Shortwave and longwave radiative contributions to global warming under increasing CO2

In response to increasing concentrations of atmospheric CO₂, high-end general circulation models (GCMs) simulate an accumulation of energy at the top of the atmosphere not through a reduction in outgoing longwave radiation (OLR)—as one might expect from greenhouse gas forcing—but through an enhancement of net absorbed solar radiation (ASR). A simple linear radiative feedback framework is used to explain this counterintuitive behavior. It is found that the timescale over which OLR returns to its initial value after a CO₂ perturbation depends sensitively on the magnitude of shortwave (SW) feedbacks. If SW feedbacks are sufficiently positive, OLR recovers within merely several decades, and any subsequent global energy accumulation is because of enhanced ASR only. In the GCM mean, this OLR recovery timescale is only 20 y because of robust SW water vapor and surface albedo feedbacks. However, a large spread in the net SW feedback across models (because of clouds) produces a range of OLR responses; in those few models with a weak SW feedback, OLR takes centuries to recover, and energy accumulation is dominated by reduced OLR. Observational constraints of radiative feedbacks—from satellite radiation and surface temperature data—suggest an OLR recovery timescale of decades or less, consistent with the majority of GCMs. Altogether, these results suggest that, although greenhouse gas forcing predominantly acts to reduce OLR, the resulting global warming is likely caused by enhanced ASR.Global conservation of energy is a powerful constraint for understanding Earth’s climate and its changes. Variations in atmospheric composition that result in a net positive energy imbalance at the top of atmosphere (TOA) drive global warming, with the world ocean as the primary reservoir for energy accumulation (1). In turn, increasing global surface temperature enhances emission of longwave (LW) radiation to space (the Planck response). A schematic of the global energy budget response to a step change in greenhouse gas (GHG) concentrations is illustrated in Fig. 1A: outgoing LW radiation (OLR) initially decreases because of enhanced LW absorption by higher GHG levels; as energy accumulates in the climate system, global temperature rises and OLR increases until the TOA energy balance is restored—when OLR once again balances the net absorbed solar radiation (ASR). In this canonical view of global warming, the net energy accumulation (shaded green area in Fig. 1A) is a consequence of decreased OLR driven by GHG forcing. In contrast, consider a hypothetical step change in solar insolation (Fig. 1B): ASR is increased, and energy accumulates until the climate warms sufficiently that OLR balances the ASR perturbation. In this case, the net energy accumulation (shaded red area in Fig. 1) is a consequence of increased ASR and opposed by the increased OLR (hatched green area in Fig. 1).Open in a separate windowFig. 1.(A) Idealized response of global mean radiation at the TOA to an instantaneous GHG forcing (green dots) assuming no SW feedback and a radiative adjustment e-folding time of 20 y. The green line shows the OLR response (anomaly from preindustrial), and the shaded green area shows the LW energy accumulation. (B) The same as in A but in response to an instantaneous SW forcing (red dots), with the red line showing the ASR response. In this case, the net energy accumulation is the difference between the SW energy accumulation (the shaded red area) and the LW increase (the hatched green area, where the hatching indicates that the LW response leads to a cooling of the climate system). (C) The ensemble average radiative response in the CMIP5 4× CO₂ simulations. The shaded area represents the energy accumulation by SW (red) and LW (green) anomalies, and the hatched area indicates energy loss by enhanced OLR. The dashed red and green lines show the predicted ensemble average ASR and OLR responses from the linear feedback model (Eqs. 1 and 2). (D) The same as in C but for the CMIP5 ensemble average radiative response in the 1% CO₂ increase per year simulations (with linear increase in forcing as shown by dotted lines).Is the present global warming caused by reduced OLR (as in Fig. 1A) or enhanced ASR (as in Fig. 1B)? Anthropogenic radiative forcing is dominated by LW active constituents, such as CO₂ and methane, and shortwave (SW) forcing agents, such as sulfate aerosols, are thought to be acting to reduce ASR compared with their preindustrial levels (2). Reduced OLR, thus, seems the likely cause of the observed global energy accumulation, although the limited length of satellite TOA radiation measurements precludes determination of the relative contributions of ASR and OLR by direct observation. Trenberth and Fasullo (3) considered global energy accumulation within the ensemble of coupled general circulation models (GCMs) participating in phase 3 of the Coupled Model Intercomparison Project (4) (CMIP3). They report that, under the Special Report on Emission Scenarios A1B emissions scenario, wherein increasing radiative forcing is driven principally by increasing GHG concentrations, OLR changes little over the 21st century and global energy accumulation is caused nearly entirely by enhanced ASR—seemingly at odds with the canonical view of global warming by reduced LW emission to space (outlined in Fig. 1A).Here, we seek insight into this surprising result. In particular, we examine CO₂-only forcing scenarios as simulated by the CMIP5 ensemble of state of the art GCMs (5). Perturbing CO₂ alone permits a clean partitioning of radiative forcing and radiative response into their respective SW and LW components and allows an investigation into the relative contributions of reduced OLR and enhanced ASR to global energy accumulation. The CMIP5 multi-GCM mean response to a compounding 1% per year CO₂ increase (hereafter, 1% CO₂) is shown in Fig. 1D. Although CO₂ radiative forcing increases approximately linearly in time for 140 y (dotted lines in Fig. 1D), OLR changes little from its preindustrial value, and global energy accumulation is accomplished nearly entirely by increased ASR, consistent with the multi-GCM mean results in the work Trenberth and Fasullo (3). Perhaps even more striking is the response to an abrupt quadrupling of CO₂ (hereafter, 4× CO₂), which is shown in Fig. 1C: OLR initially decreases, like in Fig. 1A, but recovers to its unperturbed (preindustrial) value within only two decades; beyond this initial adjustment period, energy is lost due to enhanced OLR and gained solely by enhanced ASR.Here, we propose a simple physical mechanism for this behavior. We show that the simulated global mean OLR and ASR responses (Fig. 1 C and D) and the short recovery time for OLR in particular can be understood in terms of a linear radiative feedback analysis. Moreover, the diversity of feedbacks across the CMIP5 GCMs explains the range in behavior across the models: in a majority of models, OLR recovers within several decades, and the subsequent global energy accumulation is caused by enhanced ASR; in a minority of models, OLR remains diminished for centuries, and global energy accumulation is driven by reduced OLR. Finally, we show that recent satellite observations constrain radiative feedbacks to be within the regime of relatively fast (approximately decades) OLR recovery under GHG forcing, similar to the majority of CMIP5 GCMs. Altogether, these results suggest that, although GHG forcing acts primarily in the LW, the resulting global warming is fundamentally a consequence of enhanced SW energy accumulation.     

From the Cover: Robust Hadley Circulation changes and increasing global dryness due to CO2 warming from CMIP5 model projections

In this paper, we investigate changes in the Hadley Circulation (HC) and their connections to increased global dryness (suppressed rainfall and reduced tropospheric relative humidity) under CO₂ warming from Coupled Model Intercomparison Project Phase 5 (CMIP5) model projections. We find a strengthening of the HC manifested in a “deep-tropics squeeze” (DTS), i.e., a deepening and narrowing of the convective zone, enhanced ascent, increased high clouds, suppressed low clouds, and a rise of the level of maximum meridional mass outflow in the upper troposphere (200−100 hPa) of the deep tropics. The DTS induces atmospheric moisture divergence and reduces tropospheric relative humidity in the tropics and subtropics, in conjunction with a widening of the subsiding branches of the HC, resulting in increased frequency of dry events in preferred geographic locations worldwide. Among various water-cycle parameters examined, global dryness is found to have the highest signal-to-noise ratio. Our results provide a physical basis for inferring that greenhouse warming is likely to contribute to the observed prolonged droughts worldwide in recent decades.The Hadley Circulation (HC), the zonally averaged meridional overturning motion connecting the tropics and midlatitude, is a key component of the global atmospheric general circulation. How the HC has been or will be changed as a result of global warming has tremendous societal implications on changes in weather and climate patterns, especially the occurrences of severe floods and droughts around the world (1, 2). Recent studies have suggested that the global balance requirement for water vapor and precipitation weakens the tropical circulation in a warmer climate (3, 4). So far, the most robust signal of weakening of tropical circulation from models appears to come from the Walker circulation but not from the HC, possibly because of the large internal variability in the latter (5, 6). Observations based on reanalysis data have shown weak signals of increasing, decreasing, or no change in HC strength in recent decades, with large uncertainties depending on the data source and the period of analyses (7–10). Meanwhile, studies have also shown that even though water vapor is increased almost everywhere as global temperature rises, increased dryness (lack of rainfall and reduced surface relative humidity) is found in observations and in model projections, especially in many land regions around the world (11–13). Reduction in midtropospheric relative humidity and clouds in the subtropics and midlatitude under global warming have also been noted in models and observations, suggesting the importance of cloud feedback and circulation changes (14–16). Even though robust global warming signals have been found in changing rainfall characteristics (2, 17, 18), in the widening of the subtropics, and in the relative contributions of circulation and surface warming to tropical rainfall from climate model projections and observations (19–24), the dynamical linkages between HC changes and global patterns of moistening and drying have yet to be identified and understood. In this paper, we aim at establishing a baseline understanding of the dynamics of changes in the HC and relationships with increased global dryness based on monthly outputs from 33 Coupled Model Intercomparison Project Phase 5 (CMIP5) 140-y projection experiments under a scenario of a prescribed 1% per year CO₂ emission increase. The baseline developed here hopefully will provide guidance for future observational studies in the detection and attribution of climate change signals in atmospheric circulation and in the assessment of risk of global droughts. Consistent with previous studies (3, 4, 17, 24), we find that under the prescribed emission scenario, global rainfall increases at a muted rate of 1.5 ± 0.1% K⁻¹, much slower than that for saturated water vapor as governed by the Clausius−Clapeyron relationship (∼6.5% K⁻¹). In the following, the responses of various quantities related to the climatology and anomaly of the HC, rainfall, tropical convection, global dryness, and their interrelationships are discussed. For definitions of climatology and anomaly, see Methods and Materials.     

Consumers mediate the effects of experimental ocean acidification and warming on primary producers

It is well known that ocean acidification can have profound impacts on marine organisms. However, we know little about the direct and indirect effects of ocean acidification and also how these effects interact with other features of environmental change such as warming and declining consumer pressure. In this study, we tested whether the presence of consumers (invertebrate mesograzers) influenced the interactive effects of ocean acidification and warming on benthic microalgae in a seagrass community mesocosm experiment. Net effects of acidification and warming on benthic microalgal biomass and production, as assessed by analysis of variance, were relatively weak regardless of grazer presence. However, partitioning these net effects into direct and indirect effects using structural equation modeling revealed several strong relationships. In the absence of grazers, benthic microalgae were negatively and indirectly affected by sediment-associated microalgal grazers and macroalgal shading, but directly and positively affected by acidification and warming. Combining indirect and direct effects yielded no or weak net effects. In the presence of grazers, almost all direct and indirect climate effects were nonsignificant. Our analyses highlight that (i) indirect effects of climate change may be at least as strong as direct effects, (ii) grazers are crucial in mediating these effects, and (iii) effects of ocean acidification may be apparent only through indirect effects and in combination with other variables (e.g., warming). These findings highlight the importance of experimental designs and statistical analyses that allow us to separate and quantify the direct and indirect effects of multiple climate variables on natural communities.     

Effects of explicit atmospheric convection at high CO2

The effect of clouds on climate remains the largest uncertainty in climate change predictions, due to the inability of global climate models (GCMs) to resolve essential small-scale cloud and convection processes. We compare preindustrial and quadrupled CO₂ simulations between a conventional GCM in which convection is parameterized and a “superparameterized” model in which convection is explicitly simulated with a cloud-permitting model in each grid cell. We find that the global responses of the two models to increased CO₂ are broadly similar: both simulate ice-free Arctic summers, wintertime Arctic convection, and enhanced Madden–Julian oscillation (MJO) activity. Superparameterization produces significant differences at both CO₂ levels, including greater Arctic cloud cover, further reduced sea ice area at high CO₂, and a stronger increase with CO₂ of the MJO.Clouds play an important role in the climate system by reflecting incoming shortwave solar radiation (cooling), intercepting outgoing longwave radiation from the surface (warming), and influencing temperature and circulation. Their net radiative impact at the surface is about −20 W/m² cooling in the global mean, and regional impacts can approach ∼40 W/m². Understanding how clouds will respond to rising CO₂ concentrations is thus a critical issue in climate science. Progress has been complicated by the hundred-kilometer horizontal grid spacing of most global circulation models (GCMs), which remain unable to directly resolve the much smaller-scale turbulent motions involved in atmospheric moist convection, the corresponding cloud-formation processes, and their radiative effects (1, 2).Current treatment of convection in global climate models relies on parameterizations and therefore suffers significant uncertainties, particularly relating to the representation of convection and clouds in a changing climate. Model results are sensitive to formulation and parameter choices in parameterized convection schemes. As a result, the magnitude of cloud feedbacks remains uncertain and inconsistently predicted by different models (2). An alternative approach, “superparameterization,” attempts to reduce the uncertainties of parameterization by running a higher resolution cloud-permitting model in a small domain within each grid cell of the atmospheric GCM, simulating the convection and cloud motions more explicitly (3, 4). Superparameterized GCMs have been shown to have a more realistic representation of convective variability, including the diurnal cycle (5) and intraseasonal variability such as the Madden–Julian oscillation (MJO) (6) and the Australian and Indian monsoons. They are beginning to be used to project future climate changes (7), although such work has been limited due to computational costs of about 100 times that of a standard GCM.Here we present the results of running a global coupled ocean–atmosphere model [the Community Earth System Model (CESM; ref. 8)], and its superparameterized variant (SP-CESM; refs. 3, 4, 9) at a preindustrial CO₂ concentration, as well as at 4 times higher concentration. We run CESM to near steady state for both preindustrial CO₂ concentration and 4 times this value (×1CO₂ and ×4CO₂), and then run shorter simulations of SP-CESM starting from these steady states (Materials and Methods). We choose to examine a rather significant (although not necessarily unrealistic) ×4CO₂ increase scenario because the equilibrium climate sensitivity of CESM to CO₂ doubling is on the low side of the warming range of 2.1–4.7 K seen in a recent model intercomparison (10), and to maximize the signal-to-noise ratio in the model response to superparameterization.CESM and SP-CESM are nearly identical except for their convection and cloud representation and related physics (Materials and Methods), but they show significant differences in their simulations at ×1 and ×4CO₂. Concerns have been raised that convection and cloud parameterizations may lead to either artificial amplification or weakening of the response to CO₂ increase. We find the global climate responses of CESM and SP-CESM to be broadly similar, a reassuring result in terms of present projections that are based on parameterized models. However, we find significant regional differences for Arctic sea ice and the tropical Madden–Julian oscillation on which we focus in this paper. Specifically, we find that SP-CESM shows (i) significantly less sea ice at ×1CO₂ and a larger area reduction at ×4CO₂, and (ii) a stronger MJO at ×1CO₂ and a larger increase at ×4CO₂. We analyze these differences and discuss the implications for uncertainties in climate change projections.The Arctic, and Arctic sea ice melting in particular, is strongly affected by the presence of low clouds that reduce solar heating in summer and by high clouds that induce warming in winter. Arctic sea ice has undergone rapid recent changes (11, 12), and is believed to have played a major role in past abrupt climate changes (13). Sea ice has a major impact on climate due to its high albedo and ability to insulate the atmosphere from the warmer ocean. Arctic sea ice change impacts local ecosystems (14), modulates extreme weather events in the sub-Arctic and midlatitudes (15), and has implications for shipping routes (16).Our focus on the MJO is motivated in part by numerous studies showing that present-day MJO simulations with SP-CESM are significantly improved relative to results from conventional GCMs, which have historically struggled to simulate it realistically. The MJO is characterized by an envelope of convective anomalies with a 30–70-day timescale that forms episodically over the Indian Ocean, propagates slowly eastward at around 5 m/s, and dissipates over the central Pacific (17, 18). The MJO affects the monsoons and Atlantic tropical cyclogenesis, modulates westerly wind bursts that can help trigger El Niño events, dramatically impacts tropical rainfall, and contributes to extreme precipitation events globally (18, 19). There is observational (20–23) and model (24–27) evidence of enhanced MJO activity with warming, although not all models agree on the sign of MJO change (28), and the change may be sensitive to the spatial pattern of warming (29).     

Impacts of climate warming on terrestrial ectotherms across latitude

The impact of anthropogenic climate change on terrestrial organisms is often predicted to increase with latitude, in parallel with the rate of warming. Yet the biological impact of rising temperatures also depends on the physiological sensitivity of organisms to temperature change. We integrate empirical fitness curves describing the thermal tolerance of terrestrial insects from around the world with the projected geographic distribution of climate change for the next century to estimate the direct impact of warming on insect fitness across latitude. The results show that warming in the tropics, although relatively small in magnitude, is likely to have the most deleterious consequences because tropical insects are relatively sensitive to temperature change and are currently living very close to their optimal temperature. In contrast, species at higher latitudes have broader thermal tolerance and are living in climates that are currently cooler than their physiological optima, so that warming may even enhance their fitness. Available thermal tolerance data for several vertebrate taxa exhibit similar patterns, suggesting that these results are general for terrestrial ectotherms. Our analyses imply that, in the absence of ameliorating factors such as migration and adaptation, the greatest extinction risks from global warming may be in the tropics, where biological diversity is also greatest.     

Effect of warming temperatures on US wheat yields

Climate change is expected to increase future temperatures, potentially resulting in reduced crop production in many key production regions. Research quantifying the complex relationship between weather variables and wheat yields is rapidly growing, and recent advances have used a variety of model specifications that differ in how temperature data are included in the statistical yield equation. A unique data set that combines Kansas wheat variety field trial outcomes for 1985–2013 with location-specific weather data is used to analyze the effect of weather on wheat yield using regression analysis. Our results indicate that the effect of temperature exposure varies across the September−May growing season. The largest drivers of yield loss are freezing temperatures in the Fall and extreme heat events in the Spring. We also find that the overall effect of warming on yields is negative, even after accounting for the benefits of reduced exposure to freezing temperatures. Our analysis indicates that there exists a tradeoff between average (mean) yield and ability to resist extreme heat across varieties. More-recently released varieties are less able to resist heat than older lines. Our results also indicate that warming effects would be partially offset by increased rainfall in the Spring. Finally, we find that the method used to construct measures of temperature exposure matters for both the predictive performance of the regression model and the forecasted warming impacts on yields.The potential impact of global warming and climate change on socioeconomic outcomes has become an important and growing area of scientific study and evaluation. Separate lines of study include quantifying the likely impact of climatic change on measures of civil conflict (1–5) and agricultural land values, profitability, and/or production efficiency (6–22). Both lines of literature continue to measure, discuss, and debate the effects of warming temperature. An issue that has received much attention in both sets of literature is how best to quantify exposure to extreme temperatures. This is an important concern, as many studies rely on historical spatial and temporal variations in weather outcomes to identify the effects of weather extremes. If these historical extremes are not measured correctly, estimates of their impacts will not be credibly identified, thereby raising doubts regarding any climate change projections based on these impacts.Here we use regression analysis to estimate wheat yields as a function of observed weather variables and forecast yield impacts under a variety of weather scenarios. Our main findings are as follows. First, the effect of temperature exposure varies across the September−May growing season, with the biggest drivers of yield loss being freezing temperatures in the Fall and extreme heat in the Spring. Second, the net effect of warming on yields is negative, even after accounting for the benefits of reduced exposure to freezing temperatures. Third, there exists a tradeoff between mean yield and ability to resist extreme heat across varieties, and more-recently released varieties are less able to resist heat than older ones. Fourth, warming effects are partially offset by increased rainfall in the Spring. Fifth, the method used to construct measures of temperature exposure matters for both the predictive performance of the regression model and the forecasted warming impacts.We focus on wheat as it is one of the first domesticated food crops, forms the basic staple food of major civilizations in Europe, West Asia, and North Africa, and is the most widely planted crop globally. With a 2013 harvest of 8 million hectares, the Great Plains of the United States form the largest contiguous area of low-rainfall winter wheat in the world. Five states (Kansas, Oklahoma, Texas, Colorado, and Nebraska) produce nearly all high-quality hard red winter wheat in the United States. In 2013, Kansas production generated 378 million bushels of wheat at a value of 2.8 billion US dollars. Kansas production value represents 15% of all wheat grown in the United States.Our empirical approach uses data that combine variety-specific wheat yield observations with weather data from the exact location of the field trial. This permits two major advances for estimating the relationship between weather and wheat yield: (i) Location-specific weather data purge the results of aggregation bias that might be present in studies that use weather averages (or other aggregates) across space, and (ii) variety-specific yield responses provide information about the impact of climate on a large number of past, present, and future wheat varieties. Ref. 11 discusses limitations of gridded weather data sets, which have been used extensively because there is not often a weather station in each location of interest. Our data avoid the five pitfalls associated with gridded weather datasets (11). In addition, we find that the warming effects estimated using these field trial data are consistent with effects estimated from on-farm yield data, thereby providing external validity for the results presented here.     

The effects of warming methods on temperature, cardiac function and cytokines in plateletpheresis donors

Background and Objectives   Plateletpheresis is the most frequent type of apheresis, with demand for these products continuously increasing. Hypothermia is a common side-effect of apheresis, which may have an effect on the donor's body functions. The aim of this study was to examine the effects of warming methods on plateletpheresis donors' temperature, cardiac function and cytokines.
Materials and Methods   Fifty plateletpheresis donors were randomly assigned to a control group ( n  = 25) or a warming group ( n  = 25), with air and blood warmers during plateletpheresis. The effects of the treatment were examined by comparing body temperature, heart rate, blood pressure, Holter EKG pattern, serum interleukin-1β (IL-1β), interleukin-2 (IL-2), tumour necrosis factor-α (TNF-α) concentration, the white blood count, the white blood fraction, and the platelet count at a point in time between the two groups.
Results   In the control group, the tympanic temperature decreased more during apheresis compared to the warming group ( P  = 0·014). The decrease of diastolic blood pressure was significantly greater in the control group compared to the warming group ( P  = 0·010). As for cardiac function, the frequency of abnormal beats was generally higher in the control group, but the difference was not significant. IL-2 and TNF-α decreased significantly after plateletpheresis in the control group only, while there was no change in the warming group.
Conclusion   The decrease of temperature during plateletpheresis resulted in changes in haemodynamics and cytokines. The warming methods used in this study can prevent the decrease of temperature in donors, and may be helpful in maintaining the haemodynamic and cytokine balance.     

Hydrologic impacts of past shifts of Earth’s thermal equator offer insight into those to be produced by fossil fuel CO2

Major changes in global rainfall patterns accompanied a northward shift of Earth’s thermal equator at the onset of an abrupt climate change 14.6 kya. This northward pull of Earth’s wind and rain belts stemmed from disintegration of North Atlantic winter sea ice cover, which steepened the interhemispheric meridional temperature gradient. A southward migration of Earth’s thermal equator may have accompanied the more recent Medieval Warm to Little Ice Age climate transition in the Northern Hemisphere. As fossil fuel CO₂ warms the planet, the continents of the Northern Hemisphere are expected to warm faster than the Southern Hemisphere oceans. Therefore, we predict that a northward shift of Earth’s thermal equator, initiated by an increased interhemispheric temperature contrast, may well produce hydrologic changes similar to those that occurred during past Northern Hemisphere warm periods. If so, the American West, the Middle East, and southern Amazonia will become drier, and monsoonal Asia, Venezuela, and equatorial Africa will become wetter. Additional paleoclimate data should be acquired and model simulations should be conducted to evaluate the reliability of this analog.     

Effect of increasing CO2 on the terrestrial carbon cycle

Feedbacks from the terrestrial carbon cycle significantly affect future climate change. The CO₂ concentration dependence of global terrestrial carbon storage is one of the largest and most uncertain feedbacks. Theory predicts the CO₂ effect should have a tropical maximum, but a large terrestrial sink has been contradicted by analyses of atmospheric CO₂ that do not show large tropical uptake. Our results, however, show significant tropical uptake and, combining tropical and extratropical fluxes, suggest that up to 60% of the present-day terrestrial sink is caused by increasing atmospheric CO₂. This conclusion is consistent with a validated subset of atmospheric analyses, but uncertainty remains. Improved model diagnostics and new space-based observations can reduce the uncertainty of tropical and temperate zone carbon flux estimates. This analysis supports a significant feedback to future atmospheric CO₂ concentrations from carbon uptake in terrestrial ecosystems caused by rising atmospheric CO₂ concentrations. This feedback will have substantial tropical contributions, but the magnitude of future carbon uptake by tropical forests also depends on how they respond to climate change and requires their protection from deforestation.In projections of future climate, the carbon cycle is second only to physical climate sensitivity itself in contributing uncertainty (1). Earth system model uncertainty has increased as more mechanisms have been incorporated into a growing number of increasingly sophisticated models. Terrestrial ecosystem feedbacks to atmospheric CO₂ concentration result from two mechanisms, direct effects of CO₂ on photosynthesis and effects of climate change on photosynthesis, respiration, and disturbance (2). The CO₂ effect, used here to describe the effect of increasing atmospheric CO₂ on terrestrial carbon storage by increasing photosynthetic rates, is also known as the β effect (3, 4). The effects of CO₂ on carbon uptake occur at the enyzmatic and stomatal scales but impact the global carbon cycle.The CO₂ effect on terrestrial carbon storage is a key potential negative feedback to future climate, and in models of the present, it is the largest carbon cycle feedback (5, 6). In simulations of the next century, the CO₂ effect is four times larger than the climate effect on terrestrial carbon storage and twice as uncertain (4). Land use also creates large fluxes, but these are not driven by CO₂ or climate directly and so are not feedbacks. In models of the future, the biosphere operates as a net sink, reducing the climate impact of fossil fuel and deforestation emissions, until positive feedbacks from climate change [reduced productivity, increased respiration, or dieback (7)] and land use emissions exceed the CO₂ effect. The magnitude of this negative feedback is crucial to simulating future climate, but because observational constraints on the CO₂ effect are limited, the effects of CO₂ remain controversial. The effects of CO₂ are known mainly from small-scale experimental studies, ranging from single-leaf experiments through to ecosystem-scale experiments with a spatial scale of hundreds of meters (8), but predictions from theory of a large tropical effect of CO₂ have appeared to be inconsistent with global patterns of atmospheric CO₂ (6).Photosynthesis increases with increasing CO₂ following a Michaelis−Menton curve, and this effect grows stronger at higher temperatures, implying, all else being equal, larger effects in warmer climates (9–11), especially in the tropics. Many factors control the relationship between increased photosynthetic rate and carbon storage, including how fixed carbon is allocated to plant tissues and soils with different residence times, the development of progressive nitrogen limitation, interactions with water or light limitation, and many other biological responses (12). Theory and experiments agree in suggesting a CO₂-driven net sink that should be roughly proportional to overall productivity (13) leading to a large sink in the tropics, a prediction that should be testable with global observations (11).     

Analysis of the Waste Volume and CO2-Equivalent Caused by the Use of Selected Patch Pumps

Background:The use of tube-free insulin pumps is increasing. To protect the environment, the use of resources and the amount of emissions into the environment should be kept as low as possible when designing these systems. In addition to basic waste avoidance, the composition of the waste produced must be considered.Methods:To compare current tube-free pumps from an ecological standpoint, a tube-free insulin pump with a modular design and two non-modular tube-free pumps were subjected to manual separation, manual sorting, characterization, and mass determination. The annual waste volume of a user was measured, and the recyclability was assessed. The global warming potential (GWP) resulting from extraction of raw materials, energetic utilization of waste, and landfill of the incineration residues was balanced.Results:For the modular tube-free pump, a total waste volume of 5.5 kg/a (recycling percentage 44.3%) was determined. The non-modular systems generated 4.9 kg/a (recycling percentage 14.6%) and 5.1 kg/a (recycling percentage 16.0%) waste. The product-specific GWP of the modular system was approximately 50% lower than that of the non-modular systems; the packaging-specific GWP was 2.5 times higher. In total, a GWP of 13.6 kg CO₂-equivalent per year could be determined for the modular system and a GWP of 15.5 kg CO₂-equivalent per year for the non-modular systems.Conclusions:Although the modular micropump has a higher total waste volume, a greater ecological potential can be attributed to it. This is based on the recyclability of the system due to its modularity and the possible reduction of packaging waste.     

Review of the Two-Step H2O/CO2-Splitting Solar Thermochemical Cycle Based on Zn/ZnO Redox Reactions

This article provides a comprehensive overview of the work to date on the two‑step solar H₂O and/or CO₂ splitting thermochemical cycles with Zn/ZnO redox reactions to produce H₂ and/or CO, i.e., synthesis gas—the precursor to renewable liquid hydrocarbon fuels. The two-step cycle encompasses: (1) The endothermic dissociation of ZnO to Zn and O₂ using concentrated solar energy as the source for high-temperature process heat; and (2) the non-solar exothermic oxidation of Zn with H₂O/CO₂ to generate H₂/CO, respectively; the resulting ZnO is then recycled to the first step. An outline of the underlying science and the technological advances in solar reactor engineering is provided along with life cycle and economic analyses.     

Contributions to accelerating atmospheric CO2 growth from economic activity, carbon intensity, and efficiency of natural sinks

The growth rate of atmospheric carbon dioxide (CO(2)), the largest human contributor to human-induced climate change, is increasing rapidly. Three processes contribute to this rapid increase. Two of these processes concern emissions. Recent growth of the world economy combined with an increase in its carbon intensity have led to rapid growth in fossil fuel CO(2) emissions since 2000: comparing the 1990s with 2000-2006, the emissions growth rate increased from 1.3% to 3.3% y(-1). The third process is indicated by increasing evidence (P = 0.89) for a long-term (50-year) increase in the airborne fraction (AF) of CO(2) emissions, implying a decline in the efficiency of CO(2) sinks on land and oceans in absorbing anthropogenic emissions. Since 2000, the contributions of these three factors to the increase in the atmospheric CO(2) growth rate have been approximately 65 +/- 16% from increasing global economic activity, 17 +/- 6% from the increasing carbon intensity of the global economy, and 18 +/- 15% from the increase in AF. An increasing AF is consistent with results of climate-carbon cycle models, but the magnitude of the observed signal appears larger than that estimated by models. All of these changes characterize a carbon cycle that is generating stronger-than-expected and sooner-than-expected climate forcing.     

Context- and scale-dependent effects of floral CO2 on nectar foraging by Manduca sexta

Typically, animal pollinators are attracted to flowers by sensory stimuli in the form of pigments, volatiles, and cuticular substances (hairs, waxes) derived from plant secondary metabolism. Few studies have addressed the extent to which primary plant metabolites, such as respiratory carbon dioxide (CO(2)), may function as pollinator attractants. Night-blooming flowers of Datura wrightii show transient emissions of up to 200 ppm above-ambient CO(2) at anthesis, when nectar rewards are richest. Their main hawkmoth pollinator, Manduca sexta, can perceive minute variation (0.5 ppm) in CO(2) concentration through labial pit organs whose receptor neurons project afferents to the antennal lobe. We explored the behavioral responses of M. sexta to artificial flowers with different combinations of CO(2), visual, and olfactory stimuli using a laminar flow wind tunnel. Responses in no-choice assays were scale-dependent; CO(2) functioned as an olfactory distance-attractant redundant to floral scent, as each stimulus elicited upwind tracking flights. However, CO(2) played no role in probing behavior at the flower. Male moths showed significant bias in first-approach and probing choice of scented flowers with above-ambient CO(2) over those with ambient CO(2), whereas females showed similar bias only in the presence of host plant (tomato) leaf volatiles. Nevertheless, all males and females probed both flowers regardless of their first choice. While floral CO(2) unequivocally affects male appetitive responses, the context-dependence of female responses suggests that they may use floral CO(2) as a distance indicator of host plant quality during mixed feeding-oviposition bouts on Datura and Nicotiana plants.     

脂质体－白细胞介素－2基因复合物瘤体内注射治疗肝细胞癌的实验研究

以阳离子脂质体ｌｉｐｏｆｅｃｔｉｎ介导含人白细胞介素一２（ＩＬ－２）基因的真核表达质粒ｐＭＥ１８Ｓ－ＩＬ－２转染体外培养和体内成瘤的小鼠肝癌ＨＡＣ细胞，观察ＩＬ－２基因转染的肝癌细胞表达ＩＬ－２情况及对肝癌的治疗作用。结果：体外转染ＩＬ－２基因４８小时后在培养上清中可测得人ＩＬ－２活性，９６小时达最高峰（７６Ｕ／ｍｌ）；瘤体内转染后，发现治疗组小鼠生存时间明显延长（３２．１±９．４ｄ比２０．９±７．５ｄ，Ｐ＜０．０１），肿瘤体积明显小于对照组，瘤组织内可检出ＩＬ－２的ｍＲＮＡ。实验表明，脂质体－ＩＬ－２基因复合物直接注射人瘤体后可获局部ＩＬ－２基因表达，从而诱生机体抗肿瘤效应，这为肝癌基因治疗提供了一种简便实用的模式。     

Plant uptake of CO2 outpaces losses from permafrost and plant respiration on the Tibetan Plateau

High-latitude and high-altitude regions contain vast stores of permafrost carbon. Climate warming may result in the release of CO₂ from both the thawing of permafrost and accelerated autotrophic respiration, but it may also increase the fixation of CO₂ by plants, which could relieve or even offset the CO₂ losses. The Tibetan Plateau contains the largest area of alpine permafrost on Earth. However, the current status of the net CO₂ balance and feedbacks to warming remain unclear, given that the region has recently experienced an atmospheric warming rate of over 0.3 °C decade⁻¹. We examined 32 eddy covariance sites and found an unexpected net CO₂ sink during 2002 to 2020 (26 of the sites yielded a net CO₂ sink) that was four times the amount previously estimated. The CO₂ sink peaked at an altitude of roughly 4,000 m, with the sink at lower and higher altitudes limited by a low carbon use efficiency and a cold, dry climate, respectively. The fixation of CO₂ in summer is more dependent on temperature than the loss of CO₂ than it is in the winter months, especially at higher altitudes. Consistently, 16 manipulative experiments and 18 model simulations showed that the fixation of CO₂ by plants will outpace the loss of CO₂ under a wetting–warming climate until the 2090s (178 to 318 Tg C y⁻¹). We therefore suggest that there is a plant-dominated negative feedback to climate warming on the Tibetan Plateau.

High-latitude and high-altitude regions have a harsh, cold climate that favors the storage of carbon (C) in the entire soil column, including the permafrost layer (1). This permafrost contains the largest store of C in terrestrial ecosystems (roughly 1,320 Pg C) (2). These cold ecosystems have experienced a much greater rate of climate warming (0.3 °C decade⁻¹) than the 0.12 °C decade⁻¹ of warming across the global land surface as a whole (3). Warming can result in the release of CO₂ from the permafrost layer (4–6) but can also lead to increased fixation of CO₂ by plants (7–9), which can relieve or even offset the loss of CO₂ from permafrost.The frozen soils in the high-latitude Arctic have experienced a warming rate of the permafrost ground temperature of 0.39 °C decade⁻¹ (10). This has affected the permafrost reserves of C, as well as plant growth (7), and may also provide a feedback to climate warming, although the direction and magnitude of this feedback are still highly uncertain (5, 8, 9). Tundra ecosystems might be a net CO₂ source as a result of the differential amplification of the C cycle under warming conditions (11)—that is, winter CO₂ losses are more temperature-sensitive than the uptake of CO₂ by plants during the growing season. A recent study showed that the Pan-Arctic permafrost is a net CO₂ source of 630 Tg C y⁻¹ (12), albeit with strong uncertainties (range: 15 to 975 Tg C y⁻¹). By contrast, a synthesis study and model simulations reported that the Arctic can act as a CO₂ sink at the ecosystem level (8, 13, 14), given that the uptake of CO₂ by plants is accelerating as a result of Arctic greening. These contrasting results reveal the large uncertainties in feedbacks to the present-day warming climate across Arctic permafrost ecosystems.High-altitude mountains also have vast regions of permafrost (15), but less is known about the CO₂ balance in these regions and its variation in the Earth’s currently changing climate. The Tibetan Plateau ranges from <3,000 to 8,844 m in altitude and is the largest region of alpine permafrost on Earth, contributing 10% to the global store of permafrost C (SI Appendix, Fig. S1) (16, 17). Continuous permafrost covers 84.2 million hectares of the Tibetan Plateau, discontinuous permafrost covers 15.9 million hectares, and isolated permafrost covers 23.0 million hectares (16, 17). The Tibetan Plateau has experienced climate warming of 0.3 °C decade⁻¹ in the atmospheric temperature and an increase in precipitation since the 1960s (18). In situ observations and simulations both suggest a significant increase in the ground temperature of 0.4 °C decade⁻¹ over the last 50 y, causing extensive thawing of the permafrost (19–21). High-resolution observations from remote sensing satellites and unmanned aerial vehicles have shown an acceleration in thaw slumps and thermokarst lakes (22, 23), although on relatively small scales (a few hundred meters to several kilometers). The thawing of permafrost may have affected the regional CO₂ balance by causing large losses of CO₂. In situ observations at thaw slumps, incubation experiments, and numerical modeling have all shown that permafrost is highly vulnerable to warming on the Tibetan Plateau (24–26). A recent model simulation predicted an 8% loss of C from permafrost soils by the end of the present century (25). However, repeated sampling surveys in the 2000s and 2010s suggested there has been an accumulation of soil C in these permafrost regions, largely due to increased plant growth (6), which strongly contradicts the conclusions of model simulations.Many studies, especially those using remote sensing observations, have shown that the Tibetan Plateau is becoming greener under the currently warming and wetting climate and reduced density of grazing animals (27–30), suggesting a higher input of plant C to the soils. These contrasting views—that is, the model-based projection of the loss of CO₂ from permafrost and the inventory-based accumulation of soil C and satellite-based observations of increased vegetation—mean that it is unclear whether the CO₂ balance has been altered by the changing climate on the Tibetan Plateau. The size of the net CO₂ sink of the alpine ecosystems on the Tibetan Plateau is not yet fully understood, and the large-scale patterns of CO₂ flux are still unknown. It is therefore a research priority to investigate how the release of CO₂ from alpine permafrost might affect the CO₂ balance on the Tibetan Plateau.Eddy covariance observations, owing to their high temporal resolution and landscape-scale coverage, are an ideal approach to the direct measurement of the exchange of CO₂. Eddy covariance observations can therefore be used to assess the status and variation of the CO₂ balance of permafrost regions; however, historically, the establishment of eddy covariance sites on the Tibetan Plateau has been rare and synthesis efforts limited. In this paper, we present an eddy covariance dataset covering 32 sites across the main alpine ecosystems of the Tibetan Plateau (Fig. 1, SI Appendix, Figs. S2 and S3, and Datasets S1 and S2), ranging from 3,000 to over 5,000 m in altitude during the period 2003 to 2019. We then analyze the drivers of the spatial pattern, with specific emphasis on the altitude-dependent pattern given the importance of altitudinal variation to high mountains like the Tibetan Plateau. The eddy covariance dataset was used to constrain a process-based model and project future changes in the CO₂ balance under the Representative Concentration Pathways (RCP) 2.6 to 8.5 scenarios using temperature and precipitation projections from 18 Coupled Model Intercomparison Project Phase 5 (CMIP5) models. To provide ground-based evidence about the feedback of the CO₂ balance of the alpine permafrost regions to warming, we also explored how the exchange of CO₂ reacts to changes in climate by examining 16 manipulated experiments across the Tibetan Plateau. By connecting the eddy covariance datasets, the process-based model, and the experiments, we aim to understand whether the Tibetan Plateau currently acts, and will continue to act, as a CO₂ sink under a rapidly changing climate.Open in a separate windowFig. 1.Location of the 32 eddy covariance observation sites on the Tibetan Plateau. The inset map shows the location of the Tibetan Plateau (denoted by the black line). The characters in each solid circle are the name of each eddy covariance site: BT, Batang; DX, Dangxiong; DS, Dashalong; QM, Mt Qomolangma (Everest); GL, Guoluo; HB, Haibei; LQ, La. Qinghai; HY, Haiyan; FH, Fenghuoshan; LJ, Lijiang; MZ, Muztag; MD, Maduo; NM, NamCo; NQ, Naqu; SL, Shule; SZ, Shenzha; TG, Tanggula; YK, Yakou; ZG, Zoige.     

Comparison of CO2 Separation Efficiency from Flue Gases Based on Commonly Used Methods and Materials

The comparison study of CO₂ removal efficiency from flue gases at low pressures and temperatures is presented, based on commonly used methods and materials. Our own experimental results were compared and analyzed for different methods of CO₂ removal from flue gases: absorption in a packed column, adsorption in a packed column and membrane separation on polymeric and ceramic membranes, as well as on the developed supported ionic liquid membranes (SILMs). The efficiency and competitiveness comparison of the investigated methods showed that SILMs obtained by coating of the polydimethylsiloxane (PDMS) membrane with 1-ethyl-3-methylimidazolium acetate ([Emim][Ac]) exhibit a high ideal CO₂/N₂ selectivity of 152, permeability of 2400 barrer and long term stability. Inexpensive and selective SILMs were prepared applying commercial membranes. Under similar experimental conditions, the absorption in aqueous Monoethanolamine (MEA) solutions is much faster than in ionic liquids (ILs), but gas and liquid flow rates in packed column sprayed with IL are limited due to the much higher viscosity and lower diffusion coefficient of IL. For CO₂ adsorption on activated carbons impregnated with amine or IL, only a small improvement in the adsorption properties was achieved. The experimental research was compared with the literature data to find a feasible solution based on commercially available methods and materials.