Planting Trees is Not the Solution to Climate Change
Plant trees.
It is a nice message: it is positive, straightforward to understand, and brings about wholesome images of greenness and goodness. But will it alter the course of climate change? Or is it a distraction from the scale of our CO2 emissions problem?
Today I came across a Guardian editorial called "forests can help to save us". I was glad to see that the second paragraph began with a link to an article in a peer reviewed journal. However, I quickly found that a number of groups of scientists had published "technical comments" on the article, refuting many of its results.
Unfortunately, it looked like this was on of the cases where errors had slipped through the peer review net, and landed in a major news outlet who, to their credit, were probably doing their best to quote good research. The Guardian article states that planting trees could absorb two thirds of all historical human emissions:
It turns out, however, that there are two problems with this statistic.
Firstly, the authors of the paper overestimated the carbon absorption of potential areas of reforestation by about a factor of two, as they failed to take account of the carbon currently stored in those areas.
Secondly, this statistic forgets about all of the human emissions that have already been absorbed by the world's forests and oceans. Taking these two mistakes into account, the figure is more like 15% than two thirds.
The killer conclusion of the science article is that restoring woodlands is "the most effective solution at our disposal to mitigate climate change"! This (never-mind being a magnificent leap from the evidence presented in the paper) is clearly not true for a number of reasons.
Finally, it is worth remembering that even the most ambitious tree planting plans won't replace half of the in-tact forest that is currently being destroyed. Does it make sense to simultaneously cut down pristine rainforest and justify it by converting grassy biomes and tundra into new forest?
Of course we should plant trees. But please, don't think it will solve climate change.
It is a nice message: it is positive, straightforward to understand, and brings about wholesome images of greenness and goodness. But will it alter the course of climate change? Or is it a distraction from the scale of our CO2 emissions problem?
Today I came across a Guardian editorial called "forests can help to save us". I was glad to see that the second paragraph began with a link to an article in a peer reviewed journal. However, I quickly found that a number of groups of scientists had published "technical comments" on the article, refuting many of its results.
Unfortunately, it looked like this was on of the cases where errors had slipped through the peer review net, and landed in a major news outlet who, to their credit, were probably doing their best to quote good research. The Guardian article states that planting trees could absorb two thirds of all historical human emissions:
Firstly, the authors of the paper overestimated the carbon absorption of potential areas of reforestation by about a factor of two, as they failed to take account of the carbon currently stored in those areas.
Secondly, this statistic forgets about all of the human emissions that have already been absorbed by the world's forests and oceans. Taking these two mistakes into account, the figure is more like 15% than two thirds.
The killer conclusion of the science article is that restoring woodlands is "the most effective solution at our disposal to mitigate climate change"! This (never-mind being a magnificent leap from the evidence presented in the paper) is clearly not true for a number of reasons.
- Keeping carbon in the ground as coal and gas is the obvious, surefire way of preventing it from getting it into the atmosphere. Whilst forests do absorb carbon from the atmosphere, they only do so as long as they survive, which in itself depends on the climate, as well as politics and societies that surround them.
- In northern regions, planting trees can have a net warming effect, as they absorb solar radiation and only marginally increase carbon storage. In these boreal areas, most carbon is stored underground.
- Massive scale tree planting can have a multitude of unintended consequences. Many regions that have been earmarked for restoration are in fact valuable intact ecosystems such as savannas. Irresponsible interference with these ecosystems poses a threat to biodiversity and to the livelihoods of developing communities, whilst potentially increasing the risk of fires.
Finally, it is worth remembering that even the most ambitious tree planting plans won't replace half of the in-tact forest that is currently being destroyed. Does it make sense to simultaneously cut down pristine rainforest and justify it by converting grassy biomes and tundra into new forest?
Of course we should plant trees. But please, don't think it will solve climate change.
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