Connecticut is one of 13 states expected to experience the biggest increases in air pollution and associated health problems due to climate change in the coming decades, according to a Natural Resources Defense Council analysis released Wednesday.

The negative health effects of climate change are expected to have their biggest impact nationally in 11 Northeastern states, Texas, California and Washington, D.C., according to the NRDC report. The effects include increases in the number of days with high levels of ozone smog as average temperatures rise, and higher levels of pollens from ragweed and other plants that cause allergies. Increasing levels of carbon dioxide in the atmosphere from the burning of fossil fuels causes plants to produce more pollen.

While the effects of increased smog and allergen levels are most serious for those with asthma and other respiratory problems, as well as children and the elderly, healthy people are vulnerable, too, according to the organization, an international nonprofit with 1.3 million members. Formed in 1970, the group focuses on protection of natural resources, public health and the environment.

"Climate change is one of the most serious public health threats of the 21st Century," Kim Knowlton, senior scientist in the NRDC's health and environment program and assistant clinical professor of environmental sciences at Columbia University, said during a telephone news conference. "It's time we started connecting the dots between climate change and our health."

The news conference was timed to coincide with the NRDC's release of its new web-based maps showing climate change health impacts and analysis.

The NRDC found that from 2001 to 2005, Connecticut had an average of 20 days each summer that did not meet federal air quality standards. By the end of the 21st century, its analysis found the number of days with poor air quality could be four times higher.

Knowlton said local governments, health care providers and the public need to be aware of how climate change is affecting health now and will continue to do so, to better plan and adapt to the challenges. Communities should identify neighborhoods and populations most vulnerable to smog and allergens; enhance notification systems so people can plan to limit outdoor activities and keep windows closed, shower to wash off pollen after spending time outdoors and take other steps to reduce risk of asthma attacks and other effects, she said. Frequent vacuuming and washing of bedding is also recommended to remove pollen that settles indoors.

Communities can also have an impact by reducing locally produced air pollutants by encouraging reduced driving with bike lanes, better mass transit and more walkable areas, she said.

Dr. Perry Sheffield, assistant professor in the department of pediatrics and preventive medicine at Mount Sinai School of Medicine in New York City, also cited communities that are planting trees varieties that provide shade but produce little pollen, and reducing overall carbon emissions with energy efficiency initiatives. She urged support for elected officials who propose and implement these and other strategies to address climate change and enable their community to prepare and adapt. Communities should also launch studies to better understand the specific local effects of climate change, she said.

The impacts of climate change on children's health, particularly those with asthma and severe allergies, should not be underestimated, Sheffield said. As a pediatrician, she added, she understands all too well the harmful effects asthma can have on the lives of children and their families.

In addition to increased air pollution and pollen levels, climate change is also expected to have other negative health impacts, the NRDC said in its report. In Connecticut, these include more extreme heat days; more cases of mosquito-borne diseases such as Dengue fever and West Nile virus; increasing frequency of droughts that threaten water supplies; and increasing risk of floods from rising sea levels and greater rainfall.

"We need to reduce carbon pollution and to prepare communities like climate change matters ... to our health, our children's health and the health of future generations," Knowlton said.

The maps can be found at: www.nrdc.org/climatemaps.

j.benson@theday.com