Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Tree rings may underestimate climate response to volcanic eruptions

06.02.2012
Some climate cooling caused by past volcanic eruptions may not be evident in tree-ring reconstructions of temperature change because large enough temperature drops lead to greatly shortened or even absent growing seasons, according to climate researchers, who compared tree-ring temperature reconstructions with model simulations of past temperature changes.

"We know these tree rings capture most temperature changes quite well," said Michael Mann, professor of meteorology and geosciences and director of the Penn State Earth System Science Center. "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 proxies for climate because trees create unique rings each year that often reflect the weather conditions that influenced the growing season that year. For reconstructing climate conditions, tree-ring researchers seek trees growing at the extremes of their growth range. Inferring temperature changes required going to locations either at the tree line caused by elevation or at the boreal tree line, the northern most place where the trees will grow.

For these trees, growth is almost entirely controlled by temperature, rather than precipitation, soil nutrients or sunlight, yielding a good proxy record of surface temperature changes.

"The problem is that these trees are so close to the threshold for growth, that if the temperature drops just a couple of degrees, there is little or no growth and a loss of sensitivity to any further cooling. In extreme cases, there may be no growth ring at all," said Mann. "If no ring was formed in a given year, that creates a further complication, introducing an error in the chronology established by counting rings back in time."

The researchers compared temperature reconstructions from actual tree-ring data with temperature estimates from climate models driven with past volcanic eruptions.

Comparing the model-simulated temperatures to the Northern Hemisphere temperatures reconstructed from tree-ring thickness, Mann, working with Jose D. Fuentes, professor of meteorology, Penn State, and Scott Rutherford, associate professor of environmental science, Roger Williams University, found the overall level of agreement to be quite good.

However, they report in the current issue of Nature Geoscience that "there is 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."

Following the 1258 eruption, the climate model simulations predict a drop of 3.5 degrees Fahrenheit, but the tree ring-based reconstruction shows only about a 1 degree Fahrenheit dip and the dip occurs several years too late. The other large eruptions showed the same type of discrepancy.

Using a theoretical model of tree-growth driven by the simulated temperature changes, the team determined that the cooling response recorded by the trees after a volcanic eruption was limited by biological growth effects. Any temperature drop exceeding roughly 1 degree Fahrenheit would lead to minimal tree growth and an inability of trees to record any further cooling. When growth is minimal enough, it is likely that a ring will not be detectable for that year.

The potential absence of rings in the first one to three years following eruption further degrades the temperature reconstruction. Because tree-ring information is averaged across many locations to obtain a representative estimate of northern hemisphere temperature, tree-ring records with and without missing rings for a given year are merged, leading to a smearing and reduced and delayed apparent cooling.

The researchers also noted that aerosol particles forced into the air by volcanoes block some direct sunlight causing cooling and they produce more indirect, scattered light at the surface. Trees like indirect sunlight and grow better under those conditions. However, this effect is small compared to that of lower temperatures and shorter growing seasons.

By accounting for these various effects in the tree growth model, the researchers were able to reproduce the reduced and smeared cooling seen in the actual tree-ring temperature reconstruction, including the near absence -- and delay -- of cooling following the massive 1258 eruption.

"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," said Mann. "Our findings suggest that past studies using tree-ring data to infer this sensitivity have likely underestimated it."

A'ndrea Elyse Messer | EurekAlert!
Further information:
http://www.psu.edu

More articles from Earth Sciences:

nachricht More than 100 years of flooding and erosion in 1 event
28.03.2017 | Geological Society of America

nachricht Satellites reveal bird habitat loss in California
28.03.2017 | Duke University

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A Challenging European Research Project to Develop New Tiny Microscopes

The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.

To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Transport of molecular motors into cilia

28.03.2017 | Life Sciences

A novel hybrid UAV that may change the way people operate drones

28.03.2017 | Information Technology

NASA spacecraft investigate clues in radiation belts

28.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>