Ocean Acidification: Effect on Earth Radiation and Global Warming

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CO2 increase causes ocean acidification. Photo by Squaio

Acid levels in the ocean are increasing – but aside from the effect on coral reefs and ocean creatures, why should we worry?

Ocean acidification, due to the increase in atmospheric carbon dioxide, can affect the emission of dimethylsulfide into the atmosphere. This, in turn, may affect the Earth radiation budget and, consequently, speed up global warming.

Ocean Acidification

The amount of carbon dioxide (CO2) emitted into the atmosphere increased in recent years, due to human activities. Some believe that as CO2 is a greenhouse gas, its higher concentration is one of the causes of global warming; others disagree with the theory.  Regardless of carbon dioxide’s atmospheric contributions to global warming, it can also cause damage in the environment due to its acid properties. The higher amount of CO2 in the atmosphere causes a corresponding increase in marine waters, and an increase in the acidity of these waters (decrease of pH value) follows. This phenomenon is known as ocean acidification.

Dimethyl Sulfide

Dimethyl sulfide ((CH3)2S, DMS) is a sulfur-containing organic compound present in marine waters. In this environment, DMS has a biogenic origin; in fact it is formed by living species, such as microalgae and/or phytoplankton. Subsequently these species release DMS into the waters, and from there transfers into the atmosphere (DMS cycle).

Once in the atmosphere, DMS may undergo to a series of chemical reactions, which lead to the formation of sulfur-containing aerosol particles. The aerosol attracts water vapor, which can condense and form clouds. In other words, these particles act as Cloud Condensation Nuclei (CCN).

Earth Radiation Budget

The presence of the clouds in the atmosphere plays a crucial role in the Earth radiation budget. In fact, part of the radiation from the sun reaching the Earth is reflected back by the clouds. The proportion of energy reflected may depend on many parameters, such as the amount of clouds and the characteristics of the clouds themselves. The size and the distribution of water droplets, for instance, have a definite effect.

The atmosphere absorbs energy that clouds do not reflect. Potentially, the higher the quantity of energy the atmosphere absorbs, the higher the atmosphere’s temperature will rise.

Study on DMS Emissions

Considering this, it appears clear that the DMS emission in the atmosphere from the sea is a key element for the Earth’s energy balance and temperature.

For this reason, several studies were performed in this field, to understand the mechanisms of DMS production in the sea, and CCN formation.

On the 25th of August 2013, researchers from the Max Plank Institute for Meteorology (Hamburg, Germany) published an important study in Nature Climate Change. The work was done in cooperation with the Plymouth Marine Laboratory (UK), the Bigelow Laboratory for Ocean Sciences (Maine, US) and the Pacific Northwest National Laboratory (Washington, US).

In this paper, the scientists investigated a connection between ocean acidification and DMS emission.

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