global warming refers to the increase in the average temperature of the earth

8/7/2019 Global warming refers to the increase in the average temperature of the Earth

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Global warming refers to the increase in the average temperature of the Earth's

near-surface air and oceans in recent decades and its projected continuation.

The global average air temperature near the Earth's surface rose 0.74 0.18 C

(1.33 0.32 F) during the last 100 years. The Intergovernmental Panel on Climate

Change (IPCC) concludes, "most of the observed increase in globally averaged

temperatures since the mid-20th century is very likely due to the observed increase

in anthropogenic greenhouse gas concentrations" via the greenhouse effect. Naturalphenomena such as solar variation combined with volcanoes have probably had a

small warming effect from pre-industrial times to 1950, but a small cooling effect

since 1950. These basic conclusions have been endorsed by at least 30 scientific

societies and academies of science, including all of the national academies of

science of the major industrialized countries. A few individual scientists disagree

with some of the main conclusions of the IPCC.

Climate models referenced by the IPCC project that global surface temperatures are

likely to increase by 1.1 to 6.4 C (2.0 to 11.5 F) between 1990 and 2100. The

range of values results from the use of differing scenarios of future greenhouse gas

emissions as well as models with differing climate sensitivity. Although most studies

focus on the period up to 2100, warming and sea level rise are expected to continue

for more than a millennium even if greenhouse gas levels are stabilized. This

reflects the large heat capacity of the oceans.

An increase in global temperatures is expected to cause otherchanges, including

sea level rise, increased intensity ofextreme weatherevents, and changes in the

amount and pattern ofprecipitation. Other effects include changes in agricultural

yields, glacier retreat, species extinctions and increases in the ranges ofdisease

vectors.

Remaining scientific uncertainties include the exact degree of climate change

expected in the future, and how changes will vary from region to region around the

globe. There is ongoing political and public debate on a world scale regarding what,

if any, action should be taken to reduce or reverse future warming or to adapt to its

expected consequences. Most national governments have signed and ratified the

Kyoto Protocol, aimed at reducing greenhouse gas emissions


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Causes

Carbon dioxide during the last 400,000 years and (inset above) the rapid rise since the

Industrial Revolution; changes in the Earth's orbit around the Sun, known as Milankovitch

cycles, are believed to be the pacemaker of the 100,000 yearice age cycle.

Earth's climate changes in response to external forcing, including variations in its

orbit around the sun (orbital forcing), volcanic eruptions, and atmosphericgreenhouse gas concentrations. The detailed causes of the recent warming remain

an active field of research, but the scientific consensus identifies elevated levels of

greenhouse gases due to human activity as the main influence. This attribution is

clearest for the most recent 50 years, for which the most detailed data are available.

In contrast to the scientific consensus that recent warming is mainly attributable to

elevated levels of greenhouse gases, other hypotheses have been suggested to

explain the observed increase in mean global temperature. One such hypothesis

proposes that warming may be the result of increased solar radiation associated

with greater numbers ofsunspots.

None of the effects of forcing are instantaneous. The thermal inertia of the Earth's

oceans and slow responses of other indirect effects mean that the Earth's current

climate is not in equilibrium with the forcing imposed. Climate commitment studies

indicate that even if greenhouse gases were stabilized at 2000 levels, a further

warming of about 0.5 C (0.9 F) would still occur.

Greenhouse gases in the atmosphere


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Recent increases in atmospheric carbon dioxide (CO2). The monthly CO2 measurements

display small seasonal oscillations in an overall yearly uptrend; each year's maximum is

reached during the northern hemisphere's late spring, and declines during the northern

hemisphere growing season as plants remove some CO2 from the atmosphere.

The greenhouse effect was discovered by Joseph Fourierin 1824 and was first

investigated quantitatively by Svante Arrhenius in 1896. It is the process by which

absorption and emission ofinfrared radiation by atmospheric gases warms a

planet's atmosphere and surface.

Existence of the greenhouse effect as such is not disputed. Naturally occurring

greenhouse gases have a mean warming effect of about 30 C (54 F), without

which Earth would be uninhabitable. The debate centers on how the strength of the

greenhouse effect is changed when human activity increases the atmospheric

concentrations of some greenhouse gases.

On Earth, the major natural greenhouse gases are water vapor, which causes about

36 70% of the greenhouse effect (not including clouds); carbon dioxide (CO2), which

causes 9 26%; methane (CH4), which causes 4 9%; and ozone, which causes 3

7%. Some other naturally occurring gases contribute very small fractions of the

greenhouse effect; one of these, nitrous oxide (N2O), is increasing in concentration

owing to human activity such as agriculture. The atmospheric concentrations of CO2

and methane have increased by 31% and 149% respectively above pre-industrial

levels since 1750. These levels are considerably higher than at any time during the

last 650,000 years, the period for which reliable data has been extracted from ice

cores. From less direct geological evidence it is believed that CO2 values this high

were last attained 20 million years ago. Fossil fuel burning has produced aboutthree-quarters of the increase in CO2 from human activity over the past 20 years.

Most of the rest is due to land-use change, in particulardeforestation.

The present atmospheric concentration of CO2 is about 383 parts per million (ppm)

by volume. Future CO2 levels are expected to rise due to ongoing burning of fossil

fuels and land-use change. The rate of rise will depend on uncertain economic,

sociological, technological, and natural developments, but may be ultimately limited

by the availability of fossil fuels. The IPCC Special Report on Emissions Scenarios

gives a wide range of future CO2 scenarios, ranging from 541 to 970 ppm by theyear 2100. Fossil fuel reserves are sufficient to reach this level and continue

emissions past 2100, if coal, tar sands ormethane clathrates are extensively used.

Positive (reinforcing) feedback effects such as the expected release of methane

from the melting ofpermafrostpeatbogs in Siberia (possibly up to 70,000 million

tonnes) may lead to significant additional sources of greenhouse gas emissions

not included in climate models cited by the IPCC


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Feedbacks

The effects of forcing agents on the climate are complicated by various feedback

processes.

One of the most pronounced feedback effects relates to the evaporation of water. In

the case of warming by the addition of long-lived greenhouse gases such as CO2,

the initial warming will cause more water to be evaporated into the atmosphere.

Since water vapor itself acts as a greenhouse gas, this causes still more warming;the warming causes more water vapor to be evaporated, and so forth until a new

dynamic equilibrium concentration of water vapor is reached with a much larger

greenhouse effect than that due to CO2 alone. (Although this feedback process

involves an increase in the absolute moisture content of the air, the relative humidity

stays nearly constant or even decreases slightly because the air is warmer.) This

feedback effect can only be reversed slowly as CO2 has a long average atmospheric

lifetime.

Feedback effects due to clouds are an area of ongoing research. Seen from below,

clouds emit infrared radiation back to the surface, and so exert a warming effect.

Seen from above, the same clouds reflect sunlight and emit infrared radiation to

space, and so exert a cooling effect. Whether the net effect is warming or cooling

depends on details such as the type and altitude of the cloud. These details are

difficult to represent in climate models, in part because clouds are much smaller

than the spacing between points on the computational grids of climate models

(about 125 to 500 km for models used in the IPCC Fourth Assessment Report).

Nevertheless, cloud feedback is second only to water vapor feedback and is positive

in all the models that were used in the IPCC Fourth Assessment Report. Anotherimportant feedback process is ice-albedo feedback. When global temperatures

increase, ice near the poles melts at an increasing rate. As the ice melts, land or

open water takes its place. Both land and open water are on average less reflective

than ice, and thus absorb more solar radiation. This causes more warming, which in

turn causes more melting, and this cycle continues.

Positive feedback due to release of CO2 and CH4 from thawing permafrost is an

additional mechanism contributing to warming. Possible positive feedback due to

CH4 release from melting seabed ices is a further mechanism to be considered.

The ocean's ability to sequester carbon is expected to decline as it warms, because

the resulting low nutrient levels of the mesopelagic zone limits the growth ofdiatoms


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in favour of smallerphytoplankton that are poorerbiological pumps of carbon.

Solar variation

Variations in solar output, possibly amplified by cloud feedbacks, may have

contributed to recent warming. A difference between this mechanism and

greenhouse warming is that an increase in solar activity should warm the

stratosphere while greenhouse warming should cool the stratosphere. Cooling in the

lower stratosphere has been observed since at least 1960, which would not be

expected if solar activity were the main contributor to recent warming. (Reduction of

stratospheric ozone also has a cooling influence but substantial ozone depletion did

not occur until the late 1970s.) Phenomena such as solar variation combined with

volcanoes have probably had a warming effect from pre-industrial times to 1950, but

a cooling effect since 1950. A few papers suggest that the Sun's contribution may

have been underestimated. Two researchers at Duke University have estimated that

the Sun may have contributed about 40 50% of the global surface warming over the

period 1900 2000, and about 25 35% between 1980 and 2000. Stott and coauthorssuggest that climate models overestimate the relative effect of greenhouse gases

compared to solar forcing; they also suggest that the cooling effects of volcanic dust

and sulfate aerosols have been underestimated. Nevertheless, they conclude that

even with an enhanced climate sensitivity to solar forcing, most of the warming

during the latest decades is attributable to the increases in greenhouse gases.

In 2006, a team of scientists from the United States, Germany, and Switzerland

found no net increase of solar brightness over the last thousand years. Solar cycles

lead to a small increase of 0.07% in brightness over the last 30 years. This effect isfar too minute to contribute significantly to global warming. A 2007 paper by

Lockwood and Frhlich further confirms the lack of a correlation between solar

output and global warming for the time since 1985.

Temperature changes


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Two millennia of mean surface temperatures according to

different reconstructions, each smoothed on a decadal

scale. The unsmoothed, annual value for 2004 is also

plotted for reference.

Recent

Global temperatures on both land and sea have increased by 0.75 C (1.35 F)

relative to the period 1860 1900, according to the instrumental temperature record.

This measured temperature increase is not significantly affected by the urban heat

island. Since 1979, land temperatures have increased about twice as fast as ocean

temperatures (0.25 C per decade against 0.13 C per decade). Temperatures in the

lowertroposphere have increased between 0.12 and 0.22 C (0.22 and 0.4 F) per

decade since 1979, according to satellite temperature measurements. Temperature

is believed to have been relatively stable over the one or two thousand years before

1850, with possibly regional fluctuations such as the Medieval Warm Period or the

Little Ice Age.

Sea temperatures increase more slowly than those on land both because of the

larger effective heat capacity of the oceans and because the ocean can lose heat by

evaporation more readily than the land. Since the northern hemisphere has more

land mass than the southern it warms faster; also there are extensive areas of

seasonal snow cover subject to the snow-albedo feedback. Although more

greenhouse gases are emitted in the northern than southern hemisphere this does

not contribute to the asymmetry of warming as the major gases are essentially well-

mixed between hemispheres.

Based on estimates by NASA's Goddard Institute for Space Studies, 2005 was the

warmest year since reliable, widespread instrumental measurements became

available in the late 1800s, exceeding the previous record set in 1998 by a few

hundredths of a degree. Estimates prepared by the World Meteorological

Organization and the Climatic Research Unit concluded that 2005 was the second

warmest year, behind 1998.


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Anthropogenic emissions of otherpollutantsnotably sulfate aerosolscan exert a

cooling effect by increasing the reflection of incoming sunlight. This partially

accounts for the cooling seen in the temperature record in the middle of the

twentieth century, though the cooling may also be due in part to natural variability.

Paleoclimatologist William Ruddiman has argued that human influence on the global

climate began around 8,000 years ago with the start of forest clearing to provide

land for agriculture and 5,000 years ago with the start of Asian rice irrigation. [37]

Ruddiman's interpretation of the historical record, with respect to the methane data,

has been disputed.

Pre-human climate variations

Earth has experienced warming and cooling many times in the past. The recent

Antarctic EPICA ice core spans 800,000 years, including eight glacial cycles timed

by orbital variations with interglacial warm periods comparable to present

temperatures.

A rapid buildup of greenhouse gases caused warming in the early Jurassic period

(about 180 million years ago), with average temperatures rising by 5 C (9 F).

Research by the Open University indicates that the warming caused the rate of rock

weathering to increase by 400%. As such weathering locks away carbon in calcite

and dolomite, CO2 levels dropped back to normal over roughly the next 150,000

years.

Sudden releases of methane from clathrate compounds (the clathrate gunhypothesis) have been hypothesized as a cause for other warming events in the

distant past, including the Permian-Triassic extinction event (about 251 million years

ago) and the Paleocene-Eocene Thermal Maximum (about 55 million years ago).

Climate models


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The projected temperature increase for a range ofstabilization scenarios (the coloured bands). The

black line in middle of the shaded area indicates 'best

estimates'; the red and the blue lines the likely limits.

From the work ofIPCC AR4, 2007.

Calculations of global warming prepared in or before

2001 from a range ofclimate models under the SRES

A2 emissions scenario, which assumes no action is

taken to reduce emissions.

The geographic distribution of surface warming

during the 21st century calculated by the HadCM3

climate model if a business as usual scenario is

assumed for economic growth and greenhouse gas

emissions. In this figure, the globally averaged

warming corresponds to 3.0 C (5.4 F).


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Scientists have studied global warming with computer models of the climate. These

models are based on physical principles of fluid dynamics, radiative transfer, and

other processes, with some simplifications being necessary because of limitations in

computer power. These models predict that the effect of adding greenhouse gases

is to produce a warmer climate. However, even when the same assumptions of

future GHG levels are used, there still remains a considerable range ofclimate

sensitivity.

Including uncertainties in future greenhouse gas concentrations and climate

modelling, the IPCC anticipates a warming of 1.1 C to 6.4 C (2.0 F to 11.5 F)

between 1990 and 2100 Models have also been used to help investigate the causes

of recent climate change by comparing the observed changes to those that the

models project from various natural and human derived causes.

Climate models can produce a good match to observations of global temperature

changes over the last century, but cannot yet simulate all aspects of climate. These

models do not unambiguously attribute the warming that occurred from

approximately 1910 to 1945 to either natural variation or human effects; however,

they suggest that the warming since 1975 is dominated by man-made greenhouse

gas emissions.

Most global climate models, when run to project future climate, are forced by

imposed greenhouse gas scenarios, generally one from the IPCC Special Report on

Emissions Scenarios (SRES). Less commonly, models may be run by adding a

simulation of the carbon cycle; this generally shows a positive feedback, though this

response is uncertain (under the A2 SRES scenario, responses vary between an

extra 20 and 200 ppm of CO2). Some observational studies also show a positivefeedback.

The representation of clouds is one of the main sources of uncertainty in present-

generation models, though progress is being made on this problem. There is also an

ongoing discussion as to whether climate models are neglecting important indirect

and feedback effects ofsolar variability.

Attributed and expected effects


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Sparse records indicate that glaciers have

been retreating since the early 1800s. In the

1950s measurements began that allow the

monitoring of glacial mass balance,

reported to the WGMS and the NSIDC.

Though it is difficult to connect specific weather events to global warming, an

increase in global temperatures may in turn cause otherchanges, including glacial

retreat and worldwide sea level rise. Changes in the amount and pattern of

precipitation may result in flooding and drought. There may also be changes in the

frequency and intensity ofextreme weatherevents. Other effects may include

changes in agricultural yields, reduced summerstreamflows, species extinctions and

increases in the range ofdisease vectors.

Some effects on both the natural environment and human life are, at least in part,

already being attributed to global warming. A 2001 report by the IPCC suggests that

glacier retreat, ice shelf disruption such as the Larsen Ice Shelf, sea level rise,

changes in rainfall patterns, increased intensity and frequency ofextreme weather

events, are being attributed in part to global warming. While changes are expected

for overall patterns, intensity, and frequencies, it is difficult to attribute specific

events to global warming. Other expected effects include water scarcity in some

regions and increased precipitation in others, changes in mountain snowpack, and

adverse health effects from warmer temperatures.

Increasing deaths, displacements, and economic losses projected due to extreme

weatherattributed to global warming may be exacerbated by growing populationdensities in affected areas, although temperate regions are projected to experience

some minor benefits, such as fewer deaths due to cold exposure. A summary of

probable effects and recent understanding can be found in the report made for the

IPCC Third Assessment Report by Working Group II. The newer

ummary reports that there is observational evidence for an increase in intense

tropical cyclone activity in the NorthAtlantic Ocean since about 1970, in correlation

with the increase in sea surface temperature, but that the detection of long-term


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trends is complicated by the quality of records prior to routine satellite observations.

The summary also states that there is no clear trend in the annual worldwide

number of tropical cyclones.

Additional anticipated effects include sea level rise of 110 to 770 millimeters (0.36 to

2.5 ft) between 1990 and 2100 repercussions to agriculture, possible slowing of the

thermohaline circulation, reductions in the ozone layer, increased intensity and

frequency ofhurricanes and extreme weather events, lowering of ocean pH, and the

spread of diseases such as malaria and dengue fever. One study predicts 18% to

35% of a sample of 1,103 animal and plant species would be extinct by 2050, based

on future climate projections. Two populations ofBay checkerspot butterfly are being

threatened by changes in precipitation, though few mechanistic studies have

documented extinctions due to recent climate change.

Economics

Some economists have tried to estimate the aggregate net economic costs ofdamages from climate change across the globe. Such estimates have so far failed to

reach conclusive findings; in a survey of 100 estimates, the values ran from US$-10

per tonne of carbon (tC) (US$-3 per tonne of carbon dioxide) up to US$350/tC

(US$95 per tonne of carbon dioxide), with a mean of US$43 per tonne of carbon

(US$12 per tonne of carbon dioxide) One widely-publicized report on potential

economic impact is the Stern Review; it suggests that extreme weather might

reduce global gross domestic product by up to 1%, and that in a worst case scenario

global per capita consumption could fall 20%. The report's methodology, advocacy

and conclusions have been criticized by many economists, primarily around the

Review's assumptions ofdiscounting and its choices of scenarios, while others have

supported the general attempt to quantify economic risk, even if not the specific

numbers. In a summary of economic cost associated with climate change, the

United Nations Environment Programme emphasizes the risks to insurers,

reinsurers, and banks of increasingly traumatic and costly weather events. Other

economic sectors likely to face difficulties related to climate change include

agriculture and transport. Developing countries, rather than the developed world, are

at greatest economic risk.

Adaptation and mitigation

The broad agreement among climate scientists that global temperatures will

continue to increase has led nations, states, corporations and individuals to

implement actions to try to curtail global warming oradjust to it. Many environmental

groups encourage action against global warming, often by the consumer, but also by

community and regional organizations. There has also been business action on

climate change, including efforts at increased energy efficiency and (still limited)


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moves to alternative fuels. One important innovation has been the development of

greenhouse gas emissions trading through which companies, in conjunction with

government, agree to cap their emissions or to purchase credits from those below

their allowances.

The world's primary international agreement on combating global warming is the

Kyoto Protocol, an amendment to the United Nations Framework Convention on

Climate Change (UNFCCC), negotiated in 1997. The Protocol now covers more

than 160 countries globally and over 55% of global greenhouse gas emissions. The

United States (historically the world's largest greenhouse gas emitter),Australia, and

Kazakhstan have not ratified the treaty. China (which is expected to soon overtake

the US in greenhouse gas emissions) and India have ratified the treaty, but as

developing countries, are exempt from its provisions. Chinese PremierWen Jiabao

has called on the nation to redouble its efforts to tacklepollution and global warming.

This treaty expires in 2012, and international talks began in May 2007 on a future

treaty to succeed the current one.

The world's primary body for crafting a response is the Intergovernmental Panel on

Climate Change (IPCC), a UN-sponsored activity which holds periodic meetings

between national delegations on the problems of global warming, and issues

working papers and assessments on the current status of the science of climate

change, impacts, and mitigation. It convenes four different working groups

examining various specific issues. For example, in May 2007, the IPCC held

conferences in Bonn, Germany and in Bangkok, Thailand.

In the absence of clear concerted action by the US Federal government, various

state, local, and regional governments have begun their own initiatives to indicatesupport and compliance with the Kyoto Protocol, on a local basis. For example, the

Regional Greenhouse Gas Initiative (RGGI), is a state-level emissions capping and

trading program, which was founded on January 18, 2007 and is comprised of eight

Northeastern US states.

Issue debate, political processes and laws

Over the past several years, public perceptions and attitudes concerning the causes

and importance of global warming have changed Increased awareness of thescientific findings surrounding global warming has resulted in political and economic

debate. Poor regions, particularlyAfrica, appear at greatest risk from the suggested

effects of global warming, while their actual emissions have been negligible

compared to the developed world. At the same time, developing country exemptions

from provisions of the Kyoto Protocol have been criticized by the United States and

Australia, and have been used as part of their rationale for continued non-ratification

In the Western world, the idea of human influence on climate and efforts to combat it

has gained wider acceptance in Europe than in the United StatesFossil fuel


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organizations and companies such asAmerican Petroleum Institute and

ExxonMobil, represented by individuals such as Philip Cooney and some think tanks

such as the Competitive Enterprise Institute and the Cato Institute, have

campaigned to downplay the risks of climate change, described by some as climate

change denial. Environmental groups and public figures have launched campaigns

emphasizing the risks. Recently, some fossil fuel companies have scaled back such

efforts or called for policies to reduce global warming.

This issue has sparked debate regarding the benefits of limiting industrialemissions

ofgreenhouse gases versus the effects on economic activity. In the U.S., the

political manipulation of scientific testimonies and reports has also become an issue

There has also been discussion in several countries about the cost of adopting

alternate, cleanerenergy sources in order to reduce emissions.

Another point of debate is the degree to which newly-developed economies, such as

India and China, should be expected to constrain their emissions. China's CO2

emissions (mainly from coal power plants and cars), are expected to exceed thoseof the U.S. within the next few years (and according to one report may have already

done so). China has contended that it has less obligation to reduce emissions, since

its emissions per capita are about one-fifth those of the U.S.; the U.S. contends that

if they must bear the costs of reducing emissions, so should China. India will also

soon be one of the biggest sources of industrial emissions, and has made assertions

similar to China's on this issue.

Related climatic issues

A variety of issues are often raised in relation to global warming. One is ocean

acidification. Increased atmospheric CO2 increases the amount of CO2 dissolved in

the oceans. CO2 dissolved in the ocean reacts with water to form carbonic acid

resulting in acidification. Ocean surface pH is estimated to have decreased from

approximately 8.25 to 8.14 since the beginning of the industrial era, and it is

estimated that it will drop by a further 0.14 to 0.5 units by 2100 as the ocean absorbs

more CO2.[1][84] Since organisms and ecosystems are adapted to a narrow range of

pH, this raises extinction concerns, directly driven by increased atmospheric CO2,

that could disrupt food webs and impact human societies that depend on marineecosystem services.[85] Another related issue that may have partially mitigated

global warming in the late twentieth century is global dimming, the gradual reduction

in the amount of global direct irradiance at the Earth's surface. From 1960 to 1990

human-caused aerosols likely precipitated this effect. Scientists have stated with

66 90% confidence that the effects of human-caused aerosols, along with volcanic

activity, have offset some of global warming, and that greenhouse gases would have

resulted in more warming than observed if not for these dimming agents.Ozone

depletion, the steady decline in the total amount ofozone in Earth's stratosphere, is


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frequently cited in relation to global warming. Although there are areas of linkage,

the relationship between the two is not strong

Avoiding Dangerous Climate Change: AScientific Symposium on Stabilisation

of Greenhouse Gases was a 2005 international conference that redefined the link

between atmospheric greenhouse gas concentration, and the 2C (3.6F) ceiling on

global warming thought necessary to avoid the most serious effects of globalwarming. Previously this had generally been accepted as being 550 ppm.

The conference took place under the United Kingdom's presidency of the G8, with

the participation of around 200 'internationally renowned' scientists from 30

countries. It was hosted by the Hadley Centre for Climate Prediction and Research

in Exeter, between 1 February-3 February.

ObjectivesThe conference was called to bring together the latest research into what would be

necessary to achieve the objective of the 1992 United Nations Framework

Convention on Climate Change:

to achieve, in accordance with the relevant provisions of the Convention,

stabilization ofgreenhouse gas concentrations in the atmosphere at a level that

would prevent dangerous anthropogenicinterference with the climate system.

It was also intended to encourage further research in the area. An initial assessmentof the subject had been included in the 2001 IPCC Third Assessment Report,

however the topic had received relatively little international discussion.

Specifically, the conference explored three issues:

For different levels of climate change what are the key impacts, for different regions

and sectors and for the world as a whole?

What would such levels of climate change imply in terms of greenhouse gas

stabilisation concentrations and emission pathways required to achieve such levels?

What options are there for achieving stabilisation of greenhouse gases at different

stabilisation concentrations in the atmosphere, taking into account costs and

uncertainties?


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Conclusions

Among the conclusions reached, the most significant was a new assessment of the

link between the concentration of greenhouse gases in the atmosphere and the

increase in global temperature levels. The IPCC had concluded that the most

serious consequences of global warming might be avoided if global average

temperatures rose by no more than 2C (3.6F) above pre-industrial levels (1.4C

above present levels). It had generally been assumed that this would occur ifgreenhouse gas concentrations rose above 550 ppm carbon dioxide equivalent by

volume. This concentration was, for example, informing government in certain

countries including the European Union.

The conference concluded that, at the level of 550 ppm, it was likely that 2C would

be exceeded, based on the projections of more recent climate models. Stabilising

greenhouse gas concentrations at 450 ppm would only result in a 50% likelihood of

limiting global warming to 2C, and that it would be necessary to achieve

stabilisation below 400 ppm to give a relatively high certainty of not exceeding 2C.The conference also claimed that, if action to reduce emissions is delayed by 20

years, rates of emission reduction may need to be 3 to 7 times greater to meet the

same temperature target.

Reaction

As a result of the revised opinion on the 'safe' atmospheric concentration of

greenhouse gasses, environmental groups and some political parties are demanding

that the UK Government take this into account in the Climate Change Bill, by settinga target to cut emissions by 75% to 80% by 2050.

The objective (Article 2) of the UN Framework Convention on

Climate Change (UNFCCC) is stated as follows:

The ultimate objective of this Convention and any related legal

instruments that the Conference of the Parties may adopt is to achieve,

in accordance with the relevant provisions of the Convention,stabilization of greenhouse gas concentrations in the atmosphere at a

level that would prevent dangerous anthropogenic interference with the

climate system.

Such a level should be achieved within a time-frame sufficient to allow

ecosystems to adapt naturally to climate change, to ensure that food

production is not threatened and to enable economic development to

proceed in a sustainable manner.


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This objective has been little explored in international science studies.

The IPCC presented an initial assessment of the scientific knowledge

surrounding stabilisation in its Third Assessment Report published in

2001. We believe that it is important to make progress in understanding

the ultimate scale and effect of climate, what effects need to be avoided

and what this means for actions in the near and medium term. The UK

has therefore decided to host an international scientific meeting to take

an in-depth look at the scientific issues associated with stabilising

greenhouse gases in the atmosphere.

The conference will review the likely impacts of climate change. Such

impacts could include abrupt and rapid change, irreversible changes to

the climate system and significant sectoral or regional impacts.

The meeting provides an opportunity to take stock of the scientific and

technical issues surrounding stabilisation between the IPCC 3rd (2001)

and 4th (2007) Assessment Reports, and will also encourage more

research on this particular issue.

The meeting will take as read the conclusions of the IPCC 3rd

Assessment Report that climate change due to human actions is already

happening, and that without actions to reduce emissions climate change

will continue, with increasingly adverse effects on the environment and

human society.

global warming refers to the increase in the average temperature of the earth

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