Will volcanic eruptions slow climate warming?

Source: Guangming Daily

Will volcanic eruptions slow climate warming?

On January 15, a volcano erupted violently on the South Pacific island nation of Tongahun Aha Apai, which may have been the largest in 30 years. From the 1000-meter resolution multi-channel true color composite map produced by fengyun-4 B star data on January 15, it can be seen that the volcanic ash cloud that erupted instantaneously broke through the tropospheric roof and formed an umbrella-shaped cloud with a diameter of nearly 500 kilometers, and the huge shock wave around it was clearly visible. After the volcanic eruption on the island of Tonga, there was a heated discussion about "volcanic eruptions will change the global climate" and even "volcanic eruptions can offset the impact of global warming and reduce the pressure to reduce emissions".

Some experts believe that volcanic eruptions will generally have a sustained impact on the global and East Asian climate in the next 1 to 2 years, with a cooling effect of about 0.3 °C. For the mainland, volcanic eruptions can weaken the intensity of the following year's East Asian summer winds, which in turn leads to the southward summer rain band of the continent. Some experts also said that without the premise of emission reduction, only through artificial methods to change the radiation balance of the Earth system at a large scale, the problem of climate change cannot be solved.

How volcanic eruptions affect continental and global weather and climate

From the eruption of Mount Naki in Iceland in 1783, which caused an unusually cold winter climate in Europe from 1783 to 1784, to the eruption of Mount Tambora in Indonesia in 1815, which caused a serious climatic disaster, the average global temperature dropped by about 0.4 °C to 0.7 °C in the following year of the eruption, 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 a few months later the average global temperature dropped by about 0.5 °C... These famous volcanic eruptions have proved that volcanic eruptions are indeed associated with falling global temperatures.

Zhu Congwen, deputy director and researcher of the Institute of Climate and Climate Change of the Chinese Academy of Meteorological Sciences, said that the tonga island volcano is in a low-latitude region, and 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.

"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 in the atmosphere." Zhu Congwen pointed out that it should be noted that if this causal relationship is established, an important factor must also be considered - "magnitude".

Monitoring maps from NASA's Aura (Breezy in Latin) Earth observation satellite show that the release of sulfur dioxide on the first day of a volcanic eruption on the island of Tonga was 62 kilotons. Michael Mann, a distinguished professor of atmospheric science at Penn State University, analyzed that the eruption of Mount Pinatubo, which caused a 0.5°C drop in global average temperatures, eventually released 20,000 kilotons of sulfur dioxide, so if the impact of previous eruptions on temperature drops was to be achieved, the Tonga Island volcano would need to emit more sulfur dioxide.

Zhu Congwen said: "For the mainland, volcanic eruptions can weaken the intensity of the east Asian summer winds the following year, which in turn leads to the southerly 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. ”

Can "man-made volcanic eruptions" cool the planet?

After the volcanic eruption in Tonga, Chen Ying, a researcher at the Institute of Ecological Civilization of the Chinese Academy of Social Sciences and the main author of the third working group of the FIFTH and Sixth Assessment Reports of the IPCC, has been paying close attention to this. She noticed a hotly debated topic on social media: "If volcanic eruptions have a cooling effect, then don't we just artificially create this aerosol and spread it into the atmospheric stratosphere, and then we don't have to spend a lot of effort to reduce emissions?" ”

Chen Ying objected to this view. "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." She added that SRM will not solve the problem of ocean acidification, while also creating other risks and uncertainties, such as changing temperatures and precipitation distribution.

"What is certain is that SRM cannot serve as a 'workhorse' in the fight against climate change. However, according to recent studies, SRM has the potential to serve as an adjunct to climate change if it is based on significant emission reductions. Chen Ying said.

"The currently proposed SRM method mainly includes injecting aerosols into the stratosphere, low cloud lighting in the ocean, and increasing the albedo of the ocean and land surfaces." Cao Long, a professor in 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, said that 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 offset the warming effect caused by the increase in greenhouse gases through short-wave radiation intervention.

According to Cao Long, since the ipcc's fifth evaluation report, the research on SRM has made great progress. The IPCC Sixth Assessment Report assesses the impact of SRM on the climate system and the carbon cycle, with key conclusions including that SRM can offset climate change from some of the increases in greenhouse gases at global and regional scales, but not completely offset climate change caused by increases in greenhouse gases at global and regional scales, and that SRM cannot mitigate ocean acidification.

How long does it take for SRM to move from simulation to reality?

"As the current understanding of cloud-aerosol radiation processes interactions and microphysical processes is still very limited, there is still a lot of uncertainty about the perception of the cooling potential of aerosol-based SRM, and the assessment of SRM climate effects reported by the FIRST Working Group of the IPCC Sixth Assessment Report is mainly focused on the global scale, and there is a lack of assessment of the climate impact of SRM on different regions." Cao Long pointed out that in the next research work, it is necessary to use high-resolution models including more complete cloud-aerosol-radiation processes to simulate SRM methods to further understand the cooling potential of different SRM methods and their impact on the climate system. "In addition, research on the global and regional climate impacts of different SRM methods implemented at different locations and times should be significantly strengthened."

(Reporter Cui Xingyi)