The long-term target

The Zero Carbon Act will commit New Zealand to net zero carbon by 2050.

Climate change poses serious risks to humanity. We think New Zealand’s climate change response must include a commitment of net zero carbon by 2050 or sooner.

Why zero carbon by 2050?

To stop global warming, the world needs to reduce emissions of carbon dioxide and other long-lived greenhouse gases to net zero. The Zero Carbon Act will commit New Zealand to doing this in a timeframe consistent with the global goal of keeping warming to well below 2°C. We believe this requires a target of net zero carbon by 2050 or sooner.

The planet has already warmed by around 1°C since pre-industrial times, mainly due to human greenhouse gas (GHG) emissions. Under the Paris Agreement, the world has committed to the goal of limiting the global temperature rise to “well below” 2°C. The Agreement also acknowledged we should strive to keep warming to less than 1.5°C. These goals are grounded in scientific knowledge of the serious and escalating risks that climate change poses to human society.


To stop global temperatures continuing to rise, we need to reduce emissions of carbon dioxide and most other GHGs to net zero.

Most GHGs - particularly carbon dioxide, the biggest contributor to global warming - are long-lived. They stay in the atmosphere for a very long time, and every tonne emitted adds to the long-term temperature increase. ‘Net zero’ means that any ongoing emissions are countered by removing CO2 from the atmosphere.

There is a maximum amount of carbon the world can emit to keep global warming well below 2°C, and it is fast running out. This requires global CO2 emissions to reduce to zero by around 2050, or 2060-2080 if we rely on currently unproven negative emissions technologies to suck down the excess amounts of CO2. Limiting warming to less than 1.5°C requires even more urgent action. Developed countries, like New Zealand, agreed in the Paris Agreement to take the lead by reducing emissions earlier than developing countries.

To be on a path consistent with the Paris Agreement goals, we believe New Zealand should commit to reaching net zero emissions of CO2 and other long-lived gases by 2050 or sooner. We propose that this target will be provisional in the Zero Carbon Act, subject to a review by the Climate Commission. The Commission may advise that New Zealand should aim for a more ambitious long-term target, such as net zero carbon by 2045. (See Expert advice on targets and policies).

The ‘firewall’ principle: Domestic climate change action

The Zero Carbon Act requires domestic emission reductions.

The ‘firewall’ principle means that targets in the Zero Carbon Act must be achieved by reducing New Zealand’s emissions. International carbon credits cannot be used to meet these domestic targets. To achieve zero carbon, we must reduce our domestic emissions.

The Act will create a ‘firewall’ between New Zealand’s domestic climate change action and international contributions.

We need a firewall because New Zealand’s existing climate change targets are ‘responsibility targets’, not domestic emissions reduction targets. ‘Responsibility targets’ allow New Zealand to buy international carbon credits instead of reducing our emissions.

Reducing our own emissions is at the centre of a credible climate change response. As a developed country, New Zealand cannot allow our emissions to continue rising while expecting other countries to reduce theirs.

Furthermore, it is in New Zealand’s interests to get on track for the zero carbon transition. The Paris Agreement calls for global emissions to reach net zero in the second half of the century. Over-reliance on carbon trading is a delay tactic that will cost us in the long run; the price of international credits will rise over time and we will be forced to make a more abrupt transition later. Delay also means we miss out on the many benefits and opportunities of early action. A clear domestic emissions path will help New Zealand businesses and citizens plan for their future and provide certainty for low-carbon investments.

On top of our domestic action, New Zealand can and should assist poorer developing countries to reduce their emissions and achieve low-carbon development. Such assistance is required under the Paris Agreement. This could be achieved by buying international carbon credits, contributing to the Green Climate Fund, making direct investments, or other means.

The firewall principle means that these international contributions cannot be counted towards meeting targets under the Zero Carbon Act. The Government can, however, communicate and account for these additional efforts in New Zealand’s overall contribution to global efforts under the Paris Agreement. The Zero Carbon Act will introduce transparent annual reporting on our international contributions. (See Supporting global action)

In practice, the Government could communicate separate domestic emissions targets and responsibility targets, as shown in the figure below. Several countries already do this.

In summary, the Zero Carbon Act will commit New Zealand to a clear domestic emissions path to zero carbon by 2050 or sooner. Future governments will maintain full flexibility to decide how much to contribute to emissions reductions in other countries, on top of domestic action.

The ‘two baskets’ approach: Dealing with different gases

The 2050 zero carbon target will only apply to long-lived gases like carbon dioxide, and will not include methane.

We propose that the Zero Carbon Act separate New Zealand’s greenhouse gas (GHG) emissions into two ‘baskets’: one basket for long-lived GHGs (mainly carbon dioxide and nitrous oxide), and a second basket for short-lived GHGs (mainly methane). Different targets and pathways will be set for each basket.

We propose that emissions of methane and other short-lived GHGs must be significantly reduced to sustainable levels, consistent with the goal of limiting global warming to well below 2°C. But this basket does not need to go to zero.

The world currently treats all GHG emissions similarly. The prevailing international convention is to convert all GHG emissions into a common currency of “carbon dioxide equivalents” (based on a particular comparison method called Global Warming Potentials). For example, one tonne of methane emissions is currently deemed equivalent to 25 tonnes of CO2 emissions. Under this system, nearly half of New Zealand’s CO2-equivalent emissions are from agriculture (37% from methane and 11% from nitrous oxide).

However, the current system obscures some important differences between GHGs. Most importantly, it does not adequately account for the different lifetimes of the gases and the implications this has for stabilising global temperatures.

Most GHGs can be considered long-lived. CO2 released from burning coal, oil and gas persists in the atmosphere and oceans for thousands of years. Nitrous oxide emitted today remains in the air for over 100 years, on average. We can think of these gases as semi-permanent; they accumulate in the atmosphere, and every tonne adds to the long-term warming impact. This means that there is a total quantity we can afford to emit, and emissions need to reach net zero to stop global temperatures from continually rising.

Methane and other short-lived gases are different. Methane is very potent at trapping heat, but a tonne emitted today will only stay in the atmosphere for about a decade, on average, before being converted to CO2. If this methane originated from carbon already in the atmosphere , there is no long-term change in atmospheric composition. (For example when atmospheric carbon is fixed in grass through photosynthesis, the grass is eaten by a cow, and some of the carbon is released in the form of methane.) The temperature impact is therefore much more temporary (although some effects, such as sea level rise, will linger). Crucially, a steady rate of emissions will lead to a stable temperature impact.

The challenge of keeping global warming to well below 2°C can be summarised as follows:

  • Peaking long-lived GHG emissions immediately and reducing these to net zero within a total cumulative limit;

  • Reducing the rate of short-lived GHG emissions as much as possible over time to minimise their temperature impact.

To recognise these important differences in objectives and timeframes, we propose that the Zero Carbon Act adopt a ‘two baskets’ approach. This means setting different targets and pathways for long-lived and short-lived GHGs, and not treating the two as interchangeable. The long-term target for long-lived GHGs will be net zero emissions, provisionally by 2050 or sooner. The Climate Commission will be asked to provide advice on an appropriate long-term target for short-lived GHGs, consistent with the global goal of limiting warming to well below 2°C.

New Zealand’s targets and emissions levels can still be converted back into the conventional CO2-equivalent metric for international reporting purposes.