At least a million hectares of marginal land in New Zealand could easily revert to forest and absorb carbon dioxide from the atmosphere as it grows, a new report suggests.
Parliamentary Commissioner for the Environment Jan Wright was speaking during the release of her latest report on climate change and agriculture.
Dr Wright said almost 4 percent of New Zealand's total area could revert to carbon-soaking forest without anyone having to do anything too difficult, unlike preparing it for farming which took a lot of work clearing scrub.
Read the full report online here
"Fence it off, let it go, the manuka grows, then the kanaka, and eventually the forest returns," she said.
"Such a forest would take carbon dioxide out of the air, year after year after year, for hundreds of years."
Dr Wright said she favoured native forests, but even commercial pine plantations which were eventually harvested could help buy New Zealand time, while permanent solutions were found to greenhouse gas emissions.
And there were other ways in which farmers could mitigate greenhouse gas emissions.
"Firstly, breeding low emission sheep and cattle, secondly, use low emission animal feed, thirdly deal with the 5 percent of microbes in the rumen that produce methane," she said.
"And lastly, we need to do something about the patches of animal urine (in the ground) and fertiliser that are the sources of nitrous oxide."
Forest Owners expressed reservations about planting on extremely marginal land which is prone to erosion, but said such land could revert to native bush on its own.
Elsewhere, commercial plantation forests could be valuable, according to the chairman of the joint Forest Owners Association and Farm Forestry Associations' Environment Committee Peter Weir.
"Farmers on some of their more marginal land, their less productive land, could get a very good return by planting a short rotation crop like radiata [pine].
"That is a good solution - known technology - put trees in the ground and they grow."
The commissioner aimed her focus on agriculture because it produces almost half of all New Zealand greenhouse gas emissions.
Yet farming is excluded from the emissions trading scheme, unlike transport, energy and other sectors.
Dr Wright has in the past called for this to change, but refrained from doing so this time, declaring it to be a stale debate.
Instead, she wanted to focus on the science of mitigating climate change, especially two of its worst instigators, Methane and Nitrous Oxide.
Suzi Kerr, senior fellow at Motu Economic and Public Policy Research, said Dr Wright was absolutely correct in saying agriculture must be included in the fight against climate change.
"It is not sustainable in the long term," she said.
"Farmers have improved their emissions efficiency, but going forward it would be a very risky strategy for us to stay dependent on livestock, assuming that some technology is going to come through.
"It might, but it might not and even if it does, you are still going to have a lot of emissions from that livestock."
Meanwhile, Dr Wright said New Zealand had no alternative but to deal with agriculture, because it would be very hard to meet pledges made after the Paris climate change talks without it.
Federated Farmers said the report took the right approach, focusing on specific plans of action rather than a blanket reduction.