The addition of environmentally friendly items to conventional items sometimes leads people to believe that the carbon footprint of the entire set decreases rather than increases. This negative footprint illusion is supposedly underpinned by an averaging bias: people base environmental impact estimates not on the total impact of items but on their average. Here, we found that the illusion’s magnitude increased with the addition of a greater number of “green” items when the number of conventional items remained constant (Studies 1 and 2), supporting the averaging-bias account. We challenged this account by testing what happens when the number of items in the conventional and “green” categories vary while holding the ratio between the two categories constant (Study 3). At odds with the averaging-bias account, the magnitude of the illusion increased as the category size increased, revealing a category-size bias, and raising questions about the interplay between these biases in the illusion.

People consistently act in ways that harm the environment, even when believing their actions are environmentally friendly. A case in point is a biased judgment termed the negative footprint illusion, which arises when people believe that the addition of “eco-friendly” items (e.g., environmentally certified houses) to conventional items (e.g., standard houses), reduces the total carbon footprint of the whole item-set, whereas the carbon footprint is, in fact, increased because eco-friendly items still contribute to the overall carbon footprint. Previous research suggests this illusion is the manifestation of an “averaging-bias.” We present two studies that explore whether people’s susceptibility to the negative footprint illusion is associated with individual differences in: (i) environment-specific reasoning dispositions measured in terms of compensatory green beliefs and environmental concerns; or (ii) general analytic reasoning dispositions measured in terms of actively open-minded thinking, avoidance of impulsivity and reflective reasoning (indexed using the Cognitive Reflection Test; CRT). A negative footprint illusion was demonstrated when participants rated the carbon footprint of conventional buildings combined with eco-friendly buildings (Study 1 and 2) and conventional cars combined with eco-friendly cars (Study 2). However, the illusion was not identified in participants’ ratings of the carbon footprint of apples (Study 1 and 2). In Studies 1 and 2, environment-specific dispositions were found to be unrelated to the negative footprint illusion. Regarding reflective thinking dispositions, reduced susceptibility to the negative footprint illusion was only associated with actively open-minded thinking measured on a 7-item scale (Study 1) and 17-item scale (Study 2). Our findings provide partial support for the existence of a negative footprint illusion and reveal a role of individual variation in reflective reasoning dispositions in accounting for a limited element of differential susceptibility to this illusion.

Moral spillover occurs when a morally loaded behavior becomes associated with another source. In the current paper, we addressed whether the moral motive behind causing CO2 emissions spills over on to how much people think is needed to compensate for the emissions. Reforestation (planting trees) is a common carbon-offset technique. With this in mind, participants estimated the number of trees needed to compensate for the carbon emissions from vehicles that were traveling with various moral motives. Two experiments revealed that people think larger carbon offsets are needed to compensate for the emissions when the emissions are caused by traveling for immoral reasons, in comparison with when caused by traveling for moral reasons. Hence, moral motives influence people’s judgments of carbon-offset requirements even though these motives have no bearing on what is compensated for. Moreover, the effect was insensitive to individual differences in carbon literacy and gender and to the unit (kilograms or tons) in which the CO2 emissions were expressed to the participants. The findings stress the role of emotion in how people perceive carbon offsetting.

Past research has consistently shown that carbon footprint estimates of a set of conventional and more environmentally friendly items in combination tend to be lower than estimates of the conventional items alone. This ‘negative footprint illusion’ is a benchmark for the study of how cognitive heuristics and biases underpin environmentally significant behavior. However, for this to be a useful paradigm, the findings must also be reliable and valid, and an understanding of how methodological details such as response time pressure influence the illusion is necessary. Past research has cast some doubt as to whether the illusion is obtained when responses are made on a ratio/quantitative scale and when a within-participants design is used. Moreover, in past research on the negative footprint illusion, participants have had essentially as much time as they liked to make the estimates. It is yet unknown how time pressure influences the effect. This paper reports an experiment that found the effect when participants were asked to estimate the items’ emissions in kilograms CO2 (a ratio scale) under high and under low time pressure, using a within-participants design. Thus, the negative footprint illusion seems to be a reliable and valid phenomenon that generalizes across methodological considerations and is not an artifact of specific details in the experimental setup.

The way by which various sources of external information interact in their effects on judgment is rarely investigated. Here, we report two experiments that examine how two sources of external information—an anchor (a reference price) and an eco-label—influence judgments of an objective fact (product price) and a subjective preference (willingness-to-pay for the product). Participants’ price judgments were drawn in the direction of the anchor point, whereas the eco-label resulted in higher judgments of objective fact (Experiment 1) but did not influence subjective preference (Experiment 2). Interestingly, the eco-label seemed to strengthen the effect of the high anchor in judgments of objective fact. Further, participants with higher environmental concern answered a higher price on the subjective preference questions when they received a high anchor, as well as a lower price when they received a low anchor in comparison to the low environmental concern group. This study demonstrates that various external information sources can strengthen each other’s effects on consumer belief about products, while the effects are weaker for consumers’ preferences. The implications of the results for decision making are discussed.

People’s belief that one or more environmentally friendly items that are added to a set of conventional items can reduce the total environmental impact of these items (the negative footprint illusion) could lead to unwanted environmental consequences. An averaging bias seems to underpin this illusion: people make their estimates based on the average of the environmental impact produced by the items rather than the accumulated sum. We report four studies that used various priming manipulations to explore whether people’s preoccupation to think in terms of an average can be eliminated by fostering a summative mindset. The results demonstrate that participants avoid succumbing to the negative footprint illusion when the critical judgment task is preceded by tasks that engender a summation judgment. Our evidence indicates that the negative footprint illusion can be tempered when a primed concept (summation) is used adaptively on subsequent judgments, thereby correcting for bias in environmental judgments.

One of the today’s greatest challenges is to adjust our behavior so that we can avoid a major climate disaster. To do so, we must make sacrifices for the sake of the environment. The study reported here investigates how anchors (extrinsic motivational-free information) and normative messages (extrinsic motivational information) influence people’s tradeoffs between travel time and carbon dioxide (CO2) emissions in the context of car travel and whether any interactions with environmental concern (an intrinsic motivational factor) can be observed. In this study, people received either a CO2, health or no normative message together with either a high anchor, a low anchor, or no anchor. People that received both a high anchor and a CO2 emission normative message were willing to travel for a longer time than those that only received a high anchor. If a low anchor was presented, no differences in willingness to travel for a longer time were found between the three different conditions of normative message groups, i.e., CO2 normative message, health normative message, or no normative message. People with higher concern for the environment were found to be willing to travel for a longer time than those with lower concern for the environment. Further, this effect was strongest when a high anchor was presented. These results suggest that anchors and normative messages are among the many factors that can influence people’s tradeoffs between CO2 emission and travel time, and that various factors may have to be combined to increase their influence over pro-environmental behavior and decisions.

A major part of anthropogenic climate change is due to everyday human behavior, such as transportation, food and energy consumption. As a result, it has been argued that many barriers for mitigating climate change are psychological in nature. For example, people’s decisions and behaviors are subject to heuristics and biases which sometime harm our decisions. The benchmark of the present thesis is the finding that people believe that adding environmentally friendly items to a set of conventional items reduces the impact of the whole set. This phenomenon has been coined a negative footprint illusion (NFI). How robust is this effect, is it generalizable across judgmental dimensions and what is the mechanism that underpins the effect? This thesis concerns these three questions. Paper 1 found support for the assumption that an averaging bias underpins the NFI. On this view, the NFI appears because people intuitively respond with the average of the ‘vices’ (the unfriendly objects) and ‘virtues’ (the more environmentally friendly objects) in the combined set of objects. Paper 2 demonstrated that the NFI is insensitive to some levels of expertise. Furthermore, Paper 2 also reported the first demonstration of the NFI in the context of a within-participants design. Paper 3 found that a NFI can also be demonstrated in the context of atmospheric CO₂ concentration estimates. Paper 3 also reported further evidence for the averaging bias account of the NFI and showed that the effect is at least insensitive to some variations in the framing of the problem posed to the participants. Paper 4 demonstrated that the NFI can be eliminated by priming a summative mindset before requesting participants to make the environmental impact estimates. Taken together, this thesis shows that the NFI is a robust phenomenon that can be found across various to-be-estimated stimulus materials, it appears to be underpinned by an averaging bias but can be cognitively controlled in certain conditions.

Klimatförändringarna påverkas till stor del av mänskliga beteenden, till exempel transport, mat- och energikonsumtion. Därför argumenterar ett flertal forskare för att flera barriärer för att bromsa klimatförändringarna är av psykologisk natur, snarare än teknologisk. Klimatförändringarna är till exempel beroende av hur vi människor fattar beslut, vilka i sin tur påverkas av heuristiker och kognitiva snedvridningar som ibland vilseleder vårt beslutsfattande. Den här avhandlingen studerar ett fenomen som innebär att människor ofta tror att om man lägger till ett miljövänligt objekt till en samling konventionella objekt minskar det totala koldioxidavtrycket totalt sett, ett fenomen som kallas för ”den negativa fotavtrycksillusionen” (NFI). Hur robust är den här effekten, kan den generaliseras till andra bedömningsdimensioner och vilken mekanism ger upphov till effekten? Avhandlingen behandlar dessa frågor. Artikel 1 ger stöd för att en genomsnittsprocess orsakar NFI. Mer specifikt, NFI uppstår för att människor intuitivt svarar med genomsnittet av de icke miljövänliga objekten tillsammans med de miljövänliga objekten. Artikel 2 visade att NFI är relativt okänslig för expertis och att illusionen uppstår även när människor kan jämföra sina estimat av olika objektsamlingar. Artikel 3 fann att NFI även kan uppstå i en kontext där deltagarna ombeds skatta den atmosfäriska koldioxidkoncentrationen. Artikel 3 gav också ytterligare stöd för att en genomsnittsprocess ger upphov till illusionen och demonstrerade att illusionen åtminstone till del är okänslig för hur bedömningsproblemen är presenterade för deltagarna. Artikel 4 visade att NFI kan elimineras genom att prima ett additivt tankesätt innan deltagarna gör bedömningen. Avhandlingen visar sammanfattningsvis att NFI är ett robust fenomen som uppstår för flera stimulusmaterial, att en genomsnittsprocess tycks ge upphov till NFI och demonstrerar att effekten kan kontrolleras kognitivt i vissa situationer.

Recent years have seen a marked increase in carbon emissions despite pledges made by the international community at the Paris Accord in 2015 to reduce fossil fuel production and consumption. Rebound effects could contribute to this phenomenon as, in which attempts to curb carbon emissions might have inadvertently led to an upswing in fossil fuel usage. The present study hypothesizes that rebound effects are driven by a misapplication of compensatory balancing heuristics, with the unintended outcome of producing inaccurate estimates of the environmental impact of “green” or environmentally friendly labelled products or behaviors. The present study therefore aims to investigate the relationship between participants’ degree of compensatory thinking (e.g., “Recycling compensates for driving a car”) and their susceptibility to the Negative Footprint Illusion, a widely replicated phenomenon demonstrating that the presence of “green” products biases carbon footprint estimations. One hundred and twelve participants were asked to complete a 15-item Compensatory Green Beliefs scale and to estimate the total carbon footprint of a set of 15 conventional houses, followed by a set that included 15 “green” houses in addition to 15 conventional houses. Results indicated that participants, on average, believed that the "green" houses were carbon neutral, and that susceptibility to the Negative Footprint Illusion was predicted by performance on the Compensatory Green Beliefs scale. This is the first study confirming that individual differences in cognitive processes (i.e., Compensatory Green Beliefs) are indeed related to inaccurate estimates of “green” products, providing a foundation for further investigation of the influence of “green” and compensatory beliefs on carbon footprint estimates.