SUMMARISE (30 PTS) Global Climate Change may be responsible in part for some trends in natural disasters such as extreme weather.
Based on future projections of climate change, the IPCC (International Panel on Climate Control) report makes a number of predictions. It is predicted that over most land areas, the frequency of warm spells or heat waves will very likely increase. It is likely that:
Increased areas will be affected by drought
There will be increased intense tropical cyclone activity
There will be increased incidences of extreme high sea level (excluding tsunamis)
Storm strength leading to extreme weather is increasing, such as the power dissipation index of hurricane intensity. Kerry Emanuel writes that hurricane power dissipation is highly correlated with temperature, reflecting global Climate change. However, a further study by Emanuel using current model output concluded that the increase in power dissipation in recent decades cannot be completely attributed to global Climate change. Hurricane modeling has produced similar results, finding that hurricanes, simulated under warmer, high-CO2 conditions, are more intense, however, hurricane frequency will be reduced.] 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 has increased by 7% over the twentieth century. The extent to which this is due to global Climate change as opposed to the Atlantic Multidecadal Oscillation is unclear. Some studies have found that the increase in sea surface temperature may be offset by an increase in wind shear, leading to little or no change in hurricane activity. Hoyos et al. (2006) have linked the increasing trend in number of category 4 and 5 hurricanes for the period 1970–2004 directly to the trend in sea surface temperatures.
Increases in catastrophes resulting from extreme weather are mainly caused by increasing population densities, and anticipated future increases are similarly dominated by societal change rather than climate change. The World Meteorological Organization explains that “though there is evidence both for and against the existence of a detectable anthropogenic signal in the tropical cyclone climate record to date, no firm conclusion can be made on this point.” They also clarified that “no individual tropical cyclone can be directly attributed to climate change.”
Thomas Knutson and Robert E. Tuleya of NOAA stated in 2004 that climate change induced by greenhouse gas may lead to increasing occurrence of highly destructive category-5 storms. In 2008, Knutson et al. found that Atlantic hurricane and tropical storm frequencies could reduce under future greenhouse-gas-induced climate change. Vecchi and Soden find that wind shear, the increase of which acts to inhibit tropical cyclones, also changes in model-projections of global climate change. There are projected increases of wind shear in the tropical Atlantic and East Pacific associated with the deceleration of the Walker circulation, as well as decreases of wind shear in the western and central Pacific. The study does not make claims about the net effect on Atlantic and East Pacific hurricanes of the climate change and moistening atmospheres, and the model-projected increases in Atlantic wind shear.
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. Increases in temperature are expected to produce more intense convection over land and a higher frequency of the most severe storms.