Lessons from a high-CO2 world: an ocean view from ∼3 million years ago Climate of the Past DOI 10.5194/cp-16-1599-2020 17 September 2020 We examine the sea-surface temperature response to an interval of climate ~ 3.2 million years ago, when CO 2 concentrations were similar to today and the near future. Our geological data and climate models show that global mean sea-surface temperatures were 2.3 to 3.2 ºC warmer than pre-industrial climate, that the mid-latitudes and high latitudes warmed more than the tropics, and that the warming was particularly enhanced in the North Atlantic Ocean. Read more
A semi-empirical potential energy surface and line list for H216O extending into the near-ultraviolet Atmospheric Chemistry and Physics DOI 10.5194/acp-20-10015-2020 17 September 2020 Water vapour has a complex spectrum and absorbs from the microwave to the near-UV where it dissociates. There is limited knowledge of the absorption features in the near-UV, and there is a large disagreement for the available models and experiments. We created a new ab initio model that is in good agreement with observation at 363 nm. At lower wavelengths, our calculations suggest that the latest experiments overestimate absorption. This has implications for trace gas retrievals in the near-UV. Read more
Revisiting global satellite observations of stratospheric cirrus clouds Atmospheric Chemistry and Physics DOI 10.5194/acp-20-9939-2020 15 September 2020 Cirrus clouds appearing in the upper troposphere and lower stratosphere have important impacts on the radiation budget and climate change. We revisited global stratospheric cirrus clouds with CALIPSO and for the first time with MIPAS satellite observations. Stratospheric cirrus clouds related to deep convection are frequently detected in the tropics. At middle latitudes, MIPAS detects more than twice as many stratospheric cirrus clouds due to higher detection sensitivity. Read more
Groundwater storage dynamics in the world’s large aquifer systems fromGRACE: uncertainty and role of extreme precipitation Earth System Dynamics DOI 10.5194/esd-11-755-2020 15 September 2020 Recent assessments of the sustainability of global groundwater resources using the Gravity Recovery and Climate Experiment (GRACE) satellites assume that the underlying trends are linear. Here, we assess recent changes in groundwater storage (ΔGWS) in the world’s large aquifer systems using an ensemble of GRACE datasets and show that trends are mostly non-linear. Non-linearity in ΔGWS derives, in part, from the episodic nature of groundwater replenishment associated with extreme precipitation. Read more
Inconsistencies between chemistry–climate models and observed lower stratospheric ozone trends since 1998 Atmospheric Chemistry and Physics DOI 10.5194/acp-20-9737-2020 10 September 2020 Recent lower stratospheric ozone decreases remain unexplained. We show that chemistry–climate models are not generally able to reproduce mid-latitude ozone and water vapour changes. Our analysis of observations provides evidence that climate change may be responsible for the ozone trends. While model projections suggest that extratropical ozone should recover by 2100, our study raises questions about their efficacy in simulating lower stratospheric changes in this region. Read more
Climatic information archived in ice cores: impact of intermittency and diffusion on the recorded isotopic signal in Antarctica Climate of the Past DOI 10.5194/cp-16-1581-2020 10 September 2020 The isotopic composition in ice cores from Antarctica is usually interpreted as a temperature proxy. Using a forward model, we show how different the signal in ice cores and the actual climatic signal are. Precipitation intermittency and diffusion do indeed affect the archived signal, leading to the reshuffling of the signal which limits the ability to reconstruct high-resolution climatic variations with ice cores. Read more
Bipolar volcanic synchronization of abrupt climate change in Greenland and Antarctic ice cores during the last glacial period Climate of the Past DOI 10.5194/cp-16-1565-2020 8 September 2020 We identify signatures of large bipolar volcanic eruptions in Greenland and Antarctic ice cores during the last glacial period, which allows for a precise temporal alignment of the ice cores. Thereby the exact timing of unexplained, abrupt climatic changes occurring during the last glacial period can be determined in a global context. The study thus provides a step towards a full understanding of elements of the climate system that may also play an important role in the future. Read more
ESD Ideas: Global climate response scenarios for IPCC assessments Earth System Dynamics DOI 10.5194/esd-11-751-2020 8 September 2020 Policy making on climate change routinely employs socioeconomic scenarios to sample the uncertainty in future forcing of the climate system, but the Intergovernmental Panel on Climate Change has not employed similar discrete scenarios to sample the uncertainty in the global climate response. Here, we argue that to enable risk assessments and development of robust policies this gap should be addressed, and we propose a simple methodology. Read more
Effective radiative forcing and adjustments in CMIP6 models Atmospheric Chemistry and Physics DOI 10.5194/acp-20-9591-2020 3 September 2020 The spread in effective radiative forcing for both CO 2 and aerosols is narrower in the latest CMIP6 (Coupled Model Intercomparison Project) generation than in CMIP5. For the case of CO 2 it is likely that model radiation parameterisations have improved. Tropospheric and stratospheric radiative adjustments to the forcing behave differently for different forcing agents, and there is still significant diversity in how clouds respond to forcings, particularly for total anthropogenic forcing. Read more
Emergent constraints on transient climate response (TCR) and equilibrium climate sensitivity (ECS) from historical warming in CMIP5 and CMIP6 models Earth System Dynamics DOI 10.5194/esd-11-737-2020 3 September 2020 One of the key questions in climate science is how much more heating we will get for a given rise in carbon dioxide in the atmosphere. A new generation of models showed that this might be more than previously expected. Comparing the new models to observed temperature rise since 1970, we show that there is no need to revise the estimate upwards. Air pollution, whose effect on climate warming is poorly understood, stopped rising, allowing us to better constrain the greenhouse gas signal. Read more
Open weather and climate science in the digital era Geoscience Communication DOI 10.5194/gc-3-191-2020 1 September 2020 At the 14th IEEE International eScience Conference domain specialists and data and computer scientists discussed the road towards open weather and climate science. Open science offers manifold opportunities but goes beyond sharing code and data. Besides domain-specific technical challenges, we observed that the main challenges are non-technical and impact the system of science as a whole. Read more
A global analysis of climate-relevant aerosol properties retrieved from the network of Global AtmosphereWatch (GAW) near-surface observatories Atmospheric Measurement Techniques DOI 10.5194/amt-13-4353-2020 1 September 2020 The paper establishes the fiducial reference of the GAW aerosol network providing the fully characterized value chain to the provision of four climate-relevant aerosol properties from ground-based sites. Data from almost 90 stations worldwide are reported for a reference year, 2017, providing a unique and very robust view of the variability of these variables worldwide. Current gaps in the GAW network are analysed and requirements for the Global Climate Monitoring System are proposed. Read more
Anthropogenic climate change and glacier lake outburst flood risk: local and global drivers and responsibilities for the case of lake Palcacocha, Peru Natural Hazards and Earth System Sciences DOI 10.5194/nhess-20-2175-2020 27 August 2020 There is increasing interest and need to analyze the contribution of anthropogenic climate change to negative impacts of climate change. We study the case of glacial lake Palcacocha in Peru, which poses a significant flood risk to the city of Huaraz. We found that greenhouse gas emissions; strong urbanization processes without appropriate land use planning; and social, cultural, political, and institutional factors all contribute to the existing flood risk. Read more
The shared socio-economic pathway (SSP) greenhouse gas concentrations and their extensions to 2500 Geoscientific Model Development DOI 10.5194/gmd-13-3571-2020 27 August 2020 This study provides the future greenhouse gas (GHG) concentrations under the new set of so-called SSP scenarios (the successors of the IPCC SRES and previous representative concentration pathway (RCP) scenarios). The projected CO 2 concentrations range from 350 ppm for low-emission scenarios by 2150 to more than 2000 ppm under the high-emission scenarios. We also provide concentrations, latitudinal gradients, and seasonality for most of the other 42 considered GHGs. Read more
Rainfall intensification increases the contribution of rewetting pulses tosoil heterotrophic respiration Biogeosciences DOI 10.5194/bg-17-4007-2020 25 August 2020 Carbon dioxide is produced by soil microbes through respiration, which is particularly fast when soils are moistened by rain. Will respiration increase with future more intense rains and longer dry spells? With a mathematical model, we show that wetter conditions increase respiration. In contrast, if rainfall totals stay the same, but rain comes all at once after long dry spells, the average respiration will not change, but the contribution of the respiration bursts after rain will increase. Read more
An overview of and issues with sky radiometer technology and SKYNET Atmospheric Measurement Techniques DOI 10.5194/amt-13-4195-2020 25 August 2020 This paper overviews the progress in sky radiometer technology and the development of the network called SKYNET. It is found that the technology has produced useful on-site calibration methods, retrieval algorithms, and data analyses from sky radiometer observations of aerosol, cloud, water vapor, and ozone. The paper also discusses current issues of SKYNET to provide better information for the community. Read more
CloudRoots: integration of advanced instrumental techniques and processmodelling of sub-hourly and sub-kilometre land–atmosphere interactions Biogeosciences DOI 10.5194/bg-17-4375-2020 25 August 2020 The CloudRoots field experiment has obtained an open comprehensive observational data set that includes soil, plant, and atmospheric variables to investigate the interactions between a heterogeneous land surface and its overlying atmospheric boundary layer, including the rapid perturbations of clouds in evapotranspiration. Our findings demonstrate that in order to understand and represent diurnal variability, we need to measure and model processes from the leaf to the landscape scales. Read more
A monitoring system for spatiotemporal electrical self-potential measurements in cryospheric environments Geoscientific Instrumentation, Methods and Data Systems DOI 10.5194/gi-9-317-2020 20 August 2020 In times of global warming, permafrost is starting to degrade at alarming rates, requiring new and improved characterization approaches. We describe the design and test installation, as well as detailed data quality assessment, of a monitoring system used to capture natural electrical potentials in the subsurface. These self-potential signals are of great interest for the noninvasive investigation of water flow in the non-frozen or partially frozen subsurface. Read more
Revisiting the global hydrological cycle: is it intensifying? Hydrology and Earth System Sciences DOI 10.5194/hess-24-3899-2020 20 August 2020 We overview and retrieve a great amount of global hydroclimatic data sets. We improve the quantification of the global hydrological cycle, its variability and its uncertainties through the surge of newly available data sets. We test (but do not confirm) established climatological hypotheses, according to which the hydrological cycle should be intensifying due to global warming. We outline a stochastic view of hydroclimate, which provides a reliable means of dealing with its variability. Read more
Molecular understanding of new-particle formation from α-pinene between-50 and +25 ∘C Atmospheric Chemistry and Physics DOI 10.5194/acp-20-9183-2020 18 August 2020 Highly oxygenated organic compounds (HOMs) have been identified as key vapors involved in atmospheric new-particle formation (NPF). The molecular distribution, HOM yield, and NPF from α-pinene oxidation experiments were measured at the CLOUD chamber over a wide tropospheric-temperature range. This study shows on a molecular scale that despite the sharp reduction in HOM yield at lower temperatures, the reduced volatility counteracts this effect and leads to an overall increase in the NPF rate. Read more