Environment Director of the Australian Nuclear Science and Technology Organisation (ANSTO), Professor Ann Henderson-Sellers, has told a conference that verifying model predictions of changes to the Amazon rainforest may have significant consequences for understanding the global climate.
Professor Henderson-Sellers said that isotopic analysis of water and other elements could be the key to validating or improving numerical models used to predict the effects of climate change. Isotopes, which are structurally different forms of the same element, are analysed by ANSTO to provide important data for climate modellers.
'Global Climate Models (GCMS) are the predominant tool with which we predict the future climate. In order that people can have confidence in such predictions, GCMs require validation. Isotopes are a novel and fully independent means of evaluating GCMs,' she told the conference.
Professor Henderson-Sellers said that isotopic analysis was already providing detailed information for hydrologists and ecologists about the workings of the Amazon rainforest.
Scientists have used data derived from isotopes to show that wet season water recycling is by means of transpiration (release of water from vegetation) while dry season recycling in the Amazon is primarily by re-evaporation of precipitation intercepted on the canopy.
Almost all models predict increased surface temperatures following deforestation. There is also general agreement that both precipitation and evaporation decrease but less consensus on the sign of the change in atmospheric moisture convergence.
Professor Henderson-Sellers said that there are reasons to believe that tropical deforestation could lead to impacts on climate in areas a long way distant from the forest.
It has been shown that tropical deforestation has the potential to excite large scale Rossby waves in the atmosphere. Rossby waves, also known as planetary waves, are invisible forces that owe their origin to the shape and rotation of the earth, causing changes in the jet stream and ocean currents.
"These waves can propagate from the source of their initiating disturbance into the middle and high latitudes of both hemispheres and, hence, prompt impacts far distant from deforestation in the Amazon" she said.
Professor Henderson-Sellers said that analysis performed on data gathered since the 1960s have shown significant changes in the presence of the isotope deuterium, which points to possible changes in the Amazons water cycling. However, further study needs to be done to determine whether these changes are the result of deforestation.
'At present the available GCM studies are unable to reproduce our isotopic observations. Although the regional extent of deforestation in the Amazon is great, there are other effects which seem to be contributing to the observed temporal shifts in the isotopic signatures. These could include both the direct and indirect effects of greenhouse gas increases.'
Professor Henderson-Sellers, who presented her paper to the Australian Nuclear Association Annual Conference, co-authored the first GCM simulation of the impact of Amazonian deforestation in 1984.
