The model that excluded volcanic eruptions got its prediction right
Large volcanic eruptions linked to global cooling are not accurately represented in climate models, leading to inaccurate near-term predictions, a new study published in Science Advances showed.
Large volcanic eruptions release sulphur gases, which combine with other gases in the atmosphere to form aerosols, known to scatter solar radiation and reflect it into space.
The expectation is that volcanic eruptions could predict how climate evolves post-eruption from seasons to decades, Xian Wu, a postdoctoral research associate at the National Oceanic and Atmospheric Administration Geophysical Fluid Dynamics Laboratory, told Down To Earth.
But the role of volcanic eruptions in predicting near-time climate over annual to decadal timescales “has not been extensively explored and remains unclear, except for a few case studies”, she added.
The study focused on multiyear-to-decadal variations in sea surface temperatures in the tropical Pacific, beyond the yearly fluctuations associated with El Nino and La Nina events, Wu noted.
“Specifically, we focus on predicting whether the tropical Pacific sea surface temperatures will be warmer or colder than normal over the next 5-10 years,” she highlighted
Near-term climate prediction, according to the expert, bridges the gap between existing seasonal forecasts and centennial (over 100 years timescale) climate projections.
This field has grown rapidly over the last decade, driven by high demand from stakeholders and policymakers. The tropical Pacific, according to the experts, is the most critical region for global climate predictability.
Wu and her colleagues tested the model’s ability to make past predictions from 1954-2015. They then compared the model simulations with ground reality.
During the study period, three major volcanic eruptions occurred: Agung, Indonesia (1963), El Chichón, Mexico (1982) and Pinatubo, Philippines (1991).
The researchers also ran another set of simulations without these volcanic eruptions.
They found that the model that included volcanic eruptions made errors in its predictions, at least in the tropical Pacific.
For example, it predicted a subsequent cooling of the sea surface temperatures in the tropical Pacific after volcanic eruptions.
The model that excluded volcanic eruptions got its prediction right. The Pacific region of the ocean, in reality, had warmed.
The errors stem from the fact that volcanic eruptions are not accurately represented in climate models. Wu explained that a few factors could explain this.
First, it is challenging to estimate historical volcanic eruptions due to the lack of data on volcanic sulfate aerosols before the satellite era.
Second, representing them in climate models is technically complex and third, there are model biases in simulating how the climate responds to volcanic eruptions, Wu noted.
This issue raises questions about the model’s ability to realistically simulate the volcanic effect on El Niño-Southern Oscillation, a recurring climate pattern involving changes in water temperature in the central and eastern tropical Pacific Ocean.
The same concern applies to tropical Pacific decadal variability, climate variability occurring within the tropical Pacific.
The researchers plan to next perform the same evaluations on a popular model called Coupled Model Intercomparison Project models.
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