Volcanoes may mask the predictive power of climate models

Simulating volcanic eruptions may blow our ability to predict near-term climate, according to a new study published in the journal Science advances.

The research, which was led by the National Center for Atmospheric Research (NCAR), found that the way volcanic eruptions are represented in climate models may mask the ability of models to accurately predict changes in sea surface temperatures in the tropical Pacific Ocean that unfold over multiple years. for a decade.

These decadal variations in sea surface temperatures in the equatorial Pacific are associated with worldwide climate influences, including changes in precipitation and extreme weather. Therefore, accurate forecasts can provide community leaders, farmers, water managers, and others with critical climate information that allows them to plan years in advance.

“Near-term climate forecasting on annual to decadal timescales is a rapidly growing and important field in the climate community because it bridges the gap between current seasonal forecasts and centennial climate projections,” said Xian Wu, who led the study as a postdoctoral researcher at UCLA. NCAR. “When we rely on models to make these predictions, it is important to consider carefully the accuracy of the model. In this case, we found that model errors in simulating the response to volcanic eruptions weakened our prediction skill.”

For the study, Wu and her colleagues relied on two parallel sets of climate simulations from the Large Decade Prediction Collection, a dataset produced using the NCAR-based Community Earth System model. These simulations are run as projections back and cover the years from 1954 to 2015, allowing scientists to compare simulations with what actually happened and assess their skill at predicting the future.

One set of simulations included the three major volcanic eruptions that occurred during the study period: Agung (1963), El Chichón (1982), and Pinatubo (1991). The other group did not.

Because it is well established that large volcanic eruptions can have large, long-term cooling effects on climate, Wu and her colleagues expected that a set of simulations that included volcanic eruptions would produce more accurate multi-year and decadal climate predictions. Instead, they found that the inclusion of volcanic eruptions weakened the model’s predictive capabilities, at least in the tropical Pacific, a region of particular interest due to links between sea surface temperatures and near-term climatic events.

For example, simulations involving volcanoes predicted a subsequent cooling of sea surface temperatures in the equatorial Pacific after eruptions. In fact, that region of the ocean warmed, a change predicted well by simulations that did not include volcanic eruptions.

These results highlight the difficulty of accurately representing complex climate forcings that follow a volcanic eruption in a model, a task made more difficult because researchers have only a few real-life examples in the observational record. Scientists know that volcanoes can lift sulfur gases high into the stratosphere where they can turn into aerosols that reflect sunlight. But how the resulting cooling ultimately affects the entire Earth system, including sea surface temperatures, is poorly understood.

“We don’t have enough notes,” Wu said. “And our methods of observing what’s happening in the stratosphere have only been available since the satellite era, which means we only have Chichun and Pinatubo.”

However, Wu is hopeful that the representation of volcanic eruptions and their effects in models can be improved over time, and that ultimately this work will improve our ability to predict important weather events years in advance.

“Decadal variability in the equatorial Pacific is an important source of worldwide prediction,” Wu said. “It affects the climate over the surrounding continents, as well as marine ecosystems. Better predictions will provide important information for stakeholders.”