8:38am Wednesday 20th January 2010
By Keith Thomson
Recently the thermometer on the wall of my garden shed recorded -7C. It was perishing and it raised two questions about climate change – was it really happening, and if so, were we humans causing it?
Despite the recent cold weather in the northern hemisphere, in the middle of winter, all the recorded evidence shows that the climate is changing and that this involves warming. The global statistics are very clear and use the average temperature over 30 years, from 1961 to 1990, as the baseline.
From 1850, every year except two was below this average, and yet the recent decades show that the 1980s were warmer by a tenth of a degree, the 1990s by a quarter, and the last decade was almost a half a degree warmer on average, showing that it is not only getting warmer, but it’s doing so at an increasing rate.
The same pattern is seen in Australia, with the 2000-2009 decade being the hottest on record, and 2009 the second-warmest at nearly one degree higher than the 1961-1990 average.
Many of those who question climate change admit that the planet is warming, though they dispute the reason, believing it is due to the sun and cosmic rays.
It’s quite simple to show that while this may be happening on a small scale, it is only marginal, and that the main reason is the way that climate change gases, carbon dioxide, methane, nitrous oxide, and water vapour trap some of the outgoing infra-red radiation in the atmosphere.
Most of these gases, including the necessary oxygen, occur in the lower atmosphere, the bottom six miles-or-so called the troposphere, with the very thin stratosphere above, and we know from the snow on the top of mountains that this makes it cooler higher up.
However, if the increasing temperatures were just due to a stronger sun, then it would be felt throughout both the troposphere and the stratosphere, with extra warmth all the way up.
But satellite readings show that while the troposphere is warming, the stratosphere is cooling and this is because the climate change gases, CO2 and so on, trap the heat low down and don’t let some of it through.
These gases are clearly the key to climate change, and their increase in the last 50 years is because of us, our increasing numbers and our use of fossil fuels.
The figures that should really make us sit up and take notice aren’t cold winter temperatures, but rather the fact that the CO2 in the atmosphere was 371 parts per million in 2000 and 390 in 2009.
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