Public health officials have long known that extreme temperatures are linked to more deaths, but in one Australian city, researchers have calculated how many years of life were lost due to heat waves and cold snaps.

Using this information, scientists also projected how a climate change scenario would affect life expectancies. "We've seen an increase in deaths in Australia in cold and hot weather before, but that's just the number of deaths. When you look at the number of deaths, you treat a 40-year-old's death the same as a 90-year-old's. Obviously, from a societal perspective, they're not the same," explained Adrian Barnett, a researcher at the Institute of Health and Biomedical Innovation at the Queensland University of Technology in Australia.

Barnett and his team decided to measure not only the number of deaths in temperature extremes, but differences between the ages of death and life expectancy. In other words, they wanted to find out by how many years lives were cut short. They presented their findings last month in Nature Climate Change.

The researchers looked at fatalities between 1996 and 2004 in Brisbane, located on Australia's East Coast in the state of Queensland. The city sees consistent warm temperatures year-round, usually between 20 and 25 degrees Celsius (68 and 77 degrees Fahrenheit). "What that means is that we've become quite complacent about temperature," said Barnett, explaining that about 40 percent of homes in the city don't have insulation and many don't have heating or cooling. "Whatever is the temperature is outside, we are exposed to it inside," he said.

As of late, the area has experienced a number of extreme weather events, and Brisbane's City Council warns that more such events will happen as the climate changes. In July 2007, the temperature dropped below freezing for the first time since records were kept. In August 2009, Brisbane experienced its hottest winter day, setting a record of 35.4 degrees Celsius (96 degrees Fahrenheit). Over the past decade, the region has also experienced severe drought.

Men adapt better to unusual change than women

After analyzing the data, Barnett found that on days when the average temperature dropped to 10 degrees Celsius (50 degrees Fahrenheit), men on average lost 14 years of life and women lost 52 years. (The measurements were made based on the number of temperature-related deaths that day. Collectively, the women -- who appeared less able to adapt to the cold than the men lost an aggregated total of 52 years that they might have experienced had they survived.)

When temperatures rose to 30 degrees Celsius (86 degrees Fahrenheit), men lost 32 years and women lost 42. In 2000, temperature extremes led to 3,077 years of life lost for men and 3,495 for women. For comparison, Barnett said 3,700 years of life are lost to breast cancer.

Barnett said the results were surprising. "The assumption was that temperature deaths were in frail, old people," he said. "The results seem to suggest the opposite." Younger people can still be affected by extreme hot or cold temperature, since these conditions tend to exacerbate any existing health issues. According to Barnett, most of these fatalities stem from heart and lung problems as the body tries to regulate its internal temperature.

The researchers also projected that a 2-degree-Celsius increase in average temperature by 2050 would lead to an additional 381 years of life lost among Brisbane's residents over a year. The Intergovernmental Panel on Climate Change projects that global average temperatures will increase by between 1.1 and 6.4 degrees Celsius by 2100.

However, Barnett cautioned against making specific year-to-year predictions for extreme temperature impacts around the globe. "When we try and look at trends over time, it actually becomes kind of noisy," he said. "Some years it gets really bad; in other years, it won't be nearly as bad. It's actually quite hard to predict what's going to happen in any one year."

People in different cities adapt differently

In addition, people respond to temperature differently in Brisbane than they do in Hamburg, Chicago or Dhaka, so the patterns don't translate directly to other parts of the world. There are even variations within the same country, according to Michelle Bell, a professor of environmental health at Yale University.

"In our large U.S. studies, we found that cities in the Southeastern United States actually had a lower heat impact on mortality than cities in the Northeast, even though temperatures were hotter in the Southeast," said Bell in an email. "This relates to differences in adaptation, which can involve physical adaptation, behavioral modification (drinking more water, staying inside), and building structures (air conditioning versus open windows, ventilation patterns)."

G. Brooke Anderson, who studied temperature impacts on populations with Bell, also pointed out that in their research, hot and cold extremes act differently on cities. "For heat, effects tend to be immediate, so the outdoor temperature yesterday and today affect health, while for cold, the combined temperature of a period up to a few weeks earlier was important," said Anderson, a postdoctoral fellow at the Johns Hopkins Bloomberg School of Public Health, in an email. Bell and Anderson published some of their work last year in Environmental Health Perspectives.

As the global climate gets warmer, people will likely adapt to a certain extent, but Anderson said infrastructure may not keep up as people use more resources to maintain their comfort zones. She cited the example of the summer 2006 power blackout in Queens, New York, when fans and air conditioners switched on in response to a heat wave. Such problems may become more common in the future, which in turn can have an impact on health, she said.

For Brisbane, warming may have a slight upside, but the harm will outweigh any benefits. "Interestingly, if the temperature increases by just 1 degree, then Brisbane would benefit on this measure, because of a reduction in cold-related deaths," said Barnett. "For increases in temperature of 2 degrees Celsius or more, the benefits of fewer cold-related deaths are dwarfed by increases in heat-related deaths."

As a result, Barnett said officials need to concentrate on educating people on how to respond to extreme weather and to invest in measures, like air conditioning and insulation, to help people cope. "What [the research] says to me is the best thing to do is invest in long-term strategies" instead of short-term weather predictions and temperature warning systems, he said. "Predicting on any one day what's going to happen is pretty tricky."