Editing IPCC:AR6/WGIII/Chapter-4 (section)

=== 4.2.2 Aggregate Effects of NDCs and Other Mitigation Efforts Relative to Long-term Mitigation Pathways ===

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<span id="introduction-1"></span>
==== 4.2.2.1 Introduction ====

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Near-term mitigation targets submitted as part of NDCs to the UNFCCC, as well as currently implemented policies, provide a basis for assessing potential emissions levels up to 2030 at the national, regional and global level. The following sections present an evaluation of the methods used for assessing projected emissions under NDCs and current policies (Section 4.2.2.2), and the results of these assessments at global, regional and national level assessing a broad available literature based on first NDC submissions from 2015/16 and pre-COVID economic projections (Section 4.2.2.3). The impacts of the COVID-19 pandemic and related government responses on emissions projections are then discussed in Section 4.2.2.4 and the implications of updated NDCs submitted in 2020/21 on emissions follow in Section 4.2.2.5. Section 4.2.2.6 presents an assessment of the so-called ‘implementation gap’ between what currently implemented policies are expected to deliver and what the ambitions laid out under the full implementation of the NDCs are projected to achieve. Finally, a comparison of ambitions across different countries or regions (Section 4.2.2.7) is presented and the uncertainties of projected emissions associated with NDCs and current policies are estimated, including a discussion of measures to reduce uncertainties in the specification of NDCs (Section 4.2.2.8).

The literature reviewed in this section includes globally comprehensive assessments of NDCs and current policies, both peer-reviewed and non-peer-reviewed (but not unpublished model results) as well as synthesis reports by the UNFCCC Secretariat, government reports and national studies.

The aggregate effects of NDCs provide information on where emissions might be in 2025/2030, working forward from their recent levels. [[IPCC:Wg3:Chapter:Chapter-3|Chapter 3]] of this report works backwards from temperature goals, defining a range of long-term global pathways consistent with 1.5°C, 2°C and higher temperature levels. By considering the two together, it is possible to assess whether NDCs are collectively consistent with 1.5°C, 2°C and other temperature pathways (Cross-Chapter Box 4 in this chapter).

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<span id="methods-to-project-emissions-under-ndcs-and-current-policies"></span>
==== 4.2.2.2 Methods to Project Emissions Under NDCs and Current Policies ====

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A variety of different methods are used to assess emissions implications of NDCs and current policies over the time horizon to 2025 or 2030. Some of these projections were explicitly submitted as part of an official communication to UNFCCC (e.g., Biennial Report, Biennial Update Reports or National Communications) while the majority is from independent studies.

Methods that are used in independent studies (but that can also underlie the official communications) can broadly be separated into two groups:

1. system modelling studies which analyse policies and targets in a comprehensive modelling framework such an integrated assessment, energy systems or integrated land-use model to project emissions (or other indicators) of mitigation targets in NDCs and current policies, either at the national or global scale (noting some differences in the systems); and

2. hybrid approaches that typically start out with emissions pathways as assessed by other published studies (e.g., the IEA World Energy Outlook, national emissions pathways such as those specified in some NDCs) and use these directly or apply additional modifications to them.

System modelling studies are conducted at global, regional and national scales. Global models provide an overview, are necessary for assessment of global phenomena (e.g., temperature change), can integrate climate models and trade effects. National models typically include more details on sectors, technology, behaviour and intersectoral linkages, but often use simplifying assumptions for international trade (e.g., the Armington elasticity approach). Critically, they can also better reflect local socio-economic and political conditions and their evolution (i.e., national development pathways). A variety of modelling paradigms are found, including optimisation and simulation models, myopic and with foresight, monolithic and modular (Annex III: Scenarios and Modelling Methods).

Among the hybrid approaches, three broader categories can be distinguished, (i) direct use of official emission projection as part of submitted NDC or other communication to UNFCCC, (ii) historical trend extrapolation of emissions based on inventory data, possibly disaggregated by sector and emission species, and (iii) use of Reference/Business-As-Usual pathways from an independent published study (e.g., IEA WEO). In all cases, the reductions are then estimated on top of the resulting emission trajectory. Note that globally comprehensive studies may vary the approach used depending on the country.

Beyond the method applied, studies also differ in a number of dimensions, including (i) their spatial resolution and coverage, (ii) their sectoral resolution and coverage, (iii) the GHGs that are included in the assessment, the GWPs (or other metrics) to aggregate them, the emissions inventory (official vs independent inventory data) and related accounting approaches used as a starting point for the projections, (iv) the set of scenarios analysed (Reference/Business-As-Usual, Current Policies, NDCs, etc.), and (v) the degree to which individual policies and their impact on emissions are explicitly represented (Table 4.1).

First, the studies are relevant to different spatial levels, ranging from macro-scale regions with globally comprehensive coverage to national level (Section 4.2.2.3) and sub-national and company level in a few cases (Section 4.2.3). It is important to recognise that globally comprehensive studies typically resolve a limited number of countries individually, in particular those that contribute a high share to global emissions, but have poor resolution of remaining countries or regions, which are assessed in aggregate terms. Conversely, studies with high resolution of a particular country tend to treat interactions with the global scale in a limited way. The recent literature includes attempts to provide a composite global picture from detailed national studies (Bataille et al. 2016a; [[#Deep%20Decarbonization%20Pathways%20Project--2015|Deep Decarbonization Pathways Project 2015]] ; [[#Roelfsema--2020|Roelfsema et al. 2020]] ).

A second dimension in which the studies are different is their comprehensiveness of covering different emitting sectors. Some studies focus on the contribution of a single sector, for example the agriculture, forestry and other land use (AFOLU) sector ( [[#Fyson--2019|Fyson and Jeffery 2019]] ; [[#Grassi--2017|Grassi et al. 2017]] ) or the energy system (including both energy supply and demand sectors), to emission reductions as specified in the NDC. Such studies give an indication of the importance of a given sector to achieving the NDC target of a country and can be used as a benchmark to compare to comprehensive studies, but adding sectoral contributions up represents a methodological challenge.

Third, GHG coverage is different across studies. Some focus on CO 2 only, while others take into account the full suite of Kyoto gases (CO 2 , CH 4 , N 2 O, HFCs, PFCs and SF 6 ). For the latter, different metrics for aggregating GHGs to a CO 2 -equivalent metric are being used, typically GWP 100 from different IPCC assessments (Table 4.1).

Fourth, studies typically cover a set of scenarios, though how these scenarios are defined varies widely. The literature reporting IAM results often includes ''Nationally Determined Contribution'' (NDC), which are officially communicated, and ''Current Policies'' (CP) as interpreted by modellers. Studies based on national modelling, by contrast, tend to define scenarios reflecting very different national contexts. In both cases, modellers typically include so-called ''No Policy Baseline'' scenarios (alternatively referred to as ''Reference'' or ''Business-as-Usual scenarios'' ) which do not necessarily reflect currently implemented policies and thus are not assessed as reference pathways ( [[#4.2.6.1|Section 4.2.6.1]] ). There are also various approaches to considering more ambitious action compared to the CP or NDC projections that are covered in addition.

Fifth, studies differ in the way they represent policies (current or envisioned in NDCs), depending on their internal structure. For example, a subsidy to energy efficiency in buildings may be explicitly modelled (e.g., in a sectoral model that represents household decisions relative to building insulation), represented by a proxy (e.g., by an exogenous decrease in the discount rate households use to make choices), or captured by its estimated outcome (e.g., by an exogenous decrease in the household demand for energy, say in an energy system model or in a compact CGE). Detailed representations (such as the former example) do not necessarily yield more accurate results than compact ones (the latter example), but the set of assumptions that are necessary to represent the same policy will be very different.

Finally, policy coverage strongly varies across studies with some just implementing high level targets specified in policy documents and NDCs while others represent the policies with the largest impact on emissions and some looking at very detailed measures and policies at sub-national level. In addition, in countries with rapidly evolving policy environments, slightly different cut-off dates for the policies considered in an emission projection can make a significant difference for the results ( [[#Dubash--2018|Dubash et al. 2018]] ).

The challenges described above are dealt with in the assessment of quantitative results in Section 4.2.2.3 by (i) comparing national studies with country-level results from global studies to understand systematic biases; (ii) comparing economy-wide emissions (including AFOLU) as well as energy-related emissions; (iii) using different emission metrics including CO 2 and Kyoto GHG emissions where the latter have been harmonised to using AR6 GWP100 metrics; and (iv) tracking cut-off dates of implemented policies and NDCs used in different references (Table 4.SM.1). The most notable differences in quantitative emission estimates related to current policies and NDCs relate to the COVID-19 pandemic and its implications and to the updated NDCs mostly submitted since early 2020 which are separately dealt with in Sections 4.2.2.4 and 4.2.2.5, respectively.

In addition to assessing the emissions outcomes of NDCs, some studies report development indicators, by which they mean a wide diversity of socio-economic indicators ( [[#Jiang--2013|Jiang et al. 2013]] ; [[#Chai--2014|Chai and Xu 2014]] ; [[#Delgado--2014|Delgado et al. 2014]] ; [[#La%20Rovere--2014a|La Rovere et al. 2014a]] ; [[#Zevallos--2014|Zevallos et al. 2014]] ; Benavides et al. 2015; Altieri et al. 2016; Bataille et al. 2016a; [[#Zou--2016|Zou et al. 2016]] ; [[#Paladugula--2018|Paladugula et al. 2018]] ; [[#Parikh--2018|Parikh et al. 2018]] ; [[#Yang--2021|Yang et al. 2021]] ), share of low-carbon energy (Bertram et al. 2015; [[#Riahi--2015|Riahi et al. 2015]] ), renewable energy deployment ( [[#Roelfsema--2018|Roelfsema et al. 2018]] ), production of fossil fuels ( [[#SEI--2020|SEI et al. 2020]] ) or investments into low-carbon mitigation measures ( [[#McCollum--2018|McCollum et al. 2018]] ) to track progress towards long-term temperature goals.

'''Table 4.1 | Assessment of projected 2030 emissions of current policies based on pre-COVID assumptions and original NDCs submitted in 2015/16 for 28 individual countries/regions and the world.''' The table compares projected emissions from globally comprehensive studies, national studies and, when available, official communications to UNFCCC using different emission sources (fossil fuels, AFOLU sector) and different emission metrics (CO 2 , Kyoto GHGs). The comparison allows identifying potential biases across the ranges and median estimates projected by the different sets of studies.

{| class="wikitable"
|-
! rowspan="3"| Region a

! rowspan="3"| GHG share [%] b

! rowspan="3"| Type c

! rowspan="3"| \# estimates d

! colspan="3"| Current Policies 2030 emissions

! colspan="3"| NDC 2030 emissions (conditional/unconditional)

|-
! colspan="2"| CO 2 only [GtCO 2 ] median (min–max) f

! Kyoto GHGs e [GtCO 2 -eq] median (min–max) f

! colspan="2"| CO 2 only [GtCO 2 ] median (min–max) f

! Kyoto GHGs e [GtCO 2 -eq] median (min–max) f

|-
! incl. AFOLU g

! fossil fuels

! incl. AFOLU g

! incl. AFOLU g

! fossil fuels

! incl. AFOLU g

|-
| World

| 100

| global

| 93

| 43 (38–51)

| 37 (33–45)

| 60 (54–68)

| 40 (35–45)/ 37 (35–39)

| 32 (26–39)/ 31 (27–37)

| 54 (50–60)/ 57 (49–63)

|-
| rowspan="2"| CHN

| rowspan="2"| 27

| global

| 76

| 12 (9.7–15)

| 11 (8.4–14)

| 15 (12–18)

| – /11 (9.8–13)

| – /8.8 (6.9–13)

| – /14 (13–16)

|-
| national

| 13

| 12 (12–12)

| 11 (9.2–13)

| 15 (13–15)

| – /12 (11–12)

| – /11 (10–11)

| – /15 (13–16)

|-
| rowspan="2"| USA h

| rowspan="2"| 12

| global

| 71

| 4.9 (4.4–6.6)

| 4.6 (3.5–6.5)

| 5.9 (4.9–6.6)

| – /3.8 (3.3–4.1)

| – /3.9 (3.1–5.3)

| – /4.6 (4–5.1)

|-
| national

| 5

| 4.1

| 4.5 (4.1–4.9)

| 5.9 (5.2–6.7)

| – /3.4

| – /3.5

| – /4.3

|-
| rowspan="3"| EU i

| rowspan="3"| 8.1

| global

| 24

| 2.7 (2.1–3.5)

| 2.6 (2.1–3.3)

| 3.4 (2.6–4.7)

| – /2.6 (2.1–2.8)

| – /2.4 (2.1–2.7)

| – /3.2 (2.6–3.7)

|-
| national

| 3

| 3.1

| 2.6

|
| – /2.5

|
|-
| official

| 3

|
| 3.2 (2.8–3.7)

|
|-
| rowspan="2"| IND

| rowspan="2"| 7.1

| global

| 79

| 3.7 (3–4.5)

| 3.2 (2.5–4.5)

| 4.7 (4.1–6.4)

| 3.3 (3.1–4.4)/4

| 3.3 (2.4–5.6)/3.8 (2.9–5.6)

| 5 (4.2–6.4)/5.8 (4.9–6.1)

|-
| national

| 9

| 3.4 (3.3–4)

| 3.4 (2.9–3.9)

| 5.5 (5–5.7)

| 3.4 (3.2–3.6)/3.2

| 3.4 (3.2–3.5)/2.9

| 5.1/4.9

|-
| rowspan="3"| RUS

| rowspan="3"| 4.5

| global

| 66

| 1.7 (0.84–2)

| 1.6 (1.5–2)

| 2.3 (1.6–3.3)

| – /1.7 (0.85–1.9)

| – /1.6 (1.2–1.9)

| – /2.6 (1.9–3.1)

|-
| national

| 6

|
| 1.5 (1.5–1.5)

| 2.6

|
| – /1.5 (1.5–1.5)

| – /2.5

|-
| official

| 2

|
| 2.1

|
| – /2.7

|-
| rowspan="3"| BRA

| rowspan="3"| 2.5

| global

| 69

| 1.1 (0.79–1.7)

| 0.5 (0.28–1.1)

| 1.8 (1.4–2.7)

| – /0.94 (0.52–1.5)

| – /0.38 (0.097–0.86)

| – /1.3 (1.2–2.5)

|-
| national

| 4

| 0.59

| 0.47

| 1.8

| – /0.51

| – /0.47

| – /1.2

|-
| official

| 1

|
| – /1.2

|-
| rowspan="3"| JPN

| rowspan="3"| 2.4

| global

| 66

| 1.2 (0.94–1.3)

| 1.1 (0.67–1.3)

| 1.2 (0.95–1.3)

| – /1 (0.9–1.2)

| – /0.83 (0.65–1.2)

| – /1 (0.95–1.2)

|-
| national

| 16

| 1.1 (1.1–1.6)

| 1.1 (1.1–1.5)

| 1.3 (1.2–1.7)

| – /0.93 (0.91–1.2)

| – /0.93 (0.87–1.1)

| – /1 (1–1.3)

|-
| official

| 1

|
| – /1

|-
| rowspan="2"| IDN

| rowspan="2"| 2.2

| global

| 25

| 1.1 (0.79–2)

| 0.62 (0.51–0.89)

| 1.7 (1.4–2.4)

| 0.93 (0.76–1.4)/0.99

| 0.53 (0.45–0.66)/0.68 (0.6–0.77)

| 1.8 (1.3–2.1)/2.1 (1.5–2.2)

|-
| official

| 2

|
| 1.9 (1.8–1.9)/2.2

|-
| rowspan="3"| CAN

| rowspan="3"| 1.5

| global

| 67

| 0.58 (0.4–0.8)

| 0.43 (0.38–0.72)

| 0.68 (0.51–1)

| – /0.43 (0.34–0.67)

| – /0.43 (0.31–0.64)

| – /0.53 (0.49–0.82)

|-
| national

| 2

| 0.54

|
| 0.71

| – /0.41

|
| – /0.54

|-
| official

| 2

|
| 0.67

|
|-
| rowspan="2"| MEX

| rowspan="2"| 1.5

| global

| 31

| 0.61 (0.54–1.3)

| 0.48 (0.3–0.56)

| 0.82 (0.72–1.7)

| 0.54 (0.48–1)/0.46

| 0.43 (0.27–0.54)/0.33 (0.26–0.42)

| 0.65 (0.62–1.4)/0.73 (0.63–0.79)

|-
| official

| 2

|
| 0.62/0.76

|-
| SAU

| 1.5

| global

| 6

| 0.7 (0.57–0.82)

| 0.61 (0.48–0.74)

| 1 (0.7–1.1)

| 0.7 (0.58–0.82)/ –

| 0.62 (0.49–0.74)/ –

| 0.83 (0.7–0.96)/ –

|-
| rowspan="3"| KOR

| rowspan="3"| 1.4

| global

| 64

| 0.69 (0.55–0.76)

| 0.67 (0.42–0.91)

| 0.72 (0.68–0.81)

| – /0.57 (0.5–0.65)

| – /0.4 (0.26–0.61)

| – /0.57 (0.5–0.69)

|-
| national

| 4

| 0.78 (0.75–0.81)

| 0.73 (0.7–0.76)

| 0.86 (0.83–0.89)

| – /0.62 (0.51–0.72)

| – /0.58 (0.49–0.67)

| – /0.68 (0.56–0.8)

|-
| official

| 1

|
|-
| rowspan="3"| AUS

| rowspan="3"| 1.1

| global

| 16

| 0.42 (0.34–0.49)

| 0.34 (0.28–0.46)

| 0.54 (0.46–0.69)

| – /0.36 (0.28–0.43)

| – /0.3 (0.24–0.41)

| – /0.44 (0.39–0.52)

|-
| national

| 3

|
| 0.55

|
|-
| official

| 2

|
| 0.52 (0.51–0.52)

|
|-
| rowspan="2"| TUR

| rowspan="2"| 1.1

| global

| 18

| 0.44 (0.44–0.49)

| 0.4 (0.34–0.43)

| 0.6 (0.51–0.83)

| – /0.44 (0.44–0.49)

| – /0.4 (0.27–0.43)

| – /0.94 (0.55–1)

|-
| official

| 1

|
| – /0.93

|-
| rowspan="2"| ZAF

| rowspan="2"| 1.1

| global

| 26

| 0.49 (0.35–0.62)

| 0.36 (0.23–0.56)

| 0.64 (0.45–0.85)

| – /0.4 (0.27–0.55)

| – /0.35 (0.21–0.44)

| 0.41/0.58 (0.39–0.65)

|-
| official

| 1

|
| – /0.52 (0.41–0.64)

|-
| rowspan="2"| VNM

| rowspan="2"| 0.92

| global

| 2

|
| 0.61/0.77

|-
| national

| 4

| 0.36

| 0.28

|
| 0.32 (0.28–0.36)/0.36

| 0.26 (0.24–0.28)/0.28

|
|-
| GBR

| 0.86

| global

| 4

| 0.37

| 0.33 (0.3–0.37)

|
| – /0.37

| – /0.33 (0.3–0.37)

|
|-
| FRA

| 0.85

| global

| 4

| 0.22

| 0.32 (0.24–0.4)

|
| – /0.22

| – /0.32 (0.24–0.4)

|
|-
| rowspan="2"| THA

| rowspan="2"| 0.84

| global

| 5

|
| 0.41 (0.41–0.41)

|
| 0.44/0.47

|-
| national

| 3

| 0.43

| 0.4

| 0.58

| 0.35/0.36

| 0.32/0.34

| 0.43/0.46

|-
| rowspan="3"| ARG

| rowspan="3"| 0.76

| global

| 22

| 0.33 (0.17–0.52)

| 0.2 (0.15–0.35)

| 0.51 (0.33–0.75)

| 0.25 (0.17–0.46)/0.25

| 0.21 (0.18–0.23)/0.15 (0.14–0.16)

| 0.39 (0.32–0.69)/0.51 (0.33–0.52)

|-
| national

| 2

|
| 0.42 (0.41–0.43)

|
| – /0.19

|
|-
| official

| 2

|
| 0.4/0.52

|-
| KAZ

| 0.71

| global

| 3

|
| 0.45

|
| 0.28/0.32

|-
| UKR

| 0.52

| global

| 2

|
| 0.42 (0.42–0.42)

|
| – /0.54

|-
| PHL

| 0.48

| global

| 3

|
| 0.24

|
| 0.082/ –

|-
| COL

| 0.4

| global

| 5

|
| 0.23 (0.23–0.23)

|
| 0.26 (0.26–0.26)/0.29 (0.29–0.29)

|-
| ETH

| 0.31

| global

| 5

|
| 0.022

| 0.23 (0.19–0.27)

|
| – /0.023

| 0.16 (0.15–0.16)/ –

|-
| MAR

| 0.21

| global

| 5

|
| 0.11 (0.087–0.13)

|
| 0.13 (0.1–0.15)/0.13 (0.1–0.15)

|-
| KEN

| 0.18

| global

| 5

|
| 0.022

| 0.13 (0.11–0.14)

|
| – /0.023

| 0.11 (0.11–0.11)/ –

|-
| SWE

| 0.13

| global

| 4

| –0.012

| 0.03 (0.029–0.031)

|
| – /–0.012

| – /0.03 (0.028–0.032)

|
|-
| rowspan="2"| PRT

| rowspan="2"| 0.12

| global

| 2

| 0.045

| 0.036

|
| – /0.045

| – /0.036

|
|-
| national

| 1

|
| – /0.023

|
|-
| rowspan="2"| CHE

| rowspan="2"| 0.094

| global

| 1

|
| – /0.026

|-
| national

| 1

| 0.027

| 0.025

|
|-
| rowspan="2"| MDG

| rowspan="2"| 0.065

| global

| 1

|
| 0.033/ –

|-
| national

| 3

| 0.071

| 0.0059

|
| 0.07 (0.068–0.071)/ –

| 0.0043 (0.0026–0.0059)/ –

|
|}

Notes: a Countries are abbreviated by their ISO 3166-1 alpha-3 letter codes. EU denotes the European Union. b 2018 Share of global Kyoto GHG emissions, excluding FOLU emissions, based on 2019 GHG emissions from [[IPCC:Wg3:Chapter:Chapter-2|Chapter 2]] ( [[#Minx--2021|Minx et al. 2021]] ; [[#Crippa--2021|Crippa et al. 2021]] ). c Type distinguishes between independent globally comprehensive studies (that also provide information at the country/region level), independent national studies and official communications via Biennial Reports, Biennial Update Reports or National Communications. d Different estimates from one study (e.g., data from multiple models or minimum and maximum estimates) are counted individually, if available. e GHG emissions expressed in CO 2 -eq emission using AR6 100-year GWPs (see [[IPCC:Wg3:Chapter:Chapter-2#2.2.2|Section 2.2.2]] for a discussion of implications for historical emissions). GHG emissions from scenario data is recalculated from individual emission species using AR6 100-year GWPs. GHG emissions from studies that do provide aggregate GHG emissions using other GWPs are rescaled using 2019 GHG emissions from [[IPCC:Wg3:Chapter:Chapter-2|Chapter 2]] ( [[#Minx--2021|Minx et al. 2021]] ; [[#Crippa--2021|Crippa et al. 2021]] ). f If more than one value is available, a median is provided and the full range of estimates (in parenthesis). To avoid a bias due to multiple estimates provided by the same model, only one estimate per model, typically the most recent update, is included in the median estimate. In the full range, multiple estimates from the same model might be included, in case these reflect specific sensitivity analyses of the ‘central estimate’ (e.g., Baumstark et al. 2021; [[#Rogelj--2017|Rogelj et al. 2017]] ). g Note that AFOLU emissions from national GHG inventories and global/national land use models are generally different due to different approaches to estimate the anthropogenic CO 2 sink ( [[#Grassi--2018|Grassi et al. 2018]] , 2021) ( [[IPCC:Wg3:Chapter:Chapter-7#7.2.3|Section 7.2.3]] and Cross-Chapter Box 6 in Chapter 7). h The estimates for USA are based on the first NDC submitted prior to the withdrawal from the Paris Agreement, but not including the updated NDC submitted following its re-entry. i The EU estimates are based on the 28 member states up until 31 January 2020, i.e., including UK.

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<span id="projected-emissions-under-ndcs-and-current-policies-by-20252030"></span>
==== 4.2.2.3 Projected Emissions Under NDCs and Current Policies by 2025/2030 ====

<div id="h3-3-siblings" class="h3-siblings"></div>

The emissions projections presented in this section relate to the first NDCs, as communicated in 2015 and 2016, and on which an extensive literature exists. New and updated NDCs, mostly submitted since the beginning of 2020, are dealt with in Section 4.2.2.5. Similarly, the implications of COVID-19 and the related government responses on emissions projections is specifically dealt with in Section 4.2.2.4.

Table 4.1 presents the evidence base for the assessment of projected emissions of original NDCs and current policies until 2030. It covers 31 countries and regions responsible for about 82% of global GHG emission (excluding FOLU CO 2 emissions) and draws quantitative estimates from more than 40 studies (Table 4.SM.1 in the Supplementary Material to this chapter). The table allows comparing emission projections from national and globally comprehensive studies as well as official communications by countries to the UNFCCC at the national/regional level. The global aggregates presented in Table 4.1 derive from globally comprehensive studies only and are not the result of aggregating country projections up to the global level. As different studies report different emission indicators, the table includes four different indicators: CO 2 and GHG emissions, including or excluding AFOLU emissions. Where possible, multiple indicators are included per study.

<div id="Globally comprehensive studies" class="h4-container"></div>

<span id="globally-comprehensive-studies"></span>
===== Globally comprehensive studies =====

<div id="h4-1-siblings" class="h4-siblings"></div>

The UNFCCC Secretariat has assessed the aggregate effect of NDCs multiple times. The first report considered the intended NDCs in relation to 2°C ( [[#UNFCCC--2015b|UNFCCC 2015b]] ), whereas the second considered NDCs also in relation to 1.5°C ( [[#UNFCCC--2016b|UNFCCC 2016b]] ). New submissions and updates of NDCs in 2020/21 are assessed in Section 4.2.2.5. A number of globally comprehensive studies ( [[#den%20Elzen--2016|den Elzen et al. 2016]] ; [[#Luderer--2016|Luderer et al. 2016]] ; [[#Rogelj--2016|Rogelj et al. 2016]] , 2017; [[#Vandyck--2016|Vandyck et al. 2016]] ; [[#Rose--2017|Rose et al. 2017]] ; Baumstark et al. 2021) which estimate aggregate emissions outcomes of NDCs and current policies have previously been assessed in Cross-Chapter-Box 11 of IPCC SR1.5.

According to the assessment in this report, studies projecting emissions of current policies based on pre-COVID assumptions lead to median global GHG emissions of 60 GtCO 2 -eq with a full range of 54–68 by 2030 and original unconditional and conditional NDCs submitted in 2015/16 to 57 (49–63) and 54 (50–60) GtCO 2 -eq, respectively ( ''robust evidence'' , ''medium agreement'' ) (Table 4.1). Globally comprehensive and national-level studies project emissions of current policies and NDCs to 2025 and 2030 and, in general, are in good agreement about projected emissions at the country level.

These estimates are close to the ones provided by the IPCC SR1.5, Cross-Chapter-Box 11, and the UNEP emissions gap report ( [[#UNEP--2020a|UNEP 2020a]] ). [[#footnote-003|3]]

<div id="Nat" class="h4-container"></div>

<span id="national-studies"></span>
===== National studies =====

<div id="h4-2-siblings" class="h4-siblings"></div>

A large body of literature on national and regional emissions projections, including official communications of as part of the NDC submissions and independent studies exist. A subset of this literature provides quantitative estimates for the 2030 timeframe. As highlighted in Section 4.2.1, the number of independent studies varies considerably across countries with an emphasis on the largest emitting countries. This is reflected in Table 4.1 (see also Table 4.SM.1). Despite smaller differences between globally comprehensive and national studies for a few countries, there is generally good agreement between the different types of studies, providing evidence that these quantitative estimates are fairly robust.

<div id="Sectoral studies" class="h4-container"></div>

<span id="sectoral-studies"></span>
===== Sectoral studies =====

<div id="h4-3-siblings" class="h4-siblings"></div>

Sectoral studies are essential to understand the contributions of concrete measures of NDCs and current policies. For example, approximately 98% of NDCs include the energy sector in their mitigation contributions, of which nearly 50% include a specific target for the share of renewables, and about 5% aim at increasing nuclear energy production ( [[#Stephan--2016|Stephan et al. 2016]] ). Transport is covered explicitly in 75% of NDCs, although specific targets for the sector exist in only 21% of NDCs ( [[#PPMC%20and%20SLoCaT--2016|PPMC and SLoCaT 2016]] ). Measures or targets for buildings are referred to explicitly in 27% of NDCs ( [[#GIZ--2017|GIZ 2017]] ). Additionally, 36% of NDCs include targets or actions that are specific to the agriculture sector ( [[#FAO--2016|FAO 2016]] ). LULUCF (mitigation) is included in 80% of all submitted NDCs, while 59% include adaptation and 29% refer to REDD+.

Greater sectoral expertise and involvement will be critical to accomplishing development and climate goals due to enhanced availability of information and expertise on specific sectoral options, greater ease of aligning the NDCs with sectoral strategies, and greater awareness among sector-level decision-makers and stakeholders ( [[#Fekete--2015|Fekete et al. 2015]] ; [[#NDC%20Partnership--2017|NDC Partnership 2017]] ). Sector-specific studies are assessed in the sectoral Chapters (6 to 11) of this report.

<div id="4.2.2.4" class="h3-container"></div>

<span id="estimated-impact-of-covid-19-and-governmental-responses-on-emissions-projections"></span>
==== 4.2.2.4 Estimated Impact of COVID-19 and Governmental Responses on Emissions Projections ====

<div id="h3-4-siblings" class="h3-siblings"></div>

The impacts of COVID-19 and national governments’ economic recovery measures on current ( [[IPCC:Wg3:Chapter:Chapter-2#2.2.2|Section 2.2.2]] ) and projected emissions of individual countries and globally under current policies scenarios until 2030 may be significant, although estimates are highly uncertain and vary across the few available studies. The analyses published to date (October 2021) are based on limited information about how COVID-19 has affected the economy and hence GHG emissions across countries so far in 2020, and also based on assumptions about COVID-19’s longer term impact. Moreover, the comparison of pre- and post-COVID-19 projections captures the impact of COVID-19 as well as other factors such as the consideration of recently adopted policies not related to COVID-19, and methodological changes.

Across different studies ( [[#Kikstra--2021|Kikstra et al. 2021]] ; [[#IEA--2020|IEA 2020]] ; [[#Dafnomilis--2021|Dafnomilis et al. 2021]] ; [[#Pollitt--2021|Pollitt et al. 2021]] ; [[#UNEP--2020a|UNEP 2020a]] ; [[#Climate%20Action%20Tracker--2020|Climate Action Tracker 2020]] ; [[#Keramidas--2021|Keramidas et al. 2021]] ; [[#Dafnomilis--2020|Dafnomilis et al. 2020]] ), the impact of the general slowdown of the economy due to the COVID-19 pandemic and its associated policy responses would lead to a reduced estimate of global GHG emissions in 2030 of about 1 to 5 GtCO 2 -eq, equivalent to 1.5–8.5%, compared to the pre-COVID-19 estimates (Table 4.SM.2). [[#Nascimento--2021|Nascimento et al. (2021)]] analyse the impacts of COVID-19 on current policy emission projections for 26 countries and regions and find a large range of emission reduction – between –1% and –21% – across these.

As indicated by a growing number of studies at the national and global level, how large near- to mid-term emissions implications of the COVID-19 pandemic are to a large degree depends on how stimulus or recovery packages are designed ( [[#Forster--2020|Forster et al. 2020]] ; [[#Gillingham--2020|Gillingham et al. 2020]] ; [[#IEA--2020|IEA 2020]] ; [[#Le%20Quéré--2020|Le Quéré et al. 2020]] ; [[#Malliet--2020|Malliet et al. 2020]] ; [[#Wang--2020|Wang et al. 2020]] ; [[#Obergassel--2021|Obergassel et al. 2021]] ; [[#Pollitt--2021|Pollitt et al. 2021]] ; [[#UNEP--2020a|UNEP 2020a]] ).

Four studies ( [[#Climate%20Action%20Tracker--2021|Climate Action Tracker 2021]] ; [[#den%20Elzen--2021|den Elzen et al. 2021]] ; [[#JRC--2021|JRC 2021]] ; [[#Riahi--2021|Riahi et al. 2021]] ) provide an update of the current policies assessment presented in Section 4.2.2.3 by taking into account the effects of COVID-19 as well as potential updates of policies. The resulting GHG emissions in 2030 are estimated to be 57 GtCO 2 -eq with a full range of 52 to 60 GtCO 2 -eq ( [[#_idTextAnchor043|Table 4.2]] ). This is a reduction of about 3 GtCO 2 -eq or 5% compared to the pre-COVID estimates from Section [[#_idTextAnchor016|4.2.2.3]] .

'''Table 4.2 | Projected global GHG emissions of current po''' '''licies by 2030.'''

{| class="wikitable"
|-
! Study

! Cut-off date

! Kyoto GHGs a [GtCO 2 -eq] median (min–max) b

! References

|-
| Climate Action Tracker

| 8/2020

| 54 (52–56)

| [[#Climate%20Action%20Tracker--2021|Climate Action Tracker (2021)]]

|-
| PBL

| 11/2020

| 58

| [[#den%20Elzen--2021|den Elzen et al. (2021)]] ; [[#Nascimento--2021|Nascimento et al. (2021)]]

|-
| JRC – GECO

| 12/2019

| 57

| [[#JRC--2021|JRC (2021)]]

|-
| ENGAGE c

| 7/2019

| 57 (52–60)

| [[#Riahi--2021|Riahi et al. (2021)]]

|-
| Total d

|
| 57 (52–60)

|
|}

Notes: a GHG emissions expressed in CO 2 -eq emission using AR6 100-year GWPs. GHG emissions from studies that provide aggregate GHG emissions using other GWPs are rescaled using 2019 GHG emissions from [[IPCC:Wg3:Chapter:Chapter-2|Chapter 2]] ( [[#Minx--2021|Minx et al. 2021]] ; [[#Crippa--2021|Crippa et al. 2021]] ). b If a range is available from a study, a median is provided in addition to the range. c Range includes estimates from four models: GEM-E3, MESSAGEix-GLOBIOM, POLES, REMIND-MAgPIE, based on sensitivity analysis. d To avoid a bias due to multiple estimates provided by the same model, only one estimate per model, typically the most recent update, is included in the median estimate for the total.

<div id="4.2.2.5" class="h3-container"></div>

<span id="estimated-impact-of-new-and-updated-ndcs-on-emissions-projections"></span>
==== 4.2.2.5 Estimated Impact of New and Updated NDCs on Emissions Projections ====

<div id="h3-5-siblings" class="h3-siblings"></div>

The number of studies estimating the emissions implications of new and updated NDCs and announced mitigation pledges that can be used for the quantitative assessment is limited to four (Table 4.3) ( [[#Climate%20Action%20Tracker--2021|Climate Action Tracker 2021]] ; [[#den%20Elzen--2021|den Elzen et al. 2021]] ; [[#Meinshausen--2021|Meinshausen et al. 2021]] ; [[#JRC--2021|JRC 2021]] ). One other study includes a limited number of NDC updates ( [[#Riahi--2021|Riahi et al. 2021]] ) and another ( [[#UNFCCC--2021|UNFCCC 2021]] ) excludes LULUCF emissions. They are therefore not directly comparable to the other two. In addition, the UNEP Emissions Gap Report 2021 ( [[#UNEP--2021|UNEP 2021]] ) in itself is assessment of almost the same studies included here. The evidence base for the updated NDC assessment is thus considerably smaller compared to that of the assessment of emissions implications of original NDCs presented in Section 4.2.2.3. However, it is worthwhile to note that the earlier versions of the studies summarised in Table 4.2 and Table 4.3 are broadly representative for the emissions range implied by the pre-COVID-19 current policies and original NDCs of the full set of studies shown in Table 4.1, therefore building confidence in estimates.

An additional challenge lies in the fact that these studies do not all apply the same cut-off date for NDC updates, potentially leading to larger systematic deviations in the resulting emission estimates. Another complication is the fact that publicly announced mitigation pledges on global 2030 emissions that have not been officially submitted to the UNFCCC NDC registry yet, have been included in several of the studies to anticipate their impact on emission levels (see notes to [[#_idTextAnchor044|Table 4.3]] ). In addition to the updates of NDC targets, most of the new studies also include impacts of COVID-19 on future emission levels (as discussed in Section ) which may have led to considerable downward revisions of emission trends unrelated to NDCs. Table 4.3 presents the emission estimates of the four studies that form the basis of the quantitative assessment presented here and three other studies to compare with.

Comparing the emission levels implied by the new and updated NDCs as shown in Table 4.3 with those estimated by the original NDCs from the same studies (as included in Table 4.1), a downward revision of 3.8 (3.0–5.3) GtCO 2 -eq of the central unconditional NDC estimates and of 4.5 (2.7–6.3) GtCO 2 -eq of the central conditional NDC estimate emerges ( ''medium evidence'' , ''medium agreement'' ). The emissions gaps between temperature limits and new and updated NDCs are assessed in Cross-Chapter Box 4 below. New and updated unconditional NDCs reduce the median gap with emissions pathways that limit warming to 2°C (&gt;67%) in 2030 by slightly more than 20%, from a median gap of 17 GtCO 2 -eq (9–23) to 13 (10–16). New and updated conditional NDCs reduce the median gap with emissions pathways that limt warming to 2°C (&gt;67%) in 2030 by about one third, from 14 GtCO 2 -eq (10–20) to 9 (6–14). New and updated unconditional NDCs reduce the median gap with emissions pathways that limit warming to 1.5°C (&gt;50%) with no or limited overshoot in 2030 by about 15%, from a median gap of 27 GtCO 2 -eq (19–32) to 22 GtCO 2 -eq (19–26). New and updated conditional NDCs reduce the median gap with emissions pathways that limit warming to 1.5°C (&gt;50%) with no or limited overshoot in 2030 by about 20%, from a median gap of 24 GtCO 2 -eq (20–29) to 19 GtCO 2 -eq (16–23). Box 4.1 discusses the adaptation gap.

Globally, the implementation gap between projected emissions of current policies and the unconditional and conditional new and updated NDCs is estimated to be around 4 and 7 GtCO 2 -eq in 2030, respectively ( ''medium evidence'' , ''medium agreement'' ) (Tables 4.2 and 4.3), with many countries requiring additional policies and associated climate action to meet their mitigation targets as specified under the NDCs ( ''limited evidence'' ) (Section 4.2.2.6). It should be noted that the implementation gap varies considerably across countries, with some having policies in place estimated to be sufficient to achieve the emission targets their NDCs, some where additional policies may be required to be sufficient, as well as differences between the policies in place and action on the ground.

'''Table 4.3 | Projected global GHG emissions of new and update''' '''d NDCs by 2030.'''

{| class="wikitable"
|-
! rowspan="3"| Study

! rowspan="3"| Cut-off date

! colspan="4"| Kyoto GHGs a [GtCO 2 -eq]

! rowspan="3"| References

|-
! colspan="2"| Historical

! colspan="2"| Median (min–max) b 2030

|-
! 2015

! 2019

! Unconditional NDCs

! Conditional NDCs

|-
| Climate Action Tracker c

| 5/2021

| 51

| 52

| 50

| 47

| [[#Climate%20Action%20Tracker--2021|Climate Action Tracker (2021)]]

|-
| PBL d

| 9/2021

| 52

| 54

| 53 (51–55)

| 52 (49–53)

| [[#den%20Elzen--2021|den Elzen et al. (2021)]] ; [[#Nascimento--2021|Nascimento et al. (2021)]]

|-
| JRC – GECO e

| 10/2021

| 51

|
| 48

| [[#JRC--2021|JRC (2021)]]

|-
| Meinshausen et al. f

| 10/2021

| 54

| 56

| 55 (54–57)

| 53 (52–55)

| [[#Meinshausen--2021|Meinshausen et al. (2021)]]

|-
| Total g

|
| colspan="2"|
| 53 (50–57)

| 50 (47–55)

|
|-
| colspan="6"| '''Other studies for comparison'''

|
|-
| UNEP EGR h

| 9/2021

| colspan="2"|
| 53 (50–55)

| 50 (47–53)

| [[#UNEP--2017a|UNEP (2017a)]]

|-
| UNFCCC Secretariat i

| 7/2021

| colspan="2"|
| 57 (55–58)

| 54 (52–56)

| [[#UNFCCC--2021|UNFCCC (2021)]]

|-
| ENGAGE j

| 3/2021

| colspan="2"|
|
| 51 (49–53)

| [[#Riahi--2021|Riahi et al. (2021)]]

|}

Notes: a GHG emissions expressed in CO 2 -eq emission using AR6 100-year GWPs. GHG emissions from studies that provide aggregate GHG emissions using other GWPs are rescaled using 2019 GHG emissions from [[IPCC:Wg3:Chapter:Chapter-2|Chapter 2]] ( [[#Minx--2021|Minx et al. 2021]] ; [[#Crippa--2021|Crippa et al. 2021]] ). Note that due to slightly different system boundaries across historical emission datasets as well as data uncertainties (Chapter 2, SM2.2) relative change compared to historical emissions should be calculated vis-à-vis the historical emissions data used by a particular study. b If a range is available from a study, a median is provided in addition to the range. c Announced mitigation pledges on global 2030 emissions of China and Japan included. d Announced mitigation pledges of China, Japan, Republic of Korea included. e Announced mitigation pledge of Korea not included. f Announced mitigation pledges of China and Republic of Korea not included, emissions from international aviation and shipping not included. g Ranges across four studies are calculated using the median and the full range including the minimum and maximum of studies if available. h UNEP EGR 2021 estimate listed for comparison, but since largely relying on the same studies not included in range estimate. i NDCs submitted until 30 July included, announcements not included, excluding LULUCF emissions. j NDC updates of Brazil, EU and announcement of China included as a sensitivity analysis compared to original NDCs.

<div id="4.2.2.6" class="h3-container"></div>

<span id="tracking-progress-in-implementing-and-achieving-ndcs"></span>
==== 4.2.2.6 Tracking Progress in Implementing and Achieving NDCs ====

<div id="h3-6-siblings" class="h3-siblings"></div>

Under the Enhanced Transparency Framework, countries will transition from reporting biennial reports (BRs) and biennial update reports (BURs) to reporting biennial transparency reports (BTRs) starting, at the latest, by December 2024. Each Party will be required to report information necessary to track progress made in implementing and achieving its NDC under the Paris Agreement ( [[#UNFCCC--2018b|UNFCCC 2018b]] ). Thus, no official data exists yet on tracking progress of individual NDCs.

Meanwhile, there is some literature at global and national level that aims at assessing whether countries are on track or progressing towards implementing their NDCs and to which degree the NDCs collectively are sufficient to reach the temperature targets of the Paris agreement ( [[#Rogelj--2016|Rogelj et al. 2016]] ; [[#Quéré--2018|Quéré et al. 2018]] ; [[#Höhne--2018|Höhne et al. 2018]] ; [[#Roelfsema--2020|Roelfsema et al. 2020]] ; [[#den%20Elzen--2019|den Elzen et al. 2019]] ; [[#Höhne--2020|Höhne et al. 2020]] ). Most of these studies focus on major emitters such as G20 countries and with the aim to inform countries to strengthen their ambition regularly, for example, through progress of NDCs and as part of the global stocktake ( [[#Höhne--2018|Höhne et al. 2018]] ; [[#Peters--2017|Peters et al. 2017]] ). However, a limited number of studies assess the implementation gaps of conditional NDCs in terms of finance, technology and capacity building support. Some authors conclude that finance needed to fulfil conditional NDCs exceeds available resources or the current long-term goal for finance (USD100 billion yr –1 ) (Pauw et al. 2019); others assess financial resources needed for forest-related activities ( [[#Kissinger--2019|Kissinger et al. 2019]] ) ( [[IPCC:Wg3:Chapter:Chapter-15#15.4.2|Section 15.4.2]] ). The literature suggests that consistent and harmonised approach to track progress of countries towards their NDCs would be helpful ( [[#Peters--2017|Peters et al. 2017]] ; [[#Höhne--2018|Höhne et al. 2018]] ; [[#den%20Elzen--2019|den Elzen et al. 2019]] ), and negotiations on a common tabular format are expected to conclude during COP26 in November 2021.

With an implementation gap in 2030 of 4 to 7 GtCO 2 -eq (Section 4.2.2.5), many countries will need to implement additional policies to meet their self-determined mitigation targets as specified under the NDCs. Studies that assess the level of projected emissions under current policies indicate that new policies (that have been implemented since the first assessment of the NDCs in 2015 and are thus covered in more recent projections) have reduced projections, by about two GtCO 2 -eq since the adoption of the Paris Agreement in 2015 to 2019 ( [[#Climate%20Action%20Tracker--2019|Climate Action Tracker 2019]] ; [[#UNEP--2020a|UNEP 2020a]] ; [[#den%20Elzen--2019|den Elzen et al. 2019]] ).

<div id="4.2.2.7" class="h3-container"></div>

<span id="literature-on-fairness-and-ambition-of-ndcs"></span>
==== 4.2.2.7 Literature on Fairness and Ambition of NDCs ====

<div id="h3-7-siblings" class="h3-siblings"></div>

Most countries provided information on how they consider their NDCs to be fair and ambitious in the NDCs submitted to UNFCCC and many of these NDCs refer to specific national circumstances such as social, economic and geographical factors when outlining why they are fair and ambitious. Further, several Parties provided information on specific criteria for evaluating fairness and ambition, including criteria relating to: responsibility and capability; share of emissions; development and/or technological capacity; mitigation potential; cost of mitigation actions; the degree of progression or stretching beyond the current level of effort; and the link to objectives and global goals ( [[#UNFCCC--2016a|UNFCCC 2016a]] ).

According to its Article 2.2, the Paris Agreement will be implemented to reflect equity and the principle of common but differentiated responsibilities and respective capabilities, in the light of different national circumstances, the latter clause being new, added to the UNFCCC principle ( [[#Voigt--2016|Voigt and Ferreira 2016]] ; [[#Rajamani--2017|Rajamani 2017]] ). Possible different interpretations of equity principles lead to different assessment frameworks ( [[#Lahn--2017|Lahn and Sundqvist 2017]] ; [[#Lahn--2018|Lahn 2018]] ).

Various assessment frameworks have been proposed to analyse fair share ranges for NDCs. The literature on equity frameworks including quantification of national emissions allocation is assessed in section 4.5 (Sections 13.4.2, 14.3.2 and 14.5.3). Recent literature has assessed equity, analysing how fairness is expressed in NDCs in a bottom-up manner ( [[#Mbeva--2016|Mbeva and Pauw 2016]] ; [[#Cunliffe--2019|Cunliffe et al. 2019]] ; [[#Winkler--2018|Winkler et al. 2018]] ). Some studies compare NDC ambition level with different effort sharing regimes and which principles are applied to various countries and regions ( [[#Peters--2015|Peters et al. 2015]] ; [[#Pan--2017|Pan et al. 2017]] ; [[#Robiou%20Du%20Pont--2017|Robiou Du Pont et al. 2017]] ; [[#Holz--2018|Holz et al. 2018]] ; [[#Robiou%20du%20Pont--2018|Robiou du Pont and Meinshausen 2018]] ; [[#van%20den%20Berg--2019|van den Berg et al. 2019]] ). Others propose multi-dimensional evaluation schemes for NDCs that combine a range of indicators, including the NDC targets, cost-effectiveness compared to global models, recent trends and policy implementation into consideration (Aldy et al. 2017; [[#Höhne--2018|Höhne et al. 2018]] ). Yet other literature evaluates NDC ambition against factors such as technological progress of energy efficiency and low-carbon technologies ( [[#Jiang--2017|Jiang et al. 2017]] ; [[#Kuramochi--2017|Kuramochi et al. 2017]] ; [[#Wakiyama--2017|Wakiyama and Kuramochi 2017]] ), synergies with adaptation plans ( [[#Fridahl--2017|Fridahl and Johansson 2017]] ), the obligations to deploy carbon dioxide removal technologies like bioenergy with carbon capture and storage (BECCS) in the future implied by their near-term emission reductions where they are not reflected on in the first NDCs ( [[#Peters--2017|Peters and Geden 2017]] ; [[#Fyson--2020|Fyson et al. 2020]] ; [[#Pozo--2020|Pozo et al. 2020]] ; [[#Mace--2021|Mace et al. 2021]] ). Others identify possible risks of unfairness when applying GWP* as emissions metric at national scale ( [[#Rogelj--2019|Rogelj and Schleussner 2019]] ). A recent study on national fair shares draws on principles of international environmental law, excludes approaches based on cost and grandfathering, thus narrowing the range of national fair shares previously assessed, and apply this to the quantification of national fair share emissions targets ( [[#Rajamani--2021|Rajamani et al. 2021]] ).

<div id="4.2.2.8" class="h3-container"></div>

<span id="uncertainty-in-estimates"></span>
==== 4.2.2.8 Uncertainty in Estimates ====

<div id="h3-8-siblings" class="h3-siblings"></div>

There are many factors that influence the global aggregated effects of NDCs. There is limited literature on systematically analysing the impact of uncertainties on the NDC projections with some exception ( [[#Rogelj--2017|Rogelj et al. 2017]] ; Benveniste et al. 2018). The UNEP Gap Report ( [[#UNEP--2017a|UNEP 2017a]] ) discusses uncertainties of NDC estimates in some detail. The main factors include variations in overall socio-economic development; uncertainties in GHG inventories; conditionality; targets with ranges or for single years; accounting of biomass; and different GHG aggregation metrics (e.g., GWP values from different IPCC assessments). In addition, when mitigation effort in NDCs is described as measures that do only indirectly translate into emission reductions, assumptions necessary for the translation come into play ( [[#Doelle--2019|Doelle 2019]] ). For a more elaborate discussion of uncertainties in NDCs ( [[IPCC:Wg3:Chapter:Chapter-14#14.3.2|Section 14.3.2]] ).

Some studies assume successful implementation of all of the NDCs’ proposed measures, sometimes including varying assumptions to account for some of the NDC features which are subject to assumed conditions related to finance and technology transfer. Countries ‘shall pursue domestic mitigation measures’ under Article 4.2 of the Paris Agreement ( [[#UNFCCC--2015a|UNFCCC 2015a]] ), but they are not legally bound to the result of reducing emissions ( [[#Winkler--2017a|Winkler 2017a]] ). Some authors consider this to be a lack of a strong guarantee that mitigation targets in NDCs will be implemented ( [[#Nemet--2017|Nemet et al. 2017]] ). Others point to growing extent of national legislation to provide a legal basis for action ( [[#Iacobuta--2018|Iacobuta et al. 2018]] ) ( [[IPCC:Wg3:Chapter:Chapter-13#13.2|Section 13.2]] ). These factors together with incomplete information in NDCs mean there is uncertainty about the estimates of anticipated 2030 emission levels.

The aggregation of targets results in large uncertainty ( [[#Rogelj--2017|Rogelj et al. 2017]] ; Benveniste et al. 2018). In particular, clarity on the contributions from the land use sector to NDCs is needed ‘to prevent high LULUCF uncertainties from undermining the strength and clarity of mitigation in other sectors’ ( [[#Fyson--2019|Fyson and Jeffery 2019]] ). Methodological differences in the accounting of the LULUCF anthropogenic CO 2 sink between scientific studies and national GHG inventories (as submitted to UNFCCC) further complicate the comparison and aggregation of emissions of NDC implementation ( [[#Grassi--2018|Grassi et al. 2018]] , 2021) ( [[IPCC:Wg3:Chapter:Chapter-7#7.2.3|Section 7.2.3]] and Cross-Chapter Box 6 in Chapter 7). This uncertainty could be reduced with clearer guidelines for compiling future NDCs, in particular when it comes to mitigation efforts not expressed as absolute economy-wide targets ( [[#Doelle--2019|Doelle 2019]] ), and explicit specification of technical details, including energy accounting methods, harmonised emission inventories ( [[#Rogelj--2017|Rogelj et al. 2017]] ) and finally, increased transparency and comparability ( [[#Pauw--2018|Pauw et al. 2018]] ).

<div id="cross-chapter-box-4" class="h2-container box-container"></div>

<span id="cross-chapter-box-4-comparison-of-ndcs-and-current-policies-with-the-2030-ghg-emissions-from-long-term-temperature-pathways"></span>