#paleoclimatology

The more we understand the history of Earth’s climate, the better we understand the complexities of its future.  A massive collaboration involving scientists from around the world, led by the Desert Research Institute in Nevada, has helped show the impact volcanoes have had on the climate.

When a volcano erupts, it spews tons of material into the air, which gets into the atmosphere and blocks some of the Sun’s radiation, causing a cooling effect. One example of this was in 1991, when Mt. Pinatubo in the Philippines erupted. The eruption caused a cooling of 0.5 ᵒC in the North Hemisphere. This kind of cooling can have massive consequences in predicting climate change, so a greater understanding of the effect is incredibly important.

We are able to gain this understanding by analyzing our environment.

The sulfur that volcanoes eject will always eventually land on Earth; this is taken up by trees and can be seen in tree rings. It also lands on ice and is incorporated into the ice sheets. Scientists drill into the ice and extract long cylinders of ice called ice cores, which are so sensitive to change that a drop in lead can be seen in when unleaded petrol became the norm.

It can be hard to accurately pin records from ice cores to records from tree rings, as it’s often done by simply judging that a change of sulfur in both the ice and the trees were from the same event. Using different timescales from each can often make things inaccurate.

Recently, sudden changes in an isotope of carbon, carbon-14, have been found in tree rings very soon after volcanic eruptions. We’ve been able to accurately date this using an eruption from 775 AD, and using multiple trees from all over the Northern Hemisphere. The scientists in this new study assumed that a radioactive isotope of beryllium, beryllium-10, would also be created in greater quantities during an eruption, because this isotope is made when cosmic rays interact with particles in the atmosphere. This gives us a way to pin tree data to ice core data, using independent but simultaneous events. Using this information, scientists went back through previous records of ice cores and found them to be inaccurate. Some eruptions in Greenland were found to be seven years out of line with the tree ring data.

This data allowed the scientists to create a new model spanning the last 2,500 years. The model shows hundreds of eruptions that influenced the climate, and shows that tropical eruptions were the cause of numerous cooling events. It has been found that between 500 BC and 1000 AD, 15 of the 16 coldest summers were after tropical eruptions.

They were also able to solve a mystery: there were a number of strange cooling occurrences in the early part of the sixth century. A dust cloud was observed in records in 536 AD; this was thought to have been due to an eruption, but was never proven. The new paper shows that it must have been caused by at least two tropical eruptions. This new understanding of previous events will greatly help our planning for future change.

Sources

Link to article: http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14565.html

Study on carbon 14 in tree rings: http://www.nature.com/nature/journal/v486/n7402/full/nature11123.html

Mt. Pinatubo data: http://pubs.usgs.gov/pinatubo/self/

Lead in ice cores: http://www.sciencewa.net.au/topics/environment-a-conservation/item/1271-mt-everest-ice-core-reveals-atmospheric-lead-history/1271-mt-everest-ice-core-reveals-atmospheric-lead-history

More info on paleoclimatology: http://serc.carleton.edu/microbelife/topics/proxies/paleoclimate.html

By Adam M., Discoverer.

Edited by Anna G.