Why is the temperature unchanging?
It seems probable that 2010 will be in terms of global annual average temperature statistically identical to the annual temperatures of the past decade. Some eminent climatologists, such as Professor Phil Jones of the University of East Anglia’s Climatic Research Unit, suggest the global annual average temperatures haven’t changed for the past 15 years. We are reaching the point where the temperature standstill is becoming the major feature of the recent global warm period that began in 1980. In brief, the global temperature has remained constant for longer than it has increased. Perhaps this should not be surprising as in the seven decades since 1940 the world has gotten warmer in only two of them, and if one considers each decade individually the increase in temperature in each has barely been statistically significant. Only when the warming in the 1980’s is added to that of the first half of the 1990’s does the change exceed the noise in the system.
But what does this 10-15 year temperature standstill mean?
For some it means nothing. Ten to fifteen years is too short a time period to say anything about climate they would argue pointing out that at least thirty years is needed to see significant changes. They also point out that this decade is warmer than the 1990’s and the 1990’s were warmer than the 1980’s and that is a clear demonstration of global warming.
I know few who would argue that we don’t live in the warmest decade for probably a millennium and there are now few who would argue that the period of warming ended about a decade ago leaving us with a plateau of annual temperatures. However, there is information in the decadal structure of the present warming spell that can say something about what is happening.
All would agree that the global climate is changing constantly within certain limits due to the combination of anthropogenic and natural factors. The manmade factors are postulated to be responsible for climate change whereas the natural factors are taken to be agents of climate variability. The additional greenhouse effect caused by mankind’s emissions is a unique climatic forcing factor in that it operates in one direction only, that of increasing the temperature. If that is the case then something has been cooling the planet. We can say something about what is cooling the earth. The key point about the greenhouse effect in this context is that it depends upon one factor – the concentration of greenhouse gasses in the atmosphere.
In the past decade the atmospheric CO2 levels have increased from 370 ppm to 390 ppm and using those figure the IPCC once estimated that the world should have warmed by at least 0.2 deg C. The fact that the world has not warmed at all means that all the other climatic factors have had a net effect of producing 0.2 deg C of cooling.
But there is more. The counterbalancing climatic factors have not only compensated for the postulated AGW at the end of the decade they have kept the global annual average temperature constant throughout the past 10-15 years when the AGW effect wants to increase it. The key point that makes this constancy fascinating is that for every value of CO2 there is an equilibrium temperature that is higher the greater the concentration of CO2 in the atmosphere. In other words, the higher CO2 concentration at the end of the decade exerts a stronger climate forcing than at the beginning of the decade.
This makes what has happened in the past decade all the more remarkable. Because the greenhouse effect wants to force the temperature up which in the absence of a cooling influence is what would have happened, the fact that the temperature has remained constant indicates that whatever has been cooling the planet has had to increase in strength at precisely the same rate as the CO2 warming in order to keep the temperature a constant straight line.
This means that for 10-15 years the combined effect of all the Earth’s climate variability factors have increased in such a way as to exactly compensate for the rise in temperature that the increased CO2 would have given us. It is not a question of the earth’s decadal climate cycles adding up to produce a constant cooling effect, they must produce an increasing cooling effect that increases in strength at exactly the same rate as the enhanced greenhouse effect so as to keep the earth’s temperature constant.
Can it really be the case that over the past 15 years the sum total of all the earth’s natural climatic variables such as changes in solar irradiance, volcanoes, the Pacific Decadal Oscillation, the North Atlantic Oscillation, and the Arctic Oscillation, all of which can change from cooling to warming over decadal timescales, have behaved in such as way as to produce a cooling effect that is the mirror image of the warming postulated by the anthropogenic climate forcings from CO2 and other greenhouse gasses, from the changing water vapour, from tropospheric ozone, and from a clearing aerosol burden?
Am I alone in thinking that in the dynamically changing global climate this looks like a contrived, indeed scientifically suspicious, situation?
Is it a coincidence that the human and natural factors balance out this way? I am reminded of a line written by Agatha Christie: “Any coincidence”, said Miss Marple to herself, “is always worth noticing. You can throw it away later if it is only a coincidence.”