The Christian Science Monitor has an interesting article on the increasing recognition among climate scientists of the role that variations in solar activity play in changes in Earth's climate.
Other researchers found that the sun appears to display variations in its magnetic field and solar wind that span longer time scales. According to some researchers, during the past century, the strengths of the solar wind and the sun's magnetic field have doubled.
The cosmic-ray proposition holds that when the sun's magnetic field and the field generated by the solar wind increase, Earth is increasingly shielded from cosmic rays. These charged particles are thought to have the ability to seed cloud formation by triggering processes at the micro level that generate the nuclei around which water vapor condenses. Thus, if Earth's "shield" had been strengthening over the past century, it should have led to lower average cloud cover and warmer temperatures.
Will the sun increase or decrease its output overall in the 21st century? It is not inconceivable that some day humans may seek to engage in large scale measures to compensate for trends in solar output. Imagine, for instance, that the sun began again to behave has it did in the late 17th century. Variations in solar output in are believed to have been at least partly responsible for the Little Ice Age.
Because the sun is the ultimate source of Earth's warmth, some researchers have looked to it for an answer. In the 1970s, solar researcher John Eddy, now at Saginaw Valley State University in Michigan, noticed the correlation of sunspot numbers with major ups and downs in Earth's climate. For example, he found that a period of low activity from 1645 to 1715, called the Maunder Minimum, matched perfectly one of the coldest spells of the Little Ice Age.
Judith Lean, a solar physicist at the Naval Research Laboratory in Washington, estimates that the sun may have been about a quarter of 1 percent dimmer during the Maunder Minimum. This may not sound like much, but the sun's energy output is so immense that 0.25 percent amount to a lot of missing sunshine -- enough to cause most of the temperature drop, she says.
NASA climate researcher Eric Shindell believes the decrease in overall Earth temperatures were fairly small during the Maunder Minimum but the changes were much more drastic in the North Atlantic and Europe.
Shindell noted that the effects of this period of a dimmer sun were concentrated more regionally than globally. "Global average temperature changes are small, approximately .5 to .7 degrees Fahrenheit (0.3-0.4C), but regional temperature changes are quite large." Shindell said that his climate model simulation shows the temperature changes occurring mostly because of a change in the Arctic Oscillation/North Atlantic Oscillation (AO/NAO).
Once photovoltaic cells and other means of producing energy become cheap the release of CO2 into the atmosphere will become optional. One can imagine scenarios in which solar output dropped enough that a large scale increase in CO2 produced by burning fossil fuels might usefully compensate for some of the decrease in solar radiation. On the other hand, if solar output increased one can also imagine strategies which could be used to take CO2 out of the atmosphere. Energy produced by solar cells or nuclear reactors could be used to drive chemical processes that fixed carbon from the atmosphere into a solid form.
This reminds me of an idea that I think deserves more attention than it gets: Since hydrogen is a less dense form of energy than hydrocarbon liquids it is a poor substitute for hydrocarbons in vehicles. An alternative would be to use energy from photvoltaics or nuclear reactors to drive the fixing of carbon from atmospheric carbon dioxide to hydrogen extracted from water (effectively to do what chloroplasts do in plants but without any oxygen in the resulting compounds). The resulting hydrocarbons could be used as an energy source for vehicles. This would produce what would be, in effect, an artificial carbon cycle that would operate in parallel with the natural one.
|Share |||Randall Parker, 2003 July 17 06:48 PM Climate Trends|