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Synthesising everything we know about climate change – Expert Reaction

Not only are there feasible ways to cut down greenhouse gas emissions and adapt to human-caused climate change, but these actions can be taken right now, according to a major scientific report released today.

The Intergovernmental Panel on Climate Change (IPCC) has released its Synthesis Report for the Sixth Assessment Cycle, bringing together comprehensive, previously released reports on the physical science of climate change, what can be done to adapt to it, and what can be done to reduce the amount of greenhouse gases we emit.

The SMC asked experts to comment on the report.

Dr Daniel Kingston, Senior Lecturer, University of Otago, comments:

“This synthesis report provides a summary of the three major IPCC assessments released in 2021 and 2022, plus three further special reports. It is important to note that these reports provide a summary of current understanding, rather than primary research undertaken by the IPCC itself. Some of the leading experts in the world volunteer their time to write these reports. An open review process then takes place allowing other experts to scrutinise the reports prior to publication. Finally, the synthesis report is reviewed line-by-line by member governments from all over the world, plus scientific experts, prior to release.

“One of the key headlines from this synthesis is that human activities have unequivocally caused global surface temperatures to rise. The use of the term ‘unequivocally’ is hugely meaningful here. Scientists are typically cautious and like to include many ‘ifs’ and ‘buts’ with their statements. To eliminate all doubt that humans are causing global warming highlights starkly just how overwhelming the evidence is in this case.

“Further statements go on to show how temperatures have increased faster since 1970 than any other 50-year period in the last 2000 years, and that atmospheric CO2 concentrations are higher than any time in the last two million years.

“This warming is already having major impacts on weather and climate extremes. We have already seen evidence of this in the North Island/Te Ika-a-Māui earlier in the year, and in the Pakistan floods and European heatwave of last year, to give just a few examples. The impacts of these events often hit economically and socially marginalised people the hardest.

“The situation appears dire across many sectors that the report covers. There is a substantial gap between current policy and what needs to be done to even limit warming to 2°C. However, there are reasons for optimism too. Every tenth of a degree warming that we can avoid is important. Even though they fall a long way short of what is needed, current global emission reduction policies are making a difference in terms of slowing the rate of warming. The sooner these policy ambitions are improved, the easier and cheaper it will be to limit the adverse impacts of climate change – and the less likely we will be to encounter abrupt shocks or irreversible changes to the climate system.”

No conflict of interest.

Professor Tim Naish, Professor in Earth Sciences, Victoria University of Wellington, comments:

“Another year, another report from the IPCC. This is the 4th and final report that summarises and synthesises the trilogy of the 6th Assessment Cycle. The message for urgent mitigation remains the same, while global emissions keep going up, and time runs out. There is a good chance global temperature will reach the 1.5C target before the next IPCC report comes out (the 7th Assessment Report is probably 7-9 years away). So, is there anything new in this latest report?

  • The Science. “The science remains un-controvertible. The world is warming at an unprecedented rate and it’s because of us. At current rates we could be at 1.5C in 5-10 years and 2C in 15-20 years. The associated positive feedbacks in the climate system are already occurring and their impacts are being felt (sea-level rise, extreme events, wildfires, flooding, drought, heat waves). Moreover 1.5-2C global warming is an irreversible tipping point for the Greenland and West Antarctic ice sheets, and intergenerational multi-metre sea-level rise will be unavoidable.”
  • Adaptation. “We are woefully unprepared for those impacts, and at the very least must adapt to the climate change that is unavoidable and locked in. Two billion people in the Hindu Kush rely in ice fields and glaciers in the Himalayas for their freshwater. One billion people will be affected annual coastal flooding by the end of the century. Fifteen million Bangladesh people may be displaced as early as 2050. In New Zealand with 30cm of unavoidable sea-level rise, which will happen in many places by 2050, the historic 1-in-100-year coastal flood is likely to happen annually.”
  • Mitigation. “Those who have contributed least to emissions are being disproportionately affected. This is especially the case for small island and developing states (SIDS). If the current rate of emissions continues unabated, achieving the Paris target will not be possible without overshoot. This may cross some tipping points. Yet this latest report while emphasising the urgency to reduce emissions still offers hope and some plausible pathways. However, it cautions that any measures to ameliorate climate change must now involve immediate adaptation to those impacts we can no longer avoid.”

“So, another year of hope and urgency is upon us, after the world’s governments sat on their hands at the latest COP, and another IPCC report will ‘likely’ largely be ignored.”

No conflicts of interest declared.

Dr Nick Cradock-Henry, Principal Scientist, Department of Society & Infrastructure, GNS Science, comments:

“The IPCC’s Sixth Assessment Synthesis Report pulls no punches: climate change is here, it’s now, it’s us. Drawing on the efforts of hundreds of authors, and many thousands of lines of evidence, the conclusions are unequivocal about the dramatic changes in global temperature as a result of rising emissions. Research tells us with a high degree of confidence that:

  • “Atmospheric concentrations of CO2 are at levels not seen in two million years;
  • “The rate of sea level rise is quicker now than at any time over the last two millennia; and
  • “In the last decade, human mortality from floods, droughts and storms was 15 times higher for the world’s most vulnerable, who bear the brunt of exposure to extremes.”

“Framed within the wider context of land use change and degradation, growing inequality, and rising consumer demand, adverse impacts and implications for ecological and human systems are accelerating, and transformational changes are required. Deep and lasting emissions reduction, must be coupled with changing practices, processes, capital, and infrastructure in response to actual or anticipated climate change. The report is clear: Both mitigation and adaptation are essential, and so too is the need to address the underlying, structural drivers which disproportionately deliver benefits, and assign harm to those least able to cope, and who bear the least responsibility. A climate-resilient future is an increasingly just and environmentally sustainable one.

“For Aotearoa New Zealand, weather and climate are a defining feature of our diverse regions. From long Northland summers to the cool greys of the West Coast, these have contributed to strong regional identities, provide fodder for countless conversations, and provide our diverse primary industries with a competitive advantage, nearly unmatched throughout the world. As we have seen, however, these last few months, climate change is making a difference to New Zealand now – affecting our rainfall and extremes. Resilience and adaptation have long been topical, but they have hardly ever been more acute – and this will only continue. In January, Auckland received over 45 per cent of its annual rainfall in just one month, over 500mm. Two weeks later, large portions of the North Island including two of our largest horticultural cropping areas were devastated by Tropical Cyclone Gabrielle. The effects of this storm have yet to be fully determined, however – in addition to the tragic loss of life, the consequences will have consequences for infrastructure, production, processing and distributions, and communities, that will weigh on us for months – if not years.

“Furthermore, climate change will not happen in isolation. As a society, we are contending with multiple, often interconnected challenges – from the rising cost of living, to low-frequency, high-magnitude geo-hazard events, to the continued pandemic recovery – and it can be tempting to dismiss these findings amidst other, pressing concerns. As the economist Mark Carney puts it, ‘Climate change is the Tragedy of the Horizon’; its impacts will be felt beyond the traditional frames, and management cycles of most actors, while imposing a cost on future generations.

“To overcome this, we must respond, and now. Responding to the climate change challenge – reducing risk, and reversing the upwards trend in emissions, will limit the extent to which future adaptation will be required. Taking seriously, the need to address the underlying social, physical and economic conditions which put people and property in harm’s way, can have attendant benefits for wellbeing. And openly and honestly acknowledging the intergenerational equity issues that are pushing the costs further and further down the road, might lead to novel and enduring solutions.”

Conflict of interest statement: Contributing author, IPCC AR 6 WG2, Chapter 11

Professor James Renwick, Victoria University of Wellington, comments:

“Once again, the climate science community has sounded the alarm about climate change. While at the same time explaining that we have the power to avoid future warming and the worst of coming extremes. The IPCC notes, ‘In 2018, IPCC highlighted the unprecedented scale of the challenge required to keep warming to 1.5°C. Five years later, that challenge has become even greater due to a continued increase in greenhouse gas emissions. The pace and scale of what has been done so far, and current plans, are insufficient to tackle climate change.’

“We have known about the problem of climate change for decades, yet we have avoided doing anything to solve the problem, instead we have made it a lot worse. As the Synthesis Report makes clear, greenhouse gas emissions from human activity (mostly burning fossil fuels) are unequivocally causing climate change. The globe has already warmed by around 1.1°C since pre-industrial times, and we are seeing increasing extremes of temperature and rainfall globally. Every tenth of a degree warming from here will add to the impact of extremes, with more loss of life, infrastructure damage, reduced food security, and many other impacts.

“Adaptation to climate change is happening, though there are gaps and inequalities. Currently, we have the ability to respond and take adaptation action before the next extreme event happens, but if we allow warming to continue, we will reach a point where we cannot adapt and will just have to suffer.

“The causes and the impacts of climate change are very unevenly distributed, generally with those least responsible for the problem suffering the largest consequences. To properly tackle climate change and move towards a sustainable future, humanity needs to address these inequalities and make ‘climate justice’ a priority. As the Synthesis Report makes clear, we have most of the techniques and technologies we need to bring about the necessary changes. Tackling the root causes of climate change is a huge opportunity for humanity, to bring about a more equitable and sustainable world. Failure to act will surely end in chaos.

“I really hope the governments of the world are listening – we have run out of time for thinking about the issue, now is the time for action.”

Conflict of interest statement: “I was a Coordinating Lead Author on the Working Group 1 report of the AR6, that fed into this Synthesis Report. I am active in climate research and receive funding from MBIE in this area. I am a Commissioner at the New Zealand Climate Change Commission.”

Associate Professor Inga Smith, Department of Physics, University of Otago; Co-Director of He Kaupapa Hononga: Otago’s Climate Change Research Network, University of Otago; and Associate Professor Sara Walton, Department of Management, University of Otago; Co-Director of He Kaupapa Hononga: Otago’s Climate Change Research Network, University of Otago, comment:

“A person born in 2020 is likely to experience above 3 degrees warming in their lifetime unless low emissions pathways are pursued immediately, according to this report. This ‘Synthesis Report’ is a very useful and extremely timely summary of the substantial work that the IPCC put into the three-volume, 7735 pages, Sixth Assessment Report. Getting tough on climate change is urgent; the report outlines that this will require governments to be inclusive, show political commitment, have coordinated policies, undertake stewardship of ecosystems, and cooperate nationally and internationally. Climate change is a “bread and butter issue”; the report reminds us that increasing food and water insecurity are expected due to increasing global temperatures. In the wake of recent, deadly extreme weather events hitting New Zealand, the report makes sobering reading, highlighting that heavier rainfall and other hazards increase rapidly with every increment of warming.

“Deep, rapid and sustained reductions are needed now to prevent humans, animals and plants globally, including food systems, facing potentially dangerous temperatures and damaging weather. The report recognises that diverse knowledges are needed to enable collective actions. Indigenous, local, and western-scientific knowledges are needed to collectively work together on transition pathways. There is much mahi to be done and the report stresses that time has run out for inaction. The consequences of missing this opportunity for those born today are too burdensome. The opportunity to work together and stablise our climate systems in an equitable and just way, drawing on diverse knowledges, is being strongly advised. Aotearoa New Zealand is in a prime position to lead; the time to act is now.”

Conflict of interest statement: Associate Professor Smith was an Expert Reviewer for the first-order draft of this report (IPCC “Climate Change 2023: Synthesis Report”).

Professor Alistair Woodward, University of Auckland, comments:

What are the key public health considerations in the report?

“Global greenhouse emissions have risen faster since 2000 than ever before, though the rate of increase has slowed in the last decade. There have been improvements in energy and carbon efficiency, but these have been outweighed by increased consumption of goods and other polluting activities.

“We are more certain than ever before of increases in extreme events such as flooding, extraordinary rainfall and tropical cyclones, and, notably, there is also increased confidence in attribution: it is most unlikely these extremes would have occurred without human-induced climate change.

“Climate change is damaging human health: this includes deaths and illness from heatwaves, food- and water-borne disease, mental health challenges, trauma and loss of livelihoods and culture.

“The greatest effects occur in poor, socially marginalised communities; globally in the last decade deaths from floods, droughts and storms were 15 times greater in highly vulnerable communities.”

What are their implications specifically in New Zealand?

“Water-borne and water-related health risks are a particular challenge in New Zealand and will be amplified considerably by projected climate change.

“Mental health challenges are highlighted in the Assessment Report more strongly than before, and these are highly relevant in New Zealand.

“Adaptation is critical, and we should be planning for worst plausible outcomes in the longer term, not most likely events in the immediate future.

“Adaptation will be challenged by the severity of climate extremes, and the increased frequency of compounding disasters (such as the incidence this summer in New Zealand of both unprecedented local flooding and storms caused by tropical cyclone Gabrielle).

“But we can’t give up on mitigation. Reasons: the moral argument (a rich high-emitting country like New Zealand should be leading not following); self-interest (business as usual global heating by 2100 may be three times or more what we have seen so far: in this scenario, recent storms and floods would be a pale version of disasters impacting New Zealand in the late 2000s); the economy (if New Zealand fails to meet international agreements our trading partners will apply heavy penalties); and, lost opportunity (first movers in innovation and sustainability are more likely than laggards to prosper).

“Mitigation is possible – fast, deep reductions in emissions would slow global heating within about 20 years, and there are models of success overseas: at least 18 countries have sustained absolute production-based GHG and consumption-based CO2 reductions for longer than 10 years.”

How would you like to see these concerns addressed?

“Action that serves both adaptation and mitigation e.g., better, sustainable, transport options; housing that is low energy and disaster resistant; agricultural reforms to reduce pollution and dependence on fossil fuels and better protect food supply in the face of extreme weather.

“Adaptation policies that increase social resilience and institutional capacity. Investments in physical infrastructure (roads and pipes) are only part of what is needed. We need to pay attention also to community building, poverty reduction, ending inequities and climate literacy. We need to build institutions, such as disaster response and health care, that are better prepared for the complex and fast-moving challenges of climate change. This will require trade-offs and new directions, such as built in redundancy rather than slimmed ‘efficiency’, protection of diverse response capacities, devolution of rapid response functions, shortened supply chains, greater responsiveness to and valuing of traditional and local knowledge, and an emphasis on the ability of institutions to learn rapidly.”

Conflict of interest statement: “I was a Lead Author for the Australasia chapter (as part of working group II) in the 6th Assessment Report.”

Dr Judy Lawrence, Adjunct Professor, Climate Change Research Institute, Victoria University of Wellington, comments:

“The Synthesis Report from the IPCC 6th assessment cycle has important messages for Aotearoa New Zealand in the wake of successive extreme climate events that show the scope and scale of Nature’s wrath. There is an urgent need for near-term action on both deep and rapid mitigation and accelerated adaptation action. These require multi-level governance and rapid and far reaching transition across all sectors and systems.

“Feasible, effective and low-cost options are available that are equitable and just and innovative solutions are within our sectors and communities, especially with Mātauranga Māori.

“Finance is a critical enabler for effecting the change required for climate resilient development that can reduce the losses and damages we are seeing in Aotearoa-New Zealand, but the window for action is narrowing.

“The Synthesis Report is signaling that action is not just critical across mitigation and adaptation for a climate resilient future but to avoid crossing significant thresholds of nature that sustain humans.”

Conflict of interest statement: Coordinating Lead Author, IPCC 6th Assessment Working Group II 2022

Ralph Sims, Professor Emeritus, Sustainable Energy and Climate Mitigation, Massey University, comments:

“In 1990 the IPCC published its First Assessment Report.

“Within the Summary for Policy Makers was stated: ‘Emissions from human activities are substantially increasing the atmospheric concentrations of the greenhouse gases CO2, methane, CFCs and nitrous oxide. Long-lived gases (CO2 and N2O) will require immediate reductions in emissions from human activities of over 60% to stabilise their concentrations at today’s levels.’

“Since that report, and many other analyses, models and scenarios, the world now emits 40 % more greenhouse gases each year, rising from 35 billion tonnes in 1990 to over 50 billion tonnes today.

“Today the IPCC released its Synthesis Report from its Sixth Assessment Report.

“It summarises the latest scientific understanding from recent IPCC reports (2020/2022) on the physical climate science; impacts, adaptation and vulnerability; and mitigation, as well as three recent IPCC Special Reports on Warming of 1.5oC; Land use; and Oceans. (Each of these reports, including the Synthesis report, had hundreds of co-authors from many countries, were heavily reviewed by thousands of experts and government officials and went through an approval process where each sentence in the Summary had to be approved by all country delegations present – usually around 170 – 180).

“In the Summary of the Synthesis Report it confirms that continuing unsustainable energy and land use has led to a temperature rise of 1.1oC above pre-industrial levels that has resulted in more frequent and more intense extreme weather events with dangerous impacts on nature and people in many regions of the world.

“In New Zealand this has become very apparent.

“The Report goes on to state that ‘multiple, feasible and effective options to reduce greenhouse gas emissions and adapt to human-caused climate change are available now’.

“In fact, many systems and technologies have been available since before the first IPCC report 30 years ago – but few governments, businesses, homeowners, car owners, have taken any serious notice of how to reduce their carbon footprints.

“New Zealand’s emissions have stabilised since 2005 – nothing to be proud of given that emissions in 20 or more other countries have significantly declined since then.

“However, globally there is no sign of any slowing of growth in total emissions.

“So, it’s highly likely we’ll exceed the Paris Agreement target of 1.5oC in the next few years.

“We’re all culpable (except those in developing countries with low emissions per capita – New Zealand’s being one of the highest in the world), so we’ll have to expect more droughts, storms, floods, sea level rise etc.

“We had been warned!”

Conflict of interest statement: “I was a Review editor for IPCC WG3, Mitigation that is part of the Synthesis report.”

Dr Jim Salinger CRSNZ, Climate Scientist, Victoria University of Wellington, comments:

“Over 30 years ago (1991) in my first book Greenhouse New Zealand launched by the then Minister of Science the Hon Simon Upton, highlighted that global warming was well underway (globe +0.6 degC, New Zealand region +0.6 degC) because of rapid emissions of carbon dioxide from fossil fuels and deforestation, and methane from livestock agriculture and rice production. The book warned if greenhouse gases emissions were not curbed very costly impacts would occur in the 2020s. These were detailed.

“The 2023 Synthesis Report now is documenting that these are occurring and will only get worse if emissions are unabated, with global temperatures in 2023 1.1 deg C warmer (New Zealand + 1.3 degC warmer) than the period 1850 – 1900. This last of the Sixth Assessment Reports process warns that the Earth is now at ‘system critical’ and if we don’t rapidly embark on climate resilient development with individual and collective action from the nations of the world, then increased climate risk poverty, inequality, injustice, siloed responses with ecosystem and degradation will occur. This cannot be solved by one or two (e.g. USA and China) nations alone, but requires global collective action. Limiting warming to 1.5 or 2degC requires rapid, deep cuts immediately in emissions. Nationally determined contributions (NDCs) announced by October 2021 make it likely that warming will exceed 1.5°C by 2030 and make it harder to limit warming below 2°C during the 21st century.

“However, the 2023 Synthesis Report identifies climate resilient development with global inclusive governance, ecosystem stewardship and behavioural change will lower emissions and climate risk and system transitions. This graphic illustrates what must be done, and we must seize the opportunity nationally with a climate election this year.”

No conflicts of interest declared.


Adrian Macey, Adjunct Professor, New Zealand Climate Change Research Institute, Te Herenga Waka, Victoria University of Wellington, comments:

“An effort has been made to make it readable (it’s all relative, this is still a UN document negotiated line by line among governments). Highlighted boxes and colour charts are very helpful to understanding.

“It conveys in a mostly sober tone what we already know, but with more certainty than the previous report (AR5), reflecting a further eight years of observation of the climate and advances in science:

  • causes and effects of warming
  • increasing risks and impacts across the board as temperature increases (e.g. a one in a hundred year event becoming annual)
  • the gap between current policies of states and the domestic and international goals they are serving

“The need for DEEP, RAPID, SUSTAINED action in this decade on mitigation, on adaptation, international cooperation, notably finance and technology transfer to developing countries (section C.7)

Getting to zero CO2 is the core of achieving any temperature limit and is therefore the top priority.

“Adaptation needs to be integrated with mitigation. (Note in New Zealand this is not yet happening. Further, our international mitigation pledge – essentially paying billions to buy carbon credits – is not linked either to domestic mitigation or to adaptation).

“The role(s) of all of society and all levels of government (section C.6)

“The fact that 1.5 degrees is unattainable. This is not quite stated, because the IPCC does not get into geopolitical assessment. But with an economic crisis unfolding and the recovery from Covid still incomplete it’s unrealistic to expect the huge reductions needed this decade to occur. Not a single region in the world is on track to 1.5 degrees. The modelling on which estimates of future emissions reductions is based does not correct for political-economic factors.

“Of interest to NZ, the severe risks to food production across the globe but concentrated in some areas.”

Is there anything positive?


  1. “Evidence that some policies and laws are already making a difference, both on adaptation and mitigation.
  2. “There are many opportunities for reducing emissions. Section C has a good sector by sector summary.
  3. “Many technologies and methods that can be applied to adaptation
  4. “Reducing costs of lower emissions technologies”

“On point 3 see especially the table on page 28. This is a good way of seeing where it’s most effective to direct resources. Often there is a disconnect between what people are convinced is the most important thing to do for the climate and what is actually most effective, and more cost-effective. ‘Put physics before feeling!’ This table demonstrates that energy is the big one, not surprising as this is the sector most directly concerned with getting to zero CO2.”

Other point

“A useful note of caution on the use of IPCC scenarios and modelled pathways. These have sometimes been misunderstood (including by NZ officials) as a prescriptive starting point for individual countries.”


“One issue of interest to New Zealand is the metrics used to measure the gases, especially methane. There is no acknowledgement here of the inaccuracy of the GWP100 metric’s quantification of methane’s warming, a rather important fact given methane’s prominence in global warming. This was addressed in the science working group ( WG1) but is treated perfunctorily and dismissively in a footnote here. A success for the anti-GWP* lobby (those who resist any acknowledgment of this more accurate metric because of their worry that it would be used to let farmers and/or NZ off the hook.).”

“The treatment of climate justice and ethics etc. in section C.5 isn’t very convincing. But the core responsibilities towards developing countries are well set out in the earlier part of the SPM.”

No conflicts of interest declared.