This case study explores three complex issues:

~What evidence is there to suggest that hurricanes and related storm types are increasing in frequency and/or magnitude?
~If there are changes, to what extent can these be linked to global warming, or to short-term climate change such as the El Nino Southern Oscillation (ENSO)?
~How accurate are the records of hurricanes? It could be that new satellite technology records more hurricanes than was possible before 1970, and this may explain the rise in the number of hurricanes recorded.

At a basic level, the relationship between higher global temperatures, higher North Atlantic sea-surface temperatures and more North Atlantic storms seems straightforward. Scientists have found that greenhouse gas emissions have contributed to a rise in global average temperatures, and this has had a knock-on impact on sea-surface temperatures (SSTs). Increasing SSTs provide idea conditions for spawning more and stronger storms. Higher SSTs pump up an existing storm's power and greater evaporation rates add to its rainfall.

Research into the incidence of tropical storms and hurricanes (severe tropical storms) using North Atlantic records dating back to 1880 has identified three major trends. From 1905 to 1930 there was an annual average of 6 tropical storms/hurricanes. From 1931 to 1994 the number jumped to an average of 9.4 and remained steady until 1995. From 1995 there was a 10-year period with an annual average of 15 tropical storms, of which 8 were hurricanes. In 2004, the 'year of savage storms', a series of hurricanes criss-crossed the Caribbean, and in 2005, the year of Katrina, Rita and Wilma, there were so many storms that they run out of names.

If it was a straightforward case of global warming heating the oceans, then 2006 should have continued the trend, but it had only 8 tropical storms and nothing above category 3. However, the Pacific had a year of record storms. This suggests that there might be an oscillation between the Atlantic and the Pacific.

The ENSO is basically a fluctuation in sea-surface temperature in the Pacific, but it is known that El Nino events (warming of the eastern Pacific Ocean) reduce hurricane frequency in the Atlantic. As 2006 was the start of an El Nino, this may be the reason why so few tropical storms occurred in the Atlantic that year.

Most scientists conclude that global warming is contributing to storms of greater magnitude, but that the ENSO has an important impact on frequency.

	Created by Holly Lovering over 10 years ago

Taken straight from the Edexcel AS Geography textbook.

Geography Unit 1, World At Risk Case Study 2 - Are hurricanes increasing as a result of climate change?