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Climate effects of high-latitude volcanic eruptions: Role of the time of year

2011 January 13

Climate effects of high-latitude volcanic eruptions: Role of the time of year
Ben Kravitz and Alan Roboc, 2010

A quick paper modeling the effect that time-of-year of volcanic eruption has on the ultimate climatic response.

We test how the time of year of a large Arctic volcanic eruption determines the climate impacts by conducting simulations with a general circulation model of Earth’s climate. For eruptions injecting less than about 3 Tg of SO2 into the lower stratosphere, we expect no detectable climatic effect, no matter what the season of the eruption. For an injection of 5 Tg of SO2 into the lower stratosphere, an eruption in the summer would cause detectable climate effects, whereas an eruption at other times of the year would cause negligible effects. This is mainly due to the seasonal variation in insolation patterns and sulfate aerosol deposition rates. In all cases, the sulfate aerosols that form get removed from the atmosphere within a year after the eruption by large-scale deposition. Our simulations of a June eruption have many similar features to previous simulations of the eruption of Katmai in 1912, including some amount of cooling over Northern Hemisphere continents in the summer of the eruption, which is an expected climate response to large eruptions. Previous Katmai simulations show a stronger climate response, which we attribute to differences in choices of climate model configurations, including their specification of sea surface temperatures rather than the use of a dynamic ocean model as in the current simulations


Sulfate aerosols, formed from the oxidation of SO2, have a long atmospheric lifetime in
the stratosphere of 1-3 years, if injected in the tropics [Budyko, 1977; Stenchikov et al., 1998].

I noted a 3 year cooling due to the Pinatubo stood out when I checked the NINO 3.4 record + 60 year trend against a global sea and land temperature record.

We simulated the climate response to high latitude volcanic eruptions with ModelE, a coupled atmosphere-ocean general circulation model developed by the National Aeronautics and Space Administration Goddard Institute for Space Studies [Schmidt et al., 2006].

I am reminded that a couple of years ago I had ModelE kind of running on a linux vm.

For the calendar year (2009) after the 5 Tg eruption in June, the average Northern Hemisphere surface air temperature is 0.06°C lower than the calendar year before the eruption (2007). Although not statistically significant according to GHCNv2 or CRUTEM3v, this does pose the question as to why such a temperature pattern occurred. A natural explanation for this could be ocean memory of the cooling due to the eruption [Stenchikov et al., 2009]. Although the version of the model we used to perform the simulations in this experiment does not provide us with enough information to assess changes in ocean heat content, we can still evaluate some oceanic changes.

7. Conclusions
Based on our climate modeling study, the time of year of a high latitude volcanic eruption is critical for determining the resulting climate effects, provided the eruption is large enough. Of the magnitudes we have investigated, a summer eruption was the only one that caused climate effects at a sufficient level of statistical significance. Extrapolating our results, a high latitude eruption will have larger climate effects if it occurs in the summer, and it is unlikely to have climate effects if it erupts in the winter, unless the eruption is particularly large. Regardless of the time of year, a high latitude eruption of the magnitudes we have simulated would not likely cause significant dynamical perturbations or change the general circulation.

In line with Stenchikov et al. [2009], we further conclude the ocean has memory of the cooling an eruption causes, which can serve to modulate changes in climate. However, the runs we have completed are not long enough to fully assess the impacts of the ocean on the climate system. We stress that simulations of large eruptions need to include a complex ocean to capture these potentially important effects.

From our results, the optimal time for an eruption to have the largest climate effects appears to be late spring to early summer. This study also prompts several additional questions. One such question is what are the dominant parameters that determine whether an eruption will have climate effects? It appears the summer eruption is an ideal or near-ideal combination of aerosol formation rate, deposition, and insolation. Conducting further simulations while artificially varying these parameters could be useful in determining the dominant effects. Additionally, we could ask how the details under which we run our simulations affect our results. Our comparison with Katmai could benefit from determination of the individual effect of prescribed optical depth vs. being dynamically linked to stratospheric circulation and the effect of using fixed sea surface temperatures vs. a dynamic ocean.

  1. Kelly
    2011 January 21 at 2:54 pm


    Very interesting!

    I’ve posted about volcanic dimming, ENSO and GISS here.

    My next step is to quantify the relationships between volcanic affects (SATO or Atmospheric Transmission), ENSO and temperature anomalies. Tamino has a recent post that tries to remove the affects of volcanoes, ENSO and solar variations here.

    Now that I have the data, all except solar, in one file, I need to dust off my regression notes.

  2. 2011 January 21 at 4:08 pm

    Good on you! You and Tamino are cruising into an area that I want to get into. I’ll be leaning on your stuff as I get closer to it.

  1. 2011 January 21 at 2:27 pm
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