Inside the Intergovernmental Panel on Climate Change, with Hans-Otto Pörtner

At heart, Hans-Otto Pörtner is a comparative physiologist and metabolic biochemist. From his earliest papers in Journal of Experiment Biology, he has been fascinated by the physiology of marine creatures, how they deal with hypoxia or exercise (Pörtner, 1987; Pörtner et al., 1986a,b). ‘My focus was on marine invertebrates living in the intertidal zone’, says Pörtner, recalling working with Journal of Experimental Biology greats, including Bob Boutilier, Ron O'Dor and Dan Toews, then at Acadia and Dalhousie Universities, Canada, as they investigated metabolism and acid-base status in squid (Pörtner et al., 1991a) and amphibians experiencing hypoxia (Pörtner et al., 1991b). However, by the end of the 1990s, Pörtner was becoming increasingly intrigued by the impact of carbon dioxide on the metabolism of invertebrates living on the seashore (Pörtner et al., 1998), in particular ‘how climate drivers like temperature, oxygen and CO₂ combine to shape the fundamental niche of species in different climate zones’, he says. Little did he know, but this interest would inspire an utterly unexpected diversion from his life as a research biologist into a parallel career as an international advisor on climate change.

Out of the blue in 2002, Pörtner was contacted by the United Nations' Intergovernmental Panel on Climate Change (IPCC). ‘I got an invitation to join the team of scientists that was looking at the possibility and risks of disposing of CO₂ directly into the ocean’, he explains. Pörtner joined the team of eminent scientists and after reviewing the ecological literature with Yoshihisa Shirayama (then at Kyoto University, Japan), it was clear that disposing of CO₂ in this way would be catastrophic for the biodiversity and ecology of the oceans. ‘The disturbance of acid-base status impacts metabolic performance of marine organisms, playing a major role in the effects of climate change on them’, says Pörtner. Their alarming chapter in the Carbon Dioxide Capture and Storage Special Report (Caldeira et al., 2005) led to a complete ban by 2008 on marine CO₂ dumping under the London Protocol and the Oslo and Paris Conventions.

Now Pörtner was on the IPCC's radar, and in 2009 they came knocking on his door again, inviting him to participate in outlining the structure for the IPCC's Fifth Assessment Main Report by reviewing the climate change situation at that time, its causes, potential impacts and possible responses that could alleviate the effects. This time Pörtner and his colleagues turned their attention to the impacts of ocean warming, acidification and hypoxia on marine life (Pörtner et al., 2014). The final assessment, agreed by the IPCC in 2014, was damning, with the Synthesis Report asserting that, ‘Limiting climate change would require substantial and sustained reductions in greenhouse gas emissions which, together with adaptation, can limit climate change risks’ (Pachauri and Meyer, 2014). This in turn led to the groundbreaking 2015 UNFCCC COP (United Nations Framework Convention on Climate Change, Conference of the Parties) Paris Agreement to limit global warming to 1.5°C above preindustrial levels. ‘I think this was the most important COP of recent years’, says Pörtner.

Shortly after the culmination of the Fifth Assessment period in October 2015, Pörtner was elected to one of the highest positions in the IPCC, as co-chair of Working Group II – the committee which assesses the impact of, adaptations to and areas of vulnerability to climate change – with Debra Roberts (University of KwaZulu-Natal, South Africa), to jointly oversee the Working Group's contribution to discussions through the Sixth Assessment period. ‘This assessment cycle was the busiest in IPCC history’, recalls Pörtner, explaining how he and Roberts oversaw the Working Group II Main Report in 2022, in addition to three Special Reports and the Sixth Assessment Synthesis Report in 2023 in collaboration with the four co-chairs of the other Working Groups.

The first Special Report in 2018 – entitled Global Warming of 1.5°C – outlined the impacts of a 1.5 and 2°C temperature rise on human society and biodiversity, stating that it is, ‘necessary and vital to keep global warming below 1.5°C’ (Masson-Delmotte et al., 2018). A year later, in August 2019, the ‘Climate Change and Land’ report looked at the issue of desertification, land degradation, sustainable management and greenhouse gas emissions from land (Shukla et al., 2019). One month later, the third Special Report, entitled ‘The Ocean and Cryosphere in a Changing Climate’ (Pörtner et al., 2019), reviewed the impact of climate change on the oceans and communities that live in the coastal and frozen regions of the world – including the polar and high-altitude mountain areas, collectively referred to as the ‘cryosphere’. Having considered the impact of climate change from such a diverse range of perspectives, Pörtner says that the experience, ‘emphasised [to him] that keeping global warming to 1.5°C is an existential requirement’.

But, in late 2019 a global catastrophe began to unfold. Reports of a dangerous new coronavirus were emerging and by March 2020 borders were slamming shut and individuals confined to their homes. From chairing in-person meetings with hundreds of contributing scientists and governments from all over the planet, Pörtner and Roberts were suddenly faced with the challenge of maintaining the international dialogue through Zoom calls and online meetings in the run up to release of the Sixth Assessment Main Report. ‘The new situation required quite an effort to continue our activities’, says Pörtner. One concern was that the nuances that usually convey so much in face-to-face interactions would be lost in the transition to virtual sessions. Fortunately, many of the scientists collaborating on the Sixth Assessment Report had already developed a rapport through meetings in locations as far flung as Durban, South Africa, and Faro, Portugal, so Pörtner and Roberts were able to preserve the momentum, but there were further logistical challenges. In early 2022, during the final thrust to get the report approved by 195 government delegations, Pörtner recalls being locked in a hotel in Berlin with daily COVID-19 tests, hosting virtual meetings with hundreds of delegates distributed across the globe. ‘We moved between time zones, so the first week, we held meetings early for the eastern time block, so it was easier for Asian and Australasian colleagues to join, and in the second week we moved more to an American time slot, so they found it easier to join’, Pörtner explains. ‘It was challenging’, he recalls, describing how in-person approval sessions could often go on late into – and even through – the night, leaving delegates drained and exhausted after a week. But when the process transferred online, it became even more protracted, extending over two entire weeks as each sentence was discussed painstakingly. And if that wasn't enough, on 20 February 2022, the Ukraine war broke out during the final stages of discussion. ‘The Russian and Ukrainian delegations were both on the [approval session] call’, remembers Pörtner, yet despite this, final approval for the report was reached eventually on 26 February 2022.

Pörtner is proud that through the course of these negotiations, science always had the final word. ‘There's no possibility that policy makers can tilt the scientific message’, he says, emphasising that scientists were continually on hand to provide impartial guidance to governments. But he was constantly concerned by the impact on the dialogue of states whose economies are highly dependent on petrol production, explaining how they arrived at each meeting with packs of lawyers intent on diminishing the impact of the IPCC. ‘They cannot change the material, but they can exclude material by saying, “We won't approve if this remains in the summary”’, he says. He is frustrated that it took so long for an annual COP – the 28th hosted in Dubai in December 2023 – to commit officially to phasing out fossil fuels. ‘You can see immediately how the procrastination policies used by these governments have played out and have been successful over the years’, he frowns.

Reflecting on the experience of chairing meetings with 300–500 people in the room, Pörtner recalls having to dig deep on his reserves of patience when faced with states that were determined to delay the process and even allow key action statements to drop. ‘But with all the pressure in the room and with all the energy that was moving things forward, in the end, we always reached an approval’, he says, adding that the atmosphere in all these meetings was ‘very political’. Pörtner admits that although co-chairing the approval process of each report was gruelling, he was supported by a fantastic team of colleagues. ‘You are not standing alone’, he says, recalling how he and Roberts would step in to pick up when the other had reached the limit of their stamina during the closing days and overnight sessions before a report was approved.

But then it is up to individual governments to take the IPCC's messages on board, to implement concrete policy changes in their home states, and Pörtner is frustrated by how some water down the policies. ‘In the end, it slows the process of climate mitigation and adaptation, to the extent that we are not currently on a trajectory to 1.5°C global warming, but it will be more like 2.5 to 2.9°C’, he warns, adding, ‘There need to be more ambitious efforts to reduce emissions’. He hopes also that President Trump's decision at his inauguration to withdraw the United States from the Paris agreement will not be too damaging for the planet and that other governments, including individual states in the US, will strengthen their efforts to compensate for such poor decision making.

One sector at which he takes aim in particular is the airline industry, explaining that CO₂ emissions at altitude are even more damaging than those at sea level. ‘The current situation where air travel is sometimes cheaper than going by train is wrong’, he says, as airline fuel is untaxed, essentially subsidising this most unsustainable form of transport. However, he warns that a dramatic U-turn leading to a massive expansion in railways could be equally environmentally damaging, destroying ecosystems on the ground. He is also concerned that political apathy among voters and the rise of the Far Right is diluting the will to tackle climate change, with some governments even giving up. ‘Policy makers should be leading the debate, rather than following the public mood’, he says.

After chairing multiple intergovernmental sessions culminating in three Special Reports and the Sixth Assessment Main Report, Pörtner stepped down from his IPCC responsibilities in July 2023. ‘It takes a lot of time away from the family, from your private life, sometimes more than it should’, he says, adding that he delayed his retirement by three years to see the Sixth Assessment period through to completion. Fortunately, his contributions to the defence of the planet's future have not gone unnoticed. After contributing to the Carbon Dioxide Capture and Storage Special Report in 2005, he was one of approximately 1000 scientists who were acknowledged for contributing to the work that led to the award of the Nobel Peace Prize to the IPCC and Al Gore in 2007. Pörtner was also recognised for his work by UNESCO, receiving the Roger Revelle Medal in 2022, and the United Nations, when he gave the Keynote Lecture at the United Nations Ocean Day in New York in 2023, which was streamed worldwide. The Prince Albert II of Monaco Foundation also acknowledged Pörtner in 2023 with the Planetary Health Award. ‘Sitting at the table with the Prince and talking to him about the issue, it felt like it came together’, Pörtner smiles, chuckling that he has a cupboard where he collects ‘those little medals’. But the award that seems to be closest to his heart is the Golden Pea, presented each year by the Berlin Fairy Tale Days to honour someone who has, like fairy tale heroes, ‘fought for good and awakened hope in people’. Reflecting on his contributions to the IPCC, Pörtner is most proud of having helped to raise the profile of marine environments and biodiversity up the political agenda. ‘During the Sixth Assessment Report period, we made the ocean more visible in the IPCC and also made the connection between climate and biodiversity visible to the policymakers’, he says, enforcing the need for a continued dialogue about the role of the oceans in climate stabilisation.

So, how does Pörtner recommend that we as individuals contribute to combating climate change? ‘You are a customer, you can pick and choose what you do in your daily life’, he says, pointing out that we can all reduce air travel (go by train or electric vehicle instead), switch from oil- and gas-fuelled heating to heat pumps in our homes and opt for an electric, or alternative fuel, car. But he is still concerned that political willpower remains a bottleneck in climate policy. ‘Pushing the education system to produce policymakers that are paying attention to our natural resources and life-sustaining function of the planet will be very important in the future’, he says. Pörtner is also encouraging of the next generation of comparative physiologists. ‘There should be someone from our community that wants to get involved’, he says, suggesting that anyone who is interested should send their CV to their local Focal Point (the individual in their country that nominates report authors and review editors to the IPCC; listed at https://www.ipcc.ch/apps/contact/interface/focalpoints.php) to find out how they can contribute to policy that will ensure the future of our planet and civilisation.

Pörtner's clarion call is out. It's our planet and with the wealth of knowledge and experience within the Journal of Experimental Biology community it is time for one, or more, courageous individuals to continue the fight for climate justice, which Pörtner has driven unceasingly for more than two decades. The future is now in our hands.