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Dot Points on the Science of Climate Change

  • The climate system acts in some ways like a complex, powerful but slowly responding amplifier with sensitive inputs.


  • That is, huge changes in the climate can be initiated and reinforced by small changes in circumstances. Today, the most important such change is the injection into the atmosphere of extra carbon dioxide (CO2).


  • Robust data from Antarctic ice cores document atmospheric CO2 levels and air temperatures from a hugely changing climate. During the past 400,000 years there were four great ice ages of which the last ended about 10,000 years ago.


  • The huge changes included sea-level rises of about 120 metres, with sea water locked up in the great land-based ice sheets and then released.


  • All this was part of a sensitive response to a small primary input; small changes in the Earth’s tilt and orbit. Increases in solar insolation (heating by the Sun), mainly in the high latitudes of the northern hemisphere, resulted in melting of ice sheets and warming of marine waters, triggering the release of CO2 and methane previously locked up in marine sediments.


  • Any gas in our atmosphere with more than two atoms in each molecule such as CO2, will act as a greenhouse gas, trapping heat from the Sun.


  • If we had no greenhouse gases in our atmosphere, the Earth’s surface would be roughly 30° C colder.


  • The variation in temperature between now and the coldest period of an ice age was much less than this (about 10°C).


  • CO2 is not the only greenhouse gas but is the most important due to its great chemical stability and the fact that it does not condense in conditions we are ever likely to experience on Earth (unlike water).


  • We know that (until the industrial revolution) the levels of CO2 in the atmosphere have varied over the last 400,000 years between about 180 parts per million by volume (ppmv) at the end of an ice age, and about 280 ppmv just afterwards.


  • Since the industrial revolution, during which time we have been burning more and more fossil fuels, injecting CO2 into the atmosphere, the level of CO2 has risen above 400 ppmv (412 ppmv) and the rate of rise is still increasing.


  • This is causing global warming, which is likely to be further amplified through positive feedback mechanisms that can cause ‘runaway climate change’.


  • In the early stages of the warming climate, extreme weather events will be more frequent and more severe in all forms – hotter, colder, drier, wetter, etc.


  • Variability of magnetic phenomena on the Sun, such as sunspots, has a minute effect on the Earth’s climate (about 0.1°C in 250 years).


  • If runaway climate change were allowed to take hold, then we could be heading towards a much warmer, stormier climate with no ice sheets and a sea level about 70 metres higher than at present. Positive feedback mechanisms which could result in this include methane release from permafrost and increased absorption of heat from the sun as ice sheets retreat.


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