I wore a wool coat to work today.  And I’m ashamed to say that last night I turned the heat on in my apartment.  San Francisco is obviously a special place, particularly in July.  And by “special,” I mean foggy, windy, and cold.  Weather.com says that it was in the 50’s last night and this morning, but I have trouble believing that.

So I found it a little bit hard to relate this morning on a conference call with journalists and scientists talking about climate change, heat waves, and public health.   It seems that much of the world beyond San Francisco has been experiencing some unprecedented heat lately.  According to NOAA, global combined surface and ocean temperatures for January through May 2010 are the warmest on record.   But in California, according to Tom Evans of the National Weather Service (NWS), so far this summer we’ve experienced pretty normal average temperatures, and that’s what the NWS Climate Prediction Center is forecasting for the rest of the summer for most of the state, he said, although the southeastern portion of the state may be in for some hotter-than-normal weather in the coming months.

On the call this morning, which was put together by the Union of Concerned Scientists, the speakers were careful to point out that one or two heat waves cannot be considered evidence for global warming, just at the snowstorms on the East Coast this winter couldn’t be used to refute it.  (This recent article in the Christian Science Monitor has more about the heat waves and changing attitudes about climate change.)

However, said NOAA climatologist David Easterling, “Warming temperatures increase the probability of heatwaves.  By the end of the century, what we currently consider a heat wave, or an extremely hot day, might become the norm.”

Warming temperatures can impact public health in a number of ways, said Michael McGeehin, director of the National Center for Environmental Health at the Center for Disease Control.

“Climate scientists predict that the U.S. will see an increase in the duration, intensity, and frequency of heat waves, and we know that heat waves are a public health disaster,” he said.  “They kill.”

And they could kill in large numbers in the centuries to come, according to a recent paper by Matt Huber of the Climate Change Research Center at Purdue.  Huber was on the call this morning to discuss his analysis, which found that if CO2 levels continue to rise over the next 200 years, hotter temperatures could make areas that are home to 50% of the world’s population uninhabitable during heat waves in the the centuries after 2100.  Problems start happening when the heat index is about 130, he said.  (A temperature of 105 degrees F with a humidity level of 50% has a heat index of 134.)

“I personally think that we’ve already committed to at least 2 degrees (Celsius) of warming, but the kind of warming we’re talking about here, which is on the order of at least 10 degrees Fahrenheit, maybe more like 15 degrees Fahrenheit, that’s something that we can still decide to avoid,” he said.  “And from our calculations it looks like we should really try and avoid that.”

And it looks like that potential warming could be becoming reality faster than some expected.  A new study out of Stanford announced today finds that “exceptionally long heat waves” could become commonplace in the United States in the next 30 years, particularly in the western US.  The study, headed up by Noah Diffenbaugh of the Woods Institute, used climate models to analyze what might happen if global temperatures rise two degrees C above pre-industrial levels by 2039. (An increase of two degrees Celsius is the limit agreed upon in the non-binding  2009 Copenhagen Climate Accord (PDF).)

The Stanford researchers found that “an intense heat wave – equal to the longest on record from 1951 to 1999 – is likely to occur as many as five times between 2020 and 2029 over areas of the western and central U.S.”

The analysis predicts during the 2030s the worst heat waves maybe be even more frequent.

It’s 57 degrees in San Francisco this afternoon, and I am wearing a winter scarf at my desk.  Despite all these grim predictions, right now it’s hard not to think that a little extra heat might be nice.