Mr. Red Sky, please tell us why

Rebecca Scott shares the story behind the nightmarish red skies that should keep us awake at night.

Social media has recently been inundated with pictures of San Francisco under a nightmarish red sky. These sensational images come as a result of extensive wildfires burning across the west coast of the US, with fires having thus far destroyed over 2.5m hectares of land across the states of California, Washington, and Oregon. It can be easy to chalk these wildfires and the burning skies they leave behind up to just another horror at the hands of 2020, but it’s important to understand the science behind the west coast’s burning and the impact of the rusty skies that lay in their wake.

The wildfires currently decimating the west coast are the worst this area has seen in 18 years, and have reached their present extent due to a perfect storm of meteorological, forestry mismanagement, and changing climatic factors. Meteorologically, the region has experienced a particularly arid summer with temperatures regularly exceeding 37C in California, and significantly lower rainfall than usual being recorded throughout the coastal states. Management of forests within the region have been criticised by President Trump: “I think this is more of a [forest] management situation… You go to Austria, you go to Finland, you go to many different countries [and] they don’t have fires.” However, climate scientists argue that these wildfires in the US are not entirely representative of such mismanagement, but rather an adverse impact of the wider climatic shift that the west coast is currently facing. The wildfires act as a chilling visual example of how the natural hazards that this region is facing are becoming both more severe and frequent in their incidence; this is a climate emergency, and the apocalyptic red skies hanging over the land do a terrific – if haunting – job of hitting this fact home. 

But why don’t all wildfires cause the same eerie discolouration of the sky as the west coast has experienced recently? Effectively, the burning of the land via wildfires causes an emission of smoke and ash from charred trees and structures which become trapped in the atmosphere above the region. Smoke and ash then hang in the skies and are the perfect particulate size to scatter shortwave UV radiation (eg blue light) entering the atmosphere. This prevents blue light from reaching your eyes, as only the longwave UV radiation (eg red/yellow light) is able to pass through the atmosphere without being scattered, leading to skies with a particularly yellowed tinge. The more smoke and ash emitted – i.e, the greater the extent of land burned by the wildfires – the more densely the atmosphere is packed with particulate matter refracting blue light, giving the red/yellow light a considerable prominence and leading to these haunting red skies.

The west coast has long seen regular wildfires during the summers, but those in recent years are becoming far more intense and widespread than could historically be perceived as “normal”. California has extensive forestry cover, particularly in the north, with fires in the Sierra Nevada burning over 30,000 hectares per day during September. Indeed, Professor Stefan Doerr, a wildfires expert at Swansea University stated: “Climate change … has now created a tinderbox of vegetation.” Landscapes along the west coast are increasingly arid as less rainfall occurs, leaving behind dead, brittle trees and highly flammable chaparral terrain which fuel existing fires and allow their spread across a wider area.

The red skies, such as the ones observed last month over much of the west coast, do not directly damage citizens’ physical health but are symptomatic of a larger problem: the amber haze brought about by the wildfires illustrates the amount of smoke generated as a direct result of the burning, which is causing air quality in cities and towns adjacent to fires to reach exceptionally poor levels. San Francisco was seen to have the worst air quality in the world during the beginning of last month, with levels of fine particulate matter pollution registering an all-time high for the city on 10 September. As if you needed another reason to wear a mask. 

While the human physical health impacts of wildfires are largely understood – respiratory problems, smoke inhalation and burns are common – mental health impacts lay largely unresearched. In a time where general anxieties are rife enough, the added climate anxiety of seeing the sky above oneself turn from blue to a post-apocalyptic orange would likely be enough to put one under considerable stress. Despite being as much a meteorological phenomenon as the city’s rolling fog, the burning amber hanging above San Francisco is just slightly more foreboding.  

Though the skies and air quality are slowly returning back to normal, the images from the zenith of the wildfire’s impact upon San Francisco – and indeed the west coast as a whole – are a stark reminder that our world is not static, and that the climate emergency is not a far-away concern which can be dismissed with the wave of a tiny hand.