Better Forests, Better Cities

Chapter 4


Forests inside, near and far away from cities can all help to mitigate climate change. Carefully managed inner forests only sequester modest amounts carbon but help to lower energy demands via cooling. Forests outside cities absorb and store massive amounts of atmospheric CO2, which is released when forests are cleared. Protecting these forests from clearing is essential to mitigate global climate change.


Around the world, cities are committing to bold action on climate change. Representing more than 700 million residents and one-fourth of the global economy, the dozens of members of the C40 Cities Climate Leadership Group (C40) have pledged to reduce GHG emissions in accordance with the goals of the Paris Agreement. Likewise, the ICLEI—Local Governments for Sustainability, which unites more than 1,700 cities, seeks to dramatically reduce its membership’s carbon emissions. Numerous similar initiatives—including the Climate Neutral Cities Alliance—exist to reduce carbon emissions in urban areas.

Cities are vulnerable to climate change. The effects of climate change—including heat waves, flooding, rising sea levels, and droughts—threaten the well-being of urban residents. Cities are hubs of innovation and economic activity and have a disproportionate concentration of both wealth and poverty residing in low-lying, coastal, and drought-prone areas (Rozenweig et al. 2010). Displacement due to sea level rise threatens to drive residents from some cities while causing influxes of rural climate refugees into other cities (Oppenheimer et al. 2019). Lower-income and marginalized residents are particularly vulnerable to the impacts of climate change, especially those in informal or unplanned settlements typical of rapidly growing cities. These threats are projected to continue to increase (Revi et al. 2014; Seto et al. 2014).

Urban residents’ concern about climate change is growing rapidly. City residents are demanding action from governments to take stronger, more decisive action on climate change. In September 2019, millions of city residents around the world took to the streets in protest, demanding action on climate change (Sengupta 2019; Taylor et al. 2019). Many urban-based climate action groups have started in recent years, and the demand for action from governments—including cities, by their residents—is growing and is likely to continue to grow as the impacts of climate change increase. While government action at all levels is important, more and more city governments are demonstrating their autonomy and sense of responsibility by taking action.

Reducing emissions within cities is the first important step, but forests can help cities go further. Cities consume more than 60 percent of the world’s natural resources (UN n.d.) and are responsible for approximately 75 percent of the world’s GHG emissions, when factoring in the goods consumed in cities but produced elsewhere (Seto et al. 2014). Decisions made in cities can have a large impact on climate change mitigation efforts. Unabated deforestation, especially in the tropics, may negate even the boldest reductions in emissions from fossil fuels (Griscom et al. 2017). To maintain a habitable climate, cities—the world’s largest pool of consumers—should examine how their consumption and actions affect the world’s forests at all levels and work to conserve and restore them.

Forests at all proximities to cities have a role. Increasing inner forests can have a mitigating impact on climate change in two key ways: sequestering carbon by urban trees and forests and lowering energy demands (and thereby energy-generated emissions) due to the temperature-moderating effects of the urban forests. Forests outside cities can help to mitigate climate change by absorbing and storing atmospheric CO2. The IPCC’s 2019 Special Report on Climate Change underscores the urgency: without actions in the land sector, efforts to mitigate climate change are unlikely to succeed. To limit global warming to well below the 2°C target of the 2015 Paris Agreement, action on many fronts is needed (Griscom et al. 2017; Olsson et al. 2019).

About This Section

There are many ways that forests can help cities meet their climate change mitigation targets (Box 1). Forests can directly and indirectly alter atmospheric GHG concentrations, and they also influence other important biophysical processes that affect climate stability across scales.

The following section summarizes some of the most important ways that cities can mitigate global climate change through actions related to forests:

  • Inner forests: Reduced energy emissions due to the temperature-moderating effects of the urban forests
  • Inner forests: Carbon sequestration and storage by urban trees and forests
  • Forests outside cities (near and far away): Global climate regulation and large-scale carbon sequestration and storage by forests, especially tropical forests

Box 1 | The Important Role of Forests in Mitigating Global Climate Change

Globally, forests store and sequester enormous amounts of carbon. It is estimated that forests and forest soils around the world hold between about 660 and 860 metric gigatons (Gt) of carbon (C).a This represents more carbon than the total atmospheric emissions from fossil fuel use and industry since 1870 (about 600 GtC)b and potentially more than is contained in fossil fuel reserves (estimated at about 800 Gt).c Maintaining forests as carbon stores is critical for mitigating climate change.d Globally, the world’s forests serve as a valuable carbon sink,e with more than half of gross sequestration occurring in tropical and subtropical forests.f

When cleared or degraded, however, forests can become carbon sources (Figure B1.1). Deforestation and forest degradation drastically reduce the ability of forests to store and sequester carbon. When forests are cleared, most of the carbon stored in aboveground biomass is released to the atmosphere through burning or decay, as is carbon stored in the soil, which is often drastically.g Emissions related to tropical deforestation make up about 8 percent of net global emissions annually.h Over the last twenty years, however, the absorption of carbon from the atmosphere by tropical forests has been approximately double their contributions to atmospheric carbon dioxide (CO2; Figure B1.1).i

Figure B1.1 | The Forest Carbon Cycle

Note: Forests are carbon sinks; when cleared, they become sources of carbon emissions from the burning and decay of vegetation and soils.

Source: Adapted from USDA Forest Service n.d.

Once cleared, it can take forests decades or even centuries for carbon storage to fully recover. Standing forests store vast amounts of carbon and, if left intact, will generally continue to sequester and store carbon indefinitely.j Deforestation and forest degradation release this stored carbon into the atmosphere as CO2 and eliminate a powerful, natural carbon sink.k Recovery of soil carbon stores is particularly slow. On average, resequestration of soil carbon takes around 60 years in tropical rain forests, 100 years in boreal forests, 150 years in mangroves, and more than 200 years in tropical peatlands.l Regrowth of forests following disturbance represents an important segment of the current global forest sink.m

Deforestation in tropical regions is proceeding at alarming rates.n Globally, net forest loss has decreased in recent decades, to about 4.7 million hectares (ha) per year from 2010 to 2020, and total net deforestation rates have declined to 10.2 million ha per year.o But tropical forests continue to experience much higher gross deforestation rates (at about 9.3 million ha per year lost annually from 2015 to 2020, an area the size of Hungary) than boreal (0.06 million ha per year), subtropical (0.50 million ha per year), or temperate regions (0.31 million ha per year).p Primary tropical rain forest is quickly disappearing—from 2002 to 2020, 64.7 million ha of tree cover was lost in these valuable ecosystems, an area larger than the entire country of France. In 2020 alone, this resulted in 2.6 GtCO2e, which is more than double the amount of emissions from cars on roads in the United States in 2020.q

The world is unlikely to meet atmospheric CO2 targets without reducing emissions from land use and land cover change.r Nature-based climate solutions around improved land use could offer 37 percent of necessary climate change mitigation—and in a cost-effective manner, from about US$100 per metric ton (t) of CO2e to below $10/tCO2e, in comparison to higher costs for emerging technologies, such as bioenergy with carbon capture and storage, which are estimated at about $40/tCO2e to over $1,000/tCO2e (Figure B1.2.1 and Figure B.1.2.2).s Forests, in particular, could provide a way to achieve 23 percent of necessary mitigation.t Unlike many other strategies to mitigate carbon emissions, such as geological carbon storage, better forest management, protection, and restoration can provide cascading social and environmental benefitsu as well as benefits for biodiversity and climate adaptation.v Forests at the inner, nearby, and faraway level can all contribute to climate change mitigation, although the vast majority of forests and areas suitable for reforestation are represented by the faraway forests.

Internationally, tree planting is gaining momentum as a way to combat climate change, but it is still less effective than conservation at mitigating climate change.w Restoring forest cover to degraded and formerly forested lands can have significant climate benefits,x but conserving native forests is a more effective and cost-effective way to mitigate climate change. Intact and primary forests offer enormous carbon benefits: Tropical primary forests have a higher carbon density (282 tC per ha) than tropical secondary forests (139 tC per ha).y Although they account for only 20 percent of forests in the tropics, intact primary forests (i.e., contiguous expanses of primary forests with minimal degradation) store nearly 40 percent of aboveground forest carbon of all primary tropical forests.z Avoiding tropical deforestation is also about seven to nine times more cost-effective than restoration or reforestation in many contexts.aa Modeled data suggest that avoiding conversion and deforestation of tropical forests is estimated to offer significantly greater benefits (100 tCO2e per ha per year sequestered globally) than reforestation could (3 tCO2e per ha per year sequestered globally).bb

Figure B1.2.1 | The Potential Net Reduction of Emissions by Tropical Forests

Notes: Net tropical deforestation produces 8 percent of net emissions, but halting and reversing tropical deforestation could reduce total net emissions by up to 30 percent.

Source: Authors. Adapted from Pan et al. (2011).

Figure B1.2.2 | The Carbon Flux of Tropical and Subtropical Forests

Note: The carbon flux of tropical and subtropical forests is a net carbon sink, but prevented deforestation and restoration in the tropics could provide significant necessary climate change mitigation.

Source: Authors. Data from Griscom et al. (2017) and Harris et al. (2021).

Restored, or secondary, forests may take centuries to recover the carbon stocks of an intact forest, even though they can have greater carbon sequestration In the Amazon, for example, the rate of carbon sequestration in young forests (3.05 tC per ha per year) can be 11 times greater than that of old-growth forests (0.28 tC per ha per year), but it still took more than 60 years before aboveground forest carbon stocks recovered to 90 percent of the size of old-growth stocks following deforestation.dd Restoration is nonetheless an important opportunity in places where conversion has already occurred; however, due to the immediate urgency of climate action, there is not enough time to rely on restoration projects alone to regain all the potentially lost carbon from continuing to deforest mature forests.

Sources: a. Pan et. al. 2011, FAO 2020; b. Le Quéré et al. 2018; c. Federici et al. 2018; d. Seymour and Busch 2016; e. Pan et al. 2011; f. Harris et al. 2021; g. Don et al. 2011; h. Wolosin and Harris 2018; i. Harris et al. 2021; j. Pregitzer and Euskirchen 2004; k. Seymour and Busch 2016; l. Goldstein et al. 2020; m. Pugh et al. 2019; n. Seymour and Busch 2016; Anderson, C.M., et al. 2019; Weisse and Goldman 2021; o. FAO 2020; p. FAO 2016; Olsson et al. 2019; q. Weisse and Goldman 2021; r. IPCC 2019; s. Nabuurs et al. 2007; Griscom et al. 2017; t. Wolosin and Harris 2018; u. Waring et al. 2020; v. Nabuurs et al. 2007; w. Holl and Brancalion 2020; x. Griscom et al. 2017; Bastin et al. 2019; y. Pan et al. 2011; z. Popatov et al. 2017; aa. Griscom et al. 2017; Busch et al. 2019; bb. Griscom et al. 2017; Busch et al. 2019; Griscom et al. 2020; cc. Waring et al. 2020; dd. Poorter et al. 2016.

Forests inside Cities and Climate Change: Urban Cooling and Carbon Sequestration


The urban environment creates challenging microclimates. Dense developments stifle airflow; steel, cement, and asphalt absorb heat from the sun and elevate city temperatures; and tall buildings create wind tunnels, causing discomfort in winter. When vegetation and open water are replaced with concrete, asphalt, and other materials, temperatures increase significantly (Mohajerani et al. 2017). These conditions can increase urban demand for energy for cooling (and in some cases, heating in winter), increasing emissions and further accelerating climate change.

Cities should consider strategies to limit or reduce the urban heat island effect as a way of reducing emissions. Cities are responsible for the bulk of the world’s GHG emissions (Seto et al. 2014). Transportation and industry play important roles, but maintaining habitable and comfortable indoor environments also contributes significantly. Emissions related to cooling are particularly noteworthy: urban heat islands can increase the demand for air-conditioning (Lundgren and Kjellstrom 2013) and air conditioner use—already responsible for 2 trillion kilowatt-hours of electricity annually, nearly 10 percent of global energy consumption—is expected to skyrocket in a warming world, especially in Asia (Dahl 2013; IEA 2018).

First, we examine the role of inner forests for microclimate regulation and carbon capture, following each with caveats and limitations. Then we do the same with forests outside cities.

Inner forests for microclimate regulation: What roles can trees and forests play?

Urban forests offer significant energy- and cost-saving benefits because they reduce extreme heat in summer, shade buildings, and in some settings buffer against strong winter winds. In this way, urban forests can help residents adapt to rising global temperatures—magnified by urban heat island effects—while simultaneously reducing urban emissions related to the heating and cooling of buildings.

By creating shade and lowering ambient air temperatures, trees can keep buildings cooler inside (Bowler et al. 2010a; Ko 2018). When trees shade buildings or evapotranspire, they reduce surface and ambient air temperatures, indirectly reducing the need to cool building interiors. On fossil fuel–powered electricity grids, a reduction in electricity use means a reduction in GHG emissions (Pataki et al. 2011; Roy et al. 2012; Mullaney et al. 2015). A 2018 systematic review of studies from North America suggests that cooling by trees can generate savings from 2.3 percent to as high as 90 percent of residential energy costs (Ko 2018), and another global review reported annual energy reduction benefits ranging from $2.16 to $64.00 per tree per year (Mullaney et al. 2015).

These reductions can produce significant cost savings. In the United States alone, urban forests reduce electricity use by 38.8 million megawatt-hours at a savings of $4.7 billion annually, with reductions in heating use estimated at 246 million British thermal units (savings of $3.1 billion annually) and avoided emissions savings valued at $3.9 billion annually (Nowak et al. 2017). Research from several Korean cities suggests that trees planted around multiresidential homes (totaling 32 percent of land used in Korean cities) reduced 0.367 million tCO2 per year of emissions both directly and indirectly, offsetting the emissions of these homes related to heating and cooling by 3.3 percent, and the economic benefits of these trees related to carbon reductions and cost savings totaled $51 million per year (Jo et al. 2019).

When trees shield buildings from cold winds, they may also reduce the need to heat buildings. The evidence to support this, however, remains more limited. Cost savings for heating may range from 1 percent to 20 percent of energy costs for residential buildings in North America (Ko 2018). Reducing wind speeds may reduce winter heating costs but could conversely increase summer cooling costs in temperate climates (Ko 2018).

Inner forests for microclimate regulation: Caveats and considerations

Urban forests can provide meaningful microclimate moderation to reduce urban emissions, residential and commercial cooling and heating costs, and demand on energy generation facilities, all while creating other desirable cobenefits (Case Study 6). However, potential interactions should also be considered:

  • The cooling effects of urban forests will vary between and within cities. Shading may produce only negligible reductions in indoor temperatures in areas where most residents inhabit tall multistory, multiunit residential buildings, as in many Chinese cities (Jim and Chen 2009). But in this context the cooling effects of evapotranspiration by trees can still be significant (Jim and Chen 2009).
  • Tall urban trees can conflict with solar access for rooftop solar panels (Ko 2018). But this can largely be avoided with careful species selection and proper pruning (Ko 2018).
  • In areas where water is scarce, the costs of irrigating urban trees may exceed the climate benefits provided (e.g., Pataki et al. 2011). In these contexts, selecting drought-resistant species with the ability to cool via shading may be especially important (Cameron and Blanuša 2016).
  • Interactions with the built environment matter. For example, trees and shrubs very close to buildings may prevent the nighttime radiative cooling of buildings (Bowler et al. 2010a; Wang et al. 2014; Ko 2018). By blocking solar radiation in winter months, evergreen trees near buildings can actually increase energy demands (Lyytimäki and Sipilä 2009; Ko 2018).

Case Study 6 | The Value of Urban Forests in California

Figure CS6.1 | Urban Forests Near San Francisco

Source: Kevin Wolf.

Calculating the economic value of carbon sequestration can offer incentives for cities and states to invest more heavily in these strategies. In California, the value from carbon sequestration and emissions reductions from urban forests added up to 9.8 million metric tons of carbon dioxide (MtCO2) per year (equivalent to removing 1.8 million cars and eliminating emissions from 210,280 households each year), with energy savings providing a meaningful 13 percent of this reduction.a

Using a standard price of US$12.02 per tCO2 (based on the California Carbon Allowance Futures annual average in 2014), California’s urban forest provides the state $102.35 million in carbon sequestration values.b Since 2014, the California Carbon Allowance has increased to $17.70 per tCO2 (as of January 2021), and the national social cost of carbon has increased to $51.00 per tCO2. Using these metrics, California’s urban forests would render at $145.35 million and $434.26 million, respectively. The value derived from carbon sequestration is relatively small compared to other ecosystem benefits; for example, energy savings from reduced heating and cooling totaled $568.70 million, a financial benefit that often goes straight to residents.c

Urban trees provide substantial cobenefits for local communities, yet they tend to be expensive to plant and maintain. A recent survey found that California annually spends $19.00 on maintenance for each municipal tree.d However, when accounting for an average $47.83 benefit—derived from reduced energy costs, sequestered carbon, improved air quality, intercepted rainfall, increased property value—this means that the trees still represent a good investment. In fact, for every $1 spent on tree management, Californian cities receive $2.52 in benefits. Moreover, those dollars going to tree maintenance help fuel strong local forestry economics. In California, revenues directly associated with urban forestry in 2009 totaled $2.97 billion and created 40,206 jobs.e

Sources: a, b, c. McPherson et al. 2017; d. Thompson 2006, found in McPherson et al. 2017; e. Templeton et al. 2013, found in McPherson et al. 2017.

Inner forests for carbon storage and sequestration: What roles can trees and forests play?

Canopy cover varies greatly among cities and is on the decline globally. Canopy cover varies with climate (Endreny et al. 2017) and between continents (Nowak and Greenfield 2020). Cities in forested regions typically have the greatest tree cover (averaging about 30 percent), followed by cities in grassland regions (18 percent) and cities in desert regions (12 percent; Nowak and Greenfield 2020). For example, the city of Atlanta contains 54 percent cover, compared to 8 percent in Cairo (Nowak et al. 2013; Endreny et al. 2017). Globally, urban tree cover is currently declining at a rate of 0.04 percent (about 40,000 ha) per year (Nowak and Greenfield 2020). The worst losses are occurring in Africa (1.5 percent lost per year) and modest gains are occurring in Europe (0.3 percent gained per year; Nowak and Greenfield 2020). Canopy cover is often used to estimate carbon storage in urban environments, and changes in canopy cover are used to estimate changes in carbon storage (Birdsey et al. 2019; Gibbs et al. 2022).

Total carbon storage and sequestration rates in urban forests vary with climatic and social contexts (Nowak and Crane 2002; Strobach et al. 2011; Nowak et al. 2013; Dobbs et al. 2014; Chen 2015). Cities with favorable growing seasons, robust urban forest management programs, or ample water supplies for vegetation may store more carbon than their counterparts lacking those characteristics. Variation also exists within individual cities. For example, tree-covered spaces such as urban parks and woodland patches typically store more carbon than street trees (Fares et al. 2017). More research is needed to understand carbon storage in cities globally, but some work has been conducted to date:

  • In Beijing, street trees store an estimated 0.29 MtCO2 and sequester an estimated 11,400 (+/- 6,600) tCO2 annually (Tang et al. 2016), and that sequestered CO2 is estimated to be equivalent to emissions of approximately 2,500 gasoline-powered passenger vehicles driven for one year.
  • Urban forests in the United States store approximately 3,300 MtCO2 and sequester 135 MtCO2 annually (gross) in their aboveground and belowground biomass (Nowak and Greenfield 2018b), with that sequestration equivalent to emissions from energy use in more than 17 million homes in the United States.

Carbon stored in urban forests per unit area varies widely but is nearly always lower than in forests outside cities (Figure 14). Aboveground carbon density varies from about 3 tC per ha in Bangkok to about 34 tC per ha in Camden, United Kingdom, to about 32 tC per ha in Niamey, Niger (Intasen et al. 2016; Wilkes et al. 2018; Moussa et al. 2019). Carbon density in urban forests is consistently lower than carbon density of forests outside cities (Pan et al. 2011; Goldstein et al. 2020).

Aboveground carbon density (the amount of carbon per unit area in vegetation) has been measured for a number of urban forests; however, belowground carbon is less commonly measured. When the above- and belowground biomass for forests outside of cities is considered, these forests house far more biomass per unit area: 239–64 tC per ha for boreal forests and 242–52 tC per ha for tropical forests (Pan et al. 2011; Goldstein et al. 2020).

Figure 14 | Aboveground Carbon Density of Urban Forests in Selected Cities Compared with Various Faraway Forest Types

Note: For the most part, aboveground carbon density of urban forests in cities is only a fraction of the average aboveground carbon density of forests outside cities (Pan et al. 2011; Goldstein et al. 2020; Harris et al. 2021).

Source: Authors, with data from Nowak et al. (2013), Intasen et al. (2016), Tang et al. (2016), Tigges and Lakes (2017), Wilkes et al. (2018), Moussa et al. (2019), Goldstein et al. (2020), and Speak et al. (2020).

Inner forests for carbon sequestration and storage: Caveats and considerations

Can urban forests offset city emissions? The potential of restoring the world’s forests for climate change mitigation has gained prominence in the scientific literature (e.g., Bastin et al. 2019) and in innovative global initiatives such as the Bonn Challenge,19 Initiative 20x20,20 the African Forest Landscape Restoration Initiative (AFR100),21 ECCA30,22 and Trillion Trees.23 In some cases, cities are also increasing urban forests as a way to counterbalance carbon emissions from other sources and shrink the net municipal carbon footprint. Ambitious large-scale urban tree-planting campaigns are being supported and implemented around the world, as seen in the MillionTreesNYC project24 or in Beijing’s planting of 50 million trees between 2012 and 2015 (Yao et al. 2019). Urban forests do store more carbon than many other urban land uses and provide abundant cobenefits. But expansions in urban tree canopy are unlikely to be an effective way for cities to meaningfully curb their net emissions for four reasons:

  • Urban space for trees and forests is limited and costly. Although higher canopy cover could increase benefits related to carbon sequestration and storage (Endreny et al. 2017), pressure from development and infill can make large increases in canopy cover challenging or impossible. Urban infill does, however, provide other benefits to cities’ carbon footprints, as densification in walkable neighborhoods connected to public transit reduces emissions from private transportation.
  • Urban forests can only sequester a tiny fraction—often less than half a percent—of overall city emissions (Case Study 7; Pataki et al. 2011). Research from diverse locations show similar numbers: Throughout China, the urban vegetation in 35 of its largest cities could offset only 0.33 percent of these cities’ total emissions (Chen 2015). In the United States, urban forests in cities throughout Florida mitigate between 1.8 and 3.4 percent of city emissions (Escobedo et al. 2010), whereas in Boston urban forests mitigate only 0.8 percent (Trlica et al. 2020). In Meran, Italy, forests sequester only 0.17 percent of city emissions (Speak et al. 2020). In Tabriz, Iran, urban trees currently mitigate 0.2 percent of the city’s emissions and could only be tripled to 0.6 percent over 20 years through an extensive city campaign of 150,000 new trees planted each year (Amini Parsa et al. 2019). Nonetheless, these emissions reductions can still translate into meaningful savings for cities—in the United States alone, the value of urban tree carbon sequestration is roughly $4.8 billion annually, and storage by urban trees is valued at roughly $119 billion (Nowak and Greenfield 2018b).25
  • Many urban trees require extensive, carbon-intensive care and maintenance during their life span. Planting, caring for, pruning, and removing urban trees using common fossil fuel–powered machinery releases GHG emissions (Nowak et al. 2002). Such emissions often outweigh the carbon sequestered by the tree, especially street trees and trees near buildings and infrastructure, which often require extensive maintenance. Many planted urban trees die young (Roman and Scatena 2011; Roman et al. 2014)—which could mean even more emissions related to removal and replacement. Urban vegetation may also be associated with biogenic emissions from soils and decomposition of plant material (see Velasco et al. 2016). Thus, trees planted in cities often only become carbon neutral decades after planting.
  • Although urban trees grow faster, they also die younger than some of their rural counterparts, especially street trees (McPherson et al. 1994; Roman and Scatena 2011):
    • Urban trees often grow faster. Trees tend to receive more sunlight and warmth due to low-density spacing and the urban heat island effect (Zhang et al. 2004). Indeed, these favorable growing conditions can lead to relatively higher storage on a per-tree basis of urban trees compared to trees in rural forest stands—as much as four times greater (Nowak and Crane 2002). Urban tree growth can also be augmented by pruning, fertilizing, and irrigation. Good management of urban forests could promote additional carbon storage (Fares et al. 2017).
    • Urban trees face uniquely challenging conditions that can shorten their life span, including damage from construction, pollution, pests, and vandalism. Urban soils are often compacted and contaminated with salt, have low levels of nutrients, and unfavorable pHs (Velasco and Chen 2019).
    • The estimated average life expectancy of a street tree in temperate zones is 19–28 years, although trees in yards and parks tend to live longer (Roman and Scatena 2011).

Interventions in transportation or other sectors may be more impactful (Case Study 7). Because of the challenges that urban environments pose to tree growth, the necessary carbon inputs for many urban trees, and the premium placed on urban space, carbon sequestration by urban trees is not nearly as effective or cost-effective as sequestration in rural forests. Yet unlike most carbon sequestration and storage methods, urban trees can provide myriad cobenefits (Case Study 6).

In conclusion, reducing emissions by decarbonizing the energy and transportation sectors remains essential for cities serious about reducing their net carbon footprint. Although urban forests offset only a tiny fraction of total city emissions and the overall potential for carbon sequestration or local emissions offsetting is generally low (Pataki et al. 2011; Case Study 7), their potential for reducing urban heat islands and emissions from other sectors (such as the need for energy for air-conditioning) is considerable. Forests outside of cities, on the other hand, provide significant opportunities for cities looking to go further. Climate benefits achieved by preserving or restoring tropical forests far exceed the benefits that any amount of urban tree planting can provide.

Case Study 7 | Mitigating Urban Emissions in a Tropical City: Medellín, Colombia

Figure CS7.1 | Medellín’s Location among the Surrounding Forests

Source: Natarajan 2017.

Carbon sequestration by the urban forest generally only represents a small percentage of cities' total emissions. Researchers in the Metropolitan Area of Aburrá Valley in Medellín, Colombia, used a tool from the i-Tree suite (developed by the USDA Forest Service)a to measure carbon dioxide (CO2) offsets from public trees—such as trees in parks, along roads, and along riverbanks—to compare them with other climate change mitigation strategies being pursued by the city: a new cable car transit system and two landfill gas management projects (Figure CS7.2).b

Annually, the landfill methane capture system reduced 5.84 percent of the city’s emissions, compared to 0.6 percent from cable cars and 0.23 percent from public trees. Avoided emissions from cooling alone contributed about one-third of the total reduction in emissions due to street trees. Even if street trees were planted in all feasible locations (i.e., in an additional 8 percent of the city’s area that could support more trees), this option would still not provide the same climate mitigation benefits as cable cars.c

This does not mean the urban forest is not an important asset to the city. Urban forests store a considerable amount of carbon as they provide multiple valuable services. In Medellín, public trees alone were estimated to store more than 100,000 million metric tons of CO2 (MtCO2) and are responsible for avoided emissions of 6,712 MtCO2 per yeard—roughly equivalent to removing 2,000 passenger vehicles from the road every year. Holistic urban forest management and tree maintenance is vital to protect these important carbon stores.

Figure CS7.2 | Potential Carbon Reduction Solutions in Medellín

Source: Authors. Adapted from Reynolds et al. (2017) and Phillips et al. (in press).

Sources: a. USDA Forest Service n.d., b–d. Reynolds et al. 2017.

Climate Change and Forests outside Cities, Near and Far


Forest carbon storage and sequestration potential outside of cities far exceeds the potential within city boundaries. Globally, these forests cover approximately 30 percent (FAO 2018) of Earth’s land surface (down from an estimated 55 percent at the dawn of the agricultural revolution), whereas urban areas cover only around 3 percent in total (UNSD n.d.). Investing in forest conservation outside of cities also has many cobenefits enjoyed by all people, including conserving global biodiversity, ensuring availability of future medicinal compounds, and helping to maintain global hydrological cycles, as described in the other sections of this report.

Tropical forests hold massive amounts of carbon.26 Globally, tropical forests store approximately 470 GtC, primarily in living plant tissue (Pan et al. 2011). The tropics also contain two particularly important ecosystems for carbon storage: tropical mangroves, which line the coasts of more than 110 tropical nations (FAO and UNEP 2020b), and forested peatlands, which are especially prevalent in Southeast Asia and have been subject to conversion to palm oil plantations in recent decades (Cazzolla Gatti et al. 2019). These forests store vast amounts of carbon, which is vulnerable to loss (Donato et al. 2011; Goldstein et al. 2020).

Tropical forests are being cleared at much higher rates than boreal and temperate forests, emitting vast amounts of carbon. If tropical deforestation were a country, it would rank third in annual CO2e emissions, only behind China and the United States (Figure 15). From 2015 to 2020, an average of 9.3 million ha of tropical forest was lost annually, compared to 0.06 million ha of boreal forest and 0.31 million ha of temperate forest (FAO 2020). However, on a net basis, temperate forests actually gained 2.2 million ha per year from 2010 to 2015, boreal and subtropical forests had little net change, but tropical forests experienced a net loss of 5.5 million ha per year (Keenan et al. 2015; FAO 2016). According to data from Global Forest Watch, from 2002 to 2020 the extent of primary tropical humid forests decreased by 6.3 percent, with losses of 4.2 million ha—an area roughly as large as the Netherlands—in 2020 alone. Brazil, the Democratic Republic of the Congo, Bolivia, and Indonesia continue to see the largest losses of irreplaceable primary rain forest (Weisse and Goldman 2021).

Figure 15 | If Tropical Deforestation Were a Country It Would Have the Fourth Highest Carbon Emissions Globally

Notes: GHG = greenhouse gas; MtCO2e = million metric tons of carbon dioxide equivalent.

Source: Authors. Based on data from Climate Watch (database),; and Pendrill, Persson, Godar, Kastner, Moran, et al. (2019).

The impact of cities on tropical forests around the world

Cities may cover only a tiny fraction of Earth’s surface, but they consume the majority of the world’s natural resources when factoring in the goods consumed in cities but produced elsewhere (UNSD n.d). Beef, soy, palm oil, wood fiber, coffee, and rubber are just a few examples of commodities extracted from forests or cultivated in formerly forested landscapes—often illegally—that have been associated with significant forest loss (Pendrill, Persson, Godar, and Kastner 2019).

Commercial production of key agricultural commodities—including soy, beef, and palm oil—is the largest contributor to tropical forest loss (Hosonuma et al. 2012; Seymour and Busch 2016; Weisse and Goldman 2021). Much of this goes to feed consumers in cities. Deforestation in the tropics to make space for agriculture, livestock, and establishing plantation forests is estimated to emit 2.6 GtCO2 (about 0.71 GtC) per year—around 5 percent of 2017 global emissions (Pendrill, Persson, Godar, Kastner, Moran, et al. 2019).27 Of this deforestation, roughly a quarter to a third is attributable to international demand for commodities; for example, when Brazilian beef is exported to Europe or the United States (Pendrill, Persson, Godar, and Kastner 2019; Pendrill, Persson, Godar, Kastner, et al. 2019). From 2001 to 2015, deforestation to make space for agricultural commodities was responsible for an estimated 27 percent of global tree cover loss (Curtis et al. 2018). Expansion of small-scale, often shifting agriculture, accounted for an additional 24 percent of global loss, and 93 percent of total tree cover loss in Africa (Figure 16; Curtis et al. 2018).

Figure 16 | Commodity-Driven Tree Cover Loss by Driver for the Period 2001–2018

Note: Certain types of deforestation may not be permanent—for example, forests may be able to grow back after a fire or following logging. But clearing for commodities represents a “permanent”’ transition from forest to nonforest land use, making it a much more significant source of climate-changing emissions. Within the context of this study, forest loss was categorized as shifting agriculture if the cell contained clearings that “showed signs of existing agriculture or pasture in most recent imagery as well as past clearings that contained visible forest or shrubland regrowth (gain) in historical imagery spanning the study period” (Curtis et al. 2018).

Source: Harris et al. 2020.

Beyond agricultural commodities, increased demand for timber or woody biomass for energy may also place pressure on tropical forests—now or in the future. Timber harvests can also lead to deforestation and ecological degradation, as when primary forests are replaced by fast-growing plantation forests, new logging roads are created, or forests are targeted by illegal logging (Shearman et al. 2012; Seymour and Busch 2016). Wood fuel is also implicated in the struggle to maintain tropical forest cover (Sassen et al. 2015; Pearson et al. 2017) and, as with other biofuels, can create land-use competition with food production at a global level, potentially jeopardizing a sustainable food future (Searchinger et al. 2018).

The linkage between deforestation and the urban consumption patterns that drive demand for these commodities reveals an important pathway for cities to reduce their carbon footprints. Avoiding deforestation is one of the most cost-effective ways to reduce emissions while conserving a carbon sink. Cities can act on this by practicing more sustainable sourcing of the commodities responsible for much of the world’s tropical deforestation, such as beef, soy, palm oil, coffee, and wood fiber; insisting that the countries those commodities come from stop deforesting land; and reducing the consumption of commodities such as beef. Because cities tend to use more resources than rural populations (Baabou et al. 2017) and are densely populated, changing urban consumption patterns can have a big impact on reducing deforestation (Defries et al. 2010). In the last decade, many multinational companies have committed to deforestation-free supply chains (Lyons-White and Knight 2018). Tropical timber, coffee, and chocolate can all be sourced in ways that do less harm to forests (Hylander and Nemomissa 2009; De Beenhouwer et al. 2013; Böhnert et al. 2016). Although deforestation-free sourcing has been implemented by some companies and at national levels, this strategy has yet to be widely adopted by cities. But cities can contribute meaningful action on this front, as evidenced by Oslo’s palm oil campaign and biofuel ban (Case Study 8). Promoting awareness is the first step cities can take towards these goals, as the World Wide Fund for Nature’s Earth Hour City Challenge has shown (Khan and Borgstrom-Hannson 2016).

Case Study 8 | Oslo and Palm Oil

What do cookies, cleaning supplies, and cosmetics have to do with rain forests? All can contain palm oil. To produce these consumer goods, rain forests—largely in Southeast Asia—have been cleared at alarming rates (which have declined slightly in recent years).a Palm oil is produced by the oil palm (Elaeis guineensis), an agricultural crop that grows well in the same climatic regions as tropical rain forests. From 2000 to 2011, approximately 270,000 hectares were deforested annually for palm oil production, much of this in Indonesia and Malaysia.b Indonesia’s and Malaysia’s tropical forests are home to some of the world’s last orangutans as well as the Leuser ecosystem—the only place on Earth where rhinoceroses, elephants, tigers, and orangutans are found in the same place along with countless other species.c They also store vast amounts of carbon—many are “peat forests,” which hold up to 20 times the amount of carbon in the soil as regular rain forests.d

People around the world unwittingly consume palm oil every day. And as most of the world’s population lives in cities, that is where most of this consumption happens. Measures at national and international levels are under way to stop the import of “deforestation palm oil” and to develop protocols and certification standards for sustainably produced palm oil. But these mechanisms only go so far in addressing the problem, their effectiveness is questioned by some, and they take time to implement.e

In 2012, the Oslo-based Rainforest Foundation Norway broadcast a message to consumers across Norway: “Don’t Eat the Forest.” The campaign spread the message that consuming palm oil in edible products is causing deforestation abroad—and encouraged businesses and individuals to reassess their consumption habits.f In less than a year, it swayed opinion so much that national palm oil consumption dropped by 66 percent from 2011 to 2012.g The campaign influenced the city to update its procurement policy to ban biofuels based on palm oil and tropical wood species from unsustainable sources.h

The Don’t Eat the Forest campaign coincided with a European-led effort to switch to renewable energy for transport, which increased demand for biofuel feedstocks, including palm oil. Up until 2015, Norway did not consume palm oil for biofuel; by 2017, it consumed 317 million liters.i Once again, a grassroots movement formed to change procurement policies: Indonesian Indigenous communities made their case to the European Commission, and Rainforest Foundation Norway spread the message to petroleum funds and the government. As a result, the Norwegian Government Pension Fund Global divested from unsustainable palm oil companies. The Norwegian parliament became the first in Scandinavia and Europe to eliminate palm oil–based biofuels from the government’s supply chain through the Public Procurement Act.j Shortly after, the European Commission drafted an act to phase out palm oil–based biofuel by 2030.k

This reduction in palm oil biofuel feedstocks comes at a time when countries such as Norway have also committed to increasing the domestic use of biofuels. In the Norwegian case, other feedstocks will be needed to fill the gap left by palm oil. Because the large-scale use of biofuels has been criticized,l it is important for cities to be aware of the negative impacts of biofuel feedstocks on global forests.m This example shows that although grassroots campaigns, private companies, and individuals are necessary to help raise awareness to impact collective behavior, cities such as Oslo are necessary to amplify the message and supported policies that lead to change.

Note: While palm oil is a deforestation-risk commodity, research shows that it is far more efficient (yield per hectare) than almost any other oil. The reduction in demand for palm oil by Oslo residents likely means they started buying similar goods with different oils, which may result in more land conversion than for oil palm, potentially leading (and possibly indirectly) to more deforestation than if they bought products with palm oil.

Sources: a. Vijay et al. 2016; b. Henders et al. 2015; c. Swarna Nantha and Tisdell 2009; UCS 2016; CBD Secretariat n.d.; d. Jaenicke et al. 2011; e. Dalton 2018; Gatti et al. 2019; f. Alfsen n.d.; g. Rainforest Foundation Norway 2012, 4; h. City of Oslo 2017; i. Miljø-Direktoratet 2019; j. Alfsen n.d.; k. Jong 2019; l. Searchinger and Heimlich 2015; m. Seymour and Morris 2018.

When used in concert with conserving forests, forest restoration and integrating trees into farmland through agroforestry and silvopastoral systems can also serve as important tools for climate change mitigation. Conserving forests is a more effective, and more cost-effective, means of reducing the accumulation of carbon in the atmosphere (Box 1) than forest restoration alone. But as a complementary strategy, forest restoration often increases the carbon storage in forest ecosystems (Shimamoto et al. 2018). Land can be left to regrow forests on its own (Cook-Patton et al. 2020), whereas tree planting is important to reforest areas that are too degraded or severely disturbed to recover naturally, such as degraded pastureland and areas affected by catastrophic wildfires that destroy nearby sources of seed (Wilson and Rhemtulla 2016; Holl and Brancalion 2020). Where ecological conditions allow, letting forests regenerate naturally on previously forested land can regain some of their former functions in a cost-effective way (Crouzeilles et al. 2017; Cook-Patton et al. 2020). For example, there are currently 2.4 million square kilometers of secondary-growth forests in Latin America. If allowed to continue growing, these forests could sequester 8.48 GtC from 2008 to 2048—an amount equivalent to all emissions from fossil fuel use and industrial processes from countries in Latin America and the Caribbean from 1993 to 2014 (Chazdon, Broadbent, et al. 2016). Research suggests that if the full 350 million ha pledged for restoration under the Bonn Challenge were allowed to regenerate naturally, it could provide about 42 GtC storage (about three years of current global GHG emissions) by 2100, compared with 1 GtC storage if the same volume of land were turned into plantations (Lewis et al. 2019).

Caveats and considerations

Not all forests provide the same carbon benefits: forest biodiversity creates more reliable carbon sinks and a safer investment for cities.

  • More biodiverse native forests tend to store more carbon than simplified/less biodiverse forests under similar climatic and geographic conditions (Cavanaugh et al. 2014; Poorter et al. 2015). This has been attributed to higher resource capture, more efficient resource use, and higher productivity (Poorter et al. 2015).
  • Mixed-species plantations can store greater amounts of carbon than monoculture (Díaz et al. 2009; Piotto et al. 2010; Potvin et al. 2011; Huang et al. 2018; Jactel et al. 2018; Waring et al. 2020). Carbon storage can be further increased by incorporating species with desirable traits, such as nitrogen-fixing species (Jactel et al. 2018; Marron and Epron 2019).
  • To offer long-term climate benefits, forests must be resilient. Biodiverse forests are likely to be more productive and offer more carbon benefits and other cobenefits due to increased resilience to disturbance and climate shocks (Liang et al. 2016; Jactel et al. 2018; Waring et al. 2020). But most planted forests in the tropics are planted with only one species, leaving them more vulnerable to disease and climatic disturbance (Payn et al. 2015; Seddon et al. 2019; Waring et al. 2020). Research shows that forests planted with mixed native species and mature native forests are more resilient. Whether planted, mature, or secondary, biodiverse forests are likely to be more productive. For example, intact tropical forests—which tend to be more biodiverse than degraded forests or monoculture plantations—create desirable traits by hosting nitrogen-fixing species (Jactel et al. 2018; Marron and Epron 2019) and establishing their own microclimates that reduce the risk of fire and protect them from droughts (Thompson et al. 2009).

With increasing climate uncertainty and risks as a result of climate change, it is not enough to maintain a certain area of forest; rather, maintaining forest quality and resilience will be essential to protecting forests to ensure they continue to store and sequester carbon.

Without immediate action to stop tropical deforestation and degradation, and encourage forest regrowth, these ecosystems could reach a “tipping point” where once-carbon-rich forests become drier savannah-like ecosystems (Lovejoy and Nobre 2018). Warming climates mean more drought and fires, which could double the area of land in the Amazon consumed by wildfires alone by 2050 (Brando et al. 2020). In a downward spiral, climate change harms tropical forests, inhibiting their ability to sequester carbon and releasing emissions that accelerate the rate of climate change (Baccini et al. 2017; Hubau et al. 2020; Anderegg et al 2020; Goldstein et al. 2020). When severely degraded or disturbed, forests may approach a tipping point, a threshold beyond which forest function deteriorates and becomes more vulnerable to human impact (Goldstein et al. 2020). The ability of tropical forests to sequester carbon in both Latin America and Africa is already being compromised due to degradation and the effects of climate change (Baccini et al. 2017; Hubau et al. 2020). Similarly, Harris et al. (2021) show that some of the largest tropical forests in the world are close to flipping from carbon sinks to carbon sources, with disastrous consequences for global CO2 levels. Of the three largest tropical rain forests, only the Congo’s tropical forests remain a strong carbon sink, with the Amazon teetering on the edge of becoming a source and forests across Southeast Asia becoming a net source of carbon emissions over the past 20 years (Harris et al. 2021).

Achieving carbon-neutrality commitments will require cities to integrate forests and trees into climate strategies. Conserving and restoring forests are currently some of the only natural, proven, and potentially cost-effective solutions to sequestering carbon and achieving net-negative emissions. Several cities are also exploring a number of innovative (and contested) strategies to harness the climate mitigation potential of forests, each with their own caveats and considerations (Box 2).

Box 2 | Three Contested Innovations Integrating Forests into City Climate Strategies

Timber Buildings

Many cities are exploring the use of wood to build large urban buildings in place of steel and concrete to reduce embodied emissions and store carbon. But the climate impact of using wood in long-life urban construction is based on a number of key factors, and unless very high targets are met, will more often lead to negative climate impacts.

Building construction and operations (such as home electricity consumption) are responsible for 38 percent of total global carbon dioxide (CO2) emissions.a Concrete and steel production alone accounts for 9 percent of all global CO2 emissions.b The search for low-carbon alternative building materials has become a critical aspect of urban climate strategies. Some have proposed wood as a renewable building material that could be used in place of concrete or steel for high-density urban buildings.c The technology of “mass timber” employs various lamination technologies, such as cross-laminated timber, to provide increased fire resistance and structural capacity and makes use of smaller solid wood components to increase efficiency of wood harvests.d Practitioners are positing the role of mass timber construction as a potential avenue for climate mitigation through displacement of other higher greenhouse gas (GHG) emitting materials, and as a long-term mechanism for storing terrestrial carbon.

However, the question of the net-carbon profile of wood as a building material is contentious.e Several important criteria must be considered in assessing potential climate benefits or downsides of using wood for long-life urban construction, and benefits may be difficult to achieve:

  • Most studies showing a positive climate benefit of mass timber inaccurately assume that using wood is “carbon neutral.” For example, such calculations do not factor in the forgone carbon that would have been sequestered by the trees if they had not been harvested. Once the opportunity cost of this carbon is factored in, most calculations show that using wood for mass timber is not climate friendly.
  • Increased demand for timber will result in increased “land-use competition” in lieu of other types of land use, such as conservation forests, food production, pasture, and so forth. The world is already projected to have an increase in wood demand of 50–70 percent by 2050 for “traditional” uses of wood. Mass timber represents an additional demand, further putting pressure on forest extent and forest density, especially in the context of the global land squeeze (competition for land for food, urban areas, climate protection, forest conservation, forest restoration, and so forth.).f
  • Conversion efficiency must be considered. When trees are harvested and then processed to make wood, often less than half—and sometimes as low as 5–10 percent—of the carbon is stored in building materials or products. Roots and slash left to decompose release significant amounts of carbon. The conversion from roundwood into sawnwood ranges from 45 percent to 66 percent.g This is often a function of processing technologies (e.g., logging, sawmilling) and the type of timber products (e.g., plywood versus solid sawn).

Modeling indicates that for mass timber to be climate beneficial, very high bars must be met (Searchinger et al. forthcoming):h

Conversion efficiency must be improved such that the utilization rate of the harvested timber is above 70 percent in secondary forests and above 40 percent in plantations, thereby reducing the amount of biomass residue that is left over in the forests to decompose.

Substitution rates, which refer to the climate impacts of a unit of concrete or steel versus the climate impacts of the equivalent units of timber used in a particular application, must be high. Net climate benefits from using timber are more likely when it replaces concrete or steel that has high climate impacts. Life cycle analysis tools can assist in comparing different building systems and materials, although to date most substitution rates are below threshold levels needed to be considered climate positive.

In the area where trees are harvested within a forest, the rate of regrowth must be rapid. Carbon sequestration rates will decrease while the forest regrows, so it is important that regrowth of the trees in the forest quickly returns to preharvest sequestration rates.

The longevity of forest products remaining in timber buildings is also a key factor. The length of time wood carbon is stored “in use” (i.e., not decomposed or burned) is an important factor in evaluating whether mass timber is climate beneficial or not. Perpetually reusing, upcycling, and recycling wood will help to store carbon longer.

Wood Biomass for Energy

In further efforts to reduce GHG emissions from operational energy, some cities have explored wood-based biomass energy as a substitute for fossil fuels because it is purported to be renewable and sustainable. However, this strategy has the potential to do the opposite and has become the focus of contentious debate.i Growing and clearing trees for fuel

  • may drive conversion to plantations, which can displace or compete with other important land uses such as agriculture or intact forest, leading to net deforestation and habitat loss;j
  • requires considerable carbon inputs for processing wood for biofuel;k
  • creates a carbon debt that takes decades to centuries to be resequestered by forests;l
  • requires the combustion of wood, which can result in the release of harmful air pollutants such as ultrafine particulate matter, carbon monoxide, and nitrogen oxides,m with health implications for communities near sites of combustion; and
  • detracts from investments and research in low-pollution, low-carbon renewable energy sources.

Wood-based biomass only has carbon benefits when it uses waste residues as feedstock, but problems arise when waste residue sources are exhausted and wood is used instead to meet energy demand, which comes at the expense of forests. If forests are allowed to regrow, evidence suggests that large-scale woody bioenergy will increase atmospheric emissions in the near to medium term before potentially decreasing them relative to emissions expected from fossil fuel combustionn—but this may be too late to avoid irreversible climate tipping points.

Carbon Credits, Nature-Based Solutions, and REDD+

Cities are exploring the purchase of carbon credits to “offset” their unabated emissions. Nature-based solutions (NBS) can be one source of carbon credits, including the purchase of credits that conserve, manage, and restore inner, nearby, and faraway forests, especially in the tropics. However, not all carbon credits are equally beneficial to forests, climate, biodiversity, and people, and some may have adverse outcomes.o To ensure that the use of NBS credits helps to deliver the goals of the Paris Agreement, the credits must have high environmental integrity and adhere to robust social and environmental safeguards. Ensuring environmental integrity requires that all credits are additional (i.e., the GHG mitigation would not have been implemented without the purchase of the carbon credits) as well as address risks of leakage (when an activity is displaced to another location—for instance, if forests are grown on agricultural lands and that results in the clearing of other forests to replace that demand for agriculture), reversals (when an emissions reduction or removal is reemitted—for instance, when a forest is grown on barren land but is then cut for fuel wood many years later), and double counting (when the credit is counted by more than one entity).p In addition to high environmental integrity, all credits need to have high social integrity as well. Cities purchasing NBS credits should ensure that the credits respect and project human rights and that Indigenous peoples and local communities receive a fair and equitable share of the benefits.q

One of the most prevalent types of NBS credit is called REDD+ (reducing emissions from deforestation and forest degradation, plus the sustainable management of forest and the conservation and enhancement of forest carbon stocks). Under the United Nations Framework Convention on Climate Change, REDD+ encourages developing countries to reduce forest-based emissions in return for performance-based payments from industrialized countries. Utilizing the voluntary carbon market, cities can counterbalance their unabated emissions through the purchase of NBS credits, including REDD+. More than 50 countries have launched national REDD+ initiatives, and although there is some evidence from Brazil, Indonesia, and Guyana—the first recipients of results-based finance—that REDD+ can be an effective strategy for reducing emissions from deforestation, additional finance and a transition to jurisdictional scale approaches are both urgently needed to combat underlying drivers of deforestation and provide the incentives for jurisdictional governments to act. The voluntary carbon market is one venue that can drive a significant amount of investment into NBS and at the needed scale. However, any purchase of NBS credits must be supplementary to a city’s own actions to decarbonize and not reduce the pace of its own emissions reductions.

Note: A jurisdictional approach refers to a government-led, comprehensive approach to forest and land use across one or more legally defined territories (Boyd et al. 2018).

Sources: a. UNEP 2020; b. IEA and UNEP 2018; c. Buchanan and Levine 1999; Gustavsson et al. 2006; Oliver et al. 2014; Churkina et al. 2020; Waring et al. 2020; d. Harte 2017; Milestone and Kremer 2019; e. Law et al. 2018; f. Hanson and Ranganathan 2022; g. FAO et al. 2020; h. Searchinger et al. forthcoming; i. Cornwall 2017; Searchinger et al. 2018; j. Searchinger et al. 2009; k. Sterman et al. 2018; l. Buchholz et al. 2016; m. Nussbaumer 2003; Williams et al. 2012; n. Sterman et al. 2018; IPCC 2019; Favero et al. 2020; o. Seymour and Langer 2021; p, q. Burns et al. 2022.

Concluding Thoughts

Dramatic changes in key sectors are needed to reduce global emissions and atmospheric CO2 emissions. Yet achieving these transformations in transportation, agriculture, or industry remains challenging—even politically contentious. Natural climate solutions can offer a broadly appealing and complementary pathway to avoid catastrophic damage from climate change and accrue cobenefits related to health and biodiversity.

Agile and wielding immense political power, cities are poised to be leaders in addressing climate change by reexamining their connections to forests. Although tropical forests may seem far removed from the activities of the city, consumption patterns in urban areas drive deforestation and degradation that releases massive amounts of carbon—and threaten our ability to avoid overshooting climate targets. Forests are the only natural, proven, and cost-effective carbon solution that can actually sequester carbon and produce negative emissions. And cities have the ability to protect and support these ecosystems, both directly and indirectly.

City actions that protect the world’s forests, especially tropical forests, can go a long way towards mitigating climate change. This commitment requires a multipronged approach that includes a shift towards sustainable, deforestation-free products and materials; shifting the diets of residents to more plant-based foods; and reducing food loss and waste. Forest-based approaches should not replace cuts to anthropogenic emissions—reducing emissions and sequestering carbon are both needed to meet global emissions reduction targets (Anderson, C.M., et al. 2019).