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Climate change is occurring all over the globe as a 1掳C increase in Earth's temperature has led to the rise in the sea level, melting of the Arctic ice, and unseasonable heat waves and heavy snow. To accurately predict the artificial climate changes set off by the increase in greenhouse gases, it is important to understand the effects of natural factors such as solar and volcanic activities. A recent study has shown how global precipitation decreases when volcanoes erupt in the tropics.

Professor Seung-Ki Min and Dr. Seungmok Paik of the department of environmental engineering at POSTECH and researchers from the French National Centre for Scientific Research, Zurich Institute of Technology, and Edinburgh University have released new findings that the El Ni帽o induced by volcanic eruptions plays a key role in the decrease in global precipitation. So far, studies have shown that volcanic activity reduces precipitation across the globe, but its specific mechanism had been unclear. These research results were recently published in Science Advances.

For the two to three years following Mount Pinatubo's volcanic eruption in 1991, the average global temperature fell by about 0.2 degrees. This is because the massive dust and greenhouse gases emitted by the eruption reflected the light from the sun and blocked its heat from reaching the Earth. Volcanic activities, along with these cooling effects, reduce global terrestrial precipitation but its scale greatly varies depending on each climate model simulation. For the first time, the joint research team confirmed that the main factor for the drop in precipitation after these volcanic eruptions is the difference in El Ni帽o's response.

El Ni帽o is a severe climate change that occurs every three to eight years, weakening trade winds in the equatorial Pacific Ocean and raising sea level temperatures in the East Pacific, causing extreme weather conditions across the globe including drought and heavy rains. Under El Ni帽o's influence, precipitation reduction occurs especially in the global monsoon regions, including Southeast Asia, India, South Africa, Australia and Latin America.

The team compared several climate model simulations and found that El Ni帽o appeared in the year following a volcanic eruption in most models, with a significant drop in precipitation around the global monsoon region. In particular, the strength of El Ni帽o was different for each simulation, and the stronger the El Ni帽o, the more pronounced the reduction in precipitation occurred. The research team also found that the stronger the volcanic forcing and the greater the water temperature in the western Pacific Ocean, a stronger El Ni帽o developed, which in turn intensified the reduction in precipitation.

These findings are expected to be used to identify the side effects of geoengineering techniques or to predict the climate of later years. In particular, it suggests that if geoengineering techniques are used to reduce global warming by spraying sulfur dioxide鈥攖he main component of volcanic ash鈥攊n the lower stratosphere to imitate artificial volcanoes, they could produce unexpected side effect of changing the precipitation patterns across the globe.

Professor Seung-Ki Min stated, "If geoengineering techniques are applied to mimic volcanoes and block sunlight, drought and water shortages may increase significantly in the monsoon regions鈥攈ome to two-thirds of the world's population."