On cloud nine
algae , bacteria and fungi play an important role in cloud formation, helping in condensation of water droplets, a process known as nucleation, under which, water molecules adhere to small microscopic particles. Bill Hamilton, biologist at Oxford University, uk , and Tim Lenton, biologist at East Anglia University, uk , hypothesise that in order to facilitate their own dispersal, some microbes have evolved methods of seeding clouds ( The Economist , Vol 346, No 8061).
In what they call the travel-by-cloud hypothesis, the biologists attempt to explain one such interesting phenomenon about algae. In order to get a piggy-ride on the clouds, the microbes should be able to leave the ground, facilitate the seeding of clouds while enduring the intense sunlight, and come back to the ground in the rain drops. This process starts with a moderate breeze making them airborne and sweeping them upwards. On a calm day, some algae create their own wind, according to Hamilton.
He suggests two mechanisms through which the microclimate is changed by algae. Firstly, algae floating on the surface of warm water modify the microclimate by absorbing the sunlight, and in doing so, warming the water surface as well. Air absorbs some heat from the warm water, which leads to a change in air pressure and mini thermals (rising columns of warm air), making the algae airborne. Secondly, some algae change the microclimate by releasing a gas known as dimethyl sulphide ( dms ).
dms gets oxidised into sulphate, which is one of the primary sources of cloud condensation nuclei