Climate News Network

Science pierces riddle of why clouds form

May 23, 2016, by Tim Radford

Clouds off the Swedish coast: Research is showing what helps them to form.
Image: MagnusL3D via Wikimedia Commons

Clouds that form at sea are key to regulating atmospheric temperatures, and scientists now understand more of the chemistry involved.

LONDON, 23 May, 2016 – Researchers believe they have identified a key player in the ecosystem that makes clouds over the great oceans and helps keep the planet’s thermostat at relatively predictable levels.

These vital cogs in the planetary machine are astonishingly prevalent and utterly invisible and they traffic in potent chemicals on an unbelievable scale.They make the dimethyl sulphide molecules that waft skywards to provide nuclei around which cloud droplets form.

When the sun shines brightly they get to work, and the gas they produce then makes aerosols that seed clouds which reflect sunlight and damp down the planetary temperatures again.

And according to a new study in the journal Nature Microbiology the climate-manipulating microbes are among the simplest life forms of all: the order Pelagibacterales has one of the smallest genomes of all living creatures.

Climate regulation

The knowledge that microbes make molecules of importance to all other living things is not new. That microbes may manipulate the climate and keep temperatures within a comfortable band of highs and lows is a pillar of the Gaia hypothesis, framed decades ago by James Lovelock, who was also one of the first scientists to propose the role of dimethyl sulphide in climate management

It remains a hypothesis. But what the research team led by Steve Giovannoni, a microbiologist at Oregon State University in the US, and others has established is the evolutionary box of tricks that makes planetary chemistry on such a prodigious scale possible.

Marine phytoplankton make a compound called dimethyl-sulfoproprionate or DMSP. They make it on a massive scale: an estimated 10 billion metric tons of the stuff each year.

When the skies are clear, the tiny microbial plants flourish to photosynthesise even more of the compound. And then an important group of Pelagibacterales microbes moves in to take the chemical and cleave it, to release two gases.

Telltale smells

“Everyone knows these gases by their smells”, said Professor Giovannoni. “One of these compounds – dimethyl sulphide or DMS – we recognise as the smell of the sea. The other gas – methanethiol  – makes us think of leaking gas lines. In the atmosphere, dimethyl sulphide oxidises to sulphuric acid, which some scientists think can seed cloud formation and alter heating of the Earth.”

His co-author Jonathan Todd of the University of East Anglia in the UK said: “These types of ocean bacteria are among the most abundant organisms on Earth – comprising up to half a million microbial cells found in every teaspoon of sea water.”

And Ben Temperton of the University of Exeter, UK, another member of the team, said: “The production of DMS in Pelagibacterales is like a pressure release valve. When there is too much DMSP for Pelagibacterales to handle, it flows down a metabolic pathway that generates DMS as a waste product.

“This valve is always on, but only comes into play when DMSP concentrations exceed a threshold. Kinetic regulation like this is not uncommon in bacteria, but this is the first time we’ve seen it in play for such an important biogeochemical process.” – Climate News Network

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