Heat waves, rising sea levels, drought, disease, and other problems brought on by global warming could keep tourists away from many of the world’s most popular vacation spots in coming decades, according to a report conducted by a British university and released yesterday by the World Wildlife Fund. Ski areas in Europe are likely to face reduced snowfall and shorter seasons. Mediterranean vacation spots could see more extreme heat, water shortages, and increased risk of disease. Atlantic coasts in the U.S. could become more vulnerable to erosion caused by rising sea levels. Meanwhile, dozens of tourists each year are making the trek to see the Chernobyl nuclear power plant in the Ukraine, site of the meltdown disaster in 1986. Local travel agencies tout one-day tours to abandoned villages, forests that turned red after the disaster, and the damaged reactor in its concrete casing.