A recent NASA study found that an ongoing drought in the Middle East is the worst in the last 900 years.
Scientists studied tree rings to determine the length and frequency of droughts over the last several centuries in order to determine whether the current drought, which started in 1998, was unusual.
"If we look at recent events, we start to see anomalies that are outside this range of natural variability," said study lead author Dr. Ben Cook in a NASA press release. "It looks like this particular event or this series of events had some kind of human-caused climate change contribution."
Scientists used ring patterns in tree trunks to compile a centuries-long record of wet and dry periods, and to identify patterns in the climate record. Each ring, composed of a light and a dark band, represents one year in the life of a tree.
In a wet growing season, trees grow quickly, creating a wide ring, explains Dr. Cook in a phone interview with The Christian Science Monitor. If the next year was drier, the growth ring would be correspondingly slim.
Fortunately, the researchers did not have to measure every tree ring by themselves.
“There is a new database – the International Tree Ring Data Bank – that collects hundreds of different records from around the region to put together a complete view of the region’s tree records,” says Cook.
First they compared climate records from the last several decades to tree growth, to verify the data, explains co-author Dr. Ramzi Touchan in a phone interview. Then, they examined patterns from the past 900 years.
The study encompassed records from Cyprus, Israel, Jordan, Lebanon, Palestine, Syria, and Turkey. Co-author Dr. Kevin Anchukaitis added in an email that the study also looked at records from other Mediterranean basin countries such as Spain, Morocco, Algeria, and Tunisia.
The greater density and length of dry periods in recent years tells scientists that the recent drought is likely man-made rather than natural in origin.
This recent dry period is "significantly drier than any comparable drought period," says Cook, "which strongly suggests some kind of human component. It is a smoking gun for climate change."
Cook subsequently clarified in an email that his work is one among many studies that strongly suggest that manmade climate change influences drought cycles in the region."
The lack of water is contributing to tensions in the area, the researchers say.
The World Resources Institute issued a report last summer that found water resource stresses to be a likely culprit in regional strife.
"Drought and water shortages in Syria likely contributed to the unrest that stoked the country’s 2011 civil war," said the report. "Dwindling water resources and chronic mismanagement forced 1.5 million people, primarily farmers and herders, to lose their livelihoods and leave their land, move to urban areas, and magnify Syria’s general destabilisation."
Anchukaitis agrees. "Drought is likely one of several factors exacerbating conflict in the region, including Syria," he says, citing a study from March 2015. Cook explains that climate events like drought are often threat multipliers that exaggerate existing stresses.
Some countries in the region, including Israel, have adapted to drought conditions through major desalination efforts and other water-economizing programs.