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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]

Kirschbaum (Mitig Adapt Strat Glob Change 11:1151-1164, 2006) explores the climatic impact over time of temporarily sequestering carbon from the atmosphere. He concludes that temporary storage of carbon in the terrestrial biosphere ''achieves effectively no climate-change mitigation''. His strongly worded statement begs for a response. This paper argues that Kirschbaum's conclusion is an artifact of the specific perspective of his analysis and his choice of a definition for climate-change impact. Even temporary sinks put us on a lower path for climate change, a path that will not otherwise be accessible. For carbon sinks in the terrestrial biosphere, we argue that sooner is better and longer is better, but even known temporary sinks have value. [ABSTRACT FROM AUTHOR]

The organic carbon (OC) pool accumulated in Arctic permafrost (perennially frozen ground) equals the carbon stored in the recent atmosphere. To give an idea of how Yedoma region permafrost could respond under future climatic warming, we conducted a study to quantify the organic matter quality for future decomposition of late Pleistocene (Yedoma) and Holocene (thermokarst) deposits on the Buor Khaya Peninsula, northeast Siberia. The objective of this study was to develop a stratigraphic classified organic matter quality characterization. For this purpose the degree of organic matter decomposition was estimated by using a multiproxy approach. We applied sedimentological (grain-size analyses, bulk density, ice content) and geochemical parameters (total OC, stable carbon isotopes (δ13C), carbon : nitrogen (C/N) ratios) as well as lipid biomarkers (n-alkanes, n-fatty acids, hopanes, triterpenoids, and biomarker proxies/indices: average chain length, carbon preference index (CPI), and higher plant fatty acid index (HPFA)). Our results show that the Yedoma and thermokarst organic matter qualities exhibit no obvious degradation -- depth trend. The C/N, δ13C, and hop-17(21)-ene values and the HPFA index show a better quality of the organic matter stored in thermokarst deposits compared to Yedoma deposits, but the CPI points in the other direction. As the ranges of the proxies mostly overlap, we interpret this as to indicate similar quality for both kind of deposits with perhaps slightly better thermokarst organic matter quality. Supported by principal component analyses, the sediment parameters and quality proxies of Yedoma and thermokarst deposits could not be clearly separated from each other. This lack of clear quality differences revealed that the organic matter vulnerability is heterogeneous, independent from radiocarbon age and depends on different decomposition trajectories and the previous decomposition and preservation history. Elucidating this was one of the major novelties of our multiproxy study. With the addition of biomarker data, it was possible to show that permafrost organic matter degradation likely occurs via a combination of (uncompleted) degradation cycles or a cascade of degradation steps rather than as a linear function of age or sediment facies. We conclude that the amount of organic matter in the studied sediments is high for mineral soils and of good quality and therefore susceptible to future decomposition. The missing depth trends reveal that permafrost acts like a giant freezer, preserving the constant quality of ancient organic matter independently from its age. When unde-composed Yedoma organic matter is mobilized via thermokarst processes, the fate of this carbon depends largely on the environmental conditions; the carbon could be preserved in an undecomposed state till refreezing occurs. If recent input has occurred, thermokarst organic matter could be of a better quality than that found in Yedoma deposits. [ABSTRACT FROM AUTHOR]

A reference or "no‐feedback" radiative response to warming is fundamental to understanding how much global warming will occur for a given change in greenhouse gases or solar radiation incident on the Earth. The simplest estimate of this radiative response is given by the Stefan‐Boltzmann law as −4σTe‾3≈−3.8 ${-}4\sigma {\overline{{T}_{e}}}^{3}\approx -3.8$ W m−2 K−1 for Earth's present climate, where Te‾ $\overline{{T}_{e}}$ is a global effective emission temperature. The comparable radiative response in climate models, widely called the "Planck feedback," averages −3.3 W m−2 K−1. This difference of 0.5 W m−2 K−1 is large compared to the uncertainty in the net climate feedback, yet it has not been studied carefully. We use radiative transfer models to analyze these two radiative feedbacks to warming, and find that the difference arises primarily from the lack of stratospheric warming assumed in calculations of the Planck feedback (traditionally justified by differing constraints on and time scales of stratospheric adjustment relative to surface and tropospheric warming). The Planck feedback is thus masked for wavelengths with non‐negligible stratospheric opacity, and this effect implicitly acts to amplify warming in current feedback analysis of climate change. Other differences between Planck and Stefan‐Boltzmann feedbacks arise from temperature‐dependent gas opacities, and several artifacts of nonlinear averaging across wavelengths, heights, and different locations; these effects partly cancel but as a whole slightly destabilize the Planck feedback. Our results point to an important role played by stratospheric opacity in Earth's climate sensitivity, and clarify a long‐overlooked but notable gap in our understanding of Earth's reference radiative response to warming. Plain Language Summary: Earth's climate is stable because a warmer planet loses more energy to space, at infrared wavelengths invisible to the naked eye. The rate of change of this energy loss as the planet warms provides an estimate how Earth's energy balance responds to warming, which is simple enough to write on a small piece of paper. When scientists investigate the warming predicted by climate models, they often start from a similar but not identical calculation of how Earth's energy balance responds to warming. This calculation, based on model output, is about 15% less stabilizing than the simple pencil‐and‐paper estimate. In this paper, we explore the causes of this 15% difference between the pencil‐and‐paper estimate and the calculations using climate models. We show that the difference is primarily caused by the lack of assumed warming in climate models high in Earth's atmosphere, where temperatures are not closely linked to surface warming. This lack of warming acts as a hidden destabilizing feedback in current analysis of climate models. Key Points: Earth's reference radiative response, or "Planck feedback," is ∼0.5 W m−2 K−1 less stabilizing than a Stefan‐Boltzmann estimateWe find this deviation is mostly due to the assumed lack of stratospheric warming in calculations of the Planck feedbackThe lack of stratospheric warming serves as an implicit positive feedback in analysis of climate model warming [ABSTRACT FROM AUTHOR]

Even though climate change involves much more than warming, it is the name given to a set of physical phenomena. It is a long-term change in weather patterns that characterises different regions of the world. The warming effect in the earth's atmosphere has dramatically increased through the influence of some heat-taping gases emitted by various human activities, especially fossil fuel burning. The more the input of such gases, the more will be the warming effect in the coming times. Global climate change is already visible in various parts of the larger ecosystems like forests, fisheries, biodiversity, and agriculture; however, it is now also influencing the supply of freshwater, human health, and well-being. This paper reviews climate change drivers, its global scenario, major global events, and assessing climate change impacts. The most daunting problem of economic and ecological risks, along with the threats to humanity, is also discussed. The paper further reviews the species' vulnerability to climate change and the heat waves and human migration vis-à-vis climate change. Climate change politics and coverage of climate change episodes in mass media is the special focus of this review that concludes with a few mitigation measures. [ABSTRACT FROM AUTHOR]

Abstract—The paper presents the results of a study of spatiotemporal variability of the characteristics of the wind field in the free atmosphere of the Northern Hemisphere in the SEVIRI radiometer field of view of European geostationary meteorological satellites of the second generation Meteosat 8–Meteosat 11 in the time interval 2007–2021. It is noted that the maximum wind speeds, as well as the maximum average monthly and seasonal anomalies of the wind speed modulus, are observed over the Atlantic. A feature of the temporal variability of the area-averaged wind speed modulus is revealed, which consists in a change in the sign of the trend at the turn of 2015–2017 from positive to negative. At the same time, positive linear trends in the time intervals from 2007 to the points of a change in the sign of the trend over the Atlantic, the entire region under consideration and Eurasia, including the European territory of the Russian Federation, are significantly different from zero with a probability of more than 95% and the negative trend is significant only over the Atlantic. A high correlation was noted in the area of seasonal wind speed variations with the area of Arctic sea ice and temperature characteristics of the troposphere at levels of 500 and 200 hPa. Based on the analysis of the relationship between wind speed variability and the main climatic characteristics and large-scale atmospheric processes, a scheme is proposed for the effect of the accelerating reduction in the area of Arctic sea ice associated with global warming on wind speed in the free atmosphere. [ABSTRACT FROM AUTHOR]

The Nordic Centre of Excellence CRAICC (Cryosphere–Atmosphere Interactions in a Changing Arctic Climate), funded by NordForsk in the years 2011–2016, is the largest joint Nordic research and innovation initiative to date, aiming to strengthen research and innovation regarding climate change issues in the Nordic region. CRAICC gathered more than 100 scientists from all Nordic countries in a virtual centre with the objectives of identifying and quantifying the major processes controlling Arctic warming and related feedback mechanisms, outlining strategies to mitigate Arctic warming, and developing Nordic Earth system modelling with a focus on short-lived climate forcers (SLCFs), including natural and anthropogenic aerosols. The outcome of CRAICC is reflected in more than 150 peer-reviewed scientific publications, most of which are in the CRAICC special issue of the journal Atmospheric Chemistry and Physics. This paper presents an overview of the main scientific topics investigated in the centre and provides the reader with a state-of-the-art comprehensive summary of what has been achieved in CRAICC with links to the particular publications for further detail. Faced with a vast amount of scientific discovery, we do not claim to completely summarize the results from CRAICC within this paper, but rather concentrate here on the main results which are related to feedback loops in climate change–cryosphere interactions that affect Arctic amplification. [ABSTRACT FROM AUTHOR]

The Amazon River, its huge basin, and the changes in biological processes that are rapidly occurring in this region are unquestionably of global significance. Hence, Global Change Biology is delighted to host a special thematic issue devoted to the Large-scale Biosphere-Atmosphere Experiment in Amazônia (LBA), which is a multinational, interdisciplinary research program led by Brazil. The goal of LBA is no less modest than its subject: to understand how Amazônia functions as a regional entity in the Earth system and how these functions are changing as a result of ongoing changes in land use. This compilation of 26 papers resulting from LBA-related research covers a broad range of topics: forest stocks of carbon (C) and nitrogen (N); fluxes of greenhouse gases and volatile organic compounds from vegetation, soils and wetlands; mapping and modeling land-use change, fire risk, and soil properties; measuring changes caused by logging, pasturing and cultivating; and new research approaches in meteorology to estimate nocturnal fluxes of C from forests and pastures. Some important new synthesis can be derived from these and other studies. The aboveground biomass of intact Amazonian forests appears to be a sink for atmospheric carbon dioxide (CO2), while the wetlands and soils are a net source of atmospheric methane (CH4) and nitrous oxide (N2O), respectively. Land-use change has, so far, had only a minor effect on basin-wide emissions of CH4 and N2O, but the net effect of deforestation and reforestation appears to be a significant net release of CO2 to the atmosphere. The sum of the 100-year global warming potentials (GWP) of these annual sources and sinks of CH4, N2O, and CO2 indicate that the Amazonian forest-river system currently may be nearly balanced in terms of the net GWP of these biogenic atmospheric gases. Of course, large uncertainties remain for these estimates, but the papers published here demonstrate tremendous progress, and also large remaining hurdles, in narrowing these uncertainties in our understanding of how Amazônia functions as a regional entity in the Earth system. [ABSTRACT FROM AUTHOR]

The vertical velocity distribution in the atmosphere is asymmetric with stronger upward than downward motion. This asymmetry is important for the distribution of precipitation and its extremes and for an effective static stability that has been used to represent the effects of latent heating on extratropical eddies. Idealized GCM simulations show that the asymmetry increases as the climate warms, but current moist dynamical theories based around small-amplitude modes greatly overestimate the increase in asymmetry with warming found in the simulations. Here, we first analyze the changes in asymmetry with warming using numerical inversions of a moist quasigeostrophic omega equation applied to output from the idealized GCM. The inversions show that increases in the asymmetry with warming in the GCM simulations are primarily related to decreases in moist static stability on the left-hand side of the moist omega equation, whereas the dynamical forcing on the right-hand side of the omega equation is unskewed and contributes little to the asymmetry of the vertical velocity distribution. By contrast, increases in asymmetry with warming for small-amplitude modes are related to changes in both moist static stability and dynamical forcing leading to enhanced asymmetry in warm climates. We distill these insights into a toy model of the moist omega equation that is solved for a given moist static stability and wavenumber of the dynamical forcing. In comparison to modal theory, the toy model better reproduces the slow increase of the asymmetry with climate warming in the idealized GCM simulations and over the seasonal cycle from winter to summer in reanalysis. Significance Statement: Upward velocities are stronger than downward velocities in the atmosphere, and this asymmetry is important for the distribution of precipitation because precipitation is linked to upward motion. An important and open question is what sets this asymmetry and how much it increases as the climate warms. Past work has shown that current theories greatly overestimate the increase in asymmetry with warming in idealized simulations. In this work, we develop a more complete theory and show that it is able to better reproduce the slow increase of the asymmetry with warming that is found over the seasonal cycle from winter to summer and in idealized simulations of warming climates. [ABSTRACT FROM AUTHOR]

Recent observations and model studies of the earth’s radiative energy balance have focused attention on the earth’s top of atmosphere (TOA) energy balance. This is the balance between the shortwave energy absorbed by the earth, which is represented by a spatially and temporally averaged absorbed flux , and the emitted longwave energy, which is represented by the corresponding averaged emitted flux . The TOA average net flux FN is defined as the difference between the two over the averaged area and time, which may be a local, regional, or global average. A global nonzero net flux represents a measure of imbalance between the energy being absorbed and emitted by the earth for the time interval in question. It is of interest to ask what the natural variability of the net flux might be and whether, during times of climate change, signals of important climate change processes might be detected against this natural background variation; examples of these signals include evidence of ocean heat storage, the effects of El Niño, and the radiative effects of volcanic eruptions. In this paper, the authors review the significance of the net flux, survey the observational evidence from a range of satellite instruments over several decades, and analyze some of the most recent observations from the Clouds and the Earth’s Radiant Energy System (CERES) program to determine what signals and what natural variability might be expected in the TOA net flux. Based on this analysis, the use of broadband radiation measurements for global climate change studies can be assessed. [ABSTRACT FROM AUTHOR]

Abstract: Scientific findings from the last decades have clearly highlighted the need for a more comprehensive approach to atmospheric change processes. In fact, observation of atmospheric composition variables has been an important activity of atmospheric research that has developed instrumental tools (advanced analytical techniques) and platforms (instrumented passenger aircrafts, ground-based in situ and remote sensing stations, earth observation satellite instruments) providing essential information on the composition of the atmosphere. The variability of the atmospheric system and the extreme complexity of the atmospheric cycles for short-lived gaseous and aerosol species have led to the development of complex models to interpret observations, test our theoretical understanding of atmospheric chemistry and predict future atmospheric composition. The validation of numerical models requires accurate information concerning the variability of atmospheric composition for targeted species via comparison with observations and measurements. In this paper, we provide an overview of recent advances in instrumentation and methodologies for measuring atmospheric composition changes from space, aircraft and the surface as well as recent improvements in laboratory techniques that permitted scientific advance in the field of atmospheric chemistry. Emphasis is given to the most promising and innovative technologies that will become operational in the near future to improve knowledge of atmospheric composition. Our current observation capacity, however, is not satisfactory to understand and predict future atmospheric composition changes, in relation to predicted climate warming. Based on the limitation of the current European observing system, we address the major gaps in a second part of the paper to explain why further developments in current observation strategies are still needed to strengthen and optimise an observing system not only capable of responding to the requirements of atmospheric services but also to newly open scientific questions. [Copyright &y& Elsevier]

This paper examines variations of the surface air temperature (SAT) over China and the globe in the twentieth century simulated by 19 coupled climate models driven by historical natural and anthropogenic forcings. Most models perform well in simulating both the global and the Northern Hemispheric mean SAT evolutions of the twentieth century. The inclusion of natural forcings improves the simulation, in particular for the first half of the century. The reproducibility of the SAT averaged over China is lower than that of the global and hemispheric averages, but it is still acceptable. The contribution of natural forcings to the SAT over China in the first half of the century is not as robust as that to the global and hemispheric averages. No model could successfully produce the reconstructed warming over China in the 1920s. The prescribed natural and anthropogenic forcings in the coupled climate models mainly produce the warming trends and the decadal- to interdecadal-scale SAT variations with poor performances at shorter time scales. The prominent warming trend in the last half of the century over China and its acceleration in recent decades are weakly simulated. There are discrepancies between the simulated and observed regional features of the SAT trend over China. Few models could produce the summertime cooling over the middle part of eastern China (27°–36°N), while two models acceptably produce the meridional gradients of the wintertime warming trends, with north China experiencing larger warming. Limitations of the current state-of-the-art coupled climate models in simulating spatial patterns of the twentieth-century SAT over China cast a shadow upon their capability toward projecting credible geographical distributions of future climate change through Intergovernmental Panel on Climate Change (IPCC) scenario simulations. [ABSTRACT FROM AUTHOR]

This paper develops two-period analytical and numerical models to study the question: given a stock of greenhouse gases that poses a risk of future damages of unknown magnitude, and the possibility of learning about damages, how do sunk abatement capital and a nondegradable stock of greenhouse gases affect optimal first-period investment? We show that both affect investment, the former negatively and the latter positively. Additionally, endogenous risk — the risk of damages dependent on the stock of gases — results in an increase in optimal investment for any level of capital 'sunkness' or greenhouse gas degradability. Quantitatively, the effect of sunk capital is stronger than the effect of greenhouse gas irreversibility or that of endogenous risk. [ABSTRACT FROM AUTHOR]

Water vapor in the Arctic can be attributed to local evaporation and transport from mid‐latitudes. Here we investigate the response of Arctic water vapor to declining sea ice in a climate model, using an idealized warming scenario in which the Arctic becomes ice free year‐round. We find distinct monthly patterns in water vapor change with warming, with a strong influence of sea ice loss on changes to evaporation, except in summer when transports dominate. Before the Arctic becomes ice‐free, total column water increases at a rate slower than that indicated by the Clausius‐Clapeyron relationship; once ice‐free, total column water increases at a rate equal to Clausius‐Clapeyron. The exception is summer when the increase is initially faster then becomes slower when ice‐free. The boundary layer structure changes, under global warming, from stratified to well mixed in all seasons except summer, which remains largely unchanged throughout the ice‐free transition. Plain Language Summary: Surface evaporation from the Arctic Ocean is limited by the presence of sea ice, which creates a natural barrier between the ocean and atmosphere above. We show the loss of Arctic sea ice, in a climate model affects atmospheric water vapor and find that this varies throughout the year. The greatest increase in atmospheric water vapor is in winter, during the Arctic night, whilst there is very little change in summer. There are two reasons why sea ice loss does not impact water vapor in the summer: first, the summer air temperature barely changes between ice‐covered and ice‐free, whereas in winter the loss of ice cover can increase air temperatures by at least 20°C; second the summer Arctic water budget is dominated by transport of water vapor from midlatitudes rather than local evaporation. We also show changes in the vertical structure of the near‐surface atmosphere and cloud types, with a transition from stable to turbulent regimes in autumn and winter. Key Points: As Arctic sea ice declines with increased warming, Arctic evaporation and water vapor increase most in autumn and winterArctic sea ice limits water vapor availability, but once the Arctic is ice‐free, it increases with the Clausius‐Clapeyron relationshipArctic boundary layer changes from stably stratified to well mixed, during winter and autumn, but less change in spring and summer [ABSTRACT FROM AUTHOR]

The Tibetan Plateau is a sensitive area of global climate change, where few conventional observations exist. Satellite AMSU-A microwave temperature sounding observations of brightness temperature (TB) are located in the absorption band of oxygen, which is well mixed in the atmosphere, and have microwave frequencies varying from 50.3 to 57.6 GHz. Therefore, AMSU-A TB observations at different sounding channels reflect atmospheric temperatures at different altitudes. In this study, AMSU-A TB observations during 1998-2020 from five polar-orbiting environmental meteorological satellites (POESs) are employed to investigate the interdecadal warming/cooling trends over the Tibetan Plateau. A limb correction is first applied to all AMSU-A channels before using TB observations at all fields of view for examining geographic distributions and differences of global warming/cooling trends. It is found that interdecadal trends of uppertropospheric warming and stratospheric cooling are stronger over the Qinghai Tibetan Plateau than its eastern plain areas. An interdecadal variation of the annual cycle over the Tibetan Plateau is an important factor for the enhanced tropospheric warming trend. We also applied a different approach of significance testing that is based on counting signs of local trends (sign test) and confirmed that the detected significant local trends were not a result of chance. In addition, high-frequency noise in TB observations with periods smaller than annual and semiannual oscillations do not affect the climate trends of TB very much, but significantly reduced the uncertainty of the TB trends over the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The article presents a paper that deals with a review of literature on global change and its implications for plants in general and oaks in particular. The study includes assessments of known atmospheric changes, probable effects on climate, and possible effects on California oaks. The authors summarize projected human alterations to the gaseous composition of the atmosphere. They also discuss the way their research, advocacy, and field work accumulate evidence of human-driven global climate change.

Coastal environments such as the Chesapeake Bay have long been impacted by eutrophication stressors resulting from human activities, and these impacts are now being compounded by global warming trends. However, there are few studies documenting long‐term estuarine temperature change and the relative contributions of rivers, the atmosphere, and the ocean. In this study, Chesapeake Bay warming, since 1985, is quantified using a combination of cruise observations and model outputs, and the relative contributions to that warming are estimated via numerical sensitivity experiments with a watershed–estuarine modeling system. Throughout the Bay's main stem, similar warming rates are found at the surface and bottom between the late 1980s and late 2010s (0.02 ± 0.02°C/year, mean ± 1 standard error), with elevated summer rates (0.04 ± 0.01°C/year) and lower rates of winter warming (0.01 ± 0.01°C/year). Most (~85%) of this estuarine warming is driven by atmospheric effects. The secondary influence of ocean warming increases with proximity to the Bay mouth, where it accounts for more than half of summer warming in bottom waters. Sea level rise has slightly reduced summer warming, and the influence of riverine warming has been limited to the heads of tidal tributaries. Future rates of warming in Chesapeake Bay will depend not only on global atmospheric trends, but also on regional circulation patterns in mid‐Atlantic waters, which are currently warming faster than the atmosphere. [ABSTRACT FROM AUTHOR]

The increase in CO2 concentration in the atmosphere has prompted the research community to find solutions for this environmental problem, which causes climate change and global warming. CO2 removal through the use of negative emissions technologies could lead to global emission levels becoming net negative towards the end of this century. Among these negative emissions technologies, direct air capture (DAC), in which CO2 is captured directly from the atmosphere, could play an important role. The captured CO2 can be removed in the long term and through its storage can be used for chemical processes, allowing closed carbon cycles in the short term. For DAC, different technologies have been suggested in the literature, and an overview of these is proposed in this work. Absorption and adsorption are the most studied and mature technologies, but others are also under investigation. An analysis of the main key performance indicators is also presented here and it is suggested that more efforts should be made to develop DAC at a large scale by reducing costs and improving efficiency. An additional discussion, addressing the social concern, is indicated as well. [ABSTRACT FROM AUTHOR]

Different mechanisms of glacial-interglacial cycles and of the current global warming are considered and discussed: Milankovitch astronomical cycles, self-organization processes in Earth's geospheres, variation of Solar activity, increased concentration of greenhouse gases. It is pointed out that the current global warming cycle has started, according to data presented in J.R. Petit, at al., (1999, 2001), thousands of years before the first machines, even very primitive, were made by people. It is pointed out also that release of CH4 gas into atmosphere is an irreversible, uncontrolled process triggered by global warming. It is hypothesized that the planetary overheated atmosphere is in a state similar to "boiling". This explains the increased number and severity of different natural catastrophes -- hurricanes, floods, droughts. It is also shown that in each cycle the cooling down of atmosphere follows the Newton's Law of cooling suggesting a clear conceptual view of the Physics of this process. Finally, a mechanism explaining sharp the rise of temperature of atmosphere at the end of each glacial period is suggested and evaluated. [ABSTRACT FROM AUTHOR]

A new publication by NOAA (US National Oceanic and Atmospheric Administration) claims to have removed the previously evident discrepancies between mean global temperature anomalies measured on the surface and those measured in the lower troposphere. It claims that a combination of attention to inaccuracies and the use of linear regression equations on selected climate sequences have removed these discrepancies. This paper shows that these claims are untrue. The apparent agreement of the two sets of records for the chosen sequences is dependent on the enhanced influence of volcanoes and El Niño events in the lower troposphere, compared with an additional warming factor on the surface. If a temperature sequence comparatively free from these influences, (1979 -1997) is chosen, there is no significant warming in the lower atmosphere for six of the seven records, and for the seventh, no significant warming between 1988 and 1997; whereas warming still prevails on the surface over these periods. The supposed enhanced greenhouse effect is thus currently undetectable in the lower atmosphere, where it is supposed to be most prominent, for extended periods, so the warming on the surface over these periods must have some other cause. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates whether it is possible to find a solar signature in the current Earth’s climatic warming. The attempt seems audacious as, on one hand, solar output variability on the atmosphere is far to be understood, and on the other hand, there is evidence that most of the warming observed over the last 50 years can be attributed to human activities. However, series of the annual global average temperature, from 1861 up to now are available, showing periods of warming and cooling that are statistically significant. From recent findings, it is also known that solar irradiance shows a variability and can be modeled today with a good accuracy over the last century. The idea was to compare the likelihood linear trends shown in the climatic data with those of the irradiance, during same well defined time ranges. Changes from 1861 to 1975 show an unexpected remarkable correlation, whereas the period 1976–2000 completely deviates from the previous analysis. The 1861–1975 set of data supports the suggestion of an influence of solar irradiance on global climate, which was checked as a natural forcing: the response is found to be λ =0.46°C/Wm−2, a quite reasonable value, bearing in mind the imprecision in the irradiance modeling. This analysis is also discussed in the scope of other forcings and uncertainties in the data. [Copyright &y& Elsevier]

As a result of global warming, the lengths of the four seasons, which are always taken as constant values, have experienced significant variations with rising temperature. Such changes play different roles with regard to regional climate change, with the most significant effect on drylands. To guarantee local crop yields and preserve ecosystems, identification of the changes of the four seasons in drylands is important. Our results show that, relative to humid lands, changing trends in lengths of spring, summer, and autumnwere particularly enhanced in drylands of the Northern Hemispheremidlatitudes during 1951-2020. In this period, summer length has increased by 0.51 days per year, while spring and autumn lengths have both contracted by 0.14 days per year. However, the enhanced changes in drylands did not appear in winter length. The winter has shortened by 0.23 days per year in drylands. Such changes of spring, summer, and autumn in drylands are dominated by internal variability over the entire study period, with a stronger external forcing effect on drylands than on humid lands. In drylands, the external forcing contributed to the lengths of spring, summer, and autumn by 30.1%, 42.2%, and 29.4%, respectively. The external forcing has become an increasingly important component since 1990, with the ability to dominate all seasons in drylands after 2010. Nevertheless, only 1 of the 16 models from phase 6 of the Coupled Model Intercomparison Project (CMIP6) used in this study can capture the enhanced changes in the lengths of spring, summer, and autumn in drylands. Further investigation on the local effects of changes in seasons on agriculture and ecosystem would be needed, especially for the fragile regions. [ABSTRACT FROM AUTHOR]

In a widely‐held conception, the biological carbon pump (BCP) is equal to the export of organic matter out of the euphotic zone. Using global ocean‐atmosphere model experiments we show that the change in export production is a poor measure of the biological pump's feedback to the atmosphere. The change in global true oxygen utilization (TOU), an integrative measure of the imprint of the BCP on marine oxygen, however, is in good agreement with the net change in the biogenic air‐sea flux of oxygen. Since TOU correlates very well with apparent oxygen utilization (AOU) in our experiments, we propose to measure the change of AOU from data of global float programs to monitor the feedback of the BCP to the atmosphere. For the current ocean we estimate that BCP changes effect a CO2 uptake by the ocean in the range of 0.07 to 0.14 GtC/yr. Plain Language Summary: The biological carbon pump is an important element of marine carbon cycling and climate control on millennium timescales. In a widely‐held conception the export of organic carbon from the productive surface layer of the ocean is used as the essential measure of this carbon pump. Using numerical ocean modeling, we show here that the change in export production is, however, a poor measure of the biological carbon pump's feedback to the atmosphere on centennial timescales. In the contrary, we find that an oxygen‐based measure, the apparent oxygen utilization can be used to quantify the impact of biological pump changes on the atmosphere. Since the apparent oxygen utilization is easily accessible from an existing network of marine floats, our study suggests that the atmospheric impact of any future changes of the biological carbon pump can be monitored and quantified. For past decades our study proposes a negligible CO2 feedback to climate from biological carbon processing. Key Points: Apparent oxygen utilization is proposed to quantify the feedback of the biological carbon pump to the atmosphere in a warming oceanChanges in export production are unrelated to changes in biotic oxygen air‐sea gas exchangeThe CO2‐flux due to changes of the biological carbon pump over the recent decades is negligible compared to the total marine CO2 uptake [ABSTRACT FROM AUTHOR]

Rapid adjustments--the response of meteorology to external forcing while sea surface temperatures (SST) and sea ice are held fixed--can affect the midlatitude circulation and contribute to long-term forced circulation responses in climate simulations. This study examines rapid adjustments in the Southern Hemisphere (SH) circulation using nine models from the Precipitation Driver and Response Model Intercomparison Project (PDRMIP), which perform fixed SST and coupled ocean experiments for five perturbations: a doubling of carbon dioxide (2xCO2), a tripling of methane (3xCH4), a fivefold increase in sulfate aerosol (5xSO4), a tenfold increase in black carbon aerosol (10xBC), and a 2%increase in solar constant (2%Sol). In the coupled experiments, the SH eddy-driven jet shifts poleward and strengthens for forcings that produce global warming (and vice versa for 5xSO4), with the strongest response found in austral summer. In austral winter, the responses project more strongly onto a change in jet strength. For 10xBC, which induces strong shortwave absorption, the multimodel mean (MMM) rapid adjustment in DJF jet latitude is ;75% of the change in the coupled simulations. For the other forcings, which induce larger SST changes, the effect of SST-mediated feedbacks on the SH circulation is larger than the rapid adjustment. Nevertheless, for these perturbations the magnitude of the MMM jet shift due to the rapid adjustment is still around 20%-30% of that in the coupled experiments. The results demonstrate the need to understand the mechanisms for rapid adjustments in the midlatitude circulation, in addition to the effect of changing SSTs. [ABSTRACT FROM AUTHOR]

This study investigates the effects of global and regional sea surface temperature (SST) warming from the Industrial Revolution to the present on the stratosphere using a climate model, and estimates the relative contributions of SST warming in different regions. The observed global SST warming is found to cause colder and stronger stratospheric zonal circulations in the high latitudes of both hemispheres, and a colder lower stratosphere in the tropics and ozone depletion. This occurs because the warming in the tropical Atlantic and in the north Indian Ocean and North Pacific strongly cool the stratosphere in the southern and northern high latitudes, respectively. The cooling in the lower stratosphere at lower and midlatitudes is mainly caused by SST warming in the tropical Pacific and north Indian Ocean. The changes in stratospheric temperature are related to changes in circulation and ozone. In addition, we investigate the effects on the stratosphere of ideal 1-K uniform warming of SST in different oceans and compare these effects with those caused by the realistic SST warming. The observed global SST warming and 1-K uniform global SST warming have opposite effects on the high-latitude stratosphere in both hemispheres: 1-K uniform global SST warming results in warmer and weaker stratospheric zonal circulations and a corresponding increase in ozone. This is because the 1-K uniform increase in SST in the tropical Pacific causes extremely strong warming and weakening stratospheric zonal circulations. The contribution of a 1-K uniform increase of SST in the tropical Pacific to stratospheric temperature, circulation, and ozone anomalies overwhelms that of a 1-K uniform increase of SST in other regions. [ABSTRACT FROM AUTHOR]

Satellite measurements over the last three decades show a gradual decrease in solar output, which can be indicative as a precursor to a modern grand solar minimum (GSM). Using a chemistry–climate model, this study investigates the potential of two GSM scenarios with different magnitude to counteract the climate change by projected anthropogenic greenhouse gas (GHG) emissions through the twenty-first century. To identify regions showing enhanced vulnerability to climate change (hot spots) and to estimate their response to a possible modern GSM, a multidimensional metric is applied that accounts for—in addition to changes in mean quantities—seasonal changes in the variability and occurrence of extreme events. We find that a future GSM in the middle of the twenty-first century would temporarily mitigate the global mean impact of anthropogenic climate change by 10%–23% depending on the GSM scenario. A future GSM would, however, not be able to stop anthropogenic global warming. For the GHG-only scenario, our hot-spot analysis suggests that the midlatitudes show a response to rising GHGs below global average, while in the tropics, climate change hot spots with more frequent extreme hot seasons will develop during the twenty-first century. A GSM would reduce the climate change warming in all regions. The GHG-induced warming in Arctic winter would be dampened in a GSM due to the impact of reduced solar irradiance on Arctic sea ice. However, even an extreme GSM could only mitigate a fraction of the tropical hot-spot pattern (up to 24%) in the long term. [ABSTRACT FROM AUTHOR]

Climate changes in 2015–2100 have been simulated with the use of the INM-CM5 climate model following four scenarios: SSP1-2.6, SSP2-4.5, and SSP5-8.5 (single model runs) and SSP3-7.0 (an ensemble of five model runs). Changes in the global mean temperature and spatial distribution of temperature and precipitation are analyzed. The global warming predicted by the INM-CM5 model in the scenarios considered is smaller than that in other CMIP6 models. It is shown that the temperature in the hottest summer month can rise more quickly than the seasonal mean temperature in Russia. An analysis of a change in Arctic sea ice shows no complete Arctic summer ice melting in the 21st century under any model scenario. Changes in the meridional streamfunction in atmosphere and ocean are studied. [ABSTRACT FROM AUTHOR]

Previous work showed that the poleward expansion of the annual-mean zonal-mean atmospheric circulation in response to global warming is strongly modulated by changes in clouds and their radiative heating of the surface and atmosphere. Here, a hierarchy and an ensemble of global climate models are used to study the circulation impact of changes in atmospheric cloud-radiative heating in the absence of changes in sea surface temperature (SST), which is referred to as the atmospheric pathway of the cloud-radiative impact. For the MPI-ESM model, the atmospheric pathway is responsible for about half of the total cloud-radiative impact, and in fact half of the total circulation response. Changes in atmospheric cloud-radiative heating are substantial in both the lower and upper troposphere. However, because SST is prescribed the atmospheric pathway is dominated by changes in upper-tropospheric cloud-radiative heating, which in large part results from the upward shift of high-level clouds. The poleward circulation expansion via the atmospheric pathway and changes in upper-tropospheric cloud-radiative heating are qualitatively robust across three global models, yet their magnitudes vary by a factor of 3. A substantial part of these magnitude differences are related to the upper-tropospheric radiative heating by high-level clouds in the present-day climate. A comparison with observations highlights the model deficits in representing the radiative heating by high-level clouds and indicates that reducing these deficits can contribute to improved predictions of regional climate change. [ABSTRACT FROM AUTHOR]

How the globally uniform component of sea surface temperature (SST) warming influences rainfall in the African Sahel remains insufficiently studied, despite mean SST warming being among the most robustly simulated and theoretically grounded features of anthropogenic climate change. A prior study using the NOAA Geophysical Fluid Dynamics Laboratory (GFDL) AM2.1 atmospheric general circulation model (AGCM) demonstrated that uniform SST warming strengthens the prevailing northerly advection of dry Saharan air into the Sahel. The present study uses uniform SST warming simulations performed with 7 GFDL and 10 CMIP5 AGCMs to assess the robustness of this drying mechanism across models and uses observations to assess the physical credibility of the severe drying response in AM2.1. In all 17 AGCMs, mean SST warming enhances the free-tropospheric meridional moisture gradient spanning the Sahel and with it the Saharan dry-air advection. Energetically, this is partially balanced by anomalous subsidence, yielding decreased precipitation in 14 of the 17 models. Anomalous subsidence and precipitation are tightly linked across the GFDL models but not the CMIP5 models, precluding the use of this relationship as the start of a causal chain ending in an emergent observational constraint. For AM2.1, cloud–rainfall covariances generate radiative feedbacks on drying through the subsidence mechanism and through surface hydrology that are excessive compared to observations at the interannual time scale. These feedbacks also act in the equilibrium response to uniform warming, calling into question the Sahel's severe drying response to warming in all coupled models using AM2.1. [ABSTRACT FROM AUTHOR]

Models project that Antarctic sea ice area will decline considerably by the end of this century, but the consequences remain largely unexplored. Here, the atmospheric response to future sea ice loss in the Antarctic is investigated, and contrasted to the Arctic case, using the Community Earth Systems Model (CESM) Whole Atmosphere Coupled Climate Model (WACCM). Time-slice model runs with historic sea ice concentrations are compared to runs with future concentrations, from the late twenty-first century, in each hemisphere separately. As for the Arctic, results indicate that Antarctic sea ice loss will act to shift the tropospheric jet equatorward, an internal negative feedback to the poleward shift associated with increased greenhouse gases. Also, the tropospheric response to Antarctic sea ice loss is found to be somewhat weaker, more vertically confined, and less seasonally varying than in the case of Arctic sea ice loss. The stratospheric response to Antarctic sea ice loss is relatively weak compared to the Arctic case, although it is here demonstrated that the latter is still small relative to internal variability. In contrast to the Arctic case, the response of the ozone layer is found to be positive (up to 5 Dobson units): interestingly, it is present in all seasons except austral spring. Finally, while the response of surface temperature and precipitation is limited to the southern high latitudes, it is nonetheless unable to impact the interior of the Antarctic continent, suggesting a minor role of sea ice loss on recent Antarctic temperature trends. [ABSTRACT FROM AUTHOR]

Considering the ambitious climate targets of the Paris Agreement to limit global warming to 2°C, with aspirations of even 1.5°C, questions arise on how to achieve this. Climate geoengineering has been proposed as a potential tool to minimize global harm from anthropogenic climate change. Here, an Earth system model is used to evaluate the climate response when transferring from a high CO2 forcing scenario, RCP8.5, to a middle-of-the-road forcing scenario, like RCP4.5, using aerosol geoengineering. Three different techniques are considered: stratospheric aerosol injections (SAI), marine sky brightening (MSB), and cirrus cloud thinning (CCT). The climate states appearing in the climate geoengineering cases are found to be closer to RCP4.5 than RCP8.5 and many anthropogenic global warming symptoms are alleviated. All three techniques result in comparable global mean temperature evolutions. However, there are some notable differences in other climate variables due to the nature of the forcings applied. CCT acts mainly on the longwave part of the radiation budget, as opposed to MSB and SAI acting in the shortwave. This yields a difference in the response, particularly in the hydrological cycle. The responses in sea ice, sea level, ocean heat, and circulation, as well as the carbon cycle, are furthermore compared. Sudden termination of the aerosol injection geoengineering shows that the climate very rapidly (within two decades) reverts to the path of RCP8.5, questioning the sustainable nature of such climate geoengineering, and simultaneous mitigation during any such form of climate geoengineering would be needed to limit termination risks. [ABSTRACT FROM AUTHOR]

Comments on the detail of U.S. Climate Change Science Program, which seeks to produce a comprehensive set of reports on climate change. Determination of the prelude political interference; Record of warming on the Earth's surface and change; Level of atmosphere.

Adaptation is an important approach for protecting human health, ecosystems, and economic systems from the risks posed by climate variability and change, and for exploiting beneficial opportunities providedby a changing climate. This paper presents 9 fundamental principles that should be considered when designing adaptation policy, for example, a sound understanding of the potential regional effects of climate on human and ecological systems is required to target appropriate investments in adaptive responses. The distribution of potential impacts across different populations and the mechanisms by which these impacts occur are also key to effective adaptation measures. Options forcoping with climatic changes must be considered in the context of multiple stressors. Further, adaptation is likely to exhibit varying levels of effectiveness as demonstrated by current efforts to deal withclimate variability. Potential adverse side effects of adaptive strategies must also be accounted for to avoid solutions that are worse than the problem. These issues and others are presented in this paper,with examples from various impacts studies to illustrate key points. [ABSTRACT FROM AUTHOR]

Future changes in tropical cyclone (TC) activity and structure are investigated using the outputs of a 14-km mesh climate simulation. A set of 30-yr simulations was performed under present-day and warmer climate conditions using a nonhydrostatic icosahedral atmospheric model with explicitly calculated convection. The model projected that the global frequency of TCs is reduced by 22.7%, the ratio of intense TCs is increased by 6.6%, and the precipitation rate within 100 km of the TC center increased by 11.8% under warmer climate conditions. These tendencies are consistent with previous studies using a hydrostatic global model with cumulus parameterization. The responses of vertical and horizontal structures to global warming are investigated for TCs with the same intensity categories. For TCs whose minimum sea level pressure (SLP) reaches less than 980 hPa, the model predicted that tangential wind increases in the outside region of the eyewall. Increases in the tangential wind are related to the elevation of the tropopause caused by global warming. The tropopause rise induces an upward extension of the eyewall, resulting in an increase in latent heating in the upper layers of the inclined eyewall. Thus, SLP is reduced underneath the warmed eyewall regions through hydrostatic adjustment. The altered distribution of SLP enhances tangential winds in the outward region of the eyewall cloud. Hence, this study shows that the horizontal scale of TCs defined by a radius of 12 m s−1 surface wind is projected to increase compared with the same intensity categories for SLP less than 980 hPa. [ABSTRACT FROM AUTHOR]

The present study investigates changes in the location, frequency, intensity, and dynamical processes of North Atlantic extratropical cyclones with warming consistent with the IPCC Fifth Assessment Report (AR5) representative concentration pathway 8.5 (RCP8.5) scenario. The modeling, analysis, and prediction (MAP) climatology of midlatitude storminess (MCMS) feature-tracking algorithm was utilized to analyze 10 cold-season high-resolution atmospheric simulations over the North Atlantic region in current and future climates. Enhanced extratropical cyclone activity is most evident in the northeast North Atlantic and off the U.S. East Coast. These changes in cyclone activity are offset from changes in eddy kinetic energy and eddy heat flux. Investigation of the minimum SLP reached at each grid point reveals a lack of correspondence between the strongest events in the current and future simulations, indicating the future simulations produced a different population of storms. Examination of the percent change of storms in the storm-track region shows a reduction in the number of strong storms (i.e., those reaching a minimum SLP perturbation of at least −51 hPa). Storm-relative composites of strong and moderate storms show an increase in precipitation, associated with enhanced latent heat release and strengthening of the 900-700-hPa layer-average potential vorticity (PV). Other structural changes found for cyclones in a future climate include weakened upper-level PV for strong storms and a weakened near-surface potential temperature anomaly for moderate storms, demonstrating a change in storm dynamics. Furthermore, the impacts associated with extratropical cyclones, such as strong near-surface winds and heavy precipitation, strengthen and become more frequent with warming. [ABSTRACT FROM AUTHOR]

Climate change is a complex and multi-facetted phenomenon, interpreted by an extensive body of interdisciplinary science. Although a great deal is known about the climate system, an enormous amount of uncertainty remains. Since uncertainty is usually equated with ignorance, this fact feeds scepticism onman-induced impacts on the global climate and links climate change with natural causes only. A broader concept of climate change science is presented by focusing on both early and modern scientific foundations of climate models and specific types of uncertainty usually encountered when formulating quantitative assessments of risks due to climate change. Major controversial issues of such risks and their origin is addressed with paticular attention paid to the widespread criticism for inconsistency of the reports of the Intergovernmental Panel on Climate Change, based on the assumptions found not always justified by the real scientific methods. Major inconsistencies and misleading arguments on the climate change are also discussed. [ABSTRACT FROM AUTHOR]

Climate change and global warming are two huge current threats due to continuous anthropogenic emissions of greenhouse gases (GHGs) in the Earth's atmosphere. Accurate measurements and reliable quantifications of GHG emissions in air are thus of primary importance to the study of climate change and for taking mitigation actions. Therefore, the detection of GHGs should be the first step when trying to reduce their concentration in the environment. Throughout recent decades, nanostructured metal oxide semiconductors have been found to be reliable and accurate for the detection of many different toxic gases in air. Thus, the aim of this article is to present a comprehensive review of the development of various metal oxide semiconductors, as well as to discuss their strong and weak points for GHG detection. [ABSTRACT FROM AUTHOR]

Long-term responses of terrestrial ecosystems to the combined effects of warming and elevated CO (eCO) will likely be regulated by N availability. The stock of soil N determines availability for organisms, but also influences loss to the atmosphere or groundwater. eCO and warming can elicit changes in soil N via direct effects on microbial and plant activity, or indirectly, via soil moisture. Detangling the interplay of direct- and moisture-mediated impacts on soil N and the role of organisms in controlling soil N will improve predictions of ecosystem-level responses. We followed individual soil N pools over two growing seasons in a semiarid temperate grassland, at the Prairie Heating and CO Enrichment experiment. We evaluated relationships of N pools with environmental factors and explored the role of plants by assessing plant biomass, plant N, and plant inputs to soil. We also assessed N forms in plots with and without vegetation to remove plant-mediated effects. Our study demonstrated that the effects of warming and eCO are highly dependent on individual N form and on year. In this water-constrained grassland, eCO, warming and their combination appear to impact soil N pools through a complex combination of direct- and moisture-mediated effects. eCO decreased NO but had neutral to positive effects on NH and dissolved organic N (DON), particularly in a wet year. Warming increased NO availability due to a combination of indirect drying and direct temperature-driven effects. Warming also increased DON only in vegetated plots, suggesting plant mediation. Our results suggest that impacts of combined eCO and warming are not always equivalent for plant and soil pools; although warming can help offset the decrease in NO availability for plants under eCO, the NO pool in soil is mainly driven by the negative effects of eCO. [ABSTRACT FROM AUTHOR]