Flying beyond our means – air travel and the environment
Glossary
albedo effect. A measure of how much of the Sun's energy is reflected off an object back out to space compared to how much is trapped in Earth's atmosphere. Snow, ice and clouds have a relatively high albedo so generally reflect more of the Sun's energy back to space which has a cooling effect on the Earth. However, cirrus clouds have a lower albedo transmitting more radiation through to Earth's surface and trapping Earth's reflected radiation. This increases the temperature on Earth.
babassu. A palm tree that grows naturally in Brazil and produces a seed similar to the coconut that is rich in oil. The oil of the babassu seed can be used for cooking, cosmetics and fuel production.
biofuel. Biofuels are fuels such as bioethanol or biodiesel made from plant or (less commonly) animal material and food waste. They are promoted as a renewable energy source without the environmental impacts of fossil fuels. But using annual land-based crops such as sugar cane and corn for biofuel production can be relatively energy inefficient and also competes with food production. Algae have been suggested as an alternative source of biomass which could overcome these problems. For more information see Biomass – the growing energy resource (Nova: Science in the news).
biomass. A general term for material from living things such as plants, animals, fungi, bacteria and food waste. Taken together, the Earth's biomass represents an enormous store of energy. Since biomass can be regrown, it is a potentially renewable resource. For more information see Biomass – the growing energy resource (Nova: Science in the news).
carbon offset. A means of reducing the impact of greenhouse gas emissions. Individuals and companies can purchase offsets to counteract their emissions from transport, electricity use etc. For example, many airlines allow customers to purchase carbon offsets to compensate for the emissions from their plane trip. The offset money is invested in projects that reduce greenhouse gas emissions such as renewable energy, tree planting or energy efficiency projects.
decibels (dB). One tenth of a bel. A unit used to measure sound intensity or power. One decibel is around the smallest change in sound that the ear can detect. Two power levels P1 and P2 differ by n decibels when:
n =10 log10P2/P1
ecological footprint. A measure of how much land and sea is required to support human demands and to absorb any wastes. The ecological footprint can be used as a measure of sustainability by comparing it to the biocapacity of the land (the amount available). Ecological footprints are usually expressed in units of global hectares.
emissions trading. A means of controlling greenhouse gas emissions from organisations and companies. Commonly the government places a limit on the total amount of carbon or greenhouse gases that can be released. It then provides a number of carbon 'permits' equal to the set limit. Companies then compete against each other to buy these permits. For some companies it is cheaper to develop cleaner production technologies (or reduce emissions) than to buy the permits.
fermentation. The chemical conversion of carbohydrates into alcohols or acids by microorganisms. Often fermentation refers to the conversion of sugar to ethanol and carbon dioxide by yeast according to the following equation:
This type of anaerobic fermentation is used for production of ethanol for beverages and fuels as well as to produce carbon dioxide as a raising agent in cooking.
Fisher-Tropsch process. A process that can be used to convert coal, natural gas, and low-value refinery products into fuel. Fischer-Tropsch fuel is colourless, odourless, low in toxicity and has fewer emissions than conventional diesel. The Fischer-Tropsch reaction converts carbon monoxide and hydrogen, in the presence of a catalyst, to high molecular weight hydrocarbons.
fuel cell. A cell that converts energy from chemical reactions directly into electrical energy. A simple fuel cell 'burns' hydrogen in a flameless chemical reaction with oxygen to produce electricity. For more information see Fuelling the 21st century (Nova: Science in the news).
Jatropha. A group of plants, shrubs and trees that can grow in dry, less productive land. Jatropha curcas seeds contain up to 40 per cent oil which can be used for biofuel. Because Jatropha grows on land of lower productivity, it is sometimes considered to be a biofuel that does not compete with food growing land and resources. However, commercially viable production of Jatropha can still use productive land, water and fertilisers. Jatropha curcas is considered a potential weed in Australia.
Kyoto Protocol. This working agreement of participating countries commits developed countries to reduce their emissions of six greenhouse gases by at least 5 per cent of 1990 levels by 2012. The Kyoto agreement became legally binding on 16 February 2005 when 132 signatory countries agreed to strive to decrease carbon dioxide emissions. More information can be found at the official The Kyoto Protocol site.
radiative forcing. A measure of the effect of a climatic factor (eg, greenhouse gases, cirrus cloud) on the balance of incoming and outgoing energy in the Earth-atmosphere system. This can be used to assess the factor's impact on climate change. Positive forcing tends to warm Earth's surface while negative forcing has a cooling effect. Forcing values are expressed in watts per square metre (Wm-2).
subsonic. Movement at less than the speed of sound. Most aircraft travel at subsonic speeds.
supersonic. Movement at greater than the speed of sound. Supersonic aircraft include military aircraft and Concorde (which ceased operation in 2003). At these fast speeds, air ahead of the plane is compressed, shock waves form and drag increases. Supersonic aircraft often fly at higher altitudes where the density of air is lower to reduce drag.
transesterification. A process that converts animal fats or more commonly plant oils to biodiesel. The oils (or triglycerides) are reacted with an alcohol such as ethanol in the presence of a catalyst such as sodium hydroxide. This converts the triglycerides to esters (the biodiesel) and glycerol. The biodiesel produced is used in ground transport but usually cannot be used as an aviation fuel due to its high freezing point.
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Posted February 2009.