With the UN climate talks under way in Paris, the Herald's science reporter, Jamie Morton, has been speaking with a range of experts about climate-related issues.
Here he talks to Professor Dave Frame, of Victoria University's Climate Change Research Institute, about mitigation and reduction policy.
Q. On New Zealand's new target of reducing its greenhouse gas emissions by 30 per cent from 2005 levels and 11 per cent from 1990 levels by 2030. Do you see this as a reasonable commitment?
You can see it as glass half full or glass half empty.
It's true we could be doing more; but claims that we are radically behind Europe are a bit overblown - our 2005-2020 commitments have been roughly in line with what would have been expected of us if we had been a country within Europe, with the same per capita income we currently have.
The issues for New Zealand are that it is far from clear that we will be able to purchase emissions reductions from abroad as we have done in the past; and that we seem to lack a clear plan for increasing mitigation within New Zealand.
It's not that this is necessarily difficult -- just that we have lacked a co-ordinated approach to thinking about how we'll make a long-term transition to a low carbon economy.
There is little evidence of co-ordinated thinking around this in government, and the idea that it's particularly hard for New Zealand is unconvincing given the lack of attention to the issue.
If you talk to New Zealand businesses, you get a considerably more optimistic picture.
Q. Given criticism of the effectiveness of carbon trading markets, do you hold any concerns with countries relying on systems like the NZ Emissions Trading Scheme to meet their targets?
Trading is more economically efficient than other ways of limiting emissions, such as regulation or taxes.
The issues around our weak price have more to do with policy choices such as the two-for-one deal, our access to cheap hot air units and so on.
It's not that the ETS itself is inefficient, it's that some of the policy choices that surround it are enfeebling.
Over time we're likely to see more carbon markets, rather than fewer, since without strong policy the problem will continue to get worse.
As it does so, the need to mitigate will get more obvious. One opportunity for us would be to work out how to set up some trading systems between, say, Latin American ETS systems, or Asian ones, and New Zealand.
But trading itself is a good thing, since it lets you make the emissions cuts in the places where the returns are best.
Q. Are there any areas - such as policy for developing nations - where you see New Zealand making any meaningful difference at COP21?
We can have more influence with our ideas than we can through our emissions alone.
Fossil fuel subsidy reform is arguably our most valuable contribution to date - by getting countries to focus on eliminating bad policies we can leverage emissions reductions far in excess of anything we can do at home.
So far, we've been the country that has thought the most about agriculture and climate change, but the issues we have in the agricultural sector are mirrored in many developing countries.
If we can create policies that contribute usefully to international efforts, work for us, and are attractive for others to adopt, we can help shape the way climate policy develops.
Q. In terms of the big picture: who are the big players, why, and how much depends on them to come away with a robust agreement?
There is a scale parameter to climate policy - the smaller you are the less you capture the benefits of your mitigation.
So the big guys will lead and set the precedents whatever they do -- either by creating a world where strong policy is the norm or one where weak policy is the norm.
What we can do is suggest ideas that other countries might find useful as they think about climate policy.
And that means finding attractive ways of reducing emissions -- ways of doing business and improving people's lives that other countries see as practical and in their own self-interests to adopt.
There's no point in developing policies that significantly reduce our quality of life or which harm our economic performance. Other countries won't adopt those -- countries do what's in their self-interest.
Q. What influence on commitment-setting has there been from expected advances in future technology that would significantly reduce emissions? Has there been an over-reliance from many nations on waiting for this technology and putting forward weaker targets in the short term, or up to 2050?
Technology will be a big part of successful mitigation, globally.
The years since 2000 have seen large investments in renewable energy and low carbon technologies, but we know the returns on those investments can take decades to arrive.
Governments have a role in stimulating those investments, partly because markets underprovide public goods, and partly because they can speed up the development of new technologies.
In the case of CO2 emissions, speeding things up is important because the problem worsens the longer we have a fossil-powered economy.
If technology doesn't help, it's hard to see us limiting warming to anything like 2C.
The sooner we reduce emissions, the lower the total cumulative emissions we emit and the lower the overall warming in response.
The sooner we hit the brakes, the sooner we stop. It will still take many decades to move away from fossil fuels - delaying things further just makes things worse for young people and future generations.
Q. Generally, what do you anticipate will be the biggest stumbling blocks at Paris to limiting temperature rise to 2C this century? From attending previous conferences, are you somewhat cynical about getting a good outcome?
Paris should be judged on its ability to get countries to participate in climate policy, subject to some meaningful but basically domestic compliance mechanisms.
It won't limit warming to 2C, and it's unrealistic to expect it to do so.
The three main things you need from an international climate agreement are participation, compliance and stringency.
Kyoto made a mistake by focusing on stringency for some before participation by all.
That's the wrong approach in a problem like this.
Paris is a chance to start over, focusing on getting broad buy-in and potentially signalling some carrots and sticks around compliance.
On the whole, we should judge Paris on the basis of its ability to get everyone to offer something.
Q. Much has been made of what this conference means for the fate of the planet. Is this really our last chance to achieve a 2C limit before it's too late?
We've been having these last chances for years.
There are several reasons that's a bad way to view the negotiations: (1) negotiations alone can't determine that outcome; (2) repeated threats regarding last chances have diminishing credibility; (3) the 2C target is an aspiration, not a physical threshold - there's no evidence that the world is radically different at 2.1C than it is at 1.9C; (4) choices made today to limit emissions out to 2030 or 2040 cannot guarantee remaining under 2C, because the actions of future generations matter crucially, too.
What we can and should do, is be clear about how to give those future people the best possible shot at limiting warming.
And that means focusing on limiting cumulative emissions of carbon dioxide.
The "last chance" thing is neither compelling nor constructive, nor credible.
People should choose better metaphors.
Q. In a recent study in Nature Climate Change, you proposed a global index that would allow governments to regularly review their pledges to reduce greenhouse gas emissions as time goes on and new technology comes online, ultimately providing a more pragmatic and effective approach to mitigation. What hope do you have of nations adopting such an approach at Paris or anything like it?
Ideas that look great on the whiteboard generally fail to translate cleanly to real-world situations, so our goals are a bit more modest than that.
The hope is more that if we keep thinking clearly but creatively, and we keep understanding more about the constraints that really bite on countries and negotiations, then we might be able to suggest some things that people find useful.
We've had some success in the past, notably with the cumulative emissions idea we proposed half a dozen years ago.
In this case I think we have some interesting stuff about the way high-level goals map down to more specific national and sectoral actions, and how progress might be measured sensibly so that the right outcomes are incentivised.
We're looking forward to sharing our ideas and hearing other folks' thoughts.
• Jamie Morton will be covering the Paris negotiations with the support of the NZ Science Media Centre and the Morgan Foundation.