Study

A large and persistent carbon sink in the world's forests

Pan, Y.; Birdsey, R. A.; Fang, J.; Houghton, R.; Kauppi, P. E.; Kurz, W. A.; Phillips, O. L.; Shvidenko, A.; Lewis, S. L.; Canadell, J. G.; Ciais, P.; Jackson, R. B.; Pacala, S. W.; McGuire, A. D.; Piao, S.; Rautiainen, A.; Sitch, S.; Hayes, D.

Science, 2011

Peer-reviewedmodelling studywild

What they did

Forest inventory data and long-term plot measurements from around the world were combined into a single carbon budget for global forests covering 1990 to 2007, separating established forest, regrowing forest and deforestation.

Sample size: national forest inventories and long-term plot networks

What they found

Established forests took up carbon at a large and sustained rate, while tropical deforestation released a comparable quantity. The net global forest sink was substantially smaller than the gross uptake, because losses ran against it.

What it means

The authors' reading, and ours. Where they differ, that difference is the point.

How the authors put it

The world's established forests are a persistent carbon sink of global significance, partly offset by emissions from tropical land clearance.

How NatureHQ reads it

The right frame for every "planting trees will fix it" question. Forests do take up an enormous amount of carbon and the figure is well measured. The same accounting shows why the net number is so much smaller than the gross one, and where the difference goes. It also shows that the sink is a flow rather than a property: it exists as long as uptake outruns loss, and clearance turns a sink into a source in the same accounts.

Limitations

Inventory coverage is much better in temperate and boreal regions than in the tropics, where the uncertainty is largest.
A budget for 1990–2007; the balance has shifted since, particularly in the Amazon.
Soil carbon change is the least well constrained term.