Edexcel: Topic 5, Why are global temperatures changing?

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The atmosphere is a thin layer of gases extending 100km above the Earth's surface.  It has been predicted that without an atmosphere the temperature of the earth would fluctuate between very hot days and very cold nights.  The atmosphere has a key role in keeping the earths temperature suitable for living organisms.

Keeping the earth warm - the greenhouse effect

The sun radiates energy mostly as visible light and the earth absorbs some of it.  The earth warms up and in turn radiates energy back into space as infrared radiation.  Some of this energy is absorbed by gases in the atmosphere, warming it.  The gases in the atmosphere that stop infrared radiation from escaping are called greenhouse gases.  They create the greenhouse effect which warms the earth.

Which are the greenhouse gases?

Not all gases are greenhouse gases.  The 'global warming potential' is a measure of the greenhouse effect of that gas relative to the same amount of carbon dioxide over a given time with carbon dioxide given a value of 1.  Carbon dioxide does not have the largest global warming potential it is so much more abundant than than the more potent greenhouse gases that it has the greatest effect.  Methane is produced by anaerobic decay of organic material in waterlogged conditions (bogs and rice fields) it is also found in landfill sites and in decomposition of animal waste.  It is also produced by animals digestive anzymes and is released when they release gas.  Incomplete conbustion of fossil fuels also releases methane.  Since pre-industrial times the concentration of methane has more than doubled.  methane molecules absorb more infrared radiation than molecules of Carbon dioxide but stays in the atmosphere for less time.  Methaqne emissions could be reduced through better wasre recycling and using it as a biofuel.  When ,ethane burns it turns from one serious greenhouse gas

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