The fresh fragrance released by trees in northern pine forests is a significant component in slowing climate change, according to research.
The particles that carry the forests' olfactory assault also help to cool the planet by bouncing energy from the sun back into space. Now researchers have worked out that the forests produce enough microscopic particles to load the atmosphere around them with 1,000-2,000 particles per cubic centimetre of air.
The discovery will help plug a big hole in climate change models and so help scientists to make more accurate predictions of global warming from greenhouse gases such as carbon dioxide and methane.
Hans-Christen Hansson of the Air Pollution Laboratory in Stockholm, Sweden, said airborne particles are a big unknown factor for climate scientists. "We are afraid we have totally misjudged the trend of climate change because the particles are not in the models in a comprehensive way."
The particles, called monoterpenes, give pine and spruce forests their characteristic aroma. They either affect climate directly by bouncing sunlight back into space or by seeding clouds, which do the same thing. "That gives us a very big uncertainty for projection of the effects of greenhouse gases," he added.
Industrial chimneys and emissions from cars also spew out particles which contribute to so-called "global dimming" - bouncing the sun's energy back into space - but disentangling this from the effects of natural particles has proved difficult. "We didn't know really what the natural background was before," Professor Hansson said. The new work will help researchers to separate human-made from natural effects and improve mathematical models of the climate.
The team studied particles generated by the so-called boreal forest. This occurs between 50 and 60 degrees north and covers swaths of Alaska, Canada, Siberia and Europe, a total of 15m square kilometres. "Given the large global coverage of boreal forest, this could have really big implications for climate," said a team member, Peter Tunved.
The team monitored particles collected at three locations in Sweden, including two in the Arctic circle. They found a strong correlation between the time an air mass had spent over the forest and the load of particles it carried, showing that the trees must be the source. Their results appear in the latest edition of Science.
While boreal forests lock up carbon and produce particles that keep the atmosphere cool, they should not be relied on to keep us from burning up, according to Prof Hansson. "Particles have a lifetime of up to a week while the greenhouse gases have a lifetime of years to decades. So you can't really use particles in some desperate mitigation technique to stop climate change. I don't think that's the way to stop the greenhouse gas effect."The Guardian
