Trees and CO2 – what do we know?


Despite our best attempts so far, the amount of CO2 within our atmosphere continues to grow. One big recent hope was the proposal to plant lots more trees. Alas, no, it turns out that it is all a bit more complicated than just doing that.

There was lots of excitement last July when a press release first came out from ETH. However, as I pointed out at the time, their study was misrepresented and overstated. In the very best case (likely unachievable) we can only offset about 1/3 current emissions.

OK, so what do we know, what are the facts regarding CO2 and trees?

Let’s mull over it all for a bit.

FACT: CO2 continues to increase

We know that despite our best efforts so far the CO2 levels within our atmosphere continue to increase without any pause or slowdown. We have very precise measurements. Below is exactly what has been happening since 1958, and note that it includes the seasonal variations …

Personally I rather like the following illustration …

Side Note: The seasonal variation is due to the observation that we have far more trees in the Northern Hemisphere, hence in summer the vegetation thrives, becomes a CO2 sink, and emits O2.

Common Denialist Claim: CO2 is Jolly Good for Plants

For Climate denialists, one popular theme is to advance the claim that more CO2 is beneficial because it helps plants to grow and thrive. The argument is seriously flawed.

It is of course true that some growers do pump CO2 into industrial greenhouses, but what is also true is that this is not the only factor. They maintain all the other optional conditions required as well. Meanwhile out in the real world, the increased levels of CO2 will lead to drought and heat stress. Ecosystems tend not to respond too well to that.

What do we know?

More CO2 = Shorter Plant Lifespan

Increase the CO2 to trigger faster plant growth and what then happens?

Studies show there is a risk for them to having a shorter lifespan.

Land Use results in us storing a lot less CO2

Land use significantly and systematically affects the fundamental trade-off between carbon turnover and carbon stocks

Not just CO2, but also Water is an important factor

Research published in Nature Plants this year on grasslands around the globe showed that while dry sites can profit from more CO₂, there are complex interactions with rainfall. Depending on when the rain falls, some sites show zero or even negative effects in terms of biomass production.

Plants do Absorb CO2, but much remains unknown

We think that plants absorb roughly about three gigatons of CO2. In context we currently emit far more than that. What is also clear is that there is still a great deal that we simply do not yet understand.

Yes, planting Trees will help

The study from July that led to all the media hype about it being “The” solution is this …

Bottom Line – Planting Trees is not “the” solution

It will help, but there is no avoiding the obvious – we must cut our CO2 emissions if we wish to avoid the consequences of not doing so.

Planting lots of trees is not the silver bullet for climate change.

That’s not an opinion, there is very strong scientific evidence that plants alone will not be able to solve our CO₂ problem.

Further Reading

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