China’s aggressive policy of planting trees is likely playing a significant role in tempering its climate impacts.

An international team has identified two areas in the country where the scale of carbon dioxide absorption by new forests has been underestimated.

Taken together, these areas account for a little over 35% of China’s entire land carbon “sink”, the group says.

The researchers’ analysis, based on ground and satellite observations, is reported in Nature journal.

The latest analysis examined a host of data sources. These comprised forestry records, satellite remote-sensing measurements of vegetation greenness, soil water availability; and observations of CO2, again made from space but also from direct sampling of the air at ground level.

“China is one of the major global emitters of CO2 but how much is absorbed by its forests is very uncertain,” said the IAP scientist Jing Wang, the report’s lead author.

“Working with CO2 data collected by the Chinese Meteorological Administration we have been able to locate and quantify how much CO2 is absorbed by Chinese forests.”

Prof Shaun Quegan from Sheffield University, UK, studies Earth’s carbon balance but was not involved in this research.

He said the extent of the northeast sink was not a surprise to him, but the southwest one was. But he cautioned that new forests’ ability to draw down carbon declines with time as the growth rate declines and the systems move towards a more steady state.

“This paper clearly illustrates how multiple sources of evidence from space data can increase our confidence in carbon flux estimates based on sparse ground data,” he said.

“This augurs well for the use of the new generation of space sensors to aid nations’ efforts to meet their commitments under the Paris Agreement.”

Prof Quegan is the lead scientist on Europe’s upcoming Biomass mission, a radar spacecraft that will essentially weigh forests from orbit. It will be able to tell where exactly the carbon is being stored, be it in tree trunks, in the soil or somewhere else.

Richard Black is director of the Energy and Climate Intelligence Unit (ECIU), a non-profit think-tank working on climate change and energy issues.

He commented: “With China setting out its ambition for net zero, it’s obviously crucial to know the size of the national carbon sink, so this is an important study.

“However, although the forest sink is bigger than thought, no-one should mistake this as constituting a ‘free pass’ way to reach net zero. For one thing, carbon absorption will be needed to compensate for ongoing emissions of all greenhouse gases, not just CO2; for another, the carbon balance of China’s forests may be compromised by climate change impacts, as we’re seeing now in places such as California, Australia and Russia.”