Predictions for Climate Change by 2100

The significant changes in the Earth's climate that have occurred in the past half-century, that are predicted to continue over the twenty-first century, and that are likely to have been at least partially caused by anthropogenic effects, as judged by the IPCC in its 2007 report, are summarized in Table 7-2,

According to sophisticated computer simulations of the future climate reported by the IPCC, the rise in the average global air temperature by 2100 (compared to 1990) could be as small as 1.4°C or as large as 4.0°C. As in the twentieth century, more warming will occur at night than during the day. The magnitude of the temperature increase will depend greatly on whether emissions (including those of sulfur dioxide) are controlled or not. At a minimum, however, the world will warm more than twice as fast in this century as it did in the last. Part of the rather large range of the prediction is due to uncertainty about exactly how sensitive the climate is to carbon dioxide. Indeed, research reported in 2003 indicates that aerosols have accounted for more greenhouse warming in the past than previously thought; consequently, scientists may have significantly underestimated the sensitivity of temperature to C02, in which case the predicted increases will have to be revised upward.

An increase of a few degrees in temperature may seem small, but our current average air temperature is less than 6°C warmer than that in the coldest periods of the ice ages! Snow cover and sea-ice area will continue to decline. There may well be enough melting of ice in the Arctic region for the Northwest Passage to be used for commercial transport, since the warming of all Arctic regions in winter is projected to be much greater than the global average. Indeed, the Arctic regions of Alaska and western Canada warmed at the rate of 0.3 - 0.4°C per decade in the 1961-2004 period. The Arctic (Southern) Ocean will probably become ice-free in the summer, a situation that has not

Recent Trends and Projections for Extreme Weather Events That Have Undergone Recent Change

Stable 7-2

Recent Trends and Projections for Extreme Weather Events That Have Undergone Recent Change

Stable 7-2

Likelihood That

Trend Occurred in

Likelihood of Future

Late 20th Century

Likelihood of a Human

Trends Based on

Phenomenon and

(Typically Post

Contribution to

Projections for

Direction of Trend

1960)

Observed Trend

21st Century

Warmer days and

Very likely

Likely

Virtually certain

fewer cold days and

nights over most

land areas

Warmer and more

Very likely

Likely (nights)

Virtually certain

frequent hot days

and nights over

most land areas

Warm spells/heat

Likely

More likely than not

Very likely

waves. Frequency

increases over

most land areas

Heavy precipitation

Likely

More likely than not

Very likely

events. Frequency

(or proportion of

total rainfall from

heavy falls) increases

over most areas

Area affected by

Likely in many

More likely than not

Likely

droughts increases

regions since 1970s

Intense tropical

Likely in some

More likely than not

Likely

cyclone activity

regions since 1970

increases

Increased incidence

Likely

More likely than not

Likely

of extremely high

sea level (excludes

tsunamis)

Source: IPCC, Climate Change 2007: The Physical Science Basis. Summary for Policymakers: www.ipcc.ch

Source: IPCC, Climate Change 2007: The Physical Science Basis. Summary for Policymakers: www.ipcc.ch occurred for at least a million years. A similar situation is occurring over the land; because of global warming, the land is snow-covered for a shorter duration in winter and has a much higher albedo than the soil and vegetation exposed in the spring. In addition, most of the region of permafrost—land in northern Canada, Alaska, Siberia, and northern Scandinavia that stays frozen year-round—will likely melt to a depth of 3 m or more during this century.

The total amount of global rainfall is projected to increase, since more water will evaporate at the higher surface temperatures. The global average precipitation increases by about 2% for every Centigrade degree rise in temperature. Although the world overall will become more humid, some areas will become drier. To make matters worse, most areas of the world that currently suffer from drought are predicted to become even drier. Continental interiors at mid-latitudes will have continuing risk of drought in summer due to continued drying of the soil, the increased rate of evaporation from higher air temperatures being greater than the increase in the rate of precipitation. Subtropical areas will experience less precipitation, and equatorial and high-latitude regions will experience more, continuing the twentieth-century trends.

An increase in the average atmospheric temperature means that the air and water at the Earth's surface would contain more energy and that more extreme weather disturbances could result, the effect of global warming that will affect many of us the most. The number of days having intense rain showers or very high temperatures will both increase. Storm wind intensities and heavy downpours will increase in some tropical areas.

Continue reading here: Predictions About Sea Levels

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