Global Warming

134 Climate changein the twenty-firstcenturyand beyond

Table 6.2Estimates of confidence in observed and projected changes in extreme weather and

climate events

Confidence Changes in Confidence in
in observed changes phenomenon projected changes
(latter half of the twentieth century) (during the twenty-first century)

Likelyb Higher maximum temperatures and
more hot days over nearly all land
areas

Very likely

Very likely Higher minimum temperatures, fewer
cold days and frost days over nearly
all land areas

Very likely

Very likely Reduced diurnal temperature range
over most land areas

Very likely

Likely, over many areas Increase of heat indexaover land areas Very likely, over most areas
Likely, over many Northern
Hemisphere mid to high latitude
land areas

More intense precipitation events Very likely, over most areas

Likely, in a few areas Increased summer continental drying
and associated risk of drought

Likely, over most mid-latitude
continental interior (lack of
projections consistent in other areas)
Not observed in the few analyses
available

Increase in tropical cyclone peak wind

intensities

Likely, over some areas

Insufficient data for assessment Increase in tropical cyclone mean and
peak precipitation intensities

Likely, over some areas

aHeat index is a combination of temperature and humidity that measures effects on human comfort.
bSee Note 1 of Chapter 4 for explanation of likely, very likely, etc.

Source: Table SPM-1 from Summary for policymakers. In Houghton, J. T., Ding, Y., Griggs, D. J., Noguer, M., van der
Linden, P. J., Dai, X., Maskell, K., Johnson, C. A. (eds.)Climate Change 2001: The Scientific Basis.Contribution of Working
Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge: Cambridge University
Press.

and in providingregional detail that in many cases (especially for precip-

itation) shows substantial disagreement with the averages provided by

a GCM.

Regional models are providing a powerful tool for the investigation of

detail in patterns of climate change. In the next chapter the importance

of such detail will be very apparent in studies that assess the impacts

of climate change. However, it is important to realise that, even if the

models were perfect, because much greater natural variability is apparent

in local climate than in climate averaged over continental or larger scales,

projections on the local and regional scale are bound to be more uncertain

than those on larger scales.