SAO PAULO (Reuters) - A group of scientists from more than 20 institutions around the world will gauge the impact on the world's largest rainforest if a time comes when the planet has 30 percent more carbon dioxide (CO2) than today, according to a project launched on Wednesday.
A large experiment including towers that will pump CO2 into plots of dense forests will be built in a region north of Manaus, in the Brazilian Amazonas state.
Sensors and field observation will evaluate the reaction of the trees when subject to a concentration of carbon dioxide 200 parts per million (ppm) higher than the current 400 ppm, already the highest level ever.
Predictions by the U.N.'s panel on climate change (IPCC) indicate that 600 ppm could be the level of CO2 concentration in 50 years time.
Tropical forests around the world are a key aspect on global warming.
They store billions of tonnes of carbon and their potential to continue to absorb heat-trapping gases from the atmosphere is critical to determine by how much temperatures could rise.
Little is known so far about how tropical forests will react as CO2 levels rise.
"It is the first time this kind of experiment is conducted in a tropical forest," said Carlos Nobre, a scientist who heads research policy at Brazil's Science Ministry and is a member of the IPCC.
"The outcomes will be of great importance for other tropical forests, the global carbon cycle and to understand how these forests will be affected by climate change throughout this century," he said.
Some experts believe the larger amount of carbon dioxide would be beneficial to trees that in turn could absorb larger quantities of carbon, slowing the rise on temperatures.
Others say the changing climate is likely to affect negatively part of the forests, killing many trees and reducing tropical forests' capacity to stock carbon.
Scientists using the UK-based Hadley Centre's climate model showed last year that CO2 levels in 2100 will vary greatly, from 669 to 1,130 parts per million, depending on how trees handle the higher concentration of the gas.
That range is big enough to define a temperature change around 2 degrees Celsius (35 Fahrenheit).
"The major expected outcome of this project will be an improvement of our scientific knowledge about the fate of the Amazon forest in the context of atmospheric and climatic change," said the scientists in a text presenting the project.
Resulting data could feed climate models for more accurate projections on temperature trends and future concentrations of CO2.
The program will last 13 years and its total cost is estimated at 78 million dollars.
The Brazilian government and the Inter-American Development Bank will fund the very initial phase of the project with 1.2 million dollars.
A funding proposal will later be presented to the Amazon Fund, a facility managed by Brazil's Development Bank (BNDES) with resources from donor countries, particularly Norway.
Reporting by Marcelo Teixeira; editing by Andrew Hay