Why ‘rebound effects’ may cut energy savings in half

Earth from space, showing clusters of electric lighting

This blog was originally published by Carbon Brief as a guest post from Dr Paul Brockway and Prof Steve Sorrell.

Improving the energy efficiency of everything from the lights in people’s homes to the cars they drive is a key component of global climate action.

Such efficiency gains, which are included in many influential computer models, can lower energy use and, therefore, make it easier to decarbonise the global economy. 

At the same time, they can improve quality of life, boost productivity, increase competitiveness and contribute to growing the economy.  

However, counterintuitively, gains in energy efficiency can also encourage behavioural change towards more energy use, meaning some of the anticipated energy savings may be “taken back”. This is known as the “rebound effect”.

In a new paper, published in Renewable and Sustainable Energy Reviews, we examine the economy-wide impact of these effects and find they may erode more than half of the potential energy savings from improved energy efficiency.

We also find that these rebound effects are not adequately included in the global energy and climate models used by organisations, such as the Intergovernmental Panel on Climate Change (IPCC) and the International Energy Agency (IEA), which means they may underestimate the future growth of global energy demand.

As a result, there is a risk that global climate action relies too heavily on energy savings that may not materialise.

Climate scenarios require unprecedented decoupling

Historically, GDP and energy use have been closely linked. Evidence suggests that energy demand typically increases as economies grow, while restricted access to energy can limit economic growth.

Between 1971 and 2015, global GDP rose by an annual average of 3.1% as global primary energy use rose by 2.1% each year. This is known as “relative decoupling”, where both variables increase but GDP increases faster than energy use. 

Organisations such as the IPCC use “integrated assessment models” (IAMs) to answer questions about climate change and changes in the future energy system. Similar models have been developed by the IEA and other organisations.

Most of these scenarios project little or no growth in global energy use over the next few decades, due to a combination of structural change, such as deindustrialisation and improved energy efficiency throughout the global economy.  

Several of these scenarios anticipate near-term “absolute decoupling”, where GDP rises while energy use falls. This is despite the need for large-scale investment in energy-intensive infrastructure and heavy industry in developing countries.  

This greater level of decoupling can be seen in the chart below, which shows GDP plotted against the world’s final energy demand – that is to say, the total energy consumed by end users. Energy demand falls in some of these scenarios while GDP increases, indicating absolute decoupling.

However, there is no historical precedent for absolute decoupling at the global level – and only limited experience at a national level. 

Historical trends and future scenarios for global final energy use and GDP from 1971 to 2050. Scenarios are divided into four groups: International Energy Agency models (orange), green 1.5C integrated assessment models (IAMs – green), 2C IAMs (purple) and other models (blue). SSPs are “shared socioeconomic pathways”, which are used by modellers to examine how global society, demographics and economics might change over the next century. The Shell 2018 Sky scenario sets a pathway to meet the “well-below 2C” goal of the Paris Agreement. Source: Brockway, P.E. et al. (2021).

Growing evidence of large rebound effects

A possible reason for the close links between energy use and GDP in the past is the presence of large “rebound effects” – a variety of economic shifts that offset some of the energy savings from improved energy efficiency.

For example, energy efficient lighting saves energy, but also makes lighting cheaper, which, in turn, encourages people to light up larger areas to higher levels over longer periods of time.  

Widespread adoption of energy-efficient lighting may also bring down the price of electricity, which could further encourage increased consumption.  

Another example, namely a more fuel-efficient car, is illustrated in the figure below, with examples of the direct and indirect pathways that can lead to increased energy use.

Illustration of rebound effects resulting from a more fuel-efficient car. Source: Sorrell, S. et al. (2018).

The economy-wide rebound effect is the net result of multiple adjustments of this type throughout a nation or the world. 

It is usually expressed as the percentage of the energy savings that would be achieved if none of those adjustments occurred. A 0% rebound means that all of the potential energy savings are achieved, while a 100% rebound means that all of these savings are “taken back”. 

Economy-wide rebound effects are extremely difficult to measure, but the evidence has grown substantially over the past decade. 

In our paper, we reviewed 21 studies that used ‘computable general equilibrium‘ (CGE) models to estimate the size of these effects from a variety of energy-efficiency improvements in different countries and sectors.  

These CGE model studies gave a mean estimate of 58% rebound, with a median estimate of 55%, implying that more than half of the potential energy savings from the modelled efficiency improvements were not achieved.  

We also surveyed 12 studies that used a variety of other methods to estimate economy-wide rebound effects and found a mean estimate of 71% rebound.  

In total, more than two-thirds of the studies found rebound effects larger than 50%. Six found rebound effects of 100% or more, implying that in some instances the energy savings may be eliminated altogether.

The studies varied widely in terms of methods used and types of improvement investigated, and their results were often sensitive to uncertain assumptions.  

Nevertheless, taken as a whole, they provide a consistent message of economy-wide rebound effects eroding more than half of the potential energy savings from improved energy efficiency.

Examining models

A key question is whether these rebound effects are properly factored into global energy models. 

To explore this, we examined four of the IAMs used by the IPCC, together with the models used by BPShell, the IEA and the US Energy Information Administration (EIA).  

We found that most of these models relied upon external assumptions for key variables and were unable to capture many of the mechanisms contributing to rebound effects. 

Two of the models (REMIND and MESSAGE-GLOBIOM) included more detailed modelling of the macro-economy, but did so in a simplified manner that left out important mechanisms such as changes in the relative size of different sectors.

Moreover, several of the models calibrated the magnitude of energy-efficiency improvements to an assumed outcome for energy consumption, rather than modelling the impact those improvements actually had on consumption. This precludes the investigation of rebound effects.  

We conclude that these models could result in global energy scenarios overestimating the potential for energy savings and underestimating future global energy demand.

Implications for climate action

We do not question the importance of improved energy efficiency, since it can deliver multiple economic benefits alongside real energy savings. 

However, we do have concerns about the current realism of key global climate scenarios.  

If efficiency-based energy savings are smaller than anticipated, the world may need to rely more heavily upon a low-carbon energy supply, carbon capture and storage and negative emission technologies to meet its climate goals. 

Energy sufficiency and economic degrowth are also strategies that could come more sharply into focus.   

Additionally, there is scope for using economy-wide carbon pricing to mitigate rebound effects and to increase energy savings, alongside spending the revenues on low-carbon investments.  

It may also be possible to target energy-efficiency policy at sectors and technologies that offer the potential for larger economic benefits alongside smaller rebounds.  

Most importantly, our research highlights the urgent need for the modelling community to take rebound effects more seriously, and to find ways of incorporating the full range of rebound mechanisms into their global energy models.  

Without this, the plausibility of global energy scenarios – and particularly those with absolute decoupling – is open to question.

This blog is based on the paper Energy efficiency and economy-wide rebound effects: A review of the evidence and its implications – Renewable and Sustainable Energy Reviews by Paul E.Brockway, Steve Sorrell, Gregor Semieniuk, Matthew Kuperus Heun and Victor Court.

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Introduction to Responsive Organising for Low Emission Societies (ROLES)

What is ROLES?

ROLES is exploring how European city-regions can accelerate and intensify decarbonisation, specifically looking at the role of digitalisation of energy infrastructure and focusing on pathways that also create social benefits (such as reducing fuel and transport poverty). The project is working in the UK, Italy and Norway, with case studies in all three countries. The project started in late 2020 and will run for three years.

ROLES will develop an analytical framework for creating pathways to achieve deep decarbonisation by digitalising energy systems. We will prioritise co-creation of these pathways with relevant stakeholders and explore the role of power dynamics in shaping them.

The analytical framework we produce will be applicable to any mid-sized European city-region. We will initially apply it in three case studies city regions, each focusing on a different sector/ context for digitalising energy infrastructure (e.g. smart meter, e-mobility). Results will be shared with a wide range of stakeholders, from civic leaders to bodies representing marginalised groups.

Project Update

The ROLES project is off to a good start despite the challenging pandemic circumstances. Our project involves locally rooted fieldwork across three countries – carrying out this in-depth empirical research currently presents some obvious problems. The project team met online in December for our kick-off meeting. Despite being a large group, we are a cohesive team, as country team members have worked closely together. See a photo from our kick-off meeting!

We will meet online once a month to exchange views and ensure coordinated activities across our three case study cities: Bergen (Norway), Brighton (UK) and Trento (Italy). During the second monthly meeting in January 2021 each team member picked a favourite text relevant to ROLES, giving the team a quick ‘brain dump’ of their takeaway from the text and how it could be useful for our project work. As a team with a vast range of experience and disciplinary competencies, this sort of exchange is an exciting and rewarding aspect of collaboration during ROLES.

With much of the administrative work necessary to set up the project complete, 2021 will see our research work starting to gain momentum. Team Norway had a head-start through their work on JUSTMOB (just mobility transitions) during the autumn semester of 2020, which provides a foundation for further data collection and consolidation during ROLES. See a video recording of a public seminar on just mobility transitions in Bergen.

Disseminating Our Work

An exciting event relevant to ROLES is coming up in August 2021 – a biannual workshop of the Energy Anthropology Network on the theme ‘digitisation and low-carbon energy transitions’. Siddharth Sareen, the ROLES Principal Investigator, is co-convening this workshop along with Katja Müller. The shortlisted abstracts that have been invited for discussion as workshop papers are expected to be published as an edited volume.

One of ROLES’ first public dissemination activities is coming up in February 2021 at the Literature Festival Bergen. A reflexive, data-driven and interactive event is coming up as part of the National SDG 3 Conference Day Zero co-creation workshop on just urban mobility transitions on 10th February 2021. During 10th-12th February 2021, we will introduce the project at the 5th Energy and Society Conference in Trento (online), and discuss the design of participation processes.

Sign up to the ROLES newsletter for future updates and upcoming events!

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CREDS update: The energy use impacts of 5G mobile networks

Find out more about our ongoing CREDS project, seeking to understand the emission impacts from the imminent rollout of 5G mobile networks.

Whilst 5G is primarily associated with super-fast download speeds, an important part of the purpose of 5G is to increase the energy efficiency of mobile networks. Mobile data traffic is expected to rise sharply in the coming decade, driven in particular by the use of energy-intensive services such as video streaming. As such, the challenge for mobile network operators is to extend network capacity to satisfy such demand whilst ensuring their networks remain economically and environmentally sustainable. This challenge has given rise to a burgeoning literature on green mobile networks which assesses the feasibility and energy saving potential of a range of technologies. Furthermore, over the longer term, 5G is expected to enable a range of use cases with energy use implications across various sectors, including the automotive, manufacturing and energy sectors.  

The CREDS project ‘The energy use impacts of 5G mobile network technology’ is reviewing the evidence on 5G’s expected impact on energy use, including the direct impacts of the production and use of mobile network infrastructure, potential rebound effects associated with changes in user behaviour encouraged by 5G, and the impacts of 5G as a platform for a range of use cases in various sectors of the economy. This will be supplemented by an analysis of how the promise of green mobile networks is established as credible (or not) through the discourse of key stakeholder groups.  

The project is currently part way through the review of the energy use impacts of 5G networks. Whilst a number of promising technological options have been identified and assessed in the green mobile networks literature (e.g. putting parts of the network to sleep during low traffic hours is a particularly promising approach), our emerging results suggest that there have so far been relatively few studies that model the whole-network energy use impacts of 5G. We also note that relatively little attention has so far been paid to the embodied energy use associated with the large-scale addition or replacement of network infrastructure, the potential for rebound effects associated with changes in user behaviour encouraged by 5G, and demand-side management. 

Over the next few months the project will hope to provide a clearer picture of the estimated energy saving potential of 5G, the key sociotechnical factors that determine the scope for energy saving, and the key policy challenges associated with achieving this potential. Additionally, the discourse analysis will provide an understanding of how the promise of green 5G is established as credible (or not), the assumptions and exclusions underpinning this promise (e.g. is discouraging energy-intensive consumer behaviour considered or overlooked?), and whether its credibility is challenged. 

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Parents, preeners, pets and pipes: what motivates heating decisions?

Home heating is essential through any blustery British winter, especially as Covid-19 restrictions confine us to our own living spaces and deepen our appreciation of home comforts. Accounting for 37% of the UK’s greenhouse gas emissions, the heating sector also forms a large part of the national decarbonisation puzzle.

A new research paper involving Sussex Energy Group researchers, Humanizing heat as a service: Cost, creature comforts and the diversity of smart heating practices in the United Kingdom, looks at why people heat their homes the way they do, and the underlying patterns behind personal heating preferences and practices. This blog explains some of the paper’s findings exploring the breadth of motivations to heating decisions, the many needs heat meets, and how its application isn’t always exclusively for the benefit of human residents.

Introducing energy phenomenology

‘Energy phenomenology’ is the paper’s proposed means of understanding people’s heating choices. It combines the lived experience approach with energy biographies to form a framework for understanding how experiences, practices and identities shape energy services and consumption.

The lived experience approach studies individual’s unique human actions and behaviour along with the subjective meanings associated with life events. It describes emotions and non-rational elements of behaviour not captured by many other modes of inquiry, including stated preference techniques.

Energy biographies interrogate how energy use expresses shared practices and attaches meaning to everyday behaviours which can often be taken for granted.

The paper combines both approaches to form “the energy phenomenology framework”.

Identity shapes heating use. Seeing yourself as an environmentalist or consumerist, a parent or a child, wealthy or poor, will influence energy consumption.  These identities and their associated values and priorities with domestic niceties like a warm home, a clean bathroom, a comfortable living room, or a convenient way of doing a chore will shape consumption.  “Historically shared practices, routines, habits, and norms can fuse together with infrastructure such as appliances, gas boilers, or buildings to lead to socio-material attachment. Heat practices are also dynamic and temporally complex, altering and changing across life events and stages, a process we term lifestyle changes.”

Parenting, preening, pets and pipes: what motivates heating decisions?

Researchers applied the energy phenomenology framework to experiential data gathered through the Energy Systems Catapult’s Living Lab, which provided 100 homes across Birmingham, Bridgend, Manchester and Newcastle with smart heating and digitally operable zonal heating controls.

Data collected through interviews and diaries produced hundreds of pages of qualitative data, within which researchers identified seven distinct themes recurring in participants’ energy usage.

Fig. 1: The seven phenomenological uses of smart heating controls and diversity of heating practices.

One of the most prominent themes is heat’s versatile application to provide care and compassion through adjusting a thermostat. Residents used heating to anticipate children’s discomfort, soothe arthritic joints, and relieve symptoms of illnesses or their treatments. This application of care is often extended to non-human household members, with residents recording how they would leave heating on for pets, and even houseplants, when leaving their homes otherwise empty.

Once the wellbeing and comfort of the inhabitants had been assured, residents often applied heat to the needs of the building that house them. Several households explained how their use of smart heat intended to prevent structural damp and protect pipework from the possibility of freezing.

“It’s important to keep the building warm, you know? We haven’t got damp and one of the reasons is presumably because we’ve got the heating on.”

Social signalling can also be an element behind heating decisions, projecting comfort and hospitality. What host could pass up the opportunity to bask in the approval of their well-toasted guests, as well as the warmth of their hardworking boiler?

“I want a home that is warm, comfortable, family friendly, and homely. That’s what heat is for.”

Identity, needs, attachment and transition – what lies behind heating motivations?

How can the functional uses of heating, as used by the Living Lab’s residents, be placed within the energy phenomenology of smart heat? The paper puts forward four influences behind the motivations for heating decisions.

Fig. 2. Identity, needs, attachment and transition in the energy phenomenology of smart heating controls and practices.

Individual identity. Heat controls provide an outlet for the roles an individual assumes. Heating practices help to communicate that sense of being a nurturing parent or caregiver, or conscientious homeowner. They can even replicate rituals from childhood, with one resident keen to provide their son with heated pyjamas despite his equally heated opposition.

“I used to like it when I was little, so I have passed it along to him. Sometimes he whines, and says, ‘It’s too hot, it’s too hot,’ but it’s better than having a cold pair of pyjamas, isn’t it, really?”.

Parental identities are strong influences on heating decisions

Experiential preferences and needs. The diary entries reveal how many needs can be met through the calibration of a virtual thermostat. The paper’s most memorable example comes in the unexpected form of a cat’s birthday party, where the host’s pet-loving instincts combine with social signalling and expressions of care for elderly houseguests.

“When people come over, we want to make sure the house is warm. Especially if there is something special going on, like it being the cat’s birthday or something crazy like that. We just have a party for anything. Any excuse for a party. So when I am roasting a dinner on a Sunday or something, and then we had an excuse for a cake and stuff, people will come over. And some of our friends are old, or disabled, so we need to keep it always really warm for them.”

Socio-material attachment. Domestic habits are often shaped by a mix of personal behaviours and  ingrained behaviours formed in response to an inhabitant’s surrounding infrastructure. Smart heating proved to be no exception to this. Several residents used smart heating controls to indulge a fond concept of the bathroom as “a special room” for self-confessed extravagance. Some residents use their controls to give it “an extra boost” before use, with one even leaving theirs perpetually heated. These attachments can be more sustainable (e.g. letting rooms cool before sleeping) or less sustainable (e.g. always keeping the bathroom warm). Either way, but they are a considerable factor in heating usage.

Lifestyle changes. Heating needs and experiences shift over time and as lifestyles change. Hallmarks of adult life, such as hosting guests and raising children, can give way to managing long-term illnesses and increasing sensitivity to temperatures with age. These shifts demonstrate the changing nature of heat and offer promising opportunities for predicting and improving heat management.

Humanising heat research and policy

What does energy phenomenology’s perspective of these themes and motivations mean for how we understand heating use? This research highlights that “for occupants, heating preferences must be discovered through a process of learning, engagement and living, rather than existing as something innate or predetermined, or known in advance”. Heating users may not recognise their own heating preferences and expectations without the degree of immersive involvement facilitated by initiatives like the Living Lab.

This means stated preferences, as often derived from surveys and similar research tools, acquire only an insufficient understanding of the topic. Instead, revealed preferences can allow policymakers and planners to account for the diversity, irrationality and unpredictability of heating practices shown in the study.

The paper contrasts the arguably more successful efforts to decarbonise transport, with policy approaches to decarbonise heating. Policy developments in heat have encouraged increased efficiency and encouraged the adoption of low carbon heating systems. However, with this and other studies clearly illustrating the value of heat for a multitude of other purposes, the industry could learn from carmakers’ talent for meeting consumer needs along a range of price points. Luxury home comfort items meeting similar needs, like electric powered “fire”places, have become increasingly popular. These products point to an untapped potential to capture some of the glamour and momentum of carmakers like Tesla, the principles behind their success selling a vision of “luxurious forms of electric mobility” applied to the mundane world of boilers and radiators.

Whether it’s warming pyjamas, impressing guests, comforting the elderly or bathing in extravagantly humid bathrooms, heat and its human (and often humane) application reflect the diversity of human experience and identity. Researchers, policymakers, planners and even smart heat technologists can benefit from greater insights into how these easily overlooked factors work for and against decarbonisation objectives.

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Climate strikes back: anatomy of protesters in six cities

Climate strikes protestors, one holding a board that reads Reduce Reduce Reduce

This post was originally published in The Beam. The Beam is a tri-annual printed publication covering the energy transition and the race to a zero carbon economy.

In August 2018, Swedish teenager Greta Thunberg started to strike from school on Fridays to protest against a lack of action on the climate crisis. Her actions made her the most famous teenager on the planet and sparked a historically large youth movement, leading to a series of school strikes across the world.

Over the course of one week in September 2019, striking school children, students and other grassroots movements such as Extinction Rebellion called for everyone to participate in a Global Climate Strike which was attended by more than 7 million people.

At the time, there was a genuine sense of a historic and decisive global shift on the issue of climate change. This momentum sadly has stalled with the arrival of COVID-19 just a few months later.

But the threat of the climate crisis has not disappeared just because it has disappeared from the front pages of newspapers. The world will need all the energy and determination of the Climate Strike movement to avert the impending global man-made catastrophe.

With colleagues at Southern Connecticut State University, University of Bergen, Imperial College London and The Foote School, I conducted the first global academic study into the global strikes to better understand the motivations of those taking part.

Conducting interviews with Climate Strike protesters in London and Brighton and Hove (UK), Montreal (Canada), New Haven and New York (USA) and Stavanger (Norway), we aimed to learn more about participants’ knowledge, emotions, motivations and actions in relation to climate change, including any lifestyle changes they have undertaken.

Our results indicate that – while protesters predominantly had negative feelings such as fear, anxiety and despair at the impacts of the climate crisis – responses to address climate change and collective action provided protesters also with hope for the future.

Interestingly strikers from North American cities were more likely to identify that they were “terrified” or felt “threatened” about the prospects of climate change, whereas British strikers were more likely to indicate that they were “hopeful” about taking action.

The lack of action from governments on the issue was a motivating factor for many climate strikers and this motivation was particularly prominent for US participants. This may indicate that the lack of policies, along with the climate denial of the Trump administration, helped grow a stronger climate activist movement in the US over the past four years.

Concern for the planet, the environment and climate was the most frequently mentioned motivation behind strikers participating. Wanting to influence public opinion and policy was the second most mentioned motivation and was especially prevalent in the UK city of Brighton and Hove, which also has a strong history of environmental and political protest.

Being part of a protest movement was important to many, while for others their motivation was less values-driven and more focused on taking part in something novel or impressing their peers.

The slight majority of respondents said that they knew quite a lot about climate change, but almost an equal number said that they only knew a little bit. In terms of information sources, the most important were the protesters’ own background or job and reports produced by scientists, indicating potentially a high level of education and access to information amongst protesters.

Respondents also mentioned newspapers and TV as information sources, but many were sceptical about the reliability of media coverage concerning climate change. Other sources of information included the social movement itself and what Greta Thunberg was saying on climate change.

Encouragingly, just under half of the protesters said it was their first form of climate action.

Equally encouragingly, our study indicated that climate strikers backed up their words with action in their own lives. Almost all of them (95%) said they were personally undertaking lifestyle changes to try and limit their own personal impact on climate change.

The most common personal responses to climate change were changes to modes of transport. These included reduced flying or giving up air travel altogether or swapping cars for bicycles or public transport. People had also changed their diets, reducing meat consumption and sometimes adopting a vegetarian or a vegan diet.

North American climate strikers were most likely to indicate an ambition to reduce personal car use or resort to public transport, despite the high reliance on private car ownership and poor public transport infrastructural investment in their countries. The fact that our interviewees lived in cities with relatively respectable public transport networks in place probably indicates this might not be a nationwide ambition. British and Norwegian respondents were most likely to have aimed to reduce their flying.

Increasing recycling and reusing, while reducing consumption in general, were also common steps. Some changes in the home, like adopting sustainable energy systems or switching to renewable energy suppliers or starting composting, also featured.

One of the most radical changes they were prepared to make was changing their working patterns, either by reducing working hours or undertaking more volunteer work. This, however, is not accessible to everyone, especially those who may be on a low income.

While many of the protesters were already taking action or were keen to make lifestyle changes, there were also many who found that structural and systemic factors were limiting their ability to bring about meaningful and major changes.

From our study, it seems clear that climate strikers are not confined to a particular type of person which might be at odds with their depiction by some in the media. Rather, there is a large spectrum in terms of how equipped people are in terms of knowledge about climate change, what emotions they feel about the climate crisis, what motivates them to take action and what types of action they have taken, are currently taking, or are considering to take.

Among the ranks of climate strikers, there is a great understanding of the enormity of the challenge, great passion to do what is right for the planet and future generations, and great commitment to take the necessary action in their own lives. All of that will be needed in even greater measures now if the movement is to regain the momentum post-2020 and convince those in power of the necessity to deliver meaningful change.

This blog is based on the article Contextualizing climate justice activism: Knowledge, emotions, motivations, and actions among climate strikers in six cities – Mari Martiskainen, Stephen Axon, Benjamin K. Sovacool, Siddharth Sareen, Dylan Furszyfer Del Rio, Kayleigh Axon, Global Environmental Change.

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