REPORTS - ASSESSMENT REPORTS
Synthesis Report - Question 4

Climate Change 2001: Synthesis Report


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Table 41 Examples of climate variability and extreme climate events and examples of their impacts (WGII TAR Table SPM-1). (WGII TAR Table SPM-1).
Projected Changes during the 21st Century in Extreme Climate Phenomena and their Likelihood

Representative Examples of Projected Impactsa (all high confidence of occurrence in some areas)

Higher maximum temperatures, more hot b days and heat waves over nearly all land areas (very likely)

Increased incidence of death and serious illness in older age groups and urban poor. Increased heat stress in livestock and wildlife.
Shift in tourist destinations. Increased risk of damage to a number of crops.
Increased electric cooling demand and reduced energy supply reliability.

Higher (increasing) minimum temperatures, fewer cold days, frost days, b and cold waves over nearly all land areas (very likely) Decreased cold-related human morbidity and mortality.
Decreased risk of damage to a number of crops, and increased risk to others.
Extended range and activity of some pest and disease vectors.
Reduced heating energy demand.
More intense precipitation events (very likely, over many areas) Increased flood, landslide, avalanche, and mudslide damage.
Increased soil erosion.
Increased flood runoff could increase recharge of some floodplain aquifers.
Increased pressure on government and private flood insurance systems and disaster relief.
Increased summer drying over most mid- latitude continental interiors and associated risk of drought (likely) Decreased crop yields.
Increased damage to building foundations caused by ground shrinkage.
Decreased water resource quantity and quality.
Increased risk of forest fire.
Increase in tropical cyclone peak wind intensities, mean and peak precipitation c intensities (likely, over some areas)c Increased risks to human life, risk of infectious disease epidemics and many other risks.
Increased coastal erosion and damage to coastal buildings and infrastructure. Increased damage to coastal ecosystems such as coral reefs and mangroves.
Intensified droughts and floods associated with El Niño events in many different regions (likely) (see also under droughts and intense precipitation events) Decreased agricultural and rangeland productivity in drought- and flood-prone regions. Decreased hydro-power potential in drought-prone regions.
Increased Asian summer monsoon precipitation variability (likely) Increase in flood and drought magnitude and damages in temperate and tropical Asia.
Increased intensity of mid-latitude storms b (little agreement between current models) Increased risks to human life and health.
Increased property and infrastructure losses.
Increased damage to coastal ecosystems.

a. These impacts can be lessened by appropriate response measures.
b. Information from WGI TAR Technical Summary (Section F.5).
c. Changes in regional distribution of tropical cyclones are possible but have not been established.


 
4.7 High resolution modeling studies suggest that over some areas the peak wind intensity of tropical cyclones is likely to increase by 5 to 10% and precipitation rates may increase by 20 to 30%, but none of the studies suggest that the locations of the tropical cyclones will change. There is little consistent modeling evidence for changes in the frequency of tropical cyclones.

WGI TAR Box 10.2
4.8 There is insufficient information on how very small-scale phenomena may change. Very small-scale phenomena such as thunderstorms, tornadoes, hail, hailstorms, and lightning are not simulated in global climate models.

WGI TAR Section 9.3.6
4.9 Greenhouse gas forcing in the 21st century could set in motion large-scale, high-impact, non-linear, and potentially abrupt changes in physical and biological systems over the coming decades to millennia, with a wide range of associated likelihoods.

 
4.10 The climate system involves many processes that interact in complex non-linear ways, which can give rise to thresholds (thus potentially abrupt changes) in the climate system that could be crossed if the system were perturbed sufficiently. These abrupt and other non-linear changes include large climate-induced increase in greenhouse gas emissions from terrestrial ecosystems, a collapse of the thermohaline circulation (THC; see Figure 4-2), and disintegration of the Antarctic and the Greenland ice sheets. Some of these changes have low probability of occurrence during the 21st century; however, greenhouse gas forcing in the 21st century could set in motion changes that could lead to such transitions in subsequent centuries (see Question 5). Some of these changes (e.g., to THC) could be irreversible over centuries to millennia. There is a large degree of uncertainty about the mechanisms involved and aboutthe likelihood or time scales of such changes; however, there is evidence from polar ice cores of atmospheric regimes changing within a few years and large-scale hemispheric changes as fast as a few decades with large consequences on the biophysical systems.

WGI TAR Sections 7.3, 9.3.4, & 11.5.4; WGII TAR Sections 5.2 & 5.8; & SRLULUCF Chapters 3 & 4
4.11 Large climate-induced increases in greenhouse gas emissions due to large-scale changes in soils and vegetation may be possible in the 21st century. Global warming interacting with other environmental stresses and human activity could lead to the rapid breakdown of existing ecosystems. Examples include drying of the tundra, boreal and tropical forests, and their associated peatlands leaving them susceptible to fires. Such breakdowns could induce further climate change through increased emissions of CO2 and other greenhouse gases from plants and soil and changes in surface properties and albedo.

WGII TAR Sections 5.2, 5.8, & 5.9; & SRLULUCF Chapters 3 & 4
4.12 Large, rapid increases in atmospheric CH4 either from reductions in the atmospheric chemical sink or from release of buried CH4 reservoirs appear exceptionally unlikely. The rapid increase in CH4 lifetime possible with large emissions of tropospheric pollutants does not occur within the range of SRES scenarios. The CH4 reservoir buried in solid hydrate deposits under permafrost and ocean sediments is enormous, more than 1,000-fold the current atmospheric content. A proposed climate feedback occurs when the hydrates decompose in response to warming and release large amounts of CH4 ; however, most of the CH4 gas released from the solid form is decomposed by bacteria in the sediments and water column, thus limiting the amount emitted to the atmosphere unless explosive ebullient emissions occur. The feedback has not been quantified, but there are no observations to support a rapid, massive CH4 release in the record of atmospheric CH4 over the past 50,000 years.

WGI TAR Section 4.2.1.1
 
Figure 4-2: Schematic illustration of the global circulation system in the world ocean consisting of major north-south thermohaline circulation routes in each ocean basin joining in the Antarctic circumpolar circulation. Warm surface currents and cold deep currents are connected in the few areas of deepwater formation in the high latitudes of the Atlantic and around Antarctica (blue), where the major ocean-to-atmosphereheat transfer occurs. This current system contributes substantially to the transport and redistribution of heat (e.g., the poleward flowing currents in the North Atlantic warm northwestern Europe by up to 10°C). Model simulations indicate that the North Atlantic branch of this circulation system is particularly vulnerable to changes in atmospheric temperature and in the hydrological cycle. Such perturbations caused by global warming could disrupt the current system, which would have a strong impact on regional-to-hemispheric climate. Note that this is a schematic diagram and it does not give the exact locations of the water currents that form part of the THC.
 

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