Tree Rings and Volcanic Eruptions

According to climate researchers, who compared tree-ring temperature reconstructions with model simulations of past temperature changes, climate cooling caused by past volcanic eruptions may not be evident. This is due to shortened or even absent growing seasons as a result of large temperature drops.

Michael Mann, professor of meteorology and geosciences and the director of the Penn State Earth System Science Centre, said “We know these tree rings capture most temperature changes quite well, but the problem appears to be in their response to the intense short-term cooling that occurs following a very large volcanic eruption. Explosive volcanic eruptions place particulates called aerosols into the stratosphere, reflecting back some fraction of incoming sunlight and cooling the planet for several years following the eruption”.

Tree-rings are used as a proxy measure for past climates. Unique rings are created each year that often reflect the weather conditions that influenced that particular growing season. The study, carried out by professor Mann, compared temperature reconstructions from actual tree-ring data with temperature estimates from the climate models driven with past volcanic eruptions. The report, published in Nature Geoscience, found that the overall agreement between models was good, apart from “one glaring inconsistency; the response to the three largest tropical eruptions – AD 1258/1259, 1452/1453 and the 1809+1815 double pulse of eruptions – is sharply reduced in the reconstruction”. In conclusion, Mann states that “Scientists look at the past response of the climate to natural factors like volcanoes to better understand how sensitive Earth’s climate might be to the human impact of increasing greenhouse gas concentrations. Our findings suggest that past studies using tree-ring data to infer this sensitivity have likely underestimated it”.