The study, described by the authors as the first harmonised retrospective measure of emissions alignment across national climate commitments, examines the first Kyoto commitment period of 2008–2012 and the first two Paris NDC cycles. It was designed to fill a gap between two common approaches to climate accountability. Prospective assessments compare national pledges or policies with emissions pathways consistent with global temperature goals, while national reporting tracks progress using indicators selected to fit each country’s own commitment. The new measure instead asks how realised emissions compare with the annual trajectory implied by a particular pledge, while keeping the strength of that pledge separate from the outcome.

For each country and year, the relative Gap-to-Target is calculated as 100 multiplied by the difference between observed emissions and the applicable benchmark, divided by the benchmark. A positive percentage means emissions exceeded the pathway; a negative value means they were below it; zero represents exact alignment. An absolute version of the gap retains the agreement’s emissions unit. Under Kyoto, the benchmark is a country’s five-year assigned amount divided evenly across 2008–2012, expressed in tonnes of carbon dioxide equivalent. Under Paris, the framework converts each NDC into a target-year emissions outcome and constructs a linear pathway from a pre-implementation emissions anchor to that outcome.

Paris commitments are unusually heterogeneous. Some countries set absolute emissions levels, while others use reductions from a historical base year, reductions from a business-as-usual scenario, emissions-intensity objectives, per-capita targets, or combinations of these approaches. They also differ in target years, sector and gas coverage, treatment of land use, implementation periods, and conditionality. The researchers therefore matched observed emissions to each commitment’s declared scope, retained separate pathways for unconditional and conditional targets when both were specified, and calculated the first and second NDC cycles independently. Official target information was used where possible; prospective emissions, GDP, or population inputs were introduced only when needed to convert intensity, per-capita, or business-as-usual commitments into a common emissions outcome.

The linear pathway is an accounting rule rather than a forecast or recommended policy schedule. It distributes the absolute emissions adjustment evenly between the pre-implementation anchor and the target year, without assuming that mitigation should be front-loaded, back-loaded, cheapest, technology-specific, or cost-minimising. The authors argue that more elaborate trajectories would require information about sequencing, financing, technology diffusion, abatement costs, and institutional capacity that most NDCs do not provide. A normalised example illustrates the method: if the anchor is set to 100 and the target to 70 over ten years, the benchmark falls in equal three-point steps toward 70. Such a trajectory can compare outcomes over time, but it does not establish that countries intended or followed that particular emissions path.

The contrast with Kyoto was pronounced. The median Gap moved from 0.7% in 2008 to −10.5% in 2012 under the basic assigned-amount benchmark, indicating progressively lower emissions than the annualised allowance for the median country. Accounting for land use, land-use change and forestry, as well as transactions in Kyoto units, generally shifted the median further below the benchmark. The fully adjusted and land-use-adjusted variants reached approximately −13.5% in 2012, while the transaction-adjusted median fell between them. These adjustments did not transform the overall distribution, but they produced substantial changes for individual countries and altered their rankings. The result shows why formal accounting rules are essential when comparing alignment under Kyoto.

Paris showed the opposite broad pattern. The median country’s emissions were above its target-consistent pathway in most years of both NDC cycles. Both cycles displayed an increase in the gap before 2020, a marked narrowing that year, and a subsequent rebound. The study attributes the temporary 2020 decline largely to the COVID-19 pandemic, which reduced production, transport activity, and energy demand, but treats this as a plausible explanation rather than a demonstrated cause of the full statistical pattern. By 2024, the median gap was about 8.4% under the first NDC and 14.6% under the second. Across the cycles overall, the medians were 5.2% and 9.0%, respectively, while individual countries occupied positions on both sides of their pathways.

Ambition and alignment produced four distinct groups. The most favourable configuration combined a commitment requiring lower target-year emissions than the pre-implementation level with observed emissions below the corresponding pathway; 12 countries occupied this group under the first NDC and six under the second. A much larger group pledged reductions but remained above the resulting pathway: 73 countries in NDC1 and 100 in NDC2. Another group remained below a pathway that was itself comparatively permissive because the target allowed target-year emissions to exceed the pre-implementation level. The fourth group both permitted higher emissions and recorded emissions above that pathway. The distribution demonstrates why a negative gap cannot automatically be treated as evidence of a strong target, just as a positive gap does not establish an absence of climate action.

Transitions in the 122-country common sample showed that the shift was broad rather than the product of a few outliers. Seventy-one countries remained above their pathways and 21 remained below, but 24 moved from below to above between cycles, compared with six moving in the opposite direction. The upward transition was therefore four times as frequent. Results were also sensitive to assumptions used to estimate business-as-usual pathways. The central estimates relied on the SSP2–RCP6.0 scenario, while alternative emissions and modelling sources produced country-level ranges that could be wide and occasionally changed signs. Nevertheless, the ordering remained stable: median gaps in NDC2 exceeded those in NDC1 under every specification tested. The sensitivity range is therefore not a statistical confidence interval, and individual estimates require more caution than the aggregate pattern.

Across target types, base-year and business-as-usual commitments displayed positive median gaps in both cycles, increasing from roughly 6% to 10%. Intensity targets had negative medians, while fixed-level targets shifted from negative in NDC1 to positive in NDC2. Positive central estimates also appeared in every income group, although the increase between cycles differed and scenario ranges were broad for some lower-income countries. Because sectoral, per-capita, cumulative-trajectory, and some regional samples were small, those results cannot support broad category-level conclusions. The framework also cannot establish that any particular policy caused an emissions outcome, and the observed gaps do not forecast target failure. Instead, they provide a common retrospective lens for identifying where emissions remain far from declared pathways, how accounting and target design shape the measurement, and how countries changed position as their commitments were updated.

Subject of Research: Retrospective comparison of greenhouse gas emissions with national Kyoto and Paris climate commitment pathways

Article Title: Measuring alignment with national climate commitments: A gap-to-target indicator for Kyoto and Paris NDC cycles

Article References: Richard Nikiema, P.-W. (2026). Measuring alignment with national climate commitments: A gap-to-target indicator for Kyoto and Paris NDC cycles. Environmental and Sustainability Indicators, 32, Article 101551. https://doi.org/10.1016/j.indic.2026.101551

Image Credits: AI Generated

DOI: 10.1016/j.indic.2026.101551

Keywords: climate commitments, Paris Agreement, Kyoto Protocol, national climate targets, greenhouse gas emissions, NDC tracking, emissions pathways, climate governance, target alignment, Measuring, alignment, national