The list of unusual conditions over the past year is long. According to the National Oceanic and Atmospheric Administration (NOAA), last winter was the fourth-warmest on record in the United States; spring was the warmest since record keeping began in 1895; and April marked the end of the warmest 12-month period in U.S. history.
Still, [UW-Madison senior climate scientist Steve] Vavrus says scientists need more information to determine whether global warming is to blame. But he says heat waves like the current one will become more common on a warmer planet as we continue to add greenhouse gases such as carbon dioxide to the atmosphere, primarily through the burning of fossil fuels.
“I think it’s a harbinger of what's to come under greenhouse warming,” says Vavrus. “Virtually all climate models simulate more intense and frequent heat waves as the climate warms, and most of the world has experienced increases in extreme heat during the past several decades.”
That’s not good news for air quality or human health. Tracey Holloway, an associate professor of environmental studies, atmospheric and oceanic sciences, and civil and environmental engineering, says hotter temperatures lead to more ground-level ozone. Breathing ozone can damage lungs and worsen bronchitis, emphysema and asthma, and particulate air pollutants can affect a person’s lungs and heart...
“For the last 40 years of global warming, there is nothing comparable in the instrumental record since about 1880,” [Jack] Williams says. “To find comparable analogs for the amount of warming expected for this century under standard greenhouse gas emission scenarios, you have to go back to the climate changes accompanying the last deglaciation, about 20,000 years ago.”