Air Pollutants and the “Warming Hole” of America

By Katie Lubinsky

Warming hole area shown on U.S. map

The “warming hole.” Image courtesy NASA’s Earth Observatory (click on image for more information).

“I want to be a tornado chaser when I grow up,” was probably the last thing my parents expected to hear from their 12-year-old daughter. Yet that was my goal after being born and raised smack-dab in the middle of hurricane alley. Insane weather and a “lively climate” were commonplace on Oak Island, N.C., and I was fixated by such dynamics. I planned on being the next crazy person chasing F4 tornadoes in Kansas. (I chose the safer route of journalism in the end!)

Studying weather and climate made me not only appreciate nature, but also made me realize that such lively forces play such huge roles in influencing the environment around us.

I’ve read many EPA studies about how weather and air pollutants influence climate change, and one sparked my interest: Imagine certain air pollutants (called aerosols) affecting clouds and, in turn, influencing temperatures in the continental U.S. to rapidly rise. But there seems to be a “hole” in this warming process. The continental U.S. is warming except for the middle part (central and south central) where a pocket of cooling air resides—a “hole” inside the warming, thus a “warming hole.”

EPA researchers, along with partners in China and Japan, are trying to better understand this cooling phenomenon and are using different methods to study this so-called “warming hole” including temperature data and global climate models.

Preliminary research shows that daily summertime maximum temperatures over the region have cooled over the past century. The reason? Researchers estimate that it is the air pollutant sulfate, a derivative of sulfur dioxide. Between 1950 and about 1990, sulfate increased over most of the U.S., and especially over the “hole” area. Scientists found when sulfate particles were at their highest levels in the “warming hole” area, average temperatures were a couple of degrees cooler.

The presence of sulfate has led to an increase in cloud cover during the summertime. Clouds reflect and scatter solar radiation, called the “whitehouse” effect. When sulfate particles combine with water vapor to form clouds, however, even more solar radiation is reflected back into space, which is believed to cause the cooling.

Other air pollutants, such as carbon dioxide, absorb and trap solar radiation and cause warming, called the “greenhouse” effect, and this has a greater impact in the areas that are not affected as much by sulfates.

Understanding how our climate changes means that we need to understand more than the greenhouse effect—we also need to understand how air pollution affects the atmosphere more generally. That includes not just warming trends, but all sorts of changes, including cooling trends. EPA researchers are making discoveries about how air pollutants, such as sulfate, influence our changing climate. Discoveries such as these will help to address both air quality and climate change.

I am fascinated by EPA’s atmospheric research, and the researchers’ efforts to understand the interactions between air pollution and climate change. It is a way for me to live my childhood dream without worrying about getting too close to a tornado or flying into a hurricane!

About the AuthorKatie Lubinsky is a student contractor working with EPA’s Office of Research and Development in communications and still daydreams about being a storm chaser from time-to-time.

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