Yesterday’s paradox: pine forests bad for climate

Oops. We almost forgot we had today’s paradox running as a series as well. Since for today all other science news takes a temporary break – we have time to look at yesterday’s news from a provocative viewpoint.

According to our report on ‘crop bio-geoengineering’, in the temperate climate zone coniferous forests have an average albedo of 0.16. This means of all incoming solar radiation just 16 percent is reflected and the remaining 84 percent is absorbed, whereby the energy is transformed to heat.

Other sources, like a 2007 summary by the Manchester Metropolitan University, state pine forests absorb even more sunlight: 85 to 91 percent. A 1997 study in the Journal of Geophysical Research even states pine albedo is as low as 0.08, absorbing 92 percent of solar energy.

Cropland and grassland have somewhat higher albedos – although again different studies come up with different results, somewhere between 0.12 and 0.26. What could make a lot of difference though is snow cover. Imagine a layer of snow just several centimetres thick on the forest floor, and compare that to the canopy – that during dry continental winters rids itself of most of the white burden…

Although perhaps rather nihilistic we cannot help to wonder what has greater climate value: some 600 gigatonnes of pure carbon (that is the boreal forests, including organic soils) safely locked away – or a potential 50 percent albedo increase, during Siberian and Canadian winters (when the Sun is low).

It is a question that even a special Hadley Centre study in Nature in the year 2000 had great difficulty answering. Comparing carbon sequestration to albedo influence can be hard enough – it could still ignore the important role of forests in the hydrological cycle, that may also have a tempering effect on climate change, for instance due to its influence on cloud formation, tempering of heat extremes with possible positive feedbacks – and further biomass production.

The Nature study is reassuring in that it confirms one unshaken believe: tropical forests are good. Somehow, probably, the same will go for boreal forests.

The role of the taiga may present itself more on the scientific agenda, as temperature rises around the Arctic allow trees to grow in what used to be tundra biotope, absorbing some CO2, but also adding new albedo feedbacks to the climate equation.

© Rolf Schuttenhelm |

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