which is the warming produced as greenhouse gases trap heat, plays a key role in regulating Earth's temperature.
Over the last 600 million years, carbon dioxide concentrations have varied from perhaps >5000 ppm to less than 200 ppm, due primarily to the effect of geological processes and biological innovations. Royer et al.[1] have used the CO2-climate correlation to derive a value for the climate sensitivity. There are several examples of rapid changes in the concentrations of greenhouse gases in the Earth's atmosphere that do appear to correlate to strong warming, including the Paleocene–Eocene thermal maximum, the Permian–Triassic extinction event, and the end of the Varangian snowball earth event.
During the modern era, the naturally rising carbon dioxide levels are implicated as the primary cause of global warming since 1950. According to the Intergovernmental Panel on Climate Change (IPCC), 2007, the atmospheric concentration of CO2 in 2005 was 379 ppm³ compared to the pre-industrial levels of 280 ppm³. Thermodynamics and Le Chatelier's principle explain the characteristics of the dynamic equilibrium of a gas in solution such as the vast amount of CO2 held in solution in the world's oceans moving into and returning from the atmosphere. These principles can be observed as bubbles which rise in a pot of water heated on a stove, or in a glass of cold beer allowed to sit at room temperature; gases dissolved in liquids are released under certain circumstances.
STUDENTS ARE WELCOME to send additional categories to CEEI’s climate 1000 list. Papers are also
accepted. Post papers to the CEEI web site at www.eco-pedia.org) and send your links.and new info
News of school clubs, projects successes etc. New technical papers suitable for the class room are OK. Scientific format or composition format are OK. Send to CEEI (www.eco-pedia.org). SEE ALL OTHER MAJOR CLIMATE CATEGORIES There are almost 1000 topics in this web site alone.
CLIMATE CHANGE IS A VAST SUBJECT. THE PLANET AND THE PEOPLE IN IT are still trying to define it, and understand its impacts, power, and potential. Since much is still to be learned and the future knowledge is locked into the schools and universities, this entire on going study will only succeed if the teachers and their students realize they can lean a lot ( information is no longer scarce) .The potential synergy is huge; all students be they future scientists, journalism students, lawyers, builders, teachers, everyone. Teachers do carry the heavy load..
The potential for a virtual class is possible because of the student papers can be published on the CEEI
www.eco-pedia.org that may reach 30,000, 300,000 or even 3 million more students. Think about that ! Your teachers will have a big responsibility.
Right now the Inuit tribes in the Arctic areas are wondering if the US govt will move their homes or do they just find another place to live. but where ? If it was'nt for them, the scientists found out early about the glacier ice and permafrost melting ! Lots of local and state info is missing and need research and assessment. Students can learn by doing and make an important contribution.. All Climate is local.
For example. right now the ship Knorr is research tracking the N Atlantic ( gulf stream) current. It is now partially diverted just south of Iceland east and heading directly toward the Med ! (The thawing Greenland icecap is causing this change in direction of the N Atlantic current. (CEEI is waiting for Woods Hole Oceanographers to make some educated sense of it.)
Keep in mind if this current is changing, the climate might drastically change with no warning ! Greenland is losing huge amounts of thawing ice (Mammoths have been found still frozen that are 12,000 years old !). We should not be complacent, but watch what is happening, and pay attention to the climate scientists. !
Read "Follow the Water" by Dallas Murphy. The author describes all the ocean currents and how they cool the planet by recirculating and ridding the planet of heat. A good read and is in paperback ! He talks about how all the currents were discovered and why they are so important. Science believes they play a part in generating the weather. Ask any Florida or New Orleans person. You would'nt get an argument !
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Effects of global warming
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This article may be too long to read and navigate comfortably. Please consider splitting content into sub-articles and using this article for a summary of the key points of the subject. (March 2009)
Graphical description of risks and impacts from global warming from the Third Assessment Report of the Intergovernmental Panel on Climate Change. Later revisions to this work suggest significantly increased risks.[1]
The effects of global warming and climate change[2] are of concern both for the environment and human life. Evidence of observed climate change includes the instrumental temperature record, rising sea levels, and decreased snow cover in the Northern Hemisphere.[3] According to the IPCC Fourth Assessment Report, "[most] of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in [human greenhouse gas] concentrations". It is predicted that future climate changes will include further global warming (i.e., an upward trend in global mean temperature), sea level rise, and a probable increase in the frequency of some extreme weather events. Ecosystems are seen as being particularly vulnerable to climate change. Human systems are seen as being variable in their capacity to adapt to future climate change.[4] To reduce the risk of large changes in future climate, many countries have implemented policies designed to reduce their emissions of greenhouse gases.
Contents
[hide]
* 1 Overview
* 2 Physical impacts
o 2.1 Effects on weather
+ 2.1.1 Extreme weather
+ 2.1.2 Increased evaporation
+ 2.1.3 Cost of more extreme weather
+ 2.1.4 Local climate change
o 2.2 Glacier retreat and disappearance
o 2.3 Oceans
+ 2.3.1 Sea level rise
+ 2.3.2 Temperature rise
+ 2.3.3 Acidification
+ 2.3.4 Shutdown of thermohaline circulation
+ 2.3.5 Oxygen depletion
* 3 Positive feedback effects
o 3.1 Methane release from melting permafrost peat bogs
o 3.2 Methane release from hydrates
o 3.3 Carbon cycle feedbacks
o 3.4 Forest fires
o 3.5 Retreat of sea ice
o 3.6 Effect on sulfur aerosols
* 4 Negative feedback effects
* 5 Other consequences
o 5.1 Economic and social
+ 5.1.1 Insurance
+ 5.1.2 Transport
+ 5.1.3 Effects on agriculture
# 5.1.3.1 Food
# 5.1.3.2 Distribution of impacts
+ 5.1.4 Coasts and low-lying areas
+ 5.1.5 Migration
+ 5.1.6 Northwest Passage
+ 5.1.7 Development
o 5.2 Ecosystems
+ 5.2.1 Forests
+ 5.2.2 Mountains
+ 5.2.3 Ecological productivity
o 5.3 Water scarcity
o 5.4 Health
+ 5.4.1 Direct effects of temperature rise
+ 5.4.2 Spread of disease
+ 5.4.3 Children
o 5.5 Security
* 6 See also
* 7 Notes
* 8 External links
Overview
Global mean surface temperature difference from the average for 1961–1990
Mean surface temperature change for the period 1999 to 2008 relative to the average temperatures from 1940 to 1980
Over the last hundred years or so, the instrumental temperature record has shown a trend in climate of increased global mean temperature, i.e., global warming. Other observed changes include Arctic shrinkage, Arctic methane release, releases of terrestrial carbon from permafrost regions and Arctic methane release in coastal sediments, and sea level rise.[5][6] Global average temperature is predicted to increase over this century, with a probable increase in frequency of some extreme weather events, and changes in rainfall patterns. Moving from global to regional scales, there is increased uncertainty over how climate will change. The probability of warming having unforeseen consequences increases with the rate, magnitude, and duration of climate change.[7] Some of the physical impacts of climate change are irreversible at continental and global scales.[8] Sea level is expected to rise 18 to 59 cm (7.1 to 23.2 inches) by the end of the 21st century. Due to a lack of scientific understanding, this sea level rise estimate does not include all of the possible contributions of ice sheets.[3] Slowing of the Meridional Overturning Circulation is very likely to occur this century, but temperatures in the Atlantic and Europe will probably still be higher due to global warming.[4] For a global warming of 1-4°C (relative to 1990-2000), there is a moderate chance that partial deglaciation of the Greenland ice sheet would occur over a period of centuries to millennia. Including the possible contribution of partial deglaciation of the West Antarctic Ice Sheet, sea level would rise by 4–6 m or more.[4]
The impacts on human systems of climate change will probably be distributed unevenly. Some regions and sectors are expected to experience benefits while others will experience costs. With greater levels of warming (greater than 2-3°C, relative to 1990 levels), it is likely that benefits will decline and costs increase.[4] Low-latitude and less-developed areas are probably at the greatest risk from climate change. With human systems, adaptation potential for climate change impacts is considerable, although the costs of adaptation are largely unknown and potentially large.[9] Climate change will likely result in reduced diversity of ecosystems and the extinction of many species. Adaptation potential for biological and geophysical systems is estimated to be lower than that for human systems.
Physical impacts
Effects on weather
Increasing temperature is likely to lead to increasing precipitation [10][11] 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.[12]
Extreme weather
Main article: Extreme weather
See also: Tropical cyclone#Global warming and List of Atlantic hurricane records
Global warming may be responsible in part for some trends in natural disasters such as extreme weather.
Based on future projections of climate change, the IPCC report makes a number of predictions.[3] It is predicted that over most land areas, the frequency of warm spells/heat waves will very likely increase. It is likely that:
* Increased areas will be affected by drought
* There will be increased intense tropical cyclone activity
* There will be increased incidences of extreme high sea level (excluding tsunamis)
Storm strength leading to extreme weather is increasing, such as the power dissipation index of hurricane intensity.[13] Kerry Emanuel writes that hurricane power dissipation is highly correlated with temperature, reflecting global warming.[14] However, a further study by Emanuel using current model output concluded that the increase in power dissipation in recent decades cannot be completely attributed to global warming.[15] Hurricane modeling has produced similar results, finding that hurricanes, simulated under warmer, high-CO2 conditions, are more intense, however, hurricane frequency will be reduced.[16] 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.[17] Precipitation hitting the US from hurricanes has increased by 7% over the twentieth century.[18][19][20] The extent to which this is due to global warming as opposed to the Atlantic Multidecadal Oscillation is unclear. Some studies have found that the increase in sea surface temperature may be offset by an increase in wind shear, leading to little or no change in hurricane activity.[21] Hoyos et al. (2006) have linked the increasing trend in number of category 4 and 5 hurricanes for the period 1970-2004 directly to the trend in sea surface temperatures.[22]
Increases in catastrophes resulting from extreme weather are mainly caused by increasing population densities, and anticipated future increases are similarly dominated by societal change rather than climate change.[23] The World Meteorological Organization explains that “though there is evidence both for and against the existence of a detectable anthropogenic signal in the tropical cyclone climate record to date, no firm conclusion can be made on this point.”[24] They also clarified that “no individual tropical cyclone can be directly attributed to climate change.”[24]
Thomas Knutson and Robert E. Tuleya of NOAA stated in 2004 that warming induced by greenhouse gas may lead to increasing occurrence of highly destructive category-5 storms.[25] In 2008, Knutson et al. found that Atlantic hurricane and tropical storm frequencies could reduce under future greenhouse-gas-induced warming.[26] Vecchi and Soden find that wind shear, the increase of which acts to inhibit tropical cyclones, also changes in model-projections of global warming. There are projected increases of wind shear in the tropical Atlantic and East Pacific associated with the deceleration of the Walker circulation, as well as decreases of wind shear in the western and central Pacific.[27] The study does not make claims about the net effect on Atlantic and East Pacific hurricanes of the warming and moistening atmospheres, and the model-projected increases in Atlantic wind shear.[28]
A substantially higher risk of extreme weather does not necessarily mean a noticeably greater risk of slightly-above-average weather.[29] However, the evidence is clear that severe weather and moderate rainfall are also increasing. Increases in temperature are expected to produce more intense convection over land and a higher frequency of the most severe storms.[30]
Increased evaporation
Increasing water vapor at Boulder, Colorado.
Over the course of the 20th century, evaporation rates have reduced worldwide [31]; 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 due to warmer oceans. Because the world is a closed system this will cause heavier rainfall, with more erosion. This erosion, in turn, can in vulnerable tropical areas (especially in Africa) lead to desertification. On the other hand, in other areas, increased rainfall lead to growth of forests in dry desert areas.
Scientists have found evidence that increased evaporation could result in more extreme weather as global warming progresses. The IPCC Third Annual Report says: "...global average water vapor 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."[10][32]
Cost of more extreme weather
See also: List_of_costliest_Atlantic_hurricanes
As the World Meteorological Organization explains, “recent increase in societal impact from tropical cyclones has largely been caused by rising concentrations of population and infrastructure in coastal regions.”[24] Pielke et al. (2008) normalized mainland U.S. hurricane damage from 1900–2005 to 2005 values and found no remaining trend of increasing absolute damage. The 1970s and 1980s were notable because of the extremely low amounts of damage compared to other decades. The decade 1996–2005 has the second most damage among the past 11 decades, with only the decade 1926–1935 surpassing its costs. The most damaging single storm is the 1926 Miami hurricane, with $157 billion of normalized damage.[23]
The American Insurance Journal predicted that “catastrophe losses should be expected to double roughly every 10 years because of increases in construction costs, increases in the number of structures and changes in their characteristics.”[33] 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 effects of climate change, for example through more resilient buildings and improved flood defences, could also result in considerable cost-savings in the longterm.[34]
Local climate change
Main article: Regional effects of global warming
The first recorded South Atlantic hurricane, "Catarina", which hit Brazil in March 2004
In the northern hemisphere, the southern part of the Arctic region (home to 4,000,000 people) has experienced a temperature rise of 1 °C to 3 °C (1.8 °F to 5.4 °F) 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.[35] 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.[36] 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. Furthermore, permafrost melting will eventually cause methane release from melting permafrost peat bogs.
Prior to March 2004, no tropical cyclone had been observed in the South Atlantic Ocean. The first Atlantic cyclone to form south of the equator hit Brazil on March 28, 2004 with 40 m/s (144 km/h) winds, although some Brazilian meteorologists deny that it was a hurricane.[37] Monitoring systems may have to be extended 1,600 km (1,000 miles) further south. There is no agreement as to whether this hurricane is linked to climate change,[38][39] but one climate model exhibits increased tropical cyclone genesis in the South Atlantic under global warming by the end of the 21st century.[40]
Glacier retreat and disappearance
Main article: Retreat of glaciers since 1850
A map of the change in thickness of mountain glaciers since 1970. Thinning in orange and red, thickening in blue.
In historic times, glaciers grew during a cool period from about 1550 to 1850 known as the Little Ice Age. Subsequently, until about 1940, glaciers around the world retreated as the 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, and has threatened the existence of many of the glaciers of the world. This process has increased markedly since 1995.[41]
Excluding 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.[42] Currently glacier retreat rates and mass balance losses have been increasing in the Andes, Alps, Pyrenees, Himalayas, Rocky Mountains and North Cascades.
The loss of glaciers not only directly causes landslides, flash floods and glacial lake overflow,[43] 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.[44] 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.[42]
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 Central, 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.[45] The Tibetan Plateau contains the world's third-largest store of ice. Temperatures there are rising four times faster than in the rest of China, and glacial retreat is at a high speed compared to elsewhere in the world.[46]
According to a UN climate report, the Himalayan glaciers that are the sources of Asia's biggest rivers—Ganges, Indus, Brahmaputra, Yangtze, Mekong, Salween and Yellow—could disappear by 2035 as temperatures rise.[47] Approximately 2.4 billion people live in the drainage basin of the Himalayan rivers.[48] India, China, Pakistan, Bangladesh, Nepal and Myanmar could experience floods followed by droughts in coming decades. In India alone, the Ganges provides water for drinking and farming for more than 500 million people.[49][50][51] It has to be acknowledged, however, that increased seasonal runoff of Himalayan glaciers led to increased agricultural production in northern India throughout the 20th century.[52]
The recession of mountain glaciers, notably in Western North America, Franz-Josef Land, Asia, the Alps, the Pyrenees, 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 glaciated areas. In Western North America the 47 North Cascade glaciers observed all are retreating.[53]
Retreat of the Helheim Glacier, Greenland
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 kilometres (1.9 mi) 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, Jakobshavn Isbræ 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 mi) between 2001 and 2005. It has also accelerated from 20 m (66 ft)/day to 32 m (100 ft)/day.[54] Jakobshavn Isbræ in western Greenland had been moving at speeds of over 24 m (79 ft)/day with a stable terminus since at least 1950. The glacier's ice tongue began to break apart in 2000, leading to almost complete disintegration in 2003, while the retreat rate doubled to over 30 m (98 ft)/day.[55]
Oceans
The role of the oceans in global warming is a complex one. The oceans serve as a sink for carbon dioxide, taking up much that would otherwise remain in the atmosphere, but increased levels of CO2 have led to ocean acidification. Furthermore, as the temperature of the oceans increases, they become less able to absorb excess CO2. Global warming is projected to have a number of effects on the oceans. Ongoing effects include rising sea levels due to thermal expansion and melting of glaciers and ice sheets, and warming of the ocean surface, leading to increased temperature stratification. Other possible effects include large-scale changes in ocean circulation.
Sea level rise
Main article: Current sea level rise
Sea level rise during the Holocene.
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. For most glaciers worldwide, an average volume loss of 60% until 2050 is predicted.[56] Meanwhile, the estimated total ice melting rate over Greenland is 239 ± 23 cubic kilometres (57 ± 5.5 cu mi) per year, mostly from East Greenland.[57] The Antarctic ice sheet, however, is expected to grow during the 21st century because of increased precipitation.[58] Under the IPCC Special Report on Emission Scenario (SRES) A1B, by the mid-2090s global sea level will reach 0.22 to 0.44 m (8.7 to 17 in) above 1990 levels, and is currently rising at about 4 mm (0.16 in) per year.[58] Since 1900, the sea level has risen at an average of 1.7 mm (0.067 in) per year;[58] since 1993, satellite altimetry from TOPEX/Poseidon indicates a rate of about 3 mm (0.12 in) per year.[58]
The sea level has risen more than 120 metres (390 ft) since the Last Glacial Maximum about 20,000 years ago. The bulk of that occurred before 7000 years ago.[59] Global temperature declined after the Holocene Climatic Optimum, causing a sea level lowering of 0.7 ± 0.1 m (28 ± 3.9 in) between 4000 and 2500 years before present.[60] From 3000 years ago to the start of the 19th century, sea level was almost constant, with only minor fluctuations. However, the Medieval Warm Period may have caused some sea level rise; evidence has been found in the Pacific Ocean for a rise to perhaps 0.9 m (2 ft 11 in) above present level in 700 BP.[61]
In a paper published in 2007, the climatologist James Hansen et al. claimed that ice at the poles does not melt in a gradual and linear fashion, but that another according to the geological record, the ice sheets can suddenly destabilize when a certain threshold is exceeded. In this paper Hansen et al. state:
Our concern that BAU GHG scenarios would cause large sealevel rise this century (Hansen 2005) differs from estimates of IPCC (2001, 2007), which foresees little or no contribution to twentyfirst century sealevel rise from Greenland and Antarctica. However, the IPCC analyses and projections do not well account for the nonlinear physics of wet ice sheet disintegration, ice streams and eroding ice shelves, nor are they consistent with the palaeoclimate evidence we have presented for the absence of discernible lag between ice sheet forcing and sealevel rise.[62]
Sea level rise due to the collapse of an ice sheet would be distributed nonuniformly across the globe. The loss of mass in the region around the ice sheet would decrease the gravitational potential there, reducing the amount of local sea level rise or even causing local sea level fall. The loss of the localized mass would also change the moment of inertia of the Earth, as flow in the Earth's mantle will require 10-15 thousand years to make up the mass deficit. This change in the moment of inertia results in true polar wander, in which the Earth's rotational axis remains fixed with respect to the sun, but the rigid sphere of the Earth rotates with respect to it. This changes the location of the equatorial bulge of the Earth and further affects the geoid, or global potential field. A 2009 study of the effects of collapse of the West Antarctic Ice Sheet shows the result of both of these effects. Instead of a global 5-meter sea level rise, western Antarctica would experience approximately 25 centimeters of sea level fall, while the United States, parts of Canada, and the Indian Ocean, would experience up to 6.5 meters of sea level rise.[63]
A paper published in 2008 by a group of researchers at the University of Wisconsin lead by Anders Carlson used the deglaciation of North America at 9000 years before present as an analogue to predict sea level rise of 1.3 meters in the next century[64][65], which is also much higher than the IPCC predictions. However, models of glacial flow in the smaller present-day ice sheets show that a probable maximum value for sea level rise in the next century is 80 centimeters, based on limitations on how quickly ice can flow below the equilibrium line altitude and to the sea.[66]
Temperature rise
From 1961 to 2003, the global ocean temperature has risen by 0.10 °C from the surface to a depth of 700 m. There is variability both year-to-year and over longer time scales, with global ocean heat content observations showing high rates of warming for 1991 to 2003, but some cooling from 2003 to 2007.[58] 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 [67]. As well as having effects on ecosystems (e.g. by melting sea ice, affecting algae that grow on its underside), warming reduces the ocean's ability to absorb CO2.[citation needed]
Acidification
Main article: Ocean acidification
Ocean acidification is an effect of rising concentrations of CO2 in the atmosphere, and is not a direct consequence of global warming. The oceans soak up much of the CO2 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 tonne of CO2 per person per year. It is estimated that the oceans have absorbed around half of all CO2 generated by human activities since 1800 (118 ± 19 petagrams of carbon from 1800 to 1994).[68]
In water, CO2 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, to 8.2. Predicted emissions could lower the pH by a further 0.5 by 2100, to a level probably not seen for hundreds of millennia and, critically, at a rate of change probably 100 times greater than at any time over this period.[69][70]
There are concerns that increasing acidification could have a particularly detrimental effect on corals[71] (16% of the world's coral reefs have died from bleaching caused by warm water in 1998,[72] which coincidentally was the warmest year ever recorded) and other marine organisms with calcium carbonate shells.[73]
In November 2009 an article in Science by scientists at Canada's Department of Fisheries and Oceans reported they had found very low levels of the building blocks for the calcium chloride that forms plankton shells in the Beaufort Sea.[74] Fiona McLaughlin, one of the DFO authors, asserted that the increasing acidification of the Arctic Ocean was close to the point it would start dissolving the walls of existing plankton: "[the] Arctic ecosystem may be risk. In actual fact, they'll dissolve the shells." Because cold water absorbs CO2 more readily than warmer water the acidification is more severe in the polar regions. McLaughlin predicted the acidified water would travel to the North Atlantice within the next ten years.
Shutdown of thermohaline circulation
Main article: Shutdown of thermohaline circulation
There is 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.[citation needed] This would affect in particular areas like Scandinavia and Britain that are warmed by the North Atlantic drift.
The chances of this near-term collapse of the circulation are unclear; there is some evidence for the short-term stability of the Gulf Stream and possible weakening of the North Atlantic drift.[citation needed] However, the degree of weakening, and whether it will be sufficient to shut down the circulation, is under debate. As yet, no cooling has been found in northern Europe or nearby seas.[citation needed] Lenton et al. found that "simulations clearly pass a THC tipping point this century".[75]
Oxygen depletion
The amount of oxygen dissolved in the oceans may decline, with adverse consequences for ocean life.[76][77]
Positive feedback effects
See also: Runaway climate change and Abrupt climate change
Some observed and potential effects of global warming are positive feedbacks, which contribute directly to further global warming. The IPCC Fourth Assessment Report states that "Anthropogenic warming could lead to some effects that are abrupt or irreversible, depending upon the rate and magnitude of the climate change." This is largely because of the existence of these positive feedbacks.
Methane release from melting permafrost peat bogs
See also: Arctic methane release
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Western Siberia is the world's largest peat bog, a one million square kilometer region of permafrost peat bog that was formed 11,000 years ago at the end of the last ice age. The melting of its permafrost is likely to lead to the release, over decades, of large quantities of methane. As much as 70,000 million tonnes of methane, an extremely effective greenhouse gas, might be released over the next few decades, creating an additional source of greenhouse gas emissions.[78] Similar melting has been observed in eastern Siberia [79]. Lawrence et al. (2008) suggest that a rapid melting of Arctic sea ice may start a feedback loop that rapidly melts Arctic permafrost, triggering further warming.[80][81]
Methane release from hydrates
Main article: Clathrate gun hypothesis
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, in a runaway greenhouse effect, 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 atmosphere. This theory has been proposed to explain the most severe mass extinction event on earth known as the Permian–Triassic extinction event. In 2008, a research expedition for the American Geophysical Union detected levels of methane up to 100 times above normal in the Siberian Arctic, likely being released by methane clathrates being released by holes in a frozen 'lid' of seabed permafrost, around the outfall of the Lena River and the area between the Laptev Sea and East Siberian Sea.[82][83][84]
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 CO2 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.[85] 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.[86] 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.[87] 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[88] 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).[89]
It has also been suggested (by Chris Freeman) that the release of dissolved organic carbon (DOC) from peat bogs into water courses (from which it would in turn enter the atmosphere) constitutes a positive feedback for global warming. The carbon currently stored in peatlands (390-455 gigatonnes, one-third of the total land-based carbon store) is over half the amount of carbon already in the atmosphere.[90] DOC levels in water courses are observably rising; Freeman's hypothesis is that, not elevated temperatures, but elevated levels of atmospheric CO2 are responsible, through stimulation of primary productivity.[91][92]
Tree deaths are believed to be increasing as a result of climate change, which is a positive feedback effect.[93] This contradicts the previously widely-held view that increased natural vegetation would lead to a negative-feedback effect.[citation needed]
Forest fires
The IPCC Fourth Assessment Report predicts that many mid-latitude regions, such as Mediterranean Europe, will experience decreased rainfall and an increased risk of drought, which in turn would allow 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.[94][95][96] Cook & Vizy also found that forest fires were likely in the Amazon Rainforest, eventually resulting in a transition to Caatinga vegetation in the Eastern Amazon region.[citation needed]
Retreat of sea ice
Northern Hemisphere ice trends
Southern Hemisphere ice trends
Main articles: Arctic shrinkage and Ice-albedo feedback
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 in the northern hemisphere to rise up to twice as much as those of the rest of the world. In September 2007, the Arctic sea ice area reached about half the size of the average summer minimum area between 1979 to 2000.[97][98] Also in September 2007, Arctic sea ice retreated far enough for the Northwest Passage to become navigable to shipping for the first time in recorded history.[99] The record losses of 2007 and 2008 may, however, be temporary.[100] Mark Serreze of the US National Snow and Ice Data Center views 2030 as a "reasonable estimate" for when the summertime Arctic ice cap might be ice-free.[101] The polar amplification of global warming is not predicted to occur in the southern hemisphere.[102] The Antarctic sea ice reached its greatest extent on record since the beginning of observation in 1979,[103] but the gain in ice in the south is exceeded by the loss in the north. The trend for global sea ice, northern hemisphere and southern hemisphere combined is clearly a decline.[104]
Effect on sulfur aerosols
Main articles: sulfur cycle, stratospheric sulfur aerosols, and plankton
Sulfur aerosols, especially stratospheric sulfur aerosols have a significant effect on climate. One source of such aerosols is the sulfur cycle, where plankton release gases such as DMS which eventually becomes oxidised to sulfur dioxide in the atmosphere. Disruption to the oceans as a result of ocean acidification or disruptions to the thermohaline circulation may result in disruption of the sulfur cycle, thus reducing its cooling effect on the planet through the creation of stratospheric sulfur aerosols.
Negative feedback effects
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Following Le Chatelier's principle, the chemical equilibrium of the Earth's carbon cycle will shift in response to anthropogenic CO2 emissions. The primary driver of this is the ocean, which absorbs anthropogenic CO2 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 CO2 emitted by human activities will dissolve in the ocean over a period of centuries: "A better approximation of the lifetime of fossil fuel CO2 for public discussion might be 300 years, plus 25% that lasts forever"[105]. 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, the thermal radiation of the Earth rises in proportion to the fourth power of temperature, increasing the amount of outgoing radiation as the Earth warms. The impact of this negative feedback effect is included in global climate models summarized by the IPCC.
Other consequences
Economic and social
See also: Economics of global warming
Indigenous populations in high-latitude areas are already experiencing significant adverse impacts because of climate change.[9] The impact of future climate change on human systems will likely be unevenly distributed. Africa is probably the most vulnerable continent to future climate change. Developing countries are probably more vulnerable to climate change than developed countries. With warming of 1-2°C above 1990-2000 levels, it is likely that key negative impacts would be experienced in some regions, e.g., Arctic nations and small islands. In other regions, some population groups would be threatened by this level of warming, e.g., high-altitude communities and coastal-zone communities with significant levels of poverty. Above 2-3°C warming, it is likely that most countries would experience net negative impacts.
The total economic impacts of climate change are highly uncertain.[9] Typical estimates of climate change impacts are of a change in gross world product of plus or minus a few percent. Small changes in gross world product could be associated with relatively large changes in national economies.
Insurance
An industry very directly affected by the risks is the insurance industry.[106] According to a 2005 report from the Association of British Insurers, limiting carbon emissions could avoid 80% of the projected additional annual cost of tropical cyclones by the 2080s.[107] 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."[108] 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 insurance will become unaffordable for some.
Financial institutions, including the world's two largest insurance companies, Munich Re and Swiss Re, warned in a 2002 study that "the increasing frequency of severe climatic events, coupled with social trends" could cost almost US$ 150 billion each year in the next decade.[109] These costs would, through increased costs related to insurance and disaster relief, burden customers, taxpayers, and industry alike.
In the United States, insurance losses have also greatly increased. According to Choi and Fisher (2003) each 1% increase in annual precipitation could enlarge catastrophe loss by as much as 2.8%.[110] Gross 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.[111]
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. Regions already adversely affected include areas of permafrost, which are subject to high levels of subsidence, resulting in buckling roads, sunken foundations, and severely cracked runways.[112]
Effects on agriculture
Main article: Climate change and agriculture
See also: Food security, Food vs fuel, and 2007–2008 world food price crisis
Food
Climate change is expected to have a mixed effect on agriculture, with some regions benefitting from moderate temperature increases and others being negatively affected.[113] Low-latitude areas are at most risk of suffering decreased crop yields. Mid- and high-latitude areas could see increased yields for temperature increases of up to 1-3°C (relative to the period 1980-99). According to the IPCC report, above 3°C of warming, global agricultural production might decline, but this statement is made with low to medium confidence. Most of the agricultural studies assessed in the Report do not include changes in extreme weather events, changes in the spread of pests and diseases, or potential developments that may aid adaptation to climate change.
An article in the New Scientist describes how rice crops might be strongly affected by rising temperatures.[114] At a 2005 Conference held by the Royal Society, the benefits of increased atmospheric carbon dioxide concentrations were said to be outweighed by the negative impacts of climate change.[115]
Distribution of impacts
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.[116] By the mid-21st century, in Siberia and elsewhere in Russia, climate change is expected to expand the scope for agriculture.[117] In East and Southeast Asia, crop yields could increase up to 20%, while in Central and South Asia, yields could decrease by up to 30%.[4] In drier areas of Latin America, productivity of some important crops is expected to decline, while in temperate zones, soybean yields are expected to increase.[4] In Northern Europe, climate change is expected to initially benefit crop yields.[4]Subsistence and commercial agriculture are expected to be adversely affected by climate change in small islands.[118] Without further adaptation, by 2030, production from agriculture is projected to decline over much of southern and eastern Australia, and parts of eastern New Zealand. Initial benefits are projected in western and southern areas of New Zealand.[119]
In North America, over the first few decades of this century, moderate climate change is projected to increase aggregate yields of rain-fed agriculture by 5-20%, but with important variability among regions.[4] According to a 2006 paper by Deschenes and Greenstone, predicted increases in temperature and precipitation will have virtually no effect on the most important crops in the US[120]
In Africa, climate change is expected to severely compromise agricultural production and access to food.[4] Africa's geography makes it particularly vulnerable, and 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.[121] Alongside other factors, regional climate change - in particular, reduced precipitation - is thought to have contributed to the conflict in Darfur.[122] The combination of decades of drought, desertification and overpopulation are among the causes of the conflict, because the Baggara Arab nomads searching for water have to take their livestock further south, to land mainly occupied by farming peoples.[123]
Coasts and low-lying areas
For historical reasons to do with trade, many of the world's largest and most prosperous cities are on the coast. In developing countries, the poorest often live on floodplains, 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. With future climate change, it is likely that densely populated coastal areas will face increased risk of sea level rise and damages due to more intense extreme weather events.[9] Due to differences in adaptive capacity, adaptation of the coasts of developing countries will probably be more difficult than for the coasts of developed countries.[4] A 2006 study by Nicholls and Tol considers the effects of sea level rise:[124]
[...] The most vulnerable future worlds to sea-level rise appear to be the A2 and B2 [IPCC] scenarios, which primarily reflects differences in the socio-economic situation (coastal population, Gross Domestic Product (GDP) and GDP/capita), rather than the magnitude of sea-level rise. Small islands and deltaic settings stand out as being more vulnerable as shown in many earlier analyses. Collectively, these results suggest that human societies will have more choice in how they respond to sea-level rise than is often assumed. However, this conclusion needs to be tempered by recognition that we still do not understand these choices and significant impacts remain possible.
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.[125]
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).[126][127]
Northwest Passage
Arctic ice thicknesses changes from 1950s to 2050s simulated in one of GFDL's R30 atmosphere-ocean general circulation model experiments
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 benefit for supertankers which are too big to fit through the Panama Canal and currently have to go around the tip of South America. According to the Canadian Ice Service, the amount of ice in Canada's eastern Arctic Archipelago decreased by 15% between 1969 and 2004.[128]
In September 2007, the Arctic Ice Cap retreated far enough for the Northwest Passage to become navigable to shipping for the first time in recorded history.[129]
In August, 2008, melting sea ice simultaneously opened up the Northwest Passage and the Northern Sea Route, making it possible to sail around the Arctic ice cap.[130] The Northwest Passage opened August 25, 2008, and the remaining tongue of ice blocking the Northern Sea Route dissolved a few days later. Because of Arctic shrinkage, the Beluga group of Bremen, Germany, announced plans to send the first ship through the Northern Sea Route in 2009.[130]
Development
The combined effects of global warming may have particularly harsh effects 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.[131]
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.
Ecosystems
See also: Extinction risk from global warming
Unchecked global warming could affect most terrestrial ecoregions. Increasing global temperature means that ecosystems will change; some species are being forced out of their habitats (possibly to extinction) because of changing conditions, while others are flourishing. Secondary effects of global warming, such as lessened snow cover, rising sea levels, and weather changes, may influence not only human activities but also the ecosystem. Studying the association between Earth climate and extinctions over the past 520 million years, scientists from the University of York write, "The global temperatures predicted for the coming centuries may trigger a new ‘mass extinction event’, where over 50 per cent of animal and plant species would be wiped out."[132]
Many of the species at risk are Arctic and Antarctic fauna such as polar bears[133] and Emperor Penguins[134]. 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 prefer to hunt on sea ice.[135] 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 may be hit hard.[136][137] Marine invertebrates enjoy peak growth at the temperatures they have adapted to, regardless of how cold these may be, and cold-blooded animals found at greater latitudes and altitudes generally grow faster to compensate for the short growing season.[138] Warmer-than-ideal conditions result in higher metabolism and consequent reductions in body size despite increased foraging, which in turn elevates the risk of predation. Indeed, even a slight increase in temperature during development impairs growth efficiency and survival rate in rainbow trout.[139]
Rising temperatures are beginning to have a noticeable impact on birds[140], and 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 roads. In Britain, spring butterflies are appearing an average of 6 days earlier than two decades ago [141].
A 2002 article in Nature[142] surveyed the scientific literature to find recent changes |
