AGW Observer

Observations of anthropogenic global warming

Archive for August, 2016

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.

Highlights

The Spectral Signature of Recent Climate Change (Brindley & Bantges, 2016) http://link.springer.com/article/10.1007%2Fs40641-016-0039-5

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) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069243/abstract

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) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0339.1

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) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0799.1

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) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070428/abstract

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) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025233/abstract

Assessing the Radiative Effects of Global Ice Clouds Based on CloudSat and CALIPSO Measurements (Hong et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0799.1

Which way will the circulation shift in a changing climate? Possible nonlinearity of extratropical cloud feedbacks (Tandon & Cane, 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3301-6

Regional and global temperature response to anthropogenic SO2 emissions from China in three climate models (Kasoar et al. 2016) http://www.atmos-chem-phys.net/16/9785/2016/

Effective radiative forcing from historical land use change (Andrews et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3280-7

Reassessing properties and radiative forcing of contrail cirrus using a climate model (Bock & Burkhardt, 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025112/abstract

Could the Pliocene constrain the equilibrium climate sensitivity? (Hargreaves & Annan, 2016) http://www.clim-past.net/12/1591/2016/

Influence of snow cover changes on surface radiation and heat balance based on the WRF model (Yu et al. 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1856-0

A sensitivity study of the impact of dynamic vegetation on simulated future climate change over Southern Europe and the Mediterranean (Alo & Anagnostou, 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4833/abstract

A satellite-based 13-year climatology of net cloud radiative forcing over the Indian monsoon region (Saud et al. 2016) http://www.sciencedirect.com/science/article/pii/S0169809516301983

Separating climate change signals into thermodynamic, lapse-rate and circulation effects: theory and application to the European summer climate (Kröner et al. 2016) http://rd.springer.com/article/10.1007%2Fs00382-016-3276-3

Early global radiation measurements: a review (Stanhill & Archiman, 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4826/abstract

Aerosol types and radiative forcing estimates over East Asia (Bhawar et al. 2016) http://www.sciencedirect.com/science/article/pii/S1352231016305489

Solar irradiance observed at Summit, Greenland: Possible links to magnetic activity on short timescales (Frederick, 2016) http://www.sciencedirect.com/science/article/pii/S1364682616301626

Limits to global and Australian temperature change this century based on expert judgment of climate sensitivity (Grose et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3269-2

Indirect Forcing of Black carbon on Clouds over North East India (Panicker et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/qj.2878/abstract

Contrasting radiation and soil heat fluxes in Arctic shrub and wet sedge tundra (Juszak et al. 2016) http://www.biogeosciences.net/13/4049/2016/

Aerosol radiative effects under clear skies over Europe and their changes in the period of 2001–2012 (Bartók, 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4821/abstract

Review of Aerosol-Cloud Interactions: Mechanisms, Significance and Challenges (Fan et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JAS-D-16-0037.1

Inference of Climate Sensitivity from Analysis of Earth’s Energy Budget (Forster, 2016) http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-060614-105156

Impact of absorbing aerosol deposition on snow albedo reduction over the southern Tibetan plateau based on satellite observations (Lee et al. 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1860-4

Spatiotemporal characteristics of ultraviolet radiation in recent 54 years from measurements and reconstructions over the Tibetan Plateau (Liu et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2015JD024378/abstract

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) http://onlinelibrary.wiley.com/doi/10.1002/2016JD024890/abstract

Strong modification of stratospheric ozone forcing by cloud and sea-ice adjustments (Xia et al. 2016) http://www.atmos-chem-phys.net/16/7559/2016/

Evaluation of the Arctic surface radiation budget in CMIP5 models (Boeke & Taylor, 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025099/abstract

Climate Feedback Variance and the Interaction of Aerosol Forcing and Feedbacks (Gettelman et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0151.1

Advertisements

Posted in AGW evidence, Climate claims, Climate science | Leave a Comment »

New research – past climate (August 4, 2016)

Posted by Ari Jokimäki on August 4, 2016

Some of the latest papers on past climate 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.

Highlights

Reconstructing Earth’s surface temperature over the past 2000 years: the science behind the headlines (Smerdon & Pollack, 2016) http://onlinelibrary.wiley.com/doi/10.1002/wcc.418/abstract

Abstract: The last quarter century spans the publication of the first assessment report of the Intergovernmental Panel on Climate Change in 1990 and the latest report published in 2013–2014. The five assessment reports appearing over that interval reveal a marked increase in the number of paleoclimate studies addressing the climate of the last 2000 years (the Common Era). An important focus of this work has been on reconstruction of hemispheric and global temperatures. Several early studies in this area generated considerable scientific and public interest, and were followed by high-profile and sometimes vitriolic debates about the magnitude of temperature changes over all or part of the Common Era and their comparison to 20th- and 21st-century global temperature increases due to increasing levels of atmospheric greenhouse gases. Behind the more public debates, however, several consistent themes of scientific inquiry have developed to better characterize climate variability and change over the Common Era. These include attempts to collect more climate proxy archives and understand the signals they contain, improve the statistical methods used to estimate past temperature variability from proxies and their associated uncertainties, and to compare reconstructed temperature variability and change with climate model simulations. All of these efforts are driving a new age of research on the climate of the Common Era that is developing more cohesive and collaborative investigations into the dynamics of climate on time scales of decades to centuries, and an understanding of the implications for modeled climate projections of the future.

Flat meridional temperature gradient in the early Eocene in the subsurface rather than surface ocean (Ho & Laepple, 2016) http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2763.html

Abstract: The early Eocene (49–55 million years ago) is a time interval characterized by elevated surface temperatures and atmospheric CO2, and a flatter-than-present latitudinal surface temperature gradient. The multi-proxy-derived flat temperature gradient has been a challenge to reproduce in model simulations, especially the subtropical warmth at the high-latitude surface oceans, inferred from the archaeal lipid-based palaeothermometry, TEXH86. Here we revisit the TEXH86 interpretation by analysing a global collection of multi-proxy temperature estimates from sediment cores spanning millennia to millions of years. Comparing the variability between proxy types, we demonstrate that the present TEXH86 interpretation overestimates the magnitude of past climate changes on all timescales. We attribute this to an inappropriate calibration, which reflects subsurface ocean but is calibrated to the sea surface, where the latitudinal temperature gradient is steeper. Recalibrating the proxy to the temperatures of subsurface ocean, where the signal is probably formed, yields colder TEXH86 -temperatures and latitudinal gradient consistent with standard climate model simulations of the Eocene climate, invalidating the apparent, extremely warm polar sea surface temperatures. We conclude that there is a need to reinterpret TEXH86 -inferred marine temperature records in the literature, especially for reconstructions of past warm climates that rely heavily on this proxy as reflecting subsurface ocean.

The improbable but unexceptional occurrence of megadrought clustering in the American West during the Medieval Climate Anomaly (Coats et al. 2016) http://iopscience.iop.org/article/10.1088/1748-9326/11/7/074025/meta

Abstract: The five most severe and persistent droughts in the American West (AW) during the Common Era occurred during a 450 year period known as the Medieval Climate Anomaly (MCA—850–1299 C.E.). Herein we use timeseries modeling to estimate the probability of such a period of hydroclimate change occurring. Clustering of severe and persistent drought during an MCA-length period occurs in approximately 10% of surrogate timeseries that were constructed to have the same characteristics as a tree-ring derived estimate of AW hydroclimate variability between 850 and 2005 C.E. Periods of hydroclimate change like the MCA are thus expected to occur in the AW, although not frequently, with a recurrence interval of approximately 11 000 years. Importantly, a shift in mean hydroclimate conditions during the MCA is found to be necessary for drought to reach the severity and persistence of the actual MCA megadroughts. This result has consequences for our understanding of the atmosphere-ocean dynamics underlying the MCA and a persistently warm Atlantic Multidecadal Oscillation is suggested to have played an important role in causing megadrought clustering during this period.

Reconstruction of early Holocene Thermal Maximum temperatures using present vertical distribution of conifers in the Pannon region (SE Central Europe) (Molnár & Végvári, 2016) http://hol.sagepub.com/content/early/2016/07/19/0959683616658528.abstract

Abstract: Palaeoclimatic reconstruction is a main subject of palaeoecology, clarifying fossil palaeoenvironmental patterns. Our study provides a macroecological approach to reconstruct the mean annual temperature (MAT) of the Pannon region at the early Holocene Thermal Maximum (HTM, warmest period of the Holocene), based on the absence of forest-dwelling conifers in the North Hungarian Mountains and their presence in the surrounding Carpathians on the same altitude. We suppose that the HTM was enough warm to drive conifers to extinction from elevations between 900 and 1100 m a.s.l. in the relatively isolated N-Hungarian Mts. Conversely, HTM still allowed the survival of residual dwarf pine (Pinus mugo) stands on the isolated peaks of the West Transylvanian Mountains between 1600 and 1800 m a.s.l. Our study provides an estimate for the value of MAT of HTM of Pannon region with an interval of 0.4°C, relying on macroecological considerations. We calculate the temperature of the HTM 1.3–1.7°C warmer than the present temperature. This method can be used in a general sense, if conditions meet the requirements of the method even in horizontal cases, with area isolates of climate-sensitive species.

Low atmospheric CO2 levels during the Little Ice Age due to cooling-induced terrestrial uptake (Rubino et al. 2016) http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2769.html

Abstract: Low atmospheric carbon dioxide (CO2) concentration during the Little Ice Age has been used to derive the global carbon cycle sensitivity to temperature. Recent evidence confirms earlier indications that the low CO2 was caused by increased terrestrial carbon storage. It remains unknown whether the terrestrial biosphere responded to temperature variations, or there was vegetation re-growth on abandoned farmland. Here we present a global numerical simulation of atmospheric carbonyl sulfide concentrations in the pre-industrial period. Carbonyl sulfide concentration is linked to changes in gross primary production and shows a positive anomaly during the Little Ice Age. We show that a decrease in gross primary production and a larger decrease in ecosystem respiration is the most likely explanation for the decrease in atmospheric CO2 and increase in atmospheric carbonyl sulfide concentrations. Therefore, temperature change, not vegetation re-growth, was the main cause of the increased terrestrial carbon storage. We address the inconsistency between ice-core CO2 records from different sites measuring CO2 and δ13CO2 in ice from Dronning Maud Land (Antarctica). Our interpretation allows us to derive the temperature sensitivity of pre-industrial CO2 fluxes for the terrestrial biosphere (γL = −10 to −90 Pg C K−1), implying a positive climate feedback and providing a benchmark to reduce model uncertainties.

Other papers

Destabilization of glacial climate by the radiative impact of Atlantic Meridional Overturning Circulation disruptions (Galbraith et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069846/abstract

The role of El Niño in the global energy redistribution: a case study in the mid-Holocene (Saint-Lu et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3266-5

The last interglacial climate: comparing direct and indirect impacts of insolation changes (Pedersen et al. 2016) http://rd.springer.com/article/10.1007%2Fs00382-016-3274-5

Co-evolution of oceans, climate, and the biosphere during the ‘Ordovician Revolution’: A review (Algeo et al. 2016) http://www.sciencedirect.com/science/article/pii/S0031018216301559

Are Karakoram temperatures out of phase compared to hemispheric trends? (Asad et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3273-6

Correlation between climate and grain harvest fluctuations and the dynastic transitions and prosperity in China over the past two millennia (Yin et al. 2016) http://hol.sagepub.com/content/early/2016/07/20/0959683616646186.abstract

Influence of external forcings on abrupt millennial-scale climate changes: a statistical modelling study (Mitsui & Crucifix, 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3235-z

The influence of Southern Ocean surface buoyancy forcing on glacial-interglacial changes in the global deep ocean stratification (Sun et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070058/abstract

Strong effects of tropical ice-sheet coverage and thickness on the hard snowball Earth bifurcation point (Liu et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3278-1

Reorganization of the North Atlantic Oscillation during early Holocene deglaciation (Wassenburg et al. 2016) http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2767.html

An extended and higher-resolution record of climate and land use from stalagmite MC01 from Macal Chasm, Belize, revealing connections between major dry events, overall climate variability, and Maya sociopolitical changes (Akers et al. 2016) http://www.sciencedirect.com/science/article/pii/S0031018216302425

Coexisting responses in tree-ring δ13C to high-latitude climate variability under elevated CO2: A critical examination of climatic effects and systematic discrimination rate changes (Helama et al. 2016) http://www.sciencedirect.com/science/article/pii/S0168192316303021

Strong mid-depth warming and weak radiocarbon imprints in the equatorial Atlantic during Heinrich 1 and Younger Dryas (Weldeab et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016PA002957/abstract

April–August temperatures in the Czech Lands, 1499–2015, reconstructed from grape-harvest dates (Možný et al. 2016) http://www.clim-past.net/12/1421/2016/

North Atlantic summer storm tracks over Europe dominated by internal variability over the past millennium (Gagen et al. 2016) http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2752.html

Extreme storms during the last 6500 years from lagoonal sedimentary archives in the Mar Menor (SE Spain) (Dezileau et al. 2016) http://www.clim-past.net/12/1389/2016/

Climatic effects and impacts of the 1815 eruption of Mount Tambora in the Czech Lands (Brázdil et al. 2016) http://www.clim-past.net/12/1361/2016/

Posted in Climate science | Leave a Comment »

New research – hydrosphere (August 3, 2016)

Posted by Ari Jokimäki on August 3, 2016

Some of the latest papers on hydrosphere (oceans, lakes, ponds, rivers, streams, etc.) 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.

Highlights

Comparison of Global Precipitation Estimates across a Range of Temporal and Spatial Scales (Gehne et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0618.1

Abstract: Characteristics of precipitation estimates for rate and amount from three global High-resolution precipitation products (HRPPs), four global Climate Data Records (CDRs), and four reanalyses are compared. All data sets considered have at least daily temporal resolution. Estimates of global precipitation differ widely from one product to the next, with some differences likely due to differing goals in producing the estimates. HRPPs are intended to produce the best snapshot of the precipitation estimate locally. CDRs of precipitation emphasize homogeneity over instantaneous accuracy. Precipitation estimates from global reanalyses are dynamically consistent with the large scale circulation but tend to compare poorly to rain gauge estimates since they are forecast by the reanalysis system and precipitation is not assimilated. Regional differences among the estimates in the means and variances are as large as the means and variances, respectively. Even with similar monthly totals, precipitation rates vary significantly among the estimates. Temporal correlations among data sets are large at annual and daily time scales, suggesting that compensating bias errors at annual and random errors at daily time scales dominate the differences. However, the signal to noise ratio at intermediate (monthly) time scales can be large enough to result in high correlations overall. It is shown that differences on annual time scales and continental regions are around 0.8mm/d, which corresponds to 23W m−2. These wide variations in the estimates, even for global averages, highlight the need for better constrained precipitation products in the future.

Stable reconstruction of Arctic sea level for the 1950–2010 period (Svendsen et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JC011685/abstract

Abstract: Reconstruction of historical Arctic sea level is generally difficult due to the limited coverage and quality of both tide gauge and altimetry data in the area. Here a strategy to achieve a stable and plausible reconstruction of Arctic sea level from 1950 to today is presented. This work is based on the combination of tide gauge records and a new 20-year reprocessed satellite altimetry derived sea level pattern. Hence the study is limited to the area covered by satellite altimetry (68ºN and 82ºN). It is found that timestep cumulative reconstruction as suggested by Church and White (2000) may yield widely variable results and is difficult to stabilize due to the many gaps in both tide gauge and satellite data. A more robust sea level reconstruction approach is to use datum adjustment of the tide gauges in combination with satellite altimetry, as described by (Ray and Douglas, 2011). In this approach, a datum-fit of each tide gauges is used and the method takes into account the entirety of each tide gauge record. This makes the Arctic sea level reconstruction much less prone to drifting.

From our reconstruction, we found that the Arctic mean sea level trend is around 1.5 mm +/- 0.3 mm/y for the period 1950 to 2010, between 68ºN and 82ºN. This value is in good agreement with the global mean trend of 1.8 +/- 0.3 mm/y over the same period as found by Church and White (2004).

Lake Vanda: A sentinel for climate change in the McMurdo Sound Region of Antarctica (Castendyk et al. 2016) http://www.sciencedirect.com/science/article/pii/S092181811530014X

Abstract: Lake Vanda is a perennially ice-covered, meromictic, endorheic lake located in the McMurdo Dry Valleys of Antarctica, and an exceptional sentinel of climate change within the region. Lake levels rose 15 m over the past 68 years in response to climate-driven variability in ice-cover sublimation, meltwater production, and annual discharge of the Onyx River, the main source of water to the lake. Evidence from a new bathymetric map and water balance model combined with annual growth laminations in benthic mats suggest that the most recent filling trend began abruptly 80 years ago, in the early 1930s. This change increased lake volume by > 50%, triggered the formation of a new, upper, thermohaline convection cell, and cooled the lower convection cell cooled by at least 2 °C and the bottom-most waters by at > 4 °C. Additionally, the depth of the deep chlorophyll a maximum rose by > 2 m, and deep-growing benthic algal mats declined while shallow benthic mats colonized freshly inundated areas. We attribute changes in hydrology to regional variations in air flow related to the strength and position of the Amundsen Sea Low (ASL) pressure system which have increased the frequency of down-valley, föhn winds associated with surface air temperature warming in the McMurdo Dry Valleys. The ASL has also been implicated in the recent warming of the Antarctic Peninsula, and provides a common link for climate-related change on opposite sides of the continent. If this trend persists, Lake Vanda should continue to rise and cool over the next 200 years until a new equilibrium lake level is achieved. Most likely, future lake rise will lead to isothermal conditions not conducive to thermohaline convection, resulting in a drastically different physical, biogeochemical, and biological structure than observed today.

Ocean acidification in the subpolar North Atlantic: rates and mechanisms controlling pH changes (García-Ibáñez et al. 2016) http://www.biogeosciences.net/13/3701/2016/

Abstract: Repeated hydrographic sections provide critically needed data on and understanding of changes in basin-wide ocean CO2 chemistry over multi-decadal timescales. Here, high-quality measurements collected at twelve cruises carried out along the same track between 1991 and 2015 have been used to determine long-term changes in ocean CO2 chemistry and ocean acidification in the Irminger and Iceland basins of the North Atlantic Ocean. Trends were determined for each of the main water masses present and are discussed in the context of the basin-wide circulation. The pH has decreased in all water masses of the Irminger and Iceland basins over the past 25 years with the greatest changes in surface and intermediate waters (between −0.0010 ± 0.0001 and −0.0018 ± 0.0001 pH units yr-1). In order to disentangle the drivers of the pH changes, we decomposed the trends into their principal drivers: changes in temperature, salinity, total alkalinity (AT) and total dissolved inorganic carbon (both its natural and anthropogenic components). The increase in anthropogenic CO2 (Cant) was identified as the main agent of the pH decline, partially offset by AT increases. The acidification of intermediate waters caused by Cant uptake has been reinforced by the aging of the water masses over the period of our analysis. The pH decrease of the deep overflow waters in the Irminger basin was similar to that observed in the upper ocean and was mainly linked to the Cant increase, thus reflecting the recent contact of these deep waters with the atmosphere.

Uncertainty in the Himalayan energy–water nexus: estimating regional exposure to glacial lake outburst floods (Schwanghart et al. 2016) http://iopscience.iop.org/article/10.1088/1748-9326/11/7/074005/meta

Abstract: Himalayan water resources attract a rapidly growing number of hydroelectric power projects (HPP) to satisfy Asia’s soaring energy demands. Yet HPP operating or planned in steep, glacier-fed mountain rivers face hazards of glacial lake outburst floods (GLOFs) that can damage hydropower infrastructure, alter water and sediment yields, and compromise livelihoods downstream. Detailed appraisals of such GLOF hazards are limited to case studies, however, and a more comprehensive, systematic analysis remains elusive. To this end we estimate the regional exposure of 257 Himalayan HPP to GLOFs, using a flood-wave propagation model fed by Monte Carlo-derived outburst volumes of >2300 glacial lakes. We interpret the spread of thus modeled peak discharges as a predictive uncertainty that arises mainly from outburst volumes and dam-breach rates that are difficult to assess before dams fail. With 66% of sampled HPP are on potential GLOF tracks, up to one third of these HPP could experience GLOF discharges well above local design floods, as hydropower development continues to seek higher sites closer to glacial lakes. We compute that this systematic push of HPP into headwaters effectively doubles the uncertainty about GLOF peak discharge in these locations. Peak discharges farther downstream, in contrast, are easier to predict because GLOF waves attenuate rapidly. Considering this systematic pattern of regional GLOF exposure might aid the site selection of future Himalayan HPP. Our method can augment, and help to regularly update, current hazard assessments, given that global warming is likely changing the number and size of Himalayan meltwater lakes.

Other papers

Temporal and spatial variability of rainfall over Greece (Markonis et al. 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1878-7

The marine hydrological cycle: the Ocean’s floods and droughts (Gordon, 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070279/abstract

The Contribution of Glacial Isostatic Adjustment to Projections of Sea Level Change Along the Atlantic and Gulf Coasts of North America (Love et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016EF000363/abstract

Modeled ecohydrological responses to climate change at seven small watersheds in the northeastern U.S (Pourmokhtarian et al. 2016) http://onlinelibrary.wiley.com/doi/10.1111/gcb.13444/abstract

Data-model comparison of temporal variability in long-term time series of large-scale soil moisture (Verrot & Destouni, 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025209/abstract

February drying in southeast Brazil and the Australian monsoon: Global mechanism for a regional rainfall feature (Kelly & Mapes, 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0838.1

Monotonic trends in spatio-temporal distribution and concentration of monsoon precipitation (1901–2002), West Bengal, India (Chatterjee et al. 2016) http://www.sciencedirect.com/science/article/pii/S0169809516301880

The Curious Nature of the Hemispheric Symmetry of the Earth’s Water and Energy Balances (Stephens et al. 2016) http://rd.springer.com/article/10.1007%2Fs40641-016-0043-9

Aragonite saturation states and pH in western Norwegian fjords: seasonal cycles and controlling factors, 2005–2009 (Omar et al. 2016) http://www.ocean-sci.net/12/937/2016/

Elevation change and the vulnerability of Rhode Island (USA) salt marshes to sea-level rise (Raposa et al. 2016) http://link.springer.com/article/10.1007%2Fs10113-016-1020-5

Precipitation sensitivity to warming estimated from long island records (Polson et al. 2016) http://iopscience.iop.org/article/10.1088/1748-9326/11/7/074024/meta

Stomatal response to humidity and CO2 implicated in recent decline in U.S. evaporation (Rigden & Salvucci, 2016) http://onlinelibrary.wiley.com/doi/10.1111/gcb.13439/abstract

International energy trade impacts on water resource crises: an embodied water flows perspective (Zhang et al. 2016) http://iopscience.iop.org/article/10.1088/1748-9326/11/7/074023/meta

Statistical analyses of potential evapotranspiration changes over the period 1930–2012 in the Nile River riparian countries (Onyutha, 2016) http://www.sciencedirect.com/science/article/pii/S0168192316302805

The influence from the shrinking cryosphere and strengthening evopotranspiration on hydrologic process in a cold basin, Qilian Mountains (Zongxing et al. 2016) http://www.sciencedirect.com/science/article/pii/S0921818115301508

Enhanced summer convective rainfall at Alpine high elevations in response to climate warming (Giorgi et al. 2016) http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2761.html

Assessing the impact of vertical land motion on 20th century global mean sea level estimates (Hamlington et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JC011747/abstract

No observed effect of ocean acidification on nitrogen biogeochemistry in a summer Baltic Sea plankton community (Paul et al. 2016) http://www.biogeosciences.net/13/3901/2016/

Snowmelt Rate Dictates Streamflow (Barnhart et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069690/abstract

Impacts of open-ocean deep convection in the Weddell Sea on coastal and bottom water temperature (Wang et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3244-y

Intensification of upwelling along Oman coast in a Warming Scenario (Praveen et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069638/abstract

Ocean acidification affects marine chemical communication by changing structure and function of peptide signalling molecules (Roggatz et al. 2016) http://onlinelibrary.wiley.com/doi/10.1111/gcb.13354/abstract

Posted in Climate science, Global warming effects | Leave a Comment »

 
%d bloggers like this: