Will an eruption in Tonga cause the Earth to suffer a "summerless year"? Expert interpretation

Recently, the submarine volcano in the South Pacific island nation of Tongahun Aha Apay erupted violently, causing a chain of tsunamis and volcanic ash disasters, as well as communications interruptions and road obstructions. This may be the largest eruption in 30 years.

According to the latest report from the Tonga Government, on the west side of the main island where the capital of Tonga is located, a large number of houses have been destroyed, and all the houses on some small islands have been engulfed by tsunamis; volcanic ash has polluted the water sources of the entire country; crops in the entire country have been devastating; in these days, the local air and the sea are filled with volcanic ash, and the Government has called on the people to avoid going out as much as possible.

In addition to being visible to the naked eye, volcanic eruptions can have long-term effects on the climate. After the eruption of the Tonga volcano, topics such as "volcanic eruptions change the global climate and bring about volcanic winters", "form a summerless year", and "volcanic eruptions can offset the impact of global warming and reduce the pressure of emission reduction" have aroused discussion.

Zhu Congwen, deputy director and researcher of the Institute of Climate and Climate Change of the Chinese Academy of Meteorological Sciences, said that the volcanic eruption in Tonga may have a continuous impact on the global climate in the next one to two years, with a cooling effect of about 0.3 °C. However, there are still uncertainties about the eruption of the Tonga volcano. Wei Ke, an associate researcher at the Institute of Atmospheric Physics of the Chinese Academy of Sciences, believes that if there is no larger-scale eruption in the later stage of the volcano, it can be judged that the volcanic activity is unlikely to affect the global temperature.

Volcanic eruptions are associated with falling global temperatures, but depending on the "magnitude" of the eruptions

In 1783, the eruption of Mount Naki in Iceland caused an unusually cold winter climate in Europe from 1783 to 1784; in 1815, the eruption of Mount Tambora in Indonesia caused the global average temperature to drop by about 0.4 °C to 0.7 °C the following year, and many parts of the northern hemisphere suffered a "summerless year"; in 1991, the Pinatubo volcano in the Philippines erupted, injecting a large amount of aerosol into the stratosphere, and the global average temperature dropped by about 0.5 °C a few months later... These famous volcanic eruptions have proved that volcanic eruptions are indeed related to falling global temperatures.

Tonga volcano is located in a low-latitude region, Zhu Congwen said that in the past 100 years, there have been three large-scale low-latitude volcanic eruptions, namely Agung Volcano (March 17, 1963), Elchijom Volcano (April 4, 1982) and Pinatubo Volcano (June 15, 1991). In the winter of the year after their eruption (December to February), temperatures were low in most parts of the mainland except the northeast and Xinjiang. It should also not be ignored that the occurrence of La Niña also played a cooling effect on the winter temperature of the mainland except for the Qinghai-Tibet Plateau that year.

The main reason why a volcanic eruption causes cooling is that it injects sulfur-containing aerosols into the atmosphere, which enter the stratosphere and help the Earth reflect more sunlight out, creating a cooling effect within the atmosphere.

However, it should be noted that if volcanic eruptions can lead to cooling, an important factor must also be considered - "magnitude". Monitoring maps from NASA's Aura (Breezy in Latin) Earth observation satellite show that sulfur dioxide was released at 62 kilotons on the first day of the eruption of Tonga's volcano. Michael Mann, Distinguished Professor of Atmospheric Sciences at Pennsylvania State University, analyzed that the eruption of Mount Pinatubo, which caused the global average temperature to drop by 0.5 °C, eventually released 20,000 kilotons of sulfur dioxide, so if the impact of the previous eruption on temperature drops is to be achieved, the eruption needs to emit more sulfur dioxide.

Volcanic eruptions in Tonga may cause the mainland to be southward in the summer rain band

"This Tonga eruption is likely to have a lasting impact on the global climate for the next year to two years, with a cooling effect of about 0.3°C." Zhu Congwen said that for the mainland, the eruption of the Tonga volcano could weaken the intensity of the East Asian summer winds the following year, which in turn led to the southward summer rain band of the mainland. Therefore, it is recommended that the continuing effects of volcanic eruptions be taken into account in flood precipitation forecasters.

As for whether the eruption of the Tonga volcano will lead to "volcanic winter" and "summerless year", it is too early to draw conclusions. There are still uncertainties about the eruption of the Tonga volcano, and the most important point is that the level of the eruption is not yet certain, and it depends on the follow-up.

According to Weiko, volcanic eruptions generally last for a long time, such as in 1991, when Pinatubo began to be active in March of that year, and then produced its strongest eruption on June 15 of that year, and then continued until July 1992. The volcanic activity in Tonga began at the end of December 2021 and is still active, so whether there will be a larger eruption in the future needs further monitoring.

In addition, Wei Ke also said that there is a very large gap between the sulfur dioxide release on the first day of the volcanic eruption in Tonga and the magnitude that can affect the global climate, and if there is no larger-scale eruption in the later stages of the volcano, it can be judged that the volcanic activity is not likely to affect the global temperature.

Without emissions reductions, man-made volcanic eruptions cannot resist global warming

After the volcanic eruption event in Tonga, topics such as "volcanic eruptions can offset the impact of global warming and reduce the pressure of emission reduction" have sparked discussions, and some people have proposed, "If volcanic eruptions have a cooling effect, is it not necessary to artificially manufacture this aerosol and spread it into the atmospheric stratosphere, and there is no need to spend a lot of effort to reduce emissions?" ”

Chen Ying, a researcher at the Institute of Ecological Civilization of the Chinese Academy of Social Sciences and the lead author of the third working group of the fifth and sixth assessment reports of the United Nations Intergovernmental Panel on Climate Change (IPCC), expressed opposition to the above views.

"Without the premise of reducing emissions, SRM (solar radiation intervention, that is, changing the radiation balance of the Earth system on a large scale through artificial methods to cope with global warming) will certainly not solve the problem of climate change." Chen Ying added that SRM will not solve the problem of ocean acidification, and may also bring other risks and uncertainties, such as changing the temperature and precipitation distribution.

What is certain is that SRM cannot be a "workhorse" in the fight against climate change. However, according to recent studies, solar radiation interventions have the potential to be complementary measures to combat climate change if they are based on significant emission reductions.

Cao Long, professor of the Department of Atmospheric Sciences at the School of Earth Sciences of Zhejiang University and the lead author of the first working group of the sixth assessment report of the IPCC, introduced that the currently proposed SRM method mainly includes injecting aerosols into the stratosphere, low cloud lighting of the ocean, and increasing the albedo of the ocean and land surface. The basic starting point of these methods is to increase the albedo of the earth-gas system, reduce the solar radiation reaching the atmosphere and the ground, and counteract the warming effect caused by the increase in greenhouse gases through short-wave radiation intervention.

According to Cao Long, the IPCC Sixth Assessment Report assesses the impact of SRM on the climate system and the carbon cycle, and the main conclusions include that SRM can offset some of the climate change caused by greenhouse gas increases at global and regional scales, but it cannot completely offset climate change caused by greenhouse gas increases at global and regional scales, and SRM cannot alleviate ocean acidification.

Beijing News reporter Wang Jingxi

Edited by Bai Shuang proofread by Chen Diyan