Volcanoes & Climate Change

[Kanastrous]

All right, maybe I wrote lousy search strings but I have not found this specific item on SDNet.

Something I hear in conversations of the anthropogenicity (anthropogenousness? anthropogenosity?) of climate change is that hey one or two major volcanic eruptions undo any savings in carbon etc that we could achieve with 'clean' whatever.

How to evaluate the accuracy of the claim? Yeah, big volcanoes hork out a -lot- of stuff. Enough that the claim is accurate? And, if it's accurate, is it necessarily relevant?

[Sea Skimmer]

A big enough volcanoes would be self limiting in large part, because while it throws out massive amounts of CO2, it would also throw out massive amounts of ash which would reflect the sun and linger for years.The eruption of Tambora in 1815 caused a global cooling event in 1816 bad enough to cause mass crop failures and famine in Europe. This is still a real threat today. However such large eruptions are pretty rare, the last time before Tambora one occurred is in 1620 BCE when Thera exploded. We know of others thousands of years before that, in other words not very relevant when industrial society is only about two hundred fifty years old.

Human CO2 releases meanwhile are going hand in hand with human destruction of forests and urban/pavement sprawl which all increase heating rates. The earth does have some buffering ability to deal with CO2 surges, such as increasing rates of plant growth problem is humanity has already used all of that up and done all kinds of other things to alter it.

Meanwhile this article at least, indicates that normal volcanic activity releases vastly less CO2 then humans do in a normal year.
http://news.discovery.com/earth/volcano ... 10627.html

Saying the threat of volcanoes is a reason to do nothing is basically the same as saying, were all going to die anyway. After all a giant asteroid kill us next week. Does this mean we should stop even bothering to grow food or do anything else useful? Of course not.

[Darth Wong]

All right, maybe I wrote lousy search strings but I have not found this specific item on SDNet.

Something I hear in conversations of the anthropogenicity (anthropogenousness? anthropogenosity?) of climate change is that hey one or two major volcanic eruptions undo any savings in carbon etc that we could achieve with 'clean' whatever.

How to evaluate the accuracy of the claim? Yeah, big volcanoes hork out a -lot- of stuff. Enough that the claim is accurate? And, if it's accurate, is it necessarily relevant?

Isn't this like saying that lightning could ignite a California wildfire tomorrow, so we might as well build a bonfire among the redwood trees?

PS. Or to be a bit more formal about it, their underlying logic is that our harmful activities are irrelevant since Nature can cause great harm itself. The problem is that it's an additive situation: whatever Nature could or would have done, we are making it worse by adding to it. If it would have been wonderful without our input, we're making it not so wonderful. If it would have been terrible without our input, we're making it even more terrible. Either way, we are causing harm, like throwing gasoline on a fire.

[Kanastrous]

Thanks, that's all useful on a number of levels.

[Kuja]

How to evaluate the accuracy of the claim? Yeah, big volcanoes hork out a -lot- of stuff. Enough that the claim is accurate? And, if it's accurate, is it necessarily relevant?

I won't comment on the accuracy because I don't have the knowledge to do so, but as far as relevancy goes...well.

Well, frankly, an asteroid could potentially smack into our planet tomorrow and kill us all, so why do anything ever? The fact that all our efforts to stabilize our environment and maintain a balanced, livable world for ourselves could be erased at some point is no excuse for not making the attempt to begin with.

[Kanastrous]

Where it would be meaningful would be the point at which the volcanic contributions were -so- great that no degree of moderation or elimination of emissions on our part would have a useful impact. It doesn't sound as though that is a realistic description, though.

[Junghalli]

Yeah, that article Sea Skimmer posted is the kicker.

Here's Skeptical Science tackling the same topic.

Human CO2 emissions are much larger than volcanic ones, even the output of big volcanic eruptions like Mount Pinatubo are small compared to what we're putting out every year.

I'm not sure how something like a hypothetical Yellowstone Blast would stack up but eruptions like that are rare, and if one did happen I imagine we'd have other problems than "oh dear there goes all our hard work cutting emissions". Seems rather silly to argue we shouldn't cut CO2 emissions because something like that just might happen.

[El Moose Monstero]

All right, maybe I wrote lousy search strings but I have not found this specific item on SDNet.

Something I hear in conversations of the anthropogenicity (anthropogenousness? anthropogenosity?) of climate change is that hey one or two major volcanic eruptions undo any savings in carbon etc that we could achieve with 'clean' whatever.

How to evaluate the accuracy of the claim? Yeah, big volcanoes hork out a -lot- of stuff. Enough that the claim is accurate? And, if it's accurate, is it necessarily relevant?

Examination of volcanic CO2 emissions alone is very misleading, as they can also pump out a lot of SO2 which is oxidised to H2SO4 aerosol in the atmosphere. This reflects inbound radiation back to space. Ash does have a cooling effect, but it's residence time is a lot shorter than aerosols, 99.9% (ish) falling out within weeks. Tambora was more to do with aerosol emissions than ash. The effect of the Pinatubo eruption in 1991, also attributed to SO2 emissions, was a 0.1C decrease in global mean temperatures precisely due to this reason. For supervolcanic eruptions, this cooling is even greater - current models suggest eruptions on supervolcanic scales (e.g., yellowstone) could initiate global cooling of 5-20C for around a decade after the eruption depending on the scale of SO2 emission, and would require several more decades to return to pre-eruption norms.

An occasion where an opposite effect occurs is suggested in a recent nature paper, where they speculate that some ancient flood basalt type eruptions may have ignited coal reserves, and so may have pumped out a lot more carbon for a longer period, with possible warming effects on climate. That's a hazy memory of the paper though, so don't quote me on that.

[Kanastrous]

^ thanks, that's great.

[Surlethe]

I recall reading that H2SO4 aerosols are short-lived, while CO2 is long-lived, so the cooling effect from dumping sulfur aerosols in the atmosphere is temporary. Wasn't this why Chinese industrialization caused a temporary stall in warming during the early 2000s? Lots of coal plants emitting SO2, turning back more heat than the extra CO2 trapped, until it fell out of the atmosphere as acidic rain leaving the CO2 behind.

[D.Turtle]

I recall reading that H2SO4 aerosols are short-lived, while CO2 is long-lived, so the cooling effect from dumping sulfur aerosols in the atmosphere is temporary.

Yes, that is correct. Aerosols only stay in the atmosphere for a few days or weeks.

Wasn't this why Chinese industrialization caused a temporary stall in warming during the early 2000s? Lots of coal plants emitting SO2, turning back more heat than the extra CO2 trapped, until it fell out of the atmosphere as acidic rain leaving the CO2 behind.

I have never heard of that theory before - there has been no noticeable stall in warming in the last 30ish years.

IIRC it played a role during the stall from the mid 1940s to the mid 1970s, but not since then.

If one removes the forcings from El Nino/El Nina, volcanoes, and solar variation, the trend is quite clear (as is shown in this study, and no stalling can be seen that could be the result of Chinese industrialisation:



MEI= ENSO/El Nino & El Nina
AOD = volcanoes
TSI = solar

[Sea Skimmer]

Chinese industrialisation caused more then a small amount of industry to shutdown in the US, Europe and Russia, in fact the former USSR's economic collapse from 1991 onward alone would have been a major counterbalance to Chinese expansion. So it really wouldn't make sense for China to have been able to cause a signification bump. They were expanding like crazy from the 1980s onward. Its just people didn't pay it that much attention until the 2000s when they began not just expanding industry, but actually modernizing the cities ect... in a highly visible manner.

[El Moose Monstero]

I recall reading that H2SO4 aerosols are short-lived, while CO2 is long-lived, so the cooling effect from dumping sulfur aerosols in the atmosphere is temporary.

Yes, that is correct. Aerosols only stay in the atmosphere for a few days or weeks.

Is that including the stratosphere? I'm not a climatologist, so I'll happily defer, but I recall reading that the 1/e folding time for H2SO4 aerosols was about a month or so, and that the scale of supervolcanic SO2 outputs consituted around 500-10,000 Mt injected directly into the stratosphere by a rapidly ascending plume which can end up about 30-40 km up within a few minutes. I assume in that case that it's a question of sheer scale for the largest and rarest eruptions that doesn't really apply to most volcanic eruptions, which either don't go high enough or don't put out anything like that amount of SO2 (Pinatubo - 20 Mt). In the case of the big ones, global cooling effects from H2SO4 aerosols on decadal scales have been published by multiple studies in atmospheric (ACPD) and volcanic journals.

[Surlethe]

Hmm, I had picked up that idea about China - I thought at RealClimate - last fall, but now I can't seem to find it.

[D.Turtle]

Is that including the stratosphere? I'm not a climatologist, so I'll happily defer, but I recall reading that the 1/e folding time for H2SO4 aerosols was about a month or so, and that the scale of supervolcanic SO2 outputs consituted around 500-10,000 Mt injected directly into the stratosphere by a rapidly ascending plume which can end up about 30-40 km up within a few minutes. I assume in that case that it's a question of sheer scale for the largest and rarest eruptions that doesn't really apply to most volcanic eruptions, which either don't go high enough or don't put out anything like that amount of SO2 (Pinatubo - 20 Mt). In the case of the big ones, global cooling effects from H2SO4 aerosols on decadal scales have been published by multiple studies in atmospheric (ACPD) and volcanic journals.

From what I can find, while aerosols in the stratosphere have a much longer persistence, the only real source of stratospheric aerosols is very large volcanic eruptions (the last one was Pinatubo). Aerosols from pollution mostly go up only to the troposphere where they have the mentioned persistence of days to weeks.

Hmm, I had picked up that idea about China - I thought at RealClimate - last fall, but now I can't seem to find it.

Looking some more into it, I found some recent comments linking to a post on Skeptical Science.

I'll quote the relevant part of the comment by Kevin Trenberth (the post author):

There is discussion in the comments of the supposed finding that increasing aerosol (pollution) from China may be the explanation for the stasis in surface temperatures and I do not believe this for a moment. Similarly, Jim Hansen has discussed the role of aerosol as a source of discrepancy. However, the radiation measurements at the top of the atmosphere from satellites (CERES) include all of the aerosol effects, and so they are not extra. They may well be an important ingredient regionally, and I have no doubt they are, but globally they are not the explanation.