Tree ring analysis helps IPCC determine global temperature increases

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Aster Gebrekirstos (right) identifies a tree core for dendrochronology lab analysis.

It is undeniable: the world’s temperatures have increased and greenhouse gas levels are at their highest in 800,000 years, prompting a more serious call to action than ever before.

These were the findings of a report released in early November 2014 by the Intergovernmental Panel on Climate Change; the most comprehensive appraisal of climate change ever undertaken.

But how do we know temperatures are higher than in the past?

According to an interview with Professor Lesley Hughes, one of the lead authors of the report, tree rings can provide a good indication of past temperatures.

“We also use things like tree rings and borehole temperatures as what’s called proxies for temperature in the long-term,” said Hughes on Australian television’s 7.30 Report.

Aster Gebrekirstos, a scientist with the World Agroforestry Centre explains how dendrochronology – the science of analyzing and dating tree growth rings – can reveal information about past climatic conditions such as temperature, rainfall, river flow and the frequency of wildfires.

“Dendrochronology can help us unpack the information held in trees,” explains Gebrekirstos. “Each tree ring represents a year in a trees life. By measuring the width of tree rings, the size of their vessels and stable carbon and oxygen isotope ratios in the wood, patterns of temperature and moisture can be determined for the time the ring was formed in the tree.”

In 2013, the World Agroforestry Centre opened a state-of-the-art dendrochronology laboratory at its headquarters in Nairobi, Kenya. Here, Gebrekirstos and colleagues, together with partners in Africa, are using tree ring analyses to reconstruct past climatic history, variations in atmospheric circulation patterns and the frequency of extreme events.

“We are mapping out climate conditions of the past to help provide accurate early warnings for climate variability in the future.”

Studies by Gebrekirstos and colleagues have been able to determine that droughts in East Africa have shortened from every 2 to 8 years to every 2 to 3 years over the last 70 years.

tree rings2Determining past temperatures for important documents, such as the IPCC report, is just one application of dendrochronology.

Gebrekirstos is currently working on establishing the entire growth history of Podocarpus falcatus in Ethiopia’s highlands. This conifer may hold vital information about changes to a range of environmental conditions over several centuries.

Dendrochronology is being used by other World Agroforestry Centre scientists to determine the amount of biomass produced in the past by trees in the savannas of West Africa. This information will help in developing models to estimate how much carbon these trees are sequestering. Such findings would overcome the need for high cost carbon accounting methods, of particular importance to developing countries wishing to enter carbon markets.

Watch the interview with Lesley Hughes on ABC:

Find out more about the World Agroforestry Centre’s Dendrochronology lab

Related stories:

Tree rings link climate and carbon in Africa

Uncovering the past with trees'

Kate Langford

Kate Langford is a consultant writer with close to 20 years’ experience in communicating natural resource, environmental and land management issues for various government and non-government organizations. She previously worked as Communications Specialist for the World Agroforestry Centre in Kenya and has worked in Indonesia, Laos, Vietnam and Australia. She holds a Bachelor of Science and a Graduate Diploma in Scientific Communication.

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