Global warming isn’t just making the planet hotter. It can also make the air we breathe more toxic.
Hot summer days, like the ones baking the East Coast and Midwest this week, help produce ground level ozone - one of the chemicals that makes up smog.
It happens when pollutants emitted from cars, power plants, factories, and other sources react chemically with sunlight. Weather plays an important role in determining ozone concentrations. Ozone levels build up on sunny days when there is little or no wind to disperse the chemical. Days like that happen most often during heat waves, when high pressure limits clouds and usually wind. That’s why the worst smog days happen in the summer.
Ground-level ozone is technically the same chemical as the ozone in the upper atmosphere that makes up the ozone layer. At high altitudes, ozone forms naturally and helps shield the planet from solar UV radiation. That’s why the infamous “ozone hole” is so worrisome (a gap in the ozone layer caused by manmade Chloroflurocarbons).
Ground-level ozone never floats into the stratosphere, so it doesn’t help protect us. Instead, it can harm us: it makes breathing harder, and can cause burning eyes, coughing, shortness of breath and an irritated throat. For people with asthma or respiratory illnesses, ground-level ozone can make these conditions worse.
It’s no surprise, therefore that the Environmental Protection Agency (EPA) calls ground-level ozone a harmful pollutant. Every day, the EPA monitors ozone levels in the air, and reports those levels to the public. The chart above shows how the EPA rated the air quality in San Antonio every day in 2012. The yellow, orange, and red dots all represent days when ozone levels were rated “moderate” or worse. As you can see, most of the worst days happened when temperatures climbed above 90 degrees.
According to a recent study in the journal Environmental Research Letters, almost half a million people die from the effects of ozone pollution every year. An estimated 34,400 of those deaths happen in North America. As global warming continues, and we see more frequent and intense heat waves each summer, those numbers are expected to rise.
Even though rainfall totals for the first half of the year are running above average for the U.S. as a whole, there is a distinct divide of extremes.
Across the Midwest, East, and South, recent rounds of intense rain have pushed these areas well above average. Iowa, Wisconsin, Illinois, and Michigan each had their wettest first six months of the year on record. Minnesota wasn't far behind, having experienced its third wettest start to the year. On the opposite end of the spectrum, lack of rain has been the story in California, which had its driest January-June ever. The state experienced a rainfall deficit of 9.8 inches over that period. That beats the old record by a whopping 1.5 inches. Next door, Nevada had its fourth driest start to the year.
For the first time since 2005, everywhere east of the Mississippi River is drought free. These extreme wet and dry conditions are in line with what we can expect in a warming world.