By Anders Arvesen, industrial ecology researcher and (occasional) blogger

Your wood-burning stove causes more climate warming than you might think

By on 26. February 2018 in Ukategorisert with 0 Comments

But fortunately, your wood stove causes more climate cooling than you might think too! Our new study published in Nature’s Scientific Reports sheds light on the many ways in which residential wood combustion in Norway affects climate.

The wood stove in my dwelling. Norwegians love their firewood and wood stoves. Out of 2.5 million dwellings in Norway, 1.2 million use firewood for heating. (Norwegian “kosefyring” translates roughly into “firing with wood for the purpose of relaxation and pleasure”.)

So, I’ve stated that burning firewood causes both more climate warming and cooling than you might think. Several questions then beg to be answered: How is the warming brought about? How is the cooling brought about? And if we subtract the cooling from the warming, what is the net effect? And might this net effect be more significant than you think?

I’ll address these questions but, before entering into specifics, let me introduce the two fundamental and general ways in which humans affect the climate.

How humans affect the climate

Fundamentally, humans today cause climate impacts in two ways:

A) By changing the amount of incoming solar radiation that is reflected back to space

B) By changing the amount of outgoing thermal radiation emitted from the Earth to space

The most well-known way that humans change climate is via emissions of carbon dioxide (CO2), a so-called greenhouse gas. In the atmosphere, CO2 absorbs thermal radiation, thus reducing the amount of radiation the Earth can emit to space. The same is true for other greenhouse gases, such as water vapour and methane, but the magnitude and duration of the effects vary from one gas to another. The greenhouse effect falls under category B.

Now we need an example for category A. Since the example for category B was related to emissions, let’s use a different example for category A.

Consider this picture of a forest:

A forest and a forest trail. Photo from

As you can see, the trees appear dark (dark green). This is because the trees mostly absorb, rather than reflect, sunlight (green parts of light are reflected though, which is why the trees appear green and not black).

The snow-covered forest trail in the picture, on the other hand, appears bright. This is because snow mostly reflects, rather than absorbs, light.

We can assume that humans have cleared the trees and vegetation to create the forest trail. Consequently, a smaller fraction of the surface is dark (dark green) and a greater fraction is bright; and less energy from sunlight is absorbed and more sunlight is reflected back to space. Reflecting the sunlight back means it doesn’t heat the Earth and the end result is climate cooling – and there we have our example of a category A effect.

Next, let’s turn our attention to the climate effects associated with wood-fired heating stoves, keeping the above categories A and B in mind.

How wood stoves affect the climate

Here are four notable types of climate effects caused by Norwegian residential wood burning:

Number 1:  the greenhouse effect connected to CO2 and other heat-trapping gases. Contrary to popular belief, CO2 from burning renewable biomass such as wood can contribute to climate warming. Trees – being renewable – will reabsorb the CO2, but because they need time to do so, there can be a temporary warming effect. Although different to that of fossil CO2 (because fossil fuel stocks do not regrow), there is still an effect.

In addition to CO2, wood stoves emit the greenhouse gases methane (CH4) and nitrous oxide (N2O). Stoves also emit carbon monoxide (CO) and non-methane hydrocarbons (NMVOC), precursors to ozone (O3), another greenhouse gas. We recall that the greenhouse effect (irrespective of whether it is from CO2, CH4, N2O and O3) is a category B effect.

Number 2:  harvesting wood from forests typically leads to an increase in how much sunlight is reflected from the Earth surface, and hence climate cooling, in the same way as described in our forest trail example earlier. This is the category A principle.

Number 3: wood stoves emit tiny particles called black carbon. Black carbon gets its name because it absorbs visible light (hence “black”) and is pure carbon. By absorbing sunlight, black carbon in the air exerts a climate warming effect belonging to our category A. But there is more to black carbon: when it’s deposited on snow, the snow becomes darker and loses some of its ability to reflect sunlight – another category A warming effect. Additionally, black carbon interacts with clouds and thereby influences the climate system in complex ways.

Number 4: black carbon has a sibling, called organic carbon. Opposite to sunlight-absorbing black carbon, organic carbon particles in air scatter sunlight back to space. In other words, organic carbon results in a climate cooling effect, one belonging to category A.

Estimating the climate effects of wood stoves

The figure below shows estimated climate effects associated with residential wood stoves in Norway in 2010. I’ll say more about the figure itself, but first a quick word on the comprehensive analysis underpinning it: Key elements of the analysis include an original set of emission factors for different classes of wood stoves, a mapping of wood harvest, supply and wood-stove burning activities, and a unique set of global warming potential (GWP) values. Our study combines these elements in order to analyse climate impacts of firewood burning on a national scale. GWP is just one measure that can be employed in order to study climate effects of different climate-altering pollutants and activities by one common unit, CO2-equivalents (CO2e). In our study, we use GWP evaluated on a time horizon of 100 years (GWP100), as GWP100 has been the metric of choice within climate policy to date.

Annual climate impacts of wood stove bioenergy in Norway. Based on results from Arvesen et al. (2018).

As you can see from the figure, the climate warming effects of black carbon amount to 1.6 billion tonnes (Mt) CO2e, which makes black carbon the single most important cause of climate warming impacts in our analysis. Another major cause of warming is CO2 from biomass, contributing roughly half the amount of warming as black carbon, while CH4, N2O and fossil CO2 from supply chain activities together contribute roghly half the amount of warming as CO2 from biomass. Considering all climate alterations, combined warming amounts to 3.1 Mt CO2e.

Is 3.1 Mt CO2e a lot? To get a sense of the magnitude of this number, consider that Norway’s current total emissions of fossil CO2  – that is, from industry, transport and all other sources – amount to 45 Mt CO2. Also, bear in mind Norway’s pledge under the Paris agreement to reduce greenhouse gas emissions substantially (40% by 2030). Given that perspective, I would say 3.1 Mt CO2e is quite a lot.

Fortunately, as the figure shows, land surface changes and organic carbon come to the rescue by bringing about considerable climate cooling effects. More precisely, we estimate combined cooling effects of 1.7 Mt CO2e. In other words, combined cooling offsets more than half of the combined warming effects of wood stoves.

Where does that leave us in terms of the net (warming minus cooling) effect? The answer is 3.1 – 1.7 = 1.4 Mt CO2e, corresponding to 3% of Norway’s total emissions of fossil CO2. Is that more or less than you thought?

A complex picture

Finally, our findings display a complex picture, and are subject to large uncertainty. For example, how you operate the stove has an effect, as does where you harvest the firewood from. Additional results that reveal these and further complexities can be found in our paper – which might be a more interesting read than you might think?


Full article citation:

Arvesen, A. Cherubini, F., del Alamo Serrano, G., Astrup, R., Becidan, M., Belbo, H., Goile, F., Grytli, T., Guest, G., Lausselet, C., Rørstad, P.-K., Rydså, L., Seljeskog, M., Skreiberg, Ø., Vezhapparambu, S., Strømman, A.H. 2018. Cooling aerosols and changes in albedo counteract warming from CO2 and black carbon from forest bioenergy in Norway. Scientific Reports. DOI: 10.1038/s41598-018-21559-8.


The research was a collaboration between the Norwegian University of Science and Technology (NTNU), SINTEF Energy Research, Norwegian Institute of Bioeconomy Research (NIBIO), Norwegian University of Life Sciences (NMBU). It was funded by the Research Council of Norway through the Bioenergy Innovation Centre (CenBio).


An industrial ecology perspective on climate change mitigation models

By on 22. November 2017 in Ukategorisert with 0 Comments

Figure source: IPCC AR5 WGIII. Available from:

The above IPCC figure depicts possible future trends in greenhouse gas emissions. Underpinning this display is a set of well over a thousand scenarios. The range reflects different technological and economic trajectories, in addition to uncertainties. If we want to limit warming to no more than 2 ℃, we should look at the ‘RCP2.6’ path. How did the climate analysts produce this large collection of future outlooks? Not with crystal balls, but with an army of computer models. Or, somewhat more precisely, integrated assessment models. In a recent article, lead-authored by Stefan Pauliuk, we review these models from the perspective of our field, industrial ecology.

Integrated assessment models (IAMs) are widely used to explore strategies for halting climate change. The models mimic human decision and mechanisms in natural systems over long time-scales. They operate by selecting or substituting alternatives – this can be natural resource alternatives or technology alternatives – so that costs are minimized, while respecting constraints, such as limited emission budgets. Among numerous applications, IAMs have been used to explore which fossil fuel reserves need to remain unexploited in a 2 ℃ future, to study the potential role of natural gas as a “bridge fuel” during a shift to a low-carbon society, and to compare energy system transformations in 2 ℃ or 1.5 ℃ futures.

In industrial ecology, on the other hand, we study how energy and matter flow through society, how they are transformed or used in a network of industrial processes to satisfy human needs and desires, and how the natural environment is affected as a result. Key industrial ecology methods include material flow analysis (MFA), environmental input-output analysis (IOA) and environmental life cycle assessment (LCA). Some examples of applications of industrial ecology methods are: to analyse emissions associated with products and services consumed by households; to investigate resource use, emissions and wastes associated with developing and operating material stocks in the future; to study increased material efficiency (that is, to use less materials to deliver a given service) as a strategy to reduce emissions; and to analyse environmental impacts associated with future electricity supply.

Common interests

The IAM and industrial ecology fields are both concerned with understanding industrial systems. Such systems help to create goods and services that humans utilize. They also create emissions and waste.

Looking into the future in order to evaluate possible strategies for sustainable development is, in a way, the heart of what IAMs do. Looking into the future is also at the core of what dynamic MFA is about, and is a growing trend in IOA and LCA. Furthermore, there is a shared ambition to address various types of environmental concerns, including greenhouse gas emissions, air pollution and water and land use.

Distinct approaches

Despite their common interests, each modelling approach has distinct differences. IAMs are strong at representing the dynamics that shape evolutions in human and natural systems. They are cost-led and parsimonious, weighing the costs of alternative means to an end in order to identify lowest-cost solutions. However, with few exceptions, IAMs lack explicit descriptions of physical linkages related to capital stocks and materials. This includes relationships between capital stocks and the materials you need to build the stocks, between the stocks/materials and emissions associated with producing them, and the factors that govern material cycles.

On the other hand, industrial ecology methods are less comprehensive in scope (and you could also say less integrated) than the IAMs. They focus their attention on specific types of linkages in industrial or ecological systems (as indicated in Figure 2 in our article), and often on specific products (LCA) or materials (MFA). Dynamic MFA is the only industrial ecology method that can generate scenarios itself; scenario-based LCAs and IOAs rely on exogenous scenarios as data inputs.

Potentials for interaction

Potential synergies between the two approaches exist. We believe that IAMs can generate more robust and credible emissions mitigation scenarios by adding industrial ecology linkages related to capital stocks and materials. We argue that, one the one hand, this can open the door for widening the set of potential mitigation solutions in the models, because material efficiency solutions – such as recycling, lifetime extensions, or using lightweight materials – can be added. On the other hand, it can introduce constrained availability of scrap for recycling as a new impediment to mitigation. In both cases where new solutions or obstacles come into play, model outcomes may become more realistic and useful for decision-making.

Industrial ecology can make use of IAM scenarios to improve its capability to analyse future change. One way to do this is to apply industrial ecology methods to analyse IAM scenarios; another way is to integrating IAM scenario data into industrial ecology core databases. IAMs provide insights into cost-minimizing strategies – a major concern of policy makers – something that industrial ecology does not offer frequently.

Environmental impact assessment methods developed for LCA have a potential to broaden the range of impact types considered in IAMs, while IAMs can be used to capture cross-sectoral interactions that matter for environmental impacts, such as between food and bioenergy production. Further discussions of potentials for interaction and improvement are available in our article.

In summary, IAM and industrial ecology share several important common interests, but employ entirely different approaches to achieve them. In our article, we call for more interaction between the integrated assessment and industrial ecology communities to the benefit of sustainability science as a whole.

Full article citation: Pauliuk, S., Arvesen, A., Stadler, K., Hertwich, E.G., 2017. Industrial ecology in integrated assessment models. Nature Climate Change 7, 13-20.

Read-only free version:

Grønne energivalg: Vindkraft under lupen [blog post in Norwegian]

By on 14. November 2017 in Ukategorisert with 0 Comments

En rapport fra FNs Ressurspanel evaluerer miljøbelastningene ved å produsere elektrisitet fra ulike energikilder. Jeg er medredaktør av rapporten og hovedforfatter av kapittelet om vindkraft. I denne kronikken, tidligere publisert på Naturpress, deler jeg noe av innsikten som rapporten gir, pluss egne refleksjoner på miljøaspekter ved vindkraft.

Vindturbiner drives av energi hentet fra luft i bevegelse – altså vind. I grunnleggende kontrast til uttømmende energilagre av fossil olje og gass, er vind en fornybar energiflyt. Og enda viktigere: den er tilgjengelig i rikelige mengder rundt om på kloden. Likevel er ikke vindkraft fri for effekter på miljøet.

Ressurspanelets tilnærming

Rapporten fra Ressurspanelet gjør omfattende livsløpsanalyser for å kvantifisere en rekke typer miljøpåvirkninger, inkludert klimaendringer, miljøgifter og luftforurensing. Livsløpsanalyser er analyser som tar hensyn til miljøpåvirkninger som skjer under hele livsløpet (bygging, drift og avfallshåndtering) og hele verdikjeder (for eksempel hele kjeden fra utvinning av materialer til produksjon av sluttkomponenter).

Samtidig vurderte Ressurspanelet det slik at enkelte typer miljøpåvirkninger i praksis ikke lar seg kvantifisere (måle), ettersom det ikke finnes alminnelig aksepterte målemetoder. I slike tilfeller gir rapporten kvalitative drøftinger av miljøpåvirkningene. Eksempler på ikke-målbare effekter av vindkraft inkluderer fugledødelighet og visuelle inntrykk på landskapet.

Stort potensial for å redusere forurensing

I et livsløpsperspektiv står vindkraft bak skadelige utslipp, som alle andre former for kraftproduksjon. Men hvor betydelige er utslippene? Og hvordan ser utslippsregnskapet ut for vindkraft vis-à-vis kraft fra fossile brensler? Her er svarene sammensatte, men ett resultat er uansett slående: Vindkraft oppviser glimrende resultater når det gjelder alle typer forurensningsrelaterte miljøbelastninger. Her utkonkurrerer vind den globale elektrisitetsmiksen i størrelsesorden en til to ganger.

Dette går fram av figuren over som viser en sammenlikning av de målbare miljøbelastningene forbundet med forskjellige kraftproduksjonsteknologier. For eksempel ser man at utslipp av drivhusgasser fra vindkraft bare utgjør 2 % av det man får fra gjennomsnittlig global elektrisitet. Likedan utgjør skadene fra vindkraft på menneskelig helse og økosystemer (grunnet luftforurensing eller forurensing av jord og vann) bare 4-5 prosent av det man får fra global elektrisitet. Vindkraft krever mer stål og sement enn en del andre teknologier, men kommer altså likevel ut som en miljøvinner når vi ser på utslippsrelaterte miljøbelastninger.

Dødelighet blant fugler og flaggermus

Prøv å google ordene «wind turbine» og «birds», og du blir fortalt at vindturbiner er en alvorlig trussel mot fugler. Eller du blir fortalt at det er en myte at vindturbiner utgjør en betydelig trussel mot fugler. Det avhenger av hvilken nettside du klikker på.

Det er sikkert mange årsaker til at oppfatningene om vindturbiner og fugledød er så ulike. Det er likevel klart at én forklaring ligger i at mens noen ser på det totale antallet fugler som er drept av vindturbiner og sammenlikner det med tallet på de som blir drept av bygninger, strømkabler og katter, fokuserer andre på effekten på lokale fuglebestander. I det første tilfellet tenderer man til å sette vindkraft i et gunstigere lys, fordi – og det er sant – blant alle mulige kilder til fugledød utgjør vindkraft bare en liten del. I det andre perspektivet kommer vindkraft mindre fordelaktig ut, fordi – og det stemmer også – vindparker kan skade lokale fuglebestander som er små eller sårbare, eller som er (ekstra) verdsatt av mennesker. Vindturbiner er tilbøyelige til å drepe andre typer fugler (ørner, for eksempel) enn bygninger (eksempelvis sangfugler).

Det finnes tiltak som reduserer risikoen for fuglekollisjoner, og det er oppmuntrende. Varsom arealplanlegging og optimal plassering av vindparker kan redusere negative effekter på fuglelivet.

Ikke å forglemme, det finnes også en annen (og veldig annerledes) type flyvende dyr, flaggermus. Av grunner man ikke helt forstår ser det ut som noen flaggermusarter tiltrekkes av vindmøller – og utsetter seg dermed for økt risiko for å bli skadet eller drept av roterende vingeblader. I noen regioner er man bekymret for at vindturbiner har blitt eller er i ferd med å bli en alvorlig dødstrussel for flaggermus.


Hvor stort areal legger en vindpark beslag på? Også her er oppfatningene svært delte. For ressurspanelrapporten valgte vi bare å telle opp områdene som rent faktisk okkuperes av vindmøllene og disses fundamenter, samt tilførselsveier. Hovedgrunnen til dette valget er at rommet mellom turbinene kan brukes av mennesker til andre formål, eller av landbasert dyre- og planteliv. En vindpark kan, med noen begrensninger, sameksistere med jorddyrking, beitende dyr eller dyrevilt. Det samme kan ikke sies om arealer brukt til kullgruver eller dyrking av vekster til bioenergi.

Gitt utgangspunktet som ble tatt i rapporten, er den livsløpsbaserte arealbruken knyttet til vindkraft svært liten sammenliknet med konkurrerende teknologier, som figuren viser. Samtidig, og det blir drøftet i rapporten, kan man se et mye større område som påvirket, særlig fordi vindturbiner er høye strukturer og kan være visuelt dominerende i landskap. Bekymringer om forringing av naturskjønne omgivelser kan være legitime, og bør ikke avvises som et “ikke-i-min-bakgård“-problem.

Utfasing av fossil kraft er en forutsetning for utslippsreduksjoner

Livsløpsanalyser og annen litteratur gjør ofte den antakelsen – tydelig eller underforstått – at én enhet vindkraft levert betyr én enhet fossilbasert kraft unngått. For meg er ikke det opplagt riktig, eller rimelig.

Foreløpig er jeg ikke i stand til å se grunnlag for en a priori antakelse om at vindkraft automatisk erstatter fossilkraft én-til-én, ei heller er jeg i stand til å se støtte for en slik antakelse i energistatistikk. Det virker som at det i en del litteratur foreligger et premiss om at vindkraft konkurrerer med fossil kraft alene. Premisset er kunstig, fordi vindkraft også kan brukes til å tilfredsstille nye eller økte behov, og fordi vindkraft også kan konkurrere med andre fornybare energikilder eller med energieffektivitet.

Ressurspanelrapporten viser at vindkraft har et stort potensial for å redusere utslipp av drivhusgasser og annen forurensing. Realiseringen av dette potensialet hviler på at vindkraft faktisk fører til en utfasing av fossil kraft. Og dette er igjen avhengig av at klimapolitikken som føres er virkningsfull nok.

Rapporten, inkludert kapittelet om vindkraft, kan lastes ned fra:

Green energy choices: Wind power under the microscope

By on 15. June 2016 in Ukategorisert with 2 Comments

A new report of the International Resource Panel evaluates the relative environmental merits of power generation options. I am co-editor of the report and lead author of the chapter on wind power. In this blog post, I share some insights from the report as well as own reflections on environmental aspects of wind power.

Wind turbines are driven by the energy possessed by moving air – that is, wind. In fundamental contrast to exhaustible energy stocks like oil and gas, wind is a renewable energy flow. What is more, it is available in ample quantities around the globe. Still, wind power deployment is not without environmental concerns.

Assessment approach

The International Resource Panel (IRP) report takes a two-fold approach to assessing the impacts and resource requirements of power supply:

First, comprehensive life cycle assessments are conducted to quantify environmental impacts, such as climate change, toxic effects and air pollution. Second, some impact types are essentially non-quantifiable, as agreed-upon methods for quantification do not exist. The report addresses such impact types by means of a qualitative discussion. Examples of non-quantifiable effects of wind power include bird mortality and visual intrusion in landscapes.

Great potential for reducing pollution


Overview of life cycle impacts for different power generation options. Source: Hertwich et al. (eds.). Green Energy Choices. Summary For Policy Makers. UNEP International Resource Panel. The summary report is available here.

In a life-cycle perspective, wind power causes harmful emissions, just as does any other way of power generation. Looking at the life cycle assessment results of the IRP report, one result is striking: Wind power shows excellent performance by all the assessed impact types caused by pollution, outperforming the global electricity mix by one or two orders of magnitude.

This is evident from the figure above, showing a comparison of estimated impacts for different technologies. (I am afraid image size is small. You may click on image to increase size somewhat, or see the IRP summary report.) Observe, for example, that the greenhouse gas emissions of wind power amount to only 2% of that of the average global electricity. Similarly, wind power causes adverse effects on human and ecosystem health (due to air pollution or toxic contamination of soil and water) corresponding to 4-5% of that of the global electricity.

Bird and bat fatalities

Try a Google search for “wind”, “birds” and “myth”, and you will find websites portraying wind turbines as a major threat to birds. And you will find websites presenting it as a myth that wind turbines is a significant threat to birds.

Such contrasting perceptions probably come about for a variety of reasons. It is clear though, that one explanation is that some people look at the total number of birds killed by wind turbines in comparison to buildings, transmission lines and cats, while other people focus on effects on local bird populations. The former perspective tends to put wind power in a more favourable light, because – true – in the aggregate wind power is only a minor bird-killer compared to other man-made structures. The latter perspective tends to put wind power in a less favourable light, because – also true – wind farms can do harm to local bird populations that are small or vulnerable, or valued by humans. Wind turbines tend to kill different types of birds (for example, eagles) than buildings (for example, songbirds).

Measures exist for reducing the risk of bird collisions and have demonstrated some success, which is encouraging. Perhaps in particular, careful spatial planning and optimized wind farm siting can reduce negative effects on birdlife.

Not to forget, there is also another (and very different) type of flying animals, bats. For reasons not entirely understood, some bat species seem to be attracted to wind turbines – putting the bats at increased risk of injury or death caused by moving turbine blades. There are concerns that wind turbines have become or are about to become a serious mortality factor for bats in some regions.

Land use

How much land area does a wind farm occupy? Here also, views differ greatly. For the IRP report, a choice was made to count only the area used exclusively by turbines with foundations, and access roads. The basic reason for this choice is that the spacing between turbines can be used by humans for other purposes or by terrestrial wildlife. A wind farm area can, within some limits, coexist with agricultural crops, animal grazing or wildlife. The same cannot be said for the land used by open-pit coal mines or bioenergy crops.

With the approach used in the IRP report, the life cycle land use associated with wind power is very small compared with competing technologies, as is evident from the overview of impacts in the figure above. However, as is discussed in the report, a much larger area could also be regarded as impacted, especially because wind turbines are tall structures that may be visually dominating in landscapes. Concerns about degradation of scenic attributes of landscapes can be legitimate, and should not generally be dismissed as a “not in my back-yard”-type problem.

Real benefits arise when worse alternatives are displaced

Life cycle assessments and other literature often assume, explicitly or implicitly, that one unit of wind power delivered implies one unit of fossil fuel-based power avoided. I have some reservations concerning this.

First, I am currently not able to see a basis for a priori assumptions that wind power deployment automatically reduces fossil fuel power use on a one-to-one basis. Second, it appears to be an artificial premise that wind power competes solely with fossil fuel power. It could also be seen as facilitating growth in electricity demand or as competing with other renewable options or with energy efficiency, especially in a future-oriented context assuming high carbon prices.

The IRP report shows that wind power has a great potential for reducing greenhouse gas emissions and other pollution. At the same time, realizing this potential depends on the degree to which fossil fuels are displaced. This again depends on energy and climate policies whose combined effect is to avoid fossil fuel use.

The full report, including the chapter on wind power, is available here. A summary report is available here. Other materials related to the report are available from A Norwegian version of this blog post is here.

Benefits of variable renewables outweigh costs

By on 8. February 2016 in Ukategorisert with 3 Comments

Replacing fossil fuel power with variable wind and solar power means that more energy storage and power transmission capabilities are necessary. Despite this, we find large climate benefits and a range of other pollution benefits of switching to renewables.

Solar Panel

The variability of wind and solar power makes their large-scale integration into power systems challenging. The wind does not blow on demand. The sun does not always shine. Still, power demand must be met at all times and for all locations. Our new study, lead-authored by one of our Master’s students last year, Peter Berrill, assesses the environmental impacts of high penetration renewable energy scenarios for Europe. By bringing together life cycle assessment (LCA) and power grid modelling, the study is able to capture both life cycle effects and variability issues in one single analysis.

While increased needs to store energy and to transfer electricity over large distances cause additional impacts in systems dominated by renewables, these impacts are small in comparison to the benefits of deploying renewables.

Former estimates present an incomplete picture

Results of LCAs are frequently used to compare the environmental performance of electricity generation options. One example is this graphic from the IPCC, juxtaposing life cycle emission estimates for different power generation options. However, these estimates do not consider impacts associated with accommodating large shares of variable supply in electricity networks.

Considering both life cycle effects and variability issues in one coherent assessment involves a substantial methods and data challenge. The basic reason for this is that impacts occurring as a result of variability is a property of whole systems, not of individual technologies.

How so? Well, we know that the wind does not always blow. This constitutes a challenge, because customer demand for electricity must always be satisfied. Now, we can deal with the challenge in a number of ways. We can expand transmission grids, to exploit the fact that the wind (almost) always blows somewhere. We can combine wind and solar deployment to reduce overall fluctuations. We can invest in energy storage, such as batteries or pumped hydro. We can invest in surplus capacity of flexible natural gas power, ready to be used when needed. Or – as will be the case in the real world – we can combine these measures in one way or another. Then, the impacts that arise as a result of variability depend on how all technologies are combined. The impacts cannot be determined by considering any single technology in isolation.

Our attempt to get a fuller picture

In order to capture both life cycle effects and variability effects, you need both a power system model capable of simulating the operation of entire power systems, and an LCA model capable of estimating life cycle impacts of different power system layouts, and to combine the two in a sound manner.

Our study does exactly this. First, 44 scenarios describing power system configurations for Europe in 2050 were generated by a power system optimization model, REMix, operated by DLR in Germany. Next, the scenarios were examined using NTNU’s prospective LCA modelling framework, THEMIS. This combination allows us to present the first LCA of entire electricity systems while taking into account the effects of variability on storage and transmission requirements, and losses.

Findings: Large climate benefits

Wind turbines in Copenhagen. Photo: NTNU/Maren Agdestein

Wind turbines in Copenhagen. Photo: NTNU/Maren Agdestein

The findings indicate large climate benefits and a range of other emissions reduction benefits of switching to renewables. Adopting variable renewables on a large scale does lead to additional storage and transmission capacity requirements – and hence additional environmental impacts – but these are not large enough to significantly undermine the benefits of renewable power displacing fossil fuel-based power.

Another finding is that solar photovoltaic (PV) power tends to induce larger impacts than wind power, for two main reasons. First, the supply chains of solar power plants generally involve more emissions-intensive material processing and manufacturing activities than that of wind power plants. Second, as wind power plants on average operate closer to their full capacity, systems dominated by wind power show lower needs for storage than solar-dominated systems.

Our findings can help to alleviate fears that large-scale adoptions of variable renewable energy will cause large unintended emissions. At the same time, it is worthwhile to keep in mind that simplifications and assumptions were necessary, and this contributed to uncertainty. Some of the simplifications and assumptions may be replaced by more sophisticated modelling or better data in the future.

The study is reported in Environmental Research Letters.