mardi 7 novembre 2017

118- The spirit of plants -10- Clouds


A long time ago, in the last century (at the beginning of the 90's), I had the opportunity to make a trip to Cyprus, a beautiful Mediterranean island with a particularly rich historical past. I was struck by the incredible amount of forest tree replanting in all non-agricultural areas, especially mountain areas, sometimes terraced.
I was then told that it was a government plan to stop the evolution of the local climate. Rains were becoming increasingly rare, and the island was slowly moving towards a significant risk of desertification.

We empirically know, and for a long time, that forests promote the appearance of rains, to the point that certain countries with an arid climate, as it's the case of Cyprus, have launched reforestation programs, sometimes very ambitious, of which one the main objectives are to try to increase rainfall, in addition to curbing erosion and loss of soil fertility.

What we now know, thanks to the Cloud experiment, a series of scientific works conducted by the CERN, in Geneva, Switzerland, is how this phenomenon occurs.
I advise you to read the original article (in French), full of interesting links and explanations.

"Climate: According to the CERN, trees influence cloud formation.

As the results of the Cloud experiment at CERN showed in 2016, the trees would be much talented than we thought to make clouds and cool the climate. Their action goes through aerosols.

Since 2009, the Cloud experiment, installed at the CERN in Geneva, simulates different pressure and temperature conditions to study mechanisms at work in the Earth's atmosphere, including the effect of aerosols on the climate. These small particles act like "cloud seeds", favoring the condensation of water vapor into droplets and thus the formation of nebulosities. Overall, the effect on the climate is refreshing because part of the sunlight is then reflected upwards.

Half of these aerosols are dust from soils and marine salts emitted by the ocean, and the other half from gas molecules that aggregate into particles of 50 to 100 nanometers. This is the case of sulfuric acid, derived from sulfur dioxide (SO2). Today, this gas is produced with great generosity by industrial activities. These aerosols of human origin, creating more clouds, have a cooling effect, which reduces the warming effect of carbon dioxide (CO2). It's a radiative forcing. Trees are also actors in this machinery, with molecules, such as pinene, released into the air, which also play the role of condensation nuclei.
The current amounts of sulfur dioxide emissions complicate the study of the pre-industrial atmosphere, which was different. This is what a Cloud team did, based on the results of this experiment, to build a simulation of the pre-industrial atmosphere. Their findings, published in the Pnas (and discussed in an article in The Conversation, give more details on previous studies (…).

According to these results (still uncertain, specify the authors), the quantities of aerosols present in the Earth's atmosphere before 1750 have hitherto been underestimated, because the aerosols emitted by trees are much more effective than thought to make clouds. As a result, the cooling effect of industrial aerosols would be lower than expected, by about 27%.
The authors also deduce that limiting aerosol emissions by human activities could reduce their refreshing action. But this decline could be offset by the action of trees, who are only waiting to regain the importance they had in the pre-industrial era. In short, forests are able to help us to limit global warming ... "

So, given this very interesting experience, what about climate change in Cyprus?
I found historical climate data on the World Bank web page
I found two types of information, the accumulation of rain and the average temperature, for the period 1901-2015. Here are the curves:

The analysis of the curves shows us a clear tendency towards the increase of temperatures, but a less clear tendency as regards rainfall. Because if the rains tend to become more rare (the tendency line is clear), they are also much more random. The years of insufficient rains are more frequent, but so are the years of abundant rains. In short, with regard to rainfall, the average years hardly exist anymore.

Obviously, the effects of these reforestations are not clear. There, we can imagine many possible reasons. Personally, I imagine that there is a great deal of responsibility for the age of trees. They are roughly 25 years old (for those who were planted in the 90's), and it's still very young. In addition, their first years have probably not been easy, as in most reforestations in arid regions, with difficulties of survival the first years for lack of rain during the 3 or 4 summer months, and often numerous mortalities of young trees, to which must probably be added parasitic attacks, such as certain insects fond of stunted or precarious health plants.
In short, without having seen them again, I'm sure they have a limited development. It's clear that reforestation is a very long-term job, especially in arid regions.

Unless, in fact, the fall in rainfall, proportionally lower than the increase in temperature, is a sign of a good effect of these reforestations. In this case, the desertification of Cyprus could have already progressed a lot, if this program had not been launched sufficiently early.

That said, and to return to aerosols, this very interesting work, will probably give rise to further research, to study the production of these aerosols by age, development, and especially by plant species. I imagine, as is the case for many things in living beings, that there is an important variability of aerosol production according to the plant species. One day, therefore, a list of species more likely to fight desertification by the abundance of their aerosol production will be developed.

Then humans will face again a difficult ecological choice, like the one I told you in an already old article, about the necessary freshwater savings and their environmental consequences (

Shall we massively plant species for their ability to promote rainfall even outside their origin areas?
What imbalances will we cause in the local biodiversity by the implantation of these species?
Will imbalances caused be preferable to desertification?

The eternal problem of choice ... and its consequences.

While waiting to have to make this choice, the GreenCyprusCom Foundation continues to work for the reforestation of the island of Cyprus, with native species. It's long, slow, laborious and expensive, but necessary.

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