Tuesday, May 15th 2012, 1:03 PM EDT
Variations in ozone in the lower stratosphere could be the main reason for the global warming seen in the past few decades, according to a new paper in press at the Journal of Atmospheric and Solar-Terrestrial Physics. It is claimed that the new model is capable of explaining 82% of the total Earth temperature variability.
Nataliya Kilifarska of the National Institute of Geophysics, Geodesy and Geography, in Sofia, Bulgaria, presents a powerful analysis that confirms a strong relationship between stratospheric ozone and land air temperature.
Updated below with comments from Stephen Wilde
She says that this highly significant relation raises the question about the nature of the influence, and suggests that it operates through control over the temperature and humidity in the upper troposphere/lower stratosphere by ozone variations. The ozone variability itself is initiated by variations in Galactic Cosmic Ray (GCR) intensity, which produces O3 at these levels. GCRs are in turn mediated by the Sun. An important point is that the high effectiveness of this mechanism is due to the fact that small fluctuations of the H2O vapour (in the most arid regions of the troposphere) influences the radiation balance of Earth in a highly non-linear way meaning small changes in the Sun results in a big change in Earth’s temperature.
One of the major problems when considering the influence of the Sun on climate is that the Sun’s variation in output is too small for it to have a significant climatic effect when compared to that estimated due to greenhouse gasses.
Such reasoning prompted another way of looking at the problem. What if the solar influence on climate was an indirect one mediated by other agents? What if the relationship between the Sun and those other agents was non-linear? When thinking along these lines Kilifarska says it becomes clear,”…why the linear statistical methods are powerless in detecting the solar signal in climatic time series.”
She analysed using non-linear regression techniques the annual values of Northern Hemisphere land air temperature anomalies (CRUTEM3v), Sunspot numbers for the period 1900–2011 and the longest time series of the total ozone from Arosa, Switzerland for the period 1926–2011.
Cause Not Effect
Stratospheric ozone variations during the last 30–40 years have shown a severe decline until the middle of 1990s, with a slight recovery since.
The solar influence on the total ozone (via the 11 year cycle in the solar radiation intensity) is estimated to be no more than 2–3%. The most variable part of solar irradiance (UV band) is absorbed in the upper and middle atmosphere, which means that the reasons for the lower stratospheric ozone variations were unknown. Galactic Cosmic Rays are bombarding the lower stratosphere and troposphere though there are relatively few studies examining the ozone sensitivity to the GCR’s intensity, some of them contradictory.
A key change of emphasis regards the cause of upper tropospheric water vapour variation. The IPCC states that the global warming is due to the increased concentration of greenhouse gases, but because there is no mechanism known which could increase the amount of the upper tropospheric humidity (which has been observed in recent decades) the IPCC said that the water vapour increase is a response of the climate system to the warming initiated by greenhouse gases.
Kilifarska looks at this another way. Rather than being a consequence of global warming she speculates that changing water vapour in the troposphere might be a cause of it.
There are many experiments and models that suggest a high sensitivity of climate to the lower stratospheric ozone density. Recently it was noted that the O3 decrease during the last third of 20th century was accompanied by a cooling of the lower stratosphere and an uplifting of the tropopause. Also in 1997 Spencer and Braswell pointed out that outgoing long-wave radiation (OLR) is very sensitive to the humidity fluctuations in the driest upper troposphere. Thus a small enhancement of the upper tropospheric humidity leads to a non-linear decrease of the OLR and consequently—to a greenhouse warming of the Earth’s surface.
Kilifarska suggests that variations in lower stratospheric ozone (influencing the temperature and humidity near the tropopause) appears to be a factor altering the Earth radiation balance and the greenhouse warming of the planet. Although more investigations are needed, this work offers a significant new point of view in understanding the factors affecting climate variability.
Kilifarska’s model does what all good models do, it makes predictions. Most other forecasts of near-future temperature trends say that most of the years in the next 5 years or so will break temperature records, even though the global annual average temperature has been statistically unchanged for the past 15 years. Her model predicts cooling over this period, and at first sight seems to be more in line with real climatic data that IPCC forecasts. At the right of her Fig. 4 (above) are her predictions showing a decrease of the land surface temperature until the end of the current decade.