Hurricanes: Worse than We Thought?

by Marlo Lewis on January 12, 2015

in Blog

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Is the impact of global warming on hurricanes “worse than we thought”? Look at the data and judge for yourself.

The National Oceanic and Atmospheric Administration (NOAA) uses a metric called accumulated cyclone energy (ACE) to measure the strength of individual tropical cyclones and entire tropical cyclone seasons. As explained by NOAA:

The ACE index is a wind energy index, defined as the sum of the squares of the maximum sustained surface wind speed (knots) measured every six hours for all named storms while they are at least tropical storm strength.

Dr. Ryan Maue of WeatherBell Models reports that, “In the pentad since 2006, Northern Hemisphere and global tropical cyclone ACE has decreased dramatically to the lowest levels since the late 1970s.” He also reports that “the frequency of tropical cyclones has reached a historical low.”

This chart shows global and northern hemisphere ACE during 1970-2014. What we see is “strikingly large” inter-annual and decadal variability but no long-term trend.

Hurricanes ACE 1970 - 2014 Ryan Maue Dec. 31, 2014

The next chart shows global tropical storm and hurricane frequency. Again, we see lots of inter-annual variability but no obvious trend.

Hurricanes Tropical Storm and Hurricane Frequency 1970 - 2014 Ryan Maue Dec. 31, 2014

The next chart shows global hurricane frequency (all & major). There were more major hurricanes in 1992-2014 than in 1970-1991. However, the frequency of major hurricanes did not increase since 1992 and all-hurricane frequency decreased.

Hurricanes total and major 1970 - 2014 Ryan Maue (Dec 31, 2014)

The final chart shows global, northern hemisphere, and southern hemisphere ACE. Again, we see “striking” variability but also a return, during the past seven years, to ACE levels of the 1970s.

Hurricanes Tropical Storm and Hurricane ACE 1970 - 2014, Ryan Maue Dec. 31, 2014






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