Renewed Interest by Some in Solar Forced Climate Change
It is all very predictable really! The last few years of slightly cooler temperatures in many parts of the globe has some scientists advancing the old arguement that solar forcing is the real trigger for climate changes. A slight cooling of about 0.1 to 0.2 degrees Celsius following on the heels of a 0.8 degree Celsius average world-wide climb in temperatures since about 1900, has once again resulted in some advancing the ideas that it is the sun that is the cause for most all clmate changes.
So, much like the mid 20th Century, the dates 1940's to mid 1970's to be exact, the cooling that has recently set in is being blamed by some on the sun. Further back in time during the time known as the Little Ice Age, many scientists also linked the cooling that took place to a very quiet sun. This was, it is known, a period when the sun displayed few if any sunspots. Low sunspot activity has for some years been equated with a slight decline in solar output. No period in recent times has anything approaching the lack of sunspots that were in evidence during the period 1600 to 1700. The lack of sunspot numbers, known as the Maunder Minimum, saw temperatures, especially those in Europe, drop dramatically.Some solar scientists have estimated that the reduction in solar output was approximately 0.25% (Lean et al). This figure may in fact be too liberal, that is if recent measurements of the sun's output are accurate. If true, then rather than a reduction in output from the sun, another cause may be responsible. And this cause may well be dust. The approximately thirty year period from the late 1940's to mid 1970's was being discussed by some scientists as the start of a serious downturn or cooling of the climate.
The atmosphere was seen by these same scientists as having an increased amount of aerosols that were reducing the incoming amounts of solar radiation. It is known that at times increased aerosol loads in the atmosphere can and do cause cooling. This long ago, despite some increase in industrial activity in Europe, the air pollution produced by the activities of man was still limited.
So if the aerosols did not come from an industrial source, then where? Well some scientists such as Dr. Mike Baillie have suggested the possibilty of dust from an extraterrestrial source, comets. Just as perplexing as the Little Ice Age, the two more recent intervals, that in the mid part of the 20th Century and now the recent three to four year climate downturn are proving to be equally difficult to resolve. It is possible that either a very slight decreases in solar output, or decreased receipt of solar energy because of a dustier atmosphere may cause a forcing that far exceeds what is expected. Figures even as small as a .10% to .25% decrease in solar output could have very important consequences upon such features as ENSO (El Nino and La Nina), the North Atlantic Oscillation and the Pacific Decadal Oscillation. And these are not the only features subject to change, there are countless other oceanic and terrestrial factors that are affected as well. So it is then, here we are in the present day after just a few years of cooling, having the same debate as to the possible cause of climate changes we have witnessed over the past four hundred years or so.
It will be an interesting test of these ideas over the next few years, especially as the earth is just now entering the El Nino phase of ENSO. Usually a time of warming in many parts of the globe, it comes at a time when the sun is quiet and features such as the Pacific Decadal Oscillation are in their cool phase. So will the cooling continue (as believed by the solar proponents) or will the climate resume its warming, as is expected by other climatolgists such as those at the Hadley Climate Centre in England? Time will tell!
