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The assassination of Julius Caesar in 44 BCE triggered a power struggle that ultimately ended the Roman Republic and, eventually, the Ptolemaic Kingdom, leading to the rise of the Roman Empire. Climate proxies and written documents indicate that this struggle occurred during a period of unusually inclement weather, famine, and disease in the Mediterranean region; historians have previously speculated that a large volcanic eruption of unknown origin was the most likely cause. Here we show using well-dated volcanic fallout records in six Arctic ice cores that one of the largest volcanic eruptions of the past 2,500 y occurred in early 43 BCE, with distinct geochemistry of tephra deposited during the event identifying the Okmok volcano in Alaska as the source. Climate proxy records show that 43 and 42 BCE were among the coldest years of recent millennia in the Northern Hemisphere at the start of one of the coldest decades. Earth system modeling suggests that radiative forcing from this massive, high-latitude eruption led to pronounced changes in hydroclimate, including seasonal temperatures in specific Mediterranean regions as much as 7 °C below normal during the 2 y period following the eruption and unusually wet conditions. While it is difficult to establish direct causal linkages to thinly documented historical events, the wet and very cold conditions from this massive eruption on the opposite side of Earth probably resulted in crop failures, famine, and disease, exacerbating social unrest and contributing to political realignments throughout the Mediterranean region at this critical juncture of Western civilization.

Volcanic eruptions contribute to climate variability, but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings. Here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual-to-decadal temperature variability in the Northern Hemisphere during the past 2,500 years. Our results are based on new records of atmospheric aerosol loading developed from high-resolution, multi-parameter measurements from an array of Greenland and Antarctic ice cores as well as distinctive age markers to constrain chronologies. Overall, cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes. Our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth-century pandemics, famines, and socioeconomic disruptions in Eurasia and Mesoamerica while allowing multi-millennium quantification of climate response to volcanic forcing. Ice-core and tree-ring data show that large volcanic eruptions in the tropics and high latitudes were primary drivers of temperature variability in the Northern Hemisphere during the past 2,500 years, firmly implicating such eruptions as catalysts in major sixth-century pandemics, famines, and socioeconomic disruptions. Recalibration of volcanic eruptions/climate linkage Past research has suggested that volcanic eruptions influence climate, but it has proved difficult to match the chronologies of annually resolved and precisely dated tree rings to the chronologies of volcanic variability recorded in ice cores. Michael Sigl et al . use a spike in atmospheric 10 Be — clearly linked to a cosmic-ray anomaly that left a unique atmospheric 14 C fingerprint in tree rings across Europe in the year 775 — as a means of dating a similar spike observed in ice cores from Greenland and Antarctica. In making this connection the authors establish that the ice core record should be adjusted by seven years. The data confirm that large volcanic eruptions in the tropics and high latitudes were primary drivers of temperature variability in the Northern Hemisphere during the past 2,500 years, and implicate such eruptions as catalysts in major sixth-century pandemics, famines, and socioeconomic disruptions.

The 2021 Tajogaite eruption on La Palma devastated banana production, a key crop, with a 50% loss (53,000 tons). Concerned about potential contamination from volcanic ash and magma, we investigated the elemental composition of bananas from the eruption area and control sites. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis quantified both essential and non-essential mineral elements, including potentially toxic elements identified by the Agency for Toxic Substances and Disease Registry (ATSDR), as well as rare earth elements (REEs) and other trace elements that are scarcely studied under volcanic conditions. This approach allowed for spatial and temporal comparisons. Results showed a decrease in element levels post-eruption; however, samples from the volcanic area still exhibited elevated concentrations of Fe, Co, Cd, Al, Ba, Ni, Sn, Sr, Ti, V, and REEs. Control samples from unaffected islands with higher anthropogenic pressure showed elevated levels of Mn and Mo. Despite the increased element levels, banana consumption remains safe and constitutes a valuable source for the recommended daily intake of Mo and Co. Most toxic elements were present at less than 1% of the tolerable daily intake (TDI), with the highest values for As and V reaching 3%, and no risk was associated according to the margin of exposure approach. This eruption highlights the need for continuous monitoring in volcanic regions to safeguard public health and food safety.

The Tierra Blanca Joven (TBJ) eruption from Ilopango volcano deposited thick ash over much of El Salvador when it was inhabited by the Maya, and rendered all areas within at least 80 km of the volcano uninhabitable for years to decades after the eruption. Nonetheless, the more widespread environmental and climatic impacts of this large eruption are not well known because the eruption magnitude and date are not well constrained. In this multifaceted study we have resolved the date of the eruption to 431 ± 2 CE by identifying the ash layer in a well-dated, high-resolution Greenland ice-core record that is >7,000 km from Ilopango; and calculated that between 37 and 82 km³ of magma was dispersed from an eruption coignimbrite column that rose to ∼45 km by modeling the deposit thickness using state-of-the-art tephra dispersal methods. Sulfate records from an array of ice cores suggest stratospheric injection of 14 ± 2 Tg S associated with the TBJ eruption, exceeding those of the historic eruption of Pinatubo in 1991. Based on these estimates it is likely that the TBJ eruption produced a cooling of around 0.5 °C for a few years after the eruption. The modeled dispersal and higher sulfate concentrations recorded in Antarctic ice cores imply that the cooling would have been more pronounced in the Southern Hemisphere. The new date confirms the eruption occurred within the Early Classic phase when Maya expanded across Central America.

Over the past 15 years, scientists and disaster responders have increasingly used satellite-based Earth observations for global rapid assessment of disaster situations. We review global trends in satellite rapid response and emergency mapping from 2000 to 2014, analyzing more than 1000 incidents in which satellite monitoring was used for assessing major disaster situations. We provide a synthesis of spatial patterns and temporal trends in global satellite emergency mapping efforts and show that satellite-based emergency mapping is most intensively deployed in Asia and Europe and follows well the geographic, physical, and temporal distributions of global natural disasters. We present an outlook on the future use of Earth observation technology for disaster response and mitigation by putting past and current developments into context and perspective.

On the evening of 15 January 2022, the Hunga Tonga-Hunga Ha’apai volcano 1 unleashed a violent underwater eruption, blanketing the surrounding land masses in ash and debris 2 , 3 . The eruption generated tsunamis observed around the world. An event of this type last occurred in 1883 during the eruption of Krakatau 4 , and thus we have the first observations of a tsunami from a large emergent volcanic eruption captured with modern instrumentation. Here we show that the explosive eruption generated waves through multiple mechanisms, including: (1) air–sea coupling with the initial and powerful shock wave radiating out from the explosion in the immediate vicinity of the eruption; (2) collapse of the water cavity created by the underwater explosion; and (3) air–sea coupling with the air-pressure pulse that circled the Earth several times, leading to a global tsunami. In the near field, tsunami impacts are strongly controlled by the water-cavity source whereas the far-field tsunami, which was unusually persistent, can be largely described by the air-pressure pulse mechanism. Catastrophic damage in some harbours in the far field was averted by just tens of centimetres, implying that a modest sea level rise combined with a future, similar event would lead to a step-function increase in impacts on infrastructure. Piecing together the complexity of this event has broad implications for coastal hazards in similar geophysical settings, suggesting a currently neglected source of global tsunamis. January 2022 saw the first observations of a tsunami resulting from a large emergent volcanic eruption (Hunga Tonga) captured using modern instrumentation, with broad implications for hazard management in similar geophysical settings.

The Younger Dryas Event (YDE) is the most recent and most well-understood millennial-scale cooling event. A deglacial meltwater pulse is the traditionally accepted trigger for the event, but both a bolide impact and volcanism are recently advanced alternative explanations. A high Pt/Ir and Pt/Al geochemical anomaly within the Greenland Ice Sheet Project (GISP2) ice core, broadly coinciding with the YDE initiation, provides a possible geochemical clue to the events leading up to the YDE. Previous research has suggested that the impact of an unknown type of high Pt/low Ir iron meteorite may have produced this Pt spike, but the timing is also very close to a large sulphur spike within the North Greenland Ice Core Project (NGRIP) ice core and the timing of the Laacher See volcano eruption (which occurred at approximately 13 ka), suggesting a possible volcanic origin. Here, we evaluate both suggestions by i) presenting new geochemical data from the Laacher See Tephra (LST) and ii) confirming the Pt spike timing relative to the YDE onset on the GICC05 timescale. Our geochemical results, and specifically iridium and platinum data, strongly suggest that the Laacher See eruption (LSE) was most likely not the source of the Greenland Pt spike. Additionally, we corroborate recent work showing a chronological offset of several decades between the Pt spike and the North Greenland Ice Core Project (NGRIP) sulphur spike, the initiation of the YDE at 12,870 ± 30 yr BP (years before present, where present is defined as 1950 CE), and the nearest published age estimate for the LSE (12,880 ± 40 yr BP – though we note that more recent age determinations potentially push this date back by ~130 years). Based on modern data showing that Pt spikes in ice cores and sediment can arise from volcanic eruptions, we suggest that the GISP2 Pt anomaly may represent fractionated volcanic material from another, unknown volcanic eruption. Volcanic gas condensates from submarine volcanic complexes, and in particular Niuatahi-Motutahi (Tonga rear arc), have a Platinum Group Element (PGE) geochemistry most resembling the Pt spike, and we therefore suggest that the Pt spike represents highly fractionated material from an Icelandic subglacial or submarine fissure eruption. The 14-year-long duration of the Pt spike is also more consistent with a fissure eruption than an instantaneous event.

The 2022 eruption of the Hunga Tonga‐Hunga Ha'apai volcano caused substantial impacts on the atmosphere, including a massive injection of water vapor, and the largest increase in stratospheric aerosol for 30 years. The Ozone Mapping and Profiler Suite (OMPS) Limb Profiler instrument has been critical in monitoring the amount and spread of the volcanic aerosol in the stratosphere. We show that the rapid imagery from the OMPS instrument enables a tomographic retrieval of the aerosol extinction that reduces a critical bias of up to a factor of two, and improves vertical structure and agreement with coincident lidar and occultation observations. Due to the vertically thin and heterogeneous nature of the volcanic aerosol, this impacts integrated values of aerosol across latitude, altitude, and time for several months. We also investigate the systematic impact of uncertainty in assumed particle size that result in an underestimation of the aerosol extinction at the peak of the volcanic aerosol layer. Plain Language Summary The Hunga Tonga‐Hunga Ha'apai volcano erupted in 2022. The eruption plume went higher into the atmosphere than ever observed before in the modern age. It also carried large amounts of water vapor and other gases and particles, called aerosols, into the stratosphere. The NASA satellite instrument, called the Ozone Mapping and Profiler Suite (OMPS) Limb Profiler, has given us valuable measurements of these aerosols, which are helpful in understanding the impact the volcanic eruption might have on climate. We use an advanced technique to analyze the OMPS measurements that provides a clearer view of the plume. This analysis gives somewhat different results about the thickness of the volcanic plume than the standard method. Key Points Tomographic retrievals reduce a critical bias in Ozone Mapping and Profiler Suite Limb Profiler volcanic aerosol extinction, improving agreement with Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation and Stratospheric Aerosol and Gas Experiment III/International Space Station Biases of up to a factor of two extend beyond the early plume, with zonal, temporal, and altitude integrated values affected for months Uncertainty in particle size distribution also has an impact that should be considered when analyzing aerosol loading

Aerosol-cloud interactions have a potentially large impact on climate, but are poorly quantified and thus contribute a significant and long-standing uncertainty in climate projections. The impacts derived from climate models are poorly constrained by observations, because retrieving robust large-scale signals of aerosol-cloud interactions are frequently hampered by the considerable noise associated with meteorological co-variability. The Iceland-Holuhraun effusive eruption in 2014 resulted in a massive aerosol plume in an otherwise near-pristine environment and thus provided an ideal natural experiment to quantify cloud responses to aerosol perturbations. Here we disentangle significant signals from the noise of meteorological co-variability using a satellite-based machine-learning approach. Our analysis shows that aerosols from the eruption increased cloud cover by approximately 10%, and this appears to be the leading cause of climate forcing, rather than cloud brightening as previously thought. We find that volcanic aerosols do brighten clouds by reducing droplet size, but this has a significantly smaller radiative impact than changes in cloud fraction. These results add substantial observational constraints on the cooling impact of aerosols. Such constraints are critical for improving climate models, which still inadequately represent the complex macro-physical and micro-physical impacts of aerosol-cloud interactions.

Volcanic eruptions and wildfires can impact stratospheric chemistry. We apply tracer‐tracer correlations to satellite data from Atmospheric Chemistry Experiment—Fourier Transform Spectrometer and the Halogen Occultation Experiment at 68 hPa to consistently compare the chemical impact on HCl after multiple wildfires and volcanic eruptions of different magnitudes. The 2020 Australian New Year (ANY) fire displayed an order of magnitude less stratospheric aerosol extinction than the 1991 Pinatubo eruption, but showed similar large changes in mid‐latitude lower stratosphere HCl. While the mid‐latitude aerosol loadings from the 2015 Calbuco and 2022 Hunga volcanic eruptions were similar to the ANY fire, little impact on HCl occurred. The 2009 Australian Black Saturday fire and 2021 smoke remaining from 2020 yield small HCl changes, at the edge of the detection method. These observed contrasts across events highlight greater reactivity for smoke versus volcanic aerosols at warm temperatures. Plain Language Summary An unprecedented change in HCl was observed in the lower stratosphere after the 2020 Australian New Year (ANY) wildfire using satellite records since 2004. In this study, we conduct a consistent analysis of HCl impacts using an additional satellite product with measurements since 1991 to examine effects of the catastrophic 1991 Pinatubo volcanic eruption and smaller eruptions, and compare them to the 2020 ANY fire (and remaining smoke in 2021), as well as the much smaller 2009 Australian Black Saturday (ABS) bushfire. This allows analysis of different types of particles (smoke vs. volcanic) and the extremes of each observed to date. While the Pinatubo eruption displayed 10 times greater aerosol loading in the stratosphere than the ANY fire, these two events led to similar net chemical changes in HCl. In contrast, no significant changes in HCl were observed in the lower stratosphere following the Hunga and Calbuco volcanic eruptions, which displayed similar levels of extinction to ANY. Small effects were observed from ABS fire and in 2021, allowing identification of the lower limit of the amount of smoke affecting HCl. These contrasts between events indicate that the wildfire smoke aerosols must be more reactive insofar as chlorine chemistry is concerned. Key Points The tracer‐tracer correlation method reveals chemical perturbations associated with volcanic aerosols or smoke The 1991 Pinatubo eruption and the 2020 Australian wildfire markedly perturbed HCl in the southern mid‐latitude lower stratosphere The Pinatubo eruption had 10 times more aerosol loading than the Australian wildfire, but similar decreases in HCl