Climate change refers to a change of climate which is attributed directly or
indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods.
United Nations Framework Convention on Climate Change
Some areas will be warmer, some cooler, sea levels may rise, polar ice caps may melt, deserts might spread across Europe and extreme weather events may become more frequent.The Intergovernmental Panel on Climate Change estimates that the global temperature will rise by as much as 6°C this century. Near the poles, in parts of Alaska, Canada, Siberia and the Antarctic, temperatures are rising faster than elsewhere. The permafrost is melting and plants, animals and the people that live there are already being affected. Arctic sea ice is melting at a faster rate than previously thought. A report by NASA (December 2002) warned that it might disappear completely by the end of the century. Melting sea ice doesn't raise sea levels but it could threaten ocean productivity, change current systems and disrupt global weather still further (because heat that would be reflected off the ice will be absorbed instead). Sea ice also plays an important role in keeping the ice and snow covering the Antarctic continent in place. With nothing to stop it, the Antarctic ice sheet may slide into the ocean and melt. In this extreme case, sea levels would rise by an estimated 65 to 70 metres. Evidence suggests that land glaciers are retreating at an unprecidented rate. Some scientists estimate that the impact of glacial melt water, together with other factors, such as the thermal expansion of sea water, will cause a significant change. The IPCC currently predicts a sea level rise of between 11 and 88cm this century. Some 50 million people a year already have to deal with flooding caused by storm surges. If the sea rises by half a metre, this number could double. A metre rise would inundate 1% of Egypt's land, 6% of the Netherlands and 17.5% of Bangladesh. Only 20% of the Marshall Islands would be left above water. Although the ice sheets in Greenland have been thinning, analysis of long-term climate information (presented in the journal Geophysical Review Letters) has shown that temperatures in the southern part of the island and the Labrador Sea have fallen over the last 40 years, not risen. Scientists associate this cooling with the North Atlantic Oscillation, a natural and recurring pressure pattern that has a profound impact on the weather experienced in the North Atlantic region. Countries such as the US and Australia emit more CO2 per person than other nations because of their high dependence on fossil-fuel power plants and high living standards. The US alone pumps out a quarter of the world's CO2 emissions. As global climate change shifts temperatures across the planet, species may not be able to follow fast enough. According to UNEP, they will have to migrate 10 times as fast as they did after the last ice age. Many won't make it. Species that do move will do so at different rates, breaking up existing communities. At high latitudes, entire forest types are expected to disappear, to be replaced by new ones. During this transition, carbon will be lost to the atmosphere faster than it can be replaced by new growth, accelerating climate change.
Increased warming: Eleven of the last twelve years rank among the warmest years in global surface temperature since1850. The rate of warming averaged over the last 50 years is nearly twice that for the last 100 years. The average global temperature went up by about 0.74°C during the 20th Century with the warming affecting land more than ocean areas.There is more carbon dioxide in the atmosphere: Carbon dioxide is the dominant contributor to current climate change and its atmospheric concentration has increased from a pre-industrial value of 278 parts-per million (ppm) to 379 in 2005.
More water, but not everywhere: More precipitation has been observed in the eastern parts of North and South America, northern Europe and northern and central Asia in recent decades. But the Sahel, the Mediterranean, southern Africa and parts of southern Asia have experienced drying. More intense and longer droughts have been observed over wider areas since the 1970s.Sea level is rising: The Intergovernmental Panel on Climate Change is highly confident that the rate of observed sea level rise increased from the 19th to 20th century, and the total 20th century rise is estimated to be 0.17 metre. Geological observations indicate that sea level rise over the previous 2,000 years was far less. The average temperature of the global ocean has increased to depths of at least 3,000 metres.
Less snow cover: Snow cover is decreasing in most regions, particularly in spring. The maximum extent of frozen ground in the winter/spring season has decreased by about 7 per cent in the Northern Hemisphere since 1900, and on average rivers that freeze do so some 5.8 days later than a century ago and their ice breaks up 6.5 days earlier. Glaciers are melting: Mountain glaciers and snow cover have declined, on average, in both hemispheres, and have contributed to sea level rise by 0.77 millimetres a year from 1993 to 2003. Shrinkage of the ice sheets of Greenland and Antarctica have contributed to a sea level rise of 0.4 millimetres a year between 1993 and 2003.
Arctic is warming: Average Arctic temperatures increased at almost twice the global average rate in the past 100 years.Satellite data since 1978 show that the average Arctic sea ice extent has shrunk by 2.7 per cent per decade.
New Projections Indicate Faster Warming…
Continued greenhouse gas emissions at or above the current rates would cause further warming and induce many
changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.
The degree of warming depends on the degree of emissions: If carbon dioxide concentrations were stabilized at 550 ppm — double the pre-industrial levels — the average warming expected would likely be in the range of 2-4.5°C, with the best estimate of 3°C, or 5.4°F. A warming of 0.2°C per decade is expected for each of the next two decades for a range of scenarios that do not include deliberate reductions in greenhouse gas emissions.
Other greenhouse gases contribute to warming and if their combined effect were equivalent to a carbon dioxide level of 650 ppm, the global climate would "likely" warm by 3.6°C, while a level of 750 ppm would produce warming of 4.3°C.
Projections depend on factors such as economic growth, population, new technologies and other factors....and Greater Consequences
Warmer global temperatures are already causing profound changes in many of the earth’s natural systems. Approximately 20-30 per cent of plant and animal species assessed so far are likely to be at increased risk of extinction if increases in global average temperature exceed 1.5-2.5°C.
A temperature increase of 3°C during this century would have largely negative consequences for biodiversity ecosystems that produce essential goods and services, such as water and food supply.
As a result of warmer temperatures, springtime events are occurring earlier, such as increased run-off and peak discharge in many glacier- and snow-fed rivers, "greening" of vegetation and migration and egg-laying by birds. More animal and plant species have also been observed shifting toward higher latitudes.
More precipitation in the high latitudes: Increases in precipitation are very likely in the high latitudes while decreases are likely in most subtropical land regions.Model based estimates for sea-level rise due to ocean expansion and glacier melt by the end of the century (compared to 1989-1999 levels) have narrowed from previous assessments to 18-58 cm. However, larger values cannot be ruled out if recently observed movements of ice sheets were to increase as temperature rises. Contraction of the Greenland ice sheet is projected to contribute to sea level rise into the 22nd century and the ice sheet could face complete elimination if global average warming of 1.9-4.6°C is maintained for a millennium. In that case, sea level would rise by up to 7 metres.
The poorest communities will be the most vulnerable to the impacts of climate change as they have fewer resources to invest in preventing and mitigating the effects of climate change. Some of the most at-risk people include subsistence farmers, indigenous peoples and coastal populations.
Regional Impacts
It is more difficult to anticipate how climate change will evolve at the regional than at the global level. Nevertheless, enormous strides have been made in recent years, allowing scientists to conclude that:
Africa — Very vulnerable to climate change and climate variability due to endemic poverty, weak institutions, and complex disasters and conflicts. Drought has spread and intensified since the 1970s, and the Sahel and southern Africa have already become drier during the 20th century. Water supplies and agricultural production will likely be severely compromised. Yields in some countries could drop by as much as 50 per cent by 2020, and some large regions of marginal agriculture are likely to be forced out of production. Forests, grasslands and other natural ecosystems are already changing, particularly in southern Africa. By the 2080s, the amount of arid and semi-arid land in Africa will likely increaseby 5-8 per cent.
Antarctica — This continent has proven more difficult to understand and predict. With the exception of the rapidly warming Antarctic Peninsula, both temperatures and snowfall have remained relatively constant for the continent as a whole over the past 50 years. Because this frozen continent contains almost 90 per cent of the planet’s freshwater, researchers are watching carefully for any signs that its glaciers and ice sheets may be melting.
The Arctic — Average temperatures in the Arctic have increased almost twice as fast as the global average over the past 100 years. The average extent of Arctic sea ice has been shrinking by 2.7 per cent per decade and large areas of the Arctic Ocean could lose year-round ice cover by the end of the 21st century if human emissions reach the higher end of current estimates. The Arctic is also particularly important because changes there have important global implications. For example, as ice and snow melts, the Earth’s albedo (reflectivity) is decreased, trapping heat that would otherwise be reflected and warming the earth’s surface even further.
Asia — More than a billion people could be affected by a decline in the availability of freshwater, particularly in large river basins, by 2050. Glacier melt in the Himalayas, which is projected to increase flooding and rock avalanches, will affect water resources in the next two to three decades. As glaciers recede, river flows will decrease. Coastal areas, especially heavily populated mega-delta regions, will be at greatest risk due to increased flooding from the sea and, in some cases, from river flooding.
Only the total elimination of industrial emissions will succeed in limiting climate change to a 2°C rise in temperatures, according to computer analysis of climate change. Anything above this target has been identified as "dangerous" by some scientists, and the limit has been adopted by many policymakers.
The researchers say their study highlights the shortcomings of governmental plans to limit climate change.A warming of 2°C above pre-industrial temperatures is frequently cited as the limit beyond which the world will face "dangerous" climate change. Beyond this level, analysis suggests the continents will cease to absorb more carbon dioxide than they produce. As the tundra and other regions of permafrost thaw, they will spew more gas into the atmosphere, adding to the warming effect of human emissions.
In January 2007, the European Commission issued a communication stating that "the European Union's objective is to limit global average temperature increase to less than 2°C compared to pre-industrial levels".
Andrew Weaver and colleagues at the University of Victoria in Canada say this means going well beyond the reduction of industrial emissions discussed in international negotiations.
Weaver's team used a computer model to determine how much emissions must be limited in order to avoid exceeding a 2°C increase. The model is an established tool for analysing future climate change and was used in studies cited in the IPCC's reports on climate change.
They modelled the reduction of industrial emissions below 2006 levels by between 20% and 100% by 2050. Only when emissions were entirely eliminated did the temperature increase remain below 2°C.
A 100% reduction of emissions saw temperature change stabilise at 1.5°C above the pre-industrial figure. With a 90% reduction by 2050, Weaver's model predicted that temperature change will eventually exceed 2°C compared to pre-industrial temperatures but then plateau.
The researchers conclude that governments should consider reducing emissions to 90% below current levels and remove what is left in the atmosphere by capturing and storing carbon There is a stark contrast between this proposal and the measures currently being considered. Under the UN's Kyoto protocol, most developed nations have agreed to limit their emissions to a minimum of 5% below 1990 levels by 2012. The European Union nations have agreed to limit their emissions to 20% below 1990 levels by 2020, and support dropping global emissions to 50% below 1990 levels by 2050.
"There is a disconnect between the European Union arguing for a 2°C threshold and calling for 50% cuts at 2050 - you can't have it both ways," says Weaver, who adds: "If you're going to talk about 2°C you have got to be talking 90% emissions cuts."
Even with emissions halved, Lenton says carbon dioxide will continue building up in the atmosphere and temperatures will continue to rise. For temperature change to stabilise, he says industrial carbon emissions must not exceed what can be absorbed by Earth's vegetation, soil and oceans.
At the moment, about half of industrial emissions are absorbed by ocean and land carbon "sinks". But simply cutting emissions by half will not solve the problem, Lenton says, because these sinks also grow and shrink as CO2 emissions change.
"People are easily misled into thinking that 50% by 2050 is all we have to do when in fact have to continue reducing emissions afterwards, all the way down to zero," Lenton says
Regional Impacts
It is more difficult to anticipate how climate change will evolve at the regional than at the global level. Nevertheless, enormous strides have been made in recent years, allowing scientists to conclude that:
Africa — Very vulnerable to climate change and climate variability due to endemic poverty, weak institutions, and complex disasters and conflicts. Drought has spread and intensified since the 1970s, and the Sahel and southern Africa have already become drier during the 20th century. Water supplies and agricultural production will likely be severely compromised. Yields in some countries could drop by as much as 50 per cent by 2020, and some large regions of marginal agriculture are likely to be forced out of production. Forests, grasslands and other natural ecosystems are already changing, particularly in southern Africa. By the 2080s, the amount of arid and semi-arid land in Africa will likely increaseby 5-8 per cent.
Antarctica — This continent has proven more difficult to understand and predict. With the exception of the rapidly warming Antarctic Peninsula, both temperatures and snowfall have remained relatively constant for the continent as a whole over the past 50 years. Because this frozen continent contains almost 90 per cent of the planet’s freshwater, researchers are watching carefully for any signs that its glaciers and ice sheets may be melting.
The Arctic — Average temperatures in the Arctic have increased almost twice as fast as the global average over the past 100 years. The average extent of Arctic sea ice has been shrinking by 2.7 per cent per decade and large areas of the Arctic Ocean could lose year-round ice cover by the end of the 21st century if human emissions reach the higher end of current estimates. The Arctic is also particularly important because changes there have important global implications. For example, as ice and snow melts, the Earth’s albedo (reflectivity) is decreased, trapping heat that would otherwise be reflected and warming the earth’s surface even further.
Asia — More than a billion people could be affected by a decline in the availability of freshwater, particularly in large river basins, by 2050. Glacier melt in the Himalayas, which is projected to increase flooding and rock avalanches, will affect water resources in the next two to three decades. As glaciers recede, river flows will decrease. Coastal areas, especially heavily populated mega-delta regions, will be at greatest risk due to increased flooding from the sea and, in some cases, from river flooding.
Only the total elimination of industrial emissions will succeed in limiting climate change to a 2°C rise in temperatures, according to computer analysis of climate change. Anything above this target has been identified as "dangerous" by some scientists, and the limit has been adopted by many policymakers.
The researchers say their study highlights the shortcomings of governmental plans to limit climate change.A warming of 2°C above pre-industrial temperatures is frequently cited as the limit beyond which the world will face "dangerous" climate change. Beyond this level, analysis suggests the continents will cease to absorb more carbon dioxide than they produce. As the tundra and other regions of permafrost thaw, they will spew more gas into the atmosphere, adding to the warming effect of human emissions.
In January 2007, the European Commission issued a communication stating that "the European Union's objective is to limit global average temperature increase to less than 2°C compared to pre-industrial levels".
Andrew Weaver and colleagues at the University of Victoria in Canada say this means going well beyond the reduction of industrial emissions discussed in international negotiations.
Weaver's team used a computer model to determine how much emissions must be limited in order to avoid exceeding a 2°C increase. The model is an established tool for analysing future climate change and was used in studies cited in the IPCC's reports on climate change.
They modelled the reduction of industrial emissions below 2006 levels by between 20% and 100% by 2050. Only when emissions were entirely eliminated did the temperature increase remain below 2°C.
A 100% reduction of emissions saw temperature change stabilise at 1.5°C above the pre-industrial figure. With a 90% reduction by 2050, Weaver's model predicted that temperature change will eventually exceed 2°C compared to pre-industrial temperatures but then plateau.
The researchers conclude that governments should consider reducing emissions to 90% below current levels and remove what is left in the atmosphere by capturing and storing carbon There is a stark contrast between this proposal and the measures currently being considered. Under the UN's Kyoto protocol, most developed nations have agreed to limit their emissions to a minimum of 5% below 1990 levels by 2012. The European Union nations have agreed to limit their emissions to 20% below 1990 levels by 2020, and support dropping global emissions to 50% below 1990 levels by 2050.
"There is a disconnect between the European Union arguing for a 2°C threshold and calling for 50% cuts at 2050 - you can't have it both ways," says Weaver, who adds: "If you're going to talk about 2°C you have got to be talking 90% emissions cuts."
Even with emissions halved, Lenton says carbon dioxide will continue building up in the atmosphere and temperatures will continue to rise. For temperature change to stabilise, he says industrial carbon emissions must not exceed what can be absorbed by Earth's vegetation, soil and oceans.
At the moment, about half of industrial emissions are absorbed by ocean and land carbon "sinks". But simply cutting emissions by half will not solve the problem, Lenton says, because these sinks also grow and shrink as CO2 emissions change.
"People are easily misled into thinking that 50% by 2050 is all we have to do when in fact have to continue reducing emissions afterwards, all the way down to zero," Lenton says
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