Do the large forests remove CO2 from the atmosphere?

Question

Thomas L. Friedman, the New York Times columnist, wrote yesterday:

These intact forests — from those in the Amazon and Congo River basins to ones in Canada, Russia and Ecuador — are the world’s life-support system. They sponge billions of tons of carbon dioxide out of the atmosphere, generating oxygen [...].

A forest would, over longer time periods, only be a net carbon sink — and corresponding oxygen source — if its biomass increases and/or if dead organic material is removed from the global cycle of matter, e.g. by forming peat underground.

But, for example, parts of the Amazon rain forest stand basically on a relatively thin layer of humus above infertile quartz sand (here is a popular science article); since the rain forest is millions of years old, there is no significant sequestering of organic matter over time in the Amazon.

Of course I may have overlooked something, and rain forests in Africa or Asia, let alone forests in temperate climates, all in places with very different geologies, may indeed sequester carbon. After all, our fossil fuels once were plants.

Are forests overall significant carbon sinks or should I write a letter to the editor? I suppose that Friedman should at least remove the Amazon basin from the sentence.

Answer 1

From a quick search online using your question, the consensus is forests emit carbon dioxide as well as absorb carbon dioxide, but overall they absorb more than they emit.

From NASA Finds Good News on Forests and Carbon Dioxide, dated 30 December 2014.

A new NASA-led study shows that tropical forests may be absorbing far more carbon dioxide than many scientists thought, in response to rising atmospheric levels of the greenhouse gas. The study estimates that tropical forests absorb 1.4 billion metric tons of carbon dioxide out of a total global absorption of 2.5 billion -- more than is absorbed by forests in Canada, Siberia and other northern regions, called boreal forests.

Forests and other land vegetation currently remove up to 30 percent of human carbon dioxide emissions from the atmosphere during photosynthesis. If the rate of absorption were to slow down, the rate of global warming would speed up in return.

On 12 February 2021, the World Economic Forum stated:

New research, published in Nature Climate Change and available on Global Forest Watch, found that the world’s forests sequestered about twice as much carbon dioxide as they emitted between 2001 and 2019. In other words, forests provide a “carbon sink” that absorbs a net 7.6 billion metric tonnes of CO2 per year, 1.5 times more carbon than the United States emits annually.

The Climate Council website, similarly stated, more that 3 years ago,

When forests are cleared or burnt, stored carbon is released into the atmosphere, mainly as carbon dioxide. Averaged over 2015—2017, global loss of tropical forests contributed about 4.8 billion tonnes of carbon dioxide per year (or about 8-10% of annual human emissions of carbon dioxide).

Whilst forests are important carbon sinks, meaning they draw down carbon dioxide from the atmosphere, the carbon stored in these sinks is part of an active, relatively quick carbon cycle. As living things (including trees) die and decay, the carbon that they once stored is released back into the atmosphere.

The article, Explainer: how much carbon can the world’s forests absorb?, from 2013, has a similar narrative: despite being both a carbon emitter and absorber, overall forests, particularly tropical forests are an overall absorber of carbon dioxide.

Answer 2

The article is doesn't say forests are carbon sinks, the quote says forests convert large amounts of CO2 into oxygen, which is completely correct. I didn't read the article but I suspect the point the author is making is that cutting down forests will accelerate CO2 buildup in the atmosphere, which is also correct.

Saying that forests process billions of tons of CO2 is right, that doesn't mean they are converting those billions of tons into sequestered carbon every year, it's being processed into food to sustain the tree and provide for growth. The natural process of carbon sequestration is actually pretty slow.

Answer 3

Mr. Friedman failed to consider aspects of cell respiration and loss to environment, these two factors are enough to make short term plant photosynthesis not that useful for sequestering carbon dioxide, as lots of plants release carbon during the night (cell respiration), however if you look at the long term aspects plants can use CO₂ to build plant tissue, sadly though eventually the plant would die (lets use a tree as an example) and the microorganisms will turn lots of it into carbon dioxide and the rest gets buried underground to undergo the process of being turned into coal.

One additional problem would be deforestation, the Amazon rain forest is losing vegetation at a rapid rate which would also release more CO₂. So with all this evidence in mind the Amazon having met all the CO₂ loss requirements might actually release more CO₂ than sequester. I feel like the article notes only 1 half of the "Gas exchange" process and leaves out the respiration and decomposition processes. Hopefully this answers your question.