The impacts of sport emissions on climate: Measurement, mitigation, and making a difference

Abstract As a global industry, sport makes potentially significant contributions to climate change through both carbon emissions and influence over sustainability practices. Yet, evidence regarding impacts is uneven and spread across many disciplines. This paper investigates the impacts of sport emissions on climate and identifies knowledge gaps. We undertook a systematic and iterative meta‐analysis of relevant literature (1992–2022) on organized and individual sports. Using a defined search protocol, 116 sources were identified that map to four sport‐related themes: (1) carbon emissions and their measurement; (2) emissions control and decarbonization; (3) carbon sinks and offsets; and (4) behavior change. We find that mega sport events, elite sport, soccer, skiing, and golf have received most attention, whereas grass‐roots and women's sport, activity in Africa and South America, cricket, tennis, and volleyball are understudied. Other knowledge gaps include carbon accounting tools and indicators for smaller sports clubs and active participants; cobenefits and tradeoffs between mitigation‐adaptation efforts in sport, such as around logistics, venues, sports equipment, and facilities; geopolitical influence; and scope for climate change litigation against hosts and/or sponsors of carbon‐intensive events. Among these, researchers should target cobenefits given their scope to deliver wins for both climate mitigation and risk management of sport.


INTRODUCTION
The global sports market was worth over US$500 billion in 2020 and is forecasted to exceed US$700 billion by 2026. 1 Revenues are generated from a range of activities 2 spanning sports retail (36%), infrastructure, consumables, and gambling (26%), professional sport host economy. 5 The cost is comparable to the entire 2021/22 budget ($230 billion) of the Department of Health and Social Care in England. 6 Popular sports attract massive international audiences and have large numbers of participants. 7 For example, FIFA estimates that soccer has 265 million active players worldwide and a fan base of 4 billion people-half the global population. Other sports with huge followings include cricket (2.5 billion), ice and field hockey (2 billion), and tennis (1 billion). Given the socioeconomic and cultural significance of sport, there has been growing attention to the environmental impact of the sector, 8,9 as well as to the possibilities for raising awareness and promoting greater sustainability. 10 Recurrent themes within the literature include management practices, fan engagement and behaviors, facilities management, marketing and communication, performance monitoring and evaluation, and corporate social responsibility. 11 These involve diverse disciplines, such as architecture, geography and environmental studies, sport management, tourism, urban studies, and others.
Increasingly, it is recognized that there is a bidirectional relationship between sport and climate because sport both affects and is affected by the climate system. 12 These associations are shaping a new subdiscipline of "Sport Ecology" that embraces human interaction with the natural environment, broadly and within a sport management context (Ref. 13, p. 510). Hence, recent lines of inquiry are assessing the impacts of climate change and extreme weather on the sports industry, 14,15 or the adaptation of facilities, athletes, and fans to new climate conditions. 16,17 This research examines how climate change affects the viability and fairness of sports, [18][19][20] as well as the suitability of cities to host future winter and summer Olympic and Paralympic Games. 21 Others focus on the links between climate conditions and the performances of professional and amateur athletes. 22,23 Weather conditions can also affect the inclination to exercise and adversely impact participant health. 24,25 For extreme sports, such as mountaineering, severe weather can make the difference between extraordinary triumph, 26 life, or death. 27 These examples illustrate some of the varied ways in which climate change impacts sport. A recent structured review of literature on the subject grouped research into five major themes: (1) heat impacts on athlete and spectator health; (2) heat impacts on athlete performance; (3) adaptive measures taken in sport; (4) suitability of various cities for event hosting; and (5) benchmarking conditions for sport and defining safe playing conditions for competition. 28 No such review exists for the impacts of sport on climate, apart from a preliminary estimate, suggesting that annual global emissions from the sport could be of the order of 350 million tCO 2 e. 29 This equates to about 1% of all emissions linked to energy and cement production 30

in 2019.
Aside from the initial estimate-and a review of associations between physical activity and climate, including emissions 12 -there is no synthesis of literature devoted exclusively to the impact of sport on climate. Although global emissions by sport are modest compared with other sectors, such as energy, transport, and manufacturing, they are still worthy of attention because mega sport events (MSEs), organized leagues, and mass participation sports can be "hotspots" of direct and indirect greenhouse gas emissions. Moreover, the UN Framework Convention on Climate Change (UNFCCC) Sports for Climate Action 31 recognizes that sport has an important role in achieving global climate change goals through peer-to-peer learning, sharing good practice, and development of new tools and collaboration. However, the strategy document 32 is silent about the underpinning evidence needed to support these initiatives. Global emissions by sport are also uncertain because such data are typically aggregated by country or sectors that do not specify sport.
Here, for the first time, we undertake a systematic, meta-analysis of peer-reviewed and gray literature on the impacts of sport emissions on climate. Following Orr et al., 28 we apply search criteria to elucidate coherent themes and knowledge gaps around organized sport. However, we expand their scope by including research about the 25 most popular sports in the world (according to spectator numbers and/or levels of participation). The following section describes the protocols used to structure our narrative literature review 33 of the sport-climate nexus. Qualifying material is then consolidated into emergent themes which are discussed in turn. This helps to identify knowledge gaps and opportunities for the sports industry to better engage with the climate agenda as envisaged by the UNFCCC.

METHODOLOGY
We implemented a five-step, iterative procedure for sifting literature with a view to drawing out key themes and evidence. 28 Step 3 of our protocol specifies the databases, search period, and terms. Two databases were examined for articles, book chapters, conference proceedings, theses, and reports meeting the step 2 criteria, namely: the Web of Science and Google Scholar (GS to the year 1998. GS searches were viewed as far as the first 500 entries, ordered by relevance. The Sport Ecology Group archive 35 and reference lists of key sources were also swept for overlooked materials. Three sets of search terms were applied to article titles (see Supporting Information). Set (A) covers literature associated with greenhouse gas emissions (including aerosols) and mitigation activities. Terms such as "Nationally Determined Contribution*," "NDC*," "tier*," and "scope*" were used in preliminary searches but eventually omitted from the final set because no records were found. Set (B) replicates the terms used by Orr et al. 28 to capture literature on organized, competitive sports. Set (C) focuses the search on the 25 most popular sports worldwide-either by the number of spectators or active participants. 36 "Running," "Marathon," and "Parkrun" were added in view of mass participation in these activities globally, 7 but "Walking" and "Hiking" were regarded as recreational activities rather than competitive sports, so were excluded. Later, we will return to this issue of terminology around what is defined as recreation and what is a sport, noting that our Set (C) includes "Ski*" given the deep contradictions about climate between participant attitudes and behaviors.
In step 4, duplicate articles were excluded based on their titles or where a conference proceeding replicated a journal output. Ineligible materials were rapidly filtered when this was obvious from the title or abstract. For example, an article title "Does signaling mitigate the cost of agonistic interactions? A test in a cricket that has lost its song" 37 meets the search criteria and contains two of the key terms but is clearly unrelated to the impact of sport on climate. An article on "Optimal break structures and cooling strategies to mitigate heat stress during a Rugby League match simulation" 38 uses the term mitigate, yet the abstract confirms that this article is about adapting to heat rather than mitigating impacts on climate, so does not address our RQs and was omitted. Studies of air quality were only included if there is a cobenefit from carbon emission controls (the primary motivation) rather than when driven by human health concerns (e.g., Hu et al. 39 ).
Finally, step 5 codifies short-listed articles using key terms and phrases to identify themes for subsequent narration. This was a quasiobjective and iterative procedure based on expert judgment and informed by word cloud analysis. The aim was to reduce the final set of sources into a representative but manageable number of topics rather than groupings by sport, tournament, or organization. Inevitably, there is overlap between themes, but code counts provide an indication of overall research emphasis, as well as some areas for development. Articles were also subclassified by sport, location, methodology of analysis, and source. Note that we did not attempt to cluster papers by scope

Carbon footprints
A CF may be defined as the total radiatively active greenhouse gas emissions (as CO 2 equivalent) that can be directly (Scopes 1 and 2) or indirectly (Scope 3) attributed to an organization, activity, product, or asset life-cycle. Emissions may be apportioned in various ways, but this is an essential first step for benchmarking and then reducing CFs. 43 The methodology used by the IOC views greenhouse gas accounting as a four-stage process of: (1) measuring emissions of the "Games project" (organization, services, and products); (2) understanding which activities contribute most to emissions; (3) taking action to reduce emissions in the most cost-effective way; then (4) inspiring others and raising awareness about sustainability. 44 Table 1   Some have suggested that a transport optimization approach could even be taken globally when judging cities that have qualified to host a major event, such as the FIFA World Cup. 73 The number of participating teams and the carbon intensity of tourist accommodation are important parts of the carbon calculation. 74 The CF of fans and team travel may additionally be reduced by promoting low-carbon travel options, greater vehicle-sharing, and discouraging long-distance air travel. 75 Detailed analysis of transport modes and journeys before and during the Beijing Olympic Games showed greater use of mass transit and a 36% reduction in emissions per trip. 76 More radically, the CF of travel to venues and on-site consumption can be significantly reduced by holding events with no spectators in attendance. 77  Waste management strategies may be evaluated to minimize emissions too-but sustainability practices vary greatly between teams. 88 Auditing and modeling of waste scenarios for the University of Missouri football stadium in 2014 determined that elimination of edible food waste (especially beef) would reduce emissions by 103.1 tCO 2 e, and 100%-recycling by 25.4 tCO 2 e. 89 However, for a club to achieve carbon neutrality requires much more than waste management, a transport strategy, and improved energy efficiency ( Table 2). The case of the Forest Green Rovers soccer team offers a template for others to follow. 90 Their model of climate action includes a stadium powered by 100% renewable energy, electric vehicles and charging station, shirts made from bamboo waste and recycled plastic, and a vegan-only menu.
Reading F.C. is using shirts fabricated from recycled plastic bottles and features the "climate stripes" visualization of global warming. 91 Major sporting events, such as the Beijing 2008 Olympic Games, have been held up as an example of how to decarbonize a host city, 63,92 and even cited as a turning point for low carbon development (in China).
The potential for low energy, low pollution, and low carbon development of the sport-tourism sector has been widely discussed. [93][94][95][96] Advocates for "green sports" are calling for low-carbon facilities and sports manufacturing, plus greater awareness and promotion of environmental concerns (including via sports celebrities). 97 However, there are tradeoffs between the anticipated economic benefits from visitors to MSEs plus a longer-term boost in tourist arrivals, 98 versus the associated CFs from increased travel and resource consumption. 77 Some are concerned that MSEs may divert scarce public and natural resources from other services 99 and sustainability initiatives. 100 Nonetheless, a few studies recognize that air pollution controls (such as traffic restrictions, reduced production at cement works, or even closure of polluting industries and construction sites) can have a cobenefit of smaller CFs. For example, steps taken to improve air quality during the Nanjing 2014 Youth Olympic Games yielded a 37% cut in carbon emissions. 38 The Brisbane 2032 Olympics are striving to go a step beyond carbon neutrality to become the first climate-positive Games. 101 This will require reductions in greenhouse gases that exceed the direct and indirect CF of the event, plus other climate benefits for host communities.
According to the hosts, the carbon budget will be aligned with and contribute to Queensland's emissions reduction and energy targets. These are for 50% renewable energy by 2030 and net zero emissions by 2050.
Moreover, it is claimed that the sustainability ambitions of the Brisbane Games could catalyze a "more-than-human" approach to urban design and regeneration of the city. 102

Carbon sinks/offsetting
Sports fields, parks, and facilities may be designed and managed in ways that exploit their capacity to sequester carbon, thereby neutralizing emissions caused by their activities. For instance, detailed field measurements and laboratory tests show that the plant-soil systems of golf courses can behave as carbon sinks. The amount of carbon accumula-tion depends on site-specific factors, such as the choice of turfgrass species, 103 the area of trees, 104 relative mix of tees, rough, fairways, and greens, 50 and age of the course. 105 However, these sinks are countered by emissions from course vehicles and mowing, fertilizers and fungicides, green irrigation, decomposition of grass clipping, and waste disposal. The intensity of such management varies with the season causing carbon emissions to peak in summer. The largest source of emissions from a golf course in the UK was from vehicles, followed by fertilizers and fungicides, and irrigation. 106  Some VCO schemes seek to capitalize on the assumed link between participants in outdoor sports, concern for the environment, and proenvironmental behavior. Some outdoor recreation companies now promote or provide VCO programs targeted at winter sports enthusiasts and trail runners. Research on the subject uses socioeconomic and household data to uncover predictors of VCO purchasing behavior. Evidence suggests that among runners, women, older participants, and households (rather than individuals) were most likely to buy offsets. 114 Among participants of snow-based activities in Canada, the most common characteristics were lower ages, higher education, a low carbon diet, inclination to outdoor pursuits, and awareness of VCO programs. 115 More generally, the disconnect between VCO purchase and the time taken for tangible benefits to the climate represents key obstacles to their uptake.
Local tree-planting ("event greening") has been widely adopted by hosts, such as the FIFA World Cup 107 and Olympic Games, 116 to counter CFs from new construction and activities. For example, the Birmingham 2022 Commonwealth Games (Figure 3) will offset F I G U R E 3 The Birmingham 2022 Commonwealth Games brought many benefits to the city but cost an estimated 240,000 tCO 2 e that will be offset over 35 years by new forest areas in the Midlands, UK. Photo: Author. emissions by planting 2022 acres of new forest within the Midlands, UK. 117 More generally, the optimal choice of tree and shrub species should reflect local conditions and availability of irrigation water-with the possibility of using treated sewage water in arid regions. 118 Treeplanting may be a tangible mitigation action, but it can be challenging to measure the success of community forestry schemes or to guarantee the permanence of the sequestered carbon. 119 This is because the carbon liability may take decades to neutralize. Standardization of carbon accounting techniques and measurement of above-ground carbon stocks can help to keep track of the sink performance of urban green spaces. 113,120

Behavior change
The final cluster of papers congregates around the theme of behavior change to mitigate the impact of sport on climate. This covers strategies for influencing transport decisions made by teams and participants, sustainable lifestyles, corporate social responsibility, and relationships with sponsors. Life-cycle analysis of detailed data on the travel patterns of sport spectators and teams reveals the disproportionate climate impact of a minority of fans who travel by air. 72 Strategies for reducing emissions from flights might include webcasts and big-screen live sites at off-site locations. Incentives that promote greater car occupancy rates for medium-distance (<800 km) "away" journeys and cycling to local events would reduce the overall CF of supporters. 121 This applies to those participating in mass participation (running) events. 122 Influencing the travel mode choice of local spectators and competitors has less benefit because of their relatively small contributions to the overall CF of events. During the 2022 Major League Baseball season, the 30 teams will clock up more than a million miles of travel. 123 Hence, rationalizing league boundaries and fixture schedules to reduce long-haul travel by centralizing play-offs, or clump-ing games between multiple teams in a single location, would have the largest impact on team CFs. Local reductions in emissions and operating costs can also be achieved through "Eco-driver" training to reduce average speeds, idling time, and hard deceleration/acceleration of fleet vehicles. 124 Community-based organizations, such as schools, faith groups, and sports clubs, play important roles in promoting and nudging proenvironmental behaviors among their members. 125,126 Similarly, associative and mimetic behavior enable the diffusion of proenvironmental practices between teams and leagues. 127 Empirical research provides evidence of the motivations behind behaviors and ways of strengthening the environmental impact of campaigns. For example, a study of Ipswich Town Football Club's "Save Your Energy for the Blues" campaign showed the importance of positive framing of actions and collective benefits. 128 Fans were invited to pledge energy-saving actions to offset ∼3000 tCO 2 e allowing the club to claim "first in the UK" carbon-neutral status. Similarly, Pledgeball challenges soccer fans from opposing teams to save the most carbon emissions ahead of upcoming fixtures. 129 Other research concentrates on the practical barriers to sustainability and or contradictions that might exist between awareness of environmental issues and behaviors. For example, despite awareness of environmental impacts, there are very low rates of recycling at soccer matches in Thailand because of insufficient attention to waste sorting. 130 Elsewhere, the obstacle is sociocultural: in India, cycling is generally regarded as a lower-class mode of transport (when compared with the car). 131 Moreover, cycle rallies are framed more about health benefits and road safety than around climate action. For participants of winter sports who make long-haul journeys, there is the irony of engaging in forms of transport that are harmful to the climate and hence to the snow on which their skiing depends. 132 Surveys of personal responses to this tension reveal a willingness to pay for carbon offsets when folded into "green" ski passes 133 or to car-pool for repeat, short journeys to resorts. 134 Although artificial snowmaking may be considered as an adaptation to climate change, it can reduce the attractiveness of a resort to summer skiers who are mindful of the associated high energy demand. 135 Corporate branding and sponsorship of sport also shape consumer choices and are coming under closer scrutiny. 136 One global survey itemized more than 250 prominent sports sponsorship deals with high-carbon industries (e.g., fossil fuel companies, airlines, and car makers). 61 This reflects concerns about the "greenwashing" of sport with contradictory signals to the climate action pledges made by clubs, governing bodies, and fans. Publicly visible sustainability league tables and reporting of air miles expose marked variations between clubs.
According to research by BBC Sport, 137

TA B L E 3
Steps to be taken by clubs, governing bodies, and tournaments to phase out high carbon sponsors from sport • Screen sponsors and owners to exclude companies that promote high-carbon lifestyles, products, and services, especially those in the automotive, airlines, and fossil fuel industries.
• Sign the UN Sport for Climate Action Framework and publish a detailed 10-year plan to ensure that their own activities and that of their sport (including spectator travel) are decarbonizing.
• Set annual emissions targets with steps to achieve them and clear lines of responsibility for their delivery. • Prioritize support for low-carbon, local, and grass-roots sport over the high-carbon global and professional sport.
Source: Adapted from Tricarico and Simms. 64 Conceptual frameworks are also emerging for self-regulation and greater environmental sustainability of elite sport. 139 While principles for ethical financing of sport are starting to take shape (Table 3), there are calls for greater engagement by researchers of ethics, philosophy, and ethnography. 133 As legal actions proliferate against major emitters, 140 some have imagined the possibility of indicting organizers of major sporting events for their reliance on high-carbon sponsors. 141

Knowledge gaps and opportunities
Having navigated the research landscape for sport impacts on climate, this section considers some overarching issues before then highlighting key opportunities for further research in the concluding remarks.
First, it is important to acknowledge the limitations of our metaanalysis. The search concentrated almost exclusively on materials published in the English language. This could contribute to some of the bias in the most researched sports and regions. Furthermore, "Sport," "recreation," "leisure," and "tourism" are fuzzy and overlapping terms that can dictate whether or not a source is counted; likewise, there are interdisciplinary variations in the meaning and use of terms like "sustainable" and "green." Even the distinction between sport equipment, sport apparel, and athleisure fashion was hard to discern in some cases. There are also tensions between climate action and other planetary crises of biodiversity loss and pollution. Examples of this are producing fake snow with chemical additives that damage topsoil and plant growth; or switching to artificial turfs to avoid the challenges associated with drought, thereby interrupting patch proximity and pathways for insects and small animals.
Sixth, there is a danger of greenwashing in the realm of sport and climate mitigation. There are plenty of examples of high-profile sustainability and carbon accounting reports before MSEs; follow-up, longitudinal studies that ratify claims after events have ended are much harder to find. This is especially problematic when there is a high reliance on carbon offsets, such as new forests, which can take decades to counteract the emissions intensity of sport activity over much shorter periods. A few organizations, such as IOC, have provided organizing committees with methodological guidance, but there is a wider need for standardization of CF approaches within and between sports, and to undertake this work earlier in the planning/proposal cycle.

CONCLUDING REMARKS
Based on the above observations and the body of evaluated literature, we close with several suggestions for further research. More studies are needed on the impacts of sport on climate from the perspective of: 1. Under-represented continents (principally Africa and South America), global sports (badminton, cricket, rugby, tennis, and volleyball), and data-gathering methods (qualitative).
2. Gendered aspects, especially given the lower resource implications of women's sports (due to smaller regional leagues, less budget for travel meaning, less impactful travel options, more local fanbases, and fewer international travelers attending events).
3. "Every-day" and community-level sport rather than elite sports, given the possibilities of scaling-up and scope for behavior change.
4. Geopolitical influence of sport on climate mitigation (and adaptation) given the global reach and economic significance of MSEs, leagues, and clubs. 5. Affordable and easy-to-use LCA tools, standard guidance, and indicators that can be used by smaller clubs and individuals to measure their CFs and monitor progress in mitigating emissions. 6. Potential cobenefits and tradeoffs between mitigation-adaptation efforts in sport, such as around logistics, choice of venues, sports equipment, and facilities. 7. Possible climate change litigation against the hosts and sponsors of MSEs, as well as energy-intensive tournaments and global sportstourism providers.

AUTHOR CONTRIBUTIONS
R.L.W. conducted the analysis and led the writing of the paper. M.O.
guided the methodology and conceptual development of the research.
All authors contributed to the assessment of the literature and preparation of the manuscript.