7 August 2005Jenifer Johnston
The Earthis losing its natural resistance to global warming as the oceans and forests reach capacity in their ability to soak up carbon emissions, say scientists.
Using a new computer model, researchers “fast- forwarded” 100 years to reveal that unless emissions are curbed, land and seas – the “sinks” for carbon dioxide – will become steadily less effective at removing carbon from the atmosphere, causing the planet to heat faster and increasing temperatures and droughts.
Lead researcher Dr Inez Fung of the University of California, Berkeley, told the Sunday Herald the model debunks one argument put forward by global-warming sceptics that plants will flourish and the oceans bloom in a warmer environment.
“Our work shows that if we keep going on our current course of fossil fuel emissions, the land and oceans will not be able to slow the rise of carbon dioxide in the atmosphere the way they are doing now. Land and oceans absorb about half of the carbon dioxide produced by human activity at the moment. If we accelerate our emissions, the saturation rate will increase,” she said.
Fung’s model suggests that as heat and droughts increase, plants cut back their intake of carbon dioxide to save water. Ultimately, they stop absorbing it at all. Similarly, as the oceans heat up they struggle to absorb carbon dioxide which then collects near the surface, further preventing absorption and accelerating global warming.
Using data from 1982 onwards, Fung said the northern hemisphere has “greened” each spring and summer as the climate has warmed, leading to more atmospheric CO2 being absorbed by plants.
However, since 1994, as droughts have made the world hotter and drier, plants have been unable to cope. Even though plants could take in more CO2 in spring, that has been offset by decreasing CO2 uptake during summers which have become increasingly dry, literally “browning” the Earth.
“We’re saying ‘hold on a second – plants may not be happier in a warmer and drier world’. This negative effect of hot, dry summers completely wiped out the benefits of warm, wet springs. If you look at satellite pictures of the Earth over this time you can actually see this happening now,” Fung said.
Fung’s planet model predicts that by 2050 – as the biosphere struggles to absorb CO2 being pumped into the atmosphere by humans burning fossil fuels faster and faster – the planet will not be able to keep up, and that, at a low estimate, global temperatures will rise 1.4°C .
“The Earth has a natural rate of absorption that you just cannot accelerate – you can’t make the land accept more CO2 just because more is being released,” she said. “If the rate of fossil fuel emissions is too high, the carbon storage capacity of the land and oceans decreases and climate warming accelerates.”
Last week the World Wildlife Federation warned that Scotland’s average temperature for 2005 is 1°C above average. Overall, Scotland’s average annual temperature has increased by 1°C in the past four decades.
Friends of the Earth Scotland’s Dr Dan Barlow warned: “It is not surprising that the Earth’s ability to deal with rising carbon emissions has limits and it is increasingly clear that we have a very narrow window in which to act to avert climate chaos.”
Dr David Reay of the Institute of Atmospheric and Environmental Science at the University of Edinburgh said the study’s predictions are “clearly important”.
“As scientists we’re aware that you cannot keep pumping CO2 into the atmosphere and expect the Earth to keep absorbing it. This study is very important in terms of giving us a window on the future,” he said.
Fung, one of the world’s leading climate scientists, has spent decades studying the carbon cycle of the planet, producing a sophisticated model which takes into account the tiniest of details, such as the salinity of oceans and forest floor litter decomposition rates and the effects of temperature, rainfall, clouds and wind speed on these kinds of interactions.
She told the Sunday Herald: “The Earth is entering a climate space we’ve never seen before … we don’t know where the threshold is. You might think that a one or two degree increase is not all that much but if we’re on the threshold, it could make a big difference.”
