EFFECTS ON WEATHER FROM CLIMATE CHANGE

Increasing temperature is likely to lead to increasing precipitation globally although some areas will experience less rainfall. The effects on storms are less clear. Extratropical storms partly depend on the temperature gradient, which is predicted to weaken in the northern hemisphere as the polar region warms more than the rest of the hemisphere.

Climate change is likely to affect weather, and thus humans, in a number of ways:

• More extreme weather

• Increased evaporation

• Destabilization of local climates

• Economic costs from changes in weather.

More extreme weather and climate change

Many scientists believe the maximum intensity reached by tropical storms is likely to undergo a moderate increase in a world affecting by substantial global warming, with a significant increase in the number of highly destructive category 5 storms.
The Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report “Climate Change 2001” stated that (at that time) “there is no compelling evidence to indicate that the characteristics of tropical and extratropical storms have changed.” There is, however, limited evidence from a relatively short time period that storm strength is increasing, such as the Emanuel (2005) “power dissipation index” of hurricane intensity.

Worldwide, the proportion of hurricanes reaching categories 4 or 5 – with wind speeds above 56 meters per second – has risen from 20% in the 1970s to 35% in the 1990s. Precipitation hitting the US from hurricanes also increased by 7% over the twentieth century.

The World Meteorological Organization has suggested a possible link between global warming and increasing extreme weather events, as have Hoyos et al. (2006), writing, “the increasing ... number of category 4 and 5 hurricanes ... is directly linked to” increasing temperatures. Hurricane modeling has produced similar results, e.g., “hurricanes, simulated under warmer, high-CO2 conditions, are more intense ... than under present-day conditions.... greenhouse gas–induced warming may lead to ... increasing ... occurrence of highly destructive category-5 storms.”

A paper by 14 scientists notes that “research shows very little evidence to support the claim that the rising costs associated with weather ... are associated with changes in [their] frequency or intensity.”

A substantially higher risk of extreme weather does not necessarily mean a noticeably greater risk of slightly-above-average weather. However, the evidence is clear that severe weather and moderate rainfall are also increasing.

Stephen Mwakifwamba, national coordinator of the Centre for Energy, Environment, Science and Technology - which prepared the Tanzanian government’s climate change report to the United Nations - says that change is happening in Tanzania right now. “In the past, we had a drought about every 10 years”, he says. “Now we just don’t know when they will come. They are more frequent, but then so are floods. The climate is far less predictable. We might have floods in May or droughts every three years. Upland areas, which were never affected by mosquitoes, now are. Water levels are decreasing every day. The rains come at the wrong time for farmers and it is leading to many problems”.

Greg Holland, director of the Mesoscale and Microscale Meteorology Division at the National Center for Atmospheric Research in Boulder, Colorado, said on April 24, 2006, “The hurricanes we are seeing are indeed a direct result of climate change,” and that the wind and warmer water conditions that fuel storms that form in the Caribbean are, “increasingly due to greenhouse gases. There seems to be no other conclusion you can logically draw.” Holland said, “The large bulk of the scientific community say what we are seeing now is linked directly to greenhouse gases.”

Increased evaporation, global warming & global dimming

Over the course of the 20th century, evaporation rates have reduced worldwide; this is thought by many to be explained by global dimming. As the climate grows warmer and the causes of global dimming are reduced, evaporation will increase. This may cause heavier rainfall and more erosion, and in more vulnerable tropical areas (especially in Africa), desertification due to deforestation. Many scientists think that it could result in more extreme weather as global warming progresses.

The IPCC Third Annual Report says: “...global average water vapor concentration and precipitation are projected to increase during the 21st century. By the second half of the 21st century, it is likely that precipitation will have increased over northern mid- to high latitudes and Antarctica in winter. At low latitudes there are both regional increases and decreases over land areas. Larger year to year variations in precipitation are very likely over most areas where an increase in mean precipitation is projected”.

economic Cost of weather changes

The economic impact of extreme weather is rising rapidly both because of increases in the frequency and intensity of extreme weather and because of changes in human behavior. An example of how human behavior has increased exposure to extreme weather is the movement towards greater development along vulnerable seacoasts. The economic impact of hurricanes has increased because there is more development along seacoasts vulnerable to hurricanes. Similarly, the economic impact of floods has increased because there is more development in flood plains. Choi and Fisher, writing in Climate Change, vol. 58 (2003) pp. 149, predict that each 1% increase in annual precipitation would enlarge the cost of catastrophic storms by 2.8%.

The Association of British Insurers has stated that limiting carbon emissions would avoid 80% of the projected additional annual cost of tropical cyclones by the 2080s. The cost is also increasing partly because of building in exposed areas such as coasts and flood plains. The Association claims that reduction of the vulnerability to some inevitable impacts of climate change, for example through more resilient buildings and improved flood defenses, could also result in considerable cost-savings in the long term.

Agriculture is likely to be affected by changing weather patterns. More extreme weather will increase the destruction of crops, while changes in rainfall patterns will affect agricultural yields.

Destabilization of local climates

In the northern hemisphere, the southern part of the Arctic region (home to 4,000,000 people) has experienced a temperature rise 1° to 3 °C over the last 50 years. Canada, Alaska and Russia are experiencing initial melting of permafrost. This may disrupt ecosystems and increase bacterial activity in the soil, leading to these areas releasing carbon instead of retaining it.

A study of changes to eastern Siberia’s permafrost suggests that it is gradually disappearing in the southern regions, leading to the loss of nearly 11% of Siberia’s nearly 11,000 lakes since 1971. At the same time, western Siberia is at the initial stage where melting permafrost is creating new lakes, which will eventually start disappearing as in the east. Western Siberia is the world’s largest peat bog, and the melting of its permafrost is likely to lead to the release, over decades, of large quantities of methane. This will create an additional source of greenhouse gas emissions.

Hurricanes were thought to be an entirely north Atlantic phenomenon. In April 2004, the first Atlantic hurricane to form south of the Equator hit Brazil with 40 m/s (144 km/h) winds; monitoring systems may have to be extended 1,600 km (1000 miles) further south.

Click here to go to the home page www.climatechange.110mb.com

This information is licensed under the GNU Free Documentation. It is derivative of articles on Climate Change, Global Warming and related environmental issues at http://en.wikipedia.org