According to a joint report by The Lancet and University College London's Institute for Global Health, it will be climate change fueled by global warming.
Global warming isn't usually thought of as a health threat. Maybe it's time to see it as one. It's expected to be harmful to the health of billions.
Those who place their faith in leaders should vote for those who are committed to reducing carbon dioxide emissions.
Human society is more fragile than people realize. A week-long garbage strike in the middle of summer will help bring this point home. Climate changes due to global warming are going to place severe stresses on human society which will test that fragility.
What exactly is likely to happen?
The direst effects are likely to come from problems with supplies of food and drinking water and an increase in extreme weather events such as cyclones and heat waves.
The report emphasizes that the brunt of this is going to be borne by the poorest nations - most in the Southern Hemisphere — through no fault of their own. The prime emitters of greenhouse gases are the nations of the Northern Hemisphere, particularly the United States.
The report quotes from a 2008 symposium: "The rich will find their world to be more expensive, inconvenient, uncomfortable, disrupted and colourless; in general, more unpleasant and unpredictable, perhaps greatly so. The poor will die."
Everybody has heard of global warming. Not everyone understands that it's already happening. Average temperature is estimated to have already risen three-quarters of a degree due to increased carbon dioxide. And even if all carbon dioxide emissions had ceased in the year 2000, the temperature would still rise another half a degree this century. As things stand, it is expected to go up by between 1 and 6 degrees Celsius by the end of the century. Most models of climate change are based on a 2-4 degree rise.
It's notoriously hard to predict weather, as anyone who takes their local forecast seriously knows. Predicting worldwide weather changes caused by a numerically uncertain temperature rise is extremely dicey. Models disagree about the exact extent of climate change. But they do agree that the overall changes will not be pleasant ones.
The report estimates a likely rise in sea level of 1-3 feet by the end of the century. More pessimistic estimates go above 40 feet by 2150. This would cause the flooding and abandonment of almost all low-lying coastal and river cities and towns. Definitely a health problem.
Currently, two billion people live within 60 miles of a shoreline; 13 of the world's 20 largest cities are located on a coast.
One of the many other expected effects of global warming is a northward migration of diseases such as malaria and dengue fever. As the world becomes more tropical, tropical diseases are likely to appear in places they were previously unseen.
The report is highly critical of the lifestyle of people in rich nations, which it refers to as neither sustainable nor equitable. It concludes that lowering worldwide carbon dioxide emissions will require substantial governmental cooperation, both within governments and between them. Yet it also emphasizes that individuals have an important role to play if such changes are to occur.
How can individuals help?
Those who place their faith in leaders should vote for those who are committed to reducing carbon dioxide emissions. Those who believe in the power of an individual's actions should better understand how those actions are linked to global warming. Whether this leads to changing personal consumption habits, not working for or buying the products of industries that are committed to the status quo or simply gaining a better understanding of the causes of global warming is for each person to decide. People are causing global warming; they should be able to stop it or at least limit its effects if their will to do so is strong enough.
It could mean the difference between living in Venice and living in Atlantis.
"Managing the health effects of climate change" appears in the May 16, 2009 issue of The Lancet.