Hurricane Katrina struck Louisiana and Mississippi and other southeastern states in 2005 and wreaked so much havoc and destruction on those areas of the United States that many people have been looking at global warming and wondering if that was the cause.
deep within minutes, and continued rising until it was more than 13.5 feet (4 m) deep.
An anemometer in Massachusetts recorded sustained wind speeds of 121 miles (195 km) per hour. This reading holds the record today as the second-highest winds ever recorded on Earth. Eventually, the storm moved into Canada and the Arctic, where it died out. More than 690 people were killed in this single storm. 1972—Hurricane Agnes. According to NOAA, Hurricane Agnes set inland flood records across the northeast. Its damage was estimated at $3.2 billion. Agnes came out of the Gulf of Mexico and traveled from Florida up to new York. More than 210,000 people were forced to evacuate their homes, and 122 people were killed. Agnes was unusual because it flooded so far inland. It impacted areas several hundreds of miles from the coasts. The entire state of Pennsylvania was declared a disaster area. In the central part of Virginia, almost every creek and stream overflowed its banks. Florida experienced high tides, winds, and even tornadoes.
Because of severe weather incidents like these, the national Weather Service's modernization efforts in cutting-edge technology, such as Dop-pler radar, weather satellites, and automated river and rain gauges, are able to assist in monitoring severe weather. Another forward-looking improvement is in emergency preparedness. Forecasters are now able to broadcast weather information to the public and emergency facilities faster as communications technology continues to improve. Public awareness has also improved, and more families and businesses have implemented emergency evacuation plans.
Unfortunately, science cannot tell climatologists directly if global warming specifically causes hurricanes. Scientists cannot positively say, therefore, that global warming directly caused Katrina or any other specific incident of occurrence. But just because Katrina cannot be directly linked to global warming as the sole, specific cause, it does not mean that global warming did not play a significant role in Katrina's occurrence.
Climatologists at NOAA can say with certainty that they understand the physical mechanisms of how hurricanes are formed, what sustains them, how they grow, and how they move. Because they know for a fact that hurricanes draw their strength from warm ocean water, the warmer the water is, the more powerful the storm can be. Records of sea-surface temperature confirm that the ocean water is currently more than 1°F (0.6°C) warmer than it was a century ago. This temperature can fluctuate from year to year, too, if the water gets warmer, it increases the chance of supporting a hurricane during hurricane season. It is suggested that this happened with Katrina. While Katrina was strengthening from a tropical storm to a category 5 hurricane, as it traveled between the Florida Keys and the Gulf Coast, the surface waters in the Gulf of Mexico were unusually warm—2°F (1.2°C) warmer than normal.
While there is no way to prove global warming caused Katrina, it is reasonable to say that it increased the probability of Katrina developing. Some scientists believe that global warming has created an environment under which powerful storms such as hurricanes are more likely to occur now and in the future. For example, a study published in Nature notes that during the second half of the 20th century, the average intensity of tropical storms has increased globally. This matches the same time period that sea surface temperatures have been rising. Because warm oceans are such a critical ingredient in hurricane formation, as the ocean temperatures rise, the probability of hurricanes will likely rise as well.
Not all scientists agree on this issue, however. There is some controversy in the science arena on the connection between hurricanes and global warming. Christopher Landsea, a scientist at the National Hurricane Center in Miami, Florida, believes that it only appears there are more hurricanes recently because they are monitored better than they were 100 years ago. He contends that back in the early 1900s, the only reports gathered were by ships crossing the ocean. Today there is complete satellite coverage of Earth. Landsea believes, instead, that there are multidecadal swings of "active" then "quiet" periods for the storms. Even so, Landsea does not say that global warming has not had an impact on hurricanes—just that he does not know if it has had a big enough influence to say specifically that global warming has contributed a measurable influence on hurricane frequency and intensity.
Other researchers debate past records kept in the late 1800s and early 1900s, many claiming the records inaccurately represent the true number of storms because the only method of collecting data was via ships (satellite surveillance systems were not available yet). NOAA's National Hurricane Center, which maintains HURDAT (the official record of tropical storms and hurricanes for the Atlantic Ocean, Gulf of Mexico, and Caribbean Sea) each year adds data from the hurricane season. Major revisions and reanalyses were made to the database in 2003 to update the time period from 1850 through the early 1900s.
Concerning the update and reanalysis, Chris Landsea remarked, "There are many reasons why a reanalysis of the HURDAT dataset is both needed and timely. HURDAT contained many systematic and random errors that needed correction. Additionally, as our understanding of tropical cyclones had developed, analysis techniques at the NOAA National Hurricane Center changed over the years and led to biases in the historical database that had not been addressed. Another difficulty in applying the hurricane database to studies concerned with landfall-ing events was the lack of exact locations, time and intensity information at landfall.
"Finally, recent efforts led by the late José Fernandez-Partagas, a Cuban research meteorologist in Miami, Florida, uncovered previously undocumented historical tropical cyclones in the mid-1800s to early 1900s that have greatly increased our knowledge of these past events, which also had not been incorporated into the HURDAT database."
More than 5,000 additions and alterations were approved for the years 1851 to 1910 by the NOAA National Hurricane Center's Best Track Change Committee.
According to Michael E. Mann, associate professor of meteorology at Penn State, and director of the Earth System Science Center, many scientists believe that the numbers of historic tropical storms in the Atlantic are seriously undercounted. A statistical model he developed, however, shows that the estimates currently used are only slightly below modeled numbers and indicate that the numbers of tropical storms in the recent past are increasing.
"We are not the first to come up with an estimate of the number of undercounted storms," Mann said. He believes that in the past, researchers assumed that a constant percentage of all the storms made landfall, and so they compared the number of tropical storms making landfall with the total number of reported storms for that year. Other researchers looked strictly at ship logs and ship tracks to determine how likely it was a tropical storm would have been missed. In the early 1900s and before, there were probably not sufficient ships crossing the Atlantic to obtain full coverage.
Researchers reported that "the long-term record of historical Atlantic tropical cyclone counts is likely largely reliable, with an average undercount bias at most of approximately one tropical storm per year back to 1870." This contrasts with the prior estimate of three or more undercounted storms.
Mann's model looked at how the El Niño/La Niña cycle, the pattern of the Northern Hemisphere jet stream and tropical Atlantic sea-surface temperatures, influences tropical storm generation by creating a model that includes these three climate variables. The input information was available back to 1870.
The model, trained on the tropical storm occurrence information from 1944 to 2006, showed an undercount before 1944 of 1.2 storms per year.
In addition, according to Kerry Emanuel, a professor of meteorology at the Massachusetts Institute of Technology, Landsea does not acknowledge that there was also an eastward shift in sea surface temperatures, which caused more hurricanes to form farther to the east and fewer to strike the U.S. coastlines in recent years—so that even though a hurricane may not have made landfall on the U.S. coast, it does not mean one did not occur. Another important factor is that hurricanes are currently forming closer to the equator, which gives them more warm water to move across and pick up additional energy so that they become more intense, destructive storms.
Scientists also link hurricane frequency with El Niño patterns. When El Niño occurs, there are fewer hurricanes. Scientists believe
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