Geoengineering: Can it help our planet keep its cool?

Glossary

aerosols. A suspension of fine solid particles or liquid droplets in a gas. Aerosols can be produced naturally (eg, smoke or clouds of volcanic ash) or man-made (eg. as a result of the emission of dust or reactive gases that can form particles in the atmosphere).

albedo. The fraction of incoming energy from the Sun that is reflected off an object back to space. Snow, ice and clouds have a relatively high albedo (reflectivity), typically around 80%, and so generally reflect more of the Sun's energy back to space, thus tending to have a cooling effect on the Earth. Oceans and vegetation on the other hand, have low albedo, typically less than 20%, thus tending to increase the temperature on Earth.

algae. A large group of simple organisms, ranging from single celled phytoplankton to the larger seaweeds. Like plants they are photosynthetic, but they generally have a simpler structure than plants. Algae are found in water as well as on land.

carbonate. A compound containing the anion CO32-, such as calcium carbonate (CaCO3) in limestone or magnesium carbonate (MgCO3) in dolomite.

carbon credits. A means of reducing the impact of greenhouse gas emissions by establishing a trading scheme that places a value of carbon emitted. Individuals and companies can purchase carbon credits to counteract their emissions from transport, electricity use etc. For example, many airlines allow customers to purchase carbon credits to compensate for the emissions from their plane trip. The money is invested in projects that reduce greenhouse gas emissions such as renewable energy, tree planting or energy efficiency projects.

ocean upwelling. Movement of deep oceanic waters to the ocean surface. This occurs naturally bringing cold, often nutrient-rich waters to the surface which can stimulate algal blooms. Artificial ocean upwelling – by installing vertical pipes in the ocean – has been proposed as a form of geoengineering that would remove carbon dioxide through increased algal photosynthesis. However, since deep water also contains large amounts of dissolved carbon dioxide which is released when it is brought to the surface and warmed, the extent to which this idea might work is still under review.

phytoplankton. Microscopic, photosynthetic algae that live in water. Plant-like plankton.

pyrolysis. A process which involves heating biomass to drive off volatile matter, leaving behind a black residue known as charcoal. Pyrolysis can be used to produce ‘biochar’ from waste plant matter as a means of removing carbon dioxide from the atmosphere.

stratosphere. The layer of atmosphere that lies about 15 to 50 kilometres above the Earth's surface. The concentration of ozone peaks within the stratosphere at an altitude of about 35 kilometres. This is referred to as the ozone layer. There is exchange of air between the stratosphere and the lower atmosphere, so the ozone layer stays in position.

weathering. The breakdown of rocks due to exposure to the atmosphere, weather or biological activity. ‘Physical weathering’ occurs through mechanical processes such as wind abrasion or expansion and contraction with temperature change. ‘Chemical weathering’ occurs through chemical reactions with rock minerals. When living things (eg, tree roots, lichens) cause rocks to break down it is called ‘biological weathering’. For more information see Weathering (The Geological Society, UK).

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Posted February 2010, edited August 2012.