AGW Observer

Observations of anthropogenic global warming

New research – Climate sensitivity, forcings, and feedbacks (August 8, 2016)

Posted by Ari Jokimäki on August 8, 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 Spectral Signature of Recent Climate Change (Brindley & Bantges, 2016)

Abstract: Spectrally resolved measurements of the Earth’s reflected shortwave (RSW) and outgoing longwave radiation (OLR) at the top of the atmosphere intrinsically contain the imprints of a multitude of climate relevant parameters. Here, we review the progress made in directly using such observations to diagnose and attribute change within the Earth system over the past four decades. We show how changes associated with perturbations such as increasing greenhouse gases are expected to be manifested across the spectrum and illustrate the enhanced discriminatory power that spectral resolution provides over broadband radiation measurements. Advances in formal detection and attribution techniques and in the design of climate model evaluation exercises employing spectrally resolved data are highlighted. We illustrate how spectral observations have been used to provide insight into key climate feedback processes and quantify multi-year variability but also indicate potential barriers to further progress. Suggestions for future research priorities in this area are provided.

Deep time evidence for climate sensitivity increase with warming (Shaffer et al. 2016)

Abstract: Future global warming from anthropogenic greenhouse gas emissions will depend on climate feedbacks, the effect of which is expressed by climate sensitivity, the warming for a doubling of atmospheric CO2 content. It is not clear how feedbacks, sensitivity, and temperature will evolve in our warming world, but past warming events may provide insight. Here we employ paleoreconstructions and new climate-carbon model simulations in a novel framework to explore a wide scenario range for the Paleocene-Eocene Thermal Maximum (PETM) carbon release and global warming event 55.8 Ma ago, a possible future warming analogue. We obtain constrained estimates of CO2 and climate sensitivity before and during the PETM and of the PETM carbon input amount and nature. Sensitivity increased from 3.3–5.6 to 3.7–6.5 K (Kelvin) into the PETM. When taken together with Last Glacial Maximum and modern estimates, this result indicates climate sensitivity increase with global warming.

Insights into Earth’s energy imbalance from multiple sources (Trenberth et al. 2016)

Abstract: The current Earth’s energy imbalance (EEI) can best be estimated from changes in ocean heat content (OHC), complemented by top-of-atmosphere (TOA) radiation measurements and an assessment of the small non-ocean components. Sustained observations from the Argo array of autonomous profiling floats enable near-global estimates of OHC since 2005, which reveal considerable cancellation of variations in the upper 300 m. An analysis of the monthly contributions to EEI from non-ocean (land and ice) using the CESM Large Ensemble reveals standard deviations of 0.3 to 0.4 W m-2 (global); largest values occur in August, but values are below 0.75 W m-2 >95% of the time. Global standard deviations of EEI of 0.64 W m-2 based on top-of-atmosphere observations therefore substantially constrain ocean contributions, given by the tendencies of OHC. Instead, monthly standard deviations of many Argo-based OHC tendencies are 6 to 13 W m-2 and non-physical fluctuations are clearly evident. We show that an ocean reanalysis with multi-variate dynamical data assimilation features much better agreement with TOA radiation, and 44% of the vertically-integrated short-term OHC trend for 2005-14 of 0.8±0.2 W m-2 (globally) occurs below 700 m depth. Largest warming occurs from 20 to 50°S, especially over the Southern Oceans, and near 40°N, in all ocean analyses. The EEI is estimated to be 0.9±0.3 W m-2 for 2005-2014.

Assessing the Radiative Effects of Global Ice Clouds Based on CloudSat and CALIPSO Measurements (Hong et al. 2016)

Abstract: Although it is well-established that cirrus warms the Earth, the radiative effect of the entire spectrum of ice clouds is not well understood. In this study, the role of all ice clouds in the Earth’s radiation budget is investigated by performing radiative transfer modeling using ice cloud properties retrieved from CloudSat and CALIPSO measurements as inputs. Results show that, for the 2008 period, the warming effect (~21.8 ± 5.4 W m-2) induced by ice clouds due to trapping longwave radiation exceeds their cooling effect (~-16.7 ± 1.7 W m-2) caused by shortwave reflection, resulting in a net warming effect (~5.1 ± 3.8 W m-2) globally on the earth-atmosphere system. The net warming is over 15 W m-2 in the tropical deep convective regions, whereas cooling occurs in the midlatitudes, which is less than 10 W m-2 in magnitude. Seasonal variations of ice cloud radiative effects are evident in the midlatitudes where the net effect changes from warming during winter to cooling during summer, whereas warming occurs all year round in the tropics. Ice cloud optical depth (τ) is shown to be an important factor in determining the sign and magnitude of the net radiative effect. Ice clouds with τ < 4.6 display a warming effect with the largest contributions from those with τ ~ 1.0. In addition, ice clouds cause vertically differential heating and cooling of the atmosphere, particularly with strong heating in the upper troposphere over the tropics. At Earth’s surface, ice clouds produce a cooling effect no matter how small the τ value is.

Giant natural fluctuation models and anthropogenic warming (Lovejoy et al. 2016)

Abstract: Explanations for the industrial epoch warming are polarized around the hypotheses of anthropogenic warming (AW) and Giant Natural Fluctuations (GNF’s). While climate sceptics have systematically attacked AW, up until now they have only invoked GNF’s. This has now changed with the publication by D. Keenan of a sample of 1000 series from stochastic processes purporting to emulate the global annual temperature since 1880. While Keenan’s objective was to criticize the IPCC’s trend uncertainty analysis (their assumption that residuals are only weakly correlated), for the first time it is possible to compare a stochastic GNF model with real data. Using Haar fluctuations, probability distributions and other techniques of time series analysis, we show that his model has unrealistically strong low frequency variability so that even mild extrapolations imply ice ages every ≈ 1000 years. The GNF model can easily be scientifically rejected.

Other papers

Constraining the low-cloud optical depth feedback at middle and high latitudes using satellite observations (Terai et al. 2016)

Assessing the Radiative Effects of Global Ice Clouds Based on CloudSat and CALIPSO Measurements (Hong et al. 2016)

Which way will the circulation shift in a changing climate? Possible nonlinearity of extratropical cloud feedbacks (Tandon & Cane, 2016)

Regional and global temperature response to anthropogenic SO2 emissions from China in three climate models (Kasoar et al. 2016)

Effective radiative forcing from historical land use change (Andrews et al. 2016)

Reassessing properties and radiative forcing of contrail cirrus using a climate model (Bock & Burkhardt, 2016)

Could the Pliocene constrain the equilibrium climate sensitivity? (Hargreaves & Annan, 2016)

Influence of snow cover changes on surface radiation and heat balance based on the WRF model (Yu et al. 2016)

A sensitivity study of the impact of dynamic vegetation on simulated future climate change over Southern Europe and the Mediterranean (Alo & Anagnostou, 2016)

A satellite-based 13-year climatology of net cloud radiative forcing over the Indian monsoon region (Saud et al. 2016)

Separating climate change signals into thermodynamic, lapse-rate and circulation effects: theory and application to the European summer climate (Kröner et al. 2016)

Early global radiation measurements: a review (Stanhill & Archiman, 2016)

Aerosol types and radiative forcing estimates over East Asia (Bhawar et al. 2016)

Solar irradiance observed at Summit, Greenland: Possible links to magnetic activity on short timescales (Frederick, 2016)

Limits to global and Australian temperature change this century based on expert judgment of climate sensitivity (Grose et al. 2016)

Indirect Forcing of Black carbon on Clouds over North East India (Panicker et al. 2016)

Contrasting radiation and soil heat fluxes in Arctic shrub and wet sedge tundra (Juszak et al. 2016)

Aerosol radiative effects under clear skies over Europe and their changes in the period of 2001–2012 (Bartók, 2016)

Review of Aerosol-Cloud Interactions: Mechanisms, Significance and Challenges (Fan et al. 2016)

Inference of Climate Sensitivity from Analysis of Earth’s Energy Budget (Forster, 2016)

Impact of absorbing aerosol deposition on snow albedo reduction over the southern Tibetan plateau based on satellite observations (Lee et al. 2016)

Spatiotemporal characteristics of ultraviolet radiation in recent 54 years from measurements and reconstructions over the Tibetan Plateau (Liu et al. 2016)

The whole-atmosphere response to changes in the Earth’s magnetic field from 1900 to 2000: an example of “top-down” vertical coupling (Cnossen et al. 2016)

Strong modification of stratospheric ozone forcing by cloud and sea-ice adjustments (Xia et al. 2016)

Evaluation of the Arctic surface radiation budget in CMIP5 models (Boeke & Taylor, 2016)

Climate Feedback Variance and the Interaction of Aerosol Forcing and Feedbacks (Gettelman et al. 2016)

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: