The paper \”Terrestrial biogeochemical feedbacks in the climate system\” by Professor Sandy Harrison of Macquarie University and colleagues from Sweden, Finland, UK, Germany and the USA, seeks to give a first estimate of the warming caused by additional feedbacks between the biosphere and atmosphere over the twenty-first century.
Harrison says that the two major effects of vegetation on the climate system – changes to how water and energy are exchanged between land and atmosphere; and changes to how carbon dioxide is taken up, stored and released by plants – are relatively well understood by climate modellers.
Less well understood, and not yet represented in global climate models, are many other impacts of plants on the atmosphere, particularly the release of various chemicals and gases.
\”One of the chemicals that plants release, for example, is called isoprene,\” Harrison explains. \”If you\’ve been into the Blue Mountains and seen that lovely blue haze, that\’s basically isoprene that\’s been released from the plants most probably to protect them from heat stress. When isoprene starts interacting with ozone in the atmosphere chemically, it affects how much energy the atmosphere can absorb.
\”Different sorts of plants release different amounts of isoprene, and they also release different amounts depending on the temperature that they\’re experiencing because it\’s a heat stress protector, and so changing climate changes the amount of isoprene that\’s released and then changing the amount of isoprene changes the atmospheric chemistry which in turn changes the climate.
\”That\’s one of the really key interactions, but there are a whole series of other things that are released by vegetation, including methane and nitrogen oxide, and all of those act on the atmospheric chemistry and produce changes in the atmosphere that then change the climate further.
\”On top of that, as we have global warming, we also have more fires, which is obviously a big problem here in Australia. When you burn vegetation you release a whole suite of chemicals and soot particles and these can also influence the atmospheric chemistry.
\”So what we were trying to do with this study was quantify all of those kinds of processes and see how important they were.\”
Harrison says that all of the processes mapped by the scientists would make the climate hotter, but that quantifying the final amount of temperature increase would be very difficult until the feedbacks are incorporated into a global climate model. However, she warned the temperature increase could be substantial.
\”If all of these effects operate, if they all have an additive effect, and if there is no chemistry that occurs that will negate them, then we are talking degrees – not tenths of degrees – change over a hundred year period.\”