Northland Kauri trees may hold secret to climate

Northland's ancient kauri could provide scientists with a valuable insight into climate change.

Climate scientists interested in how the El Nino and La Nina weather patterns interact with future climate change are taking an interest in the latest research using swamp kauri tree rings to build a picture of Northland's climate in the distant past.

In kauri, El Nino periods are linked to wide tree rings, and La Nina to narrow rings.

Kent Atkinson, from the NZ Science Media Centre (SMC) said if further research showed El Nino/La Nina effects on New Zealand had strengthened as the world had warmed then people in regions which had seen droughts in the past few decades could expect "more of the same".

"It is also plausible that as warming (global, not regional) continues we may see elevated impacts, something that planners might want to explore in terms of sensitivity to such changes," he said.

The scientists warned in the just-released Nature Climate Change paper that activity such as the big El Ninos that began in 1982 and 1997, and the similarly large La Nina triggered in 1973 and 1988 may not be unique in the context of the past 700 years.

"We also find evidence that there may have been significant changes in the Enso tele-connection to the New Zealand region during the 14th and 15th centuries," the paper says.

A "tele-connection" is a link between weather changes in widely separated parts of the world.

Variations in the kauri rings bottomed out around the time of the Little Ice Age (LIA) - summer cold and ice growth in the Northern Hemisphere which suddenly began around the year 1300, then stepped up a notch during 1430-1455AD.

The researchers told SMC this is critical to their inference that ENSO activity/teleconnection is strongly linked to global warmth.

"We also know from the NZ glacial record that many glaciers were more extensive during that time than present, which suggests temperatures across the western South Island and Southern Alps were cooler than present during the LIA," they said.

Many researchers are still working on the details of the LIA in New Zealand, and how it might be similar or different to what happened in Europe. But consideration of whether recent increasing El Nino/La Nina activity represents a human-forced change or perhaps is a return to pre-LIA conditions will require data covering a range of records over thousands of years.

Other projects involving some of the same scientists who wrote the paper are collecting data from "subfossil" kauri through Northland's Matakohe Kauri Museum.