Washington ? Climate scientists released a grim portrait Monday of the likely effects of global warming on the United States and Canada.

More droughts, floods, heat waves, infectious diseases and extinctions are possible for two of the most prosperous countries on the planet, according to the North American section of the latest report by the Intergovernmental Panel on Climate Change. Poor countries in tropical Africa and Asia will be hit even harder by the effects of higher temperatures and rising sea levels.

In the U.S., the Southwest, California, Alaska, and the Atlantic and Gulf coasts are the most seriously threatened, the authors of the new report said at a Washington news conference.

“The impacts are faster and larger than we ever anticipated,” said Anthony Janetos, a climate researcher at the Pacific Northwest National Laboratory. “Things are happening much more quickly than the science community imagined. It’s profoundly concerning.”

Another author, Kristi Ebi, an epidemiologist in Alexandria, Va., said matters were even worse than they appeared in the panel’s report, which is based on data previously published in peer-reviewed scientific journals.

“The scientific literature is behind what people on the ground are seeing,” Ebi said. She cited, for example, eyewitness accounts of accelerated thawing of Alaskan tundra and melting of Himalayan glaciers.

Also on Monday, 11 retired U.S. generals and admirals said that worldwide water shortages caused by global warming were a “serious threat to America’s national security” and might drag the U.S. into fights over shortages of natural resources.

The United Nations Security Council prepared to hold its first discussion of global warming Tuesday in New York.

A 23-page summary of the full 1,000-plus-page report on the worldwide impact of global warming by the Intergovernmental Panel on Climate Change was released in Brussels, Belgium, on April 6. Detailed chapters devoted to specific regions of the world are being published separately.

The North American section, Chapter 14, describes what’s happening now and what the authors think will occur as the world heats up. Here are some of the developments it forecasts as “likely” or “very likely”:

¢ By 2039, average temperatures across North America will rise by 1.8 to 5.4 degrees Fahrenheit.

¢ Less rain will fall in the Southwest, but more will fall in the rest of the continent.

¢ Warmer lake and river water will threaten fish and spread pollution.

¢ Sea levels will rise 9 to 18 inches by 2100 along U.S. coasts, higher in Canada and Alaska.

¢ Severe heat waves and more pollution will threaten human health.