Global climate change is feeding more powerful storms.

RODALE NEWS, EMMAUS, PA—As unusually wicked tornadoes tear through the United States this spring, many people are wondering if Earth's destabilized climate is behind such strong storms. The science community has known for years that the spike in man-made greenhouse gases would lead to more severe weather—more flooding, droughts, and stronger storms—but it's not clear if this season's tornadoes are caused by a drastically changing climate. "There's not a clear picture on tornadoes. But the series several weeks ago were part of a very large storm system, and the numbers and strength are outside norms," explains Paul Epstein, MD, MPH, associate director of the Center for Health and Global Environment at Harvard University. "We have some ideas about why, but this is speculative at this point. Changing land temperatures and pressure gradients, and the pattern of the jet stream—affected by shrinking Arctic ice—may all be playing a role."

While Dr. Epstein notes it's too early to say this spring's tornado activity is part of a long-term trend—that question will take monitoring and analysis for a definitive answer—he is very clear about the effects climate change is already having on human health. In his new book, Changing Planet, Changing Health: How the Climate Crisis Threatens Our Health and What We Can Do about It (University of California Press, 2011), Dr. Epstein connects the dots, explaining how climate change is, and will continue to be, a threat to the general public and our health care system. Ignoring the problem is no longer an option, which is why the author is bringing climate destabilization to a personal level. "We're really sticking our heads in the sand about the impacts of climate change," says Dr. Epstein, who notes that the fossil-fuel-industry–funded doubt campaign has been working over the last several decades. "We need to bring it home so people understand that it's affecting their health, and how it's in their backyard. In the next 10 to 20 years, expect to see a lot of very wild, severe, punishing, disease-promoting, and costly extreme weather events."

Scientists have ascertained that a sharp spike in greenhouse gases in the atmosphere is causing stronger storms, including more powerful hurricanes. So how exactly does this work? "Global warming is causing climate change through the ocean," explains Dr. Epstein. Warmer seas mean faster water-evaporation rates, which fuels hurricanes, storms, and severe flooding. The warming leads to increased water vapor in the atmosphere. That, coupled with melting arctic, antarctic, and mountain glaciers, is transforming the water cycle, leading to much more intense precipitation events in the United States and elsewhere, Dr. Epstein says.

Deserts are also drying out faster, due to a shift in winds. And when it does rain, it pours. Since 1970, Dr. Epstein says there's a 7 percent increase in instances of events producing two inches of rain in a day; four-inches-in-a-day occurrences are up 20 percent, and events dumping half a foot have risen nearly 30 percent. All of these changes are leading to pest infestations in our forests and yards, higher rates of waterborne diseases, and other ailments outlined below.

Climate change and health are connected—here's how the changes may be affecting you.

• Allergies. Researchers at Harvard and the U.S. Department of Agriculture (USDA) have discovered that excess CO2 levels—mainly from burning coal and oil—are creating super-charged ragweed plants brimming with much higher rates of hayfever-inducing pollen. Lewis Ziska, PhD, a veteran research plant physiologist with the USDA, found that jumping from preindustrial atmospheric carbon dioxide levels (280 ppm) to 1999 levels (370 ppm) doubled the amount of pollen ragweed produces. Interestingly, the high CO2 levels also create more potent pollen, which explains why lately it seems every allergy season is the worst ever. (Ziska also discovered that allergy season now lasts two to four weeks longer in many parts of the Northern Hemisphere.)