How Might This Year’s Forest Fires Impact Glaciers in the West?

Mauri Pelto, a glaciologist at Nicholls College, has directed the North Cascades Glacier Climate Project since 1983, which focuses on the glaciers of that range, located in Washington State. He has written about that project for GlacierHub, and contributed posts as well about other glaciers in Washington State and Alaska as well as  in New Zealand and Kerguelen, an island in the southern Indian Ocean.

He recently spoke with GlacierHub about the effects of this year’s forest fires in California, Oregon and Washington on the glaciers in those states. This interview has been edited for clarity and length.

GlacierHub: Have the recent fires had any effect on your own ongoing research program in the North Cascades?

Mauri Pelto: The hiking is unpleasant in the worst conditions, when the smoke is so strong that our eyes are impacted, affecting our vision and our research. To date the conditions have not prevented us from completing the measurements, though we have hiked out early to reduce exposure to the poor air quality. There have been several apocalyptic days where it was difficult to see through the smoke. The smell was just like being near a campfire and glacier melting was extreme.

We know that ash from forest fires can deposit onto glaciers, affecting their albedo, or reflectance. This darker color means they absorb more sunlight and melt faster. At the same time, however, smoke from the fires could darken skies and potentially decrease melting. What is the effect, if any, of the ash on the glaciers?

The reality is, the 2020 forest fires in Washington State will have not have a significant immediate impact on albedo changes. This lack of impact is a result of the fires starting so late in the melt season. If the ash falls in September, the melt season is almost over and much of the ash will be covered by new snow in a manner of weeks. In addition, the glacier surfaces are already quite dirty.

On the steeper blue ice areas of North Cascade glaciers, most of the ash is washed away by ensuing rainfall as the first fall and winter storms arrive, though it can deposit more thickly in some spots and remain into the next year. Where the ash does persist, it has a direct impact due to albedo changes. Next year, when the surfaces that accumulated ash are exposed after this winter’s snows have melted, there will be enhanced melt of ice due to the decreased albedo.

The more important aspect in western North America in many recent years is that significant forest fires occur as a result of prolonged warm dry periods that also lead to high glacier melt rates. This year the hottest conditions came late in the melt season when glacier albedo is already low [darker surface conditions], which further increases melt rates.

Do these points apply equally to all the glaciers in the region, or are there some differences between the mountains?

The proximity to a fire is crucial. For ash to fall in significant quantities on a glacier, typically the fire has to be within several hundred kilometers and the ash has to be at the surface for a significant part of the melt season. The North Cascade glaciers in Washington were not near most of the large 2020 fires. Mount Shasta in far northern California or Mount Hood in Oregon were closer to the fires this summer and would have experienced a greater impact.

The proximity of a glacier to a fire strongly influences the impact of ash deposited on snow surfaces in the following year, after the winter’s snow has melted and the ash-covered surfaces are exposed once again. Susan Kaspari, a geologist at Central Washington University, has noted this effect on Blue Glacier in Washington’s Olympic Range after a nearby fire in 2011.

In British Columbia in 2018, many glaciers in the province were close to the large fires. Black carbon deposition was significant and remains at the surface of many of the glaciers where snowpack from the preceding winter is lost. This certainly was visible last month to a team from the University of Northern British Columbia, led by Ben Pelto, a graduate student in glaciology (and my son).

Are there areas where you have direct observations from before the fires and after? Do you know of any efforts to study the effects on the glaciers with remote sensing?

I have examined satellite imagery for Washington from before and after the fires from Mount Rainier to Mount Baker. In typical Landsat or Sentinel images, the change in albedo is not evident. This is a combination of the small size of the glaciers and how dirty they already were. Black carbon or forest fire ash cannot be specifically distinguished from other surface particles.

Some researchers have attributed shrinking glaciers on Mount Kilimanjaro to deforestation and reductions in precipitation, though these links have been challenged by some. Do you think that there is a risk that deforestation, following the fires, could have an impact on the glaciers? 

There is solid research from the Andes of the effects on glaciers of Amazon deforestation, which deposits black carbon on the glaciers. For tropical glaciers where solar radiation importance is magnified, ash deposited on the surface would be a bigger problem.

In general, anything that lowers the albedo of glaciers or leads to temperature increases will not help glaciers.

As someone who closely follows climate change impacts, do these fires raise any questions in your mind for those who see forests as important carbon sinks, and promote reforestation and afforestation as well as forest protection to help limit concentrations of greenhouse gases?

It is a difficult situation for a forest that has developed and thrived in one climate regime to experience conditions that it is not well adapted to handle. Reforestation is also more difficult in the warmer summer conditions with higher evaporation rates. These conditions are very challenging.