We've fought cancer, immunized ourselves against a laundry list of diseases, even stayed inside our homes for fear of swine flu. But the biggest health threat of the 21st century, according to a new report. is climate change.
The joint study is from University College London and a peer-reviewed medical journal called "The Lancet."
Experts from both organizations studied climate change for a year, and say increased heat will have a major impact on mortality. Recent heatwaves in Europe have killed tens of thousands of people.
They also project that millions of people could be affected by water shortages by 2020. Water and sanitation are needed to prevent malnutrition and foodborne illnesses.
The report also indicates food supplies could become an even bigger problem in some parts of the world. Experts say crop yields could diminish by as much as 17 percent with even a 1 degree rise in global temperature.