Climate Change and...
- Climate Variability
- Climate Models
Effects of Climate Change
Volcanic Eruptions and Aerosol Emissions
ABSTRACT: Examined is the effect on surface temperature of the volcanic eruptions of Asama and Laki in 1783, Tambora in 1815, Coseguina in 1835, Krakatoa in 1883, Santa Maria, Soufrière and Pelée in 1902, and Agung in 1963, using temperature records extending back to 1781. These records include New Haven, Connecticut, in North America; Edinburgh, De Bilt, Copenhagen, Berlin and Vilnius in Northern Europe; Geneva, Basel, Hohen-peissenberg, Vienna and Budapest in Central Europe; the “Central England” data of Manley; and the merged Northern Hemisphere data of Groveman and Landsberg and Jones et al. At New Haven and in Europe there is more evidence of a cooling following eruptions in subtropical and temperate latitudes than in equatorial latitudes (despite the similarity in mean dust-veil index), with a cooling most evident following the Asama and Laki eruptions in Japan and Iceland, and next most evident following the Coseguina eruption in Nicaragua. Following the tremendous Tambora eruption, the eruption with the largest dust-veil index, there is obvious cooling at New Haven, but not in Europe and perhaps not for the hemisphere as a whole. Hemispheric cooling is indicated to have been most pronounced following the Agung eruption—of the six eruption episodes the one with the smallest dust veil index but the best temperature data. Based on an application of Student's t-test to station, regional and hemispheric data, on 27 occasions (out of a possible 96) the average temperature for the 5-year period after the eruption is significantly (at the 5% level) lower than the average temperature for the 5- year period before the eruption, but in no case is the average temperature after the eruption significantly higher. It is proposed that cooling is not more apparent following some eruptions because of the tropospheric warming associated with strong and persistent El Niño episodes occurring shortly after the eruptions.
ABSTRACT: Numerical experiments have been carried out with a two-dimensional sector averaged global climate model with a detailed radiative scheme in order to assess the possible impact of solar and volcanic activities on the Earth’s surface temperature at the secular time scale from 1700 to 1992. Our results indicate that while the general trend of the observed temperature variations on the century time scale can be generated in response to both the solar and volcanic forcings, these are clearly not sufficient to explain the observed 20th century warming and more specifically the warming trend which started at the beginning of the 1970s. However, the lack of volcanism during the period 1925–1960 could account, at least partly, for the observed warming trend in this period. Finally, while Schlesinger and Ramankutty (1994) assumed that random forcing could not be a possible source of the 65–70 year oscillation they detected in the global climate system, our results indicate that the volcanic forcing over the past 150 years could have introduced an oscillation of around 70 years in the Earth’s surface temperature.
ABSTRACT: Several catalogs of explosive volcanic eruptions are reviewed and their limitations assessed. A new, homogeneous set of high quality gridded temperature data for continental regions of the northern hemisphere is then examined in relation to the timing of major explosive eruptions. Several of the largest eruptions are associated with significant drops in summer and fall temperatures, whereas pronounced negative anomalies in winter and spring temperatures are generally unrelated to volcanic activity. The effect of explosive eruptions on temperature decreases latitudinally away from the location of the eruption. High latitude eruptions have the greatest impact on high and mid latitudes; low latitude eruptions mainly influence low and mid latitudes. Temperature depressions following major eruptions are very abrupt but short-lived (1 to 3 months) decreasing in magnitude over the course of the subsequent 1 to 3 years. Generally any signal is indistinguishable from noise after 12 months but a small recurrent drop in temperature is evident about 12 to 24 months after the initial anomaly. Considering all known eruptions which injected material into the stratosphere over the last 100 years (except the 5 largest eruptions) a significant temperature depression is observed over the continents only in the month immediately following the eruption. There is no evidence that large eruptions over the last 100 years have had a significant effect on low frequency temperature changes.
ABSTRACT: Indices of summer sea ice severity in the eighteenth and nineteenth centuries have been reconstructed from sailing ships' log-books. The ice record for Hudson Strait extends from 1751 to 1889. Ice records are available for two parts of Hudson Bay and these extend from 1751 to 1870. The three records were derived from the same sources but the method of derivation applied in the bay was different to that applied in the strait. The years having the five largest ice indices in each of these records were identified. Also identified were the years in which major volcanic eruptions occurred between 1751 and 1889. The number of concurrences between the years with severe ice in Hudson Strait and the years with major eruptions was significant at the 99.5% level. In the western part of Hudson Bay this significance level was 95%. The years with severe ice in eastern Hudson Bay did not concur with major eruptions.
ABSTRACT: Maximum latewood density data from trees at thirteen temperature-sensitive sites along the northern treeline of North America are used to evaluate the spatial patterns of response to four known volcanic events just prior to the period of modern observations: in 1640, 1783, 1815 and 1835. A previously unknown event is also postulated for 1699. This tree-ring density parameter is used because it shows a stronger and more consistent short-term, temperature-related volcanic signal than ring width. Normalized density departures following these events vary in sign and magnitude from region to region, with the coldest summer conditions inferred for the Northwest Territories in 1641, Alaska in 1783, Quebec and Labrador in 1816 and the Northwest Territories in 1836. For these as well as other events, low density values are often among the most extreme on record at their respective locations. We suggest that these regional variations in tree growth reflect cooling induced by volcanism and the distribution of cooling influenced by atmospheric circulation patterns.
ABSTRACT: We determine the volcano climate sensitivityλ and response time τ for the Mount Pinatubo eruption, using observational measurements of the temperature anomalies of the lower troposphere, measurements of the long wave outgoing radiation, and the aerosol optical density. Using standard linear response theory we find λ = 0.15± 0.06 K/(W/m2 ), which implies a negative feedback of −1.4 (+0.7, −1.6). The intrinsic response time isτ = 6.8± 1.5 months. Both results are contrary to a paradigm that involves long response times and positive feedback.
ABSTRACT: Background: The amount of carbon dioxide in the atmosphere steadily increases as a consequence of anthropogenic emissions but with large interannual variability caused by the terrestrial biosphere. These variations in the CO2 growth rate are caused by large-scale climate anomalies but the relative contributions of vegetation growth and soil decomposition is uncertain. We use a biogeochemical model of the terrestrial biosphere to differentiate the effects of temperature and precipitation on net primary production (NPP) and heterotrophic respiration (Rh) during the two largest anomalies in atmospheric CO2 increase during the last 25 years. One of these, the smallest atmospheric year-to-year increase (largest land carbon uptake) in that period, was caused by global cooling in 1992/93 after the Pinatubo volcanic eruption. The other, the largest atmospheric increase on record (largest land carbon release), was caused by the strong El Niño event of 1997/98.
Results: We find that the LPJ model correctly simulates the magnitude of terrestrial modulation of atmospheric carbon anomalies for these two extreme disturbances. The response of soil respiration to changes in temperature and precipitation explains most of the modelled anomalous CO2 flux.
Conclusion: Observed and modelled NEE anomalies are in good agreement, therefore we suggest that the temporal variability of heterotrophic respiration produced by our model is reasonably realistic. We therefore conclude that during the last 25 years the two largest disturbances of the global carbon cycle were strongly controlled by soil processes rather then the response of vegetation to these large-scale climatic events.
Gaffen, D.J., T. J. Crowley, S. K. Baum, K.-Y. Kim, W. T. Hyde (2003). Detection of volcanic, solar and greenhouse gas signals in paleo-reconstructions of Northern Hemispheric temperature. Geophysical Research Letters 30 (5): 1242, doi:10.1029/2002GL016635
ABSTRACT: We apply a multiple regression method to estimate the response to anthropogenic and natural climate forcings simultaneously from a number of paleo-reconstructions of Northern Hemispheric average temperature. These long records (600 to 1000 years) provide a unique opportunity to distinguish between different external influences on climate. The response to volcanic forcing is reliably detected in all reconstructions, and the simulated temperature response to volcanic eruptions compares favorably with observations. The response to solar forcing is detected in Hemispheric mean data only over some periods in some records, and appears weak. Although most records can be used only to the middle of the 20th century, the temperature response to CO2 can be detected by this time in most records.
ABSTRACT: Large volcanic eruptions, in addition to the well-known effect of producing global cooling for a year or two, have been observed to produce shorterterm responses in the climate system involving non-linear dynamical processes. In this study, we use the ECHAM2 general circulation model forced with stratospheric aerosols to test some of these ideas. Run in a perpetual-January mode, with tropical stratospheric heating from the volcanic aerosols typical of the 1982 El Chichón eruption or the 1991 Pinatubo eruption, we find a dynamical response with an increased polar night jet in the Northern Hemisphere (NH) and stronger zonal winds which extend down into the troposphere. The Azores High shifts northward with increased tropospheric westerlies at 60°N and increased easterlies at 30°N. Surface temperatures are higher both in northern Eurasia and North America, in agreement with observations for the NH winters of 1982–83 and 1991–92 as well as the winters following the other 10 largest volcanic eruptions since 1883.
ABSTRACT: Seasonal and annual temperature reconstructions derived from western North American semi-arid site tree-ring chronologies are used to examine the possible spatial response of North American climate to volcanic eruptions within the period 1602 to 1900. Low-latitude eruptions appear to give the strongest response. Cooling of the annual average temperatures in the central and eastern United States is reconstructed to follow volcanic eruptions with warming in the western states. The magnitude and spatial extent of the reconstructed cooling and warming varies seasonally. The warming that occurs in the west is strongest and most extensive in winter while the cooling in the east is most marked in summer. These results are based on reconstructed climate records which contain error terms unrelated to climatic factors. The suggested pattern of response to volcanic forcing is, however, supported by four independent temperature/proxy temperature series within the area of the temperature reconstructions. Additional support is provided by three independent series lying outside the area which suggest that the temperature spatial response may extend to the north beyond the area covered by the tree-ring reconstructions.
ABSTRACT: The 1815 eruption of Tambora volcano (Sumbawa island, Indonesia) expelled around 140 gt of magma (equivalent to 50 km3 of dense rock), making it the largest known historic eruption. More than 95% by mass of the ejecta was erupted as pyroclastic flows, but 40% by mass of the material in these flows ended up as ash fallout from the ‘phoenix’ clouds that lofted above the flows during their emplacement. Although they made only a minor contribution to the total magnitude of the eruption, the short-lived plinian explosions that preceded the climactic eruption and caldera collapse were powerful, propelling plumes up to 43 km altitude. Over 71 000 people died during, or in the aftermath of, the eruption, on Sumbawa and the neigh-bouring island of Lombok. The eruption injected 60 mt of sulfur into the stratosphere, six times more than was released by the 1991 Pinatubo eruption. This formed a global sulfate aerosol veil in the stratosphere, which resulted in pronounced climate perturbations. Anomalously cold weather hit the northeastern USA, maritime provinces of Canada, and Europe the following year. 1816 came to be known as the ‘Year without a summer’ in these regions. Crop failures were widespread and the eruption has been implicated in accelerated emigration from New England, and widespread outbreaks of epidemic typhus. These events provide important insights into the volcanic forcing of climate, and the global risk of future eruptions on this scale.
ABSTRACT: Ice cores from both the Arctic and Antarctic record a massive volcanic eruption in around AD 1258. The inter-hemispheric transport of ash and sulphate aerosol suggests a low-latitude explosive eruption, but the volcano responsible is not known. This is remarkable given estimates of the magnitude of the event, which range up to 5 × 1014 - 2 × 1015 kg (200-800 km3 of dense magma), which would make this the largest eruption of the historic period, and one of the very largest of the Holocene. The associated collapse caldera could have had a diameter up to 10-30 km. Palaeoclimate reconstructions indicate very cold austral and boreal summers in AD 1257-59, consistent with known patterns of continental summer cooling following tropical, sulphur-rich explosive eruptions. This suggests an eruption in AD 1257, producing a stronger climate forcing than hitherto recognized.
ABSTRACT: The Minoan eruption of Santorini was a large-magnitude natural event. However, in terms of scale it ranks smaller in erupted volume and eruptive intensity than the historical eruption of Tambora in 1815 AD, and smaller in sulphur emission and, by inference, climatic effects than both the Tambora and Mt. Pinatubo, 1991, eruptions. Eruption statistics for the past 2000 years indicate that Minoan-size eruptions typically occur at a rate of several per thousand years. Eruptions resulting in a Minoan-scale injection of sulphur to the stratosphere occur far more frequently – at a rate of one or two per century. Inferences of massive sociological, religious and political impacts from such eruptions owe more to mythology than reality.
ABSTRACT: A general feedback between volcanism and climate at times of transition in the Quaternary climate record is suggested, exemplified by events accompanying the Toba eruption (~74,000 yr ago), the largest known late Quaternary explosive volcanic eruption. The Toba paroxysm occurred during thed18 O stage 5a-4 transition, a period of rapid ice growth and falling global sea level, which may have been a factor in creating stresses that triggered the volcanic event. Toba is estimated to have produced between 1015 and 1016 g of fine ash and sulfur gases lofted in co-ignimbrite ash clouds to heights of at least 32 ± 5 km, which may have led to dense stratospheric dust and sulfuric acid aerosol clouds. These conditions could have created a brief, dramatic cooling or "volcanic winter," followed by estimated annual Northern Hemisphere surface-temperature decreases of ~3° to 5°C caused by the longer-lived aerosols. Summer temperature decreases of³10°C at high northern latitudes, adjacent to regions already covered by snow and ice, might have increased snow cover and sea-ice extent, accelerating the global cooling already in progress. Evidence for such climate-volcanic feedback, following Milankovitch periodicities, is found at several climatic transitions.
ABSTRACT: In recent years a sequence of papers has discussed the impact of volcanic eruptions upon global environments. Emphasis has been placed upon their potential role in depressing hemispheric temperatures and affecting global weather patterns. Many researchers have related ecological, environmental and historical phenomena to individual eruptions. However, the linking of spatially and temporally disparate phenomenon to eruption chronologies involves several levels of supposition and at each level in the argument greater potential for error arises. This paper examines critically a number of important issues that arise from these studies. How valid are the linkages that are drawn? Do they establish a dependent relationship or merely coincidence? The validity of linking volcanic activity with disparate spatial and temporal events in the climatic, historical and palaeoecological records is addressed. There can be little doubt that volcanoes have a great effect on proximal climates and environments, but their global impact is less well understood. The scale and magnitude of responses to large eruptions such as the historically notorious Tambora (1815) and Mt. Pinatubo (1991) is far from consistent. This paper urges the adoption of a more critical perspective when considering these issues.
D. T. Shindell, G. A. Schmidt, M. E. Mann, G. Faluvegi (2004). Dynamic winter climate response to large tropical volcanic eruptions since 1600. Journal of Geophysical Research 109 (D05104): doi:10.1029/2003JD004151
ABSTRACT: We have analyzed the mean climate response pattern following large tropical volcanic eruptions back to the beginning of the 17th century using a combination of proxy-based reconstructions and modern instrumental records of cold-season surface air temperature. Warm anomalies occur throughout northern Eurasia, while cool anomalies cover northern Africa and the Middle East, extending all the way to China. In North America, the northern portion of the continent cools, with the anomalies extending out over the Labrador Sea and southern Greenland. The analyses confirm that for two years following eruptions the anomalies strongly resemble the Arctic Oscillation/Northern Annular Mode (AO/NAM) or the North Atlantic Oscillation (NAO) in the Atlantic-Eurasian sector. With our four-century record, the mean response is statistically significant at the 95% confidence level over much of the Northern Hemisphere land area. However, the standard deviation of the response is larger than the mean signal nearly everywhere, indicating that the anomaly following a single eruption is unlikely to be representative of the mean. Both the mean response and the variability can be successfully reproduced in general circulation model simulations. Driven by the solar heating induced by the stratospheric aerosols, these models produce enhanced westerlies from the lower stratosphere down to the surface. The climate response to volcanic eruptions thus strongly suggests that stratospheric temperature and wind anomalies can affect surface climate by forcing a shift in the AO/NAM or NAO.
ABSTRACT: A reassessment of the ash density associated with the eruption of the volcano Tambora, Indonesia, in 1815 is presented by examining contemporary reports. This eruption produced the largest known ashfall in historical times. The density of the fallen ash at Makassar, about 380 km north of Tambora, can be safely stated to be 636 kg m−3 .
ABSTRACT: Dubbi volcano, located in the northeast part of the Afar triangle, erupted explosively in May 1861, showering maritime traffic in the Red Sea with pumice and plunging coastal settlements into darkness. Earthquakes associated with the opening phase of the eruption were felt in Yemen, and explosions were heard as far as Massawa, 330 km distant. More than 100 local inhabitants were reported killed, possibly as a result of pyroclastic flow emplacement. By October 1861, activity switched to basaltic fire-fountaining focused along a 4-km-long summit fissure that fed several lava flows that traveled as far as 22 km. We present a reconstruction of this unusual explosive and effusive eruption sequence based on interpretation of contemporary accounts, analysis of satellite imagery, field work, and laboratory geochemistry. The volume of lava flows alone, 3.5 km3, makes this the largest reported historical eruption in Africa. An anomalously cold Northern Hemisphere summer in 1862, recorded in tree-ring records, could be the result of Dubbi's sulfate aerosol veil.
ABSTRACT: Geochemical identification of Mount Mazama ash in the Greenland Ice Sheet Project 2 (GISP2) ice core gives a calendrical age of 7627 ± 150 cal yr B.P. (5677 ± 150 B.C.) for the eruption, thus providing a more accurate early Holocene stratigraphic time line than previously available. The GISP2 record of volcanically derived sulfate suggests a total stratospheric aerosol loading between 88 and 224 Mt spread over an 6 yr period following the eruption of Mount Mazama. Taking into account the likelihood of some tropospheric aerosol transport to Greenland, realistic estimates of the resulting atmospheric optical depth range from 0.6 to 1.5. These values may have produced a temperature depression of 0.6 to 0.7 °C at mid to high northern latitudes for 1–3 yr after the eruption. These results indicate that the 5677 B.C. eruption of Mount Mazama was one of the most climatically significant volcanic events of the Holocene in the Northern Hemisphere. We also calculate a maximum stratospheric Cl– release of 8.1 Mt by the eruption, which may have led to substantial stratospheric ozone depletion.
ABSTRACT: Determining a reliable calendrical age of the Santorini (Minoan) eruption is necessary to place the impact of the eruption into its proper context within Bronze Age society in the Aegean region. The high-resolution record of the deposition of volcanically produced acids on polar ice sheets, as available in the SO4 2− time series from ice cores (a direct signal), and the high-resolution record of the climatic impact of past volcanism inferred in tree rings (a secondary signal) have been widely used to assign a 1628/1627 BC age to the eruption. The layer of ice in the GISP2 (Greenland) ice core corresponding to 1623±36 BC , which is probably correlative to the 1628/1627 BC event, not only contains a large volcanic-SO4 2− spike, but it contains volcanic glass. Composition of this glass does not match the composition of glass from the Santorini eruption, thus severely challenging the 1620s BC age for the eruption. Similarly, the GISP2 glass does not match the composition of glass from other eruptions (Aniakchak, Mt. St. Helens, Vesuvius) thought to have occurred in the 17th century nor does it match potential Icelandic sources. These findings suggest that an eruption not documented in the geological record is responsible for the many climate-proxy signals in the late 1620s BC. Although these findings do not unequivocally discount the 1620s age, we recommend that 1628/1627 BC no longer be held as the “definitive” age for the Santorini eruption.
ABSTRACT: The time series of volcanically produced sulfate from the GISP2 ice core is used to develop a continuous record of explosive volcanism over the past 110,000 yr. We identified ~850 volcanic signals (700 of these from 110,000 to 9000 yr ago) with sulfate concentrations greater than that associated with historical eruptions from either equatorial or mid-latitude regions that are known to have perturbed global or Northern Hemisphere climate, respectively. This number is a minimum because decreasing sampling resolution with depth, source volcano location, variable circulation patterns at the time of the eruption, and post-depositional modification of the signal can result in an incomplete record. The largest and most abundant volcanic signals over the past 110,000 yr, even after accounting for lower sampling resolution in the earlier part of the record, occur between 17,000 and 6000 yr ago, during and following the last deglaciation. A second period of enhanced volcanism occurs 35,000–22,000 yr ago, leading up to and during the last glacial maximum. These findings further support a possible climate-forcing component in volcanism. Increased volcanism often occurs during stadial/interstadial transitions within the last glaciation, but this is not consistent over the entire cycle. Ages for some of the largest known eruptions 100,000–9000 yr ago closely correspond to individual sulfate peaks or groups of peaks in our record.
G. A. Zielinski, P. A. Mayewski, L. D. Meeker, S. Whitlow, M. S. Twickler, M. Morrison, D. A. Meese, A. J. Gow, R. B. Alley (1994). Record of volcanism since 7000 B.C. from the GISP2 Greenland ice core and implications for the volcano-climate system. Science 264 (5161): 948-952
ABSTRACT: Sulfate concentrations from continuous biyearly sampling of the GISP2 Greenland ice core provide a record of potential climate-forcing volcanism since 7000 B.C. Although 85 percent of the events recorded over the last 2000 years were matched to documented volcanic eruptions, only about 30 percent of the events from 1 to 7000 B.C. were matched to such events. Several historic eruptions may have been greater sulfur producers than previously thought. There are three times as many events from 5000 to 7000 B.C. as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions. This increased volcanism in the early Holocene may have contributed to climatic cooling.