Parliamentary Commissioner for the Environment Simon Upton has proposed separate trading systems for fossil and biological emissions to help tackle climate change.

Today he answered questions from The Country's Jamie Mackay about the suggestions in his report A Zero Carbon Act for New Zealand and his reasoning behind them.

Who does the report go to?

The report is a report for Parliament. Parliament will be looking at legislation shortly on where we go on climate change.

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So it's my contribution to the debate in much the same way that the Productivity Commission brought down a big report a few months ago.

Carbon dioxide remains in the atmosphere longer than methane. It makes sense to treat them differently.

I'm suggesting that we treat fossil carbon and methane differently from biological methane and nitrous oxide for the reason that you give.

There is a very long –term, virtually irreversible warming effect to releasing carbon dioxide.

Parliamentary Commissioner for the Environment Simon Upton. Photo / Supplied
Parliamentary Commissioner for the Environment Simon Upton. Photo / Supplied

Methane and nitrous oxide from the Ag sector – these are powerful greenhouse gases – they're much more powerful , certainly in the short run, than carbon dioxide, but they don't accumulate in the same way.

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We do need to reduce them – there's no debate about that – but we can certainly offset what we do using forest sinks.

Listen to the interview on The Country below:

The problem with the way we operate at present is that we say 'OK I've emitted some carbon dioxide from fossil fuel, I've planted some trees, we're all square – we're not square.

Trees have a lifetime – the warming effect virtually goes on forever.

Trees can burn down as well.

That's a real risk. That's one of the risks that worries me most. We've got no way of saying that trees planted today can be maintained in perpetuity.

We know how to replant a forest we've harvested and do it two or three times, but to say we will just go on doing this over centuries, when in fact we know that climate change itself is going to put these sinks at risk, seems to me to be a bad mismatch of risks.

Climate change is likely to mean more extreme heat days. Higher fire risk for instance. We're likely to see more pests coming here that we haven't known before which could well attack those carbon stocks.

I think it's a bad matching of long term risk versus short term solution.

You've also suggested extending the time frame through to 2075 rather than the original target 2050. Why is that?

There's nothing magic about 2050 or 2075.

I was simply using a year which represents broadly what the Paris Climate Agreement said and that was - in the second half of the century – we need to be a long way down the track by 2050. I'm not suggesting any delay in action – we need to get on with it.

What I am concerned about is giving ourselves a target in 2050 called 'net zero' which effectively is actually a target which could have a very high continuing level of carbon dioxide emissions.

In other words, if you plant enough trees from an accounting point of view it looks fine, but in terms of the emissions - it isn't.

I think we'd be better to be a bit more transparent, a bit more honest about how difficult this task is.

[We need to] give ourselves the long target time we need on carbon dioxide (and it certainly will take all of that time through to the middle half of the century to get on top of that – it'll be dependent on technology [and] most of that is technology we'll import).

Meanwhile, let's also deal with our biological emissions but don't have the farming and forestry sector competing for land with the fossil fuel sector trying to park its waste on that landscape.