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Climate change is defined as the shift in climate patterns mainly caused by greenhouse gas emissions from natural systems and human activities. So far, anthropogenic activities have caused about 1.0 °C of global warming above the pre-industrial level and this is likely to reach 1.5 °C between 2030 and 2052 if the current emission rates persist. In 2018, the world encountered 315 cases of natural disasters which are mainly related to the climate. Approximately 68.5 million people were affected, and economic losses amounted to $131.7 billion, of which storms, floods, wildfires and droughts accounted for approximately 93%. Economic losses attributed to wildfires in 2018 alone are almost equal to the collective losses from wildfires incurred over the past decade, which is quite alarming. Furthermore, food, water, health, ecosystem, human habitat and infrastructure have been identified as the most vulnerable sectors under climate attack. In 2015, the Paris agreement was introduced with the main objective of limiting global temperature increase to 2 °C by 2100 and pursuing efforts to limit the increase to 1.5 °C. This article reviews the main strategies for climate change abatement, namely conventional mitigation, negative emissions and radiative forcing geoengineering. Conventional mitigation technologies focus on reducing fossil-based CO2 emissions. Negative emissions technologies are aiming to capture and sequester atmospheric carbon to reduce carbon dioxide levels. Finally, geoengineering techniques of radiative forcing alter the earth’s radiative energy budget to stabilize or reduce global temperatures. It is evident that conventional mitigation efforts alone are not sufficient to meet the targets stipulated by the Paris agreement; therefore, the utilization of alternative routes appears inevitable. While various technologies presented may still be at an early stage of development, biogenic-based sequestration techniques are to a certain extent mature and can be deployed immediately.

How clouds respond to anthropogenic sulfate aerosols is one of the largest sources of uncertainty in the radiative forcing of climate over the industrial era. This uncertainty limits our ability to predict equilibrium climate sensitivity (ECS)—the equilibrium global warming following a doubling of atmospheric CO₂. Here, we use satellite observations to quantify relationships between sulfate aerosols and low-level clouds while carefully controlling for meteorology.We then combine the relationships with estimates of the change in sulfate concentration since about 1850 to constrain the associated radiative forcing. We estimate that the cloud-mediated radiative forcing from anthropogenic sulfate aerosols is −1.11 ± 0.43 W m−2 over the global ocean (95% confidence). This constraint implies that ECS is likely between 2.9 and 4.5 K (66% confidence). Our results indicate that aerosol forcing is less uncertain and ECS is probably larger than the ranges proposed by recent climate assessments.

The ongoing and projected impacts from human-induced climate change highlight the need for mitigation approaches to limit warming in both the near term (< 2050) and the long term (> 2050). We clarify the role of non-CO₂ greenhouse gases and aerosols in the context of near-term and long-term climate mitigation, as well as the net effect of decarbonization strategies targeting fossil fuel (FF) phaseout by 2050. Relying on Intergovernmental Panel on Climate Change radiative forcing, we show that the net historical (2019 to 1750) radiative forcing effect of CO₂ and non-CO₂ climate forcers emitted by FF sources plus the CO₂ emitted by land-use changes is comparable to the net from non-CO₂ climate forcers emitted by non-FF sources. We find that mitigation measures that target only decarbonization are essential for strong long-term cooling but can result in weak near-term warming (due to unmasking the cooling effect of coemitted aerosols) and lead to temperatures exceeding 2 °C before 2050. In contrast, pairing decarbonization with additional mitigation measures targeting short-lived climate pollutants and N₂O, slows the rate of warming a decade or two earlier than decarbonization alone and avoids the 2 °C threshold altogether. These non-CO₂ targeted measures when combined with decarbonization can provide net cooling by 2030 and reduce the rate of warming from 2030 to 2050 by about 50%, roughly half of which comes from methane, significantly larger than decarbonization alone over this time frame. Our analysis demonstrates the need for a comprehensive CO₂ and targeted non-CO₂ mitigation approach to address both the near-term and long-term impacts of climate disruption.

Satellite observations indicate a substantial increase in Earth's top‐of‐atmosphere (the top of the atmosphere (TOA)) radiative imbalance since 2010. We estimate trends in effective radiative forcing (ERF) by separating TOA flux changes into forcing and response components, using feedback parameters derived from observed and simulated interannual variability and the CO2‐forced response. From 2010 to 2024, ERF trends are ∼1.0 W m−2 per decade for both net and shortwave fluxes, exceeding those for 2001–2024 and substantially larger than projections from state‐of‐the‐art models. This discrepancy persists across a wide range of climate sensitivities and forcing scenarios and shows limited sensitivity to feedback assumptions. The largest contribution arises from the shortwave component, with spatial patterns indicating particularly strong forcing increases over northern midlatitude oceans. These results suggest that the gap between observations and models is widening, although the contribution of internal variability cannot be entirely excluded.

Aerosol processes and, in particular, aerosol‐cloud interactions cut across the traditional physical‐Earth system boundary of coupled Earth system models and remain one of the key uncertainties in estimating anthropogenic radiative forcing of climate. Here we calculate the historical aerosol effective radiative forcing (ERF) in the HadGEM3‐GA7 climate model in order to assess the suitability of this model for inclusion in the UK Earth system model, UKESM1. The aerosol ERF, calculated for the year 2000 relative to 1850, is large and negative in the standard GA7 model leading to an unrealistic negative total anthropogenic forcing over the twentieth century. We show how underlying assumptions and missing processes in both the physical model and aerosol parameterizations lead to this large aerosol ERF. A number of model improvements are investigated to assess their impact on the aerosol ERF. These include an improved representation of cloud droplet spectral dispersion, updates to the aerosol activation scheme, and black carbon optical properties. One of the largest contributors to the aerosol forcing uncertainty is insufficient knowledge of the preindustrial aerosol climate. We evaluate the contribution of uncertainties in the natural marine emissions of dimethyl sulfide and organic aerosol to the ERF. The combination of model improvements derived from these studies weakens the aerosol ERF by up to 50% of the original value and leads to a total anthropogenic historical forcing more in line with assessed values. Key Points The HadGEM3‐GA7 climate model has a large, negative aerosol ERF resulting in an unrealistic negative total anthropogenic forcing of climate The aerosol ERF is shown to be highly sensitive to the underlying physical and aerosol model processes and parameterizations Through a combination of scientific model improvements the aerosol ERF is reduced by up to 50% from –2.75 to –1.45 W/m2

The double-Intertropical Convergence Zone (ITCZ) problem, in which excessive precipitation is produced in the Southern Hemisphere tropics, which resembles a Southern Hemisphere counterpart to the strong Northern Hemisphere ITCZ, is perhaps the most significant and most persistent bias of global climate models. In this study, we look to the extratropics for possible causes of the double-ITCZ problem by performing a global energetic analysis with historical simulations from a suite of global climate models and comparing with satellite observations of the Earth’s energy budget. Our results show that models with more energy flux into the Southern Hemisphere atmosphere (at the top of the atmosphere and at the surface) tend to have a stronger double-ITCZ bias, consistent with recent theoretical studies that suggest that the ITCZ is drawn toward heating even outside the tropics. In particular, we find that cloud biases over the Southern Ocean explain most of the model-to-model differences in the amount of excessive precipitation in Southern Hemisphere tropics, and are suggested to be responsible for this aspect of the double-ITCZ problem in most global climate models.

We present results from Phase I of the Continual Intercomparison of Radiation Codes (CIRC), intended as an evolving and regularly updated reference source for evaluation of radiative transfer (RT) codes used in global climate models and other atmospheric applications. CIRC differs from previous intercomparisons in that it relies on an observationally validated catalog of cases. The seven CIRC Phase I baseline cases, five cloud free and two with overcast liquid clouds, are built around observations by the Atmospheric Radiation Measurements program that satisfy the goals of Phase I, namely, to examine RT model performance in realistic, yet not overly complex, atmospheric conditions. Besides the seven baseline cases, additional idealized “subcases” are also employed to facilitate interpretation of model errors. In addition to quantifying individual model performance with respect to reference line‐by‐line calculations, we also highlight RT code behavior for conditions of doubled CO2, issues arising from spectral specification of surface albedo, and the impact of cloud scattering in the thermal infrared. Our analysis suggests that improvements in the calculation of diffuse shortwave flux, shortwave absorption, and shortwave CO2 forcing as well as in the treatment of spectral surface albedo should be considered for many RT codes. On the other hand, longwave calculations are generally in agreement with the reference results. By expanding the range of conditions under which participating codes are tested, future CIRC phases will hopefully allow even more rigorous examination of RT codes. Key Points There is need to continuously evaluate GCM radiation codes Intercomparisons of radiation codes should be based on validated LBL calculation Our intercomparison shows aspects of radiation codes that need improvement

The effect of topography on shortwave downward radiation (SWDR) is interest in the geoscience. However, such effects are rarely quantiatively and systematically evalulated, especially over the Tibetan Plateau region. With the geostationaly satellite measurements and topographic radiation model, this study reveals a heightened significance of topography on SWDR with increasing slope. Particularly in abrupt terrain (slopes >15°) the impact becomes pronounced, wherein the topographic radiative forcing (TRF) contributes 9.5% of the annual‐average SWDR. And the ratio of TRF to SWDR reaches a peak during winter, exceeding 150%. In annual‐average scales, the SWDR is 169 ± 38.4 W/m2 and the corresponding TRF is 16.2 ± 22.6 W/m2. Seasonal variations manifest on northern and southern slopes, with the sourthern slopes significant in summer, while the northern ones significant in winter. Notably, topographic effects persist across spatial scales and remain evident at 5 km resolution, emphasizing the necessity of considering topography in SWDR product utilization. Plain Language Summary Shortwave downward radiation is the main source of surface energy. In mountainous areas, the terrain significantly alters the amount of received SWDR. This study comrephensively examines the topographic influence on SWDR across the Tibetan Plateau for the first time. We investigate the influence of diverse topographic factors on the distribution of surface shortwave radiation in mountainous terrains. With the slope increasing, the impact of topography on SWDR becomes more and more significant. The topographic impact of northern and sourthern slopes behaves obvious seasonal variations, with the sourthern slopes significant in summer, while the northern ones significant in winter. With the increasing of spatial scale, the topographic effect gradually decreases and tends to be stable, but it can never disappear. As remote sensing data resolution coarsens, topographic radiative forcing diminishes, but even at 5 km resolution, terrain significantly affects SWDR distribution. Key Points In abrupt slopes, the annual‐average proportion of topographic radiative forcing to shortwave downward radiation (SWDR) can reach up to 9.5% The proportion of topographic radiative forcing to SWDR exceeding 150% in winter on the northern slopes Despite decreasing influence with coarser spatial resolutions, topographic effects persist even at 5 km

Large‐scale re‐/afforestation projects afford sizable atmospheric CO2 removals yet questions loom surrounding their potentially offsetting biogeophysical radiative forcings. Forest area change alters not only the surface albedo but also heat, moisture, and momentum fluxes, which in turn modify the atmosphere's radiative, thermodynamical, and dynamical properties. These so‐called radiative forcing “adjustments” have been little examined in re‐/afforestation contexts, and many questions remain surrounding their relevance in relation to the instantaneous forcing from the surface albedo change—and whether they can affect Earth's radiative energy balance in regions remote from where the re‐/afforestation occurs. Here, we quantified biogeophysical radiative forcings and adjustments from realistically scaled re‐/afforestation in Europe at high spatial resolution and found that adjustments with high signal‐to‐noise were largely confined to only a few months and to the region of re‐/afforestation. Adjustments were dominated by perturbed low‐level clouds and rarely exceeded ±25% of the annual albedo change forcing. Plain Language Summary Increased forest area can boost carbon stores in the terrestrial biosphere and benefit global climate. At the same time, this modifies several biogeophysical properties of the surface that impact Earth's energy balance. The extent to which these so‐called “biogeophysical” radiative forcings are important has not been comprehensively evaluated, with much of the research focusing on only a single mechanism—or the change to the surface's reflective properties (i.e., its albedo). Other mechanisms can dampen or reinforce the albedo change forcing and can even lead to remote effects, but these are much less understood. Focusing on Europe, we used a regional climate model combined with other analytical tools to quantify these additional mechanisms and understand their relevance in relation to the local forcing caused by surface albedo changes. We found that these other mechanisms rarely manifested in regions outside the region of re‐/afforestation, and further, that they are far less important than the forcing attributable to the surface albedo change. Key Points Biogeophysical radiative forcings and adjustments of European afforestation were quantified using a climate model and radiative kernels Radiative adjustments with high signal‐to‐noise were highly localized, dominated by low cloud cover change, and heavily confined in space and time Annual effective radiative forcings were largely driven by surface albedo change

Mineral dust aerosols impact Earth's radiation budget through interactions with clouds, ecosystems, and radiation, which constitutes a substantial uncertainty in understanding past and predicting future climate changes. One of the causes of this large uncertainty is that the size distribution of emitted dust aerosols is poorly understood. The present study shows that regional and global circulation models (GCMs) overestimate the emitted fraction of clay aerosols (< 2 μm diameter) by a factor of ~2-8 relative to measurements. This discrepancy is resolved by deriving a simple theoretical expression of the emitted dust size distribution that is in excellent agreement with measurements. This expression is based on the physics of the scale-invariant fragmentation of brittle materials, which is shown to be applicable to dust emission. Because clay aerosols produce a strong radiative cooling, the overestimation of the clay fraction causes GCMs to also overestimate the radiative cooling of a given quantity of emitted dust. On local and regional scales, this affects the magnitude and possibly the sign of the dust radiative forcing, with implications for numerical weather forecasting and regional climate predictions in dusty regions. On a global scale, the dust cycle in most GCMs is tuned to match radiative measurements, such that the overestimation of the radiative cooling of a given quantity of emitted dust has likely caused GCMs to underestimate the global dust emission rate. This implies that the deposition flux of dust and its fertilizing effects on ecosystems may be substantially larger than thought.