Last night I talked about the heat index as a "feel-like" temperature to gauge how humidity increases discomfort. Now some recent research analyzes the potential impact of global warming on the heat index.

At first, this might seem like a very straightforward relationship - if summers get warmer by a certain number of degrees, the heat index will go up as well by that same number. But there's a secondary effect that has to be considered. If the air and oceans warm, more ocean water will evaporate, so in general, the air will be more humid. That would also contribute to raising the heat index.

Now, most global warming projections show more warming in the center of continents than near the coasts. But the increase in humidity would tend to be larger at places closer to water. So even if these places have smaller overall temperature increases, they might still experience a greater change in the heat index because of the increased moisture in the air.