by Michael D. Lemonick of Climate Central

A few days ago, my Climate Central colleague Andrew Freedman wrote about the climate implications of the Mt. Eyjafjallajokull eruption in Iceland. Basically, there weren’t any to speak of at that point. Volcanoes can throw reflective sulfur dioxide particles into the upper atmosphere; by bouncing some sunlight back into space, and these can temporarily cool the planet, offsetting (for a while, anyway) some of the warming caused by greenhouse gases.

To put enough particles into the air to make a significant difference, though, you need either a huge, explosive eruption like Mt. Pinatubo’s in 1991 or a smaller eruption that goes on for a long time. In this case, the experts say, Eyjafjallajokull would have to keep erupting at its current level for months. Not only that: it would have to keep erupting explosively. Spewing lava doesn’t do it. But that’s just what this volcano is likely to start doing. The eruption so far has been supercharged by water from Eyjafjallajokull’s glaciers, flashing into steam when they hit molten rock and blasting rock and volcanic gases sky-high. Now that the ice is largely melted, that driver is gone, and volcanologists suspect that the dust and gases will diminish (this LA Times story includes the voices of some of these experts).

They will diminish, that is, unless a new fissure opens somewhere Eyjafjallajokull’s ice-covered flank, dumping more water onto the hot rock. Or the rearrangement of subterranean magma chambers could send another nearby volcano into eruption. All of which would be very bad news for European air travel — but even so, the direct impact on climate from Iceland’s volcanoes will be minimal.

The indirect impact is something else, though. In addition to sulfur dioxide and ash, volcanoes emit carbon dioxide, the main greenhouse gas. This one is no exception—but the amount of CO2 kept out of the atmosphere thanks to hundreds of grounded planes rivals the volcano’s emissions. (How much? This much.)

For a nice roundup of Icelandic volcano facts, see this Christian Science Monitor story.

In the meantime, if the dust, sulfur dioxide and CO2 emissions weren’t enough of a volcano-climate connection, it’s useful to repost what Andrew wrote last week about how climate change could trigger more volcanic eruptions:

“The volcanic eruption in Iceland that has disrupted air traffic in Europe is also a reminder that other volcanoes in the region could wake up if global warming continues unabated, experts say.

Scientists say that if large icecaps on the island melt, they’ll ease the pressure on the rocks beneath the surface. Lifting the weight off the rocks would allow for more magma production, which could set off other eruptions. Says volcanologist Freysteinn Sigmundsson: “Our work suggests that eventually there will be either somewhat larger eruptions or more frequent eruptions in Iceland in coming decades” [source: Scientific American].

Scientists clarified that while the current Eyjafjallajokull eruption occurred beneath a small glacier in Iceland, the explosion was not caused by global warming. The Eyjafjallajokull glacier is too small and light to have an impact on local geology, they say.

Sigmundsson and his colleague Carolina Pagli published research in 2008 estimating that the melting of about a tenth of Iceland’s biggest icecap, Vatnajokull, over the last century had caused the land to rise about an inch a year and led to the growth of a vast mass of magma, measuring about a third of a cubic mile, underground [source: The Telegraph]. The researchers explain that heated rocks can’t melt into magma when they’re under high pressure — for example, when they’re squashed underneath the weight of an icecap. But when the ice melts, the water trickles away, and the pressure eases off, the rocks can then melt into magma, creating prime conditions for volcanic eruptions. The researchers note that the end of the Ice Age 10,000 years ago was marked by an increase in volcanic activity in Iceland.

They warn that if ice sheets shrink, we can expect to see more eruptions in other frozen places like Alaska, Patagonia, and Antarctica. Says Pagli: “The effects would be biggest with ice-capped volcanoes…If you remove a load that is big enough you will also have an effect at depths on magma production [source: Scientific American].”