Results Of Climate Model Simulations Research Articles

A sedimentary lipid biomarker record of Holocene temperature variations and drought events in northern China

Holocene hydroclimate changes are crucial not only for predicting future climate changes, but also for understanding their impacts on ancient societies. However, our knowledge about severe drought events in East Asia during the Holocene is largely fragmentary and the pattern of temperature changes is still uncertain. Here, we, for the first time, present high-resolution quantitative records of temperature and drought events in northern China throughout the Holocene from a well-dated loess-paleosol sequence (Weinan) on the southern Chinese Loess Plateau (CLP). Our inferred temperatures, derived from glycerol dialkyl glycerol tetraethers (GDGTs), indicate that the early-to-mid Holocene experienced warm conditions, with temperatures ranging from ∼17.7 to 20.2 °C. This was followed by a cooler late Holocene, which contrasts with the results of climate model simulations. In addition, our hydroclimate record reveals that severe drought conditions occurred during both the early and late Holocene. These intensified drought events coincide with the demise of several Chinese dynasties. We propose that the colder climate during the late Holocene led to a strengthening of the East Asian winter monsoon and a weakening of the East Asian summer monsoon over northern China, as well as the southward shift of the Intertropical Convergence Zone (ITCZ), causing more severe drought conditions during the late Holocene compared to the early Holocene. Our results extend the East Asian Holocene climate records, highlighting the importance of understanding how hydroclimate extremes may have impacted human civilization in East Asia.

Az antropogén éghajlatváltozás hatásainak becslése és elemzése a Ráckevei (Soroksári)-Dunán

Anthropogenic climate change in Hungary is already having direct and indirect effect on surface and near-surface waters by increasing the length of summer heat waves and dry periods, and by changing the amount and distribution of precipitation within the year. The Ráckeve (Soroksár) Danube branch (RSD) and its surrounding area are extremely exposed to the climatic conditions. Therefore, it is essential to determine the tendency of the changes, as well as to understand the complexity of the problems arising as a result of the effects of climate change. Our analyses confirm that climate change can be detected in the area of the RSD in recent decades. The results of climate model simulations show that the climate vulnerability of the region may continue to increase in the future without any appropriate interventions. Climate models are the most important tool to examine future changes; they provide indispensable help in mitigating the negative effects of climate change and in developing environmental and economic strategies. Based on our examination of the extreme weather events of RSD, the escalation of the impact processes can be expected in the future. In order to quantify the climatic effects on ecologically important organisms, as well as on the quality of the water, climate indicators were produced. They provide information on the current and future climate conditions of the area of the RSD, as well as on meteorological variables, which affect the state of RSD. In order to identify the hydrological processes affecting the RSD, climate analyses were also performed for the study area including a part of the Danube catchment. Based on the determined impacts, we made suggestions for the implementation of the most important interventions.

Using expert elicitation to strengthen future regional climate information for climate services

Climate change knowledge can inform regional and local adaptation decisions. However, estimates of future climate are uncertain and methods for assessing uncertainties typically rely on the results of climate model simulations, which are constrained by the quality of assumptions used in model experiments and the limitations of available models. To strengthen scientific knowledge for climate services and climate change adaptation decisions, we explore the use of structured expert elicitation to assess future regional climate change. Using the Lower Yangtze region in China as a case study, we elicit judgements from six experts on future changes in temperature and precipitation as well as uncertainty sources, and compare it with climate model outputs from the Couple Model Intercomparison Project phase 5 (CMIP5). We find high consensus amongst experts that the Lower Yangtze region will be warmer in the coming decades, albeit with differences in the magnitude of change. There is less consensus about the direction and magnitude of future precipitation change. Compared with CMIP5 climate model outputs, experts provide similar or narrower uncertainty ranges for temperature change and very different uncertainty ranges for precipitation. Experts considered additional factors (e.g. model credibility, observations, theory and paleo-climatic evidence) and uncertainties not usually represented in conventional modelling approaches. We argue that, in context of regional climate information provision, expert-elicited judgements can characterise less predictable, or less explored, elements of the climate system and expert-elicited reasoning provides additional information and knowledge that is absent from modelling approaches. We discuss the value in bringing together multiple lines of evidence, arguing that expert elicited information can complement model information to strengthen regional climate change knowledge and help in building dialogue between climate experts and regional stakeholders, as part of a more complete climate service.

Climate Conditions on the Tibetan Plateau During the Last Glacial Maximum and Implications for the Survival of Paleolithic Foragers

Environmental conditions on the Tibetan Plateau (TP) during the last glacial maximum (LGM) are poorly known. Existing studies of environmental proxies and climate model simulations are contradictory, with interpretations varying between cold-dry and cold-wet environmental conditions which differentially influenced lake volumes, loess deposition and vegetation communities across the TP. Genetic and archaeological studies suggest anatomically modern paleolithic foragers initially occupied the TP between 60 and 30 ka, and may have seasonally occupied the TP during the LGM. Hence, a better understanding for LGM environmental conditions is needed in order to estimate whether paleolithic foragers could have survived on the TP during the extreme LGM cold stage. Here we report the investigation of lacustrine sediments and beach deposits within two paleoshorelines around Dagze Co on the southern TP, ∼22 and ∼42 m higher than the present lake level. Optical age estimates suggest the sediments were deposited during the LGM and mid-Holocene, respectively. TraCE-21 climate model simulation results suggest that net annual LGM precipitation in the Dagze Co basin was lower than the mid-Holocene, but about the same as that of the past 1,000 years. Combining the optical age estimates with TraCE-21 and CAM4 climate model simulation results, we deduce that increased summer precipitation and glacier meltwater supply, combined with decreased lake surface evaporation, produced LGM lake levels ∼22 m higher than present. We also synthesized paleoenvironmental records reported across the TP spanning the LGM. This synthesis suggests that the LGM climate in the northern TP was cold and dry, but that some of the southern TP was cold and wet. These relatively wetter LGM conditions in the southern TP may have favored the growth of cold-resistant plants which, in turn, may have supported larger herbivore populations, and provided food for paleolithic foragers. We conclude that seasonal or short-term human occupation of the TP during the LGM was thus more likely in the southern TP than in the north.

Spectrally Dependent CLARREO Infrared Spectrometer Calibration Requirement for Climate Change Detection.

Detecting climate trends of atmospheric temperature, moisture, cloud, and surface temperature requires accurately calibrated satellite instruments such as the Climate Absolute Radiance and Reflectivity Observatory (CLARREO). Wielicki et al. have studied the CLARREO measurement requirements for achieving climate change accuracy goals in orbit. Our study further quantifies the spectrally dependent IR instrument calibration requirement for detecting trends of atmospheric temperature and moisture profiles. The temperature, water vapor, and surface skin temperature variability and the associated correlation time are derived using Modern Era Retrospective-Analysis for Research and Applications (MERRA) and European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis data. The results are further validated using climate model simulation results. With the derived natural variability as the reference, the calibration requirement is established by carrying out a simulation study for CLARREO observations of various atmospheric states under all-sky. We derive a 0.04 K (k=2, or 95% confidence) radiometric calibration requirement baseline using a spectral fingerprinting method. We also demonstrate that the requirement is spectrally dependent and some spectral regions can be relaxed due to the hyperspectral nature of the CLARREO instrument. We further discuss relaxing the requirement to 0.06 K (k=2) based on the uncertainties associated with the temperature and water vapor natural variability and relatively small delay in time-to-detect for trends relative to the baseline case. The methodology used in this study can be extended to other parameters (such as clouds and CO2) and other instrument configurations.

The G4Foam Experiment: global climate impacts of regional ocean albedo modification

Abstract. Reducing insolation has been proposed as a geoengineering response to global warming. Here we present the results of climate model simulations of a unique Geoengineering Model Intercomparison Project Testbed experiment to investigate the benefits and risks of a scheme that would brighten certain oceanic regions. The National Center for Atmospheric Research CESM CAM4-Chem global climate model was modified to simulate a scheme in which the albedo of the ocean surface is increased over the subtropical ocean gyres in the Southern Hemisphere. In theory, this could be accomplished using a stable, nondispersive foam, comprised of tiny, highly reflective microbubbles. Such a foam has been developed under idealized conditions, although deployment at a large scale is presently infeasible. We conducted three ensemble members of a simulation (G4Foam) from 2020 through to 2069 in which the albedo of the ocean surface is set to 0.15 (an increase of 150 %) over the three subtropical ocean gyres in the Southern Hemisphere, against a background of the RCP6.0 (representative concentration pathway resulting in +6 W m−2 radiative forcing by 2100) scenario. After 2069, geoengineering is ceased, and the simulation is run for an additional 20 years. Global mean surface temperature in G4Foam is 0.6 K lower than RCP6.0, with statistically significant cooling relative to RCP6.0 south of 30° N. There is an increase in rainfall over land, most pronouncedly in the tropics during the June–July–August season, relative to both G4SSA (specified stratospheric aerosols) and RCP6.0. Heavily populated and highly cultivated regions throughout the tropics, including the Sahel, southern Asia, the Maritime Continent, Central America, and much of the Amazon experience a statistically significant increase in precipitation minus evaporation. The temperature response to the relatively modest global average forcing of −1.5 W m−2 is amplified through a series of positive cloud feedbacks, in which more shortwave radiation is reflected. The precipitation response is primarily the result of the intensification of the southern Hadley cell, as its mean position migrates northward and away from the Equator in response to the asymmetric cooling.

Fast and slow climate responses to CO2 and solar forcing: A linear multivariate regression model characterizing transient climate change

AbstractClimate change in response to a change in external forcing can be understood in terms of fast response to the imposed forcing and slow feedback associated with surface temperature change. Previous studies have investigated the characteristics of fast response and slow feedback for different forcing agents. Here we examine to what extent that fast response and slow feedback derived from time‐mean results of climate model simulations can be used to infer total climate change. To achieve this goal, we develop a multivariate regression model of climate change, in which the change in a climate variable is represented by a linear combination of its sensitivity to CO2 forcing, solar forcing, and change in global mean surface temperature. We derive the parameters of the regression model using time‐mean results from a set of HadCM3L climate model step‐forcing simulations, and then use the regression model to emulate HadCM3L‐simulated transient climate change. Our results show that the regression model emulates well HadCM3L‐simulated temporal evolution and spatial distribution of climate change, including surface temperature, precipitation, runoff, soil moisture, cloudiness, and radiative fluxes under transient CO2 and/or solar forcing scenarios. Our findings suggest that temporal and spatial patterns of total change for the climate variables considered here can be represented well by the sum of fast response and slow feedback. Furthermore, by using a simple 1‐D heat‐diffusion climate model, we show that the temporal and spatial characteristics of climate change under transient forcing scenarios can be emulated well using information from step‐forcing simulations alone.

Changes of western European heat wave characteristics projected by the CMIP5 ensemble

We investigate heat waves defined as periods of at least 3 consecutive days of extremely high daily maximum temperature affecting at least 30 % of western Europe. This definition has been chosen to select heat waves that might impact western European electricity supply. Even though not all such heat waves threaten it, the definition allows to identify a sufficient number of events, the strongest being potentially harmful. The heat waves are characterised by their duration, spatial extent, intensity and severity. The heat wave characteristics are calculated for historical and future climate based on results of climate model simulations conducted during the 5th Phase of the Coupled Model Intercomparison Project (CMIP5). The uncertainty of future anthropogenic forcing is taken into account by analysing results for the Representative Concentration Pathway scenarios RCP2.6, RCP4.5 and RCP8.5. The historical simulations are evaluated against the EOBS gridded station data. The CMIP5 ensemble median captures well the observed mean heat wave characteristics. However, no model simulates a heat wave as severe as observed during August 2003. Under future climate conditions, the heat waves become more frequent and have higher mean duration, extent and intensity. The ensemble spread is larger than the scenario uncertainty. The shift of the temperature distribution is more important for the increase of the cumulative heat wave severity than the broadening of the temperature distribution. However, the broadening leads to an amplification of the cumulative heat wave severity by a factor of 1.7 for RCP4.5 and 1.5 for RCP8.5.

Statistical precipitation downscaling for small-scale hydrological impact investigations of climate change

summary Impact investigations of climate change on urban drainage require projections to be made on shortduration precipitation extremes. The relevant time scales can be as low as 10 min, which requires strong statistical downscaling of climate model simulation results. In this research, two sets of methods have been suggested and tested based on Belgian data. The first set makes direct use of the precipitation results of the climate models. They involve computation of quantile perturbations on extreme precipitation intensities, and the tested assumption that the same perturbations hold for daily and sub-daily time scales. The second set of methods is based on weather typing, and accounts for the low accuracy of daily precipitation results in current climate modelling. In these methods, climate model outputs on pressure (atmospheric circulation) are used to obtain precipitation estimates from analogue days in the past. Different criteria for defining analogue days have been tested. The weather typing methods have been further advanced accounting for the fact that precipitation change does not only depend on change in atmospheric circulation, but also on temperature rise. Results have been investigated as changes to precipitation intensity–duration–frequency (IDF) relationships. It is shown that both the quantileperturbation and advanced weather typing based methods allow precipitation biases in climate model simulation results to be largely corrected. Both types of methods moreover produce similar short-duration changes in precipitation extremes, which gives some credibility to the downscaled impacts. The corresponding changes in IDF statistics show that the extreme precipitation quantiles typically used for design of urban drainage systems, can increase up to 30% by the end of this century. Those changes mean that sewer surcharge or flooding would occur about twice more frequently than in the present climate (if no other environmental or management changes are accounted for). This would have a significant impact on future urban water management and planning.

PC2: A prognostic cloud fraction and condensation scheme. II: Climate model simulations

AbstractA prognostic cloud fraction and prognostic condensate scheme (PC2) has been developed for the Met Office Unified Model. A companion paper discussed the motivation for a new scheme and described its formulation in detail. In this paper we describe the results of climate model simulations, concentrating on the mechanisms by which the cloud and condensate predicted by the model change between the Control and new scheme. We demonstrate that the detrainment of condensate from the convection scheme directly into the large scale, as parametrized in the PC2 scheme, produces improved simulations of deep tropical cloud. We also show that the unphysical strong link between cloud fraction and condensed water content that is present in the Control scheme has been broken by using PC2, but that it is still challenging to produce optically thin cloud in a large‐scale model. Shallow convection proves to be a difficult cloud type to parametrize using a prognostic scheme, although the PC2 scheme performs well. The use of increased vertical resolution, in both the Control and PC2, improved the simulation of cloud when compared to observations. © Crown Copyright 2008. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.

Effects of warmer world scenarios on hydrologic inputs to Lake Mälaren, Sweden and implications for nutrient loads

A simple, rapid, and flexible modelling approach was applied to explore the impacts of climate change on hydrologic inputs and consequent implications for nutrient loading to Lake Malaren, Sweden using a loading function model (GWLF). The first step in the process was to adapt the model for use in a large and complex Swedish catchment. We focused on the Galten basin with four rivers draining into the western region of Malaren. The catchment model was calibrated and tested using long-term historical data for river discharge and dissolved nutrients (N, P). Then multiple regional climate model simulation results were downscaled to the local catchment level, and used to simulate possible hydrological and nutrient loading responses to warmer world scenarios. Climate change projections for the rivers of Galten basin show profound changes in the timing of discharge and nutrient delivery due to increased winter precipitation and earlier snow melt. Impacts on total annual discharge and load are minimal, but the alteration in river flow regime and the timing of nutrient delivery for future climate scenarios is strikingly different from historical conditions.

Nuclear winter revisited with a modern climate model and current nuclear arsenals: Still catastrophic consequences

Twenty years ago, the results of climate model simulations of the response to smoke and dust from a massive nuclear exchange between the superpowers could be summarized as “nuclear winter,” with rapid temperature, precipitation, and insolation drops at the surface that would threaten global agriculture for at least a year. The global nuclear arsenal has fallen by a factor of three since then, but there has been an expansion of the number of nuclear weapons states, with additional states trying to develop nuclear arsenals. We use a modern climate model to reexamine the climate response to a range of nuclear wars, producing 50 and 150 Tg of smoke, using moderate and large portions of the current global arsenal, and find that there would be significant climatic responses to all the scenarios. This is the first time that an atmosphere‐ocean general circulation model has been used for such a simulation and the first time that 10‐year simulations have been conducted. The response to the 150 Tg scenario can still be characterized as “nuclear winter,” but both produce global catastrophic consequences. The changes are more long‐lasting than previously thought, however, because the new model, National Aeronautics and Space Administration Goddard Institute for Space Studies ModelE, is able to represent the atmosphere up to 80 km, and simulates plume rise to the middle and upper stratosphere, producing a long aerosol lifetime. The indirect effects of nuclear weapons would have devastating consequences for the planet, and continued nuclear arsenal reductions will be needed before the threat of nuclear winter is removed from the Earth.

Extremely high temperatures in France at the end of the century

Power plant construction requires anticipation to achieve a liable dimensioning on the long functioning time of the installation. In the present climate change context, dimensioning towards extremely high temperature for installations intended to run until the 2070s or later implies an evaluation of plausible extreme values at this time scale. This study is devoted to such an estimation for France, using both observation series and climate model simulation results. The climate model results are taken from the European PRUDENCE (Prediction of Regional scenarios and Uncertainties for Defining European Climate change risks and Effects) project database of regional climate change scenarios for Europe. Comparison of high summer temperature distributions given by observations and climate models under current climate conditions, conducted using Generalized Extreme Value distribution, reveals that only a few models are able to correctly reproduce it. For these models, climate change under IPCC A2 and B2 scenarios leads to differences in the variability of high values, whose proportion has an important impact on future 100-year return levels.