Recent advances and future avenues in examining the impacts of volcanic aerosols on climate

Volcanic eruptions affect the climate by changing the atmospheric composition. By injecting sulfur gases into the lower stratosphere and converting them to sulfate aerosols, volcanic eruptions are important natural external forcings of climate change. Based on an overview of the basic principles of and research methods for assessing volcanic impacts on climate, recent progress in major volcanic eruption records during the past 2500 years; the impact of volcanic eruptions on the global climate, El Nino-southern oscillation (ENSO) and climate over East Asia and China; volcanic impacts on decadal climate prediction and projection; and volcanic air pollution and its human health effects are summarized in this paper. Avenues for future research are also outlined based on previous studies. We aim to provide comparative research on the impacts of natural and anthropogenic external forcings on climate change. The main conclusions are as follows: (1) A reliable reconstruction of the volcanic aerosol forcing dataset has been extended to the past 2500 years, and an average period of large volcanic eruptions of 43 +/- 7.5 years can cause a global reduction in effective radiative forcing of more than 1 W m(-2). It is challenging to use the sulfate records in ice cores to reconstruct the intensity, duration and spatial distribution of volcanic eruptions. (2) The global climate impacts of volcanic aerosols include lower global mean temperatures, winter warming in the mid-to-high latitude areas of the Northern Hemisphere, reduced global mean precipitation, weakened monsoon circulation, and decreased monsoon precipitation, which are shown in observations, reconstructions and climate model simulations. Increased stratospheric water vapor was observed by satellites during the 2022 Hunga Tonga-Hunga Ha'apai volcanic eruption, which could partially offset the cooling effect of volcanic aerosols based on an idealized model simulation. Volcanic eruptions can also lead to decadal changes in sea level height, sea surface temperature (SST) and ocean circulation and reduce the atmospheric CO2 concentration by changing the ecosystem carbon cycle. (3) Reconstructions and model simulations reveal that the tropical Pacific features a significant El Nino-like SST anomaly after tropical volcanic eruptions. Tropical and northern hemispheric, high-latitude volcanic eruptions have stronger impacts on the formation of El Nino-like SST anomalies than do southern hemispheric volcanoes, and the pre-eruption background oceanic state of the tropical Pacific can modulate the impacts of volcanic eruptions on the ENSO. (4) Volcanic aerosols reduce the temperature and cause extreme low temperature events in East Asia in both the observations and model simulations. The East Asian summer monsoon circulation is also weakened after volcanic eruptions, associated with overall reduced precipitation in eastern China, which shows heterogeneous spatial distribution under ENSO modulation. (5) Considering the impact of volcanic aerosols can improve the decadal climate prediction skill and detect phase changes in the internal variability modes of the climate system. Potential volcanic eruptions may lead to a lower-than-expected global mean temperature and reduced global monsoon precipitation during the 21st century in climate model projections. (6) Volcanic eruptions cause volcanic air pollution, which in turn have impacts on human health. (7) In the future, efforts should be focused on studying the reconstruction of historical volcanic records, inversion of volcanic aerosol characteristics based on satellite measurements during the instrumental period, underlying physical mechanisms of volcanic impacts on the global and regional climate, development of the state-of-the-art aerosol-climate models, multidisciplinary international cooperation in volcano and climate impact studies, and especially the climatic impact of small volcanic eruptions and volcanic clusters in recent decades and the role of volcanic eruptions in decadal climate variability change, decadal climate predictions and projections.