The impact of a northern peatland on the earth’s radiative budget: sustained methane emission versus sustained carbon sequestration

Northern peatlands sequester carbon and emit methane, and thus have both cooling and warming impacts on the climate system through their influence on atmospheric burdens of CO2 and CH4. These competing impacts are usually compared by the global warming potential (GWP) methodology, which determines the equivalent CO2 annual emission that would have the same integrated radiative forcing impact over a chosen time horizon as the annual CH4 emission. We use a simple model of CH4 and CO2 pools in the atmosphere to extend this analysis to quantify the dynamics, over years to millennia, of the net radiative forcing impact of a peatland that continuously emits CH4 and sequesters C. We find that for observed ratios of CH4 emission to C sequestration (roughly .01-2 mol mol-1), the radiative forcing impact of a northern peatland begins, at peatland formation, as a net warming that peaks after about 50 years, remains a diminishing net warming for the next several hundred to several thousand years, depending on the rate of C sequestration, and thereafter is or will be an ever increasing net cooling impact. We then use the model to evaluate the radiative forcing impact of various changes in CH4 and/or CO2 emissions. In all cases, the impact of a change in CH4 emissions dominates the radiative forcing impact in the first few decades, and then the impact of the change in CO2 emissions slowly exerts its influence

Cold Pools as Conveyor Belts of Moisture

Observations and simulations have found convective cold pools to trigger and organize subsequent updrafts by modifying boundary layer temperature and moisture as well as by lifting air parcels at the outflow boundaries. We study the causality between cold pools and subsequent deep convection in idealized large‐eddy simulations by tracking colliding outflow boundaries preceding hundreds of deep convection events. When outflow boundaries collide, their common front position remains immobile, whereas the internal cold pool dynamics continues for hours. We analyze how this dynamics “funnels” moisture from a relatively large volume into a narrow convergence zone. We quantify moisture convergence and separate the contribution from surface fluxes, which we find to play a secondary role. Our results highlight that dynamical effects are crucial in triggering convection, even in radiative‐convective equilibrium. However, it is the low‐level convergence resulting from this dynamics that removes inhibition, moistens the atmosphere aloft, and ultimately permits deep convection

Metodar for å samanlikne utslepp av klimagassar: GWP-konseptet og alternative metodar

I denne publikasjonen har vi søkt å presentere ulike metodar for å samanlikne effekten av utslepp av klimagassar. Det globale oppvarmingspotensialet (GWP) er utvikla av FN sitt klimapanel (IPCC) til dette formålet. Dette konseptet har ein viktig funksjon i politiske avvegingar mellom ulike klimagassar. GWP tener det formål den var sett til, nemleg å samanlikne det akkumulerte strålingspådrivet som pulsutslepp av ulike gassar resulterer i. GWP som eit mål for gassen sin oppvarmingseffekt er derimot meir problematisk. Klimagass utslepp vert vekta etter kva tidshorisont ein vel. Det er heller ikkje vilkårleg kva gass ein vel å redusere m.o.t. temperaturendring. Dette vert ytterlegare forsterka då indeksen er sensitiv overfor ulike scenario m.o.t. framtidig utslepp og atmosfæren si samansetning og kjemi. Ei økonomisk tilnærming søkjer å finne ei løysning på den naturvitskapelege statiske indeksen. Dette innebær at ein diskonterer framtidig skade. Slik vert samanlikning og avveging mellom ulike gassar basert på diskontert oppvarmingspotensial eller diskonterte marginale utsleppskostnader. Ei slik tilnærming kan kvantifisere endra oppvarmingspotensial/ utsleppskostnader. Til no viser det seg at desse alternative metodane ikkje har noko gjennomslagskraft hjå avgjerdstakarar

Emission metrics under the 2°C climate stabilization target

In multi-gas climate policies such as the Kyoto Protocol one has to decide how to compare the emissions of different greenhouse gases. The choice of metric could have significant implications for mitigation priorities considered under the prospective negotiations for climate mitigation agreements. Several metrics have been proposed for this task with the Global Warming Potential (GWP) being the most common. However, these metrics have not been systematically compared to each other in the context of the 2°C climate stabilization target. Based on a single unified modeling framework, we demonstrate that metric values span a wide range, depending on the metric structure and the treatment of the time dimension. Our finding confirms the basic salient point that metrics designed to represent different aspects of the climate and socio-economic system behave differently. Our result also reflects a complex interface between science and policy surrounding metrics. Thus, it is important to select or design a metric suitable for climate stabilization based on an interaction among practitioners, policymakers, and scientist

Emissions and Emergence: a new index comparing relative contributions to climate change with relative climatic consequences

We develop a new index which maps relative climate change contributions to relative emergent impacts of climate change. The index compares cumulative emissions data with patterns of signal-to-noise ratios (S/N) in regional temperature (Frame et al., 2017). The latter act as a proxy for a range of local climate impacts, so emergent patterns of this ratio provide an informative way of summarising the regional disparities of climate change impacts. Here we combine these with measures of regional/national contributions to climate change to develop an “emissions-emergence index” (EEI) linking regions’/countries’ contributions to climate change with the emergent regional impacts of climate change. The EEI is a simple but robust indicator which captures relative contributions to and regional impacts from climate change. We demonstrate the applicability of the EEI both for discussions of historical contributions and impacts, and for considering future relative contributions and impacts, and examine its utility in the context of existing related metrics. Finally, we show how future emissions pathways can either imply a growth or reduction of regional climate change inequalities depending on the type and compositions of socioeconomic development strategie

Metrics for linking emissions of gases and aerosols to global precipitation changes

Recent advances in understanding have made it possible to relate global precipitation changes directly to emissions of particular gases and aerosols that influence climate. Using these advances, new indices are developed here called the Global Precipitation-change Potential for pulse (GPP_P) and sustained (GPP_S) emissions, which measure the precipitation change per unit mass of emissions. The GPP can be used as a metric to compare the effects of different emissions. This is akin to the global warming potential (GWP) and the global temperature-change potential (GTP) which are used to place emissions on a common scale. Hence the GPP provides an additional perspective of the relative or absolute effects of emissions. It is however recognised that precipitation changes are predicted to be highly variable in size and sign between different regions and this limits the usefulness of a purely global metric. The GPP_P and GPP_S formulation consists of two terms, one dependent on the surface temperature change and the other dependent on the atmospheric component of the radiative forcing. For some forcing agents, and notably for CO2, these two terms oppose each other – as the forcing and temperature perturbations have different timescales, even the sign of the absolute GPP_P and GPP_S varies with time, and the opposing terms can make values sensitive to uncertainties in input parameters. This makes the choice of CO2 as a reference gas problematic, especially for the GPP_S at time horizons less than about 60 years. In addition, few studies have presented results for the surface/atmosphere partitioning of different forcings, leading to more uncertainty in quantifying the GPP than the GWP or GTP. Values of the GPP_P and GPP_S for five long- and short-lived forcing agents (CO2, CH4, N2O, sulphate and black carbon – BC) are presented, using illustrative values of required parameters. The resulting precipitation changes are given as the change at a specific time horizon (and hence they are end-point metrics) but it is noted that the GPPS can also be interpreted as the time-integrated effect of a pulse emission. Using CO2 as a references gas, the GPP_P and GPP_S for the non-CO2 species are larger than the corresponding GTP values. For BC emissions, the atmospheric forcing is sufficiently strong that the GPP_S is opposite in sign to the GTP_S. The sensitivity of these values to a number of input parameters is explored. The GPP can also be used to evaluate the contribution of different emissions to precipitation change during or after a period of emissions. As an illustration, the precipitation changes resulting from emissions in 2008 (using the GPP_P) and emissions sustained at 2008 levels (using the GPP_S) are presented. These indicate that for periods of 20 years (after the 2008 emissions) and 50 years (for sustained emissions at 2008 levels) methane is the dominant driver of positive precipitation changes due to those emissions. For sustained emissions, the sum of the effect of the five species included here does not become positive until after 50 years, by which time the global surface temperature increase exceeds 1 K

Earlier emergence of a temperature response to mitigation by filtering annual variability

The rate of global surface warming is crucial for tracking progress towards global climate targets, but is strongly influenced by interannual-to-decadal variability, which precludes rapid detection of the temperature response to emission mitigation. Here we use a physics based Green's function approach to filter out modulations to global mean surface temperature from sea-surface temperature (SST) patterns, and show that it results in an earlier emergence of a response to strong emissions mitigation. For observed temperatures, we find a filtered 2011-2020 surface warming rate of 0.24 °C per decade, consistent with long-term trends. Unfiltered observations show 0.35 °C per decade, partly due to the El Nino of 2015-2016. Pattern filtered warming rates can become a strong tool for the climate community to inform policy makers and stakeholder communities about the ongoing and expected climate responses to emission reductions, provided an effort is made to improve and validate standardized Green's functions. © 2022. The Author(s)

Stable climate metrics for emissions of short and long-lived species – combining steps and pulses

Multi-gas climate agreements rely on a methodology (widely referred to as “metrics”) to place emissions of different gases on a CO2-equivalent scale. There has been an ongoing debate on the extent to which existing metrics serve current climate policy. Endpoint metrics (such as global temperature-change potential GTP) are the most closely related to policy goals based on temperature limits (such as Article 2 of the Paris Agreement). However, for short-lived climate forcers (SLCFs), endpoint metrics vary strongly with time horizon making them difficult to apply in practical situations. We show how combining endpoint metrics for a step change in SLCF emissions with a pulse emission of CO2 leads to an endpoint metric that only varies slowly over time horizons of interest. We therefore suggest that these combined step-pulse metrics (denoted combined global warming potential CGWP and combined global temperature-change potential CGTP) can be a useful way to include short and long-lived species in the same basket in policy applications – this assumes a single basket approach is preferred by policy makers. The advantage of a combined step-pulse metric for SLCFs is that for species with a lifetime less than 20 years a single time horizon of around 75 years can cover the range of timescales appropriate to the Paris Agreement. These metrics build on recent work using the traditional global warming potential (GWP) metric in a new way, called GWP*. We show how the GWP* relates to CGWP and CGTP and that it systematically underestimates the temperature effects of SLCFs by up to 20%. These step-pulse metrics are all more appropriate than the conventional GWP for comparing the relative contributions of different species to future temperature targets and for SLCFs they are much less dependent on time horizon than GTP