China’s forests, shrublands and soils have absorbed a third or so of China’s fossil fuel emissions from 1980 to 2000. Sequestering up to 260 million tonnes of carbon per year, the Chinese land sink is more than twice as large than that of geographic Europe, and comparable in size to that of the United States.
There has been quite some controversy over the total size of the Northern Hemisphere’s terrestrial carbon sink, so this first comprehensive estimate, published in Nature today, is filling a real gap. Given China’s 1.2 billion population and rapidly growing economy, knowledge of how much of its emissions are actually staying in the atmosphere is pretty valuable information. Globally, around 40% of annual emissions stay in the atmosphere; the rest is sequestered by plants, soils and oceans.
The Chinese data come at a time of growing speculation and guesswork over the People’s Republic’s future climate and energy policies. Needless to say, the study is of no small relevance with a view to upcoming climate negotiations. The very fact that China’s land carbon sink is large is good news. But the results will also strengthen the Chinese government’s negotiation position at the United Nations climate summit in December in Copenhagen.
China contributes one-quarter to worldwide afforestation and reforestation. It will be hard to ignore that newly planted forests offset a substantial fraction of China’s emissions – a heaven-sent trump card for Chinese negotiators. However, its emissions have increased so exorbitantly over the last decade – China has last year surpassed the US as the world’s largest emitter of carbon dioxide – that planting forests will hardly be sufficient if China is serious about reducing emissions.
Determining the carbon balance of a land mass the size of China is quite a task, and there are inevitably uncertainties involved. Shilong Piao of Peking University in Beijing and colleagues combined field-site measurements with satellite observations of vegetation to quantify China’s carbon balance, and then verified the results atmospheric inversions that rely on measurements of carbon dioxide concentrations. They found that evergreen forests and shrublands in the south of the country, where the climate is getting warmer and wetter, account for the bulk of China’s total land sink. Reforestation, changes in energy consumption (e.g. if people move to cities and refrain from burning wood for cooking), and changes in agricultural practices and land use explain the large size of the Chinese sink. My colleague Jeff Tollefson has more detail in his story on Nature News here.
How and when the results will be communicated to Chinese leaders, and what they will make of it, remains to be seen. Stephen Sitch of the University of Leeds, the only non-Chinese co-author of the study, declined to speculate on its political implications when explaining the results at an improvised press conference held during the meeting of the European Geosciences Union in Vienna, Austria. Of the Chinese authors, two of whom had been announced to speak at the press conference, none showed up.