Читать книгу Global Warming and Other Bollocks - Stanley Feldman - Страница 15
ОглавлениеSTANLEY FELDMAN
DOGMA
Greenhouse gases are all the fault of human activity.
ANYONE LYING ON an English beach enjoying the summer sunshine could be excused for jumping to the conclusion that it was the occasional cloud that obscures the sun that causes their world to cool. They are probably right. Under cloudless skies the temperature drops dramatically the moment the sun sets or one moves from the sunshine into the shade, although the CO2 levels do not change.
When one listens to the weather forecast, it is clear that it is the cloud cover that determines whether the sun will shine and the weather will warm up. It is the amount of energy in the water molecules that make up the clouds that determines whether or not a particular wind will warm us up or cool us down. It would be nonsense to consider the effect of gases in the atmosphere on Earth’s temperature without accepting a major role for these clouds, especially those at the lower levels. To concentrate solely on the CO2 ignores the fact that many different processes are involved in determining the planet’s temperature.
There is one principal source of heat, and that is the sun; it far exceeds any other influence on the global temperature. Nevertheless, significant but comparatively small amounts of geothermal energy are constantly being released from the molten mass in the depths of the Earth. This energy warms areas of the oceans, through the hydrothermal vents of underwater volcanoes, and the land where the Earth’s crust is sufficiently thin to allow thermal warming, as in, for example, Arizona, Iceland, New Zealand and Antarctica. However, their global contribution of energy is tiny.
There is good evidence that the sun’s heat varies from time to time and that this is related to magnetic activity and sunspots. There is strong correlation between the number and frequency of these changes and the sun’s energy output. When there are a lot of sunspots the energy is reduced and the temperature, not only of Earth but of other planets such as Jupiter and Mars, falls slightly. Sunspots affect not only the amount of heat given off by the sun but also the amount of cosmic bombardment from outer space, due to their strong magnetic effect.
The mean temperature on Earth depends upon how much of the sun’s energy reaches the surface of our planet when the sun shines and how much of this heat is lost from the Earth when it gets dark. There is no doubt that this is affected by the atmosphere.
Over the past century, solar irradiance has increased, which in itself would account for a 0.2ºC rise in surface temperature if no other mechanism existed to affect the transfer of this energy from the sun to the Earth. However, various factors in the atmosphere affect this process.
The most obvious is the effect of the clouds.
The importance of water
Clouds are composed of water vapour and droplets; the higher the concentration of water droplets, the darker and more thunderous are the clouds. By and large the lower the clouds, the higher the concentration of water droplets. When a cloud appears to obscure the sun it does so by reflecting the sun’s energy, including that in the visible spectrum, back into space, so that its light fails to reach us on Earth. This reflective action depends largely on the concentration of water as droplets. Because molecules of water also absorb the warming, shorter-wave, infrared energy, we also lose much of the sun’s heat when it is cloudy.
The water molecules in the clouds also affect the surface temperature of the Earth in their role as a greenhouse gas. They blanket over the Earth and prevent the escape of infrared energy from its surface, stopping it cooling. That is why cloudy nights are much warmer and balmier than clear nights. On cloudless nights the temperatures tend to drop rapidly once the sun sets as the atmosphere lacks the greenhouse effect of the water in the clouds. It is evident on these occasions that our comfort depends to a much greater extent on the water in the atmosphere than it does on CO2.
We are coming to realise that clouds themselves, especially their disposition and composition, are also affected by solar activity, although the contribution this makes to the temperature of our planet is difficult to quantify.
The concentration of water in the atmosphere varies. Even on a ‘dry day’ the air we breathe is moist and the air we exhale is saturated. If one looks at the amount of ice deposited in the freezer compartment of a refrigerator it is evident that the air in the refrigerator, which may have appeared to have been dry, in fact contained a lot of water, some of which was deposited as ice when it was trapped inside the refrigerator when the temperature fell.
Greenhouse gases, like carbon dioxide and water, merely store part of the energy that originated in the sun. They absorb some of the energy that radiates from the sun when it shines and from the Earth after it has been warmed by the sun. At night CO2 and water vapour act together as a blanket over the Earth, minimising the loss of heat as the atmospheric temperature begins to fall.
The effects of the various components involved in determining the Earth’s temperature are difficult to separate quantitatively. The overall effect of the clouds is especially difficult to measure, as it varies enormously from time to time and from place to place. Its effect on the sun’s energy depends upon whether it is present as a vapour or as droplets. If all the water in the atmosphere acted effectively as a greenhouse gas it would contribute a massive 96 per cent to this effect, dwarfing any contribution from CO2.
It is generally agreed that the water vapour and droplets in the clouds contribute, at the very least, 50 per cent of the total global warming effect, although many others suggest that the figure should be much nearer 93 per cent. The trouble is that the amount of water vapour in the atmosphere varies from time to time, and it is impossible to predict.
A year without summer
A lot of polluting particles in the atmosphere will enhance the effect of the clouds in insulating Earth from the effect of the sun. It is believed to be responsible for the absence of significant global warming in southern China and parts of India over the past 15 years (2008 saw their coldest winter for 50 years). Volcanic eruptions spew out polluting particles (as well as CO2 and other greenhouse gases), which influence the climate. The Tambora volcanic eruption of 1815 produced a year without a summer due to the water vapour and the particles released when it erupted. They formed a cloud over large parts of the planet. The Krakatoa volcanic explosion of 1883, which released huge amounts of debris, CO2 and sulphur dioxide into the atmosphere, affected the temperature of the world for two to three years. Although CO2 and sulphur dioxide are greenhouse gases, the world cooled.
As a result of the reduction in the concentration of particle pollutants that used to hang in the air over London, before the Clean Air Acts of the 1950s, the sun’s rays are now better able to penetrate the atmosphere. This has led to an average increase in temperature in the city of about 2ºC. This is as great as the increase in temperature predicted in the next hundred years by some of the models of global warming! Together with urban warming, this has resulted in the temperature in central London being up to 4ºC warmer than the neighbouring countryside.
Scientific controversy centres on the relative importance of the enormous, but almost impossible-to-measure, effect of water vapour and clouds, the effect of changes in the sun’s activity and the effect of the tiny but increasing 0.038 per cent of CO2 in the atmosphere, in the production of global warming. It is because these effects are impossible to separate and measure that it so difficult to make reliable mathematical models to predict the behaviour of Earth’s temperature in the future.
