By Kim Smiley

A recent study by Britain’s Met Office weather service found that reducing pollutants in the atmosphere has had an unintended consequence, an increase in intense hurricane activity in North America.

A Cause Map, a visual root cause analysis, can be a helpful tool to understand this type of issue.  A Cause Map shows the cause and effect relationships between the different causes that contribute to an issue and can illustrate the potential consequence of changing one cause.

In this example, the problem is that hurricane activity has been increasing in the Atlantic Ocean.  Previous studies have found a link between a rise in ocean temperature and the increase in hurricane activity. Higher temperatures result in more intense hurricanes because there is more water vapor in the air because more water evaporates at higher temperatures.  More heat is released as the water vapor condenses into rain and this heat fuels the hurricane.

The surface temperature of the Atlantic Ocean has increased a small amount, about half a degree Celsius since 1970.  Scientists are not in agreement about the cause of this temperature increase.  Some people believe that the change is simply part of the natural long term variability of ocean temperatures.  Other scientists believe that global warming has caused the higher temperatures.  This new study adds a new dimension to the discussion.

The Met office study found that the reduction in aerosol pollutants in the air caused the rise in the ocean temperature.  Aerosols play a role because they affect the way clouds form.  More aerosols result in brighter, longer lasting clouds so reducing the aerosols in the atmosphere means that there will be fewer clouds over the ocean.  Fewer clouds mean that less sunlight is reflected away.  All this means that more sunlight will hit the ocean, increasing temperatures.

Fewer aerosols are in the environment because they cause acid rain and legislation was passed that limits how much can be released into the environment.

This issue is further complicated when the weather pattern is viewed on a global scale.  When the ocean temperature is cooler, there is less hurricane activity bombarding the United States, but then there are severe droughts in Africa.  Additional studies will be needed to confirm the findings on the effects of aerosol pollutants, but this new information is an interesting piece of the climate puzzle.