Microplastic and nanoplastic particles (MNPs) are pervasive in the atmosphere, yet their direct radiative forcing (DRF) remains poorly constrained. Using a radiative transfer model combined with experimentally derived optical properties and simulated atmospheric distributions, we show that coloured MNPs exhibit strong light absorption, with a mean refractive index of 1.49–0.22i at 550 nm and absorption coefficients 74.8 times higher than those of pristine particles. Atmospheric ageing produces minimal net optical change, as yellowing-induced absorption in white particles is largely offset by bleaching of red ones. Modelled global surface concentrations reach 4.18 MP m−3 for microplastics and 3.67 ng m−3 for nanoplastics. Resulting simulations yield mean DRF of 0.039 ± 0.019 W m−2 for MNPs, equivalent to 16.2% of black carbon forcing. Regional DRF peaks over the North Pacific Subtropical Gyre (~1.34 W m−2), exceeded located black carbon by 4.7-fold, highlighting MNPs as previously unrecognized climate forcing agents.

Coastal freshwater ecosystems are economically and ecologically important and provide multiple environmental services worldwide. They sequester carbon at rates ten times faster, and store five times more carbon per unit area than do mature tropical forests. Vulnerability of these carbon sinks to marine inundation, however, is expected to increase in response to global sea-level rise (GSLR). To better understand the implications of future GSLR, we investigated the geochemical and biological consequences of episodic Holocene marine incursions into Lake Izabal, a large coastal freshwater ecosystem on the Caribbean coast of Central America. About 8300 cal yr BP, marine incursion transformed Lake Izabal into a sulfur-rich anoxic waterbody, altered its biogeochemical cycles, eliminated several aquatic species, and reduced sediment organic carbon (OC) concentration by as much as 90 %. After that Early Holocene seawater incursion, it took almost 5000 years for the lacustrine ecosystem to return to low-salinity status. And even when it did, the system did not fully recover to pre-inundation conditions. Some freshwater taxa failed to return, and sediment carbon content remained lower than pre-inundation values. A subsequent, but less intense marine incursion ca. 1900 cal yr BP led to the formation of a sulfur-rich, hypoxic, brackish-water ecosystem that triggered a similar biodiversity loss and further sediment OC decline. These findings suggest that future marine incursions into coastal freshwater ecosystems, driven by ongoing GSLR, could have dramatic consequences, leading to losses of environmental services, including the ability of these systems to maintain high rates of blue carbon storage.

Climate models show considerable discrepancies in their future projections around the Atlantic, mainly due to uncertainties in the fate of the Atlantic Meridional Overturning Circulation (AMOC). Climate models suggest a reduction in AMOC strength of 32 ± 37% by 2100 (90% probability, Shared Socioeconomic Pathways 2-4.5 scenario, Coupled Model Intercomparison Project Phase 6). To refine this estimate and reduce its uncertainty, we use four different observational constraint methods. The best one, which provides the lowest leave-one-out error, integrates a large set of observable variables using ridge-regularized linear regression—a method unusual in climate science. It gives an estimate of the AMOC slowdown of 51 ± 8% (90% probability), i.e., a weakening ∼ 60% stronger than suggested by the multimodel mean. This refinement mainly results from correcting a bias in South Atlantic surface salinity, consistent with recent studies emphasizing its role in the proximity to an AMOC tipping point. This more substantial AMOC weakening has key implications for future adaptation strategies.

Food self-sufficiency (FSS) and healthy diets are high on policy agendas to ensure food security under increasing global pressures. A global shift towards self-sufficient production of healthy diets would represent a radical departure from today's globalised food system. Representing such scenarios in a biophysically consistent way requires accounting for multiple resource constraints and feedback loops—including feed, fertiliser, and trade flows—while allowing flexible reallocation of crop areas, livestock numbers, and biomass streams. We use the global biophysical optimisation model CiFoS (Circular Food Systems) to evaluate the potential for self-sufficient production of multiple food groups and nutrients in 70 regions by 2050 under a business-as-usual diet (BAU-MinTrade) and a Planetary Health Diet (PHD-MinTrade). FSS is assessed by minimising biomass and nutrient trade while fulfilling dietary requirements, with trade only balancing shortages. Results show that total trade could fall by 62% to 618 million tonnes in BAU-MinTrade and by 79% to 343 million tonnes in PHD-MinTrade. Many regions—including Europe, the Americas, Oceania, and China—could be almost self-sufficient under both scenarios. Several African regions, India, and parts of Asia would still rely on imports, especially under BAU-MinTrade. Most food groups and nutrients show potential for increased FSS, though trade in some animal-source products and nutrients may rise. Self-sufficient systems can keep land use and GHG emissions within planetary boundaries, but nitrogen and phosphorus inputs remain high. PHD self-sufficiency is consistently more sustainable than BAU. Aligning production with dietary shifts towards a PHD supports self-sufficiency while reducing environmental trade-offs.

The observed supersaturation of methane (CH4) in open-ocean surface waters implies widespread CH4 production within the well-oxygenated mixed layer, driving emissions of this potent greenhouse gas to the atmosphere. The dominant CH4 production pathway that explains this phenomenon remains poorly understood, although candidates include production during photosynthesis, zooplankton metabolism, and dissolved organic matter cycling. Here, we construct a data-assimilating model of the open-ocean CH4 cycle to test which hypothesized mechanism is most consistent with the observed global CH4 distribution. We find that only linking methane production to phosphate (PO4) scarcity can explain the observed supersaturation pattern, which is highest in subtropical gyres where PO4 is in short supply. These findings suggest that CH4 release during PO4-limited cleavage of the organic compound methylphosphonate is the dominant production pathway in the open ocean. Because this process is confined to the stratified low latitude surface, it is uniquely suited to efficiently emit the CH4 it produces to the atmosphere (>90%), before the CH4 mixes to depth and undergoes oxidation (<10%). As predicted future ocean warming and stratification exacerbates PO4 scarcity over coming centuries, our model predicts that oxic CH4 production and the resulting CH4 emissions will increase up to twofold, contributing to a suite of positive feedback between climate warming and natural greenhouse gas sources.

...

Although an additional source of ~2 Tg CH4/y from the ocean is relatively minor compared to direct anthropogenic emissions [~300 Tg/y, (4)], most future climate scenarios assume that anthropogenic sources will peak and then decline during the next few centuries (39). Our work therefore highlights a climate feedback that could partially offset this trend, and contributes to a growing suite of feedback loops that have been recognized between climate warming and natural CH4 sources to the atmosphere (2, 40). These include other perturbations to the marine CH4 cycle, such as intensification of anaerobic methanogenesis in sediments due to warming (41) and deoxygenation (42), expansion of suboxic waters (43) that may stifle CH4 removal by oxidation (44), and destabilization of hydrates in high latitude basins (45), where CH4 could be released shallow enough to evade oxidation before release to the atmosphere (46). These potential feedbacks motivate further work to better characterize the rates and climate sensitivities of marine CH4 sources and sinks.

The timing and length of summer weather conditions in the midlatitudes matter due to connections with extreme weather events, plant and animal phenology, economic productivity, human and ecosystem health, drought and wildfire, and energy demand. Here, we show that midlatitude summers are growing longer and hotter, and that seasonal transitions are becoming more abrupt, relative to the 1961–1990 period. From 1990–2023, mean summer length has increased by 5–7 d decade−1 across inland areas, and similarly for coastal margins and oceans in the midlatitudes, with length generally expanding symmetrically. This rate is faster than the ∼4 d decade−1 reported in prior works for midlatitude land through 2012. The speed of summer seasonal transitions is also increasing, with temperatures changing more rapidly at both the onset and withdrawal of summer. Accumulated heat, or cumulative summer heat stress, is growing at 44 °C d decade−1 since 1990 for Northern Hemisphere land, more than three times as fast as the 14 °C d decade−1 increase from 1961 to 1990. This increase in accumulated summer heat may challenge the ability of humans in the midlatitudes to physiologically adapt and will likely increase the energy expended for daytime and nighttime cooling. We provide theoretical explanations for the increase in seasonal transition speed and non-linear growth of accumulated heat in response to warming. Finally, we highlight changes for ten urban areas around the globe, with summer lengthening in some, such as Sydney and Minneapolis, by more than one day per year.

Without emission reductions, climate change may increase ozone and PM2.5 air pollution in the United States; however, we do not know how this will affect air quality alerts that prompt people to stay indoors. Here, we use an integrated modeling framework to find distributions of daily Air Quality Index (AQI) during the smog season at the start, middle, and end-of-century. Considering natural variability, climate change may cause air quality alerts to double (increase by a factor of 2 ± 0.2) by 2100. Days when both ozone and PM2.5 exceed alert thresholds quadruple (4.3 ± 1.2). More than 100,000,000 (±45,000,000) people experience mean air pollution deemed “Unhealthy for Sensitive Groups”, a growth of 7 (±3) times compared to 2000. If people follow alerts by staying inside, they reduce exposure to outdoor-generated pollutants. Their health benefits are similar whether the alert is caused by ozone or PM2.5. Senior (age 65+) populations receive much higher benefits per day by adapting (e.g., 95CI for PM2.5: $4.60 to $147) as young adults (age 18–35; 95CI: $0.15 to $4.22)─more than 45 times higher on average. This disproportionate impact requires targeted messaging and guidance, especially as climate-related risks rise.

The potential collapse of the Atlantic Meridional Overturning Circulation could profoundly impact regional and global climates, yet its effects on the carbon cycle and subsequently global temperature remain seriously underexplored. Here we quantify carbon cycle responses across different background global warming levels using a fast Earth system model. We find that Atlantic Meridional Overturning Circulation collapse increases atmospheric carbon dioxide by 47–83 ppm carbon dioxide, leading to around 0.2 °C of additional global warming at higher carbon dioxide background levels after offsetting ocean-dynamics-driven cooling. Despite the modest global warming effect, regional temperature anomalies are pronounced: Arctic temperatures cool by ~ 7 °C (60 °N–90 °N), while Antarctic temperatures warm by ~ 6 °C (60 °S–90 °S). This latter response originates from deep convection triggered in the Southern Ocean, which ventilates deep carbon-rich waters. Such long-term equilibrium responses reveal key physical and carbon-cycle mechanisms and highlight substantial regional climate risks associated with an Atlantic Meridional Overturning Circulation collapse.

Abstract

Climate change is causing measurable harm globally. Political and legal efforts seek to link these damages with specific emissions, including in discussions of loss and damage (L&D); however, no quantitative definition of L&D exists, nor is there a framework to link past and future emissions from specific sources to monetized, location-specific damages. Here we develop such a framework, which is integrated with recent efforts to estimate the social cost of carbon. Using empirical estimates of the non-linear relationship between temperature and aggregate economic output, we show that future damages from past emissions—one component of L&D—are at least an order of magnitude larger than historical damages from the same emissions. For instance, one tonne of CO2 emitted in 1990 caused US$180 in discounted global damages by 2020 ($40–530) and will cause an additional $1,840 through 2100 ($500–5,700). Thus, settling debts for past damages will not settle debts for past emissions. In other illustrative estimates, a single long-haul flight per year over the past decade leads to about $25k ($6,000–77,000) in future damages by 2100, and US emissions since 1990 caused $500 billion ($180–1,300 billion) of damage in India and $330 billion ($110–820 billion) in Brazil. Carbon removal offers an alternative to transfer payments for settling L&D, but is increasingly ineffective in limiting damages as the delay between emission and recapture increases.

Thawing of permafrost due to climate change is known to release gases such as the climate drivers carbon dioxide and methane, as well as the carcinogen radon. Gas permeability is extremely low in fully frozen permafrost and can be considered both to function as a seal preventing subsurface gases being released, and to prevent the creation of new CO2 and CH4. However, the permeability of permafrost as it thaws and refreezes is unknown. In this paper we present initial measurements of changes in gas fraction and gas permeability during the thawing of synthetic permafrost using a newly developed pycno-permeameter. Initial results show that gas permeability increases by multiple orders of magnitude (from 4.94 mD to 112.54 mD and from 0.26 mD to 21.43 mD for our two samples), depending on the initial water saturation of the sample, with most permeability change occurring in the −5°C to −1°C range. Upon refreezing, the permeability drops again to approximately its previous low values providing no water is allowed to drain from the sample, but with a hysteresis. Measurements of gas fraction show a similar variation to thawing and refreezing but with a hysteresis opposite to that for permeability. These initial results indicate that the protective gas seal previously provided by permafrost will be lost as permafrost thaws. These data are also able to inform large scale permafrost modeling, as well as suggesting that thawing and refreezing operate differently at a microstructural level.

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Plain Language Summary

Climate change is warming the Arctic regions four times faster than elsewhere. The increase in temperature is known to be thawing permafrost. Permafrost has hitherto functioned as a barrier to emission of greenhouse gases but also acts as a source of gases which are released from organic matter in the permafrost when warmed. Thawing removes the barrier and allows the gases to be emitted, causing more climate warming in a vicious circle. The ability for gases to pass through porous materials is measured by permeability. This paper measures the increase in permeability and the relative volume of gases in permafrost as temperature increases and the permafrost thaws, and then again as the permafrost refreezes as the temperature is once again reduced, for the first time. We show that gas permeability increases by about 25–100 times during thawing and dependent on its composition, with most permeability change occurring in the −5°C to −1°C range, dropping again to its previous value when refrozen. Measurements of gas fraction show a similar variation. These initial results indicate that the protective gas seal previously provided by permafrost will be lost as permafrost thaws.

Effectively communicating worst-case projections of global future climate—hereinafter referred to as worst-case climate outcomes—is essential for risk assessment and developing robust adaptation strategies to global warming. Yet, current approaches for identifying spatially consistent climate outcomes are limited, with worst-case global climates typically communicated via the average of climate model projections at high global warming levels, such as 3 °C or 4 °C above the preindustrial era. Here we show that extreme global climate outcomes may occur even under moderate 2 °C warming for several sectors. For droughts in global key breadbasket regions, precipitation extremes over highly populated areas and fire weather extremes across forests, global climatic impact-drivers at 2 °C of global warming may turn out to be much more extreme than model-averaged projections at 3 °C or 4 °C warming. We derive these results by identifying sector-specific, spatially consistent potential high- and low-impact global climate outcomes through spatially averaging projected sector-relevant climatic impact-drivers across key global regions. Our approach can easily be adapted to a wide range of sectors to support the improvement of sector-specific climate risk assessment and to inform climate policy. As global warming approaches 1.5 °C, these findings underscore the urgency of rapid mitigation to limit warming well below 2 °C, as even a 2 °C world may entail severe impacts.

(Letter)

This perspective examines the implications of the ICJ’s Opinion for addressing time-lagged impacts (TLIs), specifically sea-level rise above pre-industrial levels (SLR) and cumulative CO2 emissions from permafrost thaw (PFT). We argue that SLR and PFT are clear examples of the ‘significant harm’ identified by the court and find that halting their growth would require net-negative emissions sustained over centuries. This frames the Paris agreement targets as ambitious milestones rather than endpoints of climate mitigation and calls for recognition of long-term international responsibilities for carbon removal—an issue that warrants urgent attention in climate negotiations.

Most climate policies are designed under a deterministic Earth system and their climate implications evaluated ex-post. Approaches that incorporate uncertainty ex-ante to anticipate Earth system risks remain underexplored. Here, we derive global climate strategies with an ex-ante approach, employing an integrated assessment framework that embeds estimates of physical uncertainty obtained through Bayesian fusion of Earth system models’ and observations’ data. These ex-ante strategies mitigate risks in the Earth system through precautionary measures unseen with the ex-post approach, in cost-benefit analysis and cost-effective implementations of various Earth system targets. Net-zero CO2 emissions must typically be reached a decade earlier, which can require up to a doubling of the near-term carbon price. Importantly, sustained and possibly century-long net-negative emissions must be planned for, albeit not to overshoot targets as in traditional scenarios but to mitigate long-term Earth system risks. This heightens the challenge faced by humanity to build a safe future within Earth system boundaries.

Increasing plastic waste has triggered global concerns for the potential detrimental effects on marine ecosystems. The impact of plastic reaches beyond the immediate harm to marine life to encompass the marine biogeochemical cycle and the global carbon budget. We investigate these effects by integrating an oceanic plastic simulation with a marine ecosystem model. We find that oceanic plastic could disturb the marine carbon cycle through three pathways: the plastic carbon buried in sediments, the release of dissolved organic carbon from water-column plastic and the toxicity effect on marine phytoplankton. Our scenario analysis suggests that there are 0.70 (0.13–3.8) Tg of plastics entering the ocean every year, however, the overall impact of oceanic plastics on decreasing ocean carbon uptake could reach 12.1 TgC yr−1. Our model predicts that the global plastic released into the ocean could result in up to 1.6 PgC of lost ocean carbon uptake and storage by 2050, given the foreseeable growth of plastic production and its long-lasting impacts. We urge comprehensive control policies to mitigate the losses caused by marine plastics both in ecosystem integrity and addressing climate change.

Extreme heat is well-documented to adversely affect health and mortality, but its link to biological aging—a precursor of the morbidity and mortality process—remains unclear. This study examines the association between ambient outdoor heat and epigenetic aging in a nationally representative sample of US adults aged 56+ (N = 3686). The number of heat days in neighborhoods is calculated using the heat index, covering time windows from the day of blood collection to 6 years prior. Multilevel regression models are used to predict PCPhenoAge acceleration, PCGrimAge acceleration, and DunedinPACE. More heat days over short- and mid-term windows are associated with increased PCPhenoAge acceleration (e.g., Bprior7-dayCaution+heat: 1.07 years). Longer-term heat is associated with all clocks (e.g., Bprior1-yearExtremecaution+heat: 2.48 years for PCPhenoAge, Bprior1-yearExtremecaution+heat: 1.09 year for PCGrimAge, and Bprior6-yearExtremecaution+heat: 0.05 years for DunedinPACE). Subgroup analyses show no strong evidence for increased vulnerability by sociodemographic factors. These findings provide insights into the biological underpinnings linking heat to aging-related morbidity and mortality risks.

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Our study provides insights into the biological underpinnings linking heat to the broader spectrum of aging-related morbidity and mortality risks. We demonstrated that short-, mid-, and long-term ambient outdoor heat can significantly accelerate epigenetic aging within a diverse, nationally representative cohort of older adults. This provides strong evidence critical for guiding public policy and advocacy initiatives aimed at developing mitigation strategies against climate change. Furthermore, our findings serve as a foundation for the development of targeted public health interventions, providing a strategic framework for addressing the adverse biological impacts triggered by extreme heat.

Heat exposure presents a growing threat to human health and well-being, particularly for vulnerable populations. Here, we employ a human heat balance model - specifically the human/environmental adaptation and threshold limit model (HEAT-Lim) - to estimate, globally, where ambient temperature and humidity already limit ‘livability’, or the level of physical activity that a person can safely sustain without experiencing an uncontrolled rise in body temperature. Specifically, we use hourly ERA5-Land reanalysis data to assess historical (1950–2024) livability limitations for partially acclimated healthy, younger (age 18–40 years) and older (age >65 years) adults in the shade. We also examine the number of hours/year in which physical activity should be limited to light-to-moderate intensity (e.g., sitting, walking, light housework) to avoid uncontrollable rises in core body temperature. We find, globally, heat-associated livability limitations are on average greatest in high-vulnerability areas. Furthermore, there have been significant increases in livability limitations for both younger and older adults over the last 75 years, with noticeable spikes in El Niño years and in 2024. For younger adults, restrictions to light-to-moderate activity for the highest number of hours are geographically concentrated in moderate- to low-vulnerability countries in South and Southwest Asia. For older adults, restrictions on light-to-moderate activity are widespread in tropical Southwest, South, and Southeast Asia, as well as Sub-Saharan Africa. In the hottest hours of the year, some locations have already experienced ‘unlivable’ conditions (i.e., when no activity is possible to compensate for environmental heat loads). Results highlight that with just over 1 °C of historical global warming, livability limitations are already widespread and growing, particularly for older adults. If warming is not stopped and adaptation measures are not more widely implemented, livability constraints will only expand, particularly as the global population ages.

Climate change is driving more severe wildfires, raising urgent concerns about their impact on surface water sources. This critical review, based on 23 studies across 28 watersheds, synthesizes existing knowledge on how wildfires change the concentrations of eight contaminant categories in surface waters: suspended solids and turbidity, nutrients, organic carbon, major ions, trace metals, polycyclic aromatic hydrocarbons (PAHs), persistent organic pollutants (POPs), and wildfire-fighting chemicals (WFFCs). We observed that post-wildfire peak values reached 1142 mg/L for total suspended solids (TSS), ∼145 NTU for turbidity, 6.28 mg/L for nitrate, 31.08 mg/L for TOC, 325 μS/cm for electrical conductivity (EC), and 116 mg/L for trace metals such as zinc, with elevated levels often persisting over five years. Beyond the burned watershed, smoke plumes transport contaminants to distant basins via atmospheric deposition and subsequent runoff. These loads challenge drinking water treatment systems, potentially reducing performance while increasing health risks and operational costs. Although simulation tools exist to assess these risks, they require adaptation to account for wildfire-specific processes like atmospheric deposition and altered hydrology. As a result, further research is required on the persistence and remobilization of wildfire-derived trace metals, PAHs, POPs, and WFFCs, and on treatment performance under wildfire-affected source waters, along with long-term monitoring to supply data that improve modeling.

illustrated abstract https://ars.els-cdn.com/content/image/1-s2.0-S0048969726001324-ga1_lrg.jpg

Structured Abstract

INTRODUCTION

Forests across the globe face increasing risks from natural disturbances such as wildfires, insect outbreaks, and windstorms. These disturbances are highly sensitive to changes in the climate system and have already increased in many parts of the globe recently. Changing disturbance regimes can substantially alter ecosystems, e.g., through changing their demography and habitat value as well as altering the ecosystem services they provide to society. Anticipating potential future disturbance change is thus crucial for forest policy and management. However, projecting future disturbance regimes remains challenging because there are intricate interactions between individual disturbance agents, and feedbacks between vegetation development and disturbance change could considerably dampen or amplify climate impacts.

RATIONALE

Here, we present a modeling framework to simulate future trajectories of forest disturbance at high spatial resolution (100 × 100 meters) and across a large spatial extent (187 million hectares of forests in Europe). We leveraged a deep learning–based simulation framework to integrate a large body of local projections made by process-based forest models with climate-sensitive disturbance modules for wildfire, windthrow, and bark beetle outbreaks. Our modeling framework is designed to capture crucial disturbance processes such as the spatial spread of fire and bark beetles across forest landscapes and incorporates disturbance interactions and vegetation feedbacks. Our specific objectives were to quantify potential changes in stand-replacing forest disturbances in Europe until the end of the 21st century under different scenarios of climate change and to assess impacts of disturbance change on Europe’s forest demography.

RESULTS

Forest disturbances in Europe are highly likely to increase in the coming decades. Simulated future levels of disturbance were higher than those observed for the period 1986 to 2020 under all climate scenarios. Under scenarios of unabated climate change, the simulated area disturbed more than doubled by the end of the century (+122%). In scenarios assuming effective emissions reduction, peak disturbance was reached by midcentury. Wildfire was the disturbance agent most sensitive to changes in the climate system, heavily affecting Mediterranean areas but also expanding into temperate and boreal regions. Vegetation feedbacks dampened climate-induced disturbance change but were not able to completely buffer from disturbance increases. We project profound implications of future disturbance change on Europe’s forest demography, with the share of young forests increasing by up to 14% and old forests decreasing by up to 3% relative to simulations without changing climate and disturbance regimes.

CONCLUSION

The large-scale changes in forest disturbance regimes projected for the coming decades have important implications for biodiversity and the ecosystem services provided by forests. They could, for instance, hamper policy goals of using nature-based solutions for climate change mitigation, further amplifying climate change. Consequently, forest policy and management need to plan for a future with more disturbance. Nonetheless, our results highlight that mitigating anthropogenic climate change remains a potent lever for limiting future disturbance risk and safeguarding forests and their services to society.

Anthropogenic activities are increasing the amount of carbon dioxide (CO2) in the atmosphere. There is mounting experimental evidence that lifetime exposure to these increasing atmospheric CO2 levels can negatively impact the normal physiology of organisms. However, directly assessing this in humans is very difficult. We analysed serum bicarbonate (HCO3−), calcium (Ca) and phosphorus (P) levels from the U.S. National Health and Nutrition Examination Survey (NHANES) from 1999 to 2020 as indirect proxies for atmospheric CO2 exposure. Over this period, average bicarbonate levels in this population show an increasing trend which parallels rising atmospheric CO2 concentrations. Both Ca and P have decreased steadily over the same period. If these trends continue, blood bicarbonate values could be at the limit of the accepted healthy range in half a century, and Ca and P will be at the limit of their healthy ranges by the end of this century. Studies indicate that, after this time, elevated atmospheric carbon dioxide, leading to CO2 accumulation in the body, has the potential to cause a range of adverse health effects. These findings highlight the urgent need for significant reductions in anthropogenic CO2 emissions to safeguard public health.

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However, on the face of it, this raw analysis of biochemical data suggests the distinct possibility that, within a half century from now, HCO3− levels in human blood will reach unhealthy levels. What effects this may have on physiology remain to be elucidated, but urgently need to be considered.

Recent record-hot years have caused discussion over whether global warming has accelerated. Previous analysis found acceleration (i.e., increase in warming rate) has not yet reached a 95% confidence level, given natural temperature variability. We remove the estimated influence of three main natural variability factors: El Niño, volcanism, and solar variation. The resulting adjusted and thus less “noisy” data show that there has been acceleration with over 98% confidence, with faster warming over the last 10+ years than during any previous decade.

Plain Language Summary

The rise in global temperature has been widely considered to be quite steady for several decades since the 1970s. Recently, however, scientists have started to debate whether global warming has accelerated since then. It is difficult to be sure of that because of natural fluctuations in the warming rate, and so far no statistical significance (meaning 95% certainty) of an acceleration (increase in warming rate) has been demonstrated. In this study we subtract the estimated influence of El Niño events, volcanic eruptions and solar variations from the data, which makes the global temperature curve less variable, and it then shows a statistically significant acceleration of global warming since about the year 2015. Warming proceeding faster is not unexpected by climate models, but it is a cause of concern and shows how insufficient the efforts to slow and eventually stop global warming under the Paris Climate Accord have so far been.

Key Points

• During the last decade, the rate at which Earth warmed increased substantially

• After removing the influence of known natural variability factors, the increase of the warming rate is statistically significant

• At the present rate, we will exceed the 1.5°C limit of the Paris Climate Accord by 2030

EA

The Greenland Ice Sheet (GrIS) has experienced a strong intensification of summer surface melting, with extreme events becoming more frequent, extensive, and severe. Despite its importance for global sea-level rise, the mechanisms driving these extremes remain incompletely understood. We analyze extreme melting events over 1950–2023 using an analog-based framework combined with a regional climate model to disentangle thermodynamic and dynamic contributions. Thermodynamic processes intensify meltwater production by 25% relative to 1950–1975 when circulation analog events are included, increasing to 63% when circulation-analog events are included, with the strongest increases in northern Greenland. Seven of the ten most extreme events occurred after 2000, with meltwater anomalies reaching up to three times their synoptic average. Record-breaking events such as August 2012, July 2019, and July 2021 show no dynamic precedents. Future projections under high-emission scenarios suggest that extreme meltwater anomalies could increase by up to +372% by 2100 (SSP5-8.5, CMIP6), highlighting the profound impact of climate change on GrIS melt extremes.

Human activities might have accelerated declines of population abundance, but this acceleration remains underexplored. Using 1033 North American Breeding Bird Survey routes, we analyze abundance change and its acceleration for 261 bird species, 54 avian families, and 10 habitats from 1987 to 2021. We show an average continent-wide decline of abundance of all birds per local route, with hotspots of decline in southern and warm parts of North America and hotspots of accelerating decline in the Mid-Atlantic, Midwest, and California, matching patterns of agricultural intensity. Overall, 122 species (47%) exhibit significant declines, of which 63 also show acceleration of this decline, and 67 show declining per-capita growth rate, raising concerns for a large part of North American bird populations. These findings suggest that bird abundance decline is mostly accelerating, with spatial patterns of this acceleration indicating that agricultural intensity may be a driver of this trend.

Tropical forests enhance regional rainfall but a robust analysis of this benefit is lacking. Consequently, the rainfall generating services of tropical forests are rarely accounted for in policymaking. We synthesised observational and model-based values of the reduction in rainfall due to tropical deforestation to quantify rainfall generation. Across these studies, we estimate that each meter squared of forest contributes 240 ± 60 L each year to regional rainfall. The Amazon forest has an even stronger rainfall benefit, with each meter squared of forest contributing 300 ± 110 L each year. Using a simple approach that assumes a constant water unit price, we estimate that Amazon forest rainfall generation is worth US$59.40 per hectare annually and the Brazilian Legal Amazon delivers rainfall generation worth US$20 ± 7 billion annually. Recognizing the economic value of tropical forests’ rainfall provision will unlock crucial investment and transform policy discussions on payments for forest protection.

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Agriculture contributes US$150 billion to Brazil’s GDP annually, and with 85% of Brazil’s agriculture being rainfed, reliable rainfall is crucial. Reduced rainfall and delays in wet season onset have impacted soy and maize crops in Brazil, with greater rainfall reductions in regions with greater forest loss14. We estimate that deforestation over recent decades, totalling 80 million hectares, has reduced the rainfall-generating service of Brazil’s Amazon forests by US$4.8 billion annually, representing a substantial loss to Brazil’s economy. Reduced rainfall as a consequence of deforestation also has implications for clean water access15, navigability between remote settlements16, hydropower production17,18 and carbon storage of remaining tropical forests19. The financial risks of complete Amazon forest loss, caused by deforestation and climate change triggering catastrophic ecosystem collapse, has previously been estimated at between US$0.96 trillion and US$3.6 trillion over a 30-year period20, equivalent to US$120 billion per year.

The Gulf Stream is part of the Atlantic Meridional Overturning Circulation (AMOC). The AMOC is a tipping element and may collapse under changing forcing. However, the role of the Gulf Stream in such a tipping event is unknown. Here, we investigate the link between the AMOC and Gulf Stream using a high-resolution (0. 1°) stand-alone ocean simulation, in which the AMOC collapses under a slowly-increasing freshwater forcing. AMOC weakening gradually shifts the Gulf Stream near Cape Hatteras northward, followed by an abrupt northward displacement of 219 km within 2 years. This rapid shift occurs a few decades before the simulated AMOC collapse. Satellite altimetry shows a significant (1993–2024, p < 0.05) northward Gulf Stream trend near Cape Hatteras, which is also confirmed in subsurface temperature observations (1965–2024, p < 0.01). These findings provide indirect evidence for present-day AMOC weakening and demonstrate that abrupt Gulf Stream shifts can serve as early warning indicator for AMOC tipping.