Search

Supervolcano eruptions have occurred throughout Earth’s history and have major environmental impacts. These impacts are mostly associated with the attenuation of visible sunlight by stratospheric sulfate aerosols, which causes cooling and deceleration of the water cycle. Supereruptions have been assumed to cause so-called volcanic winters that act as primary evolutionary factors through ecosystem disruption and famine, however, winter conditions alone may not be sufficient to cause such disruption. Here we use Earth system model simulations to show that stratospheric sulfur emissions from the Toba supereruption 74,000 years ago caused severe stratospheric ozone loss through a radiation attenuation mechanism that only moderately depends on the emission magnitude. The Toba plume strongly inhibited oxygen photolysis, suppressing ozone formation in the tropics, where exceptionally depleted ozone conditions persisted for over a year. This effect, when combined with volcanic winter in the extra-tropics, can account for the impacts of supereruptions on ecosystems and humanity. Stratospheric sulfur emissions from the Toba supereruption about 74,000 years ago suppressed ozone formation which caused severe tropical ozone layer depletion and enhanced solar ultraviolet radiation stress, according to Earth system model simulations.

The volcanic eruption of Toba in northern Sumatra at 71 kyBP (±5 kyBP) emitted sulfur gas and deposited thick layers of dust throughout the surrounding region. It is thought to have had a significant and dramatic cooling impact on the paleoclimate worldwide. Ambrose [1] conjectured this to be the cause of the contemporaneous (50-100 kyBP) population bottleneck observed in humans. We hypothesize that a volcanic winter of sufficient magnitude to cause a population bottleneck in humans would similarly affect other mammals. To test this hypothesis, we estimated pairwise mismatch distributions using mtDNA control region sequences of 28 mammal species archived on NCBI to assess whether each species underwent a population bottleneck. For any species fitting the sudden expansion model, we estimated the timing of the bottleneck and compared it to the date range of the Toba eruption. Only 3 of the 28 species show evidence of rapid population expansion overlapping in time with the Toba eruption. Therefore, the hypothesis that the volcanic winter triggered by the Toba eruption caused a significant bottleneck impacting mammal species worldwide is not supported by mitochondrial evidence. Our results question the hypothesis that the Toba eruption contributed to the bottleneck observed in humans at this time.

The temporal proximity of the ∼74 ka Toba supereruption to a putative 100-50 ka human population bottleneck is the basis for the volcanic winter/weak Garden of Eden hypothesis, which states that the eruption caused a 6-year-long global volcanic winter and reduced the effective population of anatomically modern humans (AMH) to fewer than 10,000 individuals. To test this hypothesis, we sampled two cores collected from Lake Malawi with cryptotephra previously fingerprinted to the Toba supereruption. Phytolith and charcoal samples were continuously collected at ∼3-4 mm (∼8-9 yr) intervals above and below the Toba cryptotephra position, with no stratigraphic breaks. For samples synchronous or proximal to the Toba interval, we found no change in low elevation tree cover, or in cool climate C3 and warm season C4 xerophytic and mesophytic grass abundance that is outside of normal variability. A spike in locally derived charcoal and xerophytic C4 grasses immediately after the Toba eruption indicates reduced precipitation and die-off of at least some afromontane vegetation, but does not signal volcanic winter conditions. A review of Toba tuff petrological and melt inclusion studies suggest a Tambora-like 50 to 100 Mt SO2 atmospheric injection. However, most Toba climate models use SO2 values that are one to two orders of magnitude higher, thereby significantly overestimating the amount of cooling. A review of recent genetic studies finds no support for a genetic bottleneck at or near ∼74 ka. Based on these previous studies and our new paleoenvironmental data, we find no support for the Toba catastrophe hypothesis and conclude that the Toba supereruption did not 1) produce a 6-year-long volcanic winter in eastern Africa, 2) cause a genetic bottleneck among African AMH populations, or 3) bring humanity to the brink of extinction.

We use transient GFDL-CM3 chemistry-climate model simulations over the 2006-2100 period to show how the influence of volcanic aerosols on the extent and timing of ozone recovery varies with a) future greenhouse gas scenarios (RCP4.5 and RCP8.5) and b) halogen loading. Current understanding is that elevated volcanic aerosols reduce ozone under high halogen loading, but increase ozone under low halogen loading when the chemistry is more NOx dominated. With extremely low aerosol loadings (designated here as ‘background’), global stratospheric ozone burden is simulated to return to 1980 levels around 2050 in the RCP8.5 scenario, but remains below 1980 levels throughout the 21st century in the RCP4.5 scenario. In contrast, with elevated volcanic aerosols, ozone column recovers more quickly to 1980 levels, with recovery dates ranging from the mid-2040s in RCP8.5 to the mid-2050s to early 2070s in RCP4.5. The ozone response in both future emission scenarios increases with enhanced volcanic aerosols. By 2100, the 1980-baseline adjusted global stratospheric ozone column is projected to be 20-40% greater in RCP8.5 and 110-200% greater in RCP4.5 with elevated volcanic aerosols compared to simulations with the extremely low background aerosols. The weaker ozone enhancement at 2100 in RCP8.5 than in RCP4.5 in response to elevated volcanic aerosols is due to a factor of 2.5 greater methane in RCP8.5 compared with RCP4.5. Our results demonstrate the substantial uncertainties in stratospheric ozone projections and expected recovery dates induced by volcanic aerosol perturbations that need to be considered in future model ozone projections.

The Middle East and North Africa (MENA) regional climate appears to be extremely sensitive to volcanic eruptions. Winter cooling after the 1991 Pinatubo eruption far exceeded the mean hemispheric temperature anomaly, even causing snowfall in Israel. To better understand MENA climate variability, the climate responses to the El Chichon and Pinatubo volcanic eruptions are analyzed using observations, NOAA/National Centers for Environmental Prediction Climate Forecast System Reanalysis, and output from the Geophysical Fluid Dynamics Laboratory's High-Resolution Atmospheric Model. A multiple regression analysis both for the observations and the model output is performed on seasonal summer and winter composites to separate out the contributions from climate trends, El Nino–Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Indian summer monsoon, and volcanic aerosols. Strong regional temperature and precipitation responses over the MENA region are found in both winter and summer. The model and the observations both show that a positive NAO amplifies the MENA volcanic winter cooling. In boreal summer, the patterns of changing temperature and precipitation suggest a weakening and southward shift of the Intertropical Convergence Zone, caused by volcanic surface cooling and weakening of the Indian and West African monsoons. The model captures the main features of the climate response; however, it underestimates the total cooling, especially in winter, and exhibits a different spatial pattern of the NAO climate response in MENA compared to the observations. The conducted analysis sheds light on the internal mechanisms of MENA climate variability and helps to selectively diagnose the model deficiencies.

The Holuhraun eruption in 2014-15 was the largest in Iceland for more than 200 years. It resulted in emissions of large quantities of volcanic gases into the atmosphere (11 Mt SO2, 0.1 Mt HCl and 0.05 Mt HF). During the eruption the volcanic gases had major effects on F, SO4 and to a lesser extent Cl concentrations in precipitation throughout Iceland, effects not observed in recent decades. The concentrations of F, Cl and SO4 (n = 705) reached values of 444 μM, 12,270 μM and 17,324 μM during the eruption and were on average ~20 times higher for F and SO4 and much lower for Cl compared to pre-eruption times. The concentrations of major cations (Si, Na, K, Ca, Mg, Al and Fe) (n = 151) in the precipitation, were taken as having originated from seawater spray and dissolution of rock dust and aerosol. Based on the mixing model developed here, it is demonstrated that the source of the enrichment of F and SO4 was indeed the volcanic gas emissions with >60-100 mol% of SO4 and F in the precipitation originated from volcanic gas, whereas the Cl originated mostly from seawater spray, making the volcanic gas input of Cl relatively less important than for F and SO4. The results showed that large volcanic eruptions can have major effects on atmospheric chemistry and impact the composition of precipitation.

A volcanic eruption in the Americas, producing both a world famine and a world cycle of literature, is one of history’s stranger tricks, yet seemingly happened in the year 535. The traditional susp...

An 8 year volcanic SO2 emission inventory for 2005–2012 is obtained based on satellite measurements of SO2 from OMI (Ozone Monitoring Instrument) and ancillary information from the Global Volcanism Program. It includes contributions from global volcanic eruptions and from eight persistently degassing volcanoes in the tropics. It shows significant differences in the estimate of SO2 amount and injection height for medium to large volcanic eruptions as compared to the counterparts in the existing volcanic SO2 database. Emissions from Nyamuragira (DR Congo) in November 2006 and Grimsvotn (Iceland) in May 2011 that were not included in the Intergovernmental Panel on Climate Change 5 (IPCC) inventory are included here. Using the updated emissions, the volcanic sulfate (SO42−) distribution is simulated with the global transport model Goddard Earth Observing System (GEOS)-Chem. The simulated time series of sulfate aerosol optical depth (AOD) above 10 km captures every eruptive volcanic sulfate perturbation with a similar magnitude to that measured by Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). The 8 year average contribution of eruptive SO42− to total SO42− loading above 10 km is ~10% over most areas of the Northern Hemisphere, with a maxima of 30% in the tropics where the anthropogenic emissions are relatively smaller. The persistently degassing volcanic SO42− in the tropics barely reaches above 10 km, but in the lower atmosphere it is regionally dominant (60%+ in terms of mass) over Hawaii and other oceanic areas northeast of Australia. Although the 7 year average (2005–2011) of eruptive volcanic sulfate forcing of −0.10 W m−2 in this study is comparable to that in the 2013 IPCC report (−0.09 W m−2), significant discrepancies exist for each year. Our simulations also imply that the radiative forcing per unit AOD for volcanic eruptions can vary from −40 to −80 W m−2, much higher than the −25 W m−2 implied in the IPCC calculations. In terms of sulfate forcing efficiency with respect to SO2 emission, eruptive volcanic sulfate is 5 times larger than anthropogenic sulfate. The sulfate forcing efficiency from degassing volcanic sources is close to that of anthropogenic sources. This study highlights the importance of characterizing both volcanic emission amount and injection altitude as well as the key role of satellite observations in maintaining accurate volcanic emissions inventories.

Mt. Merapi in Java, Indonesia, erupted in November 2010. The eruption was proved to be the source of the aerosol layer observed by a ground-based lidar at Biak, Indonesia, in January 2011 using data on the global distribution of aerosols observed by the spaceborne cloud-aerosol lidar with orthogonal polarization (CALIOP). These data were used to describe how the volcanic aerosols produced by the volcanic eruption diffused throughout the tropical tropopause layer (TTL). The equivalent maximum total amount of volcanic SO2 estimated from the spatially integrated total amount of aerosols was 0.09 Tg, which is one-third to half that of gaseous SO2 after the eruption was observed by the ozone monitoring instrument satellite. The obtained cirrus-cloud-appearance frequency data exhibit a seasonal cycle having its maximum in winter and no detectable variations that are synchronized with the increase in TTL volcanic aerosols.

The impact of the ca. 75 ka Mount Toba (Indonesia) supereruption on regional and global climate has been controversial. East Africa is pivotal for qualifying this impact, specifically in addressing a hypothesis that this eruption caused a volcanic winter leading to a genetic bottleneck in anatomically modern human populations. If the Toba eruption caused a volcanic winter in East Africa, effects should be recorded in sediments from climatologically sensitive ecosystems. In deep tropical lakes, cooler temperatures would have reduced the density contrast between the epilimnion and hypolimnion, causing increased mixing, hypolimnion oxygenation, and enhanced nutrient advection. Such environmental changes produce noticeable and predictable responses in lake fossil assemblages and sediment loading. Here we present the first paleoecological evidence from East Africa of environmental conditions surrounding the eruption in a high-resolution (∼8–9 yr) analysis of two cores collected by the Lake Malawi Drilling Project. These cores contain an undisturbed record of sedimentation before, during, and after deposition of the youngest Toba Tuff. Concentrations of climate-sensitive ecological indicators such as phantom midges, diatoms, and other algae through a >270 yr interval bracketing the Toba cryptotephra show no unusual or sustained deviations from background variability within Lake Malawi associated with the hypothesized post-Toba cooling. We find no evidence for significantly enhanced mixing or ecosystem disturbance that would be anticipated following a volcanic winter.

The role of volcanogenic aerosols in the formation of ozone and temperature anomalies in the tropical stratosphere recorded after the eruption of Mount Pinatubo in June, 1991, is analyzed in the work on the basis of 30-year balloon measurement data series at the Hilo station (Hawaii). Positive temperature and negative ozone deviations in vertical profiles ≥2σ from normal annual are considered as anomalies. The stratospheric anomalies observed in the second half of 1991 agree well with the presence of volcanic ash remaining in the stratosphere for about six months. However, temperature anomalies and stratospheric ozone depression, observed during next 2–3 years, cannot be explained by long-lived sulfuric acid aerosol. A mechanism is suggested for the formation of long-lived volcanic soot particles in the stratosphere due to thermal decomposition of methane in the eruption column, which actively absorb solar radiation and destroy ozone on their surfaces. The largest ozone anomaly observed in the lower stratosphere in the second half of 1992 is explained by the soot deposition rate calculated accounting for the high efficiency of ozone destruction on its surface.

Assessment of the synchroneity between the Siberian Traps and the Permo-Triassic boundary (PTB) mass extinction has led to the proposition that the Siberian flood volcanism was responsible for the severest biotic crisis in the Phanerozoic. However, recent studies suggest that the Siberian Traps may have postdated the main extinction horizon. In this paper, we demonstrate, using stratigraphy, a time and intensity coincidence between PTB volcanic ash and the main extinction horizon. Geochemistry of the PTB volcanic ashes in five sections in South China indicates that they were derived from continental magmatic arc. Zircons extracted from the PTB volcanic ashes have negative e Hf(t) (− 12.9 to − 2.0) and δ 18 O (6.8 to 10.9‰), consistent with an acidic volcanism and a crustal-derived origin, and therefore exclude a genetic link between the PTB mass extinction and the Siberian Traps. On the basis of spatial variation in the number of the PTB volcanic ash layers and the thickness of the ash layers in South China, we propose that the PTB volcanic ash may be related to Paleo-Tethys continental arc magmatism in the Kunlun area. Ignimbrite flare-up related to rapid plate subduction during the final assemblage of the Pangea super-continent may have generated a volcanic winter, which eventually triggered the collapse of ecosystem and ultimately mass extinction at the end of the Permian. The Siberian Traps may have been responsible for a greenhouse effect and so have been responsible for both a second pulse of the extinction event and Early Triassic ecological evolution.

An important key for the understanding of the dynamic response to large tropical volcanic eruptions is the warming of the tropical lower stratosphere and the concomitant intensification of the polar vortices. Although this mechanism is reproduced by most general circulation models today, most models still fail in producing an appropriate winter warming pattern in the Northern Hemisphere. In this study ensemble sensitivity experiments were carried out with a coupled atmosphere-ocean model to assess the influence of different ozone climatologies on the atmospheric dynamics and in particular on the northern hemispheric winter warming. The ensemble experiments were perturbed by a single Tambora-like eruption. Larger meridional gradients in the lower stratospheric ozone favor the coupling of zonal wind anomalies between the stratosphere and the troposphere after the eruption. The associated sea level pressure, temperature, and precipitation patterns are more pronounced and the northern hemispheric winter warming is highly significant. Conversely, weaker meridional ozone gradients lead to a weaker response of the winter warming and the associated patterns. The differences in the number of stratosphere-troposphere coupling events between the ensembles experiments indicate a nonlinear response behavior of the dynamics with respect to the ozone and the volcanic forcing.

[1] Large-volume (>0.3 × 106 km3) basaltic lavas that erupted ~260 Ma ago in southwest China form the Emeishan large igneous province. The relationship between the Emeishan volcanism and the end-Guadalupian mass extinction is still unresolved. In order to evaluate the impact of Emeishan flood volcanism on the climate and environment, we have measured sulfur contents in olivine-hosted melt inclusions from Dali picrites. The highest S content of melt inclusions is up to 1311 ppm, which represents that of the undegassed magmas. Comparing the S contents in the undegassed magma and in the degassed posteruptive basaltic lavas, we calculate that eruptions of the Emeishan lavas could have released at least ~900 ppm of S, which equates to 5 Mt of SO2 per cubic kilometer of basaltic lavas. During an individual eruption, SO2 could have been added to the atmosphere at a rate of 1.5 × 102–103 Mt/yr, creating 3.1 × 102–103 Mt of H2SO4 aerosols. The quick release of such a huge amount of volatiles into the atmosphere may have absorbed and reflected solar radiation, causing a temperature decrease and eventually leading to a “volcanic winter”. This scenario demonstrates that the Emeishan flood volcanism was responsible for the end-Guadalupian mass extinction.

[1] An 800 year volcanic record is constructed from high-resolution chemical analysis of recently obtained West Antarctica and central Greenland ice cores. The high accuracy and precision of the ice core chronologies are a result of dating by annual ice layer counting. Nineteen bipolar volcanic signals in this record represent large, explosive eruptions in the tropics with probable climatic impact. One of the two bipolar volcanic signals dated at 1453 and 1459 is probably left by the eruption of the submarine volcano Kuwae in the tropical Pacific, one of the largest volcanic eruptions in the last millennium. The discovery of the two signals in the 1450s casts doubt on the eruption year of 1452 or 1453 for Kuwae based on previous ice core records. The volcanic sulfate deposition patterns in this bipolar record suggest that the later signal is likely from the Kuwae eruption in 1458, although a firm attribution is not possible. Sulfur isotope composition in the volcanic sulfate in the central Greenland cores indicates that both eruptions in the 1450s injected sulfur gases into the stratosphere with probable impact on the global climate. These results are in agreement with tree ring records showing two short cold episodes during that decade. The bipolar volcanic record supports the hypothesis that unusually active volcanism in the thirteenth century contributed to the onset of the Little Ice Age and another active period in the mid fifteenth century may have helped to sustain the Little Ice Age.

The most explosive volcanic event of the Quaternary was the eruption of Mt. Toba, Sumatra, 75,000 y ago, which produced voluminous ash deposits found across much of the Indian Ocean, Indian Peninsula, and South China Sea. A major climatic downturn observed within the Greenland ice cores has been attributed to the cooling effects of the ash and aerosols ejected during the eruption of the Youngest Toba Tuff (YTT). These events coincided roughly with a hypothesized human genetic bottleneck, when the number of our species in Africa may have been reduced to near extinction. Some have speculated that the demise of early modern humans at that time was due in part to a dramatic climate shift triggered by the supereruption. Others have argued that environmental conditions would not have been so severe to have such an impact on our ancestors, and furthermore, that modern humans may have already expanded beyond Africa by this time. We report an observation of the YTT in Africa, recovered as a cryptotephra layer in Lake Malawi sediments, >7,000 km west of the source volcano. The YTT isochron provides an accurate and precise age estimate for the Lake Malawi paleoclimate record, which revises the chronology of past climatic events in East Africa. The YTT in Lake Malawi is not accompanied by a major change in sediment composition or evidence for substantial temperature change, implying that the eruption did not significantly impact the climate of East Africa and was not the cause of a human genetic bottleneck at that time.

[1] Observations suggest that the optical depth of the stratospheric aerosol layer between 20 and 30 km has increased 4–10% per year since 2000, which is significant for Earth's climate. Contributions to this increase both from moderate volcanic eruptions and from enhanced coal burning in Asia have been suggested. Current observations are insufficient to attribute the contribution of the different sources. Here we use a global climate model coupled to an aerosol microphysical model to partition the contribution of each. We employ model runs that include the increases in anthropogenic sulfur dioxide (SO2) over Asia and the moderate volcanic explosive injections of SO2 observed from 2000 to 2010. Comparison of the model results to observations reveals that moderate volcanic eruptions, rather than anthropogenic influences, are the primary source of the observed increases in stratospheric aerosol.

Volcanic eruptions are important causes of natural variability in the climate system at all time scales. Assessments of the climate impact of volcanic eruptions by climate models almost universally assume that sulfate aerosol is the only radiatively active volcanic material. We report satellite observations from the Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite after the eruption of Mount Kelud (Indonesia) on 13 February 2014 of volcanic materials in the lower stratosphere. Using these observations along with in situ measurements with the Compact Optical Backscatter AerosoL Detector (COBALD) backscatter sondes and optical particle counters (OPCs) made during a balloon field campaign in northern Australia, we find that fine ash particles with a radius below 0.3 µm likely represented between 20 and 28% of the total volcanic cloud aerosol optical depth 3 months after the eruption. A separation of 1.5–2 km between the ash and sulfate plumes is observed in the CALIOP extinction profiles as well as in the aerosol number concentration measurements of the OPC after 3 months. The settling velocity of fine ash with a radius of 0.3 µm in the tropical lower stratosphere is reduced by 50% due to the upward motion of the Brewer‐Dobson circulation resulting a doubling of its lifetime. Three months after the eruption, we find a mean tropical clear‐sky radiative forcing at the top of the atmosphere from the Kelud plume near −0.08 W/m2 after including the presence of ash; a value ~20% higher than if sulfate alone is considered. Thus, surface cooling following volcanic eruptions could be affected by the persistence of ash and should be considered in climate simulations., Key Points In situ and spaceborne observations of the Kelud plumePersistence of ash in the lower stratosphereAsh can impact climate on longer time scale than previously thought

The Youngest Toba Tuff (YTT) eruption, which occurred in Indonesia 74,000 years ago, is one of Earth's largest known volcanic events. The effect of the YTT eruption on existing populations of humans, and accordingly on the course of human evolution, is debated. Here we associate the YTT with archaeological assemblages at Jwalapuram, in the Jurreru River valley of southern India. Broad continuity of Middle Paleolithic technology across the YTT event suggests that hominins persisted regionally across this major eruptive event.

Volcanic eruptions can have a significant impact on the Earth's weather and climate system. Besides the subsequent tropospheric changes, the stratosphere is also influenced by large eruptions. Here changes in stratospheric water vapour after the two major volcanic eruptions of El Chichón in Mexico in 1982 and Mount Pinatubo on the Philippines in 1991 are investigated with chemistry–climate model simulations. This study is based on two simulations with specified dynamics of the European Centre for Medium-Range Weather Forecasts Hamburg – Modular Earth Submodel System (ECHAM/MESSy) Atmospheric Chemistry (EMAC) model, performed within the Earth System Chemistry integrated Modelling (ESCiMo) project, of which only one includes the long-wave volcanic forcing through prescribed aerosol optical properties. The results show a significant increase in stratospheric water vapour induced by the eruptions, resulting from increased heating rates and the subsequent changes in stratospheric and tropopause temperatures in the tropics. The tropical vertical advection and the South Asian summer monsoon are identified as sources for the additional water vapour in the stratosphere. Additionally, volcanic influences on tropospheric water vapour and El Niño–Southern Oscillation (ENSO) are evident, if the long-wave forcing is strong enough. Our results are corroborated by additional sensitivity simulations of the Mount Pinatubo period with reduced nudging and reduced volcanic aerosol extinction.

To understand the impact of volcanic aerosol on multiyear seasonal and decadal climate predictions, we performed Coupled Model Intercomparison Project Phase 5-type hindcasts without volcanic aerosol using the German Mittelfristige Klimaprognosen prediction system and compared them to the corresponding simulations including aerosols. Our results show that volcanic aerosol significantly affects the prediction skill for global mean surface air temperature in the first five years after strong volcanic eruptions. Also, on the regional scale a volcanic imprint on decadal-scale variability is detectable. Neglecting volcanic aerosol leads to a reduced prediction skill over the tropical and subtropical Atlantic, Indic, and west Pacific but to an improvement over the tropical east Pacific, where the model has in general no skill. Multiseasonal differences in the skill for seasonal mean temperatures are evident over Continental Europe with significant skill loss due to neglection of volcanic aerosol in boreal winter over central Europe, Scandinavia and over southeastern Europe, and the East Mediterranean in boreal summer.

We have sampled atmospheric ice nuclei (IN) and aerosol in Germany and in Israel during spring 2010. IN were analyzed by the static vapor diffusion chamber FRIDGE, as well as by electron microscopy. During the Eyjafjallajökull volcanic eruption of April 2010 we have measured the highest ice nucleus number concentrations (>600 l−1) in our record of 2 yr of daily IN measurements in central Germany. Even in Israel, located about 5000 km away from Iceland, IN were as high as otherwise only during desert dust storms. The fraction of aerosol activated as ice nuclei at −18 °C and 119% rhice and the corresponding area density of ice-active sites per aerosol surface were considerably higher than what we observed during an intense outbreak of Saharan dust over Europe in May 2008. Pure volcanic ash accounts for at least 53–68% of the 239 individual ice nucleating particles that we collected in aerosol samples from the event and analyzed by electron microscopy. Volcanic ash samples that had been collected close to the eruption site were aerosolized in the laboratory and measured by FRIDGE. Our analysis confirms the relatively poor ice nucleating efficiency (at −18 °C and 119% ice-saturation) of such "fresh" volcanic ash, as it had recently been found by other workers. We find that both the fraction of the aerosol that is active as ice nuclei as well as the density of ice-active sites on the aerosol surface are three orders of magnitude larger in the samples collected from ambient air during the volcanic peaks than in the aerosolized samples from the ash collected close to the eruption site. From this we conclude that the ice-nucleating properties of volcanic ash may be altered substantially by aging and processing during long-range transport in the atmosphere, and that global volcanism deserves further attention as a potential source of atmospheric ice nuclei.

The stratospheric circulation is an important element of climate as it determines the concentration of radiatively active species like water vapor and aerosol above the tropopause. Climate models predict that increasing greenhouse gas levels speed up the stratospheric circulation. However, these results have been challenged by observational estimates of the circulation strength, constituting an uncertainty in current climate simulations. Here, we quantify the effect of volcanic aerosol on the stratospheric circulation focusing on the Mount Pinatubo eruption and discussing further the minor extratropical volcanic eruptions after 2008. We show that the observed pattern of decadal circulation change over the past decades is substantially driven by volcanic aerosol injections. Thus, climate model simulations need to realistically take into account the effect of volcanic eruptions, including the minor eruptions after 2008, for a reliable reproduction of observed stratospheric circulation changes.

The volcanic eruption of Grimsvötn in Iceland in May 2011 affected surface-layer air quality at several locations in Northern Europe. In Helsinki, Finland, the main pollution episode lasted for more than 8 h around the noon of 25 May. We characterized this episode by relying on detailed physical, chemical and optical aerosol measurements. The analysis was aided by air mass trajectory calculations, satellite measurements, and dispersion model simulations. During the episode, volcanic ash particles were present at sizes from less than 0.5 μm up to sizes >10 μm. The mass mean diameter of ash particles was a few μm in the Helsinki area, and the ash enhanced PM10 mass concentrations up to several tens of μg m−3. Individual particle analysis showed that some ash particles appeared almost non-reacted during the atmospheric transportation, while most of them were mixed with sea salt or other type of particulate matter. Also sulfate of volcanic origin appeared to have been transported to our measurement site, but its contribution to the aerosol mass was minor due the separation of ash-particle and sulfur dioxide plumes shortly after the eruption. The volcanic material had very little effect on PM1 mass concentrations or sub-micron particle number size distributions in the Helsinki area. The aerosol scattering coefficient was increased and visibility was slightly decreased during the episode, but in general changes in aerosol optical properties due to volcanic aerosols seem to be difficult to be distinguished from those induced by other pollutants present in a continental boundary layer. The case investigated here demonstrates clearly the power of combining surface aerosol measurements, dispersion model simulations and satellite measurements in analyzing surface air pollution episodes caused by volcanic eruptions. None of these three approaches alone would be sufficient to forecast, or even to unambiguously identify, such episodes.

Explosive volcanic eruptions have the potential to inject gases including sulphur dioxide (SO2) and silicate ash into the upper and lower stratospheres, which not only has climatic implications but...

Satellite measurements from the Moderate Resolution Imaging Spectroradiometer MODIS on Aqua were used to study changes of the ocean and atmosphere following the eruption of a submarine volcano in March 2009 in the southern tropical Pacific. Significant increase of water turbidity was observed in an area of ∼368 km2 near the location of the eruption due to the deposition of volcanic ash. In the ocean region close to the volcanic eruption, the diffuse attenuation coefficient at a wavelength of 490 nm, Kd490, increased from ∼0.025 to 0.16 m−1 before and after the volcanic eruption. Within two weeks of the event, the coverage of the ash-laden waters decreased to ∼30 km2, and after four weeks the satellite-measured marine environment parameters returned back to the pre-eruption condition. The normalized water-leaving reflectance spectra, derived from the combined near-infrared NIR and shortwave infrared SWIR atmospheric correction algorithm for the ash-laden water, show some unique optical features, different from those of the sediment-dominated turbid waters, river plume waters or other productive waters. No significant sea surface temperature SST change was detected from satellite measurements near the eruption site. Volcanic ash plumes in the atmosphere were observed moving north-eastward following the ocean winds on 18 March 2009. The aerosol optical thickness increased from 0.06 on the previous day to 0.25 at a location ∼60 km north-east of the volcanic eruption site.

Conchostracan-rich beds between the Siberian Trap flood basalts and within the thick underlying Hungtukun tuffs of the Tunguska Basin can be closely correlated with conchostracan faunas of Dalongkou (NW China) and the Germanic Basin. The Germanic Basin faunas in turn can be closely correlated with the marine international stratigraphic time scale, and the accuracy of the biostratigraphic correlation of the Permian–Triassic boundary (PTB) is confirmed by a minimum in δ13Ccarb values at this level. These high-resolution correlations demonstrate conclusively that the PTB is located within the temporally brief but thick Siberian Trap flood basalt sequence. The PTB lies slightly above the level of the main Permo-Triassic extinction event in low latitude marine beds, which occurred at the base of the C. meishanensis–H. praeparvus conodont zone and correlates with the beginning of the Siberian Trap flood basalt event. The main end-Permian continental extinction event was somewhat earlier, within the middle of the C. changxingensis–C. deflecta conodont zone. This horizon marks a mass extinction that devastated a diverse conchostracan fauna and left only low diversity faunas at low and high latitudes. This continental extinction event horizon lies within the middle of the Hungtukun tuffs of the Tunguska Basin and 107 m above the base of the Guodikeng Formation at Dalongkou (NW China). A “Triassic type” pioneer flora with numerous lycopod spores appears immediately above this level. Severe high northern and southern latitude marine extinctions occurred concurrently with this continental event, but low latitude marine biota was not then affected. This earlier event is best explained by global warming. The main low latitude extinction event in marine warm water faunas occurred somewhat later and left no signature in high latitude marine faunas or in continental faunas, but it does coincide with a rapid collapse of tropical rain forest environments (disappearance of the highly diverse Gigantopteris flora). This collapse likely was caused by global cooling due to a volcanic winter event.

For the first time, we have identified evidence that the disappearance of Neanderthals in the Caucasus coincides with a volcanic eruption at about 40,000 BP. Our data support the hypothesis that the Middle to Upper Paleolithic transition in western Eurasia correlates with a global volcanogenic catastrophe. The coeval volcanic eruptions (from a large Campanian Ignimbrite eruption to a smaller eruption in the Central Caucasus) had an unusually sudden and devastating effect on the ecology and forced the fast and extreme climate deterioration (“volcanic winter”) of the Northern Hemisphere in the beginning of Heinrich Event 4. Given the data from Mezmaiskaya Cave and supporting evidence from other sites across the Europe, we guess that the Neanderthal lineage truncated abruptly after this catastrophe in most of its range. We also propose that the most significant advantage of early modern humans over contemporary Neanderthals was geographic localization in the more southern parts of western Eurasia and Africa....

Augustine Volcano (located in the Cook Inlet of South Central Alaska at 59.4oand 153.4oW) erupted in January 2006 and released, among other things, water vapor, radiation heat, and aerosols into the atmosphere. To determine the potential impact of volcanic emissions and ashfall on local weather, 16 simulations assuming artificial emission and ashfall scenarios were performed with the Weather Research and Forecasting model for 24 consecutive days starting the day before the first eruption. These simulations include (1) the control simulation without consideration of any volcanic perturbation, (2) four simulations with simplified scenarios for each individual volcanic factor [radiative heat from the caldera, water vapor, cloud condensation nuclei (CCN) and/or ice nuclei (IN) aerosols, and albedo change due to ashfall], and (3) 11 simulations containing all possible combinations of these factors. These 11 simulations serve to examine interactions among impacts of the different perturbations under the assumed scenarios. The impact of volcanic factors on local weather depends on the synoptic situation, emission strength, (combination of) volcanic factors, and interaction among impacts of factors if they occur concurrently. ANalysis Of VAriance shows that the greatest (statistically significant at the 95% or higher confidence level) volcanic impact occurs on relatively humid days and immediately downwind of the volcano (

We describe a novel mechanism that can significantly lower the amplitude of the climatic response to certain large volcanic eruptions and examine its impact with a coupled ocean-atmosphere climate model. If sufficiently large amounts of water vapour enter the stratosphere, a climatically significant amount of water vapour can be left over in the lower stratosphere after the eruption, even after sulphate aerosol formation. This excess stratospheric humidity warms the tropospheric climate, and acts to balance the climatic cooling induced by the volcanic aerosol, especially because the humidity anomaly lasts for a period that is longer than the residence time of aerosol in the stratosphere. In particular, northern hemisphere high latitude cooling is reduced in magnitude. We discuss this mechanism in the context of the discrepancy between the observed and modelled cooling following the Krakatau eruption in 1883. We hypothesize that moist coignimbrite plumes caused by pyroclastic flows travelling over ocean rather than land, resulting from an eruption close enough to the ocean, might provide the additional source of stratospheric water vapour.

Stratospheric aerosol, noted after large volcanic eruptions since at least the late 1800s, were first measured in the late 1950s, with the modern continuous record beginning in the 1970s. Stratospheric aerosol, both volcanic and non-volcanic are sulfuric acid droplets with radii (concentrations) on the order of 0.1–0.5 µm (0.5–0.005 cm − 3 ), increasing by factors of 2–4 (10–10 3 ) after large volcanic eruptions. The source of the sulfur for the aerosol is either through direct injection from sulfur-rich volcanic eruptions, or from tropical injection of tropospheric air containing OCS, SO 2 , and sulfate particles. The life cycle of non-volcanic stratospheric aerosol, consisting of photo-dissociation and oxidation of sulfur source gases, nucleation/condensation in the tropics, transport pole-ward and downward in the global planetary wave driven tropical pump, leads to a quasi steady state relative maximum in particle number concentration at around 20 km in the mid latitudes. Stratospheric aerosol have significant impacts on the Earth's radiation balance for several years following volcanic eruptions. Away from large eruptions, the direct radiation impact is small and well characterized; however, these particles also may play a role in the nucleation of near tropopause cirrus, and thus indirectly affect radiation. Stratospheric aerosol play a larger role in the chemical, particularly ozone, balance of the stratosphere. In the mid latitudes they interact with both nitrous oxides and chlorine reservoirs, thus indirectly affecting ozone. In the polar regions they provide condensation sites for polar stratospheric clouds which then provide the surfaces necessary to convert inactive to active chlorine leading to polar ozone loss. Until the mid 1990s the modern record has been dominated by three large sulfur-rich eruptions: Fuego (1974), El Chichon (1982) and Pinatubo (1991), thus definitive conclusions concerning the trend of non-volcanic stratospheric aerosol could only recently be made. Although anthropogenic emissions of SO 2 have changed somewhat over the past 30 years, the measurements during volcanically quiescent periods indicate no long term trend in non-volcanic stratospheric aerosol.

Significant new information shows that the Campanian Ignimbrite (CI) eruption from the Phlegrean Fields, southern Italy, was much larger than hitherto supposed and in fact one of the largest late Quaternary explosive events. The eruption can be dated to 40,000 calendar years ago, within the interval of the so-called Middle to Upper Paleolithic 'transition'. Its position can be precisely correlated with a number of other environmental events, including Heinrich Event 4 (HE4), the Laschamp excursion, and a particular cosmogenic nuclide peak. In view of this unique combination of factors, we studied the CI volcanic catastrophe with particular attention to its impact on climate and human ecosystems, including potential interference with ongoing processes of cultural evolution (biological evolution is best left aside for the moment). The contribution of this research is chronological and ecological. The CI volcanic event provides an unequalled means of correlating stratigraphic sequences across Western Eurasia, either directly or indirectly, and affords a unique opportunity to establish the age and climatic context of important archaeological sequences. Ecologically, the CI eruption inevitably interacted with the beginning of HE4 in terms of atmospheric feedback systems. Their combined forcing produced a sudden and at least hemispheric climatic deterioration; a 'volcanic winter' scenario cannot be ruled out. Paleolithic occupation was severely altered throughout the direct-impact zone of the eruption and likely along fringe areas in southern and southeastern Europe. The above observations call for a reconsideration of the processes and rhythms involved in the Middle to Upper Paleolithic 'transition'. A tentative model is suggested that links the exceptional environmental stress at 40,000 BP with processes already active in Paleolithic societies, leading to a period of accelerated change in cultural configurations. These eventually evolved into an Upper Paleolithic proper at a later date. The evidence to invoke allochthonous cultural input or invasionist scenarios is not considered compelling.

The climate changes that occured following the volcanic eruption of Mount Pinatubo in the Phillippines on 15 June 1991 have been simulated using the ARPEGE atmosphere general circulation model (AGCM). The model was forced by a reconstructed spatial-time distribution of stratospheric aerosols intended for use in long climate simulations. Four statistical ensembles of the AGCM simulations with and without volcanic aerosols over a period of 5 years following the eruption have been made, and the calculated fields have been compared to available observations. The model is able to reproduce some of the observed features after the eruption, such as the winter warming pattern that was observed over the Northern Hemisphere (NH) during the following winters. This pattern was caused by an enhanced Equator-to-pole temperature gradient in the stratosphere that developed due to aerosol heating of the tropics. This in turn led to a strengthening of the polar vortex, which tends to modulate the planetary wave field in such a way that an anomalously positive Arctic Oscillation pattern is produced in the troposphere and at the surface, favouring warm conditions over the NH. During the summer, the model produced a more uniform cooling over the NH.

Rare but extremely large explosive supereruptions lead to the catastrophic formation of huge calderas, devastation of substantial regions by pyroclastic flow deposits, and ash falls that cover continent-sized areas. The effects of future supereruptions will be felt globally or at least by a whole hemisphere. The most widespread effects are likely to derive from the volcanic gases released, particularly sulfur gases that are converted into sulfuric acid aerosols in the stratosphere. These will remain for several years, promoting changes in atmospheric circulation and causing surface temperatures to fall dramatically in many regions, bringing about temporary reductions in light levels and producing severe and unseasonable weather ('volcanic winter'). Major disruptions to global societal infrastructure can be expected for periods of months to years, and the cost to global financial markets will be high and sustained.

Large explosive volcanic eruptions are capable of injecting considerable amounts of particles and sulfur gases above the tropopause, causing large increases in stratospheric aerosols. Five major volcanic eruptions after 1960 (i.e.; Agung, St. Helens, El Chichón, Nevado del Ruiz and Pinatubo) have been considered in a numerical study conducted with a composition-climate coupled model including an aerosol microphysics code for aerosol formation and growth. Model results are compared between an ensemble of numerical simulations including volcanic aerosols and their radiative effects (VE) and a reference simulations ensemble (REF) with no radiative impact of the volcanic aerosols. Differences of VE-REF show enhanced diabatic heating rates; increased stratospheric temperatures and mean zonal westerly winds; increased planetary wave amplitude; and tropical upwelling. The impact on stratospheric upwelling is found to be larger when the volcanically perturbed stratospheric aerosol is confined to the tropics, as tends to be the case for eruptions which were followed by several months with easterly shear of the quasi-biennial oscillation (QBO), e.g.; the Pinatubo case. Compared to an eruption followed by a period of westerly QBO, such easterly QBO eruptions are quite different, with meridional transport to mid- and high-latitudes occurring later, and at higher altitude, with a consequent decrease in cross-tropopause removal from the stratosphere, and therefore longer decay timescale. Comparing the model-calculated e-folding time of the volcanic aerosol mass during the first year after the eruptions, an increase is found from 8.1 and 10.3 months for El Chichón and Agung (QBO westerly shear), to 14.6 and 30.7 months for Pinatubo and Ruiz (QBO easterly shear). The corresponding e-folding time of the global-mean radiative flux changes goes from 9.1 and 8.0 months for El Chichón and Agung, to 28.7 and 24.5 months for Pinatubo and Ruiz. © 2016 by the authors.

The radiative perturbation associated to stratospheric aerosols from major explosive volcanic eruptions may induce significant changes in stratospheric dynamics. The aerosol heating rates warm up the lower stratosphere and cause a westerly wind anomaly, with additional tropical upwelling. Large scale transport of stratospheric trace species may be perturbed as a consequence of this intensified Brewer-Dobson circulation. The radiatively forced changes of the stratospheric circulation during the first two years after the eruption of Mt. Pinatubo (June 1991) may help explain the observed trend decline of long-lived greenhouse gases at surface stations (approximately -8 and -0.4 ppbv/year for CH4 and N2O, respectively). This decline is partly driven by the increased mid- to high-latitude downward flux at the tropopause and also by an increased isolation of the tropical pipe in the vertical layer near the tropopause, with reduced horizontal eddy mixing. Results from a climate-chemistry coupled model are shown for both long-lived trace species and the stratospheric age-of-air. The latter results to be younger by approximately 0.5 year at 30 hPa for 3-4 years after the June 1991 Pinatubo eruption, as a result of the volcanic aerosols radiative perturbation and is consistent with independent estimates based on long time series of in situ profile measurements of SF6 and CO2. Younger age of air is also calculated after Agung, El Chichón and Ruiz eruptions, as well as negative anomalies of the N2O growth rate at the extratropical tropopause layer. This type of analysis is made comparing the results of two ensembles of model simulations (1960-2005), one including stratospheric volcanic aerosols and their radiative interactions and a reference case where the volcanic aerosols do not interact with solar and planetary radiation.. © 2016 by the authors.

Large explosive eruptions inject volcanic gases and fine ash to stratospheric altitudes, contributing to global cooling at the Earth’s surface and occasionally to ozone depletion. The modelling of the climate response to these strong injections of volatiles commonly relies on ice-core records of volcanic sulphate aerosols. Here we use an independent geochemical approach which demonstrates that the great 1257 eruption of Samalas (Lombok, Indonesia) released enough sulphur and halogen gases into the stratosphere to produce the reported global cooling during the second half of the 13th century, as well as potential substantial ozone destruction. Major, trace and volatile element compositions of eruptive products recording the magmatic differentiation processes leading to the 1257 eruption indicate that Mt Samalas released 158 ± 12 Tg of sulphur dioxide, 227 ± 18 Tg of chlorine and a maximum of 1.3 ± 0.3 Tg of bromine. These emissions stand as the greatest volcanogenic gas injection of the Common Era. Our findings not only provide robust constraints for the modelling of the combined impact of sulphur and halogens on stratosphere chemistry of the largest eruption of the last millennium, but also develop a methodology to better quantify the degassing budgets of explosive eruptions of all magnitudes.