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Volcanic ash from Iceland snarled air traffic across Europe for a second day Friday, causing the cancellation of some 16,000 flights, according to the intergovernmental body that manages European air travel.

The ash cloud is expected to drift farther south and eastward through Europe on Friday night, Eurocontrol said, raising concerns that more countries and airports could be affected.

The cloud comes from an eruption under an Icelandic glacier that began early Wednesday. The eruption under the Eyjafjallajokull glacier -- the latest in a series that began on March 20 -- blew a hole in the mass of ice and created a cloud of smoke and ash that went high into the air.

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Besides releasing clouds of ash into the atmosphere that can disrupt visibility and damage airplane engines, eruptions can cool the climate with the reflection of incoming solar radiation from the troposphere by volcanic sulfur-rich ash, which can decrease temperatures significantly for months or years in some cases.

Just such an aerosol effect is believed to have disrupted the Earth's thermal balance during the Laki event, cooling some Northern Hemisphere regions by as much as 1 or more degrees Celsius below the long-term average.

Highly unusual conditions were described in the summer of 1783 after Laki, including poisonous volcanic fumes that killed perhaps 25 percent of the population of Iceland, persistent haze and oppressive heat in Europe, and blood-red sunrises over North America, Europe and other locations. The Laki eruption was believed to have caused thousands of deaths because of unusual conditions in Europe that summer, along with the severe cold of the following winter.

Benjamin Franklin was one of the first to suggest that the extreme cold of 1783-84 over much of the Northern Hemisphere was connected to the Laki event. In North America, Laki has been blamed for the starvation of Inuit populations from severe cold in northwestern Alaska, based on Inuit oral history as well as tree-ring density data investigated by Gordon Jacoby and others, who estimated that conditions were about 4 degrees Celsius colder than the mean.

The density record of temperature-sensitive white spruce for this region showed extremely low values in the summer of 1783, known in Inuit lore as "the summer that did not come".

This observation was used to infer that this was the coldest summer in at least the past 400 years.

Such tree-ring records, along with other so-called proxy archives, can provide a wealth of information about volcanic events and their varying impacts around the globe because of resulting shifts in atmospheric circulation and other climate changes, dating for centuries prior to the period of instrumental record.

The effects of major volcanic eruptions such as Laki can also be felt elsewhere on the globe, often far from their actual location. For example, significant cooling and strong dynamical effects after the Laki event and other high-latitude eruptions are believed to have caused decreased flow of the Nile River in Egypt and weakened African and Asian monsoons based on climate model simulations, with potentially very significant impacts on food and water supplies.

Tree-ring, coral and ice core records also indicate the effect of major volcanic events in the tropics of monsoon Asia for low-latitude eruptions such as that of Tambora, Indonesia, in 1815 and other such events of the past several centuries, although this climate signal is also complicated by the El Niño-Southern Oscillation.

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• According to the Air Transport Association of America, U.S. carriers have canceled 196 flights so far on Friday between the United States and volcano-affected areas in Europe.

• British Airways is flying a number of flights from North America to Scotland overnight.

• Ryanair has decided to cancel all scheduled flights to and from the United Kingdom, Ireland, Denmark, Finland, Norway, Sweden, Belgium, Holland, northern France, northern Germany, Poland and the Baltic states into Monday.

• IATA's initial and conservative estimate of the financial impact on airlines is in excess of $200 million per day in lost revenues. The group is an international trade body created more than 60 years ago by a group of airlines.

• The Swedish airspace authority LFV said almost all Swedish airspace will close again. Only the country's two most northern airports, Lulea and Kiruna, will be able to have limited air traffic, and these restrictions will most likely remain in place throughout the weekend, LFV said.

• Total airspace closures include: Austria, Belgium, Netherlands, Denmark, Finland, Estonia, Lithuania and Hungary.

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