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googletemperature is rising
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increase in extrem adwerse
Abrupt Climate Change
is defined not simply as average temperature and precipitation but also
by the type, frequency and intensity of weather events. Human-induced
climate change has the potential to alter the prevalence and severity
of extremes such as heat waves, cold waves, storms, floods and
droughts. Though predicting changes in these types of events under a
changing climate is difficult, understanding vulnerabilities to such
changes is a critical part of estimating vulnerabilities and future
climate change impacts on human health, society and the environment.
current level of understanding, as summarized in the Intergovernmental
Panel on Climate Change Fourth Assessment Report (IPCC,
2007), is as follows:
1950, the number of heat waves has increased and widespread increases
have occurred in the numbers of warm nights. The extent of regions
affected by droughts has also increased as precipitation over land has
marginally decreased while evaporation has increased due to warmer
conditions. Generally, numbers of heavy daily precipitation events that
lead to flooding have increased, but not everywhere. Tropical storm and
hurricane frequencies vary considerably from year to year, but evidence
suggests substantial increases in intensity and duration since the
1970s.In the extratropics, variations in tracks and intensity of storms
reflect variations in major features of the atmospheric circulation,
such as the North Atlantic Oscillation.
IPCC projects the following likely, very likely, or virtually certain
changes in extreme events and associated effects between now and 2100 (IPCC, 2007):
Impacts by Sector
cold days/nights; warmer/more hot days/nights over most land areas.
yields in colder environments; decreased yields in warmer environments;
on water resources relying on snow melt
human mortality from decreased cold exposure
energy demand for heating; increased demand for cooling; declining air
quality in cities; reduced effects of snow, ice etc.
spells/heat waves: frequency increases over most land areas
yields in warmer regions due to heat stress at key devel. stages; fire
water demand; water quality problems, e.g., algal blooms
risk of heat-related mortality
in quality of life for people in warm areas without air conditioning;
impacts on elderly and very young; reduced thermoelectric power
precipitation events: frequency increases over most areas
to crops; soil erosion, inability to cultivate land, water logging of
effects on quality of surface and groundwater; contamination of water
injuries, infectious diseases, allergies and dermatitis from floods and
of settlements, commerce, transport and societies due to flooding;
pressures on urban and rural infrastructures
affected by drought: increases
degradation, lower yields/crop damage and failure; livestock deaths;
widespread water stress
risk of food and water shortage and wild fires; increased risk of
water- and food-borne diseases
shortages for settlements, industry and societies; reduced hydropower
generation potentials; potentials for population migration
of intense tropical cyclones: increases
to crops; windthrow of trees
outages cause disruption of public water supply
risk of deaths, injuries, water- and food-borne diseases
by flood and high winds; withdrawal of risk coverage in vulnerable
areas by private insurers
of extreme high sea level: increases
of irrigation and well water
freshwater availability due to saltwater intrusion
in deaths by drowning in floods; increase in stress-related disease
of coastal protection versus
costs of land-use relocation;
also see tropical cyclones above
is important to understand that directly linking any one specific
extreme event (e.g., a severe hurricane) to human-caused climate change
is not possible. However, climate change may increase the probability
of some ordinary weather events reaching extreme levels or of some
extreme events becoming more extreme. For example, according
it is probable that heat waves will become more likely and
progressively more intense over the course of decades under current
climate change scenarios. Changes in the frequency and intensity of
heat waves and other extreme events across North America will be
comprehensively assessed in the forthcoming Climate Change Science
and Assessment Product 3.3: Climate Extremes.
climate change has a specific definition and should not be confused
with climate changes that occur slowly or individual extreme events
that affect relatively small areas. Abrupt climate change refers to
sudden (on the order of decades), large changes in some major component
of the climate system, with rapid, widespread effects. The potential
for abrupt climate changes cannot be predicted with confidence;
however, abrupt climate changes are an important consideration because,
if triggered, they could occur so quickly and unexpectedly that human
or natural systems would have difficulty adapting to them (NRC, 2002).
climate changes occur when a threshold in the climate system is crossed
– a trigger that causes the climate to rapidly shift from one
state to a new, different one. Crossing thresholds in the climate
system may lead to large and widespread consequences (Schneider et al.,
triggers can be forces that are “external” or
“internal” to the climate system. Examples of these
in the Earth’s orbit
brightening or dimming of the sun
or surging ice sheets
or weakening of ocean currents
of climate-altering gases and particles into the atmosphere
than one of these triggers can operate simultaneously, since all
components of the climate system are linked.
data show that abrupt changes in the climate at the regional scale have
occurred throughout history and are characteristic of the
climate system (NRC, 2002).
During the last glacial
period, abrupt regional warmings (likely up to 16°C within
over Greenland) and coolings occurred repeatedly over the North
Atlantic region (Jansen et al., 2007).
warmings likely had some large-scale effects such as major shifts in
tropical rainfall patterns and redistribution of heat within the
climate system but it is unlikely that they were associated with large
changes in global mean surface temperature.
state of knowledge is not yet sufficient to predict the timing of the
future abrupt climate changes or pinpoint their effects. However, the
National Academies of Sciences did conclude that anthropogenic forcing
could increase the risk of abrupt climate change:
warming and other human alterations of the Earth system may increase
the possibility of large, abrupt, and unwelcome regional or global
climatic events. The abrupt changes of the past are not fully explained
yet, and climate models typically underestimate the size, speed, and
extent of those changes. Hence, future abrupt changes cannot be
predicted with confidence, and climate surprises are to be expected.
- National Research Council, 2002
in weather patterns can result from abrupt changes that might occur
spontaneously due to interactions in the atmosphere-ice-ocean system,
or from the crossing of a threshold from slow external forcing (as
described above) (Meehl et al., 2007).
In a warming
climate, changes in the frequency and amplitudes of these patterns
might not only evolve rapidly, but also trigger other processes that
lead to abrupt climate change (NRC, 2002).
of these patterns include the El Niño Southern Oscillation
(ENSO) and the North Atlantic Oscillation/Arctic Oscillation (NAO/OA).
have investigated the possibility of an abrupt slowdown or shutdown of
the Atlantic meridional overturning circulation (MOC) triggered by
greenhouse gas forcing. The MOC transfers large quantities of heat to
the North Atlantic and Europe, so an abrupt change in the MOC could
have important implications for the climate of this region (Meehl et al., 2007).
However, according to Meehl et al. (2007), the probability of an abrupt
change in (or shutdown of) the MOC is low: “It is very
that the MOC will undergo a large abrupt transition during the 21st
century. Longer-term changes in the MOC cannot be assessed with
confidence.” The slowdown in the MOC projected by most models
gradual, so the resulting decrease in heat transport to the North
Atlantic and Europe would not be large enough to reverse the warming
that results from the increase in greenhouse gases.
rapid disintegration of the Greenland Ice Sheet (GIS), which would
raise sea levels 7 meters, is another commonly discussed abrupt change.
Although models suggest the complete melting of the GIS would only
require sustained warming in the range 1.9°C to 4.6°C
to the pre-industrial temperatures), it is expected to be a slow
process that would take many hundreds of years to complete (Meehl et al., 2007).
A collapse of the West Antarctic Ice Sheet (WAIS), which would raise
seas 5-6 meters, has been discussed as a low-probability, high-impact
response to global warming (NRC, 2002;
Meehl et al., 2007).
The weakening or collapse of ice shelves, caused by melting on the
surface or by melting at the bottom by a warmer ocean, might contribute
to a potential destabilization of the WAIS. If ice discharge
accelerates, it is possible that sea level could rise faster than
projected in the IPCC scenarios. However, there is presently no
consensus on the long-term future of the WAIS or its contribution to
sea level rise (Meehl et al., 2007).
more information on this issue, visit NOAA's Abrupt
Climate Change Web site and
see the National Resource Council report "Abrupt
Climate Change: Inevitable Surprises" (a short
4 page summary is also available (PDF, 4
pp., 714 KB,About
addition, visit the CCSP
Web site for
more information about ongoing multi-agency research on abrupt climate
change. An analysis on this topic is underway and will be completed by
Top of page
- IPCC, 2007:
Climate Change 2007: Impacts, Adaptation, and Vulnerability .
Contribution of Working Group II to the Third Assessment Report of the
Intergovernmental Panel on Climate Change [Parry, Martin L., Canziani,
Osvaldo F., Palutikof, Jean P., van der Linden, Paul J., and Hanson,
Clair E. (eds.)]. Cambridge University Press, Cambridge, United
Kingdom, 1000 pp.
E., J. Overpeck, K.R. Briffa, J.-C. Duplessy, F. Joos, V.
Masson-Delmotte, D. Olago, B. Otto-Bliesner, W.R. Peltier, S.
Rahmstorf, R. Ramesh, D. Raynaud, D. Rind, O. Solomina, R. Villalba and
D. Zhang (2007) Palaeoclimate. In: Climate Change 2007: The Physical
Science Basis. Contribution of Working Group I to the Fourth Assessment
Report of the Intergovernmental Panel on Climate Change [Solomon, S.,
D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and
H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United
Kingdom and New York, NY, USA.
G.A. et al. (2007) Global Climate Projections. In: Climate
Change 2007: The Physical Science Basis. Contribution of Working Group
I to the Fourth Assessment Report of the Intergovernmental Panel on
Climate Change [Solomon,
S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and
H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United
Kingdom and New York, NY, USA.
S.H. et al. (2007) Assessing key vulnerabilities and the risk from
climate change. Climate Change 2007: Impacts, Adaptation and
Vulnerability. Contribution of Working Group II to the Fourth
Assessment Report of the Intergovernmental Panel on Climate Change,
M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E.
Hanson, Eds., Cambridge University Press, Cambridge, UK, 779-810.
2002: National Research Council, Abrupt Climate Change: Inevitable
Committee on Abrupt Climate Change.§
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