Tropical Eruptions Research Articles

Divergent responses of tropical cyclone genesis factors to strong volcanic eruptions at different latitudes

To understand the behaviors of tropical cyclones (TCs), it is very important to explore how TCs respond to anthropogenic greenhouse gases and natural forcings. Volcanic eruptions are a major natural forcing mechanism because they inject sulphate aerosols into the stratosphere, which modulate the global climate by absorbing and scattering solar radiation. The number of Atlantic hurricanes is thought to be reduced following strong tropical eruptions, but whether the response of TCs varies with the locations of the volcanoes and the different ocean basins remains unknown. Here, we use the Community Earth System Model-Last Millennium Ensemble to investigate the response of the large-scale environmental factors that spawn TCs to strong volcanic eruptions at different latitudes. A composite analysis indicates that tropical and northern hemisphere volcanic eruptions lead to significantly unfavorable conditions for TC genesis over the whole Pacific basin and the North Atlantic during the 3 years post-eruption, relative to the preceding 3 years. Southern hemisphere volcanic eruptions result in obviously unfavorable conditions for TC formation over the southwestern Pacific, but more favorable conditions over the North Atlantic. The mean response over the Indian Ocean is generally muted and insignificant. It should be noted that volcanic eruptions impact on environmental conditions through both the direct effect (i.e. on radiative forcing) and the indirect effect (i.e. on El Nino-Southern Oscillation), which is not differentiated in this study. In addition, the spread of the TC genesis response is considerably large for each category of eruptions over each ocean basin, which is also seen in the observational/proxy-based records. This large spread is attributed to the differences in stratospheric aerosol distributions, initial states and eruption intensities, and makes the short-term forecast of TC activity following the next large eruption challenging.

European hydroclimate response to volcanic eruptions over the past nine centuries

ABSTRACTThe climatic aftermath of the 1815 Tambora eruption in Europe suggests that large volcanic eruptions can introduce environmental and societal consequences in this region. Here, we analyse the European summer hydrological response to 31 tropical and 44 Northern Hemisphere mid‐to‐high latitude eruptions over the past nine centuries, using a newly published reconstruction of global volcanism and a proxy record of hydrological conditions (Old World Drought Atlas) together with a superposed epoch analysis. Our results show a significant wetting response (at the 95% confidence level) for year 0 and year +1 after tropical eruptions, followed by a significant drying in year +2. Spatially, wetting occurs in northeast and southern Europe, while a drying response develops in central and northwest Europe. Both the wetting and drying responses are more significant for the group of eruptions with higher sulphate injection magnitudes than the eruptions with low magnitudes. Large high latitude eruptions tend to cause a drying response in western‐central Europe in year +2, which shifts south‐eastwards in years +3 and +4. Correcting for the effects of El Nino does not noticeably change the response patterns. The response to eruptions counteracts the hydroclimate response to global warming in some regions, e.g. the Mediterranean, but exaggerates is in others, such as central Europe. Our results verify previous modelling studies from a longer term proxy perspective, and illuminate potential effects of stratospheric geoengineering in Europe.

Role of eruption season in reconciling model and proxy responses to tropical volcanism

The response of the El Niño/Southern Oscillation (ENSO) to tropical volcanic eruptions has important worldwide implications, but remains poorly constrained. Paleoclimate records suggest an "El Niño-like" warming 1 year following major eruptions [Adams JB, Mann ME, Ammann CM (2003) Nature 426:274-278] and "La Niña-like" cooling within the eruption year [Li J, et al. (2013) Nat Clim Chang 3:822-826]. However, climate models currently cannot capture all these responses. Many eruption characteristics are poorly constrained, which may contribute to uncertainties in model solutions-for example, the season of eruption occurrence is often unknown and assigned arbitrarily. Here we isolate the effect of eruption season using experiments with the Community Earth System Model (CESM), varying the starting month of two large tropical eruptions. The eruption-year atmospheric circulation response is strongly seasonally dependent, with effects on European winter warming, the Intertropical Convergence Zone, and the southeast Asian monsoon. This creates substantial variations in eruption-year hydroclimate patterns, which do sometimes exhibit La Niña-like features as in the proxy record. However, eruption-year equatorial Pacific cooling is not driven by La Niña dynamics, but strictly by transient radiative cooling. In contrast, equatorial warming the following year occurs for all starting months and operates dynamically like El Niño. Proxy reconstructions confirm these results: eruption-year cooling is insignificant, whereas warming in the following year is more robust. This implies that accounting for the event season may be necessary to describe the initial response to volcanic eruptions and that climate models may be more accurately simulating volcanic influences than previously thought.

Explosive eruption of El Chichón volcano (Mexico) disrupted 6th century Maya civilization and contributed to global cooling

Abstract A remarkably long period of Northern Hemispheric cooling in the 6th century CE, which disrupted human societies across large parts of the globe, has been attributed to volcanic forcing of climate. A major tropical eruption in 540 CE is thought to have played a key role, but there is no consensus about the source volcano to date. Here, we present evidence for El Chichón in southern Mexico as the most likely candidate, based on a refined reconstruction of the volcano’s eruption history. A new chronological framework, derived from distal tephra deposits and the world’s largest Holocene beach ridge plain along the Gulf of Mexico, enabled us to positively link a major explosive event to a prominent volcanic sulfur spike in bipolar ice core records, dated at 540 CE. We speculate that voluminous tephra fall from the eruption had a severe environmental impact on Maya societies, leading to temporary cultural decline, site abandonment, and migration within the core area of Maya civilization.

Climatic aftermath of the 1815 Tambora eruption in China

The 1815 eruption of the Tambora volcano led to the “Year without a Summer” and caused serious crop failure and famines in 1816 across Europe and North America. However, few reports are available on Tambora’s influence in China despite the region’s susceptibility to monsoonal volcanic perturbation. This study presents a systemic analysis of the climatic and related social responses to the Tambora perturbation in China, by using two independent lines of proxy records and projecting the responses on top of the impacts averaged over all tropical eruptions of the past millennium. Both the tree ring and Chinese documentary proxies show that Tambora induced a cold excursion, which caused severe frost damage, snow and ice accumulations that are uncommonly seen in southern China. Cold temperature tends to cause drought by suppressing evaporation and monsoonal circulation—a hydroclimate response that is evident in the tree-ring-based Monsoon Asia Drought Atlas but largely missing in a multiproxy precipitation reconstruction. Historical records of drought, flood, frost, and famine also show fairly mild responses outside southern China, which may be partially due to the insensitivity of documentary records to the Tambora-induced perturbation, or the cold background climate set up by the low solar insolation of the coincident Dalton Minimum and a preceding unknown eruption in 1809. The results presented here provide new insights into the spatial extent and characteristics of the Tambora perturbation, by providing a systematic evaluation of the climatic aftermath in China in parallel to that in Europe and North America. They also argue for the integral use of multiple proxies from different regions of the world to gain a better understanding of the climatic impacts for individual volcanic eruptions.

Climatic response of extratropics to intense tropical eruptions

Climatic response of extratropics to intense tropical eruptions

Winter warming and summer monsoon reduction after volcanic eruptions in Coupled Model Intercomparison Project 5 (CMIP5) simulations

AbstractThough previous studies have shown that state‐of‐the‐art climate models are rather imperfect in their simulations of the climate response to large volcanic eruptions, the results depend on how the analyses were done. Observations show that all recent large tropical eruptions were followed by winter warming in the first Northern Hemisphere (NH) winter after the eruption, with little such response in the second winter, yet a number of the evaluations have combined the first and second winters. We have looked at just the first winter after large eruptions since 1850 in the Coupled Model Intercomparison Project 5 historical simulations and find that most models do produce a winter warming signal, with warmer temperatures over NH continents and a stronger polar vortex in the lower stratosphere. We also examined NH summer precipitation responses in the first year after these large volcanic eruptions and find clear reductions of summer monsoon rainfall.

“El Niño Like” Hydroclimate Responses to Last Millennium Volcanic Eruptions

Abstract The hydroclimate response to volcanic eruptions depends both on volcanically induced changes to the hydrologic cycle and on teleconnections with the El Niño–Southern Oscillation (ENSO), complicating the interpretation of offsets between proxy reconstructions and model output. Here, these effects are separated, using the Community Earth System Model Last Millennium Ensemble (CESM-LME), by examination of ensemble realizations with distinct posteruption ENSO responses. Hydroclimate anomalies in monsoon Asia and the western United States resemble the El Niño teleconnection pattern after “Tropical” and “Northern” eruptions, even when ENSO-neutral conditions are present. This pattern results from Northern Hemisphere (NH) surface cooling, which shifts the intertropical convergence zone equatorward, intensifies the NH subtropical jet, and suppresses the Southeast Asian monsoon. El Niño events following an eruption can then intensify the ENSO-neutral hydroclimate signature, and El Niño probability is enhanced two boreal winters following all eruption types. Additionally, the eruption-year ENSO response to eruptions is hemispherically dependent: the winter following a Northern eruption tends toward El Niño, while Southern volcanoes enhance the probability of La Niña events and Tropical eruptions have a very slight cooling effect. Overall, eruption-year hydroclimate anomalies in CESM disagree with the proxy record in both Southeast Asia and North America, suggesting that model monsoon representation cannot be solely responsible. Possible explanations include issues with the model ENSO response, the spatial or temporal structure of volcanic aerosol distribution, or data uncertainties.

Impacts of high-latitude volcanic eruptions on ENSO and AMOC

Large volcanic eruptions can have major impacts on global climate, affecting both atmospheric and ocean circulation through changes in atmospheric chemical composition and optical properties. The residence time of volcanic aerosol from strong eruptions is roughly 2-3 y. Attention has consequently focused on their short-term impacts, whereas the long-term, ocean-mediated response has not been well studied. Most studies have focused on tropical eruptions; high-latitude eruptions have drawn less attention because their impacts are thought to be merely hemispheric rather than global. No study to date has investigated the long-term effects of high-latitude eruptions. Here, we use a climate model to show that large summer high-latitude eruptions in the Northern Hemisphere cause strong hemispheric cooling, which could induce an El Niño-like anomaly, in the equatorial Pacific during the first 8-9 mo after the start of the eruption. The hemispherically asymmetric cooling shifts the Intertropical Convergence Zone southward, triggering a weakening of the trade winds over the western and central equatorial Pacific that favors the development of an El Niño-like anomaly. In the model used here, the specified high-latitude eruption also leads to a strengthening of the Atlantic Meridional Overturning Circulation (AMOC) in the first 25 y after the eruption, followed by a weakening lasting at least 35 y. The long-lived changes in the AMOC strength also alter the variability of the El Niño-Southern Oscillation (ENSO).

Influence of volcanic eruptions on midlatitude upper tropospheric aerosol and consequences for cirrus clouds

AbstractThe influence of downwelling stratospheric sulfurous aerosol on the UT (upper troposphere) aerosol concentrations and on cirrus clouds is investigated using CARIBIC (Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container observations) (between 1999–2002 and 2005–2013) and the cirrus reflectance product from Moderate Resolution Imaging Spectroradiometer (MODIS). The initial period, 1999–2002, was volcanically quiescent after which the sulfurous aerosol in the LMS (lowermost stratosphere) (SLMS) became enhanced by several volcanic eruptions starting 2005. From 2005 to 2008 and in 2013, volcanic aerosol from several tropical eruptions increased SLMS. Due to consequent subsidence, the sulfur loading of the upper troposphere (SUT) was increased by a factor of 2.5 compared to background levels. Comparison of SLMS and SUT during the seasons March–July and August–November shows a close coupling of the UT and LMS. Finally, the relationship between SLMS and the cirrus cloud reflectance (CR) retrieved from MODIS spectrometer (on board the satellites Terra and Aqua) is studied. SLMS and CR show a strong anticorrelation, with a factor of 3.5 increase in SLMS and decrease of CR by 8 ± 2% over the period 2001–2011. We propose that the increase of SLMS due to volcanism has caused the coinciding cirrus CR decrease, which would be associated with a negative radiative forcing in the Northern Hemisphere midlatitudes.

Effect of recent minor volcanic eruptions on temperatures in the upper troposphere and lower stratosphere

The impact of the recent minor volcanic eruptions during 2001–2010 in the temperature of the upper troposphere and lower stratosphere (UTLS) is investigated using data from the Global Positioning System Radio Occultation (GPS RO), three radiosonde compilations and two reanalyses (ERA-Interim and MERRA). The volcanic signals are identified in the residual temperature time series after removal of the linear trend, the quasi-biennial oscillation and El Nino Southern Oscillation components. Eight minor volcanic eruptions (six from the tropics and two from midlatitude) over the last decade (2001–2010) are analyzed in this study. We found significant volcanic signals in the UTLS temperature only in association with the tropical Soufrière Hills and Tavurvur eruptions (in May 2006 and in October 2006, respectively). Other four tropical eruptions had very small aerosol perturbations and did not show any significant UTLS temperature change. Out of the two midlatitude eruptions, Sarychev peak had similar stratospheric aerosol perturbations as Soufrière Hills and Tavurvur eruptions, but did not show any significant UTLS temperature change. The volcanic signals in the UTLS temperature from the tropical Soufrière Hills and Tavurvur eruptions were observed for the period of 7 months after August 2006. A warming of 0.5–0.8K in the tropical 16–18.5km (100–70hPa) layer was observed in association with these two tropical eruptions.

Inter-hemispheric asymmetry in the sea-ice response to volcanic forcing simulated by MPI-ESM (COSMOS-Mill)

Abstract. The decadal evolution of Arctic and Antarctic sea ice following strong volcanic eruptions is investigated in four climate simulation ensembles performed with the COSMOS-Mill version of the Max Planck Institute Earth System Model. The ensembles differ in the magnitude of the imposed volcanic perturbations, with sizes representative of historical tropical eruptions (1991 Pinatubo and 1815 Tambora) and of tropical and extra-tropical "supervolcano" eruptions. A post-eruption Arctic sea-ice expansion is robustly detected in all ensembles, while Antarctic sea ice responds only to supervolcano eruptions, undergoing an initial short-lived expansion and a subsequent prolonged contraction phase. Strong volcanic forcing therefore emerges as a potential source of inter-hemispheric interannual-to-decadal climate variability, although the inter-hemispheric signature is weak in the case of eruptions comparable to historical eruptions. The post-eruption inter-hemispheric decadal asymmetry in sea ice is interpreted as a consequence mainly of the different exposure of Arctic and Antarctic regional climates to induced meridional heat transport changes and of dominating local feedbacks that set in within the Antarctic region. Supervolcano experiments help to clarify differences in simulated hemispheric internal dynamics related to imposed negative net radiative imbalances, including the relative importance of the thermal and dynamical components of the sea-ice response. Supervolcano experiments could therefore serve the assessment of climate models' behavior under strong external forcing conditions and, consequently, favor advancements in our understanding of simulated sea-ice dynamics.

Impact of known local and tropical volcanic eruptions of the past millennium on the WAIS Divide microparticle record

AbstractWe present a new method for inferring the relative location (low‐ versus high‐southern latitude), and therefore the potential climatic impact, of past eruptions based on the particle size distribution (PSD) of micrometer‐sized ash measured continuously in the West Antarctic Ice Sheet (WAIS) Divide ice core. We find that particles from a high‐southern latitude eruption (Buckle Island, Antarctica (1839 Common Era, C.E.)) have a PSD with mode diameter ≥5 µm coarser than the background dust (mode 5.1 µm), while ash particles originating from stratospheric tropical eruptions, including Tambora (1815 C.E.), Kuwae (1458 C.E.), and Unknown (1258 C.E.), have PSDs with mode diameters ~0.6–1.5 µm finer than the background. In addition, volcanic ash particles from global‐scale eruptions are deposited ~3–6 months earlier and over a shorter time interval than sulfate aerosols. We hypothesize that this phasing is driven by differences in atmospheric processing and aerosol/particle transport and deposition.

El Niño modulations over the past seven centuries

Predicting how the El Niño/Southern Oscillation (ENSO) will change with global warming is of enormous importance to society1,2,3,4. ENSO exhibits considerable natural variability at interdecadal–centennial timescales5. Instrumental records are too short to determine whether ENSO has changed6 and existing reconstructions are often developed without adequate tropical records. Here we present a seven-century-long ENSO reconstruction based on 2,222 tree-ring chronologies from both the tropics and mid-latitudes in both hemispheres. The inclusion of tropical records enables us to achieve unprecedented accuracy, as attested by high correlations with equatorial Pacific corals7,8 and coherent modulation of global teleconnections that are consistent with an independent Northern Hemisphere temperature reconstruction9. Our data indicate that ENSO activity in the late twentieth century was anomalously high over the past seven centuries, suggestive of a response to continuing global warming. Climate models disagree on the ENSO response to global warming3,4, suggesting that many models underestimate the sensitivity to radiative perturbations. Illustrating the radiative effect, our reconstruction reveals a robust ENSO response to large tropical eruptions, with anomalous cooling in the east-central tropical Pacific in the year of eruption, followed by anomalous warming one year after. Our observations provide crucial constraints for improving climate models and their future projections.

Exploring the climate response to the Tambora in 1815 and the 1809 tropical eruption

Exploring the climate response to the Tambora in 1815 and the 1809 tropical eruption

Modeling the climatic effects of large explosive volcanic eruptions

AbstractLarge volcanic eruptions are an important driving factor of natural climate variability. A sound assessment of the role of volcanoes in the climate system in comparison to other forcing factors is therefore a prerequisite for understanding future and past climate variability. New advances in understanding volcanic climate effects have been achieved by using comprehensive climate and Earth system models. New insights have been gained over the last decade about volcanic impacts on atmospheric composition and dynamics, but most notably also about their impact on ocean dynamics, the hydrological and the carbon cycle and on marine and terrestrial biogeochemistry. An important achievement is the improved understanding of the volcanic imprint on decadal to multidecadal time scales. Climate model simulations of past eruptions are highly dependent not only on the quality of the model and of the volcanologcial input data but also on the treatment of the aerosol size distribution in chemistry and radiation calculations. Further knowledge has to be achieved about the relation between the initial climate state at the time of the eruption and the volcanic climatic impact. A challenging task for climate models is also the simulation of the Northern Hemisphere winter climate response after a large tropical eruption. Model intercomparison studies and cross validations of model simulations with observations are essential to better constrain the radiative forcing of large volcanic eruptions and their climate impact.WIREs Clim Change2012, 3:545–564. doi: 10.1002/wcc.192This article is categorized under:Climate Models and Modeling > Earth System Models

Coupled Model Intercomparison Project 5 (CMIP5) simulations of climate following volcanic eruptions

The ability of the climate models submitted to the Coupled Model Intercomparison Project 5 (CMIP5) database to simulate the Northern Hemisphere winter climate following a large tropical volcanic eruption is assessed. When sulfate aerosols are produced by volcanic injections into the tropical stratosphere and spread by the stratospheric circulation, it not only causes globally averaged tropospheric cooling but also a localized heating in the lower stratosphere, which can cause major dynamical feedbacks. Observations show a lower stratospheric and surface response during the following one or two Northern Hemisphere (NH) winters, that resembles the positive phase of the North Atlantic Oscillation (NAO). Simulations from 13 CMIP5 models that represent tropical eruptions in the 19th and 20th century are examined, focusing on the large‐scale regional impacts associated with the large‐scale circulation during the NH winter season. The models generally fail to capture the NH dynamical response following eruptions. They do not sufficiently simulate the observed post‐volcanic strengthened NH polar vortex, positive NAO, or NH Eurasian warming pattern, and they tend to overestimate the cooling in the tropical troposphere. The findings are confirmed by a superposed epoch analysis of the NAO index for each model. The study confirms previous similar evaluations and raises concern for the ability of current climate models to simulate the response of a major mode of global circulation variability to external forcings. This is also of concern for the accuracy of geoengineering modeling studies that assess the atmospheric response to stratosphere‐injected particles.

Tephrochronology of the Siple Dome ice core, West Antarctica: correlations and sources

A total of 24 tephra-bearing volcanic layers have been recognized between 550 and 987 m depth in the Siple Dome A (SDM-A) ice core, in addition to a number already recognized tephra in the upper 550 m ( Dunbar et al., 2003; Kurbatov et al., 2006). The uniform composition and distinctive morphological of the particles composing these tephra layers suggest deposition as a result of explosive volcanic eruptions and that the layers therefore represent time-stratigraphic markers in the ice core. Despite the very fine grain size of these tephra (mostly less than 20 microns), robust geochemical compositions were determined by electron microprobe analysis. The source volcanoes for these tephra layers are largely found within the Antarctic plate. Statistical geochemical correlations tie nine of the tephra layers to known eruptions from Mt. Berlin, a West Antarctic volcano that has been very active for the past 100,000 years. Previous correlations were made to an eruption of Mt. Takahe, another West Antarctic volcano, and one to Mt. Hudson, located in South America ( Kurbatov et al., 2006). The lowest tephra layer in the ice core, located at 986.21 m depth, is correlated to a source eruption with an age of 118.1 ± 1.3 ka, suggesting a chronological pinning point for the lower ice. An episode of anomalously high volcanic activity in the ice in the SDM-A core between 18 and 35 ka ( Gow and Meese, 2007) appears to be related to eruptive activity of Mt. Berlin volcano. At least some of the tephra layers found in the SDM-A core appear to be the result of very explosive eruptions that spread ash across large parts of West Antarctica, off the West Antarctic coast, as well as also being recognized in East Antarctica ( Basile et al., 2001; Narcisi et al., 2005, 2006). Some of these layers would be expected to should be found in other deep Antarctic ice cores, particularly ones drilled in West Antarctica, providing correlative markers between different cores. The analysis of the tephra layers in the Siple Dome core, along with other Antarctic cores, provides a timing framework for the relatively proximal Antarctic and South American volcanic eruptive events, allowing these to be distinguished from the tropical eruptions that may play a greater role in climate forcing.

Centennial-scale climate change from decadally-paced explosive volcanism: a coupled sea ice-ocean mechanism

Northern Hemisphere summer cooling through the Holocene is largely driven by the steady decrease in summer insolation tied to the precession of the equinoxes. However, centennial-scale climate departures, such as the Little Ice Age, must be caused by other forcings, most likely explosive volcanism and changes in solar irradiance. Stratospheric volcanic aerosols have the stronger forcing, but their short residence time likely precludes a lasting climate impact from a single eruption. Decadally paced explosive volcanism may produce a greater climate impact because the long response time of ocean surface waters allows for a cumulative decrease in sea-surface tempera- tures that exceeds that of any single eruption. Here we use a global climate model to evaluate the potential long-term climate impacts from four decadally paced large tropical eruptions. Direct forcing results in a rapid expansion of Arctic Ocean sea ice that persists throughout the eruption period. The expanded sea ice increases the flux of sea ice exported to the northern North Atlantic long enough that it reduces the convective warming of surface waters in the subpolar North Atlantic. In two of our four simulations the cooler surface waters being advected into the Arctic Ocean reduced the rate of basal sea-ice melt in the Atlantic sector of the Arctic Ocean, allowing sea ice to remain in an expanded state for ( 100 model years after volcanic aerosols were removed from the stratosphere. In these simulations the coupled sea ice-ocean mechanism main- tains the strong positive feedbacks of an expanded Arctic Ocean sea ice cover, allowing the initial cooling related to the direct effect of volcanic aerosols to be perpetuated, potentially resulting in a centennial-scale or longer change of state in Arctic climate. The fact that the sea ice-ocean mechanism was not established in two of our four simu- lations suggests that a long-term sea ice response to vol- canic forcing is sensitive to the stability of the seawater column, wind, and ocean currents in the North Atlantic during the eruptions.

Climate response to large, high‐latitude and low‐latitude volcanic eruptions in the Community Climate System Model

Explosive volcanism is known to be a leading natural cause of climate change. The second half of the 13th century was likely the most volcanically perturbed half‐century of the last 2000 years, although none of the major 13th century eruptions have been clearly attributed to specific volcanoes. This period was in general a time of transition from the relatively warm Medieval period to the colder Little Ice Age, but available proxy records are insufficient on their own to clearly assess whether this transition is associated with volcanism. This context motivates our investigation of the climate system sensitivity to high‐ and low‐latitude volcanism using the fully coupled NCAR Community Climate System Model (CCSM3). We evaluate two sets of ensemble simulations, each containing four volcanic pulses, with the first set representing them as a sequence of tropical eruptions and the second representing eruptions occurring in the mid‐high latitudes of both the Northern and Southern hemispheres. The short‐term, direct radiative impacts of tropical and high‐latitude eruptions include significant cooling over the continents in summer and cooling over regions of increased sea‐ice concentration in Northern Hemisphere (NH) winter. A main dynamical impact of moderate tropical eruptions is a winter warming pattern across northern Eurasia. Furthermore, both ensembles show significant reductions in global precipitation, especially in the summer monsoon regions. The most important long‐term impact is the cooling of the high‐latitude NH produced by multiple tropical eruptions, suggesting that positive feedbacks associated with ice and snow cover could lead to long‐term climate cooling in the Arctic.