UNHEALTHY HEAT: Boston is expected to be among the cities hardest hit by rising temperatures.
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Global warming will bring increased summer heat waves nationwide that are especially harmful to low-income and minority populations in urban areas and the elderly, according to a new report by environmental and public health groups.

"This is another reason why we must take steps to curb global warming pollution as much and as quickly as possible," said Amanda Staudt, a climate scientist with the National Wildlife Federation, which released the report today with Physicians for Social Responsibility.

The report, citing the U.S. Global Change Research Program, notes projected increases in the number of days on which temperatures exceed 100 degrees Fahrenheit.

The report says urban areas, with their asphalt and concrete, are as much as 10 degrees hotter than more rural regions.

More than 3,400 people died in the United States from exposure to excessive heat between 1999 and 2003, the study states, adding that heat accounts for more weather-related deaths than any other single source.

Heat waves will worsen ozone pollution when temperatures soar, the report warns, citing a 2008 paper in the Journal of Geophysical Research that found global warming could increase eight-hour ground-level ozone levels in coming decades in the Northeast and Midwest, especially during heat waves.

This "climate penalty" will make it tougher for cities to meet the eight-hour U.S. EPA ozone standard of 75 parts per billion, the report states.

It cites several public health risks associated with very high temperatures. Heat waves can be deadly, due to heat stroke, and can exacerbate underlying health problems, the report says, making the elderly particularly vulnerable. Extreme heat boosts risks of heart attacks, strokes and asthma, it notes.

Children also face increased risks, it adds. "The increased air pollution that typically accompanies heat waves can especially harm children, who have a higher risk of developing asthma, have lungs that are still developing and growing, and have higher exposure because they breathe at a higher rate than adults and spend more time outdoors engaging in vigorous physical activity."

Peter Wilk, the executive director of Physicians for Social Responsibility, cited the 1995 Chicago heat wave that killed more than 700 people as a sign of things to come. Such events require short-term medical and emergency responses, such as access to cooling centers, he said on a conference call this morning.

But cutting emissions linked to global warming is needed to limit increases in heat waves, Wilk added.

"The most cost-effective and preferred approach is to take actions that will prevent the problem or reduce its scope in the future," he said. "Cutting greenhouse gas emissions may be difficult, but it is a medical necessity."

The report lists 30 cities that face increased health risks from heat waves worsened by global warming, based on a combination of four factors: average number of summer days with "oppressive" summer heat, the percentage of households without central air conditioning, ground-level ozone levels, and the percentage of households below the poverty line.

Cities in the top tier of risk include Boston, Houston, Phoenix, New York and Los Angeles.

The report says heat waves are especially harmful to black people, who live in urban areas in higher percentages than whites, and who are also more likely to be low-income than other Americans and already suffer from higher asthma rates than whites.