Scientists urge the world’s leaders to get serious about cutting carbon dioxide emissions during the upcoming climate summit, reports Alok Jha
The Earth’s natural ability to absorb carbon dioxide is declining and global temperatures are on course to rise by 6°C by the end of the century, according to a study.
Scientists said that carbon dioxide emissions have risen by 29% in the past decade alone and called for urgent action by leaders at the United Nations climate talks in Copenhagen to agree on drastic emissions cuts in order to mitigate dangerous climate change.
By studying 50 years of data on carbon emissions from human and natural sources, such as volcanoes, a team of international researchers was able to estimate how much carbon dioxide is being absorbed naturally by forests, oceans and soil.
They concluded, in the journal Nature Geoscience, that those natural sinks are becoming less efficient, absorbing 55% of the carbon now, compared with 60% half a century ago.
The drop in the amount absorbed is equivalent to 405-million tonnes of carbon, or 60 times the annual output of a large coal-fired power station.
The carbon dioxide absorbed by a natural carbon sink can be adversely affected by annual variations in weather and rising concentrations of the gas in the atmosphere.
Professor Corinne Le Quéré of the University of East Anglia, who led the study at the British Antarctic Survey, suggested that rapidly rising human emissions of carbon dioxide might have initiated a feedback mechanism in the climate system, whereby natural sinks become even more inefficient as the amount of the greenhouse gas increases.
The research gives greater urgency to the diplomatic manoeuvring ahead of the Copenhagen summit. Earlier this week, United States President Barack Obama acknowledged that time had run out to secure a legally binding climate deal next month and said he would support plans to delay a formal pact until next year at the earliest.
The study is the most comprehensive analysis to date of how economic changes and shifts in the way people have used the land in the past five decades have affected the concentration of carbon dioxide in the atmosphere.
“The global trends we are on with carbon dioxide emissions from fossil fuels suggest that we’re heading towards 6°C of global warming,” said Le Quéré.
“This is very different to the trend we need to be on to limit global climate change to 2°C [the level required to avoid dangerous climate change].” That would require carbon dioxide emissions to peak between 2015 and 2020 and that the global per capita emissions be decreased to one tonne of carbon dioxide by 2050. The average US citizen emits 19,9 tonnes a year.
Le Quéré added: “Based on our knowledge of recent trends in carbon dioxide emissions and the time it takes to change energy infrastructure around the world, and the response of the sinks to climate change and variability, the Copenhagen conference is our last chance to stabilise the climate at 2°C above pre-industrial levels in a smooth and organised way.
“If the agreement is too weak or if the commitments are not respected, we will be on a path to 5°C or 6°C.”
Le Quéré’s work, part of the Global Carbon Project, showed that carbon dioxide emissions from burning fossil fuels increased at an average of 3,4% a year between 2000 and 2008 compared with 1% a year in the 1990s. Despite the global economic downturn, emissions still increased by 2% in 2008. Most of the recent increase has come from China and India, though a quarter of their emissions are a result of trade with the West.
Based on projected changes in GDP, the scientists said emissions for 2009 were expected to fall to 2007 levels, before increasing again in 2010.
But Le Quéré’s conclusion on the decline of the world’s carbon sinks is not universally accepted. Dr Wolfgang Knorr, of the University of Bristol, England, recently published a study in Geophysical Research Letters, using similar data to Le Quéré, in which he argued that the natural carbon sinks had not noticeably changed. “Our apparently conflicting results demonstrate what doing cutting-edge science is really like and just how difficult it is to accurately quantify such data,” he said.
But the scientists agreed that an improved understanding of land and ocean carbon sinks was crucial because it had implications for targets set by governments at climate negotiations. —