The weather of Arabia - Sinan Khalaf - some described it as a year without a summer. We are talking here about the year 1991 AD, when unusual weather systems dominated the world, and the temperature decreased by 0.5 degrees Celsius in the world. This happened after the eruption of the volcano "Pinatubo" in the Philippines in the year 1991 AD, to prove to the world that massive volcanic eruptions have a direct impact on the climate.
Volcanoes pump millions of tons of sun-blocking particles and fumes into the atmosphere, which can cool the Earth for nearly 5 years.
However, it is becoming increasingly clear that even these formidable forces are being altered by human-driven climate change. Decreased ice sheets can lead to frequent volcanic eruptions near the poles, in Iceland and elsewhere. An increasingly layered ocean would allow more cooling from volcanoes to remain on Earth's surface. Now, a new study suggests that an increase in greenhouse gases will help plumes from large eruptions reach higher, spread faster and reflect more sunlight, causing more sudden and intense cooling.
Before humanity embarked on its path to changing the planet, volcanoes were one of the biggest climatic factors. In the long run, they took carbon dioxide out of the Earth's interior, which caused the temperature to rise. But in the short term, sulfur gases often react with water to form highly reflective molecules called sulfates, leading to bouts of global cooling. The dark smudges of ash scattering the ice core—the best evidence we have for these early eruptions—are a faint reflection of the weather left in their wake.
Climate can have a big impact on volcanoes, too. In the new study, University of Cambridge geophysicist Thomas Aubrey and colleagues combined computer simulations of typical volcanic eruptions with a global climate model. They simulated the response of plumes from large and medium-sized volcanoes under both historical conditions and by the year 2100, in a scenario in which very rapid global warming is expected.
The researchers found two parallel trends. Normally only one or two medium-sized volcanic eruptions shoot through the troposphere each year, bypassing this cradle of Earth's weather to reach the stratosphere, the quiet, dry region above. As the reflective particles scatter through the stratosphere, they cause a small surge of global cooling. But when the troposphere gets warmer, it expands in height, which eventually puts the stratosphere out of reach of these volcanic eruptions.
"It's as if the regulation hoops of basketball around the world have suddenly been lifted a few inches, making it difficult to score," says Benjamin Black, a volcanologist at Rutgers University, New Brunswick. However, the story changes with the eruptions of the "Pinatubo" volcano. In a world that will warm by 6°C by 2100 - an increase that matches only the most dire and unlikely projections of the latest IPCC report - the troposphere will grow to 1.5km. But colossal explosions will still be able to penetrate the stratosphere. What's more, their gases would actually reach a higher level and travel faster than the current climate, amplifying the cooling effect by 15%, the researchers reported.
As greenhouse gases trap heat near the Earth's surface, the stratosphere cools, especially in its upper layers. This allows air to mix more easily up and down in this layer of the atmosphere. By the year 2100, this mixing should help plumes travel about 1.5 kilometers higher than before, according to the team's model. In addition, warming will accelerate the pattern of primary winds in the stratosphere, causing reflective volcanic particles to spread more rapidly throughout the upper atmosphere to the poles before they have time to coalesce into larger particles. And the smaller the particle, the more light it reflects.
“The fact that medium-sized volcanic eruptions may no longer reach the stratosphere is interesting and important,” says Michael Mills, an atmospheric chemist at the National Center for Atmospheric Research, who was not involved in the study. “Several trends have already been seen in Identified in the new model - cold stratosphere, troposphere high." Mills adds that it remains uncertain whether the limited particle growth simulated by the new model reflects what would happen in the real world.
In fact, the study raises more questions than it answers, says Aubrey. It only studies tropical volcanic eruptions, not those closer to the poles, where the stratosphere is closer. It is difficult to say whether increased cooling from large volcanoes or decreased cooling from small volcanoes will win out for the largest climate effect.
The next step will be to test how these trends work under more realistic levels of future warming and in additional climate models. Researchers also hope to incorporate other trends, including the increased explosiveness expected to occur with melting glaciers from some polar volcanoes and increased ocean stratification, which would allow more volcanic cooling to remain on the surface of the water, cooling the atmosphere.
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