Readers letters
GHL Glover (PE On-line Letters) appears to have rummaged in the climate change sceptics toolbox to find his reasons for rejecting the proposition that global warming is occurring. None of the reasons he cites appear to be supported by mainstream, peer reviewed science.
In the often misquoted BBC interview, Professor Jones’ reply to the question:
“Do you agree that from 1995 to the present there has been no statistically-significant global warming” was:
“Yes, but only just. I also calculated the trend for the period 1995 to 2009. This trend (0.12C per decade) is positive, but not significant at the 95% significance level. The positive trend is quite close to the significance level. Achieving statistical significance in scientific terms is much more likely for longer periods and much less likely for shorter periods.”
Not being a statistician, this statement seems to imply that there is a greater than 5% probability that temperatures due to random variations and Jones has less than 95% confidence that the trend is genuine.
Urban heat islands are often cited as a source of inaccuracy in global temperature readings. However, Peterson (Journal of Climate Volume 16, No 18 (September 2003)) found no difference between temperature readings in urban and rural areas across the USA.
Glover’s assertion regarding arctic sea ice does not appear to be supported by the National Snow and Ice Data Center (NSIDC) at University of Colorado at Boulder. The ice extent in 2007 was a record low and it recovered slightly in 2008. This year has seen the ice extent at its second lowest for August, third lowest for September, third lowest for October and second lowest for November, based on the period since satellite monitoring began. These observations do not appear to indicate signs of a recovery. The NSIDC also report that multiyear ice appears to be melting, leaving the surface ice thinner than normal.
It is true that the relationship between atmospheric concentrations of CO2 and temperature are not linear. I understand that doubling the CO2 concentration will result in a temperature rise of up to 1.2 deg C. This increase in temperature will result in more water vapour in the atmosphere, further increasing the greenhouse gas effect (positive feedback). If the water vapour forms more clouds, these could reduce the temperature increase by reflecting incoming sunlight (negative feedback), or could enhance the temperature increase by reflecting more outgoing radiation back to the surface (positive feedback).
It is true that, historically, there have been several periods when the planet’s climate has changed; these have been caused by natural phenomenon, including changes in solar activity, orbital variations and massive volcanic activity, none of which have been reliably associated with the present warming.
The statement that climate scientists in the 1970’s were predicting a new ice age is not supported by a search of peer reviewed science journals. A literature and citation search by Peterson for the period 1965 to 1979, found 7 articles predicting cooling, 19 articles with a neutral position and 42 predicting warming. To judge the influence of the articles, the search was extended to citations for the period from 1965 to 1983, which found 325 for cooling, 424 neutral and 1,958 for warming.
As a final point, I actually share Glover’s concern regarding geo engineered solutions to global warming, but for different reasons. In addition to the probable increase in average surface temperature, increasing the atmospheric concentration of CO2 also causes acidification of the oceans with unpredictable effects on ocean bio-diversity that are unlikely to be beneficial to us. If we do adopt geo engineering solutions, they must be reversible and preferably act on the primary problem by reducing atmospheric CO2.
Robin Trow