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.
- Science – A matter of tree longevity
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
- Nature Geoscience (2016) – Biomass turnover time in terrestrial ecosystems halved by land use.
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.
- Nature Plants (Feb 2019) – Globally consistent influences of seasonal precipitation limit grassland biomass response to elevated CO2
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.
- Nature (2017) – Uncertainty in the response of terrestrial carbon sink to environmental drivers undermines carbon-climate feedback predictions
Yes, planting Trees will help
The study from July that led to all the media hype about it being “The” solution is this …
- Science (July 2019) – The global tree restoration potential (Side Note: to really make deep inroads and drop this means that we would need to turn agricultural land back to forest)
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
- The Conversation (Aug 2019) – Climate explained: why plants don’t simply grow faster with more carbon dioxide in air
- The Conversation (July 2019) – Exaggerating how much CO₂ can be absorbed by tree planting risks deterring crucial climate action
- AGU Publications (2017) – The Limits to Global-warming Mitigation by terrestrial carbon removal
- Real Climate (July 2019) – Can planting trees save our climate?
- SkepticalScience (July 2015) – Plants cannot live on CO2 alon