While most of the United States is coming out of a wet winter, large fires are ravaging Alberta and British Columbia just north of Montana. Ninety large fires have burned a million acres in 2023, burning 150 times more area than fires in the last five years combined. While May is typical fire season in western Canada, fires are going to new extremes this year, burning north into forests still covered with snow.

Record heat for this time of year in the Pacific Northwest swelters people while drying fuels across the region, including southwest Canada. High pressure-driven winds spread fire widely through conifer and birch forests. The inconvenient truth is that human-driven climate change is causing the firestorm, which could shift southward and start to burn forests in the interior Northwest of the United States soon.

We now understand why these extreme fire conditions are happening, and we know it is directly related to human air pollution changing the climate.

The Changing Jet Stream

Two facts loom large in 2023. First, the earth's polar regions are warming four times faster than the rest of the globe. Second, the jet stream, that river of air that rushes about 5 miles above the earth's surface in the northern hemisphere, drives our weather patterns, our wet and dry cycles over time.

The jet stream gets its energy from the equatorial region's warmth and the polar region's cold. The contrast between these two temperature areas drives the strength of the jet stream's winds. But the jet stream weakens when the polar region warms because of increased greenhouse gas emissions from people. The polar region is warming five times faster than other parts of the earth. As a result, we see the jet stream weakening, and it will continue to weaken as people continue to pollute the atmosphere with fossil fuel emissions.

As the jet stream loses some of its "steam," it wavers more. Instead of blasting along in a focused gush, it gets big waves in it, and these waves slow down the progression of high- and low-pressure systems moving across the country like a train under the power of the jet stream. Low-pressure systems usually bring moisture, while high-pressure bring dryness. Okay, as long as they keep moving along in succession.

But when the jet stream slows and gets wavey, ridges of high-pressure form and get stuck, creating atmospheric damns that block and divert wet low-pressure systems away from the land below the high-pressure ridge. The stuck high pressure heats the air and the land, and extreme fire weather conditions appear along with winds. Dry air also pulls moisture out of trees, increasing their flammability.

These conditions exist in western Canada and persisted in New Mexico a year ago when the expansive Hermit Peak Fire cooked the southern Rocky Mountains for weeks. Rain eventually extinguished that fire when the high-pressure ridge weakened and allowed a wet low pressure to cross the region, dousing the fire.

Sweltering conditions in Oregon and Washington this May follow from the high-pressure ridge stuck to the north. The heat will speed snowmelt, causing some flooding, and heat will dry forest fuels, bringing an active fire season unless the jet stream shifts and allows wet conditions to flow forward.

Repeated stuck high-pressure ridges batter western Canada. Bark beetles killed millions of trees in the expansive forests of British Columbia as the climate warms and dries. Forests that used to be relatively wet year-round now bake under stuck high pressure ridges in the spring. People start fires, and these fires grow over millions of acres.

Even if we stopped pumping greenhouse gases into the atmosphere today, Mike Flannagan of Thompson Rivers University in Canada told the BBC that the atmosphere would continue warming up for at least another 30 years. But we aren't stopping our air pollution. We continue to increase greenhouse gas emissions for various reasons, including political polarization and poverty.

Nobody can argue with the science explaining the big fires in Canada (and Siberia) right now. We can avert our eyes and wish the people in Canada and Europe breathing thick fire smoke well. But we have yet another natural disaster driven by climate change that portends things to come.

The high-severity Canadian forest fires burn trees that mitigate climate change through photosynthesis. People need some of these trees for saw timber. We are falling into a climate change vortex regarding our vast northern forests.

The hour is getting late.