Is the world growing warmer

Measurements from surface stations record an increase in global temperature of about 0.27°F (0.15°C) per decade. Weather balloons and satellites both record a slight cooling, the balloons by 0.036°F (0.02°C) and MSUs by 0.018°F (0.01°C) per decade.

The discrepancies are real and probably reflect the true state of affairs. The air temperature is rising immediately above the surface, but it is remaining steady or falling slightly in the upper troposphere.

The Central England temperature record shows that since 1800 the temperature in the area covered has risen by about 1.26°F (0.7°C) and that most of this rise has taken place in winter. In other words, winters are becoming milder, but summer temperatures are changing very little.

The temperature in the stratosphere is falling by 0.9°F (0.5°C) at 49,000 feet (15 km), rising to 4.5°F (2.5°C) at 31 miles (50 km). This is due to the depletion of the ozone layer. Stratospheric processes by which ozone forms and is broken down again absorb shortwave solar radiation, warming the stratosphere, but cooling the troposphere by reducing the amount of radiation that penetrates to the surface (see "The radiation balance" on pages 135-142).

When people talk confidently about the rate at which the world is growing warmer, it is as well to bear in mind the complexity of measuring small changes. The scientists who summarize research findings for the Intergovernmental Panel on Climate Change are more cautious. In Climate Change 2001: The Scientific Basis (paragraph 2.2.4, page 123) they state that: ".. . it is very likely that the surface has warmed in the global average relative to the troposphere, and the troposphere has warmed relative to the stratosphere since 1979. However, the relative warming is spatially very variable and most significant in the tropics and sub-tropics." They also say the difference between the change near the surface and that at higher levels is still not understood and requires further research. Taking the temperature of the atmosphere is not a straightforward task.

City air is drier, but rainfall is higher

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