THEGREENGROK    Planetary Watch

Another Volcano, Another Cold Snap

by Bill Chameides | November 13th, 2009
posted by Erica Rowell (Editor)

Permalink | 13 comments

 


In the aftermath of the 1991 Mount Pinatubo explosion, global temperatures plummeted, providing direct evidence volcanic explosions can be a driver of global cooling. (USGS / J.N. Marso, July 1991)

Analysis of sulfur isotopes in ice cores fingers a volcano in the 19th-century dip in global temperatures.

Studying the climate is kind of like putting together a jigsaw puzzle. We’ve got enough puzzle pieces in place to know the basic picture — for example that greenhouse gases have contributed to the recent global warming trend. But there are still parts of the puzzle that remain fuzzy, and scientists continue to debate which puzzle pieces belong there.

We know that global temperature fluctuations can be caused by a variety of factors. In addition to greenhouse gases, solar variations and oscillations in the Southern Ocean between El Nino and La Nina are important. On longer time scales, variations in the Earth’s orbit about the sun can also be a factor.

Volcanoes, Sulfur Dioxide, and Global Cooling

Large volcanic eruptions that inject huge amounts of material into the stratosphere also drive climate change — but unlike greenhouse gases, they cause global cooling. You can chalk that up to the presence of sulfur dioxide (SO2) in the volcanic output.

Once in the stratosphere, that SO2 is spread around the globe and oxidized into sulfate particles, which typically remain there for a few years. The sulfate particles scatter and reflect sunlight and in so doing cause a cooling of global temperatures. (Another effect of those sulfate particles in the stratosphere is spectacular sunsets.)

A prime example of volcanic cooling is the 1991 Mount Pinatubo eruption. Inspection of the global temperature record clearly shows a precipitous drop following the explosion and then a slow recovery over several years. Such events serve as great experiments for climate scientists who can use them to quantify how the climate responds to other perturbations such, as greenhouse gas warming.

Pinatubo and global temperatures. (From Hegrel et al (2006) http://www.nature.com/nature/journal/v440/n7087/abs/nature04679.html and GISS http://data.giss.nasa.gov/gistemp/graphs)

The 19th-Century Puzzle Piece

One of the coldest decades of the last few centuries occurred between 1810 and roughly 1819. Particularly extreme was 1816 — the “year without a summer.”

Scientists have debated for decades over the cause of those cool temperatures. Was it volcanoes ? Was it a decrease in solar activity? Was it both?

The evidence for solar activity is significant. The decade was midway through the period known as the Dalton Minimum, during which solar activity was anomalously low. The Little Ice Age, which lasted about 400-600 years, had peaked during the Maunder Minimum (somewhere between 1645 and 1715), another period of extremely low solar activity.

Yet the evidence in favor of a role for volcanoes is also strong. One of the largest eruptions in recent history was observed from Indonesia’s Mount Tambora in 1815, just before the year without a summer. But what about those anomalously cool temperatures between 1810 and 1815?

A new paper in press in Geophysical Research Letters by Jihong Cole-Dai of South Dakota State University and colleagues provides new evidence pointing to an earlier volcanic eruption as the culprit.

Variations in the relative concentrations of two sulfur isotopes (S-34 and S-33) in ice cores recovered from Greenland and Antarctica suggest that the sulfur in those ice cores came from a volcanic eruption. The simultaneous appearance of the sulfur signature in ice cores from both poles (i.e., Greenland and Antarctica) suggests that the sulfur was globally distributed and thus must have come from the stratosphere. In addition, the timing of the sulfate deposition in cores from both locations suggests that the as-yet-identified eruption occurred in 1809 just before the cool decade began.

This is cool stuff, and pretty compelling, but I suspect the debate is not over and we can look forward to seeing the solar-variation camp and volcano camp joust over this puzzle piece for many years to come.

filed under: Antarctica, El Nino-Southern Oscillation, faculty, global warming, La Nina, Planetary Watch
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13 Comments

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  1. MattN
    Nov 15, 2009

    Good entry. Nice to see someone in the AGW-camp acknowledge there are significant natural factors that we don’t fully understand yet. The observational data favors the theory that the bulk of 20th century warming has been driven by the oceans (indirectly by increased solar activity), not CO2. In addition, there’s a new paper in publication right now that has found ~50% of the warming since 1950 has been the result of land-use changes. Read about it here: http://wattsupwiththat.com/2009/11/11/georgia-tech-50-percent-of-the-usa-warming-that-has-occurred-since-1950-is-due-to-land-use-changes/

    • Bill Chameides
      Nov 18, 2009

      MattN: This is not the proper place to get into a critique of Brian Stone’s work, but let me just make one point. Even if you accept his conclusions, it does not mean that 50 percent of the globe’s warming has been the result of land-use changes — the work only applied to the United States.

      • MattN
        Nov 18, 2009

        No problem, but I think that is totally naiive to think this can not apply to other parts of the world. Understand every corner of the planet has undergone a similar rapid increase in population and the same rapid change in land (mis)use. A lot of people, alot of cleared land for them, and where exactly are those thermometers located again…?

        • Bill Chameides
          Nov 20, 2009

          MattN – 70 percent of the Earth’s surface is ocean.

          • MattN
            Dec 2, 2009

            The vast, vast, vast majority of temperature data for the last 100+ years is land based. What’s your point again?

            • Bill Chameides
              Dec 8, 2009

              MattN: How about if we just focus on the last 30 years. How do you explain increasing sea-surface temperature trends from satellites? From the extensive data sets from ocean-going vessels? Do you think the heat-island effects the authors were talking about as a result of land-use change can explain melting glaciers in the Andes, in Greenland?

              • MattN
                Dec 8, 2009

                A completely, totally, 100% natural phenomemon driven by a positive PDO. By the way, what satellite data are you looking at? I’m looking directly at UAH data here: http://vortex.nsstc.uah.edu/data/msu/t2lt/uahncdc.lt Ocean surface temp anomaly 1979 (1st full year of observations:) -.047C 2008: -.027C Not seeing it, Doc. 30 years and all we have is .02C??? Hardly significant. Besides, the REAL measure of global warming is ocean heat content (I suspect you know this and wanted me to take the SST bait). Every climatologist including Hansen agree on this. And since the ARGO bouys were deployed in 2003, they have measured exactly zero, zip, nada increase in ocean heat content. Explain that please….

                • Bill Chameides
                  Dec 15, 2009

                  MattN: Four and a half years of data do not make a climate trend. For the long-term trend, see Levitus’s 2009 paper, which includes the Argo buoys. To wit: “the linear trend in ocean heat content remain similar to our earlier estimate.” http://www.agu.org/pubs/crossref/2009/2008GL037155.shtml

              • MattN
                Dec 8, 2009

                Here’s a peer reviewed paper on the recent trend in upper ocean heat content since ARGO deployment: http://www.ncasi.org/publications/Detail.aspx?id=3152

                • Bill Chameides
                  Dec 15, 2009

                  MattN: The paper you cite only looked at four and a half years of data — hardly a climatic record. And I’ll take the paper by Levitus (of NOAA’s Oceanographic Data Center) and colleagues published in Geophysical Research Letters ( http://www.agu.org/pubs/crossref/2009/2008GL037155.shtml ) over a paper (by Craig Loehle, a Mathematica consultant) published on the web site of National Council for Air and Stream Improvement, Inc, a nonprofit research institute that focuses on environmental topics of interest to the forest-products industry.

                  • MattN
                    Dec 16, 2009

                    Had tha data shown 4 1/2 years of increased ocean heat content, you would have made a blog entry about it. And you KNOW you would have. But it doesn’t, so it’s “hardly climatic”. Intresting…

                    • Bill Chameides
                      Dec 16, 2009

                      Hey, MattN: Global temperatures have been on the rise in recent months. Is that a climatic trend? No it is not.

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