Studying effects of ozone depletion on global warming

Recent assessments of chlorofluorocarbon (CFC)-induced ozone depletion in lower stratosphere (and related surface cooling) appear to be significantly greater than previously estimate near the equator, offset by lower estimates in mid latitudes. Studies continue to imply that such depletion and related cooling force may largely compensate for the direct radiative effects of CFCs on the climate system. Meanwhile, estimates for the global warming effect of a 2% per decade increase in ozone concentrations throughout the troposphere are significant, but would add less than 10% to anticipated changes due to carbon dioxide (CO₂) increase.

Defining the role of clouds as a feedback to climate change is one of the largest sources of uncertainties in assessing climate system sensitivity to changes in radiative forcing. Satellite data indicate that, in the current climate system, the average global cooling effect of clouds due to increased reflection of solar radiation back to space (the albedo effect) exceeds the concurrent warming influence caused by increase downward long wave radiation emitted by clouds (greenhouse effect). Hence the net global effect of clouds in zone of surface cooling. This net cooling effect is evident at all latitudes in summer. However, in winter, mid to high latitudes indicate a net warming effect due to clouds. The liquid water path of low clouds, which is highly variable (both regionally and seasonally) is an important factor; also is their temperature and optical thickness, and the amount of water vapour in the atmosphere.

A fall of up to 30 Centigrade in the last three decades has been detected by scientists in 1999 studying the layer of atmosphere that lies more than 30 miles up. Scientists said the worst-hit regions would be above northern Europe and the Arctic.

In terms of overall impact, ozone depletion interacts with the climate change process. Stratospheric loss of ozone has caused a cooling of the global lower stratosphere: changes in stratospheric ozone since the late 1970s may have offset about 30 per cent of the warming effect of other greenhouse gases over the same period (WMO, UNEP, NOAA, NASA and EC 1998). There are also complex interactions between ozone depletion, climate change and the abundance of methane, nitrous oxide, water vapour and sulphate aerosols in the atmosphere. For example, carbon is an important element in the absorption of UV radiation. Climate change and acid rain have led to decreases in the dissolved organic carbon concentration in many North American lakes (Schindler and others 1996). As organic carbon levels have decreased, UV radiation has been able to penetrate much more deeply into surface waters, resulting in greater UV-B exposure of fish and aquatic plants.