FAQ: Hurricanes and global warming
Q: News stories regularly say that global warming will bring even more frequent and stronger hurricanes. Is this true?
A: Scientists who study hurricanes say that right now there is not a lot that can be said about how a warmer world will affect hurricanes.
The Intergovernmental Panel on Climate Change (IPCC), an international group of scientists produced its latest report in 2001. In the the first of three reports, Climate Change 2001: The Scientific Basis, the scientists said that during the 21st century, hurricanes, typhoons, and Indian Ocean and South Pacific cyclones are likely to produce higher winds and heavier rain in some areas, but there's no way to tell whether the frequency and locations of these storms could change.
A January 2001 USATODAY.com story has more on the 2001 climate change report, including a link to its full text.
The latest detailed look at this question from knowledgeable scientists is an article, ''Tropical Cyclones and Global Climate Change: A Post-IPCC Assessment'' in the January 1998 issue of the Bulletin of the American Meteorological Society. It's on pages 19 - 38 of the Bulletin, which is Volume 79, number 1.
This group met to see if the 1995 IPCC report needed updating. An abstract and the complete text of the article are available on the American Meteorological Society Web site. You can find this article online by going to the AMS journals archive and then scrolling down to the bottom of the page where you’ll see available issues of the Bulletin that are available, which include Vol. 79 for 1998.
A good starting point for more information, without going to the detailed sources, is Chris Landsea's hurricane FAQ on the Web. Landsea, by the way, is one of the authors of the AMS Bulletin article. Click here to go to the part of his FAQ on ''What may happen to tropical cyclone activity in a 2xCO2 world.'' (2xCO2 world refers to having twice as much carbon dioxide in the air as now.)
Q: Aren't we already getting more and stronger hurricanes, such as Andrew in 1992?
A: World wide, the number of hurricanes seems to have stayed about the same for the last few decades. But, world-wide figures are hard to come by, especially for the years before the 1970s when weather satellites made it possible to really keep track of the world's tropical cyclones.
From the mid-1960s until the mid-1990s, the number of hurricanes hitting the U.S. declined from the previous two decades. For more on this question, click here to a question like this one in the huge hurricane FAQ maintained by Chris Landsea of the National Oceanic and Atmospheric Administration's Hurricane Research Division.
The 2001 IPCC report mentioned in the first question says that, "No global changes have been noted during the 20th century in terms of the numbers of storms or their strength. "No systematic changes in the frequency of tornadoes, thunder days, or hail events are evident in the limited areas analyzed."
The number of hurricanes that form over the Atlantic, Caribbean and Gulf of Mexico (the Atlantic Basin) varies greatly. It happens that from 1995 through 2003 there was an upswing in Atlantic Basin hurricanes.
But, this upswing seems to be making the current era one like the 1940s and 1950s, which many more hurricanes that the years from the mid 1960s through 1994. However, while the number of Atlantic Basin storms increased from 1995 through 2001, the number of hurricanes in the eastern Pacific and typhoons in the western Pacific decreased.
In 2003, the National Oceanic and Atmospheric Administration's project to reexamine 19th century storms concluded that the 1886 hurricane season was the busiest on record for the USA, with seven hurricanes hitting the nation. This study also concluded that the decade of the 1890s was an extremely busy one for the U.S. East Coast with four major (Category 3 or stronger) storms hitting the U.S. Atlantic Coast. Only the decade of the 1950s saw more strong hurricanes hit the U.S. East Coast.
For more on why the 1940s and 50s brought large numbers of Atlantic Basin hurricanes while the mid 1960s to mid 1990s saw few, see a July 2001 news story that describes a scientific report and why the number of Atlantic Basin hurricanes seems to run in cycles that last 20 or 30 years.
Q: But aren't hurricanes doing more damage to the U.S. than in the past? Doesn't this mean they are stronger?
A: Hurricanes are doing more damage, but this is because more people with more expensive homes are living in areas that hurricanes hit. Click here to go to a USA TODAY story with more on this.
Q: What would happen to the numbers of hurricanes if global warming changed El Niño?
A: Here's what Chris Landsea has to say about this in his FAQ: "ENSO is the largest single factor controlling year-to-year variability of tropical cyclones globally If the warm phase of ENSO (the "El Niño" events) occurred more often and/or with more intensity, then the inhabitants along the Atlantic basin and Australia would have fewer tropical cyclones to worry about. But people living in Hawaii and in the South Central Pacific would have more storms to deal with. The reverse would be true if the cold phase (or "La Niña") became more prevalent." The question below has a link to this part of Landsea's FAQ.
For information on El Niño and climate change, go to the last question in USA TODAY's FAQ about El Niño.
Q: What is "greenhouse" warming?
A: Carbon dioxide and some other gases in the atmosphere keep the Earth warm enough for life to thrive. This is the natural greenhouse effect. But, "greenhouse effect" is often used to describe potential climate changes caused by an enhanced greenhouse warming brought about by carbon dioxide and other substances that human activities add to the air. A USA TODAY online graphic explains how this works. You'll find links to a lot more information about climate change on our Resources: Climate change science page.
Q: If the Earth's atmosphere warms up, won't the oceans also warm up? Wouldn't this increase the numbers of hurricanes and make them stronger since warm ocean temperatures supply energy for hurricanes?
A: Warm ocean water is the major source of energy for hurricanes. But, warm ocean water is only one of several factors needed for hurricane formation. These factors are described in a USA TODAY online graphic on the ingredients hurricanes need.
A hurricane's strength depends on the temperature contrast between the ocean's water and the air high in the atmosphere, at the storm's top. If the world's oceans warm up, it's also possible that the upper atmosphere will also warm up. The result could be temperature contrasts much like those now. In other words, warmer oceans wouldn't necessarily mean more frequent or stronger hurricanes. Researchers say they don't know enough about all of the potential results of climate change to say how it will effect hurricanes.
Q: Wouldn't warmer oceans increase the size of the area of the 80-degree plus water needed for hurricanes to form and grow? For instance, wouldn't hurricanes form farther north in the Atlantic than they do now?
A: This might happen, but it won't necessarily be the case. Even if the water becomes warm enough farther north for hurricanes to form, other conditions might not be favorable. For example, for a storm to form and grow, winds at all levels of the atmosphere need to be fairly light and from the same direction. As you go farther north over the Atlantic you're more likely to encounter stronger winds and winds from different directions.
Q: Does this mean that an enhanced greenhouse warming will give the world fewer hurricanes or weaker hurricanes?
A: No. Right now climate and hurricane scientists can't say much about how a world with more carbon dioxide in the air than now would change all of the factors that determine the number and strength of hurricanes. The computer models used to study potential effects of climate change can't model the factors that affect hurricanes in enough detail to say what will happen if the global climate warms.
Q: Haven't scientists said that global warming will bring "hypercanes" with winds near the speed of sound?
A: I haven't found anything like this in any scientific publication. The idea is based on the calculations used to find a hurricane's possible maximum strength. The maximum possible strength (few, if any, hurricanes reach this strength) depends on the temperature of the ocean water and the temperature of the air flowing out of the top of the hurricane.
Kerry Emanuel of the Center for Meteorology and Physical Oceanography at the Massachusetts Institute of Technology is one of the scientists who has studied maximum possible storm strength. Here is what he has to say about hypercanes: Computer experiments "at very high sea surface temperature and low outflow temperatures ... produce very intense storms (with wind speeds near the speed of sound), and it has been speculated that such storms may have formed over pools of very hot water created by large asteroid impacts with the ocean. But we do not have to worry about hypercanes otherwise!"
Q: When did the possibility that global warming could affect hurricanes first come up?
A: Hurricane Andrew in 1992 seemed to spur a lot of the talk about global warming increasing the number of hurricanes, even through 1992 was one of the coolest of years in the late 1980s and 1990s because the huge eruptions of the Mount Pinatubo volcano in the Philippines had spread a veil of tiny drops of sulfuric acid around the stratosphere, which blocked some sunlight.
But, the idea is older than the 1990s.
The earliest reference to the idea that I've found was in the book, The Hurricane Hunters, by Ivan Ray Tannehill, first published in 1955. In the 1957 printing he describes, beginning on page 267, how after the end of the very costly 1954 hurricane season: "... the executives of the big insurance companies were in conference with grave faces... Reports had been circulated to the effect that the slow warming of the earth in the present century is bringing more hurricanes with greater violence and paths shifting northward to devastate areas with greater populations." Also, he adds, "There was speculation about the effects A-bombs and H-bombs on hurricanes." This was during the period when nuclear weapons were being tested in the atmosphere, and being blamed for no good reason for any weather that anyone thought was not normal.
Q: Where can I learn more about climate change and about hurricanes?
A: USA TODAY's online pages on Resources: Climate change science and Hurricane information have many links to USA TODAY text and graphics and also to scores of outside Web sites with good information. To learn more about the science of hurricanes, go to our hurricane science index.
The book Hurricane Watch: Forecasting the Deadliest Storms on Earth by Dr. Bob Sheets and Jack Williams discusses the question of hurricanes and climate change at length in its last chapter.