The world economy is growing, and combined with an increase in its carbon intensity, this has led to a rapid growth in carbon dioxide emissions since 2000. Indeed, the new study performed by researchers working at the Global Carbon Project, at the University of East Anglia and the British Antarctic Survey, shows that the growth rate of emissions has increased from 1.3% to 3.3% each year since 2000. The team also found that the fraction of carbon dioxide that remains in the atmosphere has increased over the last 50 years. This implies that natural carbon dioxide sinks, on land and in the ocean, are therefore less efficient at absorbing this greenhouse gas.
As a result, the growth rate of atmospheric carbon dioxide has increased a huge 35% faster than expected since 2000, say the scientists. The results also show that global carbon dioxide emissions from all human activities had increased to 9.9 billion tonnes in 2006, which is 35% higher than emissions in 1990 – the "reference year" in the Kyoto Protocol.
The researchers obtained their results by bringing together information on atmospheric carbon dioxide growth since 1959, energy consumption, GDP and carbon uptake by oceans and land with several modelling tools. "We found that for every tonne of carbon dioxide emitted to the atmosphere 50 years ago, the natural sinks removed 600 kg,” said Pep Canadell of the Global Carbon Project. “Now, only 550 kg is being removed. This quantity is falling and will continue falling well into the 21st century."
Although the scientists do not know exactly why the oceans are absorbing less carbon dioxide, they believe that it is partially related to an intensification of the Southern Ocean winds over recent years as a response to increased greenhouse gas emissions and the hole in the ozone layer.
The carbon intensity of the global economy is also increasing. "Or more strictly speaking, it has stopped going down – as was the case over the last 100 years," explained Canadell. "This is because more wealth is being produced globally using increasingly carbon-intense energy systems compared with before 2000." According to Canadell, a higher proportion of worldwide wealth is being generated using coal – the dirtiest of all ways to produce energy. “This is due, mainly but not exclusively, to the large wealth created by China, which is still using very inefficient processes largely based on coal," he said.
The team warns that we must act now, because the longer we wait to reduce emissions the harder it will be to stabilize carbon dioxide emissions in the future.
The researchers now plan to look at why the efficiency of the natural ocean carbon dioxide sinks is declining. "We will also scrutinise better what happens on land sinks, where droughts and warmer temperatures are having major effects," added Canadell.
The work was reported in PNAS.