Climate sensitivity and response

Results from climate change simulations indicate a reasonably robust proportionality between global mean radiative forcing and global mean surface air temperature response. The "constant" of proportionality is a measure of the overall strength of climate feedback processes and hence of global climate sensitivity. Geographically, however, temperature response patterns are generally not proportional to, nor do they resemble, their parent forcing patterns. Temperature response patterns, nevertheless, exhibit a remarkable additivity whereby the sum of response patterns for different forcings closely resembles the response pattern for the sum of the forcings. The geographical distribution of contributions to the climate sensitivity/feedback are obtained diagnostically from simulations with the Canadian Centre for Climate Modelling and Analysis (CCCma) coupled global climate model (GCM). There is positive feedback over high-latitude oceans, over northern land areas, and over the equatorial Pacific. The remaining regions over oceans and tropical land areas exhibit negative feedback. The feedback results are decomposed into components associated with short-and longwave radiative processes and in terms of cloud-free atmosphere/surface and cloud feedbacks. While the geographic pattern of the feedbacks may generally be linked to local processes, all feedback processes display regions of both positive and negative values (except for the solar atmosphere/surface feedback associated with the retreat of ice and snow which is positive) and all vary from place to place so that there is no simple physical picture that operates everywhere. The stable geographical pattern of the feedback is a consequence of the balance between local physical processes rather than the dominance of a particular process. The feedback results indicate that, to first order, temperature response patterns are determined by the geographical pattern of local feedback processes. The feedback processes act to localize forcing changes and to generate temperature response patterns which depend firstly on the pattern of feedbacks and only secondarily on the pattern of the forcing. The geographical distribution of feedback processes can be regarded as a feature of the climate model (and by inference of the climate system) and not (or only comparatively weak) functions of forcing and climate state. An illustrative model is able to reproduce qualitatively the kinds of forcing/temperature response behavior seen in the CCCma GCM including the quasi-independence of forcing and response patterns, the additivity of temperature response patterns, and the resulting "non-constancy" of the global climate sensitivity.     

Transient response of net radiometers

Summary The response of a net radiometer to a sudden irradiation is shown to give generally a marked overshoot which during calibration is mostly overlooked. This overshoot also simulates a high speed of response. An improved design of net radiometer minimizes this effect and also gives a high sensitivity.

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Zusammenfassung Es wird gezeigt, daß ein Strahlungsbilanzmesser auf eine plötzliche Bestrahlung mit einem merklichen Überschwingen reagiert, welches während der Eichung meistens übersehen wird. Dieses Überschwingen täuscht auch eine kurze Ansprechzeit vor. Eine verbesserte Konstruktion eines Strahlungsbilanzmessers verringert diesen Effekt und gibt gleichzeitig eine hohe Empfindlichkeit.

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Résumé On a demonstré qu'un bilanmètre de rayonnement réagit à une exposition brusque par une élongation exagérée à laquelle on ne prend pas garde lors de l'étalonnage et qui réduit en apparence le temps de réaction. Une construction améliorée permet de diminuer cet effect et de fournir en outre une plus grande sensibilité.

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With 2 Figures     

Stratospheric response to chemical perturbations

The paper presents a coupled chemical-radiative one-dimensional model which is used to assess the steady-state and time-dependent composition and temperature changes in relation to the release in the atmosphere of chemicals such as CO₂, N₂O, CH₄, NO _x and chlorofluorocarbons.The model indicates that a doubling in CO₂ leads to an increase in temperature of 12.7 K near the stratopause and to an increase in total ozone of 3.3% with a local enhancement of 17% at 40 km altitude. Additional release of N₂O leads to an ozone reduction in the middle stratosphere. The reduction in the ozone column is predicted to be equal to 8.8% when the amount of N₂O is doubled. The chemical effect of CH₄ on ozone is particularly important in the troposphere. A doubling in the mixing ratio of this gas enhances the O₃ concentration by 11% at 5 km. The predicted increase of the ozone column is equal to 1.4%. A constant emission of CFCl₃ (230 kT/yr) and CF₂Cl₂ (300 kT/yr) leads to a steady-state reduction in the ozone column of 1.9% compared to the present-day situation. The effect of some uncertainties in the chemical scheme as well as the impact of a high chlorine perturbation are briefly discussed.Finally the results of a time dependent calculation assuming a realistic scenario for the emission of chemical species are presented and analyzed.     

The response of moving radiometers

The output of a radiometer passing over a field of varying emittance or reflectance will not, in general, provide a faithful reproduction of the variations. The space-weighted averaging effect of the radiometer's hemispherical view plus the distortion produced by the first-order response of the radiometer sensor will result in low-pass filtering of the data. By means of a simplified model of the moving radiometer system, this paper provides guidelines for the interpretation of information from such systems. Faithful reproduction requires instruments with a fast time constant, operating close to the surface with a relatively slow speed of translation.     

Modelling geomorphic response to climatic change

This paper develops a three-step thaw model to assess the impact of predicted warming on an ice-rich polar desert landscape in the Canadian high Arctic. Air temperatures are established for two climate scenarios, showing mean annual increases of 4.9 and 6.5°C. This leads to a lengthening of the summer thaw season by up to 26 days and increased thaw depths of 12–70 cm, depending on the thermal properties of the soil. Subsidence of the ground surface is the primary landscape response to warming and is shown to be a function of the amount and type of ground ice in various cryostratigraphic units. In areas of pore ice and thin ice lenses with a low density of ice wedges, subsidence may be as much as 32 cm. In areas with a high density of ice wedges, subsidence will be slightly higher at 34 cm. Where massive ice is present, subsidence will be greater than 1 m. Landscape response to new climate conditions can take up to 15 years, and may be as long as 50 years in certain cases.     

Lags in vegetation response to greenhouse warming

Fossil pollen in sediments documents vegetation responses to climatic changes in the past. Beech (Fagus grandifolia), with animal-dispersed seeds, moved across Lake Michigan or around its southern margin, becoming established in Wisconsin about 1000 years after populations were established in Michigan. Hemlock (Tsuga canadensis), with wind-dispersed seeds, colonized a 50,000 km² area in northern Michigan between 6000 and 5000 years ago. These tree species extended ranges northward at average rates of 20–25 km per century. To track climatic changes in the future, caused by the greenhouse effect, however, their range limit would need to move northward 100 km per °C warming, or about 300 km per century, an order of magnitude faster than range extension in the past. Yet range extension in the future would be less efficient than in the past, because advance disjunct colonies have been extirpated by human disturbance, and because the seed source is reduced due to reductions in tree populations following logging. Many species of trees may not be able to disperse rapidly enough to track climate, and woodland herbs, which have less efficient seed dispersal mechanisms, may be in danger of extinction.     

Transient response to well-mixed greenhouse gas changes

A change in CO₂ concentration induces a direct radiative forcing that modifies the planetary thermodynamic state, and hence the surface temperature. The infrared cooling, by assuming a constant temperature lapse-rate during the process, will be related to the surface temperature through the Stefan–Boltzmann law in a ratio proportional to the new infrared opacity. Other indirect effects, such as the water vapor and ice-albedo feedbacks, may amplify the system response. In the present paper, we address the question of how a global climate model with a mixed layer ocean responds to different rates of change of a well-mixed greenhouse gas such as CO₂. We provide evidence that different rates of CO₂ variation may lead to similar transient climates characterized by the same global mean surface temperature but different values of CO₂ concentration. Moreover, it is shown that, far from the bifurcation points, the model’s climate depends on the history of the radiative forcing displaying a hysteresis cycle that is neither static nor dynamical, but is related to the memory response of the model. Results are supported by the solutions of a zero-dimensional energy balance model.     

Deep-ocean heat uptake and equilibrium climate response

We integrate the coupled climate model ECHAM5/MPIOM to equilibrium under atmospheric CO₂ quadrupling. The equilibrium global-mean surface-temperature change is 10.8 K. The surface equilibrates within about 1,200 years, the deep ocean within 5,000 years. The impact of the deep ocean on the equilibrium surface-temperature response is illustrated by the difference between ECHAM5/MPIOM and ECHAM5 coupled with slab ocean model (ECHAM5/SOM). The equilibrium global-mean surface temperature response is 11.1 K in ECHAM5/SOM and is thus 0.3 K higher than in ECHAM5/MPIOM. ECHAM5/MPIOM shows less warming over the northern-hemisphere mid and high latitudes, but larger warming over the tropical ocean and especially over the southern-hemisphere high latitudes. ECHAM5/MPIOM shows similar polar amplification in both the Arctic and the Antarctic, in contrast to ECHAM5/SOM, which shows stronger polar amplification in the northern hemisphere. The southern polar warming in ECHAM5/MPIOM is greatly delayed by Antarctic deep-ocean warming due to convective and isopycnal mixing. The equilibrium ocean temperature warming under CO₂ quadrupling is around 8.0 K and is near-uniform with depth. The global-mean steric sea-level rise is 5.8 m in equilibrium; of this, 2.3 m are due to the deep-ocean warming after the surface temperature has almost equilibrated. This result suggests that the surface temperature change is a poor predictor for steric sea-level change in the long term. The effective climate response method described in Gregory et al. (2004) is evaluated with our simulation, which shows that their method to estimate the equilibrium climate response is accurate to within 10 %.     

IPCC AR6报告解读：气候系统对二氧化碳移除响应

IPCC AR6报告中控温1.5℃和2℃的低排放情景需要在21世纪中叶以后实现净负CO₂排放,这需要在很大程度上依赖CO₂移除措施。AR6对CO₂移除的主要评估结论如下：CO₂移除有潜力从大气中去除CO₂（高信度);如果CO₂移除量超过CO₂排放量,将实现净负CO₂排放,降低大气CO₂浓度,减缓海洋酸化（高信度);通过CO₂移除方法从大气中去除的CO₂会部分被海洋和陆地释放的CO₂抵消（非常高信度);如果净负CO₂排放可以实现并且持续,CO₂引起的全球升温趋势将会逐渐扭转,但是气候系统的其他变化（例如海平面升高）仍会在未来的几十年到千年尺度上持续（高信度);不同CO₂移除方法会对生物化学循环和气候产生广泛的影响,这些影响会加强或减弱CO₂移除的降温潜力,并且影响水资源、食物生产和生物多样性（高信度）。     

Particle size dependent response of aerosol counters

During an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (IAMAS-IUGG), 10 instruments for aerosol number concentration measurement were studied, covering a wide range of methods based on various different measuring principles. In order to investigate the detection limits of the instruments considered with respect to particle size, simultaneous number concentration measurements were performed for monodispersed aerosols with particle sizes ranging from 1.5 to 50 nm diameter and various compositions.The instruments considered show quite different response characteristics, apparently related to the different vapors used in the various counters to enlarge the particles to an optically detectable size. A strong dependence of the 50% cutoff diameter on the particle composition in correlation with the type of vapor used in the specific instrument was found. An enhanced detection efficiency for ultrafine hygroscopic sodium chloride aerosols was observed with water operated systems, an analogous trend was found for n-butanol operated systems with nonhygroscopic silver and tungsten oxide particles.     

IPCC AR6报告解读：气候系统对太阳辐射干预响应

IPCC第六次评估报告（AR6）第一工作组报告评估了太阳辐射干预（Solar radiation modification,SRM）对气候系统和碳循环的影响。在大幅度减排基础上,太阳辐射干预有潜力作为应对气候变化的备用措施。目前,对于太阳辐射干预气候影响的评估都是基于模式模拟结果。评估主要结论如下：太阳辐射干预可以在全球和区域尺度上抵消一部分温室气体增加造成的气候变化（高信度);但是太阳辐射干预无法在全球和区域尺度上完全抵消温室气体增加引起的气候变化（几乎确定);有可能通过适当的太阳辐射干预设计,同时实现多个温度变化减缓目标（中等信度);在高强度温室气体排放情景下,如果太阳辐射干预实施后突然终止,并且这种终止长时间持续,将会造成快速的气候变化（高信度);如果在减排和CO₂移除的情况下,太阳辐射干预的实施强度逐渐减小至零,将显著降低太阳辐射干预突然终止产生的快速气候变化风险（中等信度);太阳辐射干预会通过降温作用,促进陆地和海洋对大气CO₂的吸收（中等信度),但是太阳辐射干预无法缓解海洋酸化（高信度);太阳辐射干预对其他生物化学循环影响的不确定性大。由于对云-气溶胶-辐射过程的相互作用和微物理过程认知有限,目前对平流层气溶胶注入、海洋低云亮化、高层卷云变薄等太阳辐射干预方法的冷却潜力和气候效应的认知还有很大的不确定性。     

How weather impacts the forced climate response

The new interactive ensemble modeling strategy is used to diagnose how noise due to internal atmospheric dynamics impacts the forced climate response during the twentieth century (i.e., 1870?C1999). The interactive ensemble uses multiple realizations of the atmospheric component model coupled to a single realization of the land, ocean and ice component models in order to reduce the noise due to internal atmospheric dynamics in the flux exchange at the interface of the component models. A control ensemble of so-called climate of the twentieth century simulations of the Community Climate Simulation Model version 3 (CCSM3) are compared with a similar simulation with the interactive ensemble version of CCSM3. Despite substantial differences in the overall mean climate, the global mean trends in surface temperature, 500?mb geopotential and precipitation are largely indistinguishable between the control ensemble and the interactive ensemble. Large differences in the forced response; however, are detected particularly in the surface temperature of the North Atlantic. Associated with the forced North Atlantic surface temperature differences are local differences in the forced precipitation and a substantial remote rainfall response in the deep tropical Pacific. We also introduce a simple variance analysis to separately compare the variance due to noise and the forced response. We find that the noise variance is decreased when external forcing is included. In terms of the forced variance, we find that the interactive ensemble increases this variance relative to the control.     

Frequency response corrections for eddy correlation systems

Simplified expressions describing the frequency response of eddy correlation systems due to sensor response, path-length averaging, sensor separation and signal processing are presented. A routine procedure for estimating and correcting for the frequency response loss in flux and variance measurements is discussed and illustrated by application to the Institute of Hydrology's Hydra eddy correlation system.The results show that flux loss from such a system is typically 5 to 10% for sensible and latent heat flux, but can be much larger for momentum flux and variance measurements in certain conditions.A microcomputer program is included which, with little modification, can be used for estimating flux loss from other eddy correlation systems with different or additional sensors.     

Cultivating resilience by empirically revealing response diversity

Intensified climate and market turbulence requires resilience to a multitude of changes. Diversity reduces the sensitivity to disturbance and fosters the capacity to adapt to various future scenarios. What really matters is diversity of responses. Despite appeals to manage resilience, conceptual developments have not yet yielded a break-through in empirical applications. Here, we present an approach to empirically reveal the ‘response diversity’: the factors of change that are critical to a system are identified, and the response diversity is determined based on the documented component responses to these factors. We illustrate this approach and its added value using an example of securing food supply in the face of climate variability and change. This example demonstrates that quantifying response diversity allows for a new perspective: despite continued increase in cultivar diversity of barley, the diversity in responses to weather declined during the last decade in the regions where most of the barley is grown in Finland. This was due to greater homogeneity in responses among new cultivars than among older ones. Such a decline in the response diversity indicates increased vulnerability and reduced resilience. The assessment serves adaptive management in the face of both ecological and socio-economic drivers. Supplier diversity in the food retail industry in order to secure affordable food in spite of global price volatility could represent another application. The approach is, indeed, applicable to any system for which it is possible to adopt empirical information regarding the response by its components to the critical factors of variability and change. Targeting diversification in response to critical change brings efficiency into diversity. We propose the generic procedure that is demonstrated in this study as a means to efficiently enhance resilience at multiple levels of agrifood systems and beyond.     

Effective dynamic response of paired Gill anemometers

It is shown that the instrument transfer functions for the longitudinal and transverse components of wind measured by paired Gill anemometers are for practical purposes the same as for individual anemometers even when the mean wind direction is at some angle to the anemometers. However, the effective response time is a function of the relative wind direction, and appropriate values are given.     

Low-level wind response to mesoscale pressure systems

Observations are presented which show a strong correlation between low-level wind behaviour (e.g., rotation near the surface) and the passage of mesoscale pressure systems. The latter are associated with frontal transition zones, are dominated by a pressure-jump line and a mesoscale high pressure area, and produce locally large horizontal pressure gradients. The wind observations are simulated by specifying a time sequence of perturbation pressure gradient and subsequently solving the vertically-integrated momentum equations with appropriate initial conditions. Very good agreement is found between observed and calculated winds; in particular, (i) a 360 ° rotation in wind on passage of the mesoscale high; (ii) wind-shift lines produced dynamically by the pressure-jump line; (iii) rapid linear increase in wind speed on passage of the pressure jump.     

On the climate response to zero ozone

Although ozone appears in the Earth’s atmosphere in a small abundance, it plays a key role in the energy balance of the planet through its involvement in radiative processes. Its absorption of solar radiation leads to the temperature increase with height defining the tropopause and the stratosphere. Moreover, excluding water vapor, O₃ is the third most important contributor (after CO₂ and CH₄) to the greenhouse radiative forcing. Thus, the total removal of O₃ content in an Earth-like atmosphere may cause interesting response of the climate system that deserves further investigation. The present paper addresses this issue by means of a global climate model where the atmosphere is coupled with a passive ocean of a given depth. The model, after reaching the statistical equilibrium under present climate conditions, is perturbed by a sudden switch off of the O₃ content. Results obtained for the new equilibrium suggest that the model gets in a colder state mainly because of the water vapor content decrease. Most of the cooling occurs in the Southern Hemisphere while in the Northern Hemisphere the ice cap melts quite consistently. This process appears to be governed by the northward cross-equatorial heat transports induced by changes in the general circulation.     

Probability distributions for carbon emissions and atmospheric response

Probability distributions for carbon burning, atmospheric CO₂, and global average temperature are produced by time series calibration of models of utility optimization and carbon and heat balance using log-linear production functions. Population growth is used to calibrate a logistically evolving index of development that influences production efficiency. Energy production efficiency also includes a coefficient that decreases linearly with decreasing carbon intensity of energy production. This carbon intensity is a piecewise linear function of fossil carbon depletion. That function is calibrated against historical data and extrapolated by sampling a set of hypotheses about the impact on the carbon intensity of energy production of depleting fluid fossil fuel resources and increasing cumulative carbon emissions. Atmospheric carbon balance is determined by a first order differential equation with carbon use rates and cumulative carbon use as drivers. Atmospheric CO₂ is a driver in a similar heat balance. Periodic corrections are included where required to make residuals between data and model results indistinguishable from independently and identically distributed normal distributions according to statistical tests on finite Fourier power spectrum amplitudes and nearest neighbor correlations. Asymptotic approach to a sustainable non-fossil energy production is followed for a global disaggregation into a tropical/developing and temperate/more-developed region. The increase in the uncertainty of global average temperature increases nearly quadratically with the increase in the temperature from the present through the next two centuries.