Studies have attempted to 'isolate' the volcanic signal in noisy temperature data. This assumes that it is possible to isolate a distinct volcanic signal in a record that may have a combination of forcings (ENSO, solar variability, random fluctuations, volcanism) that all interact. The key to discovering the greatest effects of volcanoes on short-term climate may be to concentrate on temperatures in regions where the effects of aerosol clouds may be amplified by perturbed atmospheric circulation patterns. This is especially true in subpolar and midlatitude areas affected by changes in the position of the polar front. Such climatic perturbation can be detected in proxy evidence such as decrease in tree-ring widths and frost rings, changes in the treeline, weather anomalies, severity of sea-ice in polar and subpolar regions, and poor grain yields and crop failures. In low latitudes, sudden temperature drops were correlated with the passage overhead of the volcanic dust cloud (Stothers, 1984). For some eruptions, such as Tambora, 1815, these kinds of proxy and anectdotal information were summarized in great detail in a number of papers and books (e.g., Post, 1978; Stothers, 1984; Stommel and Stommel, 1986; C. R. Harrington, in press). These studies lead to the general conclusion that regional effects on climate, sometimes quite severe, may be the major impact of large historical volcanic aerosol clouds

Rampino, Michael R.

English

NASA Technical Reports Server

N91-21643
Climatic Impact of Volcanic Eruptions
MICHAEL R. RAMPINO
Earth Systems Group, New York University, New York, NY 10003, and NASA,
Goddard Space Flight Center, Institute for Space Studies, New York, NY 10025
Volcanoes and Climate
Connections between volcanic eruptions and climatic change have been suggested on
timescales from days to 108 years. On short timescalcs, one approach to the
volcano/climate problem has been to compare the times of historic volcanic eruptions with
changes in yearly, monthly or seasonal surface temperatures on regional, hemispheric and
global scales. These studies involve either a direct comparison of the times of significant
eruption years with temperature records (e.g., Rampino and Self, 1982, 1984; Stothers,
1984; Angell and Korshover, 1984; Mass and Portman, 1989) (Table 1) or a study of
composited temperature records for a number of years (months, seasons) before and after a
chosen set of eruptions (e.g., Mass and Schneider, 1977; Self et al., 1981, Taylor et al.,
1980). Eruptions are usually chosen using various measures of volcanic intensity
including the VEI (Volcanic Explosivity Index) of Newhall and Self, 1982, or the DVI
(Dust Veil Index) after Lamb, 1970, or on the basis of the stratospheric aerosol loading
determined dh'ectly by observations or indir_fly from the acidity record of ice cores. The
various studies give similar resultsmthe composites show a Nonhero Hemisphere cooling
of 0.2 to 0.3°C for 1 to 3 years after eruptions for a number of eruptions grouped together
(Fig. 2 ), and individual volcanic events that produced significant aerosol clouds such as
Krakatau, 1883 or Tambora, 1816 are followed by Northern Hemisphere coolings of 0.3
to 0.7°C for 1 to 3 years after the eruption (Table 1) (Baldwin et al., 1976; Rampino and
Self, 1984; Stothers, 1984; Angell and Korshover, 1985). Zonally, the cooling is
amplified at high latitudes. Regional records show more variability , especially
mcridionally.
Bradley (1988) has used monthly and seasonal temperature data, and finds that several
of the larger eruptions of the past 100 years are followed by significant negative anomalies
in summer and fall temperatures. Temperature decreases after major eruptions are found to
be abrupt and short lived (1 to 3 months), with a recurrence of the cooling about 12 and 24
months after the eruptions. The maximum effect of about 0.4°C occurs in the summer and
fall months immediately following the eruptions, and falls off in the same seasons over the
next 2 years.
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https://ntrs.nasa.gov/search.jsp?R=19910012330 2020-03-19T18:52:17+00:00Z
Massand Portman (1989) recently suggested that the volcanic signal was present in
temperature records, but smaller than previously thought. It was limited to those eruptions
that created the densest aerosol clouds in the last 100 years, and was enhanced by
subtracting out other sources of interannual variability, e.g. the El Nino/Southem
Oscillation. Mass and Portman stressed that the volcanic "signal" of 0.1 to 0.2°C is of the
same order as "background" temperature variations in non-volcanic years, and found no
evidence of large coolings in the first few months after the eruptions. It may be, however,
that stratospheric aerosol clouds have some effect on the ENSO phenomena, either
triggering them, or intensifying already existing ENSO patterns (Handler, 1984). Handler
(1986) has also suggested a connection between stratospheric aerosols and the strength of
the yearly Indian monsoonal precipitation.
These studies have attempted to "isolate" the volcanic signal in noisy temperature data.
Thyis assumes that it is possible to isolate a distinct volcanic signal in a record that may
have a combination of forcings (ENSO, solar variability, random fluctuations, volcanism)
that all interact. The key to discovering the greatest effects of volcanoes on short-term
climate may be to concentrate on temperatures in regions where the effects of volcanic
aerosol clouds may be amplified by perturbed atmospheric circulation patterns. This is
especially true in sub-polar and mid-latitude areas affected by changes in the position of the
polar front. Such climatic perturbations can be detected in surface temperatures and in
proxy evidence such as decreases in tree-ring widths and frost rings, changes in the
treeline,weather anomalies such as unusually cold summers, severity of sea-ice in polar and
sub-polar regions, and poor grain yields and crop failures (for a review see Rampino et al.,
1988). In low latitudes, sudden temperature drops have been correlated with the passage
overhead of the volcanic dust cloud (Stothers, 1984). For some eruptions, such as
Tambora, 1815, these kinds of proxy and anectdotal information have been summarized in
great detail in a number of papers and books (e.g., Post, 1978; Stothers, 1984; Stommel
and Stommel, 1986; C.R. Harrington, in press). These studies lead to the general
conclusion that regional effects on climate, sometimes quite severe, may be the major
impact of large historical volcanic aea'osol clouds.
Tambora and 1816: The Test Case?
Instead of searching for the small climatic effects of small historic eruptions in climate
data sets, it may be instructive to look in detail at the strongest volcanic perturbation in
recent history, the Tambora eruption of April, 1815 and the events that followed it. Perhaps
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smallereruptions(in terms of aerosolsreleased)might have similar, but lessextreme,
effectson climate that can be detectedif one knows what to look for. Stothers(1984)
estimatesanopticaldepthof about1.0following theTamboraeruption,andthepresenceof
largeaciditypeaksin icecoresfrom GreenlandandAntarcticaarguesfor aglobaldisperesal
of theaerosolcloudof some1014g. In moststudiesof weatherrecordsor proxy data,the
year 1816, following the Tambora eruption, displays the strongestsignal of possible
"volcanoweather"in historical times. For example,in a key areain theEasternHudson
Bay region in midsummer1816,the reduction in meandaily temperaturefrom the long-
term averagewasabout 5 to 6o. It hasbeensuggestedthat a reduction in mean daily
temperaturein thisrangecould leadto theformation of perennialsnowcoverin northern
Canada(Wilson, 1985). The negativeanomalyin July 1816brought theabsolutemean
temperatureto below 5oc, more than 2° lower than the modernrecord in 1965. The
medianheightof the freezing level aboveeasternHudsonBay in July 1965(two years
afterthe Agungeruption)wasabout600 to 700 m lower thanthemodern 10yearvalue.
This suggeststhatthe-6°C anomalyin 1816might haveproduceda 1000m drop, to bring
thefreezing level to within 1500m of the surface.Suchconditionswere maintainedfor
only two years, 1816and 1817, but one may wonder how manyyearsof consecutive
extremeseasonalweatherwould berequiredto establishaneffectivesnowcover,andbring
ice/albedofeedbackintoplay. Frequentandextendedsnowfallalsotookplacein theregion
in 1816-1817-- in 1816,therewere only five weekswithout measurablesnowfall (mid-
July to mid-August).Furthermore,theatmosphericcirculationpatternwasdominatedbya
high pressureareaover the surfaceof HudsonBay, which remainedicecoveredthrough
thesummerof 1816(Wilson, 1985).
CatchpoleandFaurer(1983)show seaicepatternsin 1816thatarealsoconsistentwith
ahighly meridionalatmosphericcirculation patternovereasternNorthAmerica, showing
strong north to northwest winds in July and August of 1816 (Catchpole and Faurer, 1983).
Northwesterly winds brought cold air southward into the northeastern United States,
bringing the "Year without a Summer". The meridional circulation pattern also brought
cold weather to western Europe, and there is some evidence that, between these two
waves, warmer weather dominated, with an opening of the usually ice-covered Greenland
Sea between 74 ° and 80°N (wilson, 1985).
It should be pointed out however, that the cold weather in the Hudson Bay area began
before April 1815, with unusually cold years beginning in 1811/12, so that the Tambora
eruption cannot be the only cause of the climate shift. Perhaps the coincidence of the
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Tambora eruption with a time of low sunspot numbers (indicating lower solar activity) led
to the unusually cold weather of the 1811-1817 period.
Frost tings in trees in the Western U.S. also show a correspondence with years of
volcanic eruptions (LaMarche and Hirschboeck, 1984). These may indicate outbreaks of
exceptionally cold weather during the summer months, again possibly the result of
increased meridional circulation. Light tings in subarctic trees from northern Quebec also
show a correspondence with volcanic eruptions; for example, damage is most widespread
in 1816-1817 ( Filion et al., 1986). Tree tings have also been used to create synoptic
summer temperature patterns for Europe, which show significantly cooler summers from
1812 to 1816 (Briffa et al., 1988). The same kinds of data can be assembled for the other
major volcanic aerosol clouds of the last 200 years, and similarities noted. If one can
establish patterns that appear to be characteristic of "volcanic" perturbation, then it may be
possible to detect such patterns even for the smaller eruptions, and to see how well climate
models simulate such perturbations. It may be necessary not only to model the volcanic
perturbation, but also to include the effects of ENSO events and possible solar variations in
the model runs.
VOLCANISM AND LONG-TERM CLIMATE CHANGE
One problem with studying historical eruptions is that they are quite small compared to
those in the geologic record. The largest explosive eruption in historic times was probably
the Tambora, 1815 explosion, with about 50 km 3 of erupted magma. This can be
compared with large ignimbrite forming eruptions such as the Toba event of 75,000 yr BP,
which erupted more than 2,800 km3 of magma (Rose and Chesner, 1987). For effusive
eruptions, the largest historic event was Laid, 1783, which produced 12 km 3 of basalt,
compared with great flood basalt eruptions like the Roza flow in the Columbia River Group
(14 Myr BP), composed of 700 kin3 of basaltic lava in a single flow (Devine et al., 1984;
Rampino et al., 1988). Both of these eruptions may have released about 1016 g of
sulfurous gases. The effects of these and other pre-historic eruptions on climate are not
known. Both the Roza and Toba events appear to coincide with climatic coolings, but no
cause and effect relationship has been established.
If historic eruptions can cause small changes in climate, then perhaps larger eruptions
or groups of eruptions can cause major climate change. A number of authors have claimed
correlation between volcanic eruptions and glacial fluctuations on 10 3 to 10 5 year time
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scales. For example,BradleyandEngland(1978) and Porter(1981,1986)proposedthat
second-order"Little Ice Age"glacialadvancesduring theHolocenecouldhavebeendriven
by eruptions,sincetheglacial advancescorrelatewith peaksof acidity in polar icecores.
Porter (1981) estimatesthata global cooling of I°K could leadto a snowlinedepression
sufficient to causeglacieradvancesequivlentto thoseof thelastseveralcenturies,but this
seemsto be greaterthan the measuredvolcanic perturbations. Bray (1977, 1979a,b)
proposedthat largeeruptionsprecededglacial periods,with the glaciationstriggeredby
atmosphericaerosolclouds. However,in thiscase,becauseof theinaccuraciesin dating,it
is oftendifficult to determinewhichcamefirst, theeruptionsor theglaciation.
On evenlonger timescales,studiesby Kennett et al (1977)havedelineatedpulsesof
explosivevolcanicactivity in theCircum-Pacificregion for the last 30million yearsfrom
studiesof agedeterminations(mostly K/Ar dates)on igneousrocks, and countsof ash
layersin deep-seasedimentcores. They find significant pulsesof volcanismin thePlio-
Pleistocene(about2 Myr BP), latestMiocene to Early Pliocene(6 to 3 Myr BP), Late
Miocene (11 to 8 Myr BP) and Middle Miocene (16-14 Myr BP). Combinedwith other
data(e.g.,Hein et al., 1978),it seemsthatpulsesof widespread(perhapsglobal) explosive
volcanism took placenear0.5, 2.5, 5, 10,15,20 and 40 Myr BP (Kennettet al., 1985).
Someof thesespurtsin volcanismcorrelatewith timesof apparentpulsesof platemotion
andsealevel changes(Masuda,1986;Rampinoand Stothers,1987),sothe threemaybe
linked. Thesevolcanicpulsescanbealsobecorrelatedwith timesof globalcooling andice
formationasseenin oxygen-isotopedatafor theCenozoic.Flood basaltepisodesat 65,35,
and 17 Myr BP also correlatewith global coolings (Devine et al., 1984).This apparent
correlation of volcanic episodeswith times of global cooling may be coincidental,
however,andthere is no direct causeandeffect mechanismto suggestbeyondpossible
ice/albedofeedback.
Recommendations
1. Look at the strongest aerosol perturbations, e.g. Tambora, Krakatau, Agung, El
Chichon, etc. Don't average together the effects of small and large eruptions.
2. Use regional and seasonal climate data sets where the effects of volcanism on climate
may be amplified.
3. Study the spread of aerosol clouds for volcanic eruptions in different parts of the world
at different times of the year. Compare with tracer models.
4. Look for changes in atmospheric circulation patterns that could be studied with GCMs.
Observed temperature series and tree-ring studies could provide synoptic weather patterns.
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5. Establisha newvolcanic index based on VEI and data from ice cores, petrologic studies,
optical depth rneasurements, etc.
6. Look at climate records that have both climate and volcanic signals, e.g. ice cores.
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Climatic impact of volcanic eruptions

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