Short podcasts on nature cannot only lend a fresh new perspective on things you thought you knew about, but also show you how nature works its own way out for everything.. There is one particular section titled, “Questions a five-year-old would ask”. In this series, a question that was answered was how are clouds made.
You would think that is simple! “Water droplets gather around tiny aerosol particles and anything small enough to be floating through the air…enough of that happens and you get a cloud.” But physicists want to know where the aerosol particles come from. It is an important question for climate scientists too who find clouds difficult to model but know it can have important effects on global warming. Scientists thought that man-made emissions, particularly sulphur dioxide were key to the creation of aerosols and lead to the formation of clouds. “But,” says the podcast, “sulphur dioxide may not be the only player. A much more natural process may be conjuring up clouds.”
Scientist Jasper Kirby who has been creating clouds in his chamber at the European Organization for Nuclear Research (CERN) says, “If you were to go up into a cloud and pick out a small droplet, it would be very small. But if you evaporated it you would find a seed inside. That is called the cloud condensation nucleus. It’s a small suspended liquid or solid particle in the air and all air on earth has thousands of these in every cubic centimetre… without them there would be no clouds in the sky. What was previously known was that sulphuric acid was the key. Sulphuric acid is created by the oxidation of sulphur dioxide and 80-90 per cent of the sulphur dioxide in the atmosphere is being produced by burning fossil fuels. So up to now it was thought human activities and human pollution was essential to make small particles in the atmosphere. But we found it was not sufficient. It needs a helper. It needs other vapours to help these particles form. We have been finding out what these vapours are. Pre-industrially, before human activities altered the climate and our conclusion, it was thought that there was much less cloud then, than there is today. The amount is not well known. The only way we can understand how cloudy it was in the pre-industrial period is to measure the basic chemical and physical processes and put those into global aerosol models.”
Kirby describes his experiment which tried to replicate the skies atop a forest as, “The cloud chamber is a large stainless steel chamber, ultra clean and filled with humidified air and selected trace gases that exactly reproduce the conditions and temperature of a chosen part of the atmosphere. We have been assembling the list of key vapours that are essential for particle formation in the air. We did a series of experiments where we only out into the chamber ultra pure air, water vapour, ozone and some biogenic vapours (these are vapours emitted by pine trees and that is what gives the fragrance in pine forests.) We then watched what happens. According to present wisdom no particle should have formed but we found abundant particles forming. In other words, these so called biogenic vapours after oxidation, they form vapours which can form particles readily and they do not need any pollution.”
Forests thus create their own climate. However, Kirby says that it is all speculation about why the pine trees do produce these vapours. They obviously do not do it just to make our walk through the woods exciting and romantic. “Trees cannot run from the sun for shade, but what they can do is emit vapours and create cloud droplets and offer themselves some periodic showers! They are not just helping themselves but all vegetation and inhabitation within the radius of the cloud burst. Trees are definitely helping the atmosphere. It is a beautiful mechanism for trees to control their environment. “
A cautious Kirby says, “The new cloud finding is going to lead to a reduction of climate sensitivity and less warming.”
The take away for today, however, is that it is very exciting to think trees create their own fun by building their canopy of showers and sharing it with their neighbours for greater fun.
sudhamahi@gmail.com
Web link: http://stitcher.acast.com/nature/naturepodcast-26may
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