‘Remarkable’ carbon sink in NZ
A recent study of atmospheric carbon dioxide produced a surprise result. Will Harvie finds out more.
Something unexpected may be going on in southwest New Zealand, a recently published study shows. The area – covering portions of Fiordland,westland, Otago and Southland – might be absorbing much more atmospheric carbon dioxide than expected, up to 60 per cent more, say two Niwa scientists, Dr Sara Mikalofffletcher and Dr Kay Steinkamp.
Much of this uptake is likely occurring in native forests in the region, which is ‘‘a big surprise to scientists’’, Mikaloff-fletcher said.
It was generally thought that young and fast growing forests absorb the most CO, whereas the indigenous forests of southwest New Zealand were mostly mature and relatively slow growing.
‘‘Carbon uptake... tends to slow as forests mature.
‘‘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,’’ Mikaloff-fletcher said.
CO is a primary greenhouse gas and responsible for most of the human-caused warming in the atmosphere. Oceans and forests mitigate the effects of climate change by absorbing about half of the CO emitted by human activities over recent decades.
The new study was published in the journal Atmospheric Chemistry and Physics, with postdoctoral fellow Steinkamp as the lead author.
Her supervisor, Mikalofffletcher, said the pair couldn’t rule out ’’an important role for carbon uptake in the hill country or from pasture from our current data’’. In the interview, she also said that West Coast erosion could be taking Co-laden sediment into fiords and the Tasman Sea. ‘‘We don’t know yet.’’ But the ‘‘the areas that seem to be responsible are those largely dominated by indigenous forests’’.
Understanding how a New Zealand forest might be different from overseas forests took Mikaloff-fletcher, an atmosphere and ocean scientist, out of her areas of expertise.
If upheld by future studies, the result could have an impact on New Zealand’s ability to meet its Paris climate change commitments, she said.
The Ministry for the Environment estimates the amount of carbon being absorbed by all New Zealand forests at 82 million metric tons over 2011-2013, the same period studied by Mikaloff-fletcher’s team.
Once accounting rule differences are corrected for, the new Niwa measurement approach finds that actual carbon uptake could be up to 60 per cent higher, she said.
The change, if validated, would not fulfil New Zealand’s Paris commitments. ‘‘You could plant every square inch of the world and you would still need to cut emissions, Mikaloff-fletcher said.
The research relied on Niwa’s atmospheric measuring stations at Baring Head, near Wellington, and at Lauder, in Central Otago, as well as a commercial ship that travels between Japan and Nelson about every six weeks. As well as cargo, it carries atmospheric sampling equipment.
When the wind is blowing in the right direction, Baring Head instruments measure air that is ‘‘clean’’, meaning it has not passed over land or human activity. It provides what is effectively a baseline measurement of CO for the purposes of the study.
When the wind is blowing in the right direction, Lauder instruments measure airflow over southwest New Zealand.
After running the data through a series of complex models, Mikaloff-fletcher and colleagues concluded there must be a carbon ‘‘sink’’ in the southwest and it was most likely the indigenous forest.
This technique is called an ‘‘inverse model’’ and Mikalofffletcher said it was like ‘‘smelling an amazing barbecue somewhere in your neighbourhood.
‘‘If you sniff the air in a few different places, and notice the direction the wind is blowing from at each spot, you’ll probably be able to work out where the barbecue is.’’
Further investigation is required and Niwa recently created a new atmospheric research station near Rotorua. Researchers hope to start adding data from it within months. Mikaloff-fletcher expects a ‘‘pretty big story’’ to come out of that data but wouldn’t be drawn further.
The area is a mix of exotic and indigenous forests, agricultural land and bush.
This year, Niwa will also build stations that measure atmospheric chemistry somewhere on the Canterbury Plains and near Auckland. Neither spot has been identified yet, but both needed wind coming at them from various directions at different times.
In Canterbury, she hoped for insight into intensive agriculture as well as the hill country and the Southern Alps. Near Auckland, data from human intensive human activity would be brought into models. The stations measure more than CO.
The recently published study ‘‘produced results that are bigger than we expected, and with less certainty than we need‘‘, Mikalofffletcher said. ‘‘While that suggests the current models could be improved, our techniques need improving as well.”