Tiny marine organisms could be affecting the Earth's climate, cooling our world, environmentalists believe. These sea creatures are responsible for creating clouds which block sunlight, reducing the amount of light striking the surface of our world.
Each summer, cloud droplets collect over the Southern Ocean, which circles Antarctica. Researchers have found that this effect is driven, in part, by the tiny creatures living in the ocean.
Marine phytoplankton multiply during summer months due to increased sunlight, releasing microscopic particles called aerosols into the atmosphere. Investigators found this process nearly doubles the concentration of water droplets in the air above the water body. This additional concentration of water causes clouds to grow in brightness. This results in an increase in the amount of sunlight reflected back to space, decreasing temperatures on Earth.
"The clouds over the Southern Ocean reflect significantly more sunlight in the summertime than they would without these huge plankton blooms. In the summer, we get about double the concentration of cloud droplets as we would if it were a biologically dead ocean," said Daniel McCoy, a doctoral student in atmospheric sciences at the University of Washington.
Cloud formation is a challenging field of study, leaving many questions unanswered for climatologists. Some investigators had previously theorized that plankton and other microorganisms could play a role in cooling the globe, although the effect had not been documented until now.
In 2014, researchers began analyzing data collected by NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instrument, which was launched into space in 1999 in an effort to measure the size of water droplets in the atmosphere around the planet. Water droplets in the atmosphere, including those within clouds, can range in size from smaller than one-hundredth of an inch to a half-inch in diameter. They looked at NASA satellite data for clouds over the parts of the Southern Ocean that are not covered in sea ice and have year-round satellite data.
Using satellite data, researchers found droplets are smaller in size during summer months compared with other times of year. This finding was unexpected, as the ocean is calmer during warmer months, sending less moisture into the air. This finding led researchers to investigate marine life as a potential driving force responsible for clouds becoming brighter.
This new study could help researchers learn more about the way cloud formation affects, and is affected by, a changing climate.
"Phytoplankton in the oceans are a really important source for cloud-droplet-forming aerosols in remote marine air, and we can see the effect they have on clouds is big. Southern Ocean clouds play a large role in the global climate, and hopefully this will help us get a better sense of how sensitive the Earth is to greenhouse gases," said Susannah Burrows from the Pacific Northwest National Laboratory.
Analysis of how plankton and other sea creatures can alter climate was detailed in the journal Science Advances.