quinta-feira, 26 de abril de 2007

Climate Change 2007

IPCC WGII Fourth Assessment Report

Summary for Policymakers April 6


, 2007


Working Group II Contribution to the

Intergovernmental Panel on Climate Change

Fourth Assessment Report

Climate Change 2007:

Climate Change Impacts, Adaptation and Vulnerability

Summary for Policymakers

This version has yet to be copy-edited

Drafting Authors:

Neil Adger, Pramod Aggarwal, Shardul Agrawala, Joseph Alcamo, Abdelkader Allali, Oleg

Anisimov, Nigel Arnell, Michel Boko, Osvaldo Canziani, Timothy Carter, Gino Casassa,

Ulisses Confalonieri, Rex Victor Cruz, Edmundo de Alba Alcaraz, William Easterling,

Christopher Field, Andreas Fischlin, B. Blair Fitzharris, Carlos Gay García, Clair Hanson,

Hideo Harasawa, Kevin Hennessy, Saleemul Huq, Roger Jones, Lucka Kajfež Bogataj, David

Karoly, Richard Klein, Zbigniew Kundzewicz, Murari Lal, Rodel Lasco, Geoff Love, Xianfu

Lu, Graciela Magrín, Luis José Mata, Roger McLean, Bettina Menne, Guy Midgley, Nobuo

Mimura, Monirul Qader Mirza, José Moreno, Linda Mortsch, Isabelle Niang-Diop, Robert

Nicholls, Béla Nováky, Leonard Nurse, Anthony Nyong, Michael Oppenheimer, Jean

Palutikof, Martin Parry, Anand Patwardhan, Patricia Romero Lankao, Cynthia Rosenzweig,

Stephen Schneider, Serguei Semenov, Joel Smith, John Stone, Jean-Pascal van Ypersele,

David Vaughan, Coleen Vogel, Thomas Wilbanks, Poh Poh Wong, Shaohong Wu, Gary


IPCC WGII Fourth Assessment Report

Summary for Policymakers April 6


, 2007


A. Introduction

This Summary sets out the key policy-relevant findings of the Fourth Assessment of Working Group II of the

Intergovernmental Panel on Climate Change (IPCC).

The Assessment is of current scientific understanding of impacts of climate change on natural


managed and

human systems, the capacity of these systems to adapt and their vulnerability


. It builds upon past IPCC

assessments and incorporates new knowledge gained since the Third Assessment.

Statements in this Summary are based on chapters in the Assessment and principal sources are given at the

end of each paragraph



B. Current knowledge about observed impacts of climate

change on the natural and human environment

A full consideration of observed climate change is provided in the IPCC Working Group I Fourth

Assessment. This part of the Summary concerns the relationship between observed climate change and

recent observed changes in the natural and human environment.

The statements presented here are based largely on data sets that cover the period since 1970. The number of

studies of observed trends in the physical and biological environment and their relationship to regional

climate changes has increased greatly since the Third Assessment in 2001. The quality of the data sets has

also improved. There is, however, a notable lack of geographic balance in data and literature on observed

changes, with marked scarcity in developing countries.

These studies have allowed a broader and more confident assessment of the relationship between observed

warming and impacts than was made in the Third Assessment. That Assessment concluded that “there is

high confidence


that recent regional changes in temperature have had discernible impacts on many physical

and biological systems”.

From the current Assessment we conclude the following.

Observational evidence from all continents and most oceans shows that many

natural systems are being affected by regional climate changes, particularly

temperature increases.

With regard to changes in snow, ice and frozen ground (including permafrost)


, there is high confidence that

natural systems are affected. Examples are:

enlargement and increased numbers of glacial lakes [1.3];

increasing ground instability in permafrost regions, and rock avalanches in mountain regions [1.3];

changes in some Arctic and Antarctic ecosystems, including those in sea-ice biomes, and also

predators high in the food chain [1.3, 4.4, 15.4].

, 2007, 3

Based on growing evidence, there is high confidence that the following types of hydrological systems are

being affected around the world:

increased run-off and earlier spring peak discharge in many glacier- and snow-fed rivers [1.3];

warming of lakes and rivers in many regions, with effects on thermal structure and water quality


There is very high confidence, based on more evidence from a wider range of species, that recent warming is

strongly affecting terrestrial biological systems, including such changes as:

earlier timing of spring events, such as leaf-unfolding, bird migration and egg-laying [1.3];

poleward and upward shifts in ranges in plant and animal species [1.3, 8.2, 14.2].

Based on satellite observations since the early 1980s, there is high confidence that there has been a trend in

many regions towards earlier ‘greening’


of vegetation in the spring linked to longer thermal growing

seasons due to recent warming. [1.3, 14.2]

There is high confidence, based on substantial new evidence, that observed changes in marine and freshwater

biological systems are associated with rising water temperatures, as well as related changes in ice cover,

salinity, oxygen levels and circulation [1.3]. These include:

shifts in ranges and changes in algal, plankton and fish abundance in high-latitude oceans [1.3];

increases in algal and zooplankton abundance in high-latitude and high-altitude lakes [1.3];

range changes and earlier migrations of fish in rivers [1.3].

The uptake of anthropogenic carbon since 1750 has led to the ocean becoming more acidic with an average

decrease in pH of 0.1 units [IPCC Working Group I Fourth Assessment]. However, the effects of observed

ocean acidification on the marine biosphere are as yet undocumented. [1.3]

A global assessment of data since 1970 has shown it is likely6 that anthropogenic

warming has had a discernible influence on many physical and biological systems.

Much more evidence has accumulated over the past five years to indicate that changes in many physical and

biological systems are linked to anthropogenic warming. There are four sets of evidence which, taken

together, support this conclusion:

1. The Working Group I Fourth Assessment concluded that most of the observed increase in the

globally averaged temperature since the mid-20th century is very likely due to the observed increase

in anthropogenic greenhouse gas concentrations.

2. Of the more than 29,000 observational data series


, from 75 studies, that show significant change in

many physical and biological systems, more than 89% are consistent with the direction of change

expected as a response to warming. (Figure SPM-1) [1.4]


Measured by the Normalised Difference Vegetation Index, which is a relative measure of the amount of green vegetation in an area

based on satellite images.


See Endbox 2.


A subset of about 29,000 data series was selected from about 80,000 data series from 577 studies. These met the following criteria:

(1) Ending in 1990 or

later; (2) spanning a period of at least 20 years; and (3) showing a significant change in either

direction, as assessed in individual studies.

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Summary for Policymakers April 6


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3 A global synthesis of studies in this Assessment strongly demonstrates that the spatial agreement

between regions of significant warming across the globe and the locations of significant observed

changes in many systems consistent with warming is very unlikely to be due solely to natural

variability of temperatures or natural variability of the systems.(see Figure SPM-1) [1.4]

4 Finally, there have been several modelling studies that have linked responses in some physical and

biological systems to anthropogenic warming by comparing observed responses in these systems

with modelled responses in which the natural forcings (solar activity and volcanoes) and

anthropogenic forcings (greenhouse gases and aerosols) are explicitly separated. Models with

combined natural and anthropogenic forcings simulate observed responses significantly better than

models with natural forcing only. [1.4]

Limitations and gaps prevent more complete attribution of the causes of observed system responses to

anthropogenic warming. First, the available analyses are limited in the number of systems and locations

considered. Second, natural temperature variability is larger at the regional than the global scale, thus

affecting identification of changes due to external forcing. Finally, at the regional scale other factors (such

as land-use change, pollution, and invasive species) are influential. [1.4]

Nevertheless, the consistency between observed and modelled changes in several studies and the spatial

agreement between significant regional warming and consistent impacts at the global scale is sufficient to

conclude with high confidence that anthropogenic warming over the last three decades has had a discernible

influence on many physical and biological systems. [1.4]

Other effects of regional climate changes on natural and human environments are

emerging, although many are difficult to discern due to adaptation and non-climatic


Effects of temperature increases have been documented in the following systems (medium confidence):

effects on agricultural and forestry management at Northern Hemisphere higher latitudes, such as

earlier spring planting of crops, and alterations in disturbance regimes of forests due to fires and

pests [1.3];

some aspects of human health, such as heat-related mortality in Europe, infectious disease vectors in

some areas, and allergenic pollen in Northern Hemisphere high and mid-latitudes [1.3, 8.2, 8.ES];

some human activities in the Arctic (e.g., hunting and travel over snow and ice) and in lowerelevation

alpine areas (such as mountain sports). [1.3]

Recent climate changes and climate variations are beginning to have effects on many other natural and

human systems. However, based on the published literature, the impacts have not yet become established

trends. Examples include:

Settlements in mountain regions are at enhanced risk to glacier lake outburst floods caused by

melting glaciers. Governmental institutions in some places have begun to respond by building dams

and drainage works. [1.3]

In the Sahelian region of Africa, warmer and drier conditions have led to a reduced length of

growing season with detrimental effects on crops. In southern Africa, longer dry seasons and more

uncertain rainfall are prompting adaptation measures. [1.3]

Sea-level rise and human development are together contributing to losses of coastal wetlands and

mangroves and increasing damage from coastal flooding in many areas. [1.3]

IPCC WGII Fourth Assessment Report

Summary for Policymakers April 6


, 2007


Changes in physical and biological systems and

surface temperature 1970-2004

Figure SPM-1.

Locations of significant observed changes in physical systems (cryosphere, hydrology, and

coastal processes) and biological systems (terrestrial, marine, and freshwater biological systems), for studies

ending in 1990 or later with at least 20 years of data, shown together with surface temperature changes for

1970-2004 . Data for the system changes are taken from ~75 studies (of which ~70 are new since the Third

Assessment) containing around 29,000 data series, of which about 27,800 are from European studies. White

regions do not contain sufficient observational climate data to estimate a temperature trend. Boxes show the

significant changes for (i) continental regions: North America (NAM), Latin America (LA), Europe (EUR),

Africa (AFR), Asia (AS), Australia and New Zealand (ANZ), and Polar Regions (PR) and (ii) global-scale:

Terrestrial (TER), Marine and Freshwater (MFW), Global (GLO) changes in physical and biological systems

based on the studies available. Top row of boxes shows number of observed time series with a significant

trend and bottom row shows percentage of these in which the trend is consistent with warming. [F1.8, F1.9] ]

Figure SPM-1.

Locations of significant changes in observations of physical systems (snow, ice and frozen

ground; hydrology; and coastal processes) and biological systems (terrestrial, marine, and freshwater

biological systems), are shown together with surface air temperature changes over the period 1970-2004. A

subset of about 29,000 data series was selected from about 80,000 data series from 577 studies. These met

the following criteria: (1) Ending in 1990 or later; (2) spanning a period of at least 20 years; and (3) showing

a significant change in either direction, as assessed in individual studies. These data series are from about 75

studies (of which ~70 are new since the Third Assessment) and contain about 29,000 data series, of which

about 28,000 are from European studies. White areas do not contain sufficient observational climate data to

estimate a temperature trend. The 2 x 2 boxes show the total number of data series with significant changes

(top row) and the percentage of those consistent with warming (bottom row) for (i) continental regions:

North America (NAM), Latin America (LA), Europe (EUR), Africa (AFR), Asia (AS), Australia and New

IPCC WGII Fourth Assessment Report

Summary for Policymakers April 6


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Zealand (ANZ), and Polar Regions (PR) and (ii) global-scale: Terrestrial (TER), Marine and Freshwater

(MFW), and Global (GLO). The numbers of studies from the seven regional boxes (NAM, …, PR) do not

add up to the global (GLO) totals because numbers from regions except Polar do not include the numbers

related to Marine and Freshwater (MFR) systems. [F1.8, F1.9; Working Group I Fourth Assessment F3.9b]

IPCC WGII Fourth Assessment Report

Summary for Policymakers April 6


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C. Current knowledge about future impacts

The following is a selection of the key findings regarding projected impacts, as well as some findings on

vulnerability and adaptation, in each system, sector and region for the range of (unmitigated) climate changes

projected by the IPCC over this century

8 judged to be relevant for people and the environment9

. The impacts

frequently reflect projected changes in precipitation and other climate variables in addition to temperature,

sea level and concentrations of atmospheric carbon dioxide. The magnitude and timing of impacts will vary

with the amount and timing of climate change and, in some cases, the capacity to adapt. These issues are

discussed further in later sections of the Summary.

More specific information is now available across a wide range of systems and

sectors concerning the nature of future impacts, including for some fields not

covered in previous assessments.

Fresh water resources and their management

By mid-century, annual average river runoff and water availability are projected to increase by 10-40% at

high latitudes and in some wet tropical areas, and decrease by 10-30% over some dry regions at mid-latitudes

and in the dry tropics, some of which are presently water stressed areas. In some places and in particular

seasons, changes differ from these annual figures. ** D



Drought-affected areas will likely increase in extent. Heavy precipitation events, which are very likely to

increase in frequency, will augment flood risk. ** N [Working Group I Fourth Assessment, 3.4]

Adaptation procedures and risk management practices for the water sector are being developed in some

countries and regions that have recognised projected hydrological changes with related uncertainties. *** N


In the course of the century, water supplies stored in glaciers and snow cover are projected to decline,

reducing water availability in regions supplied by meltwater from major mountain ranges, where more than

one-sixth of the world population currently lives. ** N [3.4]


Temperature changes are expressed as the difference from the period 1980-1999. To express the change relative to the period 1850-

1899, add 0.5




Criteria of choice: magnitude and timing of impact, confidence in the assessment, representative coverage of the system, sector and



In the Section C text, the following conventions are used:

Relationship to the Third Assessment:

D Further development of a conclusion in the Third Assessment

N New conclusion, not in the Third Assessment

Level of confidence in the whole statement:

*** Very high confidence

** High confidence

* Medium confidence

IPCC WGII Fourth Assessment Report

Summary for Policymakers April 6


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The resilience of many ecosystems is likely to be exceeded this century by an unprecedented combination of

climate change, associated disturbances (e.g., flooding, drought, wildfire, insects, ocean acidification), and

other global change drivers (e.g., land use change, pollution, over-exploitation of resources). ** N [4.1 to


Over the course of this century net carbon uptake by terrestrial ecosystems is likely to peak before midcentury

and then weaken or even reverse


, thus amplifying climate change. ** [4.ES]

Approximately 20-30% 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. * N [4.4, T4.1]

For increases in global average temperature exceeding 1.5-2.5°C and in concomitant atmospheric carbon

dioxide concentrations, there are projected to be major changes in ecosystem structure and function, species’

ecological interactions, and species’ geographic ranges, with predominantly negative consequences for

biodiversity, and ecosystem goods and services e.g., water and food supply. ** N [4.4]

The progressive acidification of oceans due to increasing atmospheric carbon dioxide is expected to have

negative impacts on marine shell forming organisms (e.g., corals) and their dependent species. * N [B4.4,


Food, fibre and forest products

Crop productivity is projected to increase slightly at mid to high latitudes for local mean temperature

increases of up to 1-3°C depending on the crop, and then decrease beyond that in some regions. * D [5.4]

At lower latitudes, especially seasonally dry and tropical regions, crop productivity is projected to decrease

for even small local temperature increases (1-2°C), which would increase risk of hunger. * D [5.4]

Globally, the potential for food production is projected to increase with increases in local average

temperature over a range of 1-3°C, but above this it is projected to decrease. * D [5.4, 5.ES]

Adaptations such as altered cultivars and planting times allow low and mid- to high latitude cereal yields to

be maintained at or above baseline yields for modest warming. * N [5.5]

Increases in the frequency of droughts and floods are projected to affect local production negatively,

especially in subsistence sectors at low latitudes. ** D [5.4, 5.ES]

Globally, commercial timber productivity rises modestly with climate change in the short- to medium-term,

with large regional variability around the global trend. * D [5.4]

Regional changes in the distribution and production of particular fish species are expected due to continued

warming, with adverse effects projected for aquaculture and fisheries. ** D[5.4.6]


Assuming continued greenhouse gas emissions at or above current rates and other global changes including land use changes

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Coastal systems and low-lying areas

Coasts are projected to be exposed to increasing risks, including coastal erosion, due to climate change and

sea-level rise and the effect will be exacerbated by increasing human-induced pressures on coastal areas. ***

D [6.3, 6.4]

Corals are vulnerable to thermal stress and have low adaptive capacity. Increases in sea surface temperature

of about 1 to 3°C are projected to result in more frequent coral bleaching events and widespread mortality,

unless there is thermal adaptation or acclimatisation by corals. *** D [B6.1, 6.4]

Coastal wetlands including salt marshes and mangroves are projected to be negatively affected by sea-level

rise especially where they are constrained on their landward side, or starved of sediment. *** D [6.4]

Many millions more people are projected to be flooded every year due to sea-level rise by the 2080s. Those

densely-populated and low-lying areas where adaptive capacity is relatively low, and which already face

other challenges such as tropical storms or local coastal subsidence, are especially at risk. The numbers

affected will be largest in the mega-deltas of Asia and Africa while small islands are especially vulnerable.

*** D [6.4]

Adaptation for coastal regions will be more challenging in developing countries than developed countries

due to constraints on adaptive capacity. ** D [6.4, 6.5, T6.11]

Industry, Settlement and Society

Costs and benefits of climate change for industry, settlement, and society will vary widely by location and

scale. In the aggregate, however, net effects will tend to be more negative the larger the change in climate. **

N [7.4, 7.6]

The most vulnerable industries, settlements and societies are generally those in coastal and river flood plains,

those whose economies are closely linked with climate-sensitive resources, and those in areas prone to

extreme weather events, especially where rapid urbanisation is occurring. ** D [7.1, 7.3, 7.4, 7.5]

Poor communities can be especially vulnerable, in particular those concentrated in high-risk areas. They

tend to have more limited adaptive capacities, and are more dependent on climate-sensitive resources such as

local water and food supplies. ** N [7.2, 7.4, 5.4]

Where extreme weather events become more intense and/or more frequent, the economic and social costs of

those events will increase, and these increases will be substantial in the areas most directly affected. Climate

change impacts spread from directly impacted areas and sectors to other areas and sectors through extensive

and complex linkages. ** N [7.4, 7.5]


Projected climate change-related exposures are likely to affect the health status of millions of people,

particularly those with low adaptive capacity, through:

increases in malnutrition and consequent disorders, with implications for child growth and


increased deaths, disease and injury due to heat waves, floods, storms, fires and droughts;

the increased burden of diarrhoeal disease;

the increased frequency of cardio-respiratory diseases due to higher concentrations of ground level

ozone related to climate change; and,

the altered spatial distribution of some infectious disease vectors. ** D [8.4, 8.ES, 8.2]

Climate change is expected to have some mixed effects, such as the decrease or increase of the range and

IPCC WGII Fourth Assessment Report

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transmission potential of malaria in Africa. ** D [8.4]

Studies in temperate areas


have shown that climate change is projected to bring some benefits, such as

fewer deaths from cold exposure. Overall it is expected that these benefits will be outweighed by the

negative health effects of rising temperatures world-wide, especially in developing countries. ** D [8.4]

The balance of positive and negative health impacts will vary from one location to another, and will alter

over time as temperatures continue to rise. Critically important will be factors that directly shape the health

of populations such as education, health care, public health prevention and infrastructure and economic

development. *** N [8.3]

More specific information is now available across the regions of the world

concerning the nature of future impacts, including for some places not covered in

previous assessments.


By 2020, between 75 and 250 million people are projected to be exposed to an increase of water stress due to

climate change. If coupled with increased demand, this will adversely affect livelihoods and exacerbate

water-related problems. ** D [9.4, 3.4, 8.2, 8.4]

Agricultural production, including access to food, in many African countries and regions is projected to be

severely compromised by climate variability and change. The area suitable for agriculture, the length of

growing seasons and yield potential, particularly along the margins of semi-arid and arid areas, are expected

to decrease. This would further adversely affect food security and exacerbate malnutrition in the continent. In

some countries, yields from rain-fed agriculture could be reduced by up to 50% by 2020. ** D [9.2, 9.4,

F9.4, 9.6, 8.4]

Local food supplies are projected to be negatively affected by decreasing fisheries resources in large lakes

due to rising water temperatures, which may be exacerbated by continued over-fishing. ** N [9.4, 5.4, 8.4]

Towards the end of the 21st century, projected sea-level rise will affect low-lying coastal areas with large

populations. The cost of adaptation could amount to at least 5-10% of GDP. Mangroves and coral reefs are

projected to be further degraded, with additional consequences for fisheries and tourism. ** D [9.4]

New studies confirm that Africa is one of the most vulnerable continents to climate variability and change

because of multiple stresses and low adaptive capacity. Some adaptation to current climate variability is

taking place, however, this may be insufficient for future changes in climate. ** N [9.5]


Glacier melt in the Himalayas is projected to increase flooding, rock avalanches from destabilised slopes,

and affect water resources within the next two to three decades. This will be followed by decreased river

flows as the glaciers recede. * N [10.2, 10.4]

Freshwater availability in Central, South, East and Southeast Asia particularly in large river basins is

projected to decrease due to climate change which, along with population growth and increasing demand

arising from higher standards of living, could adversely affect more than a billion people by the 2050s. ** N



Studies mainly in industrialised countries.

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Coastal areas, especially heavily-populated mega-delta regions in South, East and Southeast Asia, will be at

greatest risk due to increased flooding from the sea and in some mega-deltas flooding from the rivers. ** D


Climate change is projected to impinge on sustainable development of most developing countries of Asia as

it compounds the pressures on natural resources and the environment associated with rapid urbanisation,

industrialisation, and economic development. ** D [10.5]

It is projected that crop yields could increase up to 20% in East and Southeast Asia while it could decrease

up to 30% in Central and South Asia by the mid-21st century. Taken together and considering the influence

of rapid population growth and urbanization, the risk of hunger is projected to remain very high in several

developing countries. * N [10.4.1]

Endemic morbidity and mortality due to diarrhoeal disease primarily associated with floods and droughts are

expected to rise in East, South and Southeast Asia due to projected changes in hydrological cycle associated

with global warming. Increases in coastal water temperature would exacerbate the abundance and/or toxicity

of cholera in South Asia. **N [10.4.5]

Australia and New Zealand

As a result of reduced precipitation and increased evaporation, water security problems are projected to

intensify by 2030 in southern and eastern Australia and, in New Zealand, in Northland and some eastern

regions. ** D [11.4]

Significant loss of biodiversity is projected to occur by 2020 in some ecologically-rich sites including the

Great Barrier Reef and Queensland Wet Tropics. Other sites at risk include Kakadu wetlands, south-west

Australia, sub-Antarctic islands and the alpine areas of both countries. *** D [11.4]

Ongoing coastal development and population growth in areas such as Cairns and Southeast Queensland

(Australia) and Northland to Bay of Plenty (New Zealand), are projected to exacerbate risks from sea-level

rise and increases in the severity and frequency of storms and coastal flooding by 2050. *** D [11.4, 11.6]

Production from agriculture and forestry by 2030 is projected to decline over much of southern and eastern

Australia, and over parts of eastern New Zealand, due to increased drought and fire. However, in New

Zealand, initial benefits to agriculture and forestry are projected in western and southern areas and close to

major rivers due to a longer growing season, less frost and increased rainfall. ** N [11.4]

The region has substantial adaptive capacity due to well-developed economies and scientific and technical

capabilities, but there are considerable constraints to implementation and major challenges from changes in

extreme events. Natural systems have limited adaptive capacity. ** N [11.2, 11.5]


For the first time, wide ranging impacts of changes in current climate have been documented: retreating

glaciers, longer growing seasons, shift of species ranges, and health impacts due to a heat wave of

unprecedented magnitude. The observed changes described above are consistent with those projected for

future climate change. *** N [12.2, 12.4, 12.6]

Nearly all European regions are anticipated to be negatively affected by some future impacts of climate

change and these will pose challenges to many economic sectors. Climate change is expected to magnify

regional differences in Europe’s natural resources and assets. Negative impacts will include increased risk of

inland flash floods, and more frequent coastal flooding and increased erosion (due to storminess and sealevel

rise). The great majority of organisms and ecosystems will have difficulties adapting to climate change.

Mountainous areas will face glacier retreat, reduced snow cover and winter tourism, and extensive species

losses (in some areas up to 60% under high emission scenarios by 2080). *** D [12.4]

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In Southern Europe, climate change is projected to worsen conditions (high temperatures and drought) in a

region already vulnerable to climate variability, and to reduce water availability, hydropower potential,

summer tourism, and in general, crop productivity. It is also projected to increase health risks due to heat

waves and the frequency of wildfires. ** D [12.2, 12.4, 12.7]

In Central and Eastern Europe, summer precipitation is projected to decrease, causing higher water stress.

Health risks due to heat waves are projected to increase. Forest productivity is expected to decline and the

frequency of peatland fires to increase. ** D [12.4]

In Northern Europe, climate change is initially projected to bring mixed effects, including some benefits such

as reduced demand for heating, increased crop yields and increased forest growth. However, as climate

change continues, its negative impacts (including more frequent winter floods, endangered ecosystems and

increasing ground instability) are likely to outweigh its benefits. ** D [12.4]

Adaptation to climate change is likely to benefit from experience gained in reaction to extreme climate

events, by specifically implementing proactive climate change risk management adaptation plans. *** N


Latin America

By mid-century, increases in temperature and associated decreases in soil water are projected to lead to

gradual replacement of tropical forest by savanna in eastern Amazonia. Semi-arid vegetation will tend to be

replaced by arid-land vegetation. There is a risk of significant biodiversity loss through species extinction in

many areas of tropical Latin America


** D [13.4]

In drier areas, climate change is expected to lead to salinisation and desertification of agricultural land.

Productivity of some important crops are projected to decrease and livestock productivity to decline, with

adverse consequences for food security. In temperate zones soybean yields are projected to increase. ** N

[13.4, 13.7]

Sea-level rise is projected to cause increased risk of flooding in low-lying areas. ** N [13.4, 13.7] Increases

in sea surface temperature due to climate change are projected to have adverse effects on Mesoamerican

coral reefs, and cause shifts in the location of south-east Pacific fish stocks. ** N [13.4]

Changes in precipitation patterns and the disappearance of glaciers are projected to significantly affect water

availability for human consumption, agriculture and energy generation. ** D [13.4]

Some countries have made efforts to adapt, particularly through conservation of key ecosystems, early

warning systems, risk management in agriculture, strategies for flood drought and coastal management, and

disease surveillance systems. However, the effectiveness of these efforts is outweighed by: lack of basic

information, observation and monitoring systems; lack of capacity building and appropriate political,

institutional and technological frameworks; low income; and settlements in vulnerable areas, among others.

** D [13.2]

North America

Moderate climate change in the early decades of the century is projected to increase aggregate yields of rainfed

agriculture by 5-20%, but with important variability among regions. Major challenges are projected for

crops that are near the warm end of their suitable range or depend on highly utilised water resources. ** D


Warming in western mountains is projected to cause decreased snowpack, more winter flooding, and reduced

summer flows, exacerbating competition for over-allocated water resources. *** D [14.4, B14.2]

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Disturbances from pests, diseases, and fire are projected to have increasing impacts on forests, with an

extended period of high fire risk and large increases in area burned. *** N [14.4, B14.1]

Cities that currently experience heat waves are expected to be further challenged by an increased number,

intensity and duration of heat waves during the course of the century, with potential for adverse health

impacts. The growing number of the elderly population is most at risk. *** D [14.4]

Coastal communities and habitats will be increasingly stressed by climate change impacts interacting with

development and pollution. Population growth and the rising value of infrastructure in coastal areas increase

vulnerability to climate variability and future climate change, with losses projected to increase if the intensity

of tropical storms increases. Current adaptation is uneven and readiness for increased exposure is low. *** N


Polar Regions

In the Polar Regions, the main projected biophysical effects are reductions in thickness and extent of glaciers

and ice sheets, and changes in natural ecosystems with detrimental effects on many organisms including

migratory birds, mammals and higher predators. In the Arctic, additional impacts include reductions in the

extent of sea ice and permafrost, increased coastal erosion, and an increase in the depth of permafrost

seasonal thawing. ** D [15.3, 15.4, 15.2]

For Arctic human communities, impacts, particularly resulting from changing snow and ice conditions, are

projected to be mixed. Detrimental impacts would include those on infrastructure and traditional indigenous

ways of life. ** D [15.4]

Beneficial impacts would include reduced heating costs and more navigable northern sea routes. * D [15.4]

In both polar regions, specific ecosystems and habitats are projected to be vulnerable, as climatic barriers to

species’ invasions are lowered. ** D [15.6, 15.4]

Already Arctic human communities are adapting to climate change, but both external and internal stressors

challenge their adaptive capacities. Despite the resilience shown historically by Arctic indigenous

communities, some traditional ways of life are being threatened and substantial investments are needed to

adapt or re-locate physical structures and communities. ** D [15.ES]

Small Islands

Small islands, whether located in the Tropics or higher latitudes, have characteristics which make them

especially vulnerable to the effects of climate change, sea level rise and extreme events. *** [16.1, 16.5]

Deterioration in coastal conditions, for example through erosion of beaches and coral bleaching, is expected

to affect local resources, e.g., fisheries, and reduce the value of these destinations for tourism. ** D [16.4]

Sea-level rise is expected to exacerbate inundation, storm surge, erosion and other coastal hazards, thus

threatening vital infrastructure, settlements and facilities that support the livelihood of island communities.

*** D [16.4]

Climate change is projected by the mid-century to reduce water resources in many small islands, e.g., in the

Caribbean and Pacific, to the point where they become insufficient to meet demand during low rainfall

periods. *** D [16.4]

With higher temperatures, increased invasion by non-native species is expected to occur, particularly on

middle and high-latitude islands. ** N [16.4]

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Magnitudes of impact can now be estimated more systematically for a range of

possible increases in global average temperature.

Since the IPCC Third Assessment, many additional studies, particularly in regions that previously had been

little researched, have enabled a more systematic understanding of how the timing and magnitude of impacts

may be affected by changes in climate and sea level associated with differing amounts and rates of change in

global average temperature.

Examples of this new information are presented in Table SPM-1. Entries have been selected which are

judged to be relevant for people and the environment and for which there is high confidence in the



. All entries of impact are drawn from chapters of the Assessment, where more detailed

information is available.

Depending on circumstances, some of these impacts could be associated with ‘key vulnerabilities’, based on

a number of criteria in the literature (magnitude, timing, persistence/reversibility, the potential for adaptation,

distributional aspects, likelihood and “importance” of the impacts). Assessment of potential key

vulnerabilities is intended to provide information on rates and levels of climate change to help decisionmakers

make appropriate responses to the risks of climate change. [19.ES]

The ‘reasons for concern’ identified in the Third Assessment remain a viable framework for considering key

vulnerabilities. Recent research has updated some of the findings from the Third Assessment. [19.3.7]


See Endbox 2

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Table SPM-1.

Illustrative examples of global impacts projected for climate changes (and sea-level and

atmospheric carbon dioxide where relevant) associated with different amounts of increase in global average

surface temperature in the 21st century. [T20.7] The black lines link impacts, dotted arrows indicate impacts

continuing with increasing temperature. Entries are placed so that the left hand side of text indicates

approximate onset of a given impact. Quantitative entries for water scarcity and flooding represent the

additional impacts of climate change relative to the conditions projected across the range of SRES scenarios

A1FI, A2, B1 and B2 (see Endbox 3). Adaptation to climate change is not included in these estimations. All

entries are from published studies recorded in the chapters of the Assessment. Sources are given in the right

hand column of the Table. Confidence levels for all statements are high.

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Impacts due to altered frequencies and intensities of extreme weather, climate, and

sea level events are very likely to change.

Since the IPCC Third Assessment, confidence has increased that some weather events and extremes will

become more frequent, more widespread and/or more intense during the 21st century; and more is known

about the potential effects of such changes. A selection of these is presented in Table SPM-2.

See Working Group I Fourth Assessment Table 3.7 for definitions


Warming of the most extreme days and nights each year


Extreme high sea level depends on average sea level and on regional weather systems. It is defined as the highest 1%

of hourly values of observed sea level at a station for a given reference period


In all scenarios, the projected global average sea level at 2100 is higher than in the reference period [Working Group I

Fourth Assessment 10.6]. The effect of changes in regional weather systems on sea level extremes has not been


Table SPM-2.

Examples of possible impacts of climate change due to changes in extreme weather and

climate events, based on projections to the mid to late 21st century. These do not take into account any

changes or developments in adaptive capacity. Examples of all entries are to be found in chapters in the full

Assessment (see source at top of columns). The first two columns of this table are taken directly from the

Working Group I SPM (Table SPM-2). The likelihood estimates in Column 2 relate to the phenomena listed

in Column 1. The direction of trend and likelihood of phenomena are for IPCC SRES projections of climate


Some large-scale climate events have the potential to cause very large impacts,

especially after the 21st century.

Very large sea-level rises that would result from widespread deglaciation of Greenland and West Antarctic

ice sheets imply major changes in coastlines and ecosystems, and inundation of low-lying areas, with

greatest effects in river deltas. Relocating populations, economic activity, and infrastructure would be costly

and challenging. There is medium confidence that at least partial deglaciation of the Greenland ice sheet, and

possibly the West Antarctic ice sheet, would occur over a period of time ranging from centuries to millennia

for a global average temperature increase of 1- 4°C (relative to 1990-2000), causing a contribution to sea

level rise of 4-6 m or more. The complete melting of the Greenland ice sheet and the West Antarctic ice

sheet would lead to a contribution to sea-level rise of up to 7 m and about 5 m, respectively. [Working Group

I Fourth Assessment 6.4, 10.7; Working Group II Fourth Assessment 19.3]

Based on climate model results, it is very unlikely that the Meridional Overturning Circulation (MOC) in the

North Atlantic will undergo a large abrupt transition during the 21st century. Slowing of the MOC this

century is very likely, but temperatures over the Atlantic and Europe are projected to increase nevertheless,

due to global warming. Impacts of large-scale and persistent changes in the MOC are likely to include

changes to marine ecosystem productivity, fisheries, ocean carbon dioxide uptake, oceanic oxygen

concentrations and terrestrial vegetation. [Working Group I Fourth Assessment 10.3, 10.7; Working Group II

Fourth Assessment 12.6, 19.3]

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D. Current knowledge about responding to climate change

Some adaptation is occurring now, to observed and projected future climate change,

but on a limited basis.

There is growing evidence since the IPCC Third Assessment of human activity to adapt to observed and

anticipated climate change. For example, climate change is considered in the design of infrastructure projects

such as coastal defence in the Maldives and The Netherlands, and the Confederation Bridge in Canada.

Other examples include prevention of glacial lake outburst flooding in Nepal, and policies and strategies

such as water management in Australia and government responses to heat waves in, for example, some

European countries. [7.6, 8.2, 8.6, 17.ES, 17.2, 16.5, 11.5]

Adaptation will be necessary to address impacts resulting from the warming which

is already unavoidable due to past emissions.

Past emissions are estimated to involve some unavoidable warming (about a further 0.6°C by the end of the

century) even if atmospheric greenhouse gas concentrations remain at 2000 levels (see Working Group I

Fourth Assessment). There are some impacts for which adaptation is the only available and appropriate

response. An indication of these impacts can be seen in Table SPM-1.

A wide array of adaptation options is available, but more extensive adaptation than

is currently occurring is required to reduce vulnerability to future climate change.

There are barriers, limits and costs, but these are not fully understood.

Impacts are expected to increase with increases in global average temperature, as indicated in Table SPM-1.

Although many early impacts of climate change can be effectively addressed through adaptation, the options

for successful adaptation diminish and the associated costs increase with increasing climate change. At

present we do not have a clear picture of the limits to adaptation, or the cost, partly because effective

adaptation measures are highly dependent on specific, geographical and climate risk factors as well as

institutional, political and financial constraints. [7.6, 17.2, 17.4]

The array of potential adaptive responses available to human societies is very large, ranging from purely

technological (e.g., sea defences), through behavioural (e.g., altered food and recreational choices) to

managerial (e.g., altered farm practices), to policy (e.g., planning regulations). While most technologies and

strategies are known and developed in some countries, the assessed literature does not indicate how effective

various options


are to fully reduce risks, particularly at higher levels of warming and related impacts, and

for vulnerable groups. In addition, there are formidable environmental, economic, informational, social,

attitudinal and behavioural barriers to implementation of adaptation. For developing countries, availability

of resources and building adaptive capacity are particularly important. [See Sections 5 and 6 in Chapters 3-

16; also 17.2, 17.4].

However, adaptation alone is not expected to cope with all the projected effects of climate change, and

especially not over the long run as most impacts increase in magnitude [Table SPM-1].



A table of options is given in the Technical Summary

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Vulnerability to climate change can be exacerbated by the presence of other


Non-climate stresses can increase vulnerability to climate change by reducing resilience and can also reduce

adaptive capacity because of resource deployment to competing needs. For example, current stresses on

some coral reefs include marine pollution and chemical runoff from agriculture as well as increases in water

temperature and ocean acidification. Vulnerable regions face multiple stresses that affect their exposure and

sensitivity as well as their capacity to adapt. These stresses arise from, for example, current climate hazards,

poverty and unequal access to resources, food insecurity, trends in economic globalisation, conflict, and

incidence of disease such as HIV/AIDS. [7.4, 8.3, 17.3, 20.3] Adaptation measures are seldom undertaken in

response to climate change alone but can be integrated within, for example, water resource management,

coastal defence, and disaster planning [17.2, 17.5].

Future vulnerability depends not only on climate change but also on development


An important advance since the IPCC Third Assessment has been the completion of impacts studies for a

range of different development pathways taking into account not only projected climate change but also

projected social and economic changes. Most have been based on characterisations of population and

income level drawn from the IPCC Special Report on Emission Scenarios (SRES). [2.4]

These studies show that the projected impacts of climate change can vary greatly due to the development

pathway assumed. For example, there may be large differences in regional population, income and

technological development under alternative scenarios, which are often a strong determinant of the level of

vulnerability to climate change. [2.4]

To illustrate, in a number of recent studies of global impacts of climate change on food supply, risk of

coastal flooding and water scarcity, the projected number of people affected is considerably greater under the

A2-type scenario of development (characterised by relatively low

per capita

income and large population

growth) than under other SRES futures. [T20.6] This difference is largely explained, not by differences in

changes of climate, but by differences in vulnerability. [T6.6] This difference is largely explained, not by

differences in changes of climate, but by differences in vulnerability. [T6.6]

Sustainable development15can reduce vulnerability to climate change, and climate

change could impede nations’ abilities to achieve sustainable development


Sustainable development can reduce vulnerability to climate change by enhancing adaptive capacity and

increasing resilience. At present, however, few plans for promoting sustainability have explicitly included

either adapting to climate change impacts, or promoting adaptive capacity. [20.3]

On the other hand, it is very likely that climate change can slow the pace of progress toward sustainable

development either directly through increased exposure to adverse impact or indirectly through erosion of

the capacity to adapt. This point is clearly demonstrated in the sections of the sectoral and regional chapters

of this report that discuss implications for sustainable development. [See Section 7 in Chapters 3-8, 20.3,



The Brundtland Commission definition of sustainable development is used in this Assessment: “development that

meets the needs of the present without compromising the ability of future generations to meet their own needs”. The

same definition was used by the IPCC Working Group II Third Assessment and Synthesis Reports.

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The Millennium Development Goals (MDGs) are one measure of progress towards sustainable development.

Over the next half-century, climate change could impede achievement of the MDGs. [20.7]

Many impacts can be avoided, reduced or delayed by mitigation.

A small number of impact assessments have now been completed for scenarios in which future atmospheric

concentrations of greenhouse gases are stabilised. Although these studies do not take full account of

uncertainties in projected climate under stabilisation, they nevertheless provide indications of damages

avoided or vulnerabilities and risks reduced for different amounts of emissions reduction. [2.4, T20.6]

A portfolio of adaptation and mitigation measures can diminish the risks associated

with climate change.

Even the most stringent mitigation efforts cannot avoid further impacts of climate change in the next few

decades, which makes adaptation essential, particularly in addressing near-term impacts. Unmitigated

climate change would, in the long term, be likely to exceed the capacity of natural, managed and human

systems to adapt. [20.7]

This suggests the value of a portfolio or mix of strategies that includes mitigation, adaptation, technological

development (to enhance both adaptation and mitigation) and research (on climate science, impacts,

adaptation and mitigation). Such portfolios could combine policies with incentive-based approaches, and

actions at all levels from the individual citizen through to national governments and international

organizations. [18.1, 18.5]

One way of increasing adaptive capacity is by introducing consideration of climate change impacts in

development planning [18.7], for example, by:

including adaptation measures in land-use planning and infrastructure design [17.2];

including measures to reduce vulnerability in existing disaster risk reduction strategies [17.2, 20.8].

Impacts of climate change will vary regionally but, aggregated and discounted to

the present, they are very likely to impose net annual costs which will increase over

time as global temperatures increase.

This Assessment makes it clear that the impacts of future climate change will be mixed across regions. For

increases in global mean temperature of less than 1 to 3


C above 1990 levels, some impacts are projected to

produce benefits in some places and some sectors, and produce costs in other places and other sectors . It is,

however, projected that some low latitude and polar regions will experience net costs even for small

increases in temperature. It is very likely that all regions will experience either declines in net benefits or

increases in


costs for increases in temperature greater than about 2 to 3°C [9.ES, 9.5, 10.6, T109, 15.3,

15.ES]. These observations re-confirm evidence reported in the Third Assessment that, while developing

countries are expected to experience larger percentage losses, global mean losses could be 1-5% Gross

Domestic Product (GDP) for 4


C of warming. [F20.3]

Many estimates of aggregate net economic costs of damages from climate change across the globe (i.e., the

social cost of carbon (SCC), expressed in terms of future net benefits and costs that are discounted to the

present) are now available. Peer-reviewed estimates of the social cost of carbon for 2005 have an average

value of US$43 per tonne of carbon (tC) (i.e., US$12 per tonne of carbon dioxide) but the range around this

mean is large. For example, in a survey of 100 estimates, the values ran from US$-10 per tonne of carbon

(US$-3 per tonne of carbon dioxide) up to US$350/tC (US$130 per tonne of carbon dioxide) [20.6].

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The large ranges of SCC are due in the large part to differences in assumptions regarding climate sensitivity,

response lags, the treatment of risk and equity, economic and non-economic impacts, the inclusion of

potentially catastrophic losses and discount rates. It is very likely that globally aggregated figures

underestimate the damage costs because they cannot include many non-quantifiable impacts. Taken as a

whole, the range of published evidence indicates that the net damage costs of climate change are likely to be

significant and to increase over time. [T20.3, 20.6, F20.4].

It is virtually certain that aggregate estimates of costs mask significant differences in impacts across sectors,

regions, countries, and populations. In some locations and amongst some groups of people with high

exposure, high sensitivity, and/or low adaptive capacity, net costs will be significantly larger than the global

aggregate. [20.6, 20.ES, 7.4]

E. Systematic observing and research needs

Although science to provide policymakers with information about climate change impacts and adaptation

potential has improved since the Third Assessment, it still leaves many important questions to be answered.

The chapters of the Working Group II report include a number of judgements about priorities for further

observation and research, and this advice should be considered seriously (a list of these recommendations is

given in the Technical Summary Section TS-6).

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Endbox 1.

Definitions of key terms

Climate change

in IPCC usage refers to any change in climate over time, whether due to natural variability

or as a result of human activity. This usage differs from that in the Framework Convention on Climate

Change, where

climate change

refers to a change of climate that is attributed directly or indirectly to human

activity that alters the composition of the global atmosphere and that is in addition to natural climate

variability observed over comparable time periods.

Adaptive capacity

is the ability of a system to adjust to climate change (including climate variability and

extremes) to moderate potential damages, to take advantage of opportunities, or to cope with the



is the degree to which a system is susceptible to, or unable to cope with, adverse effects of

climate change, including climate variability and extremes. Vulnerability is a function of the character,

magnitude, and rate of climate change and variation to which a system is exposed, its sensitivity, and its

adaptive capacity.

This box of key definitions is exactly as used in the TAR and has been subject to prior line-by-line approval by the Panel

Endbox 2.

Likelihood and confidence language

In this Summary for Policymakers, the following terms have been used to indicate: the assessed likelihood of

an outcome or a result:

Virtually certain

> 99% probability of occurrence, Extremely likely > 95%, Very likely > 90%, Likely

> 66%,

More likely than not >

50%, Very unlikely <>Extremely unlikely


The following terms have been used to express confidence in a statement:

Very high confidence

At least a 9 out of 10 chance of being correct, High confidence

About an 8 out of 10


Medium confidence About a 5 out of 10 chance, Low confidence About a 2 out of 10 chance,


low confidence

Less than a 1 out of 10 chance.

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Endbox 3.

The Emission Scenarios of the IPCC Special Report on Emission Scenarios (SRES)*

A1. The A1 storyline and scenario family describes a future world of very rapid economic growth, global

population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more

efficient technologies. Major underlying themes are convergence among regions, capacity building and

increased cultural and social interactions, with a substantial reduction in regional differences in per capita

income. The A1 scenario family develops into three groups that describe alternative directions of

technological change in the energy system. The three A1 groups are distinguished by their technological

emphasis: fossil intensive (A1FI), non fossil energy sources (A1T), or a balance across all sources (A1B)

(where balanced is defined as not relying too heavily on one particular energy source, on the assumption that

similar improvement rates apply to all energy supply and end use technologies).

A2. The A2 storyline and scenario family describes a very heterogeneous world. The underlying theme is

self reliance and preservation of local identities. Fertility patterns across regions converge very slowly,

which results in continuously increasing population. Economic development is primarily regionally oriented

and per capita economic growth and technological change more fragmented and slower than other storylines.

B1. The B1 storyline and scenario family describes a convergent world with the same global population, that

peaks in mid-century and declines thereafter, as in the A1 storyline, but with rapid change in economic

structures toward a service and information economy, with reductions in material intensity and the

introduction of clean and resource efficient technologies. The emphasis is on global solutions to economic,

social and environmental sustainability, including improved equity, but without additional climate initiatives.

B2. The B2 storyline and scenario family describes a world in which the emphasis is on local solutions to

economic, social and environmental sustainability. It is a world with continuously increasing global

population, at a rate lower than A2, intermediate levels of economic development, and less rapid and more

diverse technological change than in the B1 and A1 storylines. While the scenario is also oriented towards

environmental protection and social equity, it focuses on local and regional levels.

An illustrative scenario was chosen for each of the six scenario groups A1B, A1FI, A1T, A2, B1 and B2. All

should be considered equally sound.

The SRES scenarios do not include additional climate initiatives, which means that no scenarios are included

that explicitly assume implementation of the United Nations Framework Convention on Climate Change or

the emissions targets of the Kyoto Protocol.

*This box summarizing the SRES scenarios is exactly as used in the TAR and has been subject to prior line by line

approval by the Panel.

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