Photograph by Tyrone Turner, National Geographic

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Rescuers check for survivors in New Orleans, Louisiana, after Hurricane Katrina.

Photograph by Tyrone Turner, National Geographic

Rising Temperatures May Cause More Katrinas

Small increases in temperature found to add power to storms in the Atlantic.

Hurricanes that form in the Atlantic Ocean are expected to gain considerable strength as the global temperature continues to rise, a new study has found.

Using modeling data focused on the conditions in which hurricanes form, a group of international researchers based at Beijing Normal University found that for every 1.8ºF (1ºC) rise of the Earth's temperature, the number of hurricanes in the Atlantic that are as strong or stronger than Hurricane Katrina will increase twofold to sevenfold.

Hurricane strength is directly related to the heat of the water where the storm forms. More water vapor in the air from evaporating ocean water adds fuel to hurricanes—also called cyclones and typhoons in different parts of the world—that build strength and head toward land.

Hurricane Katrina is widely considered the measure for a destructive storm, holding the maximum Category 5 designation for a full 24 hours in late August 2005. It lost strength as it passed over the Florida peninsula, but gained destructive power right before colliding with New Orleans, killing more than 200 people and causing $80 billion in damage.

The study points to a gradual increase of Katrina-like events. The warming experienced over the 20th century doubled the number of such debilitating storms. But the ongoing warming of the planet into the 21st century could increase the frequency of the worst kinds of storms by 700 percent, threatening coastlines along the Atlantic Ocean with multiple Category 5 storms every year.

"Our results support the idea that changes in regional sea surface temperatures is the primary cause of hurricane variability," said Aslak Girnstead, a researcher with the Center for Ice and Climate at the University of Copenhagen. The large impact of small sea-surface temperature increases was more than Girnstead and his colleagues had anticipated. The entire study was published in the Proceedings of the National Academy of Sciences.

Global temperatures have steadily increased, making the past decade the warmest on record. Earlier this year, climate researchers reported that the Earth's temperatures have risen faster in the last century than at any point since the last ice age, 11,300 years ago. The primary cause, a consensus of scientists has said, is the rising emissions of greenhouse gases like carbon dioxide and methane.

Past hurricanes have supported the study's finding that global temperature rise is linked to more destructive storms. According to the National Center for Atmospheric Research, while the frequency of storms doesn't appear to have increased, the percentage of strong ones has risen sharply over the past few decades. The trend may be similar further back in time, but comprehensive hurricane data doesn’t exist.