The Word For World Really Might Be Forest

This is fascinating new research.

The idea that forests bring the rain, and cutting them down can affect local weather patterns, is not new. But Russian physicists Makarieva and Gorshkov argue forests also create winds that sweep rain inland, allowing forests to grow far from the coast.
The theory runs that Australia is so dry in large part because we don’t have forests, not the other way around. The last two hundred years has obviously been a big contributor to this, but Aboriginal fire practices appear to have also been significant.

Everyone agrees that the pressure changes caused by condensation and evaporation can cause winds, but the standard models have this as an effect small enough to be ignored. Some models factor it in, but as a marginal effect. This research suggests it is actually the largest wind generator, at least those travelling from the coast to the centre of continents – the ones that carry rain.

You might think that most of the evaporation occurs over the Earth’s oceans, but this is not really true. Forests have many times as much leaf area as the ground they cover, and these leaves all perspire water. Rainforest trees perspire a lot. So per square kilometre a rainforest will release much more than the ocean, sometimes ten times more.

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February 21, 2013 Stephen Luntz

Two weeks ago (sorry about the delay) I interviewed a scientist over what might be world-changing research. The paper I covered is only a modest reworking of something that some of the authors have previously published a few times, and it actually has got a reasonable amount of coverage. Nevertheless, the implications here are so huge, and so appealing to the environment movement, it’s a bit surprising that it isn’t all over social media at the very least.

My guess as to the reason why it isn’t is that it’s also work that is incredibly easy to distort, and inevitably the usual suspects are out there doing just that. Like trolls in the comments section of an intelligent article I suspect these figures are not so much convincing anyone but closing down opportunities for thoughtful discussion. This is my best effort to open it back up.

The core of this idea is that two Russian physicists have proposed the idea that it is evaporation and condensation, rather than temperature differences that are the primary drivers of wind patterns. When water condenses out of the air it lowers the atmospheric pressure, causing air to sweep in from surrounding locations – ie wind. Moreover, most of the water vapour in the atmosphere sits fairly close to the ground and condenses as it rises into cooler air so winds sweep in to replace the condensing water vapour. This airflow encourages further evaporation, followed by more condensation in the air column above, creating a positive feedback loop. Anastassia Makarieva and Victor Gorshkov argue this is a much larger contributor to wind generation than anyone has previously recognised.

If true, this would be a huge shake-up for our mental model of the Earth. I learned that temperature variations produced wind when I was still in primary school. A lot of textbooks would have to be rewritten. So too would climate models. Naturally this is the part the denialist movement has jumped on. When I interviewed Professor Derek Shiel, co-author on the most recent paper, he ruefully acknowledged that, yes The Australian had made his statements sound harsher on climate modellers than he intended, and yes he pretty much knew this was coming before they interviewed him.

However, while acceptance of this idea would change our ideas as to which parts of the planet will warm the most, become drier or wetter etc, I can’t see any reason why it should change the overall temperature estimates based on a specific level of carbon dioxide in the atmosphere, or the estimated sea level rise. The fact that things might be a bit better in one place and a bit worse in another is hardly a reason to back off on climate action. Arguably the uncertainty is all the more reason to do something – you can no longer be sure you’ll be one of those who will get off lightly.

But that doesn’t mean there are no policy implications. You might think that most of the evaporation occurs over the Earth’s oceans, but Sheil, a forest ecologist at Southern Cross University, says this is not really true. Forests have many times as much leaf area as the ground they cover, and these leaves all, to some degree, perspire water. Rainforest trees perspire a lot. So per square kilometre a rainforest will release much more than open ocean, sometimes ten times more.

The idea that forests bring the rain, and cutting them down can affect local weather patterns, is not new. But Makarieva, Gorshkov and Sheil argue forests also create winds that sweep rain inland.

Sheil says he became interested in the idea having noticed that over most of the planet rain drops the further you get in from the coast (mountain ranges aside, I presume). However, over the great rainforests such as the Amazon this doesn’t happen – it rains just as much inland as near the coast. Even more suggestively, he says that in the great boreal forests of Russia the rain and snow also fall inland, except in the depths of winter when the snow sticks to the coast. Why? He thinks it is because “it’s so cold the forests shut down” and no longer transpire much water.

The theory runs that Australia is so dry in large part because we don’t have forests, not the other way around. The last two hundred years has obviously been a big contributor to this, but Aboriginal fire practices appear to have also been significant.

Everyone agrees that the pressure changes caused by condensation and evaporation can cause winds, but the standard models have this as an effect small enough to be ignored. Some models factor it in, but as a marginal effect. Sheil and his colleagues think it is actually the largest wind generator, at least those travelling from the coast to the centre of continents – that is the ones that bear rain.

If true forests are even more important than we realised. Without coastal forests there will not be enough rain to support forests inland. There may even not be enough rain to support agriculture inland. The authors hypothesise that the drying out of inland Australia and the Sahara is largely due to deforestation setting up a vicious circle where not enough rain came in to support forests, which then dried areas out even further. The survival of America’s waving fields of corn may depend on preserving the Redwoods.

And here’s the kicker. It’s not just trees that matter, the trio believe, it’s diverse forests. Monoculture plantations lack the the understory that mediates transpiration. Makarieva has claimed there are complex feedback loops that mean intact forest releases a sustainable amount of water, where plantations have something more akin to a boom and bust cycle. With very long busts.

Now it should be stressed that this theory is far from established. Most atmospheric scientists don’t accept it, and Makarieva, Gorshkov and Sheil had a difficult time getting it published in an atmospheric journal. Even when the did, it was only with a note from the editors saying they were unconvinced of its accuracy and were publishing in the hope of sparking debate. Obviously denialists jumped on this as evidence of how close minded climate scientists are. However, it is instructive that publication did indeed occur in one of the most prestigious climate journals around, Atmospheric Chemistry and Physics. Given that the trio had previously been published several times on the topic in physics journal the idea that peer review is closed to radically new ideas doesn’t get much support. Indeed publication elsewhere could easily have given Atmospheric Chemistry and Physics‘ editors the excuse that this paper wasn’t new enough to justify publication. The authors have set the challenge for anyone to find flaws in their work that might mean they are exaggerating the effect.

Moreover, if Makarieva, Gorshkov and Sheil are even halfway right the climate system is even more complex than we thought, and even more in danger of disruption from human behaviour. If humans were disrupting climate on a continental scale even before we invented agriculture it should be obvious industrialised society could mess with the planet’s thermostat with ease.

The physics aside, the primary implications of this theory are:
1) The Earth is a delicate system and we mess with it at our peril.
2) Forests matter, and are worth much more standing than as paper.
3) Intact ecosystems do their jobs much better than crude imitations we like to put in their place after was have destroyed them.

Yet The Australian and Watts Up With That are using it to discredit environmentalists. You have to give them credit for chutzpah.

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