Hurricanes: Worse than We Thought?

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.

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

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.

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.