Text of farewell lecture at Delft University of Technology, 24 May 2023

Mijnheer de Rector Magnificus, leden van het College van Bestuur, collegae hoogleraren en andere leden van de universitaire gemeenschap, zeer gewaardeerde toehoorders, dames en heren, ladies and gentleman:

The energy transition is now about 50 years old.

Fifty years ago, I was still in high school. It was a talk by a classmate – probably about the well-known report by the Club of Rome – that triggered my interest in energy issues. Soon after, the first Oil Crisis brought energy scarcity to the newspaper headlines. What triggered me was the huge challenge: the rapid growth of production and consumption versus the planetary limits. The need to preserve all the value we got for the next generation.

But I wasn’t aware that by then there was a paradigm change in the world of energy:

  • Before that, there was little interest in what energy was used for, and the ever-growing energy use was considered a given. Afterward, the demand side was intensively analysed and opportunities to use energy more efficiently became clear.
  • Before that, renewable energy was considered to be only interesting for niche applications. Afterward, research and development in this area took off rapidly. 

But as said, I was still in high school then. I embarked on studying physics. And in physics, energy is everywhere, but not so much as a social challenge. When I advanced in my university programme, it became clear to me, that this would be my profession – and since then, I have spent my entire professional life on what is now called the energy transition.

The first thing I did was explore whether an energy system fully covered by renewable sources would be possible for the Netherlands. The driver to explore this was the concern about resource depletion and pollution of air and water. The answer was yes – an energy system 100% based on renewable energy is possible [i].

Today, I want to look forward – in the light of the developments over the past 50 years.

  • I first want to discuss why there is a ‘need for speed’
  • Then move on to the two critical elements of the energy transition: energy efficiency and renewable energy.
  • Finally, I will consider the prospects for reaching ambitious targets.

The need for speed

Why are we in such a hurry, why is there a need for speed? Why did we last year at Delft University of Technology choose as the theme of our lustrum celebrations ‘speeding up the energy transition’?

When I started my professional career, in 1981, climate change was hardly on the agenda. That changed rapidly in the middle of the eighties of the last century. It was in 1988 that I had my first climate change-related publication. It was on something very basic: how to determine emission factors of fuels to calculate CO2 emissions. But since then, climate change has begun dominating the energy agenda. Also for me. In 1991, I defended my Ph.D. thesis. Currently, the title wouldn’t be considered very specific: it covered topics ranging from energy efficiency to carbon-capture-and-storage.

Let us first look back. Energy-related CO2 emissions have grown over the past fifty years, and despite all efforts so far, they are still increasing, be it at a somewhat slower rate. Energy-related CO2 emissions are important: they make up about two-thirds of total greenhouse gas emissions [ii].

CO2 emissions from energy and industry. Source: Our World in Data, retrieved May 2023.

Now we look ahead to what is needed. We showed that in one of the last IPCC reports.

In this graph, we show the development of greenhouse gas emissions over the coming decades. First of all, you see where we are heading without additional climate action (red line). We will get to more or less stable emissions, resulting in a temperature increase of about 3 °C by the end of this century. This is the average global temperature, compared to the pre-industrial level. This is too high, but let me also stress that this is already quite an achievement. If we would have shown such a current-policy scenario 15 years ago, we would have ended up around 4 °C or more. Three °C is better but clearly not good enough.

Development of greenhouse gas emissions according to certain scenarios (for details, see text). Adapted from IPCC [iii]

At the Paris Agreement, it was agreed that the global temperature increase should be limited to well below 2 °C and efforts should be pursued to keep it below 1.5 °C. What is needed for that? Keeping it at well below 2 °C will require rapid reductions – already in this decade, by 25% compared to the current level (green line). For 1.5 °C we even need to be more ambitious: a reduction of over 40% is necessary (blue line). These are extremely ambitious reductions. And for well below 2 °C, we can catch up later, but for 1.5 °C that is no longer possible – according to our current understanding.

Is it possible to achieve such strong and rapid reductions? In the IPCC report, we have made an overview of the 40 most important options that can play a role until the year 2030, and the answer is: yes, it is possible. The total is sufficient to reduce emissions by more than 50% [iv]. So, if we don’t achieve the ambitions needed for 2030 – it is not because of a lack of options.

I will focus my lecture today on two important families of options: energy efficiency and renewable energy. But that is not exhaustive – in our list of 40 options there are a lot more that can contribute: carbon-capture-and-storage, nuclear energy, stopping deforestation, sequestration of carbon in the soil, dietary change, circular economy options, etc., etc

First, I will discuss energy efficiency.

Energy efficiency

Let’s first have a look at the final energy use in the world – the energy as it is consumed by end-users in industry, transport,  households, and the service sector. In this graph, you can see the development over the past 50 years.

Global final energy use by sector. Based on data extracted from IEA World Energy Balances, release April 2023.

It is clear that total energy use has been growing in all sectors. But that is not the case everywhere. In this picture, you see that final energy use shows stabilization in industrialised countries – the OECD countries. How is that caused?

Final energy use in OECD countries by sector. Based on data extracted from IEA World Energy Balances, release April 2023.

One of the important tools that we have developed in energy systems analysis is the decomposition of energy use into different factors. In this figure, the black line is the actual development of energy use. You can see what the contribution is of each of the three factors that determine the growth of energy use. You can see that the volume of activities has increased – we drive more kilometres in our cars, we have more appliances and higher industrial production – this is the yellow line. But at the same time, it can be seen that energy efficiency has improved and that had a decreasing impact on energy use – the green line. There are also structural changes in the economies but the overall impact of these is relatively modest – the red line. What we see here,  is that roughly speaking energy efficiency improvements have offset economic growth – leading to stable energy use in industrialised countries.

Decomposition of energy demand in IEA member states. Source: IEA [v]

Looking at the underlying mechanisms that have led to energy efficiency improvement, it is good to distinguish between new equipment and existing equipment. On the one hand, there is new equipment like new household appliances, cars, and electric motors, but also new buildings. Here we encounter what is probably the most successful energy policy that was introduced in the past decades. And this policy is: energy efficiency standards. Energy efficiency standards set a maximum for the energy that products are allowed to use per unit of functionality. For a washing machine, that can be kWh per kg of laundry,  and for a car that would be litres of gasoline per hundred km driven.

Such standards were introduced first in the United States, later in Japan and the European Union and now they are in place all around the world. In this graph, you see the fraction of the energy use that is covered by energy efficiency standards. For air conditioners, fridges and freezers, and lighting that is already more than 50%. But also for other energy-using equipment, this fraction is also rapidly growing, including industrial motors, and cars and trucks. A recent investigation [vi] showed that electricity consumption in the US and the European Union would have been 15% higher than it is today if all these standards would not have been in place. It is quite invisible for most of us, but a silent technological revolution took place behind the doors of our fridges and washing machines.

Global coverage of energy efficiency standards. Source: IEA [vii]

This doesn’t mean that energy efficiency standards are without problems. Standards are set for standard conditions and these are not always representative of real-life conditions – we know that for example for cars. Compliance is not always sufficiently managed. And standard-setting is a dynamic process: technology develops, so standards should be updated every few years. And all kinds of new types of equipment should be brought under the standard. This all should be taken into account – and often already is. So, also for the future, setting energy efficiency standards is a relatively simple and convenient way of energy policy making.

It is much more difficult to improve the energy efficiency of existing energy-using equipment. The most notable examples are existing buildings and existing industrial plants. They have a lifetime of 30, 50, or even 100 years and we cannot wait for the autonomous replacement of all these. That doesn’t mean that nothing has happened over the past 50 years. For example, homes that were already there in the 70s of the past century have been insulated, they got double glazing, they now have condensing boilers, etc. This has certainly led to a reduction in energy use for these buildings. But at the same time, we see that the development is not going fast enough. The IEA has found out [viii] that currently 1% of the buildings in the world are retrofitted per year. That is way too slow. To make a meaningful contribution to our targets for the year 2050, the rate should be increased to two and a half percent per year. We see something similar for industrial processes. Globally, the investments in industrial energy efficiency are very modest. The lack of progress can also be seen in the Netherlands’ industry. Data from the Netherlands’ Emission Authority suggest that compared to the European benchmark for some sectors savings of up to 25% are still possible, just by adopting the best technology.

Policies that are used so far for existing buildings and existing industrial plants include subsidies, information campaigns, financing support, and energy and carbon taxes. But one policy that I would like to draw attention to also here is energy efficiency standards. So far, there is little experience with that. However, there are some examples. Office buildings in the Netherlands need to have a minimum energy label of C. Another example is the obligation to take energy-efficiency measures with a payback time of less than five years for small and medium enterprises. Both are modestly enforced, and it is too early to say what impact they could have. Also, internationally, there is increasing interest in energy efficiency standards for existing buildings, but they are in an early stage of implementation [ix] – anyway, this is certainly a pathway that could be pursued further.

Before I stop talking about energy efficiency, one question must still be discussed: should we keep having energy efficiency as a separate target? In the end, we are not primarily interested in reducing energy use but we are interested in reducing the negative impacts – like CO2 emissions. And as we move to an energy system without fossil fuel-related CO2 emissions, why would we care about energy use? There are a number of arguments, for why it is nevertheless important to keep on paying attention to energy efficiency improvement:

  • First of all, in all scenarios that lead to a drastic reduction of greenhouse gas emissions,  energy efficiency plays an important role. In fact, in most scenarios global energy use typically remains stable for the coming decades – mainly because of energy efficiency efforts.
  • Second, with a strong focus on energy efficiency, it is possible to reach a low-carbon energy system with much smaller resource use. In general, energy-efficient technologies are often less material-intensive than low-carbon supply technologies.
  • And finally,  and probably most important,  by using a combination of energy efficiency and low-carbon sources we can reduce greenhouse gas emissions much faster. And this is what we need: speed!

Renewable energy: wind and solar

I leave energy efficiency behind me and turn to renewables. I will first focus on solar and wind energy and then turn my attention to bio-energy. The progress in wind and solar energy can really be considered one of the success stories of the energy transition. Let me start sharing my own journey. Our first PV system in 1995 consisted of 2 small panels, each 100 W. A few years later, we moved and installed 500 W, which could still be simply plugged into a socket. We moved again, and in 2008 we installed 3 kW. A few years ago, we needed more electricity, for the heat pump and the car, and we added another 5 kW. This looks like rapid growth, but in the world, things went much faster.

Fifty years ago,  solar and wind energy were in an early stage of development. Around 1985, we started doing experiments on the Terschelling energy project with an installed capacity of 30 kW of solar energy and – ultimately – 80 kW of wind energy. That is very small according to current standards, but by then it was one of the largest solar energy systems in the world. The system could work both autonomously and grid-connected. And we learned a lot about the aging of PV panels, wind turbine, and batteries. I can assure you, the technology is much more durable nowadays!

But the application of solar and wind energy started growing. Despite this growth, in the year 2000, the contribution was still very limited: 0.2% of total power generation in the world. But it kept on growing and in the last decade we reached the stage in which the costs of wind and solar energy became comparable to the costs of conventional energy production. Over the past 10 years, solar electricity generation grew by a factor of 12, and wind energy generation grew by a factor of four. In the last year, solar and wind energy contributed 12% to global electricity generation, in the EU it is even 22% [x]. All this was achieved thanks to continuous technological progress. If we compare it to our Terschelling technology, for example, we have much more efficient solar cells and wind turbines that are 200 times as powerful.

Development of electricity generation [xi] based on solar and wind energy until 2000 (top) and until 2022 (bottom). Note that vertical scales are different.

In the IPCC report, we concluded that wind energy and solar energy were among the major options to reach greenhouse gas emission reductions in the short term. But it requires significantly faster growth. If solar and wind should contribute to reaching ambitious climate targets, the rate at which these technologies are deployed should be tripled: three times more per year should be installed until 2030 than we did in the past years. Such strong growth is unprecedented in the history of energy system transitions [xii].

If we look at the world as a whole, we observe continuously accelerating growth. But let’s have a look at the development in individual countries. These countries are among those that have the largest contribution of solar energy as a share of the total electricity generation. A number of things can be observed. At the level of individual countries, we do not see such nice growth pathways as we observed for the world as a whole. On the one hand, you see rapid scale-up, 15 years ago for Germany and Italy and recently for a variety of countries like Australia, Vietnam, and also the Netherlands. The good news is that in just a few years the share of solar energy in electricity generation can grow from virtually zero to 10% and more. But – on the other hand – you also see that developments can suddenly stop or get delayed.

Share of solar energy in total energy generation for selected countries with high shares of solar energy in 2021. Analysis based on the BP Statistical Review of World Energy, 2022.

We have policies that work, like feed-in tariffs and renewable energy tenders, which are in place in more than 100 countries worldwide. Initially, the financial burden played a role as a barrier, for example in Germany. But we should also be aware of other factors that delay the construction of more renewable energy capacity, like opposition by vested interests, lack of public acceptance, and limits to the capacity of the electricity grid. The important message is: don’t take the positive developments for granted – continuous efforts are needed to keep developments going.

But there is also some good news here. In energy systems analysis, so far, we have been focussing very much on the optimum systems, the system with the lowest costs – given a certain target, for example, zero CO2 emissions. Recent research shows that there are many variants that may not be exactly the lowest cost, but that come close [xiii]. My colleagues Stefan Pfenninger and Francesco Lombardi have shown that there are many ways to a climate-neutral Europe. For example, it can be achieved with a variety of grid configurations, as shown here. For those of you that play Ticket-to-Ride, this may look familiar. This is just an illustration. But it is also possible with different ratios of solar energy versus wind energy (for example 2/3 wind and 1/3 solar, or the other way around). It can be done with a variety of roles for battery storage, firm power, etc. So, my key takeaway from this study is: we don’t have to be that picky. Let’s build what we can, as fast as we can. We need speed.

Many different configurations of the European energy system can lead to a climate-neutrality. Taken from Pickering et al. (2022), reference [xiii].

Renewable energy: bio-energy

The world not only needs electricity but also fuels. In most global energy scenarios the share of electricity in final energy use will increase from less than 20% to 40 or 50% of final energy. But we also will need a lot of fuel and heat.

We have a variety of options to supply heat and fuels. To start with: the direct production of heat by solar or geothermal energy – and talking about the latter: so happy that exactly this week preparations will start for drilling the geothermal well that will supply heat to our campus and beyond.

For fuels, we have many options. Hydrogen will become important. And fossil fuels with carbon-capture-and-storage. But so far, the most important low-carbon source of heat and fuels is: bio-energy. Here, you see the development of bio-energy use over the past 50 years. Forgive me for the statistical hick-ups in the early period. We see increasing use of bio-energy in industry – mainly the bio-based industries, like food and paper; we see strong growth in bio-energy use for transport and electricity generation. Relative growth rates are much less than what we have observed for solar and wind energy. Still, the growth of bio-energy use – about 15 EJ – so far is contributing more to our energy system than solar and wind energy together.

Contibution of bio-energy to global final energy use (excluding traditional use of bio-energy). Based on data extracted from IEA World Energy Balances, release April 2023.

And there is substantial potential for further scaling up bio-energy. I want to pay special attention to what I call blending applications of bio-energy: mixing fractions of biofuels with fossil fuels.

  • Blending is very common for automotive applications. Every time you go to the petrol station – in case you still do that – you get a few liters of biofuels.
  • Another one is the injection of biomethane into the gas grid. The European Union has a concrete programme to rapidly expand the use of biomethane, to about 10% of natural gas use in 2030 [xiv]. The main sources for the production of biomethane are animal manure, agricultural residues, and sequential crops [xv]. Globally it is possible to increase the use of biomethane to over 20% of the use of natural gas [xvi].
  • And finally, I want to mention the co-firing of biomass with coal in power plants and industrial boilers. In Europe, the interest in co-firing is rapidly declining – simply because coal is rapidly phased out. But there are a number of countries in the world in which rapid phase-out of coal is more difficult: there is limited availability of natural gas and upscaling non-fossil alternatives just takes time. Such countries are China, India, and Indonesia.

Of course, if we consider bio-energy, sustainability is of utmost importance. Negative impacts need to stay limited. As much as possible residues should be used. Based on the current understanding it seems to be possible to rapidly increase the use of bio-energy to about two or three times the current level [xvii]. Blending applications do not require substantial adaptations to end-use equipment, so they probably can be more easily scaled up. They can also be considered as a transition option until other alternatives like electric transportation and the use of hydrogen have taken off substantially.

Countries with biofuel blending mandates. Adapted from Renewables 2022, Global Status Report, REN21.

How to realize all this? Biofuels are generally more expensive than their fossil fuel counterpart. One policy that stands out as very effective is biofuel blending mandates. Every supplier of fuel needs to have – on average – a certain percentage of biofuels in its products. Already 65 countries globally have such mandates. Such blending mandates could be expanded to also apply to natural gas and coal. The European Union will do this for the introduction of biomethane.

Bio-energy is – especially in the Netherlands – highly contested. But let it be clear – we also need the less popular options, if we really want to realize a rapid energy transition. The need for speed forces us.

Outlook

It’s time to sketch the overall outlook We have seen that over the past 50 years, there has been a lot of progress from the moment that energy efficiency and renewable energy were hardly on anyone’s agenda to the situation that there is a broad and global effort to scale up both elements of the sustainable energy transition. There have been tremendous successes in upscaling solar wind energy and improving the energy efficiency of many different types of appliances and other equipment. But there are also areas where we have seen less progress. And even in the areas that were successful, past results are never a guarantee for the future. A lot still needs to be done, let me make it very clear: the hardest part is still ahead of us. We need to do a lot up until 2030,  but also beyond that year, we need to continue. There will be new challenges in terms of system integration. New technologies, new processes, and new fuels will have to be introduced and applied. Think for example of floating wind turbines, e-fuels, high-temperature heat storage, ocean energy sources, advanced nuclear, etc., all technologies that we are working on at this university.

The final question is: can we be confident that the transition can be done? My answer is yes – at least to a large extent. Three reasons.

First of all,  we can build on the substantial progress that was already made in the past decades, progress in terms of the development and deployment of new technology.

The second reason to be optimistic has to do with a special feature of the Paris Agreement. It has taken long from the original Climate Agreement in 1992 to the Paris Agreement in 2015. But the latter one finally provides a solid basis for international policy making. One of the critical elements of the Paris Agreement is the so-called ratchet mechanism. The ratchet mechanism means that every five years countries need to come up with more and more ambitious targets to reduce greenhouse gas emissions. This mechanism really works. For the first time, countries came up with pledges in the run-up to the Paris Agreement. By then, it was calculated that all commitments together would bring us to a 2.7 °C temperature increase. The real test of the mechanism was in 2021 in Glasgow: and indeed, countries came up with more ambitious targets for 2030, which already brought us a step further. But many, including the United States, the European Union, and China also committed to zero greenhouse gas emissions or zero CO2 targets. Taking also these into account means that 2 °C may be within reach. Let it be clear that there is uncertainty around these numbers and policy implementation is lagging behind target setting. But overall, the indication is that – on average – countries live up to their promises.

Expected global average temperatures by the end of this century compared to pre-industrial levels, according to various pledges. Based on data from Climate Action Tracker [xviii].

The fact that 2 °C is within reach, also means that still work needs to be done to get beyond that. In the end, we want to be well below 2 °C and preferably at 1.5 °C. That becomes the big challenge in the coming years for international policymaking. But, as the IPCC concluded: every 10th of a degree matters,  if we don’t manage to reach 1.5 degrees then 1.6 or 1.7 is a lot better than 1.8 or 1.9 °C so it’s more than worth to keep on pursuing:  every 10th of a degree will limit human suffering and damage to ecosystems.

A third element that makes me hopeful is that climate action no longer is considered as something that is only the responsibility of nation-states. In this lecture, I have paid quite some attention to the role of governments and national policies. And let it be clear – their role is important.  But one of the important by-products of the Paris Agreement in 2015 was that others, like cities and companies, were also considered important players to reach climate targets. One of the initiatives that started then was the so-called Science-Based Targets initiative which challenges companies to reduce greenhouse gas emissions in line with what science requires to reach 1.5 °C or well below 2 °C. It is encouraging that nearly 5000 companies have already subscribed and want to go into that direction including over 100 of the world’s biggest companies. I have contributed to building this initiative in 2015 and I’m happy that I was recently appointed as chairman of its Technical Council. I look forward to helping build it further.

So let me conclude.

The energy transition is developing rapidly, but there is a need to further accelerate. We need speed. Energy efficiency and renewable energy need to be further deployed in an unprecedented way. But by doing so, we limit the unprecedented impacts of climate change.

Closing remarks

My formal appointment at Delft University of Technology is coming to an end now. I have dedicated my professional life to bringing forward the energy transition. I certainly remain active in this space but I’m so encouraged there are now so many thousands and thousands of professionals doing the same. We really need everyone.

Finally, there is nothing I can say but thank you. It was a great pleasure for me to work in the area of sustainable energy and especially here at Delft University of Technology. I have worked together in many ways with colleagues in all faculties and in most corporate departments. It is so inspiring to work with so many gifted and ambitious people. The interaction with many students was very rewarding. Thanks to the board of the university and the management team of the faculty of Technology Policy and Management (TPM) for the trust they have always given me.

Thanks also to my family who was always there. Thanks especially to my wife Hermien, with whom I share my life now for over 40 years and who was always there on this journey. Thanks for your love.

Finally, I want to mention our grandchildren: Benjamin, Fleur, Femke, Lotte, Marijne, Seb en Lena. Great that you are here today and thanks for your patience during this long story! You are the future generation and I see it as our task to keep this planet livable – for you – and for all children worldwide.

Ik heb gezegd.

[i] K. Blok: Onbeperkt Houdbaar (Unlimited Sustainability), Stichting Natuur en Milieu, Utrecht, The Netherlands, 1984.

[ii] IPCC, 2022: Summary for Policymakers. In: Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [P.R. Shukla, J. Skea, R. Slade, A. Al Khourdajie, R. van Diemen, D. McCollum, M. Pathak, S. Some, P. Vyas, R. Fradera, M. Belkacemi, A. Hasija, G. Lisboa, S. Luz, J. Malley, (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA. doi: 10.1017/9781009157926.001, Figure SPM.1a.

[iii] See reference [ii], Figure SPM.4a.

[iv] See reference [ii], Figure SPM.7 and Section C12.1.

[v] Energy Efficiency 2022, IEA, Paris, France, 2022.

[vi] Achievements of Energy Efficiency Appliance and Equipment Standards and Labelling Programmes, International Energy Agency, Paris, France, 2021.

[vii] Energy Efficiency 2022, IEA, Paris, France, 2022.

[viii] Energy Efficiency 2022, IEA, Paris, France, 2022.

[ix] A. Kamenders, R. Stivrins, G. Zogla: Minimum Energy Performance Standards for the Residential Sector, Riga Technical University/European Economic and Social Committee, 2022.

[x] M. Wyatros-Motyka, Global Electricity Review 2023, Ember, London Fields, UK, 2023.

[xi] Based on data from IEA World Energy Balances, release April 2023 (until 2020). Data for 2021 are based on the BP Statistical Review of World Energy 2022, data for 2022 were based on Wyatros-Motyka (2023), see reference [x].

[xii] A. Cherp, V. Vinichenko, J. Tosun, J.A. Gordon, J. Jewell: National growth dynamics of wind and solar power compared to the growth required for global climate targets, Nature Energy, 6(2021)742-754.

[xiii] B. Pickering, F. Lombardi, S. Pfenninger: Diversity of options to eliminate fossil fuels and reach carbon neutrality across the entire European energy system, Joule 6(2022)1253-1276.

See also: F. Neumann, T. Brown: The near-optimal feasible space of renewable power system model, Electric Power Systems Research, 190(2021)106690.

[xiv] The ambition is 35 billion m3. Source: RePowerEU Plan, Communication from the European Commission, COM(2022) 230 final, Brussels, 18 May 2022.

[xv] S. Alberici, W. Grimme and G. Toop: Biomethand production potentials in the EU, Gas for Climate/Guidehouse, 2022.

[xvi] Outlook for biogas and biomethane, International Energy Agency, Paris, France, 2020.

[xvii] For example, blending 20% in liquid automotive fuels, 10% in total natural gas use, 10% in industrial coal-fired boilers and 20% in coal-fired power plants would lead to total contribution of bio-energy in final energy use of 60 PJ, all based on fuel consumption in the Announced Pledges Scenario, World Energy Outlook 2022, IEA, 2022. This is on top of what is already assumed for industry in the Stated Policies Scenario, excluding any traditional bio-energy use.

[xviii] For references, see an earlier blog. The findings are confirmed in a recent paper: D.-J. van de Ven, S. Mittal, A. Gambhir, et al.: A multimodel analysis of post-Glasgow climate targets and feasibility challenges. Nat. Clim. Chang. 13, 570–578 (2023). https://doi.org/10.1038/s41558-023-01661-0.