Volcanoes and Long Cycles - Bumps and Wiggles (4)

Volcanoes and Long Cycles - Bumps and Wiggles (4):

Introduction: This is the fourth in a series on understanding climate variability, global warming, and what we might do about it. The series focuses on the past 30 years and the next 30 years. The volcano in Iceland and the end of the semester have thrown me off track.

Comments to the last couple of blogs have included one of the usual type that all of climate change is due to “cycles,” as well as a statement that the Icelandic volcano, Eyjafjallajökull, had put an enormous amount of carbon dioxide into the atmosphere. Both of these statements were meant, I presume, to imply that the emissions due to burning of fossil fuels was either inconsequential or that we were at the fate of powers that are out of our control; hence, we should march on our merry ways. Well … ?

First on the emissions that come from volcanoes – I wrote to Alan Robock at Rutgers University to ask him about Eyjafjallajökull. Alan is my go to scientist on volcanoes and I use material from his research in my class. He sent me a good web link for current information on the eruption.

On very long time scales volcanoes, or more generally, emission of CO2 by out gassing from the Earth is very important. Again on geologic time scales, millions of years, out gassing from the Earth is balanced by formation of rocks.

When we consider climate change of the past 1000 years or so, we take into account volcanoes. In the absence of observations or theory to the contrary, we assume that, in our current temperate climate, volcanic activity is sporadic and the frequency of eruptions is not changing. With this assumption, we say that there is “no change” in volcanic activity, which is NOT the same as saying that volcanoes are unimportant. They are an important natural ingredient of the Earth’s climate.

Usually, when we think about volcanoes we think about them in terms of cooling the Earth. Explosive eruptions place particles or droplets with high concentrations of sulfate (SO2) into the stratosphere, above say, 18 kilometers altitude. These droplets are called sulfate aerosols; aerosol is the term used to characterize particles in the atmosphere. Sulfate aerosols in the stratosphere 1) stay there a couple of years, and 2) reflect sunlight back to space. (Gee, if I do an image search I find an ancient blog of relevance. No copyright issues with this figure.) This is expressed schematically in the figure below.




Figure 1: The role of aerosols in the Earth’s climate.

On the time scales of a few years, say 5, we don’t usually concentrate on the role of CO2 emitted from volcanoes. One of people who commented on my blog said that “40 years” worth of CO2 had been emitted by Eyjafjallajökull. I know of no observational evidence or theory to support this assertion. In general, the CO2 emission by a single volcano is not significant enough to cause a substantial bump in the carbon dioxide data. Here is the current figure of the Mauna Loa CO2, from the excellent Earth System Research Laboratory web site on CO2 trends.



Figure 2: Up to date times series of CO2 at Mauna Loa.

I use this figure to point out that the explosive eruptions of El Chichon (1982) and Mount Pinatubo (1991) did not change this curve in any easily perceptible way. (You can find tables of numbers on this web page.) If you think about the enormous eruptions of Krakatoa and Tambora, we associate these with documented cooling from the aerosols, but not with surges in long-lived CO2 increases.

It is simply not true that current volcanic emissions in anyway compare with or overwhelm emissions from burning fossil fuels. We will see what the global record brings us in the next few months. It will be interesting to compare the emissions from the volcano with the reduction of emissions by grounding aircraft.

But the ideas about climate cycles did get me thinking, and my thinking was placed into a different context by the geologist Henry Pollack. Henry has a new book called A World Without Ice. This is a very well written book, which I strongly recommend. I was at an event with Henry where he pointed out that humans today are the largest geological force altering the surface of the Earth. (I can’t help think of the oil flowing into the Gulf of Mexico. We open it up and take it out.)

It is true that the Earth’s climate experiences cycles and perhaps jumps from one stable-for-a-while climate to another – on geologic time scales. But these jumps do not absolve us from our role; they aren’t unexplained magic. The jumps in climate are associated with large changes in greenhouse gases, especially carbon dioxide and methane. Large jumps in greenhouse gases are associated with either geology, absorption by and emission from the ocean, or changes in life. Changes in life? Plants and animals exist in a balance and cause a tension between carbon dioxide and oxygen. Life is a crucial controller of atmospheric composition. Humans are the current dominant life form, and we are a dominant geological force.

Yes the climate cycles. We know that the cycles generally have great shifts in greenhouse gases. Right now, we are the life, the force that is causing a great shift in greenhouse gases. We dig and pump and burn. It is convenient to say that the climate cycles, but this is the only cycle that has ever had us in it. With the knowledge that we have of the role of greenhouse gases in climate change, we have a wonderful opportunity and knowledge to perhaps start to manage the cycles and maintain a planet that is sustaining for our particular form of life. Otherwise yes it is a cycle and on the epochs of cycles it’s the time when some life form decided to burn stuff.


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Bumps and Wiggles (1): Predictions and Projections

Bumps and Wiggles (2): Some Jobs for Models and Modelers (Sun and Ocean)

Bumps and Wiggles (3): Simple Earth



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