Forests are generally assumed to be a good thing for the climate, absorbing the carbon dioxide that we continue to throw out into the atmosphere. However, under certain conditions forests start to release more carbon dioxide than they absorb. 'There are vast stores of carbon held globally in trees and soils, if these stores start to become net sources of carbon dioxide as the climate changes then we will enter a frightening positive feedback situation,' says Phil Ineson of the University of York.
Phil and colleagues in Edinburgh and Sheffield are carrying out research into what happens to the carbon cycle in forests when atmospheric carbon dioxide increases. 'Trees convert carbon dioxide into living solid matter,' says Phil. 'As levels of atmospheric carbon dioxide increase so rates of growth increase.' Increasing growth rates in forests have been observed worldwide and are estimated to take out 10% of our global carbon dioxide emissions, shielding us from global warming. Unfortunately, research indicates that forests will not continue to make this contribution as carbon dioxide levels increase.
A variety of techniques are used to measure carbon dioxide levels in samples of air. The very reason why carbon dioxide is a problem is actually the basic principle behind each of the technologies we use,' says Phil. 'Carbon dioxide in the air absorbs heat leading to global warming, so we measure how much heat is absorbed in an air sample to tell us the concentration of carbon dioxide.' The analysers used can respond in fractions of a second and are automated with robotic devices left out in the field to take measurements.
'The carbon taken up by the tree is transferred to the soil via the tree's roots and taken up by microorganisms. The microorganisms' metabolisms speed up and increased levels of carbon dioxide are emitted into the atmosphere. If this were to happen on a global scale then the consequences would be severe,' says Phil.
Research to refine climate change models incorporating the carbon cycle of forests continues, but it is clear we cannot rely on trees to solve global warming.