AGW Observer

Observations of anthropogenic global warming

New research – climate sensitivity, forcings, and feedbacks (September 22, 2016)

Posted by Ari Jokimäki on September 22, 2016

Some of the latest papers on climate sensitivity, forcings, and feedbacks are shown below. First a few highlighted papers with abstracts and then a list of some other papers. If this subject interests you, be sure to check also the other papers – they are by no means less interesting than the highlighted ones.


The Effects of Ocean Heat Uptake on Transient Climate Sensitivity (Rose & Rayborn, 2016)

Abstract: Transient climate sensitivity tends to increase on multiple timescales in climate models subject to an abrupt CO2 increase. The interdependence of radiative and ocean heat uptake processes governing this increase are reviewed. Heat uptake tends to be spatially localized to the subpolar oceans, and this pattern emerges rapidly from an initially uniform distribution. Global climatic impact of heat uptake is studied through the lens of the efficacy concept and a linear systems perspective in which responses to individual climate forcing agents are additive. Heat uptake can be treated as a slowly varying forcing on the atmosphere and surface, whose efficacy is strongly determined by its geographical pattern. An illustrative linear model driven by simple prescribed uptake patterns demonstrates the emergence of increasing climate sensitivity as a consequence of the slow decay of high-efficacy subpolar heat uptake. Evidence is reviewed for the key role of shortwave cloud feedbacks in setting the high efficacy of ocean heat uptake and thus in increasing climate sensitivity. A causal physical mechanism is proposed, linking subpolar heat uptake to a global-scale increase in lower-tropospheric stability. It is shown that the rate of increase in estimated inversion strength systematically slows as heat uptake decays. Variations in heat uptake should therefore manifest themselves as differences in low cloud feedbacks.

Understanding Climate Feedbacks and Sensitivity Using Observations of Earth’s Energy Budget (Loeb et al. 2016)

Abstract: While climate models and observations generally agree that climate feedbacks collectively amplify the surface temperature response to radiative forcing, the strength of the feedback estimates varies greatly, resulting in appreciable uncertainty in equilibrium climate sensitivity. Because climate feedbacks respond differently to different spatial variations in temperature, short-term observational records have thus far only provided a weak constraint for climate feedbacks operating under global warming. Further complicating matters is the likelihood of considerable time variation in the effective global climate feedback parameter under transient warming. There is a need to continue to revisit the underlying assumptions used in the traditional forcing-feedback framework, with an emphasis on how climate models and observations can best be utilized to reduce the uncertainties. Model simulations can also guide observational requirements and provide insight on how the observational record can most effectively be analyzed in order to make progress in this critical area of climate research.

Insights from a Refined Decomposition of Cloud Feedbacks (Zelinka et al. 2016)

Abstract: Decomposing cloud feedback into components due to changes in several gross cloud properties provides valuable insights into its physical causes. Here we present a refined decomposition that separately considers changes in free tropospheric and low cloud properties, better connecting feedbacks to individual governing processes and avoiding ambiguities present in a commonly used decomposition. It reveals that three net cloud feedback components are robustly nonzero: positive feedbacks from increasing free tropospheric cloud altitude and decreasing low cloud cover and a negative feedback from increasing low cloud optical depth. Low cloud amount feedback is the dominant contributor to spread in net cloud feedback but its anticorrelation with other components damps overall spread. The ensemble mean free tropospheric cloud altitude feedback is roughly 60% as large as the standard cloud altitude feedback because it avoids aliasing in low cloud reductions. Implications for the “null hypothesis” climate sensitivity from well-understood and robustly simulated feedbacks are discussed.

Rapid systematic assessment of the detection and attribution of regional anthropogenic climate change (Stone & Hansen, 2016)

Abstract: Despite being a well-established research field, the detection and attribution of observed climate change to anthropogenic forcing is not yet provided as a climate service. One reason for this is the lack of a methodology for performing tailored detection and attribution assessments on a rapid time scale. Here we develop such an approach, based on the translation of quantitative analysis into the “confidence” language employed in recent Assessment Reports of the Intergovernmental Panel on Climate Change. While its systematic nature necessarily ignores some nuances examined in detailed expert assessments, the approach nevertheless goes beyond most detection and attribution studies in considering contributors to building confidence such as errors in observational data products arising from sparse monitoring networks. When compared against recent expert assessments, the results of this approach closely match those of the existing assessments. Where there are small discrepancies, these variously reflect ambiguities in the details of what is being assessed, reveal nuances or limitations of the expert assessments, or indicate limitations of the accuracy of the sort of systematic approach employed here. Deployment of the method on 116 regional assessments of recent temperature and precipitation changes indicates that existing rules of thumb concerning the detectability of climate change ignore the full range of sources of uncertainty, most particularly the importance of adequate observational monitoring.

One Year of Downwelling Spectral Radiance Measurements from 100 to 1400 cm−1 at Dome-Concordia: Results in Clear Conditions (Rizzi et al. 2016)

Abstract: The present work examines downwelling radiance spectra measured at the ground during 2013 by a Far Infrared Fourier Transform Spectrometer at Dome-C, Antarctica. A tropospheric backscatter and depolarization Lidar is also deployed at same site and a radiosonde system is routinely operative. The measurements allow characterization of the water vapor and clouds infrared properties in Antarctica under all sky conditions. In this paper we specifically discuss cloud detection and the analysis in clear sky condition, required for the discussion of the results obtained in cloudy conditions. Firstly, the paper discusses the procedures adopted for the quality control of spectra acquired automatically. Then it describes the classification procedure used to discriminate spectra measured in clear-sky from cloudy conditions. Finally a selection is performed and 66 clear cases, spanning the whole year, are compared to simulations. The computation of layer molecular optical depth is performed with line-by-line techniques and a convolution to simulate the REFIR-PAD measurements; the downwelling radiance for selected clear cases is computed with a state-of-the-art adding-doubling code. The mean difference over all selected cases between simulated and measured radiance is within experimental error for all the selected micro-windows except for the negative residuals found for all micro-windows in the range 200 to 400 cm−1, with largest values around 295.1 cm−1. The paper discusses possible reasons for the discrepancy and identifies the incorrect magnitude of the water vapor total absorption coefficient as the cause of such large negative radiance bias below 400 cm−1.

Other papers

Dependence of global radiative feedbacks on evolving patterns of surface heat fluxes (Rugenstein et al. 2016)

Understanding the varied influence of mid-latitude jet position on clouds and cloud-radiative effects in observations and global climate models (Grise & Medeiros, 2016)

Effect of land cover change on snow free surface albedo across the continental United States (Wickham et al. 2016)

Forced response and internal variability of summer climate over western North America (Kamae et al. 2016)

Detection and attribution of climate change at regional scale: case study of Karkheh river basin in the west of Iran (Zohrabi et al. 2016)

Atmospheric lifetimes, infrared absorption spectra, radiative forcings and global warming potentials of NF3 and CF3CF2Cl (CFC-115) (Totterdill et al. 2016)

A long-term study of aerosol–cloud interactions and their radiative effect at the Southern Great Plains using ground-based measurements (Sena et al. 2016)

Detection of dimming/brightening in Italy from homogenized all-sky and clear-sky surface solar radiation records and underlying causes (1959–2013) (Manara et al. 2016)

Effects of 20–100 nm particles on liquid clouds in the clean summertime Arctic (Leaitch et al. 2016)

Assessment of the first indirect radiative effect of ammonium-sulfate-nitrate aerosols in East Asia (Han et al. 2016)

Sensitivity of precipitation extremes to radiative forcing of greenhouse gases and aerosols (Lin et al. 2016)

Global climate forcing of aerosols embodied in international trade (Lin et al. 2016)

Reprocessing of HIRS Satellite Measurements from 1980-2015: Development Towards a Consistent Decadal Cloud Record (Menzel et al. 2016)

Radiative Forcing from Anthropogenic Sulfur and Organic Emissions Reaching the Stratosphere (Yu et al. 2016)

Near miss: the importance of the natural atmospheric CO2 concentration to human historical evolution (Archer, 2016)

Long-Term Variations of Noctilucent Clouds at ALOMAR (Fiedler et al. 2016)

Estimating Arctic sea-ice shortwave albedo from MODIS data (Qu et al. 2016)

Surface albedo raise in the South American Chaco: Combined effects of deforestation and agricultural changes (Houspanossian et al. 2016)

New Observational Evidence for a Positive Cloud Feedback that Amplifies the Atlantic Multidecadal Oscillation (Bellomo et al. 2016)

Surface water and heat exchange comparison between alpine meadow and bare land in a permafrost region of the Tibetan Plateau (You et al. 2016)

foF2 vs Solar Indices for the Rome station: looking for the best general relation which is able to describe the anomalous minimum between cycles 23 and 24 (Perna & Pezzopane, 2016)

Comparison of Methods: Attributing the 2014 record European temperatures to human influences (Uhe et al. 2016)

Relevance of long term time – series of atmospheric parameters at a mountain observatory to models for climate change (Kancírová et al. 2016)

An energy balance perspective on regional CO2-induced temperature changes in CMIP5 models (Räisänen, 2016)

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