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Understanding the impact of various climate forcing agents, such as aerosols, on extreme precipitation is socially and scientifically vital. While anthropogenic absorbing aerosols influence Earth's energy balance and atmospheric convection, their role in extreme events remains unclear. This paper uses convective‐resolving radiative‐convective‐equilibrium simulations, with fixed solar radiation, to investigate the influence of absorbing aerosols on extreme precipitation comprehensively. Our findings reveal an underappreciated mechanism through which absorbing aerosols can, under certain conditions, strongly intensify extreme precipitation. Notably, we demonstrate that a mechanism previously reported for much warmer (hothouse) climates, where intense rainfall alternates with multi‐day dry spells, can operate under current realistic conditions due to absorbing aerosol influence. This mechanism operates when an aerosol perturbation shifts the lower tropospheric radiative heating rate to positive values, generating a strong inhibition layer. Our work highlights an additional potential effect of absorbing aerosols, with implications for climate change mitigation and disaster risk management. Plain Language Summary: Aerosols, particles suspended in the atmosphere, can interact with the incoming solar radiation by scattering or absorbing it. Aerosol species that absorb solar radiation generate local warming of the atmosphere. This local warming changes the vertical profile of temperature and by that affects cloud and precipitation development. In this paper we use idealized computer simulations to investigate the effect of absorbing aerosols on precipitation, and specifically on extreme precipitation events in the tropics. We demonstrate that under certain conditions, absorbing aerosols can strongly enhance extreme precipitation even despite reducing the mean. We show that this trend can be explained by a mechanism previously reported for much warmer climate conditions than currently found on Earth, involving heating by radiation of the lower part of the troposphere. These results have implications for climate change mitigation and disaster risk management. Key Points: The effect of absorbing aerosol on extreme precipitation is examined in idealized convective‐resolving radiative‐convective‐equilibrium simulationsAerosol perturbation that shifts the lower tropospheric radiative heating rate to positive values strongly enhances extreme precipitationThis trend is explained by a mechanism reported before for hothouse climate conditions involving a shift into an "episodic deluge" regime [ABSTRACT FROM AUTHOR]

The cloud feedback may result in amplification or damping of Arctic warming. Two common techniques used to diagnose the top‐of‐the‐atmosphere cloud feedback are the Adjusted Cloud Radiative Effect (AdjCRE) method and the Cloud Radiative Kernel (CRK) method. We apply both to CMIP5 and CMIP6 model data, finding that the AdjCRE calculated Arctic shortwave cloud feedback is twice as correlated with sea ice loss in CMIP5, and four times in CMIP6, as the CRK method. We find that the CRK method produces Arctic all‐sky residual percentages exceeding 20% in 15 of 18 models. We use the CRK method to decompose the feedback in CMIP5 and CMIP6 finding that its median value changed from negative to positive driven by a less‐negative cloud optical depth feedback. Despite its lack of closure, we conclude that the CRK method is better suited for Arctic SW feedbacks as it is less impacted by surface albedo changes. Plain Language Summary: The cloud feedback is the process by which cloud property changes in a warming climate can either further enhance warming or damp it. The Arctic is warming faster than the rest of the globe, and one of the largest sources of uncertainty in its climate projections is the cloud feedback. There are two popular methods to calculate the cloud feedback: the Adjusted Cloud Radiative Effect technique, and the Cloud Radiative Kernel technique. In this paper we compare the two methods in a suite of climate models by considering the extent to which changes in Arctic sea ice impact the cloud feedbacks. From this analysis we conclude that the Cloud Radiative Kernel method is less affected by sea ice loss. We then apply the Cloud Radiative Kernel technique to data from the two most recent generations of global climate models to investigate how polar day Arctic cloud feedbacks have changed between these generations. We find that the median value of these Arctic feedbacks is slightly positive in the newest generation of models, a change from slightly negative in the previous generation that is largely fueled by a weakening of the feedback associated with changes in cloud optical depth. Key Points: The Cloud Radiative Kernel method is less sensitive to surface albedo changes than the Adjusted Cloud Radiative Effect techniqueThe Cloud Radiative Kernel method provides poor radiative closure in a suite of global climate modelsThe median shortwave Arctic cloud feedback in recent climate models is slightly positive due to a weakened cloud optical depth feedback [ABSTRACT FROM AUTHOR]

Scafetta (2022, https://doi.org/10.1029/2022gl097716) purports to test Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models through a comparison of temperature changes over three decades. Unfortunately, the paper contains numerous conceptual and statistical errors that undermine all of the conclusions. First, no uncertainty is given for the observational temperature difference, making it impossible to assess compatibility with any model result. Second, the CMIP6 data are the ensemble means for each model, but the metric being tested is sensitive to the internal variability and so the full ensemble for each model must be used. When this is corrected, the conclusion that "all models with ECS > 3.0°C overestimate the observed global surface warming" is not sustained. Third, the statistical test in Section 2 would reject all models even in a perfect model setup given sufficient ensemble members, thus the second conclusion "that spatial t‐statistics rejects the data‐model agreement" is also not sustainable. Plain Language Summary: Comparisons of models and observations need to account from multiple sources of uncertainty in both the observations and due to the chaotic dynamics of the weather. The analyses in Scafetta (2022, https://doi.org/10.1029/2022gl097716) do not take either of these issues into account and thus the conclusions in that paper are not supportable. Key Points: Scafetta (2022) contains errors in both of the statistical tests used that make the conclusions unsupportable [ABSTRACT FROM AUTHOR]

In response to global warming, ozone is predicted to increase aloft due to stratospheric cooling but decrease in the tropical lower stratosphere. The ozone reductions have been primarily attributed to a strengthening Brewer‐Dobson circulation, which upwells ozone‐poor air. Yet, this paper finds that strengthening upwelling only explains part of the reduction. The reduction is also driven by tropospheric expansion under global warming, which erodes the ozone layer from below, the low ozone anomalies from which are advected upwards. Strengthening upwelling and tropospheric expansion are correlated under global warming, making it challenging to disentangle their relative contributions. Therefore, chemistry‐climate model output is used to validate an idealized model of ozone photochemistry and transport with a tropopause lower boundary condition. In our idealized decomposition, strengthening upwelling and tropospheric expansion both contribute at leading order to reducing tropical ozone. Tropospheric expansion drives bottom‐heavy reductions in ozone, which decay in magnitude into the mid‐stratosphere. Plain Language Summary: The ozone layer absorbs ultraviolet light otherwise harmful to life. Due to compliance with the Montreal Protocol, the ozone layer is generally recovering from depletion. But, at the same time, global warming is predicted to impact ozone, increasing ozone in the upper stratosphere and decreasing ozone in the tropical lower stratosphere. These decreases are typically argued to result from a strengthening of tropical stratospheric upwelling under global warming. Yet, this paper shows that in addition to contributions from strengthening upwelling, much of the ozone loss arises from a deepening of the troposphere under global warming. The deepening of the troposphere erodes the ozone layer from below, with the low ozone anomalies in the eroded region subsequently transported upwards by the background upwelling. Deepening of the troposphere therefore helps to explain the predicted ozone reductions throughout the tropical lower stratosphere. Key Points: Global warming reduces ozone in the tropical lower stratosphere, an effect typically attributed to strengthening stratospheric upwellingYet, global warming also deepens the troposphere, which erodes the ozone layer and reduces transport of ozone into the lower stratosphereAlong with strengthening upwelling, tropospheric expansion contributes at leading order to reductions in tropical lower stratospheric ozone [ABSTRACT FROM AUTHOR]

Blooms of various types of seaweeds have been reported worldwide, with recent expansions in surface waters. While most of the expansions have been attributed to eutrophication due mainly to human activities, any potential role of climate change is unclear. Here we show that, in the East China Sea and Yellow Sea, increased biomass of Sargassum horneri (S. horneri, brown seaweed) from 2000 to 2021 appears to be caused primarily by ocean warming, as S. horneri prefers a certain temperature range to grow. In contrast, while increases of Ulva prolifera (U. prolifera, green seaweed) in the same regions might also be related to ocean warming, during the same period, human activities such as coastal aquaculture or seaweed mitigation may muddle such effects. With the projected ocean warming in the next decades, we hypothesize that S. horneri blooms may occur earlier during the year and may continue to expand in the future. Plain Language Summary: Seaweed macroalgae blooms have been reported around the world in the last two decades, yet the exact reasons are often unclear. This paper attempts to solve this puzzle for the Sargassum and Ulva seaweeds in the East China Sea and Yellow Sea using long‐term observations and laboratory‐based seaweed physiology measurements. The paper shows not only how seaweeds have expanded in the two marginal seas in the past four decades, but also how a warming ocean (due to climate variability) and nutrient enrichment (due mainly to human activities) controlled such expansions. Among 63 large marine ecosystems (LMEs) in the world, the East China Sea (where seaweeds expanded) is one of the three LMEs that experienced "super‐fast" warming. Given the IPCC‐projected seawater temperature rise of 1.6°C by 2050, will these seaweeds continue to expand? Key Points: Multi‐sensor satellite data show significant and near‐synchronized expansions of Sargassum horneri and Ulva prolifera in the past 38 yearsOcean warming appears to be a main factor behind the recent expansions of S. horneri because of its physiological requirementOcean warming may also play a role in U. prolifera expansions, but the effect appears confounded by human mitigation efforts [ABSTRACT FROM AUTHOR]

Cirrus clouds provide a significant radiative forcing on the Earth's climate system. This paper looks at the connection in space and time between monthly mean lightning activity observed from the Lightning Imaging Sensor on board the International Space Station, and the global monthly mean cirrus cloud cover obtained from the MERRA‐2 reanalysis product. The correlation coefficient between the global monthly mean cloud optical thickness of the cirrus clouds (clouds at altitudes above the 400 hPa pressure levels) with the monthly mean lightning flash counts is 0.84, implying that monthly mean lightning can explain 70% of monthly variability of the global high cloud optical thickness. In addition, lightning amount explains nearly 60% of the monthly mean global area coverage of cirrus clouds. Given these statistically significant connections between lightning and cirrus clouds, we propose using global lightning data as an additional tool for monitoring monthly variability of cirrus clouds. Plain Language Summary: Cirrus clouds are one of the most important components maintaining the Earth's radiation budget. They reflect shortwave radiation from the Sun while absorbing the longwave radiation from the Earth. The net cloud radiative forcing for cirrus clouds results a warming of the climate. More/less cirrus clouds result in more/less warming of the planet. The moisture for the formation of cirrus clouds in the upper atmosphere is transported there in large part via deep convective storms, many associated with lightning activity and hence defined as thunderstorms. An increasing in cirrus clouds in a warmer atmosphere will amplify the initial warming. We explored in this study the relationship between global cirrus cloud coverage and global lightning activity. The results of the research show that 60%–70% of the monthly variability in global cirrus clouds can be explained by mean global lightning activity. Key Points: Cirrus clouds are one of the essential components in the atmosphere, with many important feedbacks on the radiation balance of EarthMonthly mean lightning can explain 70% of the monthly variability of the global high cloud optical thicknessLightning explains nearly 60% of the monthly mean global area coverage of cirrus clouds [ABSTRACT FROM AUTHOR]

Since the early 1990s the Pacific Walker circulation shows a multi‐decadal strengthening, which contradicts future model projections. Whether this trend, evident in many climate indices especially before the 2015 El Niño, reflects the coupled ocean‐atmosphere response to global warming or the negative phase of the Pacific Decadal Oscillation (PDO) remains debated. Here we show that sea surface temperature trends during 1980–2020 are dominated by three signals: a spatially uniform warming trend, a negative PDO pattern, and a Northern Hemisphere‐Indo‐West Pacific warming pattern. The latter pattern, which closely resembles the transient ocean thermostat‐like response to global warming emerging in a subset of CMIP6 models, shows cooling in the central‐eastern equatorial Pacific but warming in the western Pacific and tropical Indian Ocean. Together with the PDO, this pattern drives the Walker circulation strengthening in the equatorial band. Historical simulations appear to underestimate this pattern, contributing to the models' inability to replicate the Walker cell strengthening. Plain Language Summary: This paper investigates the observed changes in the tropical Pacific during the satellite era, including the recent decadal strengthening of the atmospheric zonal circulation—the Walker cell. We aim to understand the extent to which these changes represent a forced response to rising CO2 concentrations versus natural variability. We apply an approach in which we decompose the observed sea surface temperature trends into three components—a pattern associated with the Pacific Decadal Oscillation, which is part of natural variability, a uniform warming pattern, and a residual pattern. This residual pattern shows a remarkable resemblance to a forced ocean thermostat‐like transient response generated in some of the climate models, characterized by equatorial Pacific (EP) cooling, and a broad warming of the Northern Hemisphere, and the Indian Ocean and West Pacific. These results challenge studies arguing that the recent strengthening of the Pacific Walker cell can be explained simply by multi‐decadal natural variability in the tropics. Furthermore, the inability of climate models at large to fully capture this forced pattern with historical forcing puts into focus the reliability of future projections of climate change in the tropical Pacific, specifically the timing of emergence of the eastern EP warming. Key Points: A multi‐decadal strengthening of the Pacific Walker cell is observed in a wide range of indices, especially after 1990A Northern Hemisphere ‐ Indo West Pacific warming sea surface temperature pattern, which differs from the Pacific Decadal Oscillation, is evident since 1980This pattern resembles a forced response to abrupt CO2 forcing, emerging in a subset of climate models, and contributes to the Walker circulation strenthening [ABSTRACT FROM AUTHOR]

The magnitude and distribution of the ocean's biological pump (the downward flux of organic carbon (OC) from the ocean surface) influences the pCO2 of the atmosphere and the O2 content of the deep sea, but has not been well quantified. We determine this flux in the ocean's five subtropical gyres using upper‐ocean oxygen mass balance and measurements of T, S, and pO2 by autonomous profiling floats. Our results suggest that the biological OC pump is not globally uniform among the subtropical gyres: values in the North Pacific and Atlantic indicate distinct autotrophy (1–2 mol C m−2 yr−1) while near zero values in the S. Indian Ocean suggest the possibility of net heterotrophy. There is a correlation between the surface water iron/nitrate ratio and the magnitude of the biological pump suggesting an important role for nitrogen fixation in controlling the global distribution. Plain Language Summary: The ocean's biological pump is the most important natural flux controlling ocean and atmosphere carbon concentrations on decadal to millennial time scales, with a value that is fortuitously about the same as the present anthropogenic flux of carbon to the atmosphere. Understanding this flux is key to determining the marine carbon cycle feedback to global warming, but presently even the sign of this flux is debated in some subtropical ocean regions. This paper demonstrates how it is possible to determine the global value of the biological pump by remote measurements on autonomous profiling floats. Our findings suggest that the ocean's biological pump is very different in the subtropical northern and southern hemispheres probably because of the geographic variability of the flux of iron to the surface ocean. Key Points: The geographic distribution of the downward flux of biological organic carbon from the upper ocean (the ocean's biological pump) is uncertain and difficult to determine from observationsT, S, and pO2 measurements from 21 profiling floats in the world's subtropical oceans are interpreted in terms of the net biological oxygen production in the upper oceanThe measured net biological oxygen flux is higher in the northern hemisphere subtropics than in the southern subtropics and correlated with surface‐water iron concentration [ABSTRACT FROM AUTHOR]

Under the context of global warming, we identified a significant increase in lightning activity in the last two decades over the Tibetan Plateau (TP), the highest plateau on earth, based on two data sets. The largest rise of lightning activity was found over the region with high lightning density represented by the eastern TP at a rate of 0.072 ± 0.069 fl km−2 yr−1 during 1996–2013 from Optical Transient Detector/Lightning Imaging Sensor. World Wide Lightning Location Network data also showed a remarkable increase in lightning strokes during 2010–2019 in the maximum lightning density region, while the change was insignificant in the low lightning density region. Further investigations revealed that most of the TP region experienced a significant increase in thunderstorm frequency, which was responsible for the increase in lightning activity, rather than an increase in thunderstorm intensity. Increased lightning activity implies a potential risk to human beings and the fragile ecosystem over the TP in a warmer climate. Plain Language Summary: Lightning is a natural source of nitrogen oxides and wildfires, and thus has important effects on atmospheric chemistry and ecosystem. Lightning is also a serious threat to human life and property. Using satellite‐based and ground‐based data, the trend of lightning activity over the Tibetan Plateau (TP) in the past two decades has been investigated in this paper. In the global warming context, TP experienced an increase in lightning activity. The lightning increase was significant in the high lightning density region, such as the central and eastern TP, and insignificant in the lower lightning density region, such as the western TP and the Brahmaputra Valley. The thunderstorm frequency also experienced an increase over most parts of the TP, which caused the rising trend in lightning activity. However, the thunderstorm intensity shows weak and insignificant changes. Since the TP is getting warmer much faster than that observed over the globe, the increased lightning activity over the TP may exert enhanced potential threat to human beings and impacts on the fragile ecosystem over the Plateau. Key Points: Lightning activity over the Tibetan Plateau increased significantly in the past two decades based on the Optical Transient Detector/Lightning Imaging Sensor and World Wide Lightning Location Network datasetsLightning activity in the high‐flash‐density region increased faster than that in the low‐flash‐density regionThe apparent rise in lightning activity is due to increase in thunderstorm rate rather than change in thunderstorm intensity [ABSTRACT FROM AUTHOR]

In this paper, we investigate whether the relationship between the El Niño‐Southern Oscillation and tropical cyclone (TC) rain rate over the western North Pacific (WNP) changes between the global warming slowdown (2001–2012) and resumption (2013–2020) periods. Using high‐resolution satellite rainfall data, we show that the average TC rain rate increases by 9% but decreases by 14% during the recent El Niño and La Niña years (since 2013), respectively. During the El Niño years, the increase is related to higher TC track density at lower latitudes, where more water vapor and stronger convergence are present. On the other hand, the decrease in TC rain rate during the recent La Niña years is mainly related to an increase in track density at higher latitudes and a decrease in TC intensity. These changes in TC track density and intensity are both associated with the strengthening of the subtropical high since 2013. Plain Language Summary: The impacts on various weather phenomena associated with the global surface warming slowdown (or "hiatus": 1998–2012) and its subsequent resumption since 2013 have been extensively investigated. An unresolved issue is whether the tropical cyclone (TC) rain rate over the western North Pacific (WNP) basin has also changed, especially during the El Niño (or La Niña) years. Considering the availability of high‐resolution satellite rainfall data, we mainly focus on the period of 2001–2020 (slowdown period: 2001–2012; resumption period: 2013–2020). Our results show that, consistent with the increase in atmospheric water vapor after the global warming resumption, the average TC rain rate has increased by ∼2%. However, TC rain rate increases in El Niño years but decreases in La Niña years during the resumption period. This opposite change in TC rain rate is mainly influenced by the strengthened WNP subtropical high. Our findings suggest that it is necessary to properly consider the influence of the subtropical high on the projections in TC migration, intensity, and rain rate under global warming. Key Points: Compared with El Niño‐Southern Oscillation (ENSO) years in the global warming slowdown period, tropical cyclone (TC) rain rate increases and decreases in recent El Niño and La Niña yearsThis opposite change in TC rain rate in recent ENSO years is mainly affected by the changes in TC track density and TC intensityChanges in TC track density and intensity are both influenced by the extremely strengthened subtropical high since 2013 [ABSTRACT FROM AUTHOR]

Using four reanalysis data sets and ground‐based observations, this paper uncovers that on average, 30% of the time, Northern Hemisphere snow cover experiences unfrozen bottom soil. It is demonstrated that the probability of occurrence of unfrozen soils is correlated with the snow types and is maximum over the ephemeral followed by the maritime and prairie snow. The results based on reanalysis data unveil that the seasonal evolution of the unfrozen soil areas is not synchronous with the snow cover extent and exhibits sub‐annual bi‐modality with two annual maxima in April and October. Interannual trend analyses indicate that shrinkage of spring snow in the past few decades has been accompanied by an increase in the proportion of unfrozen bottom soils, more significantly over polar climate regimes dominated by the tundra and taiga snow. The findings imply that the snowpack basal melting could have increased due to global warming. Plain Language Summary: Unfrozen bottom soils below snow layers play an important role in the persistence and stability of snowpack, yet less knowledge is known about its spatial variability and seasonal evolution on a global scale. This study uncovers that, on average, around 30% of annual Northern Hemisphere's snow cover extent is over unfrozen soils with a spatial variability that is highly correlated with snow types. Specifically, unfrozen soils appear more frequently below the ephemeral followed by the maritime and prairie snow. In addition, it is demonstrated that the unfrozen soil areas exhibit different seasonal evolution from snow cover extent with two annual peaks in April and October. The results show that the areas of unfrozen soils are expanding in spring as the snow cover extent is shrinking. Key Points: On average 30% of the year the soil below global snowpack is unfrozenSeasonal evolution of the areas of unfrozen soil below snowpack is not synchronous with snow cover extentBasal snowpack melting could have increased in a warming climate [ABSTRACT FROM AUTHOR]

Orbital Earth Radiation Budget measurement comparisons to models, are critical for climate prediction confidence. Satellite systems must reduce calibration drifts for this purpose. NASA Clouds and the Earth's Radiant Energy System (CERES) measures Earth albedo reductions that if correct, would increase solar forcing and suggest greater sunlight absorption is driving much of recent temperature increases. Such results are presented, alongside those from the Moon and Earth Radiation Budget Experiment (MERBE). MERBE uses constant lunar reflectivity for tracking and compensation of instrument telescope degradation, undetectable by CERES. MERBE finds Earth albedo constant compared to that of the Moon, because Arctic solar warming effects are balanced by solar cooling elsewhere, likely due to negative feedbacks. Contrary to NASA, this shows the Sun is not increasing warming and that CERES results are not as stable as claimed and assumed. Furthermore, MERBE can actually resolve Cloud Radiative Forcing (CRF) signals from the existing record, rather than in decades with official observations. Plain Language Summary: In contrast to NASA Clouds and the Earth's Radiant Energy System results, this paper shows that the Earth reflectivity has not changed since the year 2000, by comparing the sunlight bouncing off it to that from the Moon. Disagreeing with NASA, this provides physical evidence that global warming is not being increased by the Sun. It also immediately brings data to the standard requested by the climate community for cloud forcing/feedback signal detection. The Moon and Earth Radiation Budget Experiment data is being staged for free on the FAIR compliant website Pangaea for climate scientists. Key Points: The Sun is not causing climate change and Cloud Radiative Forcing (CRF) signals can now be detected immediatelyArctic heating is being balanced by reflectivity increases elsewhereThe calibration accuracy of data is sufficient to detect uncertain cloud feedback signals immediately, rather than in decades [ABSTRACT FROM AUTHOR]