Reforesting parts of the planet to offset carbon emissions could do more damage than good if the biophysical effects of introducing certain species of trees to different geographical zones are not accounted for before planting takes place.

A group of environmental scientists from America, Australia and Argentina is calling for formal mechanisms to be introduced to all carbon offsetting schemes which involve forestation, in a paper published in Environmental Research Letters.

The team of 15 researchers from Duke University in New York, the University of California, The Global Carbon Project in Canberra, The National Center for Atmospheric Research in Colorado, Stanford University, North Arizona University, Purdue University in Indiana and the Universidad Nacional de San Luis & CONICET in Argentina works through various scenarios to show how a framework could be introduced.

Carbon sequestration has a long-term global cooling effect but the planting of certain species of trees in different geographical zones can have a more immediately detrimental effect if biophysical factors are not considered.

Projects like forest restoration and afforestation, the conversion of open land into a forest, have greater benefit in tropical regions because that is where carbon storage and biophysics can align to cool the Earth, assisting the water cycle, creating cloud feedbacks and slowing the build up of carbon dioxide in air.

In snow-covered zones the benefits are much less clear cut; darkening the land surface with more trees can lead to higher sun light absorption and therefore increased regional warming.

In temperate zones such as Western Europe and North America, the effects of forestation are simply badly understood. Those in favour can argue for increased evapotranspiration, helping keep water in the local environment so that it can have a cooling effect, whereas those against can argue that trees have a warming effect, darkening the landscape and absorbing more of the sun’s heat.

There are other dangers too. For example, some trees are fire-prone or just use more water than native vegetation which can be disastrous in semi-arid regions; the use of fertilisers to plant trees can lead to the emission of nitrous oxide which has 310 times the warming effect of carbon dioxide; and, if biodiversity and wildlife habitats are not accounted for, natural and important forest services will be destroyed.

As the researchers state: "Currently, there are no formal mechanisms to account for biophysics in climate policy. Simple rules can be developed to encourage best practices. Ignoring this challenge could result in millions of dollars invested in some mitigation projects that provide little climate benefit or, worse, are counter-productive."