Recent Advances and Future Avenues in Examining the Impacts of Volcanic Aerosols on Climate
Abstract
Volcanic eruptions primarily influence climate anomalies by modifying atmospheric composition. Sulfate aerosols formed in the stratosphere following volcanic eruptions are significant natural external forcing factors for climate change. This paper provides an overview of the fundamental principles and research methods underlying the impact of volcanoes on climate. It focuses on the reconstruction of records of major volcanic events over the past 2500 years, the effects of volcanic eruptions on global climate, El Niño-Southern Oscillation (ENSO), East Asian and Chinese climate, the influence of volcanic eruptions on decadal climate prediction and future climate projections, volcanic air pollution, and its impact on human health. Key progress in recent years is summarized, and directions for urgent research enhancements are discussed. The main conclusions are as follows:
- Reconstruction of Volcanic Aerosol Forcing: A relatively reliable reconstruction of volcanic aerosol forcing data has been extended back to 2500 years ago. The average interval of large volcanic eruptions (those causing an effective radiative forcing reduction of >1 W m⁻² globally) is 43±7.5 years. Challenges in record reconstruction include using sulfate records in ice cores to reconstruct volcanic intensity, duration, and spatial distribution.
- Global Climate Impacts of Volcanic Aerosols: Volcanic aerosols lead to a reduction in global average temperature and winter warming in the mid-to-high latitudes of the Northern Hemisphere. They also decrease global average precipitation, weaken monsoon circulation, and reduce monsoon precipitation. Satellite observations during the 2022 Hunga Tonga-Hunga Ha’apai eruption revealed increased stratospheric water vapor, which can partially offset the cooling effect of volcanic aerosols. Volcanic eruptions also affect decadal changes in sea level, sea surface temperature, and ocean circulation, and reduce atmospheric CO₂ concentrations by influencing ecosystem carbon cycling.
- Impacts on ENSO: Tropical volcanic eruptions induce an El Niño-type sea surface temperature response in the Pacific. Volcanic eruptions in the tropical and Northern Hemisphere high latitudes have a stronger influence on the formation of El Niño-type sea surface temperature anomalies than those in the Southern Hemisphere. The pre-eruption background state of the tropical Pacific can modulate the impact of volcanic eruptions on ENSO.
- Impacts on East Asian and Chinese Climate: Volcanic aerosols cause temperature declines and extreme cold events in East Asia. They also weaken the East Asian summer monsoon circulation and lead to overall reduced precipitation in eastern China, with uneven spatial distribution.
- Decadal Climate Prediction and Future Projections: Accounting for volcanic aerosol impacts enhances decadal climate prediction skills and drives phase changes in internal climate variability modes. Potential volcanic eruptions could result in a lower-than-expected global average temperature over the next century and reduced precipitation in global monsoon regions.
- Volcanic Air Pollution and Human Health: Volcanic eruptions generate air pollution that affects human health, though scientific understanding of long-term health impacts remains limited.
1. Principles and Research Methods of Volcanic Impact on Climate
1.1 Basic Principles of Volcanic Impact on Climate
Volcanoes influence climate by altering radiative balance. Eruptions inject sulfur gases (e.g., SO₂ and H₂S) into the lower stratosphere, where they oxidize to form sulfate aerosols. These aerosols spread globally, reflecting shortwave radiation and cooling the surface while warming the stratosphere. The volcanic explosivity index (VEI) quantifies eruption intensity, but climate effects depend on factors like SO₂ emissions.
1.2 Research Methods
- Proxy Reconstructions: Ice core records are used to reconstruct volcanic aerosol forcing over the past 1500–2500 years.
- Climate Modeling: Forcing volcanic aerosols into climate models (e.g., CMIP5/CMIP6) simulates their impacts. Techniques like superposed epoch analysis (SEA) and Monte Carlo methods assess climate responses to volcanic eruptions.
2. Major Volcanic Events Over the Past 2500 Years
2.1 Reconstruction of Volcanic Aerosol Forcing
Polar ice cores provide records of volcanic sulfate deposits, extending reconstructions to 2500 years ago. Large eruptions (effective radiative forcing >1 W m⁻²) occur on average every 43±7.5 years. Uncertainties remain in converting ice core sulfate records to volcanic intensity and spatial distribution.
2.2 Challenges in Reconstruction
Ice core sulfate records lack precision in identifying eruption location and distinguishing between tropical/high-latitude eruptions. Multidisciplinary approaches (e.g., combining geological, historical, and modeling data) help address these challenges.
3. Global Climate Impacts of Volcanic Eruptions
3.1 Temperature and Precipitation Responses
- Temperature: Volcanic aerosols cool the global surface, with Northern Hemisphere mid-to-high latitudes warming in winter.
- Precipitation: Global precipitation decreases, monsoon circulation weakens, and precipitation patterns vary regionally (e.g., wet regions dry, dry regions wet).
3.2 Stratospheric Water Vapor and Feedback
Satellite observations show increased stratospheric water vapor after eruptions, partially offsetting cooling via enhanced greenhouse effect.
4. Impacts of Volcanic Eruptions on ENSO
4.1 El Niño-Type SST Response
Tropical volcanic eruptions induce El Niño-like sea surface temperature anomalies in the Pacific. Hemispheric differences exist, with Northern Hemisphere and tropical eruptions having stronger impacts than Southern Hemisphere ones.
4.2 Modulation by Pre-eruption Conditions
The pre-eruption state of the tropical Pacific (e.g., El Niño/La Niña) modulates the impact of volcanic eruptions on ENSO.
5. Impacts on East Asian and Chinese Climate
5.1 Temperature and Monsoon Responses
Volcanic aerosols reduce East Asian temperatures and weaken the summer monsoon, leading to reduced precipitation in eastern China with uneven spatial distribution.
6. Volcanic Impacts on Future Climate Projections
6.1 Decadal Climate Prediction
Including volcanic aerosol impacts improves decadal climate prediction skill by influencing internal variability modes (e.g., ENSO, NAO).
6.2 Future Climate Projections
Potential volcanic eruptions could lower global average temperature and reduce monsoon precipitation in the 21st century.
7. Volcanic Air Pollution and Human Health
Volcanic eruptions release pollutants (e.g., ash, SO₂) that harm health, though long-term effects are poorly understood.
8. Areas for Future Research
- Historical Volcanic Record Reconstruction: Strengthen ice core-based reconstructions and satellite inversion of volcanic aerosol data.
- Physical Mechanisms: Elucidate the physics behind volcanic impacts on global/regional climate and internal variability modes.
- Model Development: Advance stratospheric chemistry-aerosol-climate coupled models.
- International Collaboration: Foster multidisciplinary international cooperation in volcanic climate impact research.
- Small Volcanic Eruptions: Study the climate impact of modern small eruptions and eruption clusters.
- Decadal Climate Variability: Explore the role of volcanic eruptions in decadal climate variability and prediction.
DOI: doi.org/10.1360/TB-2023-0140
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