Category Archives: Climate, carbon, and biophysical forcings

Fire, carbon & climate interactions

This post relates the interactions between atmospheric energy and emissions and other effects of wildland fire. This is a topic that is very poorly-understood these days. I suspect that’s because it’s complicated, and policy-makers in particular do not respond well to a complicated decision-making environment.

The case for anthropogenic climate change in Canada remains very strong. I won’t debate this here. Sure, there’s some uncertainty over the degree of warming, the spatial and temporal scale of variability, and the various feedback mechanisms. But no one worth taking seriously is in doubt of the basic mechanisms; so far, the data is also supporting the model rather well. In any case, read the IPCC 4th Assessment Report (AR4), delve into the primary literature, do your due diligence on this.

The primary link of interest here is between carbon emissions from fossil fuels combustion and atmospheric energy. Fossil fuels burn, atmospheric energy is trapped in the lower atmosphere, temperature goes up. It’s not that simple, but it’s still relatively simple.There is no expectation that other landscape parameters would change as a result of the extraction and refinement of oil or its combustion to power passenger vehicles, for example.

When wildland fires burn, there are also carbon emissions released. But many other variables affecting atmospheric energy are also altered. These complicate the picture immensely.

The earth’s surfaces have a degree of reflectivity – the albedo – that indicates how much light of various wavelengths they absorb and how much they reflect back toward the atmosphere. Dark surfaces, such as asphalt, conifer forests, certain rocks, etc. absorb energy readily. They have low albedo. They heat up quickly in the sun (reradiating the energy as long-wave radiation). Other surfaces, such as snow, deciduous vegetation, light-coloured sand – these have high albedo and are much better reflectors of energy. They heat up less.

Putting it this way, it should not be surprising that when landscape characteristics change dramatically – such as what occurs following a wildland fire, logging operation, agricultural clearing, or subdivision construction – the albedo can change significantly. For example, Brian Amiro and colleagues found that both summertime and wintertime albedo varied along a successional gradient in boreal conifer stands in Canada, Alaska, and Russia: old conifer stands (> 100 years) had low albedo levels in both winter and summer, while younger stands (e.g. < 25 years) had much higher albedo, particularly in winter. This reflects partly the reflectivity of snow-covered relatively flat surfaces (young stands) as well as factors such as foliar moisture content and canopy height.

More to come…