IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group II: Impacts, Adaptation and Vulnerability

19.3.1 Introduction to Table 19.1

Table 19.1 provides short summaries of some vulnerabilities which, in the judgment of the authors of this chapter and in the light of the WGI AR4 and chapters of the WGII AR4, may be considered ‘key’ according to the criteria set out above in Section 19.2. The table presents vulnerabilities grouped by the following categories, described in the following text:

  • Global social systems
  • Regional systems
  • Global biological systems
  • Geophysical systems
  • Extreme events

The table attempts to describe, as quantitatively as the literature allows, how impacts vary with global mean temperature increase above 1990-2000 levels. In addition, the authors of this chapter have assigned confidence estimates to this information. Where known, the table presents information regarding the dependence of effects on rates of warming, duration of the changes, exposure to the stresses, and adaptation taking into account uncertainties regarding socio-economic development. However, only in a few cases does the literature address rate or duration of warming and its consequences. As entries in the table are necessarily short, reference should be made to the relevant chapters and to the accompanying text in this chapter for more detailed information and cross-referencing, including additional caveats where applicable.

Table 19.1. Examples of potential key vulnerabilities. This list is not ordered by priority or severity but by category of system, process or group, which is either affected by or which causes vulnerability. Information is presented where available on how impacts may change at larger increases in global mean temperature (GMT). All increases in GMT are relative to circa 1990. Entries are necessarily brief to limit the size of the table, so further details, caveats and supporting evidence should be sought in the accompanying text, cross-references, and in the primary scientific studies referenced in this and other chapters of the AR4. In many cases, climate change impacts are marginal or synergistic on top of other existing and changing stresses. Confidence symbol legend: *** very high confidence, ** high confidence, * medium confidence, • low confidence. Sources in [square brackets] are from chapters in the WGII AR4 unless otherwise indicated. Where no source is given, the entries are based on the conclusions of the Chapter 19 authors.

Systems, processes

or groups at risk [cross-references]


Prime criteria for ‘key

vulnerability’ (based on the seven criteria listed in Section 19.2)


Relationship between temperature and risk.

Temperature change by 2100 (relative to 1990-2000)













Global social systems 
Food supply [, Magnitude   Productivity decreases for some cereals in low latitudes */• [5.4    
 Productivity increases for some cereals in mid/high latitudes */• [5.4Cereal productivity decreases in some mid/high-latitude regions */• [5.4
   Global production potential increases to around 3°C * [5.4, 5.6Global production potential very likely to decrease above about 3°C * [5.4, 5.6
Infrastructure [19.3.2]  Distribution, Magnitude, Timing Damages likely to increase exponentially, sensitive to rate of climate change, change in extreme events and adaptive capacity ** [3.5, 6.5.3, 7.5]. 
Health [19.3.2]  Distribution, Magnitude, Timing, Irreversibility Current effects are small but discernible * [1.3.7, 8.2].    Although some risks would be reduced, aggregate health impacts would increase, particularly from malnutrition, diarrhoeal diseases, infectious diseases, floods and droughts, extreme heat, and other sources of risk */**. Sensitive to status of public health system *** [8.ES, 8.3, 8.4, 8.6]. 
Water resources [19.3.2Distribution, Magnitude, Timing Decreased water availability and increased drought in some mid latitudes and semi-arid low latitudes ** [3.2, 3.4, 3.7]. Severity of floods, droughts, erosion, water-quality deterioration will increase with increasing climate change ***. Sea-level rise will extend areas of salinisation of groundwater, decreasing freshwater availability in coastal areas *** [3.ES]. Hundreds of millions people would face reduced water supplies ** [3.5].  
Migration and conflict  Distribution, Magnitude Stresses such as increased drought, water shortages, and riverine and coastal flooding will affect many local and regional populations **. This will lead in some cases to relocation within or between countries, exacerbating conflicts and imposing migration pressures * [19.2]. 
Aggregate market impacts and distribution Magnitude, Distribution Uncertain net benefits and greater likelihood of lower benefits or higher damages than in TAR •. Net market benefits in many high-latitude areas; net market losses in many low-latitude areas. * [20.6, 20.7]. Most people negatively affected •/*. Net global negative market impacts increasing with higher temperatures * [20.6]. Most people negatively affected *.  

Systems, processes

or groups at risk [cross-references]


Prime criteria for ‘key

vulnerability’ (based on the seven criteria listed in Section 19.2)


Relationship between temperature and risk.

Temperature change by 2100 (relative to 1990-2000) 
0°C 1°C 2°C 3°C 4°C 5°C 
Regional systems 
Africa [19.3.3Distribution, Magnitude, Timing, Low Adaptive Capacity Tens of millions of people at risk ofincreased water stress; increased spread of malaria • [9.2, 9.4.1, 9.4.3]. Hundreds of millions of additional people at risk of increased water stress; increased risk of malaria in highlands; reductionsin crop yields in many countries, harm to many ecosystemssuch as Succulent Karoo • [9.4.1, 9.4.3, 9.4.4, 9.4.5]. 
Asia [19.3.3]  Distribution, Magnitude, Timing, Low Adaptive Capacity About 1 billion people would face risks from reduced agricultural production potential, reduced water supplies or increases in extremes events • [10.4]. 
Latin America [19.3.3Magnitude, Irreversibility, Distribution, and Timing, Low Adaptive Capacity Tens of millions of people at risk of water shortages • [13.ES, 13.4.3]; many endemic species at risk from land-use and climate change • (~1ºC) [13.4.1, 13.4.2]. More than a hundred million people at risk of water shortages •[13.ES, 13.4.3]; low-lying coastal areas, many of which are heavily populated, at risk from sea-level rise and more intensecoastal storms • (about 2-3ºC) [13.4.4]. Widespread loss of biodiversity, particularly in the Amazon • [13.4.1, 13.4.2]. 
Polar regions [19.3.3Timing, Magnitude, Irreversibility, Distribution, Low Adaptive Capacity Climate change is already having substantial impacts on societal and ecological systems ** [15.ES]. Continued warming likely to lead to further loss of ice cover andpermafrost ** [15.3]. Arctic ecosystems further threatened **,although net ecosystem productivity estimated to increase **[15.2.2, 15.4.2]. While some economic opportunities will open up (e.g., shipping), traditional ways of life will be disrupted ** [15.4, 15.7].  
Small islands [19.3.3Irreversibility, Magnitude, Distribution, Low Adaptive Capacity Many islands already experiencing some negative effects ** [16.2].   
 Increasing coastal inundation and damage to infrastructure due to sea-level rise ** [16.4]. 
Indigenous, poor or isolated communities [19.3.3Irreversibility, Distribution, Timing, Low Adaptive Capacity Some communities already affected ** [11.4, 14.2.3, 15.4.5].  Climate change and sea-level rise add to other stresses **. Communities in low-lying coastal and arid areas are especiallythreatened ** [3.4, 6.4]. 
Drying in Mediterranean, western North America, southern Africa, southern Australia, and north-eastern Brazil [19.3.3Distribution, Magnitude, Timing  Climate models generally project decreased precipitation in these regions [3.4.1, 3.5.1, 11.3.1]. Reduced runoff will exacerbate limited water supplies, decrease water quality, harm ecosystems and result in decreased crop yields ** [3.4.1, 11.4]. 
Inter-tropical mountain glaciers and impacts on high-mountain communities [19.3.3Magnitude, Timing, Persistence, Low Adaptive Capacity, Distribution Inter-tropical glaciers are melting and causing flooding in some areas; shifts in ecosystems are likely to cause water security problems due to decreased storage */** [Box 1.1, 10.ES, 10.2, 10.4.4, 13.ES, 13.2.4, 19.3]. Accelerated reduction of inter-tropical mountain glaciers. Some of these systems will disappear in the next few decades * [Box 1.1, 9.2.1, Box 9.1, 10.ES, 10.2.4, 10.4.2, 13.ES,]. 
Global biological systems 
Terrestrial ecosystems and biodiversity [19.3.4]  Irreversibility, Magnitude, Low Adaptive Capacity, Persistence, Rate of Change, Confidence Many ecosystems already affected *** [1.3]. circa 20-30% species at increasingly high risk of extinction *[4.4]. Major extinctions around the globe ** [4.4
 Terrestrial biosphere tends toward a net carbon source ** [4.4
Marine ecosystems and biodiversity [19.3.4]  Irreversibility, Magnitude, Low Adaptive Capacity, Persistence, Rate of Change, Confidence IIncreased coral bleaching **[4.4Most corals bleached ** [4.4Widespread coral mortality *** [4.4
Systems, processes or groups at risk [cross-references]  Prime criteria for ‘key vulnerability’ (based on the seven criteria listed in Section 19.2)  

Relationship between temperature and risk.

Temperature change by 2100 (relative to 1990-2000) 
0°C 1°C 2°C 3°C 4°C 5°C 
Global biological systems 
Freshwater ecosystems [19.3.4Irreversibility, Magnitude, Persistence Low Adaptive Capacity Some lakes already showing decreased fisheries output; pole-ward migration of aquatic species ** [1.3.4, 4.4.9]. Intensified hydrological cycles, more severe droughtsand floods *** [3.4.3]. Extinction of manyfreshwater species **, major changes in limnology of lakes **, increased salinityof inland lakes **. 
Geophysical systems 
Biogeochemical cycles [WGII 4.4.9,; WGI 7.3.3, 7.3.4, 7.3.5,, 10.4.1, 10.4.2]  Magnitude, Persistence, Confidence, Low Adaptive Capacity, Rate of Change 

Ocean acidification already occurring, increasing further as atmospheric CO2 concentration increases ***; ecological changes are potentially severe * [1.3.4, 4.4.9].

Carbon cycle feedback increases projected CO2 concentrations by 2100 by 20-220 ppm for SRES[2] A2, with associated additional warming of 0.1 to 1.5°C **. AR4 temperature range (1.1-6.4°C) accounts for this feedback from all scenarios and models but additional CO2 and CH4 releases are possible from permafrost, peat lands, wetlands, and large stores of marine hydrates at high latitudes * [4.4.6, 15.4.2].

Permafrost already melting, and above feedbacks generally increase with climate change, but eustatic sea-level rise likely to increase stability of hydrates *** [1.3.1].

Greenland ice sheet [WGII 6.3,; WGI,]  Magnitude, Irreversibility, Low Adaptive Capacity, Confidence Localised deglaciation (already observed, due to local warming); extent would increase with temperature increase *** [19.3.5]. Commitment to widespread ** to near-total * deglaciation, 2-7 m sea-level rise[3] over centuries to millennia * [19.3.5]. Near-total deglaciation **[19.3.5
West Antarctic ice sheet [WGII 6.3,; WGI,] Magnitude, Irreversibility, Low Adaptive Capacity Localised ice shelf loss and groundingline retreat *(already observed,due to local warming)[1.3.1, 19.3.5

Commitment to partial deglaciation,

1.5-5 m sea-level rise over centuries

to millennia •/* [19.3.5]

Likelihood of near-total deglaciation increases with

increases in temperature ** [19.3.5]

Meridional overturning circulation [WGII; WGI, 10.3.4]  Magnitude, Persistence, Distribution, Timing, Low Adaptive Capacity, Confidence Variations including regional weakening (already observed but no trend identified) Considerable weakening **. Commitment to large-scale and persistent change including possible cooling in northern high-latitude areas near Greenland and north-west Europe • highly dependent on rate of climate change [12.6, 19.3.5]. 
Extreme events  
Tropical cyclone intensity [WGII 7.5, 8.2, 11.4.5, 16.2.2, 16.4, 19.3.6; WGI Table TS-4, 3.8.3, Q3.3,, Q10.1]  Magnitude, Timing, Distribution Increase in Category 4-5 storms*/**, with impacts exacerbated by sea-level rise Further increase in tropical cyclone intensity */** exceeding infrastructure design criteria with large economic costs ** and many lives threatened **. 
Flooding, both large-scale and flash floods [WGII 14.4.1; WGI Table TS-4,, Q10.1]  Timing, Magnitude Increases in flash flooding in many regions due to increased rainfall intensity** and in floods in large basins in mid and high latitudes **. Increased flooding in many regions (e.g., North America and Europe) due to greater increase in winter rainfall exacerbated by loss of winter snow storage **. Greater risk of dam burst in glacial mountain lakes ** []. 
Extreme heat [WGII 14.4.5; WGI Table TS-4,, Q10.1]  Timing, Magnitude Increased heat stress and heat-waves, especially in continental areas ***. Frequency of heatwaves (according to current classification) will increase rapidly, causing increased mortality, crop failure, forest die-back and fire, and damage to ecosystems ***. 
Drought [WGI Table TS-4,]  Magnitude, Timing  Drought already increasing * []. Increasing frequency and intensity of drought in mid-latitude continental areas projected ** [WGI]. Extreme drought increasing from 1% land area to 30% (SRES A2 scenario) [WGI]. Mid-latitude regions seriously affected by poleward migration of Annular Modes ** [WGI]. 
Fire [WGII 1.3.6; WGI 7.3]  Timing, Magnitude Increased fire frequency and intensity in many areas, particularly where drought increases ** [4.4, 14.2.2]. Frequency and intensity likely to be greater, especially in boreal forests and dry peat lands after melting of permafrost ** [4.4.5, 11.3, 13.4.1, 14.4.2, 14.4.4]. 

  1. ^  SRES: Special Report on Emissions Scenarios, see Nakićenović et al., 2000.
  2. ^  Range is based on a variety of methods including models and analysis of palaeo data []