During the 1930s, the Dust Bowl drove millions of people out of the Great Plains. Thousands of the residents who left New Orleans after Hurricane Katrina never went back. Not that many thousands of years ago, shifts in Ice Age glaciers drew people from Siberia across a then-existing land bridge to spread through the Americas.

So America has experienced climate migration before. But it’s different when you see it coming.

Especially if it’s coming toward you.

California is in the midst of the worst drought in five centuries. But even if this drought ends, it seems another is coming. An online paper in the Journal of Climate this summer, by a group led by Toby R. Ault of the Department of Earth and Atmospheric Sciences at Cornell University, projected at least an 80% chance of a 10-year megadrought in the Southwest this century, and a 20% to 50% chance of one lasting at least 35 years.

As Lynn Wilson, chief executive of the Sea Trust Institute, said this summer, “We may have to migrate people out of California.”

Naturally, here in Oregon, we’re terrified. Especially when we read things like what James Howard Kunstler wrote in his book “The Long Emergency”: “The Pacific Northwest’s benefits of mild climate, abundant water and good farmland may be overwhelmed by populations fleeing the problems of Southern California.”

The great issue of the West, at least on this side of the legendary 100th meridian, has always been the shortage of water. The situation is different only in one small corner: the strip of Oregon and Washington west of the Cascade Range. Here, rain comes in from the Pacific, and rivers from the interior.

Clifford Mass, a professor of atmospheric sciences at the University of Washington, writes a weather blog that can read like a direction pointer. By the time he’d finished marking up the map of the United States for vulnerability to sea rise (notably the East and Gulf coasts), water shortages (especially in the Southwest and Plains), hurricanes and superstorms (everything east and south of the Appalachian Mountains), and heat waves (almost every place else), he’s left with a multicolored national disaster map. All that’s left is the Pacific Northwest, looking like a survivor peeking out from a storm cellar.

You can see why Mass concludes, “The Northwest may well become a climate refuge during the upcoming century.”

In British Columbia, the alarm is also rising. In “American Exodus: Climate Change and the Coming Flight for Survival,” Canadian environmental writer Giles Slade forecasts vast numbers of Americans fleeing across the northern border. Vancouverites, he says, should think about retreating north to the Yukon, to Dawson and Yellowknife.

Oregon and Washington don’t have even the nominal barrier of Canadian border crossings to stop people from coming. To plenty of people in Oregon, all they need to know about climate change is that California wineries have been buying vineyards in the Willamette Valley.

The Northwest has worried about internal migration before. In the 1970s, Oregon Gov. Tom McCall tried to dissuade arrivals with his famous plea, “Visit, but don’t stay.” Still, the state population grew 25% during his eight years in office.

But this time looks different.

As Bill Bishop points out in “The Big Sort,” Americans have been internally resettling to places that fit their lifestyle and attitudes. In the recent history of the West, Californians looking for more conservative, family values-based societies and places where they could bring their guns to church have moved to Idaho and Utah; people looking for mass transit, Gay Pride parades featuring the chief of police, and artfully pulled lattes have loaded up for Washington and Oregon.

Over the coming decades, that could change dramatically. As Jason Jurgevich, assistant director of the Population Research Center at Portland State University, explains, the Pacific Northwest faces a “much more heterogeneous migration than what we’ve seen in the past.”

What happens when suburb-loving, car-committed Californians are driven, in a quest for water and temperatures below 93 degrees, to the land of militant bike commuters and food-cart diners? All of Oregon has only five freeways, fewer than some Los Angeles neighborhoods. (One of them, in Portland, is about a mile long.)

The Seattle-based online environmental magazine Grist recently warned potential climate migrants about the region’s current inhabitants: “These people lord over newcomers with weird cherries, fresh seafood and nuclear coffee. The bookstores make your feet hurt. You’ll never be dry again. At least 85 of their 2,675 beers are too hoppy.”

Sure, the Pacific Northwest has water. For California climate migrants, though, the problem might be the atmosphere.