HFC-125 and HFC-32 are fluorinated greenhouse gases of great concern due to their high GWPs and increasing background atmospheric concentrations. Long-term atmospheric observations of HFC-125 and HFC-32 were carried out in four representative cities of China (Beijing, Guangzhou, Hangzhou, and Lanzhou) from January 2012 to October 2019. Overall, the annual mean atmospheric concentrations of HFC-125 and HFC-32 both showed increasing trends, with average rates of 4.8 ppt yr-1 and 7.9 ppt yr-1. The average concentrations of HFC-125 and HFC-32 in urban areas were significantly higher than those in suburban areas. Significant differences in atmospheric concentrations of the two HFCs were observed among the four cities. HFC-125 and HFC-32 emissions were estimated accordingly, averaging 6.2 Gg yr-1 (23.6 Mt. CO2-eq) and 5.7 Gg yr-1 (4.3 Mt. CO2-eq) during 2012 and 2019 and growing at rates of 0.8 Gg yr-1 (3.1 Mt. CO2-eq) and 0.8 Gg yr-1 (0.6 Mt. CO2-eq), respectively, with an increasing contribution to global radiative forcing. The bottom-up inventories of HFC-125 and HFC-32 in the four cities increased annually from 2012 to 2019, with the highest emissions in Beijing, while the top-down emissions fluctuated during the research period. SYNOPSIS: The atmospheric concentrations of HFC-125 and HFC-32 were measured from 2012 to 2019 in four representative cities of China. Both HFC emissions at national and city levels were estimated using observation-based and inventory methods.

From the beginning of May 2023 to the end of August 2023, the Northern Hemisphere experienced significant wildfire activity with the most widespread fires occurring in Canada. Forest fires in Canada destroyed more than 15.6 million hectares of forests. These wildfires worsened air quality across the region and other parts of the world. The smoke reached southern Europe by the end of June 2023. To better understand the consequences of such forest fires far from the site of origin, aerosol optical, microphysical and radiative properties were analyzed during this event for southern Europe using data from the Visible Infrared Imaging Radiometer Suite (VIIRS), TROPOspheric Monitoring Instrument (TROPOMI), and Aerosol Robotic Network (AERONET). TROPOMI aerosol index (AI) and the carbon monoxide (CO) product confirm that the smoke originated directly from these forest fires. AERONET data from the El Arenosillo site in southern Spain showed maximum aerosol optical depth (AOD) values on June 27 reached 2.36. Data on Angstrom Exponent (AE), aerosol volume size distribution (VSD), single scattering albedo (SSA), fine mode fraction (FMF), volume particle concentration, effective radius (REff), absorption AOD (AAOD), extinction AE (EAE) and absorption AE (AAE) showed that fine-mode particles with carbonaceous aerosols contribution predominated in the atmosphere above the El Arenosillo site. Direct aerosol radiative forcing (DARF) at the top (DARFTOA) and bottom of atmosphere (DARFBOA) were -103.1 and -198.93 Wm-2, respectively. The atmospheric aerosol radiative forcing (DARFATM) was found to be 95.83 Wm-2 and with a heating rate 2.69 K day-1, which indicates the resulting warming of the atmosphere.

Permafrost thaw in northern peatlands causes collapse of permafrost peat plateaus and thermokarst bog development, with potential impacts on atmospheric greenhouse gas exchange. Here, we measured methane and carbon dioxide fluxes over 3 years (including winters) using static chambers along two permafrost thaw transects in northwestern Canada, spanning young (~30 years since thaw), intermediate and mature thermokarst bogs (~200 years since thaw). Young bogs were wetter, warmer and had more hydrophilic vegetation than mature bogs. Methane emissions increased with wetness and soil temperature (40 cm depth) and modelled annual estimates were greatest in the young bog during the warmest year and lowest in the mature bog during the coolest year (21 and 7 g C-CH4 m-2 year-1, respectively). The dominant control on net ecosystem exchange (NEE) in the mature bog (between +20 and -54 g C-CO2 m-2 year-1) was soil temperature (5 cm), causing net CO2 loss due to higher ecosystem respiration (ER) in warmer years. In contrast, wetness controlled NEE in the young and intermediate bogs (between +55 and -95 g C-CO2 m-2 year-1), where years with periodic inundation at the beginning of the growing season caused greater reduction in gross primary productivity than in ER leading to CO2 loss. Winter fluxes (November-April) represented 16% of annual ER and 38% of annual CH4 emissions. Our study found NEE of thermokarst bogs to be close to neutral and rules out large CO2 losses under current conditions. However, high CH4 emissions after thaw caused a positive net radiative forcing effect. While wet conditions favouring high CH4 emissions only persist for the initial young bog period, we showed that continued climate warming with increased ER, and thus, CO2 losses from the mature bog can cause net positive radiative forcing which would last for centuries after permafrost thaw.

Agricultural systems in the 21st Century face the double challenge of achieving climate neutrality while maintaining food security. Synthetic fertilizers rich in nitrogen (N-fertilizers) boost agricultural production at the expense of increasing climate impact. Public policies, such as the Farm-to-Fork (F2F) Strategy, aim to reduce the extensive use of N-fertilizers with the ultimate goal of achieving a climate neutral European Union (EU). However, the strong link between N-fertilizers and GHG emissions (i.e., CO2, CH4 and, especially, N2O) highlights the need to better understand the climate impact of this sector. The present study conducts a climate impact analysis of Spanish N-fertilizer sector for two periods: (i) from 1960 to 2020 using real data and (ii) from 2021 to 2100 considering five forecasted scenarios. The scenarios range from business-as-usual practices to a full accomplishment of the goals pursued by the EU\'s F2F strategy. The system\'s climate stability and neutrality are analysed for the different scenarios based on radiative forcing (RF) metrics. Additionally, the study evaluates the short-term impact of the EU decarbonization goals on the climate impact of the Spanish N-fertilizer sector. The results of the study illustrate that the long-lasting climate impact of N2O and CO2 emissions compromise the capacity of N-fertilizer sector to achieve climate stability and approach climate neutrality. However, the decarbonisation of transport and N-fertilizer production activities is an important driver to substantially reduce the life cycle CH4 and CO2 emissions in the Spanish N-fertilizer sector. The results also highlight that more severe reductions on N-cycles than those suggested by the EU\'s F2F are required, especially to reduce the long-lasting N2O emissions in the N-fertilizer sector. Overall, the study concludes that using RF-based metrics increases robustness and transparency of climate assessments, which is necessary for a higher integration of climate science within public policymaking.

Reindeer (Rangifer tarandus) pastoralism utilizes vast boreo-arctic taiga and tundra as grazing land. Highly fluctuating population sizes pose major challenges to the economy and livelihood of indigenous herder communities. In this study we investigated the effect of population fluctuations on core provisioning and regulating ecosystem services in two Sámi reindeer herding districts with contrasting fluctuation trends. We compared 50-year long time series on herd size, meat production, forage productivity, carbon footprint, and CO2-equivalence metrics for surface albedo change based on the radiative forcing concept. Our results show, for both districts, that the economic benefits from the provisioning services were higher than the costs from the regulating services. Still, there were major contrasts; the district with moderate and stable reindeer density gained nearly the double on provisioning services per unit area. The costs from increasing heat absorption due to reduction in surface albedo caused by replacement of high-reflective lichens with low-reflective woody plants, was 10.5 times higher per unit area in the district with large fluctuations. Overall, the net economic benefits per unit area were 237 % higher in the district with stable reindeer density. These results demonstrate that it is possible to minimize trade-offs between economic benefits from reindeer herding locally and global economic costs in terms of climate-regulating services by minimizing fluctuations in herds that are managed at sustainable densities.

Freshwater wetlands have a disproportionately large influence on the global carbon cycle, with the potential to serve as long-term carbon sinks. Many of the world\'s freshwater wetlands have been destroyed or degraded, thereby affecting carbon-sink capacity. Ecological restoration of degraded wetlands is thus becoming an increasingly sought-after natural climate solution. Yet the time required to revert a degraded wetland from a carbon source to sink remains largely unknown. Moreover, increased methane (CH4) and nitrous oxide (N2O) emissions might complicate the climate benefit that wetland restoration may represent. We conducted a global meta-analysis to evaluate the benefits of wetland restoration in terms of net ecosystem carbon and greenhouse gas balance. Most studies (76 %) investigated the benefits of wetland restoration in peatlands (bogs, fens, and peat swamps) in the northern hemisphere, whereas the effects of restoration in non-peat wetlands (freshwater marshes, non-peat swamps, and riparian wetlands) remain largely unexplored. Despite higher CH4 emissions, most restored (77 %) and all natural peatlands were net carbon sinks, whereas most degraded peatlands (69 %) were carbon sources. Conversely, CH4 emissions from non-peat wetlands were similar across degraded, restored, and natural non-peat wetlands. When considering the radiative forcings and atmospheric lifetimes of the different greenhouse gases, the average time for restored wetlands to have a net cooling effect on the climate after restoration is 525 years for peatlands and 141 years for non-peat wetlands. The radiative benefit of wetland restoration does, therefore, not meet the timeframe set by the Paris Agreement to limit global warming by 2100. The conservation and protection of natural freshwater wetlands should be prioritised over wetland restoration as those ecosystems already play a key role in climate change mitigation.

The Earth\'s radiative cooling is a key driver of climate. Determining how it is affected by greenhouse gas concentration is a core question in climate-change sciences. Due to the complexity of radiative transfer processes, current practices to estimate this cooling require the development and use of a suite of radiative transfer models whose accuracy diminishes as we move from local, instantaneous estimates to global estimates over the whole globe and over long periods of time (decades). Here, we show that recent advances in nonlinear Monte Carlo methods allow a paradigm shift: a completely unbiased estimate of the Earth\'s infrared cooling to space can be produced using a single model, integrating the most refined spectroscopic models of molecular gas energy transitions over a global scale and over years, all at a very low computational cost (a few seconds).

A declining trend in Indian summer monsoon precipitation (ISMP) in the latter half of the 20th century is a scientifically challenging and societally relevant research issue. Heavy aerosol loading over India is one of the key factors in modulating the ISMP. Using the state-of-the-state-of-the-art chemistry-climate model, ECHAM6-HAMMOZ, the impacts of South Asian anthropogenic sulfate aerosols on the Indian summer monsoon precipitation were investigated against: (1) 2010 La Niña (excess monsoon), (2) 2015 El Niño (deficit monsoon) in comparison to (3) normal monsoon 2016. Sensitivity simulations were designed with 48% enhancement in South Asian SO2 emissions based on a trend estimated from Ozone Monitoring Instrument (OMI) satellite observations during 2006-2017. The model simulations showed that sulfate aerosols reduce ISMP by 27.5%-43.3 %, while simulations without sulfate loading enhanced ISMP by 23% in 2010 La Niña and reduction by 35% in 2015 El Niño. This paper reports that sulfate aerosols loading over India reduce precipitation by aerosol-induced direct and indirect effects by inducing atmospheric cooling, weakening in the convection, and reduction in moisture transport to Indian landmass. This paper emphasizes the necessity of alternate use of energy to reduce sulfate aerosol emissions to solve water issues in South Asia.

Atmospheric pollution in the Arctic has been an important driver for the ongoing climate change there. Increase in the Arctic aerosols causes the phenomena of Arctic haze and Arctic amplification. Our analysis of aerosol optical depth (AOD), black carbon (BC), and dust using ground-based, satellite, and reanalysis data in the Arctic for the period 2003-2019 shows that the lowest amount of all these is found in Greenland and Central Arctic. There is high AOD, BC, and dust in the northern Eurasia and parts of North America. All aerosols show their highest values in spring. Significant positive trends in AOD (> 0.003 year-1) and BC (0.0002-0.0003 year-1) are found in the northwestern America and northern Asia. Significant negative trends are observed for dust (- 0.0001 year-1) around Central Arctic. Seasonal analysis of AOD, BC, and dust reveals an increasing trend in summer and decreasing trend in spring in the Arctic. The major sources of aerosols are the nearby Europe, Russia, and North America regions, as assessed using the potential source contribution function (PSCF). Anthropogenic emissions from the transport, energy, and household sectors along with natural sources such as wildfires contribute to the positive trends of aerosols in the Arctic. These increasing aerosols in the Arctic influence Arctic amplification through radiative effects. Here, we find that the net aerosol radiative forcing is high in Central Arctic, Greenland, Siberia, and Canadian Arctic, about 2-4 W/m2, which can influence the regional temperature. Therefore, our study can assist policy decisions for the mitigation of Arctic haze and Arctic amplification in this environmental fragile region of the Earth.

Suppression of carbon emissions through photovoltaic (PV) energy and carbon sequestration through afforestation provides complementary climate change mitigation (CCM) strategies. However, a quantification of the \"break-even time\" (BET) required to offset the warming impacts of the reduced surface reflectivity of incoming solar radiation (albedo effect) is needed, though seldom accounted for in CCM strategies. Here, we quantify the CCM potential of PV fields and afforestation, considering atmospheric carbon reductions, solar panel life cycle analysis (LCA), surface energy balance, and land area required across different climatic zones, with a focus on drylands, which offer the main remaining land area reserves for forestation aiming climate change mitigation (Rohatyn S, Yakir D, Rotenberg E, Carmel Y. Limited climate change mitigation potential through forestation of the vast dryland regions. 2022. Science 377:1436-1439). Results indicate a BET of PV fields of ∼2.5 years but >50× longer for dryland afforestation, even though the latter is more efficient at surface heat dissipation and local surface cooling. Furthermore, PV is ∼100× more efficient in atmospheric carbon mitigation. While the relative efficiency of afforestation compared with PV fields significantly increases in more mesic climates, PV field BET is still ∼20× faster than in afforestation, and land area required greatly exceeds availability for tree planting in a sufficient scale. Although this analysis focusing purely on the climatic radiative forcing perspective quantified an unambiguous advantage for the PV strategy over afforestation, both approaches must be combined and complementary, depending on climate zone, since forests provide crucial ecosystem, climate regulation, and even social services.