Northern Hemisphere Winter Warming and Summer Monsoon Reduction after Volcanic Eruptions over the Last Millennium

Regional transportation and influence of atmospheric aerosols triggered by Tonga volcanic eruption

A cataclysmic submarine volcano at Hunga Tonga-HungaHa'apai (HTHH) near Tonga, erupted violently on 15 January 2022, which injected a plume of ash cloud soaring into the upper atmosphere. In this study, we examined the regional transportation and potential influence of atmospheric aerosols triggered by HTHH volcano, based on active and passive satellite products, ground-based observations, multi-source reanalysis datasets and atmospheric radiative transfer model. The results indicated that about 0.7 Tg (1 Tg = 10⁹ kg) sulfur dioxide (SO₂) gas were emitted into stratosphere from the HTHH volcano, and were lifted to an altitude of 30 km. The regional averaged SO₂ columnar content over the western Tonga increased by 10-36 Dobson Units (DU), and the mean aerosol optical thickness (AOT) retrieved from satellite products increased to 0.25-0.34. The stratospheric AOT values caused by HTHH emissions increased to 0.03, 0.20, and 0.23 on 16, 17, and 19 January, respectively, accounting for 1.5%, 21.9%, and 31.1% of total AOT. Ground-based observations also showed an AOT increase of 0.25-0.43, with the maximum daily average of 0.46-0.71 appeared on 17 January. The volcanic aerosols were remarkably dominated by fine-mode particles and posed strong light-scattering and hygroscopic abilities. Consequently, the mean downward surface net shortwave radiative flux was reduced by 2.45-11.9 Wm^-2 on different regional scales, and the surface temperature decreased by 0.16-0.42 K. The maximum aerosol extinction coefficient was 0.51 km^-1 appeared at 27 km, which resulted in an instantaneous shortwave heating rate of 1.80 Khour^-1. These volcanic materials stayed stable in the stratosphere and completed one circle around the earth within 15 days. This would exert a profound influence on the energy budget, water vapor and ozone exchange in the stratosphere, which deserves to be further studied.

Long-term impacts of climate change on coastal and transitional eco-systems in India: an overview of its current status, future projections, solutions, and policies

Urbanization and industrial development are increasing rapidly. These are accompanied by problems of population explosion, encroachment of agricultural, and construction lands, increased waste generation, effluent release, and escalated concentrations of several greenhouse gases (GHGs) and pollutants in the atmosphere. This has led to wide-scale adverse impacts. Visible effects are fluctuations in temperatures and precipitation, rising sea levels, unpredictable floods, storms and cyclones, and disruption to coastal and transitional ecosystems. In a country like India with a massive population of nearly 1.4 billion and around 420 million people dwelling on or near the coasts, this effect is pre-dominant. India has extensive coastlines on both sides that are subject to greater contact and high impact from the water bodies. The factors impacting climate change, its consequences, and future predictions must be analyzed immediately for implementing precautionary measures to ameliorate the detrimental effects. Several endemic species have been endangered as these changes have resulted in the loss of habitat and interfered with the food webs. Climatic impacts on transitional ecosystems also need to be considered to preserve the diversity of each. The cooperation of governmental, independent organizations and policymakers throughout the world is essential to control and mediate the impacts on health, agriculture, and other related sectors, the details of which have been elaborated in this review. The review analyses the trends in climatic variation with time and discusses a few extremities which have left permanent effects on the population primarily concerning the coastal - Indian scenario and its eco-systems.

Volcanic-induced global monsoon drying modulated by diverse El Niño responses

There remains large intersimulation spread in the hydrologic responses to tropical volcanic eruptions, and identifying the sources of diverse responses has important implications for assessing the side effects of solar geoengineering and improving decadal predictions. Here, we show that the intersimulation spread in the global monsoon drying response strongly relates to diverse El Niño responses to tropical eruptions. Most of the coupled climate models simulate El Niño-like equatorial eastern Pacific warming after volcanic eruptions but with different amplitudes, which drive a large spread of summer monsoon weakening and corresponding precipitation reduction. Two factors are further identified for the diverse El Niño responses. Different volcanic forcings induce systematic differences in the Maritime Continent drying and subsequent westerly winds over equatorial western Pacific, varying El Niño intensity. The internally generated warm water volume over the equatorial western Pacific in the pre-eruption month also contributes to the diverse El Niño development.

Warm Deep Water Variability During the Last Millennium in the CESM–LME: Pre-Industrial Scenario versus Late 20th Century Changes

Water transformation around Antarctica is recognized to significantly impact the climate. It is where the linkage between the upper and lower limbs of the Meridional Overturning Circulation (MOC) takes place by means of dense water formation, which may be affected by rapid climate change. Simulation results from the Community Earth System Model Last Millennium Ensemble (CESM–LME) are used to investigate the Weddell Sea Warm Deep Water (WDW) evolution during the Last Millennium (LM). The WDW is the primary heat source for the Weddell Sea (WS) and accounts for 71% of the Weddell Sea Bottom Water (WSBW), which is the regional variety of the Antarctic Bottom Water (AABW)—one of the densest water masses in the ocean bearing directly on the cold deep limb of the MOC. Earth System Models (ESMs) are known to misrepresent the deep layers of the ocean (below 2000 m), hence we aim at the upper component of the deep meridional overturning cell, i.e., the WDW. Salinity and temperature results from the CESM–LME from a transect crossing the WS are evaluated with the Optimum Multiparameter Analysis (OMP) water masses decomposition scheme. It is shown that, after a long–term cooling over the LM, a warming trend takes place at the surface waters in the WS during the 20th century, which is coherent with a global expression. The subsurface layers and. mainly. the WDW domain are subject to the same long–term cooling trend, which is decelerated after 1850 (instead of becoming warmer like the surface waters), probably due interactions with sea ice–insulated ambient waters. The evolution of this anomalous temperature pattern for the WS is clear throughout the three major LM climatic episodes: the Medieval Climate Anomaly (MCA), Little Ice Age (LIA) and late 20th century warming. Along with the continuous decline of WDW core temperatures, heat content in the water mass also decreases by 18.86%. OMP results indicate shoaling and shrinking of the WDW during the LM, with a ~6% decrease in its cross–sectional area. Although the AABW cannot be directly assessed from CESM–LME results, changes in the WDW structure and WS dynamics have the potential to influence the deep/bottom water formation processes and the global MOC.

South Atlantic Surface Boundary Current System during the Last Millennium in the CESM-LME: The Medieval Climate Anomaly and Little Ice Age

Interocean waters that are carried northward through South Atlantic surface boundary currents get meridionally split between two large-scale systems when meeting the South American coast at the western subtropical portion of the basin. This distribution of the zonal flow along the coast is investigated during the Last Millennium, when natural forcing was key to establish climate variability. Of particular interest are the changes between the contrasting periods of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). The investigation is conducted with the simulation results from the Community Earth System Model Last Millennium Ensemble (CESM-LME). It is found that the subtropical South Atlantic circulation pattern differs substantially between these natural climatic extremes, especially at the northern boundary of the subtropical gyre, where the westward-flowing southern branch of the South Equatorial Current (sSEC) bifurcates off the South American coast, originating the equatorward-flowing North Brazil Undercurrent (NBUC) and the poleward Brazil Current (BC). It is shown that during the MCA, a weaker anti-cyclonic subtropical gyre circulation took place (inferred from decreased southern sSEC and BC transports), while the equatorward transport of the Meridional Overturning Circulation return flow was increased (intensified northern sSEC and NBUC). The opposite scenario occurs during the LIA: a more vigorous subtropical gyre circulation with decreased northward transport.

Volcanically Triggered Ocean Warming Near the Antarctic Peninsula

Explosive volcanic eruptions are the largest non-anthropogenic perturbations for Earth's climate, because of the injection of sulfate aerosols into the stratosphere. This causes significant radiation imbalances, resulting in surface cooling for most of the globe. However, despite its crucial importance for Antarctic ice sheet mass balance, the response of the Southern Ocean to eruptions has yet to be understood. After the eruption of Mt. Pinatubo in 1991, much of the Southern Ocean cooled; however, off the Antarctic Peninsula a warming of up to 0.8 °C is found in the observations. To understand the physical mechanisms associated with this counter-intuitive response, we combine observational analysis from the Mt. Pinatubo eruption with the Last Millennium Ensemble (850-1850) conducted with the Community Earth System Model. These results show not only that the observed warming off the Peninsula following the Mt. Pinatubo eruption is consistent with the forced response to low-latitude eruptions but further, that this warming is a response to roughly 16% weakening of subsurface Weddell Gyre outflow. These changes are triggered by a southward shift of the Southern Hemisphere polar westerlies (∼2°latitude). Our results suggest that warming induced by future volcanic eruptions may further enhance the vulnerability of the ice shelves off the Antarctic Peninsula.