The analysis comes from the Natural Resources Defense Council (NRDC).
The group said the Western United States experienced more days of extreme heat and a high rate of drought from 2000 through 2009.
The NRDC said projected climate change will worsen the increase in heat and dry conditions and associated health problems.
The biggest impacts are expected in Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Texas, Utah, Washington and Wyoming.
A new web tool unveiled by NRDC lets users read just how badly their states might be impacted by climate change.
Users can see San Diego and California and data from other areas, along with maps detailing extreme weather patterns throughout the country.
The website also shows local climate-change vulnerabilities.
The effects of climate change at the regional and state level is based on an analysis of weather-station data gathered by the National Climatic Data Center and other sources.
The NRDC used the data to create the "Climate Change Threatens Health" website, which lets users see the effects of climate change at a regional and state level.
NRDC scientist Miriam Rotkin-Ellman said the tool allows users to drill down and find out about the public-health threats to their communities from climate change.
"It also gives information on the science behind the health threats and how they are linked to climate change," said Rotkin-Ellman. "Our analysis looked at five different threats across the United States: Extreme heat, air pollution, infectious diseases, drought and flooding."
She said California is one of twelve states which faces all five threats in different locations and in different degrees.
"Each community faces different threats depending on where they're located, what their resources are and what the local weather pattern may be," said Rotkin-Ellman. "The website lets people check the specific vulnerabilities for their area."
A quick check of the risks for San Diego shows the area faces the highest or nearly the highest threats in all five areas including a vulnerability to dengue fever infection.
