A volcanic winter is a reduction in global temperatures caused by droplets of sulfuric acid obscuring the Sun and raising Earth's albedo (increasing the reflection of solar radiation) after a large, sulfur-rich, particularly explosive volcano. Climate effects are primarily dependent upon the amount of injection of Sulfur dioxide and Hydrogen sulfide into the stratosphere where they react with Hydroxide and H2O to form H2SO4 on a timescale of a week, and the resulting H2SO4 aerosols produce the dominant radiative effect. Volcanic stratospheric aerosols cool the surface by Backscatter and warm the stratosphere by absorbing terrestrial radiation for several years. Moreover, the cooling trend can be further extended by atmosphere–ice–ocean feedback mechanisms. These feedbacks can continue to maintain the cool climate long after the volcanic aerosols have dissipated.
The subsequent dispersal of a volcanic cloud in the stratosphere and its impact on climate are strongly influenced by several factors, including the season of the eruption, the latitude of the source volcano, and the injection height. If the SO2 injection height remains confined to the troposphere, the resulting H2SO4 aerosols have a residence time of only a few days due to efficient removal through precipitation. The lifetime of H2SO4 aerosols resulting from extratropical eruptions is shorter compared to those from tropical eruptions, due to a longer transport path from the tropics to removal across the mid- or high-latitude tropopause, but extratropical eruptions strengthens the hemispheric climate impact by confining the aerosol to a single hemisphere. Injections in the winter are also much less radiatively efficient than injections during the summer for high-latitude volcanic eruptions, when the removal of stratospheric aerosols in polar regions is enhanced.
The sulfate aerosol interacts strongly with Solar irradiance through scattering, giving rise to remarkable atmospheric optical phenomena in the stratosphere. These phenomena include Global dimming, coronae or Bishop's rings, peculiar twilight coloration, and dark total . Historical records that documented these atmospheric events are indications of volcanic winters and date back to periods preceding the Common Era.
Surface temperature observations following historic eruptions show that there is no correlation between eruption size, as represented by the VEI or eruption volume, and the severity of the climate cooling. This is because eruption size does not correlate with the amount of SO2 emitted.
During the first few years following a volcanic eruption, the presence of H2SO4 aerosols can induce a significant cooling effect. This cooling can lead to a widespread lowering of Snow line, enabling the rapid expansion of sea ice, and Glacier. As a result, ocean temperatures decrease, and surface albedo increases, further reinforcing the expansion of sea ice, ice caps, and glacier. These processes create a strong positive feedback loop, allowing the cooling trend to persist over centennial-scale or even longer periods of time.
It has been proposed that a cluster of closely spaced, large volcanic eruptions triggered or amplified the Little Ice Age, Late Antique Little Ice Age, , Younger Dryas, , and Dansgaard-Oeschger events through the atmosphere-ice-ocean positive feedbacks.
The rapid emplacement of mafic large igneous provinces has the potential to cause a swift decline in atmospheric CO2 content, leading to a multi-million-year-long icehouse climate. A notable example is the Sturtian glaciation, which is considered the most severe and widespread known glacial event in Earth's history. This glaciation is believed to have been caused by the weathering of erupted Franklin Large Igneous Province.
+Northern Hemisphere cooling episodes definitively attributed to volcanic eruptions !Cooling episode (CE/BCE) !Volcanic eruptions !N.H. peak temperature anomaly !Notes !Ref. | ||||
1991–1993 | 1991 eruption of Mount Pinatubo | −0.5 K | ||
1883–1886 | 1883 eruption of Krakatoa | −0.3 K | ||
1809–1820 | 1808 mystery eruptions, 1815 eruption of Mount Tambora | −1.7 K | Year Without a Summer | |
1453–1460 | 1452 N.H. mystery eruption, 1458 S.H. mystery eruption | −1.2 K | The attribution of the 1458 eruption to Kuwae remains controversial. | |
1258–1260 | 1257 Samalas eruption | −1.3 K | The single largest sulfur injection of the Common Era. | |
536–546 | 535 N.H. mystery eruptions, 540 tropical mystery eruption | −1.4 K | The first phase of Late Antique Little Ice Age. | |
−43–41 | Mount Okmok | −2–3 K |
Sulfate concentration and isotope measurements from polar ice cores taken around the time of 74,000 years BP have identified four atmospheric aerosol events that could potentially be attributed to YTT. The calculated stratospheric sulfate loadings for these four events range from 219 to 535 million tonnes, which is 1 to 3 times greater than that of the Samalas eruption in 1257 CE. Global climate models simulate peak global mean cooling of 2.3 to 4.1 K for this amount of erupted sulfate aerosols, and complete temperature recovery does not occur within 10 years.
Empirical evidence for cooling induced by YTT, however, is mixed. YTT coincides with the onset of Greenland Stadial 20 (GS-20), which is characterized by a 1,500-year cooling period. GS-20 is considered the most isotopically extreme and coldest stadial, as well as having the weakest Asian monsoon, in the last 100,000 years. This timing has led some to speculate on the relation between YTT and GS-20. The stratigraphic position of YTT in relation to the GS-20 transition suggests that the stadial would have occurred without YTT, as the cooling was already underway. There is the possibility that YTT contributed to the extremity of GS-20. The South China Sea shows a 1 K cooling over 1,000 years following the deposition of YTT, while the Arabian Sea shows no discernible impact. In India and the Bay of Bengal, initial cooling and prolonged desiccation are observed above the YTT ash layer, but it is argued that these environmental changes were already occurring prior to YTT. Lake Malawi sediments do not provide evidence supporting a volcanic winter within a few years after the eruption of YTT, but the resolution of the sediments is questioned due to sediment mixing. Directly above the YTT layer in Lake Malawi, there is evidence of a 2,000-year-long megadrought and cooling period. Greenland ice cores identify a 110-year period of accelerated cooling immediately following what is likely the YTT aerosol event.
Geochronology dates the rapid emplacement of Franklin large igneous province just 1 million year before the onset of Sturtian glaciation. Multiple large igneous provinces on the scale of were also emplaced on Rodinia between 850 and 720 million years ago. Weathering of massive amount of fresh mafic materials initiated runaway cooling and ice-albedo feedback after 1 million year. Chemical isotopic compositions show a massive flux of weathered freshly erupted materials entering the ocean, coinciding with the eruptions of large igneous provinces. Simulations demonstrate that the increased weatherability led to drop in atmospheric CO2 of the order of 1,320 ppm and an 8 K cooling of global temperatures, triggering the most extraordinary episode of climate change in the geologic record.
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