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. 2020 Jul 7;11(1):3261.
doi: 10.1038/s41467-020-17001-1.

Delayed emergence of a global temperature response after emission mitigation

B H Samset  1 , J S Fuglestvedt  2 , M T Lund  2
Affiliations

Delayed emergence of a global temperature response after emission mitigation

B H Samset et al. Nat Commun. .

Abstract

A major step towards achieving the goals of the Paris agreement would be a measurable change in the evolution of global warming in response to mitigation of anthropogenic emissions. The inertia and internal variability of the climate system, however, will delay the emergence of a discernible response even to strong, sustained mitigation. Here, we investigate when we could expect a significant change in the evolution of global mean surface temperature after strong mitigation of individual climate forcers. Anthropogenic CO2 has the highest potential for a rapidly measurable influence, combined with long term benefits, but the required mitigation is very strong. Black Carbon (BC) mitigation could be rapidly discernible, but has a low net gain in the longer term. Methane mitigation combines rapid effects on surface temperature with long term effects. For other gases or aerosols, even fully removing anthropogenic emissions is unlikely to have a discernible impact before mid-century.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Surface temperature response to multi-component mitigation.
Emergence of a temperature signal when going from one RCP emissions pathway to another. Thick lines show calculations from MAGICC6. Thin lines show evolutions of interannual variability of global mean surface temperature, extracted from the CESM1 LENS. Triangles above the graphs indicate the number of ensemble members where the temperature difference between the RCPs is significant, when accounting for internal variability.
Fig. 2
Fig. 2. Single component mitigation.
Example of the emergence of a temperature signal when mitigating one climate forcer. a MAGICC6 calculations following RCP4.5 (black line), and then modified by mitigating BC emissions according to one of three idealized scenarios starting in 2020 (zero emissions, −5% per year, or switching to RCP2.6). b The number of ensemble members where the temperature time series, from 2020 and up to that year, is significantly different from zero (t-test, p < 0.05). Black dot: 21 significant ensemble members (66%). c The (detrended) temperature difference when variability from CESM1 LENS is taken into account.
Fig. 3
Fig. 3. Emergence times after single forcer mitigation.
Time of emergence of a global mean surface temperature signal for idealized individual mitigation efforts of a range of short- and long lived climate forcers. The colored expanding bars show the evolution of a statistically significant signal (t-test, p < 0.05), from zero (minimum) to 32 (maximum) ensemble members. The circles show the first year when 66% (21 members) show significant signals. The error bars show the 25–75% range (8 and 24 significant members respectively). The underlying calculations are illustrated in Fig. 2. Hatching indicates a positive global temperature change in response to the mitigation (i.e. loss of cooling).
Fig. 4
Fig. 4. The impact of single component mitigation on rates of warming.
a Example calculation for the CO2 mitigation scenarios (dashed lines). The solid lines show the 10-year average trends for 2031-2040. b Warming rates for three coming decades (columns), for each component and scenario (colored bar-and-whiskers), compared to RCP4.5 (black lines and hatching). Projections calculated with MAGICC6, internal variability is taken from CESM1 LENS (32 ensemble members). Dots and whiskers show the mean and ±1 standard deviation of the rates in the mitigated scenarios. Solid lines indicate where the mean trend is outside a third of the standard deviation of trends from LENS evolution added to RCP4.5 (dense hatching). Large symbols and fat lines show when the trend is outside one standard deviation in RCP4.5 (open hatching).
Fig. 5
Fig. 5. Potential versus effort for single forcer mitigation.
Mitigation potential (avoided temperature increase in 2100) versus mitigation effort, here quantified through the total mass of mitigated emissions at time-of-emergence. Global mean surface temperature change in 2100 was calculated using MAGICC6. The symbol size scales with time-of-emergence, large symbols indicate early emergence, small symbols later emergence. See Table 3 for time-of-emergence numbers.
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