Atmosphere Daily Earth Science Repost

Liquid clouds or ice clouds: Geotagged bacteria genes help to decide

Understanding climate change requires accurate climate models. However, models are only as good as the data fed to them. Clouds are a critical component of climate models because they reflect sunlight, but some types of clouds reflect more sunlight than others. Geo-mapping of bacteria genes helps scientists figure out what kind of clouds to expect.

What’s in a cloud?

Clouds form through moist air rising in the atmosphere until temperatures are low enough for the moisture to condense into liquid drops or ice crystals. So, clouds consist of water droplets, ice crystals, or a combination of the two. But the two end members, ice clouds and liquid clouds, have very different properties. Ice clouds have a lower albedo and thus reflect less sunlight. They also don’t last as long as liquid clouds and produce more precipitation.

When moist air rises high enough to condense, the water droplets or ice crystals form around small particles in the air. However, what happens next depends on the particle. Some types of particles are prone to ice crystal nucleation, and others encourage the formation of water droplets. 

These atmospheric particles come from many sources, both natural and human-made. Dust, pollen, bacteria, sea spray, and particulates from cars and power plants all form these tiny bits floating around in the wind. But terrestrial particles like dust tend to seed ice clouds, and marine particles favor liquid clouds.

Climate researchers know that most climate models predict too many ice clouds over the Southern Ocean that rings Antarctica. To understand why they turned to the lowly bacteria.

Bacteria: geotagged genes

Bacteria fill the atmosphere and travel at the mercy of the wind, drifting thousands of miles around the globe. But their DNA is a geotag, traveling with them wherever they go. Because bacteria are well-studied, the bacteria’s DNA reveals its place of origin. This DNA-tag provides a way to map the geographical source of bacteria and other particles that control cloud formation.

Geo-mapping bacteria sources from the Southern Ocean revealed that there were almost no land-based bacteria in this region’s atmosphere. The bacteria were all marine sourced and prone to forming liquid clouds. These observations explain why the Southern Ocean has more liquid clouds than models predict. Previous climate modeling assumed wrongly that the atmospheric particle composition over the Southen Ocean was similar to the northern hemisphere, where significant land-sourced particles cause the formation of ice clouds.  

The revised particle source assumptions result in more accurate predictions for liquid clouds over the Southern Ocean.  This revision also affects projections of warming from solar radiation, frequency of rainfall, and the life-span of individual cloud formations. Ultimately, more accurate models provide better long-range predictions of future climate change.


We caught bacteria from the most pristine air on earth to help solve a climate modeling mystery (By Kathryn Moore, Jun Uetake, Thomas Hill; The Conversation) –  Also:

Feature Image: Clouds (Modified) – By Yamato – Own work, CC BY-SA 3.0,

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.