Global warming could increase the health risks of everything from the common cold to insect-carried diseases like malaria and dengue fever.

The depletion of ozone could cause skin tumors and damage natural defense systems that help the body avoid common viruses, according to speakers at a program on climate change Monday in Ventura. Diseases like the flesh-eating leishmaniasis, which strikes in tropical climates, could be carried more often into the United States.

Stressing that many of the effects are theoretical and societies might still find ways to protect themselves, Ventura County Public Health Officer Robert Levin said the continued warming of the planet could bring huge shortages of food and drinking water.

"We will have more wars," he said. "People do not realize how important water is unless they've experienced no water from the tap. People will fight over this."

Monday's program, put on by the Ventura County Health Care Agency, focused on the magnitude of potential risks and explored what people and government agencies can do.

Levin said there could be epidemics involving malnutrition and diarrhea. Climate change could increase the risk of weather-related disasters like floods and hurricanes.

"This is a social justice problem," said county Supervisor Steve Bennett, noting that while Americans emit the most greenhouse gases, poor people in places like Africa will likely suffer the most from global warming. "The people who are most at risk have contributed the least to the problem."

Ventura County already recycles methane gas found in landfills and has implemented a strategy to help the state with its plan to dramatically reduce greenhouse gases.

Other energy-saving measures have been adopted as well, ranging from 40 hybrid cars in the county fleet to computers that automatically shut down when not being used.

Some speakers objected to the bottles of drinking water placed in front of them for the program, noting the plastic is part of the problem.

"This silly little thing is going to be polluting the environment for 500 to 1,000 years," said Dan Jordan, a research psychologist with the county's Public Health Department.

Speakers urged people to conserve by turning computers and televisions all the way off, rather than allowing what was called "vampire power" to suck away electricity. They encouraged people to trade in their gas lawn mowers for electrical ones and to keep tires inflated so cars use less energy.

Nancy Settle, a manager in the county's Planning Division, called on people to support land-use policies aimed at lessening the reliance on cars so people can bicycle or walk to work.

Levin urged people to get immunized.

But Jordan said the first step is for people to acknowledge the dangers represented by global warming are real and that action can help.

"The first thing we can do is just get beyond denial," he said.