You know things have gone off the rails if people are arguing about whether it looks like Mars or Venus where they live. In case you missed it, fires are burning across the Western U.S., and thick wildfire smoke has enveloped regions of California and Oregon. As a result, residents of Salem and San Francisco are experiencing eerie orange-red skies.
A quick peek at satellite images drives home just how severe the smoke is. It blankets the entire western portions of those two states, creating darkened skies that resemble dusk, even in the middle of the day. Some report that as more smoke rolls in, the day is growing darker by the hour.
The smoke is also what’s to blame for that creepy red glow. To understand what’s going on, let’s go back to grade school science class. You might remember learning that visible light travels in waves, and that those waves can have different wavelengths and frequencies. You might also remember ROY G BIV, the acronym representing the order of colors that make up a rainbow. That order arranges colors by the length of their light wavelengths: The R and O, red and orange, have the longest wavelengths, while I and V, indigo and violet, have the shortest ones. Smoke blocks shorter wavelength colors, leaving everything looking red and orange.*
As a result, air quality is also terrible across the West Coast. In Washington, where I live, the skies are hazy but mostly blue. Yet the Environmental Protection Agency’s numbers indicate worse air quality than in San Francisco, where the sky is completely red. That’s likely because the air quality index is a measure of surface air quality, says Roya Bahreini, an atmospheric scientist at University of California, Riverside. “The smoke from the wildfires can get injected higher in the atmosphere,” she says. In other words: That smoke might not affect surface-level measures of air quality, but it can, of course, still blot out the sun and filter light. And according to Daniel Swain, a UCLA climate scientist, smoke and ash are now traveling up to 50,000 feet—“20,000 above cruising altitude of jet airliners,” he wrote in a recent tweet. “Dense smoke throughout entire atmospheric column is blocking nearly all sunlight at surface.”
If that high-flying smoke moves closer to ground level, that could dramatically worsen already-poor air quality across these red-tinged areas. The Bay Area’s National Weather Service outpost says that if the winds let up, things will only get smokier. “This is beyond the scope of our models so we rely on your reports!” it tweeted. This really underscores the unprecedented nature of this fire weather: Models can’t predict what will happen, and as the situation changes, individual reports from citizens will be the most reliable measure.
Correction, Sept. 9, 2020: This article originally misstated that red and orange have the shortest wavelengths and that smoke blocks longer wavelength colors. Red and orange have the longest wavelengths, and smoke blocks shorter wavelength colors.