There are recent articles about hand-wringing on presenting the Global Surface Temperature Data in the upcoming IPCC report. Since I am not a climate scientist or modeler, I should keep my mouth shut, and leave the presentation to the experts and international community. But I have studied fluctuating data and statistical fallacies, and have the freedom to comment because I am not an expert or involved in the IPCC report. Certainly that puts me in a category no worse than many climate change deniers.
First, I will make a physics observation about the use of surface temperature data. If the atmosphere was all water and condensed, it would form a layer of about 30 feet deep around the earth. The specific heat of sea water is about 2.5 times that of the atmosphere for the same weight. Since the temperature will equilibrate, 2.5 times as much heat will be absorbed by the same weight of sea water. The mixing layer of the oceans for temperature varies with season and location. Roughly, it is about 90 feet in the Northern Hemisphere and 180 feet in the Southern Hemisphere in their peak seasons. Taking the size ratio of 3 to 9 times the 2.5 specific heat, means that 8 to 23 times as much heat will be absorbed by well mixed ocean layers. Ocean temperature increases go down to 800 meters or a half mile or 2,500 feet. With the factor of 2.5 specific heat ratio, that is about 200 times the heat capacity of the atmosphere. The latest IPCC report says that over 90% of radiative forcing heat has gone into the oceans .
Taking only the surface, where weather and surface heating occurs as well as ocean atmosphere interactions is even dicier than using the whole atmosphere. This doesn’t mean that surface temperature doesn’t have some significance, but interpreting every glitch in it is not a meaningful interpretation of its relevance to global planetary heating. Yet, since we live on the surface, it is the most meaningful for our lives.
The surface temperature curve and five year average from the Goddard Institute for Space Studies through 2012 is at http://data.giss.nasa.gov/gistemp/graphs_v3/Fig.A2.gif
(I actually had a wonderful summer course in 1961 in atmospheric physics at Columbia University taught by Prof. Robert Jastrow and members of GISS.)
Examining the yearly temperatures, everyone has been struck by the large El-Nino caused upward fluctuation in 1998 of about 0.2 degrees C over its surrounding years. To make misleading statistical claims, it is convenient to have the privilege of picking your starting year. Deniers usually pick 1998, and then talk about the last 15 years as being significant, where there has not been dramatic change after that. To get around the embarrassment of looking to the amazing jump over earlier years, or even for the two years following 1998, they just claim that warming has ceased or is even reversing. So beside the freedom of choice of their starting year, they are also exercising the freedom to create a myth about the unknown future record.
However, I just celebrated by 20th wedding anniversary, so I had better take 1993 as the significant starting point for my new life. In 1993, the temperature anomaly was at a significant low fluctuation, and the current average is not 0.2 degrees C greater as in 1998, but double that at 0.4 degrees C greater than in 1993. So your result all depends on the freedom of choosing your starting point. The difference between the starting points is just the five year distance between 15 years ago and 20 years ago, yet the increase is doubled.
Climate change believers have always cited the last decade in terms of how many years are in the top ten of all time, to avoid the argument around continued rise. It is interesting to note that the downward fluctuations since 1998 have not even gotten halfway back to the 1996, 1999, or 2000 year figures of a 0.5 degree C anomaly.
It also is important to notice the green point and error bars on the determination of the global temperature are plus or minus 0.05 degrees C. If this is a standard “1-sigma” distribution, about two thirds of determinations fall within these error bars of the true result.
The surface temperature curve has all sorts of serious fluctuations, yet none has yet signified a long term downturn in warming.
Several explanations have been given for the current trend, such as some volcanic cooling, solar fluctuations, many La Niñas, and ocean mixing of heat. Lets see if the IPCC can evaluate these and decide between them.
As a possible future scenario, imagine that in the next year or so that the temperature takes another 0.2 degree C jump. Will the deniers quit? (I’m kidding of course.) They will just say it is a one year fluctuation that will go away. If it persists, they will point out, as I have, that you can prove anything by choosing your starting point arbitrarily.
