New Zealand carbon sink finding could influence global climate treaties

New Zealand's forests and other land areas could be absorbing up to 60 percent more carbon dioxide (CO2) than previously thought, government scientists said Thursday.

A study by the National Institute of Water and Atmospheric Research (NIWA) could have important implications for international climate treaties, said the researchers.

Globally, carbon sinks, such as oceans and forests, have helped mitigate the effects of climate change by absorbing about half the carbon dioxide emitted by human activities over the past few decades.

Forest carbon uptake played a key role in meeting New Zealand's commitments under the Kyoto climate treaty and was expected to play an important role in meeting its international COP21 commitments.

The study used an "inverse" modeling approach to estimate the amount of carbon uptake by measuring CO2 present in the atmosphere at a network of sites, and then using high resolution weather models to determine what parts of New Zealand the air had passed over before reaching the site.

The team calculated the best combinations of sources and sinks to match the data.

"The story the atmosphere is telling us is that there's a big carbon sink somewhere in the South Island, and the areas that seem to be responsible are those largely dominated by indigenous forests," researcher Dr Kay Steinkamp said in a statement.

"However, we cannot rule out an important role for carbon uptake in the hill country or from pasture from our current data."

Indigenous forests covered about 6.2 million hectares in New Zealand.

The result was very surprising result mainly because strong carbon sinks were expected when there was a lot of forest regrowth, researcher Dr Sara Mikaloff-Fletcher said in the statement.

"Carbon uptake this strong is usually associated with peak growth of recently planted forests and tends to slow as forests mature," said Mikaloff-Fletcher.

"This amount of uptake from relatively undisturbed forest land is remarkable and may be caused by processes unique to New Zealand or part of a wider global story."

The Ministry for the Environment reported annually on New Zealand's carbon uptake using the national inventory method.

This internationally standardized methodology put the amount of carbon being absorbed by all New Zealand forests at 82 teragrams (a teragram is 1 million tonnes) in total over 2011 to 2013, the period studied by the team.

The NIWA method found the actual uptake could be up to 60 percent higher.

The inventory-based method estimated carbon uptake using measurements of tree growth taken from about 100 sampling areas, and extrapolated this to the entire country.

Considerable work was still needed in comparing the two independent approaches.

"We need to find out definitively what processes are controlling this unexpectedly large carbon uptake, in order to understand the implications for land management and climate treaties," said Mikaloff-Fletcher.

"We need additional measurements to tell us if this is unique to the southern half of the South Island or holds across a wider range of New Zealand." Endit