The explosive eruption of a volcano in Iceland has had various local and distant effects.

In Iceland, volcanic ash is settling on the land, threatening the health of grazing livestock, while mud flows, known as lahars, and glacial floods, known as jokulhlaup, threaten the tourists who have converged on the area since the eruption began last month.

Across Europe, thousands of flights have been cancelled, with economic losses thought to be in the billions, with the only upshot being unusually pretty sunsets. Dignitaries including Prime Minister Stephen Harper have been forced to make alternate travel plans for Polish president Lech Kaczynski's funeral in Krakow, or cancel completely.

Even the Coachella music festival in California felt the impact, as British indie band the Cribs (who do the song in the Telus ad, "Someone's got their eye on you...") could not get a flight out of Britain and will miss their performance slot.

But as the volcano continues to burble, and gases that were once dissolved in magma deep within the Earth are released as vapour and carried on the wind, scientists are watching for possible changes in the weather and, more controversially, the wider climate.

Reports indicate that the Iceland eruption, while relatively small, has sent its plume high enough into the atmosphere to reach the fast-moving winds that can spread it around the globe. Some estimates put the cloud of ash and vapour as high as 10km, with a trajectory that has roughly pushed it eastwards over Scandinavia and the rest of Europe, and possibly further north over the Arctic toward Canada in the coming days.

That vapour typically contains a great deal of water, followed by carbon dioxide and sulfur dioxide. As both CO2 and H20 are odourless, the sulfur tends to give volcanic vapour an acidic, rotten egg smell, which was mentioned yesterday by the World Health Organization. It said there are as yet no reports of particulate at ground level, but if that happens, people with lung conditions should stay indoors.

Although meteorologists were predicting minor effects on the weather, if any, one thing a plume of volcano vapour can do is deflect sunlight. Sulfur dioxide molecules turn to aerosols high in the stratosphere, creating a white haze that reflects sunlight.

The effect is less heat and a drop in temperatures, although the aerosols break down and dissipate over a time-scale measured in months, so the effect is generally localized and temporary.

It can be severe, though. The prime historical example of this was another Icelandic volcano, Laki, which erupted in 1783 and coincided with a boom in literacy in Europe, which ensured plenty of written records about its climatic effects.

Iceland itself was devastated, with livestock deaths and famine, but across Europe the following winter was unusually harsh and the summer unusually cold.

Benjamin Franklin, then Ambassador to France, was among the first to realize the potential effects of volcanoes on weather, when he wrote that the sun's "effect of heating the Earth was exceedingly diminished. Hence the surface was early frozen. Hence the first snows remained on it unmelted. Hence the air was more chilled. Hence perhaps the winter of 1783-84 was more severe than any that had happened for many years."

Likewise, when Mount Pinatubo in the Philippines erupted in 1991, this effect was said to have cooled global temperatures over the next year, which inspired speculation about artificially pumping sulfur into the stratosphere as part of a "geo-engineering" effort to counteract global warming.

Volcanoes are also frequently mentioned as a driver of observed, long-term global warming, because they emit the greenhouse gas carbon dioxide, although not as much as human industry. That leaves a cool summer as the likeliest possible legacy of the Iceland eruption.

But if Pinatubo, which was vastly more powerful, only affected the weather for a year, things in Iceland will have to get seriously worse if they are to have any measurable global effects.