When CO2 levels became too low for plants to grow properly, forests appear to have kept the climate in check by slowing down the removal of carbon dioxide from the atmosphere. The results are now published in Biogeosciences, an open access journal of the European Geosciences Union (EGU).
Digital images of trenches in a mineral made by networks of fungi
“As CO2 concentrations in the atmosphere fall, the Earth loses its greenhouse effect, which can lead to glacial conditions,” explains lead-author Joe Quirk from the University of Sheffield. “Over the last 24 million years, the geologic conditions were such that atmospheric CO2 could have fallen to very low levels – but it did not drop below a minimum concentration of about 180 to 200 parts per million. Why?”
Before fossil fuels, natural processes kept atmospheric carbon dioxide in check. Volcanic eruptions, for example, release CO2, while weathering on the continents removes it from the atmosphere over millions of years. Weathering is the breakdown of minerals within rocks and soils, many of which include silicates. Silicate minerals weather in contact with carbonic acid (rain and atmospheric CO2) in a process that removes carbon dioxide from the atmosphere. Further, the products of these reactions are transported to the oceans in rivers where they ultimately form carbonate rocks like limestone that lock away carbon on the seafloor for millions of years, preventing it from forming carbon dioxide in the atmosphere.
Forests increase weathering rates because trees, and the fungi associated with their roots, break down rocks and minerals in the soil to get nutrients for growth. The Sheffield team found that when the CO2 concentration was low – at about 200 parts per million (ppm) – trees and fungi were far less effective at breaking down silicate minerals, which could have reduced the rate of CO2 removal from the atmosphere.
“We recreated past environmental conditions by growing trees at low, present-day and high levels of CO2 in controlled-environment growth chambers,” says Quirk. “We used high-resolution digital imaging techniques to map the surfaces of mineral grains and assess how they were broken down and weathered by the fungi associated with the roots of the trees.”
As reported in Biogeosciences, the researchers found that low atmospheric CO2 acts as a ‘carbon starvation’ brake. When the concentration of carbon dioxide falls from 1500 ppm to 200 ppm, weathering rates drop by a third, diminishing the capacity of forests to remove CO2 from the atmosphere.
The weathering rates by trees and fungi drop because low CO2 reduces plants’ ability to perform photosynthesis, meaning less carbon-energy is supplied to the roots and their fungi. This, in turn, means there is less nutrient uptake from minerals in the soil, which slows down weathering rates over millions of years.
“The last 24 million years saw significant mountain building in the Andes and Himalayas, which increased the amount of silicate rocks and minerals on the land that could be weathered over time. This increased weathering of silicate rocks in certain parts of the world is likely to have caused global CO2 levels to fall,” Quirk explains. But the concentration of CO2 never fell below 180-200 ppm because trees and fungi broke down minerals at low rates at those concentrations of atmospheric carbon dioxide.
“It is important that we understand the processes that affect and regulate climates of the past and our study makes an important step forward in understanding how Earth’s complex plant life has regulated and modified the climate we know on Earth today,” concludes Quirk.
Please mention the name of the publication (Biogeosciences) if reporting on this story and, if reporting online, include a link to the paper or to the journal website (http://www.biogeosciences.net).*More information*
The scientific article is available online, free of charge, from the publication date onwards, at http://www.biogeosciences.net/recent_papers.html. To obtain a copy of the paper before the publication date, please email Bárbara Ferreira at firstname.lastname@example.org.
The discussion paper (before peer review) and reviewers’ comments are available at http://www.biogeosciences-discuss.net/10/15779/2013/bgd-10-15779-2013.html
The team is composed of J. Quirk, J. R. Leake, S. A. Banwart, L. L. Taylor and D. J. Beerling, from the University of Sheffield, UK.
The European Geosciences Union (www.egu.eu) is Europe’s premier geosciences union, dedicated to the pursuit of excellence in the Earth, planetary, and space sciences for the benefit of humanity, worldwide. It is a non-profit interdisciplinary learned association of scientists founded in 2002. The EGU has a current portfolio of 15 diverse scientific journals, which use an innovative open access format, and organises a number of topical meetings, and education and outreach activities. Its annual General Assembly is the largest and most prominent European geosciences event, attracting over 11,000 scientists from all over the world. The meeting’s sessions cover a wide range of topics, including volcanology, planetary exploration, the Earth’s internal structure and atmosphere, climate, energy, and resources. The 2014 EGU General Assembly is taking place is Vienna, Austria from 27 April to 2 May 2014. For information regarding the press centre at the meeting and media registration, please check http://media.egu.eu.
If you wish to receive our press releases via email, please use the Press Release Subscription Form at http://www.egu.eu/news/subscribe/. Subscribed journalists and other members of the media receive EGU press releases under embargo (if applicable) 24 hours in advance of public dissemination.*Contact*
Dr. Bárbara Ferreira | European Geosciences Union
Over 70% of glacier volume in Everest region could be lost by 2100
27.05.2015 | European Geosciences Union
Climate engineering may save coral reefs, study shows
26.05.2015 | University of Exeter
The only professorship in Germany to date, one master's programme, one laboratory with worldwide unique equipment and the corresponding research results: The University of Würzburg is leading in the field of biofabrication.
Paul Dalton is presently the only professor of biofabrication in Germany. About a year ago, the Australian researcher relocated to the Würzburg department for...
Physicists have developed an innovative method that could enable the efficient use of nanocomponents in electronic circuits. To achieve this, they have developed a layout in which a nanocomponent is connected to two electrical conductors, which uncouple the electrical signal in a highly efficient manner. The scientists at the Department of Physics and the Swiss Nanoscience Institute at the University of Basel have published their results in the scientific journal “Nature Communications” together with their colleagues from ETH Zurich.
Electronic components are becoming smaller and smaller. Components measuring just a few nanometers – the size of around ten atoms – are already being produced...
Development and implementation of an advanced automobile parking navigation platform for parking services
To fulfill the requirements of the industry, PolyU researchers developed the Advanced Automobile Parking Navigation Platform, which includes smart devices,...
The world's first electrical car and passenger ferry powered by batteries has entered service in Norway. The ferry only uses 150 kWh per route, which...
On Tuesday, 19 May 2015 the research icebreaker Polarstern will leave its home port in Bremerhaven, setting a course for the Arctic. Led by Dr Ilka Peeken from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) a team of 53 researchers from 11 countries will investigate the effects of climate change in the Arctic, from the surface ice floes down to the seafloor.
RV Polarstern will enter the sea-ice zone north of Spitsbergen. Covering two shallow regions on their way to deeper waters, the scientists on board will focus...
20.05.2015 | Event News
18.05.2015 | Event News
12.05.2015 | Event News
27.05.2015 | Health and Medicine
26.05.2015 | Ecology, The Environment and Conservation
26.05.2015 | Life Sciences