Fish that spawn in the south and in the summer will die first as the world warms. Idaho's high-elevation runs may offer one of the best chances the species has.
The Pacific Northwest has spent two decades retooling dams, rebuilding damaged watersheds and restoring stream flows to keep salmon from disappearing.
The United States has invested billions in the effort - $350 million in 2004 alone - by far the most money spent on any endangered species.
But a new threat is more devastating than the gill nets that sent dozens of salmon runs into extinction. It is more deadly than the hydroelectric turbines that still kill millions of migrating smelts. In fact, it raises doubts about whether salmon will survive in the Northern Pacific at all.
Climate change already has made rivers warmer and spring runoff earlier, disrupting the life cycle of the fish that are an icon of the region.
No matter what actions the world takes to reduce greenhouse gases, river temperatures in more than half of the lower-elevation watersheds may exceed 70 degrees by 2040 - too hot for salmon.
"The only salmon that are going to survive the century mark are the ones in the large populations in the higher elevations that are still going to have snow and cold water," said Jim Martin, a former chief of fisheries for the state of Oregon.
But even these runs and those as far north as Alaska would be threatened if the world does not reduce gases like carbon dioxide over the next 50 years.
