Trouble in the Greenhouse?

Finally, media attention has focused on the important shifts in climate that have been affecting our planet for the past number of decades. The principal reason for the warming and other changes in climate appear to be largely in response to increases in greenhouse gases. Man is being blamed for adding to the atmosphere copious amounts of carbon dioxide and other greenhouse gases, which include methane and nitrogen oxides. Interestingly, some greenhouse gas is of benefit to most life on Earth, for without them, rather than the overall average temperature of 15 degrees Celsius, the planet would be about thirty to thirty-five degrees colder. However, the beneficial level of greenhouse gases is rapidly being exceeded, with the result there may be trouble brewing in the greenhouse. Throughout Earth history temperatures have ranged from approximately 5 degrees Celsius colder during full glacial conditions to as much as 15 degrees Celsius warmer at times such as when the dinosaurs roamed the Earth around one hundred million years ago (1). During earlier times, more than a billion years ago, our planet was subjected to energy output from a much weaker sun. Compensating for the lower solar output was a much higher amount of carbon dioxide residing in the planet’s atmosphere. Gradually, as life began to flourish, and formation of the oceans and carbonate rocks took place, increasingly more carbon was removed from the Earth’s atmosphere. While all this was occurring the sun’s energy output was gradually increasing.

As far as life in the present day is concerned, the situation in our small part of the solar system can be likened to the well known children’s nursery rhyme – Goldilocks. The Earth’s two neighbouring planets Venus and Mars tell the story of Venus, an environment too hot for life, and the other neighbour Mars, a place too cold for most, if not all life. The Earth on the other hand is just right for life. Venus was once regarded as Earth’s sister planet, in that it is close to the same size and really is not that much closer to the sun. Actually though, the approximately forty-eight million kilometres that Venus is closer to the sun has dire consequences. Although only receiving 1.9 times the amount of energy as our planet, the extremely dense atmosphere makes the conditions on Venus inhospitably hot. Carbon dioxide dominates the atmosphere of Venus, an atmosphere that is nearly one hundred times more dense than that of Earth. The very large amount of carbon dioxide along with the planet Venus makes being in closer proximty to the sun, result in what is called a “super greenhouse” (2). Temperatures with this “run away greenhouse” reach 475 degrees Celsius on average. Mars on the other hand, is at least presently, much too cold to be very conducive to most, if not all life. Approximately 225 million kilometres from the sun, Mars also does have an atmosphere, although it is very thin, just 1% the volume of that of Earth. Still, as the Martian atmosphere is almost entirely carbon dioxide, once again the nature of this gases greenhouse properties are brought into play. Despite the Martian atmosphere being warmed by a few degrees Celsius, the planet must still endure a bone chilling –120 degrees Celsius at the poles and only a slightly less cold –75 degrees Celsius towards the mid latitudes (4). A look now to the “just right” planet, Earth. Located about 150 million kilometres from the sun, the Earth has a very different atmosphere than does Mars or Venus. Two gases dominate, with nitrogen comprising about 78% and oxygen 20% by volume, this in an assumed dry atmosphere. Also comprising relatively small amounts by volume are the greenhouse gases, the most important of which is water vapour in terms of the warming provided. Water vapour is not only important for moderating the climate, but for providing life-giving precipitation as well. The presence of water vapour in the atmosphere varies from 0.5% to 1.5%, though amounts can reach as much as 3% in the tropics (5). Water vapour is the most effective absorber of outgoing longwave radiation. This explains why a desert environment (lacking in water vapour), even one quite close to the tropics can experience a diurnal temperature range of thirty degrees Celsius. Along coastal margins in the tropics (where moisture is much more prevalent), in direct contrast to the desert environment, the diurnal range is hard pressed to exceed five or six degrees Celsius

The preceding discussion tells us that even very small changes in gases such as water vapour can have significant ramifications upon the climate. The second most important greenhouse gas here on Earth, and becoming more so, is carbon dioxide. Comprising only about .04% of the Earth’s total atmospheric volume, it is surprising that so little can be so influential. It must be emphasised that the source of some of the scepticism held by portions of the scientific community as to the perceived role of carbon dioxide, originate from not only there being relatively little CO2 in the atmosphere, but also the rather small increases since man has been using fossil fuels. Another development that has raised the sceptic’s ire is what is perceived as a 0.1 to 0.2 degree Celsius cooling that has occurred over the past few years. Some of these same sceptics go on to say that the climate shifts we have been witness to are the result of changes in output from our sun. As already mentioned in a previous submission at this website, the sun’s variation in output has been estimated as about 0.1% throughout its eleven year solar cycle. Also, as also mentioned, an approximately 0.25% decrease in the sun may take place over longer intervals, such as during the Little Ice Age.These are times when there are few, if any, sunspots evident on the sun’s face.  Periods such as the Maunder Minimum (1645-1715), and also the Dalton Minimum (1810-1830), were two such times when the sun had few if any sunspots. However, a quite recent revelation is that our sun’s output may not vary by as much as was previously believed just a few years ago. As was also discussed previously, the estimates of solar variation were based primarily upon nearby sun-like stars. But now as a sufficient number of observations have become available, it is evident that the sun only varies by about one-quarter as much as was previously thought. This would seem to suggest that the sun may not play as large a role as was once perceived. This, as well as the possibility expressed earlier, that even the Little Ice Age may not have been initiated by a less active sun, may place some doubt as to the importance of the sun in triggering short-term climate changes.

One last test that has satisfied me as to the main cause of the recent climate changes has involved a close examination of four long-term climate stations scattered throughout the northern hemisphere. The stations located in 1) Oxford, England (1854-2008), 2) Stornoway, Scotland ( 1875-2008), 3) Sable Island, Nova Scotia, Canada (1898-2008), and 4) Agassiz, British Columbia Canada (1895-2008) have been analyzed as to their long-term temperature trends. The periods concentrated upon were a supposed solar minima that extended from 1903-1913, and also a more lengthy solar maximum that covered the interval from the 1950’s presumably to around 2000. The period 1903-1913 was inconclusive for the two North American stations. Only the two British Isle stations displayed a tendency for some cooling. Whether this can be attributed to reduced solar activity, it is not possible to say, as any number of other causes may be at play instead. And with respect to the later period, 1950 to near 2000, the only upward trend appears to take hold during the mid 1970’s at the earliest, and this is more likely due to an anthropogenic cause.

My conclusion therefore, is that the most recent climate warming, as well as many other shifts in weather patterns are due to the inexorable rise in greenhouse gases. The increase began about 1850 when there was approximately 280 ppm. was present in the atmosphere. Steadily rising, the concentration has become 315 ppm by the mid 1950’s and 385 ppm. at present, and is still increasing. The temporary hiatus from warming that I believe we are seeing will, as the Hadley Climate Centre also contends, soon be replaced by the renewed onset of warming and all the problems it will bring. Stay Tuned!

References:

  1. Steven H. Schneider, Global Warming, p.37.
  2. Doug Macdougall, Frozen Earth, p.235.
  3. Jeffrey S. Kargel, Mars – A Warmer Wetter Planet, p. 101.
  4. Steven H. Schneider, Global Warming, p.18.
  5. Hubert Lamb, Climate, Past, Present and Future, p. 46.