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Arrhenius, Svante (August) - GLOBAL WARMING

power atmosphere water temperature

[a ray neeus] (1859–1927) Swedish physical chemist: proposed theory of ionic dissociation; he foresaw the greenhouse effect in 1896.

Arrhenius came from a family of farmers, and his father was an estate manager and surveyor. He attended Uppsala University and did very well in physical science, and then moved to Stockholm to work for a higher degree on aqueous solutions of electrolytes (acids, bases and salts); he concluded that such solutions conduct a current because the electrolyte exists in the form of charged atoms or groups of atoms (positive cations and negative anions), which move through the solution when a current is applied. He obtained good evidence for this during the 1880s but his theory was only slowly accepted, especially in Sweden. (Since then, further evidence has substantially confirmed his views, and has also shown that salts are largely ionic even in the solid state.) In 1903 he was awarded the Nobel Prize for chemistry. His work was surprisingly varied and included immunology, cosmic physics and the first recognition of the ‘greenhouse effect’ (heat gain by the atmosphere due to carbon dioxide). He also studied the effect of temperature on the rates of chemical reactions, and showed that where k is the rate constant for the reaction, A is the frequency factor, E is the activation energy for the reaction, R is the gas constant and T the Kelvin temperature (this is the Arrhenius equation).


Before the industrial revolution (roughly pre-1800) there had been large regional or global changes in climate: notably a series of ice ages. The last ice age ended about 20 000 years ago, and we now live in an interglacial period. These pre-1800 changes, resulting from causes such as change in solar radiation, or dust and gas from volcanoes, owe nothing to human activity. However, since the mid-19th-c human activity has played an increasing part. Over a century before this was considered, the idea of the ‘greenhouse effect’ was born. , in 1827, recognized that the Earth’s atmosphere acts somewhat like the glass of a greenhouse in raising the temperature, and about 1860 showed that water vapour and carbon dioxide (CO 2 ) are important in the matter. The Sun’s radiation is partly reflected by clouds before it reaches the Earth, but the solar energy that arrives warms it; nearly 300 W m –2 on average. The Earth in turn re-radiates energy, but mainly in the longer wavelength infrared region; this radiation is strongly absorbed by water vapour and CO 2 (0.03% of the atmosphere) and so the atmosphere absorbs the radiation and re-emits much of it back to Earth. The net result is that the atmosphere has a blanketing effect akin to glass. It keeps the Earth some 20°C warmer than it would be without the effect. The main constituents of air, nitrogen and oxygen, do not absorb in the infrared.

In 1896 calculated that doubling the atmospheric CO 2 content would increase the global average temperature by between 5 and 6°C; a result close to modern values based on more refined calculation. In 1940 G S Callendar calculated the warming due to a smaller increase in CO 2 , which he estimated as arising from burning fossil fuels (coal and oil). Neither of these calculations aroused very much general interest at the time.

In 1957 R Revelle (1909– ) and H E Suess (1909– ) of the Scripps Institute of Oceanography, CA, noted that mankind’s ever-increasing contribution of CO 2 to the atmosphere constituted a global climatic experiment, whose progress and outcome needed study. Measurement of atmospheric CO 2 levels began in that year at Mauna Kea in Hawaii, and other studies followed.

Water and CO 2 are the main natural greenhouse gases. The former is outside human control, as is some CO 2 emission (eg from volcanoes). But much CO 2 emission is now man-made, by burning of fuels. Of course CO 2 is absorbed by green plants for photosynthesis, a process diminished by human deforestation, especially in the tropics; CO 2 is also absorbed by the oceans. Historically, atmospheric CO 2 has steadily increased since 1800, as shown by the graph.

Another important greenhouse gas is methane, CH 4 , ‘marsh gas’. As the last name implies it is generated by bacterial action on wet organic matter in lakes, peatland, and increasingly in man-made landfill rubbish sites, and reservoirs. It is also released in the coal and oil extraction industries, and from termites, and both ends of cattle by enteric fermentation of their diet. Itself a potent greenhouse gas, it is ultimately converted to CO 2 in the atmosphere by oxidation.

From about 1980 the Earth as a whole has seen many unusually warm years and a high incidence of extreme climatic events – droughts, floods and storms. Figure 2 shows temperatures from 1860 to 2000; and when allowance is made for natural variations in solar energy reaching the Earth’s surface, the trend roughly correlates with the increase in CO 2 . Sophisticated studies led the IPCC in 2000 to conclude that man-made additions to the atmosphere, the ‘enhanced greenhouse effect’, provides the dominant cause of this global warming.

The IPCC conclusion is that on present trends the global average temperature will rise by about 5°C. The certain and probable effects of this will be dramatic, but difficult to predict in detail. Positive and negative feedback, and interactions between many of the primary effects of climate change make the overall climatic change a complex case for modelling.

For example, Europe in general will become warmer by 2100, but for the UK the position is less certain: if change in ocean currents diverts the Gulf Stream (which makes Britain’s climate milder than its latitude would imply) this greatly affects prediction. However, some major effects are clearly foreseeable. Agricultural practices will need to change over large areas; disease patterns will alter, as will the availability of fresh water.

A dramatic and predictable effect will be that on sea level. This will rise in part because of simple expansion of water with rise in temperature; and also because of melting of glaciers and mountain ice caps, and of polar ice, notably the Antarctic continent. Sea level is predicted to rise between 60 cm and 1 m by 2100. Worldwide, half of humanity lives in coastal areas. Some islands will be inundated, as will much of Page 17  Bangladesh, the Nile delta in Egypt, and large areas in the USA and China. The Netherlands has at least the advantage of experience, and should be able to enhance existing technology and use experience not available in other areas, where population surges will result from inability to control land loss.

Attempts to alleviate these huge global problems have led to calls for reduction of CO2 emissions worldwide, or at least (and more realistically) reduction of the rate of CO2 increase. The burning of fossil fuels (coal and gas) for domestic heating, industrial power use, and transport are clear targets for reduction: the industrialized northern hemisphere emits most CO2 but the development of industry in Russia, China and India will worsen the problems. More efficient usage, and better insulation, can only slightly reduce CO2 emissions. So also will contributions of renewable ‘clean’ (ie CO2 -free) power from hydroelectricity, geothermal, tide, wind and wave power, despite the enthusiasm of their supporters. More substantial help can come from wider use of nuclear fission power (as in France) but public confidence in nuclear safety has been disturbed by the Chenobyl disaster and the UK and Germany seem unwilling to follow this path. Nuclear fusion, the source of the Sun’s power, has yet to prove itself as a practical earthly power source. If photovoltaic (solar) power to generate electricity can be further developed, it shows real promise: it could, for example, be used not only to meet static needs, but also for all forms of transport. Unless storage batteries can be made much lighter than existing types, it is possible that a ‘hydrogen economy’ will develop. In this scheme photovoltaic current is used to decompose water to give hydrogen, which is then liquefied and distributed much as petrol and diesel now is – but requiring high refrigeration (it boils at –252°C). In a vehicle, the hydrogen would feed a fuel cell, re-generating electricity to power a motor. The only exhaust product in the cycle would be water. A full-scale trial in Iceland from 2002 of part of this scheme, although valuable, is limited in so far as Iceland has a small population (276 000) and abundant hydroelectric power to generate hydrogen.

Alternative and very different ideas have also been put forward; for example group believe that reflective particles in the upper atmosphere, to reduce incoming solar radiation, could be cost-effective. Another philosophy is offered by the US economist Frances Cairncross (1944– ), who has argued that it is hopeless to try to prevent a massive rise in CO2 emission from the developing world. There at present the fuel consumption is only the equivalent of 1 to 2 barrels of oil per person annually, compared with 10 for Europeans and 40 for Americans. Her view is that humanity in the past has adapted to and survived great climatic changes, and can do so again; and that other globe-wide problems (eg water pollution) ‘deserve greater priority than global warming’.

Global warming has become essentially a political problem. For the wealthy and democratic Western world and Japan, making the social and economic changes needed to deal with the foreseeable climatic change would be political suicide. Good general intentions conflict with national interests. International agreements made at Kyoto and elsewhere are limited in scope and are unlikely to be fulfilled. Fossil fuel interests, notably in the USA, argue that causes other than human activities are responsible for the climatic changes that are already discernible; and that action should be delayed until further evidence is available. But the weight of scientific opinion is clearly different, and scientists generally are dismayed by governmental delay and complacency.

Moving away from high dependency on fossil fuels would reduce the influence of OPEC on world economies, and defer the not-too-distant date when fossil fuel supplies become exhausted.

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