Editing IPCC:AR6/WGIII/Chapter-2 (section)

=== 2.4.2 Sectoral Drivers ===

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GHG emissions continued to rise since 2010 across all sectors and subsectors, most rapidly in electricity production, industry, and transport. Decarbonisation gains from improvements in energy efficiency across different sectors and worldwide have been largely wiped out by increases in demand for goods and services. Prevailing consumption patterns have also tended to aggravate energy use and emissions, with the long-term trend led by developed regions. Decarbonisation trends in some developed regions are limited in size and geographically. Globally, there are enormous unexploited mitigation potentials from adopting best available technologies.

The following subsections discuss main emissions drivers by sector. More detailed analyses of sectoral emissions and mitigation options are presented in Chapters 6–11.

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==== 2.4.2.1 Energy Systems ====

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Global energy system emissions growth has slowed down in recent years, but global oil and gas use was still growing ( [[#Jackson--2019|Jackson et al. 2019]] ) and the sector remained the single largest contributor to global GHG emissions in 2019 with 20 GtCO 2 -eq (34%) ( ''high confidence'' ) (Figure 2.17). Most of the 14 GtCO 2 -eq from electricity and heat generation (23% of global GHG emissions in 2019) were due to energy use in industry and in buildings, making these two sectors also prominent targets for mitigation ( [[#Davis--2018|Davis et al. 2018]] ; Crippa et al. 2019) (see subsections 2.4.2.2 and 2.4.2.3 below).

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[[File:a9fbb7e28d049e20bdcbeab8226f3368 IPCC_AR6_WGIII_Figure_2_17.png]]

'''Figure 2.17''' '''|''' '''Trends and drivers of global energy sector emissions (see Figure 2.16 caption for details) with energy measured as primary energy supply.'''

Growth in CO 2 emissions from energy systems has closely tracked rising GDP per capita globally ( [[#Lamb--2021b|Lamb et al. 2021b]] ), affirming the substantial literature describing the mutual relationship between economic growth and demand for energy and electricity ( ''robust evidence'' , ''high agreement'' ) ( [[#Khanna--2009|Khanna and Rao 2009]] ; [[#Stern--2011|Stern, 2011]] ). This relationship has played out strongly in developing regions, particularly in Asia, where a massive scale up of energy supply has accompanied economic growth – with average annual increases of energy demand between 3.8–4.3% in 2010–2019 (Figure 2.17). The key driver for slowing the growth of energy systems CO 2 emissions has been declining energy intensities in almost all regions. Annually, 1.9% less energy per unit of GDP was used globally between 2010 and 2019.

The carbon intensity of power generation varies widely between (and also within) regions (Chapter 6). In North America, a switch from coal to gas for power generation (Peters et al. 2017, 2020; [[#Feng--2019|Feng 2019]] ; [[#Mohlin--2019|Mohlin et al. 2019]] ) as well as an overall decline in the share of fossil fuels in electricity production (from 66% in 2010 to 59% in 2018) ( [[#Mohlin--2019|Mohlin et al. 2019]] ) has decreased carbon intensity and CO 2 emissions. Since 2007, Europe’s carbon intensity improvements have been driven by the steady expansion of renewables in the share of electricity generation ( ''medium evidence'' , ''high agreement'' ) (Peters et al. 2017, 2020; [[#Le%20Quéré--2019|Le Quéré et al. 2019]] ; [[#Rodrigues--2020|Rodrigues et al. 2020]] ). Some studies attribute these effects to climate policies, such as the carbon floor price in the UK, the EU emissions trading scheme, and generous renewable energy subsidies across the continent ( [[#Dyrstad--2019|Dyrstad et al. 2019]] ; H. [[#Wang--2020|Wang et al. 2020]] ). South-East Asian developed countries and Australia, Japan and New Zealand stand out in contrast to other developed regions, with an increase of regional carbon intensity of 1.8 and 1.9% yr –1 , respectively (Figure 2.17). Generally, the use of natural gas for electricity production is growing strongly in most countries and gas has contributed to the largest increase in global fossil CO 2 emissions in recent years ( [[#Jackson--2019|Jackson et al. 2019]] ; [[#Peters--2020|Peters et al. 2020]] ). Furthermore, gas brings the risk of increased methane (CH 4 ) emissions from fugitive sources, as well as large cumulative emissions over the lifetime of new gas power plants that may erase early carbon intensity reductions ( [[#Shearer--2020|Shearer et al. 2020]] ).

The growth of emissions from coal power slowed after 2010, and even declined between 2011 and 2019, primarily due to a slowdown of economic growth and fewer coal capacity additions in China ( [[#Friedlingstein--2019|Friedlingstein et al. 2019]] ; [[#Peters--2020|Peters et al. 2020]] ). Discussions of a global ‘peak coal’, however, may be premature, as further growth was observed in 2019 ( [[#Friedlingstein--2019|Friedlingstein et al. 2019]] ; [[#Peters--2020|Peters et al. 2020]] ). Large ongoing and planned capacity increases in India, Turkey, Indonesia, Vietnam, South Africa, and other countries has become a driver of thermal coal use after 2014 ( [[#UNEP--2017|UNEP 2017]] ; [[#Edenhofer--2018|Edenhofer et al. 2018]] ; Steckel et al. 2019).

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==== 2.4.2.2 Industry Sector ====

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When indirect emissions from electricity and heat production are included, industry becomes the single highest emitting sector of GHGs (20.0 GtCO 2 -eq in 2019) ( ''high confidence'' ). Facilitated by globalisation, East Asia has been the main source and primary driver of global industry emissions growth since 2000 ( ''robust evidence'' , ''high agreement'' ) (Lamb et al. 2021). However, while East Asia has emitted 45% of the world’s industry GHG emissions in 2019, a remarkable decrease of 5.0% yr –1 in energy intensity and 1.6% in carbon intensity helped to stabilise direct industrial CO 2 emissions in this region (–0.3% yr –1 between 2010 and 2019; Figure 2.18). Direct industry CO 2 emissions have also declined in Latin America, Europe and Australia, Japan and New Zealand, and – to a smaller extent – in North America. In all other regions, they were growing – most rapidly in southern Asia (+4.3% annually for direct CO 2 emissions since 2010) (Figure 2.18).

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[[File:e4ffa05f76cc6e1b98e6bc52bd25ed42 IPCC_AR6_WGIII_Figure_2_18.png]]

'''Figure 2.18''' '''|''' '''Trends and drivers of global industry sector emissions (see Figure 2.16 caption for details) with energy measured as total final energy consumption.'''

The main global driver of industry emissions has been a massive rise in the demand for products that are indirectly used in production, such as cement, chemicals, steel, aluminium, wood, paper, plastics, lubricants, fertilisers, and so on. This demand was driven by economic growth, rising affluence, and consumption, as well as a rapid rise in urban populations and associated infrastructure development ( ''robust evidence'' , ''high agreement'' ) ( [[#Krausmann--2018|Krausmann et al. 2018]] ). There is strong evidence that the growing use of concrete, steel, and other construction materials is particularly tightly coupled to these drivers ( [[#Pauliuk--2013|Pauliuk et al. 2013]] ; [[#Cao--2017|Cao et al. 2017]] ; [[#Krausmann--2017|Krausmann et al. 2017]] ; [[#Plank--2018|Plank et al. 2018]] ; [[#Haberl--2020|Haberl et al. 2020]] ). Per capita stocks of cement and steel show a typical pattern of rapid take-off as countries urbanise and industrialise, before slowing down to low growth at high levels of GDP. Hence, in countries that have recently been industrialising and urbanising – that is Eastern, Southern and South-Eastern Asia – a particularly strong increase of emissions from these subsectors can be observed. Selected wealthy countries seem to stabilise at high per capita levels of stocks, although it is unclear if these stabilisations persist and if they result in significant absolute reductions of material use ( [[#Wiedenhofer--2015|Wiedenhofer et al. 2015]] ; [[#Cao--2017|Cao et al. 2017]] ; [[#Krausmann--2018|Krausmann et al. 2018]] ). Opportunities for prolonging lifetimes and improving end of life recycling in order to achieve absolute reductions in extraction activities are as yet unexploited ( [[#Krausmann--2017|Krausmann et al. 2017]] ; [[#Zink--2017|Zink and Geyer, 2017]] ).

On the production side, improvements in the efficiency of material extraction, processing, and manufacturing have reduced industrial energy use per unit of output (J. [[#Wang--2019|]] [[#Wang--2019|]] [[#Wang--2019|Wang et al. 2019]] ). These measures, alongside improved material substitution, lightweight designs, extended product and servicing lifetimes, improved service efficiency, and increased reuse and recycling will enable substantial emissions reductions in the future ( [[#Hertwich--2019|Hertwich et al. 2019]] ). In absence of these improvements in energy intensity, the growth of population and GDP per capita would have driven the industrial CO 2 emissions to rise by more than 100% by 2017 compared with 1990, instead of 56% ( [[#Lamb--2021b|Lamb et al. 2021b]] ). Nonetheless, many studies point to deep regional differences in efficiency levels and large globally unexploited potentials to improve industrial energy efficiency by adopting best available technologies and practices for metal, cement, and chemical production ( [[#Gutowski--2013|Gutowski et al. 2013]] ; [[#Schulze--2016|Schulze et al. 2016]] ; [[#Hernandez--2018|Hernandez et al. 2018]] ; [[#Talaei--2018|Talaei et al. 2018]] ).

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==== 2.4.2.3 Buildings Sector ====

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Global direct and indirect GHG emissions from the buildings sector reached 9.7 GtCO 2 -eq in 2019, or 16% of global emissions). Most of these emissions (66%, or 6.4 GtCO 2 -eq) were upstream emissions from power generation and commercial heat (Figure 2.19). The remaining 33% (3.3 GtCO 2 -eq) of emissions were directly produced in buildings, for instance by gas and coal boilers, and cooking and lighting devices that burn kerosene, biomass, and other fuels (Lamb et al. 2021). Residential buildings accounted for the majority of this sector’s emissions (64%, 6.3 GtCO 2 -eq, including both direct and indirect emissions), followed by non-residential buildings (35%, 3.5 GtCO 2 -eq) ( ''high confidence'' ).

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'''Figure 2.19''' '''|''' '''Trends and drivers of global buildings sector emissions (see Figure 2.16 caption for details) with energy measured as total final energy consumption.'''

Global buildings sector GHG emissions increased by 0.7% yr –1 between 2010 and 2019 (Figure 2.19), growing the most in absolute terms in East and South Asia, whereas they declined the most in Europe, mostly due to the expansion of renewables in the energy sector and increased energy efficiency (Lamb et al. 2021). North America has the highest per capita GHG emissions from buildings and the second highest absolute level after East Asia (Figure 2.19).

Rising wealth has been associated with more floor space being required to service growing demand in the retail, office, and hotel sectors ( ''medium evidence'' , ''high agreement'' ) ( [[#Daioglou--2012|Daioglou et al. 2012]] ; [[#Deetman--2020|Deetman et al. 2020]] ). In addition, demographic and social factors have driven a cross-national trend of increasing floor space per capita. As populations age and decrease in fertility, and as individuals seek greater privacy and autonomy, households declined in size, at least before the COVID-19 pandemic ( [[#Ellsworth-Krebs--2020|Ellsworth-Krebs 2020]] ). These factors led to increased floor space per capita, even as populations stabilise. This in turn is a key driver for building sector emissions, because building characteristics such as size and type, rather than occupant behaviour, tend to explain the majority of energy use within dwellings ( [[#Guerra%20Santin--2009|Guerra Santin et al. 2009]] ; [[#Ürge-Vorsatz--2015|Ürge-Vorsatz et al. 2015]] ; [[#Huebner--2017|Huebner and Shipworth 2017]] ) (Chapter 9).

Energy activity levels further drive regional differences. In Eurasia, Europe and North America, thermal demands for space heating dominate building energy use, at 66%, 62% and 48% of residential energy demand, respectively ( [[#IEA--2020a|IEA 2020a]] ). In contrast, cooking has a much higher share of building energy use in regions of the Global South, including China ( [[#Cao--2016|Cao et al. 2016]] ). And, despite temperatures being on average warmer in the Global South, electricity use for cooling is a more prominent factor in the Global North ( [[#Waite--2017|Waite et al. 2017]] ). This situation is changing, however, as rapid income growth and demographic changes in the Global South enable households to heat and cool their homes ( [[#Ürge-Vorsatz--2015|Ürge-Vorsatz et al. 2015]] , 2020).

Steady improvements in building energy intensities across regions can be attributed to baseline improvements in building fabrics, appliance efficiencies, energy prices, and fuel shifts. Many countries have adopted a mix of relevant policies, such as energy labelling, building energy codes, and mandatory energy performance requirements ( [[#Nie--2014|Nie and Kemp 2014]] ; [[#Nejat--2015|Nejat et al. 2015]] ; [[#Economidou--2020|Economidou et al. 2020]] ). Efforts towards building refurbishments and retrofits have also been pursued in several nations, especially for historical buildings in Europe, but evidence suggests that the recent retrofit rates have not made a significant dent on emissions ( [[#Corrado--2016|Corrado and Ballarini 2016]] ). The Chinese central government launched various policies, including command and control, economic incentives, and technology measures, but a big gap remains between the total rate of building green retrofit in the nation and the future retrofit potential (G. [[#Liu--2020a|Liu et al. 2020a]] , 2020b). Still, one major global factor driving down energy intensities has been the global transition from inefficient coal and biomass use in buildings for heating and cooking, towards natural gas and electricity, in part led by concerted policy action in Asian countries ( [[#Ürge-Vorsatz--2015|Ürge-Vorsatz et al. 2015]] ; [[#Kerimray--2017|Kerimray et al. 2017]] ; [[#Thoday--2018|Thoday et al. 2018]] ). As developing countries construct new buildings, there is sizable potential to reduce and use less carbon-intensive building materials and adopt building designs and standards that lower lifecycle buildings energy use and allow for passive comfort. [[IPCC:Wg3:Chapter:Chapter-9|Chapter 9]] describes the mitigation options of the buildings sector.

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==== 2.4.2.4 Transport Sector ====

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With a steady, average annual growth of +1.8% yr –1 between 2010 and 2019, global transport GHG emissions reached 8.9 GtCO 2 -eq in 2019 and accounted for 15% of all direct and indirect emissions (Figure 2.20). Road transport passenger and freight emissions represented by far the largest component and source of this growth (6.1 GtCO 2 -eq, 69% of all transport emissions in 2019) ( ''high confidence'' ). National plus international shipping and aviation emissions together accounted for 2.0 GtCO 2 -eq or 22% of the sector’s total in 2019. North America, Europe and Eastern Asia stand out as the main regional contributors to global transport emissions and together account for 50% of the sector’s total.

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'''Figure 2.20''' '''|''' '''Trends and drivers of global transport sector emissions (see Figure 2.16 caption for details) with energy measured as total final energy consumption.'''

The proportion of total final energy used in transport (28%) and its fast expansion over time weighs heavily on climate mitigation efforts, as 92% of transport energy comes from oil-based fuels ( [[#IEA--2020b|IEA 2020b]] ). These trends situate transport as one of the most challenging sectors for climate change mitigation – no country has so far been able to realise significant emissions reductions in the sector. North America’s absolute and per capita transport emissions are the highest amongst world regions, but those of South, South-East and East Asia are growing the fastest ( ''high confidence'' ) (between +4.6% and +5.2% yr –1 for CO 2 between 2010 and 2019) (Figure 2.20).

More so than any other sector, transport energy use has tracked GDP per capita growth (Figure 2.20), (Lamb et al. 2021). With the exception of road gasoline demand in OECD countries, the demand for all road fuels generally increases at least as fast as the rate at which GDP per capita increases ( [[#Liddle--2020|Liddle and Huntington 2020]] ). Developments since 1990 continue a historical trend of increasing travel distances and a shift from low- to high-speed transport modes that goes along with GDP growth ( [[#Schäfer--2009|Schäfer et al. 2009]] ; [[#Gota--2019|Gota et al. 2019]] ). Modest improvements in energy efficiency have been realised between 2010 and 2019, averaging –1.5% yr –1 in energy intensity globally, while carbon intensities of the transport sector have remained stable in all world regions (Figure 2.20). Overall, global increases in passenger and freight travel activity levels have outpaced energy efficiency and fuel economy improvements, continuing a long-term trend for the transport sector ( ''medium evidence'' , ''high agreement'' ) ( [[#Gucwa--2013|Gucwa and Schäfer 2013]] ; Grübler 2015; [[#McKinnon--2016|McKinnon 2016]] ).

Despite some policy achievements, energy use in the global transport system remains to the present deeply rooted in fossil fuels ( ''robust evidence'' , ''high agreement'' ) ( [[#Figueroa--2014|Figueroa et al. 2014]] ; [[#IEA--2019|IEA 2019]] ). In part this is due to the increasing adoption of larger, heavier combustion-based vehicles in some regions, which have tended to far outpace electric and hybrid vehicle sales (Chapter 10). Yet, stringent material efficiency and lightweight design of passenger vehicles alone would have the potential to cut cumulative global GHG emissions until 2060 by 16–39 GtCO 2 -eq ( [[#Pauliuk--2021|Pauliuk et al. 2021]] ).

While global passenger activity has expanded in all world regions, great disparities exist between low- and high-income regions, and within countries between urban and rural areas ( [[#ITF--2019|ITF 2019]] ). While private car use is dominant in OECD countries ( [[#EC--2019|EC 2019]] ), the growth of passenger-km (the product of number of travellers and distance travelled) has considerably slowed there, down to an increase of just 1% yr –1 between 2000 and 2017 ( [[#SLoCaT--2018|SLoCaT 2018]] ) (Chapter 10). Meanwhile, emerging economies in the Global South are becoming more car-dependent, with rapidly growing motorisation, on-demand private transport services, urban sprawl, and the emergence of local automotive production, while public transport struggles to provide adequate services ( [[#Dargay--2007|Dargay et al. 2007]] ; [[#Hansen--2017|Hansen and Nielsen 2017]] ; [[#Pojani--2017|Pojani and Stead 2017]] ).

Freight travel activity grew across the globe by 68% in the last two decades, driven by global GDP increases, together with the proliferation of online commerce and rapid (i.e., same-day and next-day) delivery ( [[#SLoCaT--2018|SLoCaT 2018]] ). Growth has been particularly rapid in heavy-duty road freight transport.

While accounting for a small share of total GHG emissions, domestic and international aviation have been growing faster than road transport emissions, with average annual growth rates of +3.3% and +3.4%, respectively, between 2010 and 2019 ( [[#Crippa--2021|Crippa et al. 2021]] ; [[#Minx--2021|Minx et al. 2021]] ;). Energy efficiency improvements in aviation were considerably larger than in road transport, but were outpaced by even larger increases in activity levels ( [[#SLoCaT--2018|SLoCaT 2018]] ; [[#Lee--2021|Lee et al. 2021]] ) (Chapter 10).

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==== 2.4.2.5 AFOLU Sector ====

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GHG emissions from agriculture, forestry and other land use (AFOLU) reached 13 GtCO 2 -eq globally in 2019 ( ''medium confidence'' ) (Figure 2.21). AFOLU trends, particularly those for CO 2 -LULUCF, are subject to a high degree of uncertainty ( [[#2.2.1|Section 2.2.1]] ). Overall, the AFOLU sector accounts for 22% of total global GHG emissions, and in several regions – Africa, Latin America, and South-East Asia – it is the single largest emitting sector, which is also significantly affected itself by climate change (AR6 WGI Chapters 8, 11, and 12; and AR6 WGII Chapter 5). Latin America has the highest absolute and per capita AFOLU GHG emissions of any world region (Figure 2.21). CO 2 emissions from land-use change and CH 4 emissions from enteric fermentation together account for 74% of sector-wide GHGs. Note that CO 2 -LULUCF estimates included in this chapter are not necessarily comparable with country GHG inventories, due to different approaches to estimating anthropogenic CO 2 sinks ( [[#Grassi--2018|Grassi et al. 2018]] ) (Chapter 7).

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'''Figure 2.21''' '''|''' '''Trends and drivers of global AFOLU sector emissions: (a) trends of GHG emissions by subsectors 1990–2019; (b) share of total sector and per capita GHG emissions by world region in 2019; and (c) Kaya decomposition of GHG emissions drivers.''' Based on the equation H=P(A/P)(L/A)(H/L), where P is population, A/P is agricultural output per capita, L/A is the land required per unit of agricultural output (land efficiency), and H/L is GHG emissions per unit of land (GHG intensity) ( [[#Hong--2021|Hong et al. 2021]] ). GHG emissions H comprise agricultural CH 4 and N 2 O emissions from EDGAR v6.0. The indicated annual growth rates are averaged across the years 2010–2019 – LULUCF CO 2 emissions are excluded in panel (c). (Note: due to different datasets, the population breakdown for AFOLU emissions is slightly different than that in the other sector figures above).

Unlike all other sectors, AFOLU emissions are typically higher in developing compared to developed regions ( ''medium confidence'' ). In Africa, Latin America, and South-East Asia, CO 2 emissions associated with land-use change and management predominate, dwarfing other AFOLU and non-AFOLU sources and making AFOLU the single largest sector with more than 50% of emissions in these regions ( [[#Lamb--2021b|Lamb et al. 2021b]] ). Land-use and land-management emissions are associated with the expansion of agriculture into carbon-dense tropical forest areas ( [[#Vancutsem--2021|Vancutsem et al. 2021]] ), where large quantities of CO 2 emissions result from the removal and burning of biomass and draining of carbon rich soils ( [[#Pearson--2017|Pearson et al. 2017]] ; [[#IPCC--2018|IPCC 2018]] ; [[#Hong--2021|Hong et al. 2021]] ). Ruminant livestock rearing takes place on vast tracts of pasture land worldwide, contributing to large quantities of CH 4 emissions from enteric fermentation in Latin America (0.8 GtCO 2 -eq in 2018), Southern Asia (0.6 GtCO 2 -eq), and Africa (0.5 GtCO 2 -eq), while also playing a sizable role in the total AFOLU emissions of most other regions ( [[#Lamb--2021b|Lamb et al. 2021b]] ).

In all regions, the amount of land required per unit of agricultural output has decreased significantly from 2010 to 2019, with a global average of –2.2% yr –1 (land efficiency metric in Figure 2.21). This reflects agricultural intensification and technological progress. However, in most regions this was mirrored by an increase in output per capita, meaning that absolute GHG emissions in most regions increased over the last decade. A significant increase in total AFOLU emissions occurred in Africa, driven by both increased GHG emissions per unit of land and increased populations (Figure 2.21).

The AFOLU sector and its emissions impacts are closely tied to global supply chains, with countries in Latin America and South-East Asia using large portions of their land for agricultural and forestry products exported to other countries (Chapter 7). The strong increases in production per capita and associated GHG emissions seen in these regions are at least partly attributable to growing exports and not national food system or dietary changes. At the same time, efforts to promote environmental sustainability in regions such as the EU and the USA (but also fast-growing emerging economies such as China) can take place at the cost of increasing land displacement elsewhere to meet their own demand ( [[#Meyfroidt--2010|Meyfroidt et al. 2010]] ; [[#Yu--2013|Yu et al. 2013]] ; [[#Creutzig--2019|Creutzig et al. 2019]] ).

Global diets are a key driver of production per capita, and thus land pressure and AFOLU emissions (Chapter 7). As per capita incomes rise and populations urbanise, traditional, low-calorie diets that emphasise starchy foods, legumes, and vegetables transition towards energy-intensive products such as refined sugars, fats, oils, and meat ( [[#Pradhan--2013|Pradhan et al. 2013]] ; [[#Tilman--2014|Tilman and Clark 2014]] ). At a certain point in national development, affluence and associated diets thus override population growth as the main driver of AFOLU emissions ( [[#Kastner--2012|Kastner et al. 2012]] ). Very high calorie diets have high total GHG emissions per capita ( [[#Heller--2015|Heller and Keoleian 2015]] ) and are common in the developed world ( [[#Pradhan--2013|Pradhan et al. 2013]] ). Over the last few decades, a ‘westernisation’ of diets has also been occurring in developing countries ( [[#Pradhan--2013|Pradhan et al. 2013]] ). Low- and middle-income countries such as India, Brazil, Egypt, Mexico, and South Africa have experienced a rapid dietary shift towards western-style diets (De [[#Carvalho--2013|Carvalho et al. 2013]] ; [[#Pradhan--2013|Pradhan et al. 2013]] ; [[#Popkin--2015|Popkin 2015]] ). Another driver of higher food requirements per capita is food waste, which has increased more or less continuously since the 1960s in all regions but Europe ( [[#Porter--2016|Porter and Reay 2016]] ).

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