The phenomenon of Arctic amplification is causing the Arctic (north of 66∘ N) to warm at almost 4 times the global average rate . However, this statistic is of limited direct relevance to policy-makers because it is not framed in terms of the central metric of climate policy: global mean temperature change. Here we use the latest generation of climate model outputs to reframe Arctic amplification in terms of the direct contribution of faster temperature rises in the Arctic to global warming. Specifically, we characterise the influence of Arctic amplification on the timing of breaches of the 1.5 and 2 ∘C warming levels identified in the Paris Agreement, with the aim of providing a more intuitive quantification of the significance of amplified Arctic warming. Arctic amplification is strongest in the winter months and is driven by positive feedbacks involving the vertical structure of the lower atmosphere, changing cloud cover, temperature-dependent increases in thermal radiation to space, and the retreat of sea ice and snow cover . The 2.7 ∘C Arctic warming since the pre-industrial has contributed around 10 % of Earth's globally averaged warming to date , despite the region occupying only 4 % of the Earth's surface.

To characterise future global and Arctic warming, we analyse surface air temperature data from the Coupled Model Intercomparison Project Phase 6 CMIP6;. We focus here on future temperature change under the Shared Socioeconomic Pathway 2-4.5 (SSP2-4.5) but also report results for a low- (SSP1-2.6) and a high-emissions (SSP3-7.0) pathway. The SSP2-4.5 pathway is a plausible intermediate scenario of future greenhouse gas emissions, which would likely meet neither of the Paris temperature goals . Our analysis compares the year in which global average temperatures breach the two Paris targets in this dataset with the year in which those targets are breached in a modified version of the dataset which excludes the area north of 66∘ N. Crucially, the latter case is equivalent to an alternative world in which the Arctic warms at the global mean rate. The difference between the two timings therefore represents the time contribution of Arctic amplification to breaches of the Paris Agreement's temperature thresholds. Our definition of Arctic amplification differs from some analyses e.g. which use the tropics as the baseline region, rather than the world outside the Arctic.

Our method does not simulate a world without Arctic amplification. Such a world would be radically different to ours since the phenomenon is in large part driven by the Arctic being colder than the rest of the planet . Neither do we quantify the impacts of Arctic change on temperature rise outside the region, such as via the albedo feedback from loss of snow and ice , greenhouse gas emissions from permafrost thaw , and altered atmospheric and oceanic circulation . Instead, we quantify the rate of local Arctic warming in terms of its direct contribution to global mean temperature change. We also note that our analysis does not imply any change from current estimates in the expected timing of breaching Paris limits, which refer explicitly and only to global mean temperature .

The Paris Agreement is not breached when just 1 year is warmer than the target temperature . Instead a multi-decadal average must be used to minimise the effect of internal variability . We therefore define breaches of a temperature threshold as the fractional year when the 20-year running-average temperature crosses that threshold. Many climate models significantly over- or underestimate the warming to date since the pre-industrial. To account for this, we scale the modelled temperature anomalies from the pre-industrial baseline to match the observed present-day temperature anomaly. Our results are qualitatively insensitive to the choice of bias correction method (see Methods).

Figure  shows that under the SSP2-4.5 emissions pathway, the 1.5 ∘C temperature threshold would be breached 4.7 (± 0.4) years later in the absence of Arctic amplification. Across the ensemble of models, the 1.5 ∘C threshold is exceeded in the year 2031.8 (± 0.9), whereas without Arctic amplification, this scenario breaches the 1.5 ∘C threshold in 2036.6 (± 1.1). Measuring from 2023, the world would therefore breach the 1.5 ∘C threshold 53 % later without amplified warming in the Arctic. The uncertainty value of the difference in crossing years represents the standard error of the bias-corrected multi-model ensemble. The 2 ∘C threshold is passed 8.3 (± 1.0) years later without Arctic amplification, in 2060.0 (± 2.6) rather than 2051.7 (± 1.8), 29 % later. Under a plausible high-emissions scenario (SSP3-7.0, not shown) without Arctic amplification, the 1.5 ∘C temperature threshold would be breached 3.7 (± 0.2) years (48 %) later, moving the date from 2030.8 (± 0.7) to 2034.5 (± 0.8). Under a low-emissions pathway (SSP1-2.6), without Arctic amplification the passing of the 1.5 ∘C threshold is delayed by 6.6 (± 1.4) years (81 %). These results demonstrate the key impact of Arctic warming on the central metric of climate policy: the global mean temperature. Amplified Arctic warming reduces the expected time to crossing the 1.5 ∘C threshold by 4–7 years relative to a world without such amplification.

Our approach also allows assessment of how uncertainty in Arctic warming over the coming decades contributes to uncertainty in the crossing year for the 1.5 ∘C threshold. In the multi-model ensemble, the 10th-to-90th percentile range in 1.5 ∘C crossing year is 13.9 years. To quantify the impact of near-term Arctic warming on this uncertainty, it is necessary to account for the strong correlation (r=0.53) between Arctic warming and the warming south of 66∘ N across the multi-model ensemble. We therefore calculate a partial correlation coefficient between the rate of Arctic warming and the crossing year across the multi-model ensemble, controlling for warming outside the Arctic. This partial correlation coefficient is equal to -0.39 (significant at 95 % confidence). The square of this coefficient, 15 %, gives the variance in crossing year for the 1.5 ∘C threshold explained by the near-term Arctic warming rate under the SSP2-4.5 scenario. We find that while occupying only 4 % of the global surface area, variability in near-term Arctic warming contributes 15 % of the inter-model uncertainty in the crossing year. Despite this, Fig. c shows a larger spread in crossing year for the case without Arctic amplification. The reason for the apparent discrepancy is that the warming to date for the CMIP6 model ensemble, which we adjust to match present-day observations, is smaller in the case without Arctic amplification, so there is more time for models to diverge before crossing the temperature thresholds.

We can also assess how the year in which the 1.5 ∘C limit is exceeded varies between low and high scenarios for Arctic amplification influence. To do this we perform a multiple linear regression on the crossing year using two variables: Arctic warming and warming outside of the Arctic (see Methods). Holding the warming outside of the Arctic constant at its multi-model mean of 0.26 ∘C per decade, our regression model predicts that the 10th and 90th percentiles of near-term Arctic warming are represented by crossing years of 2033.2 and 2030.4, respectively, a difference of 2.9 years. We note that this difference in crossing year associated with the lower and upper bounds on projected Arctic warming is larger than the 1.6 year difference between the mean crossing years for the low- and high-emissions scenarios assessed here (2032.4 and 2030.8, respectively).

While we focus here only on the direct impact of Arctic warming on global temperature change, the local impacts should not be overlooked. Under 2 ∘C of global warming, Arctic temperatures are expected to rise by 4 ∘C in the annual mean and 7 ∘C in winter, with profound consequences for local people and ecosystems . Additionally, amplified Arctic warming contributes to the global challenges that motivated the 1.5 ∘C target, such as sea level rise and permafrost thaw. These local and global impacts are a primary motivation for improving the representation of the Arctic in Earth system models and for accurate observational monitoring in the region. Our findings offer additional motivation for such work – that Arctic warming has an outsized influence on both the timing of and uncertainty in projected breaches of the Paris Agreement's temperature targets.