Approaching 1.5°C from above: Why overshoot demands more from New Zealand, not less
On 2 September 2026, the UN Environment Programme released its Limiting Overshoot: Navigating exceedance of 1.5°C and pathways towards return (Overshoot Report). The report lays bare the hard truth that 1.5°C - being the temperature goal agreed under the 2015 Paris Agreement - will be exceeded in the near future. While the world has made some progress on climate change, it has not been fast enough to avoid exceeding 1.5°C above pre-industrial levels in the next few years.
The Overshoot Report is a sobering read: “there are no benign scenarios with global temperature rise above [1.5°C].” Glaciers could lose more than a quarter of their mass and permanently alter water availability; small-island developing states and low-lying cities could be partially or completely submerged; and there is likely to be declines of up to 14% in global food production, along with increased risks of heatwaves, flooding and wildfires. Some of these changes will be irreversible.
With the release of this report, some will likely argue that if we are exceeding 1.5°C, then why hold governments and countries to this goal? Why not soften our domestic efforts here in New Zealand to match the ‘reality’ of exceedance? This rationale has already seeped into some policy decisions New Zealand has seen in the climate sphere in the last few years - for example, it was implicit in the New Zealand Government’s decision last year to reduce the legislated 2050 Methane Target to a level explicitly inconsistent with 1.5°C.
However, this is a fundamental misunderstanding of the Overshoot Report, and the exact opposite of what the report states countries must do. As the report makes clear:
"The inevitable overshoot of 1.5°C should not be interpreted as justification for reduced ambition. On the contrary, it reinforces the urgency of accelerated climate action. The lower the peak warming reached, and the shorter the duration of exceedance, the lower the risks faced by people and ecosystems."
This article explores some of the findings of the Overshoot Report. It describes what overshooting 1.5°C means in the New Zealand context, to show why the urgency of mitigation (and adaptation) should be increased, not decreased.
No benign overshoot: the report's key findings for Aotearoa New Zealand
Overshoot is not a point of no return. The key point the report makes is that we now must follow a pathway of exceedance, peak, and decline, where the world must act quickly to limit how high temperatures climb above 1.5°C and how long they stay above 1.5°C before returning down to below 1.5°C. Essentially 1.5°C must now be approached “from above.” The Overshoot Report makes it clear that this is neither an acceptable nor a preferred pathway; rather, it is simply the best remaining option.
Other key findings of the report for New Zealand include:
There is no benign overshoot pathway, but its magnitude, duration and consequences are not predetermined: Exceeding 1.5°C should not be considered safe, and will likely lead to irreversible consequences. However, every fraction of a degree and every year above 1.5°C increases exposure to climate hazards and the likelihood of irreversible loss. As such, it is critical to limit the consequences of overshoot by limiting how much 1.5°C is exceeded and for how long. The argument is frequently made that New Zealand’s contribution to global emissions is too small to make a difference. However, the Overshoot Report makes it clear that every fraction by which we exceed 1.5°C matters. While it is critical that the large emitters reduce their emissions rapidly, New Zealand’s pace of transition will contribute to how severe the consequences of overshoot will be.
Urgent reductions in methane and other short-lived climate pollutants, alongside long-lived greenhouse gases are needed: Because of the need to limit overshoot and return to below 1.5°C as quickly as possible, reductions in methane will play a particularly important role. This is because methane is a “short-lived GHG”, meaning that while it does not last as long in the atmosphere as other GHGs such as carbon dioxide, it has a much higher warming effect than many other GHGs. This is particularly relevant for New Zealand, where methane makes up a significant amount of our overall GHG emissions. However, the importance of reductions in methane emissions set out in the report is a stark contrast to law and action on methane in New Zealand. In 2025 the Government reduced the ambition of the 2050 Methane Target to a level that is incompatible with 1.5°C, and New Zealand is currently off track to meet its 2030 Methane Target. The Climate Change Commission has recommended practical areas of focus for policymakers in New Zealand regarding methane reductions.
Adaptation and mitigation must happen hand in hand: Approaching the 1.5°C target from above through a pathway of exceedance, peaking and decline must be done concurrently with extensive adaptation. Weak mitigation will create greater need for adaptation and divert more costs to emergency response. Adaptation planning in its current form may also not be sufficient to account for the profound shifts that will occur globally due to exceedance of the temperature goal. While adaptation will be especially difficult for developing countries that are particularly exposed to climate change, New Zealand is by no means immune. As the Climate Change Commission found last month, there are “critical gaps” in New Zealand’s adaptation planning, with the country too often paying to react and recover rather than preparing in advance.
Existing and new forms of carbon dioxide removal (CDR) will be needed, but in addition to, not instead of sustained reductions in greenhouse gas emissions: While the Overshoot Report is clear that CDR will play a role in a decline back to 1.5°C, it also notes it can only credibly contribute if all other emissions are reduced at source. This conclusion conflicts with the current operation of New Zealand’s main tool to reduce emissions - the Emissions Trading Scheme - where the removal of emissions from forestry is considered interchangeable with emissions reductions at source. This was a point made recently by the Parliamentary Commissioner for the Environment in his report Adrift: what future does the Emissions Trading Scheme have? As noted in that report, forestry has an important role to play in New Zealand’s climate policy, but that role should not be delivered through the Emissions Trading Scheme.
The international temperature goal remains 1.5°C despite overshoot
Even while the world moves towards a period of overshoot, it has also become increasingly clear that 1.5°C is the legally recognised temperature goal. For example, last year, the International Court of Justice, in its Advisory Opinion, found that:
1.5°C has “become the scientifically based consensus target under the Paris Agreement”. The ICJ drew attention to the scientific fact that the “[r]isks and projected adverse impacts and related losses and damages from climate change escalate with every increment of global warming (very high confidence)”.
The Paris Agreement’s long-term temperature goal (LTTG) (being 1.5°C) serves the UNFCCC’s “ultimate objective” of “stabiliz[ing] greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system”. The ICJ noted that the LTTG represents an “important concretization” of the UNFCCC’s ultimate objective.
The ICJ also held that there had been subsequent agreement of the parties to the Paris Agreement that are relevant to interpreting the LTTG, and show the centrality of 1.5°C, including, for example:
In 2021, the parties to the Paris Agreement “resolve[d] to pursue efforts to limit the temperature increase to 1.5 [degrees]”; and
In 2023, the parties reiterated this resolve and encouraged all parties to submit “ambitious, economy-wide emission reduction targets… aligned with limiting global warming to 1.5, as informed by the latest science”;
Accordingly, the ICJ held that the Paris Agreement’s 1.5°C aim was the parties' “agreed primary temperature goal”, and that its achievement is an obligation of result on the parties as a whole.
While the Advisory Opinion did not expressly address the legal implications of overshoot pathways, its reasoning indicates that overshoot would not alter the legal framework for mitigation. For example, states’ due diligence evolves with scientific knowledge and the probability and gravity of harm. The greater risks of higher and longer overshoots are thus relevant to the question of whether State action is adequate. Because exceedance increases the probability and severity of climate harm, due diligence becomes more demanding – especially as temperatures rise above 1.5°C – reinforcing the need for deep, rapid, and sustained reductions to limit peak warming and the duration of overshoot, and continued efforts to return warming to below 1.5°C.
It follows that states remain bound, under the stringent standard of due diligence, to limit the magnitude and duration of any exceedance and to return warming to 1.5°C as soon as possible, informed by the best available science. Academic commentary reaches the same conclusion. For example, Rogelj and Rajamani explain that the legal and policy implications of 1.5°C do not "switch off" at a crossing point: they gradually strengthen in importance before, at, and after crossing, and exceedance shifts the long-term focus to achieving and managing net-negative emissions to limit the overshoot.
This relevance is particularly heightened for New Zealand, as recent free-trade agreements, including those with the United Kingdom and the European Union, include obligations to “effectively implement” the Paris Agreement, which sets the temperature goal.
1.5°C is hard-wired into New Zealand law, and this doesn’t change if we overshoot it
In New Zealand's domestic legal context, the 1.5°C temperature goal is embedded throughout the Climate Change Response Act 2002 (CCRA), and exceedance of 1.5°C does not change this. For example:
Any person exercising a power or discretion under the CCRA must do so “in a manner that is consistent with the purpose of the [CCRA]”, which includes contributing to the global effort under the Paris Agreement to limit the global average temperature increase to 1.5°C above pre-industrial levels.
The relevance of 1.5°C is even more heightened when it comes to New Zealand’s domestic emissions budgets under the CCRA: Section 5W establishes a “dual purpose” for emissions budgets: budgets are to be set with a view both to meeting the 2050 Target and contributing to the global effort under the Paris Agreement to limit warming to 1.5°C.
The CCRA is correct to incorporate reference to 1.5°C. As set out above, this is the agreed international target, based on the best available science. Overshoot does not mean this goal has changed, only that in an overshooting world, "contributing to the global effort to limit warming to 1.5°C" means contributing to limiting exceedance and enabling a return below 1.5°C. That is a more demanding task, not a lesser one.
Overshoot is not an argument for resignation, but for urgency. In New Zealand, that urgency is not a matter of policy preference. It is what the law already requires.
Written by Laura MacKay & Molly McDouall.