In San Francisco, we’re finally starting to put away our masks. With 74% of the city’s residents over 12 fully vaccinated, for the first time in more than a year we’re enjoying walking, shopping, and eating out, our faces naked. So I was startled when my partner reminded me that we need to buy masks again very soon — N95 masks, that is. The California wildfire season has already begun, earlier than ever, and we’ll need to protect our lungs during the months to come from the fine particulates carried in the wildfire smoke that’s been engulfing this city in recent years.

I was in Reno last September, so I missed the morning when San Franciscans awoke to apocalyptic orange skies, the air freighted with smoke from burning forests elsewhere in the state. The air then was bad enough even in the high mountain valley of Reno. At that point, we’d already experienced “very unhealthy” purple-zone air quality for days. Still, it was nothing like the photos that could have been from Mars then emerging from the Bay Area. I have a bad feeling that I may get my chance to experience the same phenomenon in 2021 — and, as the fires across California have started so much earlier, probably sooner than September.

The situation is pretty dire: this state — along with our neighbors to the north and southeast — is now living through an epic drought. After a dry winter and spring, the fuel-moisture content in our forests (the amount of water in vegetation, living and dead) is way below average. This April, the month when it is usually at its highest, San Jose State University scientists recorded levels a staggering 40% below average in the Santa Cruz Mountains, well below the lowest level ever before observed. In other words, we have never been this dry.

Under the Heat Dome

When it’s hot in most of California, its often cold and foggy in San Francisco. Today is no exception. Despite the raging news about heat records, it’s not likely to reach 65 degrees here. So it’s a little surreal to consider what friends and family are going through in the Pacific Northwest under the once-in-thousands-of-years heat dome that’s settled over the region. A heat dome is an area of high pressure surrounded by upper-atmosphere winds that essentially pin it in place. If you remember your high-school physics, you’ll recall that when a gas (for example, the air over the Pacific Northwest) is contained, the ratio between pressure and temperature remains constant. If the temperature goes up, the pressure goes up.

The converse is also true; as the pressure rises, so does the temperature. And that’s what’s been happening over Oregon, Washington, and British Columbia in normally chilly Canada. Mix in the fact that climate change has driven average temperatures in those areas up by three to four degrees since the industrial revolution, and you have a recipe for the disaster that struck the region recently.