Introduction
This diary is about how the current crop of U.S. forest fires are degrading the weather and public health, and then a further section on the potential impact on the global scale climate. Above, the banner graphic is a photo taken from the upper level of Yankee Stadium on 20 July of this year, showing the level of impact that fires up to over 3000 miles away can have under extraordinary circumstances.
Weather Causes and Effects
Extreme heat and drought, or high winds can create wildfires. When the two combine, as they have increasingly done during this time of global warming, this can result in extreme fire events. The graphic below shows four of the ongoing extreme events over central and northern California on 19 August, from the National Interagency Fire Center (NIFC).
The well-reported heat dome from late June/early July over the Pacific NW resulted in numerous wildfires, many of which are still burning. Active fires as of 19 August can be seen in this screenshot from the NIFC below.
Overall, there have been 99 large fires during this fire season over the Continental U.S., of which 88 are currently still burning. These fires have placed a tremendous amount of particulate matter into the atmosphere.
Large fires can create their own weather through strong updrafts, including fire cumulonimbus clouds (fireCbs). In the process of creating fireCBs, fire tornadoes can develop within the updraft, with winds that can exceed 100 mph. The fire tornado in this 15 August video is from the Dixie Fire in northwest California.
Video of fire tornado from the Dixie Fire, taken on 15 August. Courtesy of the Press-Democrat
FireCbs can also help spread the large fires that create them. The graphic below from the Bulletin of Atomic Scientists shows the mechanisms that result in a positive feedback acting to further spread these fires.
Hot wildfires result in air from outside the fire area converging on the fire. The resulting updraft is fed by this air and reinforced by the heat from the file. Smoke is entrained into the updraft, which then cools. As it does so, water condenses on the particulate matter that makes up the smoke, resulting in a fireCb. The fireCb will continue to develop vertically and move downwind, as long as the smoke plume is warmer than the surrounding environment. Precipitation sometimes forms and evaporates as it falls into dry air below. This causes evaporative cooling and. potentially, strong downburst winds that also can spread the fire. Finally, the particles in fireCBs are good at generating enough of a positive-negative charge difference to create cloud-to-ground lighting, which can also expand the wildfire.
Often, a fireCb updraft can shoot into the lower stratosphere and deposit smoke particles where they may remain for many months or even years, transported by the winds. This has climate implications that I’ll talk more about later.
Public Health Impacts
Many of us have seen the haze from the western U.S. wildfires even though we live one thousand or more of miles from their source. This is the result at least in part, of all those fireCBs lofting particulate matter into the upper troposphere (around 5-10 km above sea level) or lower stratosphere (10-15km above sea level). By itself, it would take quite some time for these particulates to settle down into a near-surface layer where it could affect public health. However, the atmospheric flow was such that a large area of sinking air, beneath high pressure aloft, allowed the particulates to reach the surface at long distances to the east, such as New York, Washington DC, and Boston MA. The picture at the lower right shows how New York City appeared during the event. The general sinking also suppressed precipitation, so the smoke didn’t get washed out.
By the time the particulate matter reached the East Coast, there was no smell of smoke by all accounts, so why would there be significant health concerns? Over time, particulates from forest fires interact chemically with the atmosphere to create new, potentially more dangerous products. That along with the lack of experience with smoke-related air quality issues has resulted in problems with breathing, hacking coughs, runny noses and headaches. It can also aggravate:
… chronic heart and lung diseases and triggering asthma attacks. It can also cause headaches, a runny nose, cough and difficulty breathing. Younger people and older people tend to be more susceptible.
source: CPR News
According to The Gothamist, long-term particulate matter becomes more oxidized, thus increasing the free radical content. The particles by this time are small enough to penetrate deep into the lungs. The long term impacts of this are not well understood, but:
… in vivo studies [involving animals or humans] have shown possible mechanisms explaining wildfire-specific PM have higher toxicity that produced inflammation and increased respiratory infections.
source: The Gothamist
It’s suggested in this article that it’s potentially not enough to stay inside; air filters that can remove the 2.5 micron particles commonly found in aged smoke would be good to have installed in your home. Additionally, the author emphasizes paying daily attention to air quality reports and forecasts. Such reports are available nationally at ….
Are there long-term climate impacts too? Well, maybe ….
About 40 years ago, a a group of American and Russian scientists used a simple climate model to simulate the effects of global nuclear conflicts of various sizes. The results showed a dramatic cooling of the climate, mostly in the Northern Hemisphere, and with some dependence on the season in which the nuclear war took place. This was dubbed “Nuclear Winter”, as has been confirmed through testing with increasingly sophisticated climate models in 1989, 2007, and as recently as 2019. It’s also been confirmed that regional nuclear conflict can also wreak havoc on climate and crop yields in areas far dispersed from the conflict itself.
Now why do I bring up nuclear winter? The impacts of nuclear war on a global scale inform the impact of significant forest burning on the climate. Observational studies of large fires on temperatures by Dr. Alan Robock (a member of my PhD thesis committee!!) showed maximum surface temperatures more than 15°C (27°F) below normal for1 week and more than 5°C (9°F) below
normal for 3 weeks after a northern California wildfire in 1987. Later, four cases showed observed high temperatures in western Canada in 1981 and 1982, in northern China and Siberia in 1987, and in Yellowstone National Park in northwestern Wyoming in 1988, from 1.5°C (2.7F) to 7°C (12.6°F) below normal. In all cases, minimum temperatures were not affected.
The decrease in high temperatures was the result of reflection of incoming solar radiation by the layer of smoke that set up in the valleys located within the fire areas. This not only reduced surface heating but set up a situation where the atmospheric conditions that trapped the smoke were being reinforced. What ended the siege was, in all cases, a strong disturbance that was able to remove the smoke from the low lying areas.
If the smoke were trapped in the lower stratosphere for a long enough time and continued to accumulate with more large fires, the likely result would be lower atmosphere (i.e. near-surface) cooling. Whether or not such a scenario would take place short of a regional nuclear conflict seems to me unlikely, one fireCb that formed in British Columbia in 2017 produced a plume that persisted in the stratosphere for 10 months. Maybe a climate model could be used to test the amount of cooling that would result from a high, but not outrageous, number of fireCbs.
In other words, stay tuned.
The writers in Climate Brief work to keep the Daily Kos community informed and engaged with breaking news about the climate crisis around the world while providing inspiring stories of environmental heroes, opportunities for direct engagement, and perspectives on the intersection of climate activism with spirituality, politics, and the arts.
Climate Brief posts every evening at 5pm ET.