AGW Observer

Observations of anthropogenic global warming

New research from last week 29/2011

Posted by Ari Jokimäki on July 25, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Systematic depth errors found in XBTs

Direct Evidence of a Changing Fall-rate Bias in XBTs Manufactured During 1986–2008 – DiNezio & Goni (2011) “We present direct evidence of systematic depth errors consistent with a fall-rate bias in 52 temperature profiles collected using eXpendable BathyThermographs (XBTs). The profiles were collected using the same recording system and under the same ocean conditions, but with XBTs manufactured during years 1986, 1990, 1991, 1995, and 2008. The depth errors are estimated by comparing each XBT profile with a co-located profile obtained from Conductivity Temperature Depth (CTD) casts using a methodology that unambiguously separates depth errors from temperature errors. According to the manufacture date of the probes, the XBT fall-rate error has changed from (−3.77 ± 0.57) % of depth in 1986 to (−1.05 ± 1.34) % of depth in 2008. The year dependence of the fall-rate bias can be identified with statistical significance (1σ) below 500 m, where the effect of the fall-rate bias is larger. This result is the first direct evidence of changes in the XBT fall-rate characteristics. Therefore, for the 1986–2008 period, the hypothesis that the XBT errors are due to a time-varying fall-rate bias, as hypothesized by Wijffels et al. (2008), cannot be rejected. Additional implications for current efforts to correct the historical temperature profile database are discussed.” Pedro N. DiNezio and Gustavo J. Goni, Journal of Atmospheric and Oceanic Technology 2011 ; e-View, doi: 10.1175/JTECH-D-11-00017.1. [Full text]

Model study on black carbon global situation

Black carbon in the atmosphere and snow, from pre-industrial times until present – Skeie et al. (2011) “The distribution of black carbon (BC) in the atmosphere and the deposition of BC on snow surfaces since pre-industrial time until present are modelled with the Oslo CTM2 model. The model results are compared with observations including recent measurements of BC in snow in the Arctic. The global mean burden of BC from fossil fuel and biofuel sources increased during two periods. The first period, until 1920, is related to increases in emissions in North America and Europe, and the last period after 1970 are related mainly to increasing emissions in East Asia. Although the global burden of BC from fossil fuel and biofuel increases, in the Arctic the maximum atmospheric BC burden as well as in the snow was reached in 1960s, with a slight reduction thereafter. The global mean burden of BC from open biomass burning sources has not changed significantly since 1900. With current inventories of emissions from open biomass sources, the modelled burden of BC in snow and in the atmosphere north of 65° N is small compared to the BC burden of fossil fuel and biofuel origin. From the concentration changes radiative forcing time series due to the direct aerosol effect as well as the snow-albedo effect is calculated for BC from fossil fuel and biofuel. The calculated radiative forcing in 2000 for the direct aerosol effect is 0.35 W m−2 and for the snow-albedo effect 0.016 W m−2 in this study. Due to a southward shift in the emissions there is an increase in the lifetime of BC as well as an increase in normalized radiative forcing, giving a change in forcing per unit of emissions of 26 % since 1950.” Skeie, R. B., Berntsen, T., Myhre, G., Pedersen, C. A., Ström, J., Gerland, S., and Ogren, J. A., Atmos. Chem. Phys., 11, 6809-6836, doi:10.5194/acp-11-6809-2011, 2011. [Full text]

Spatially and seasonally complex medieval climate anomaly in Europe

The medieval climate anomaly in Europe: comparison of the summer and annual mean signals in two reconstructions and in simulations with data assimilation – Goosse et al. (2011) “The spatial pattern and potential dynamical origin of the Medieval Climate Anomaly (MCA, around 1000 AD) in Europe are assessed with two recent reconstructions and simulations constrained to follow those reconstructions by means of paleoclimate data assimilation. The simulations employ a climate model of intermediate complexity (LOVECLIM). The data assimilation technique is based on a particle filter using an ensemble of 96 simulations. The peak winter (and annual mean) warming during the MCA, in our analyses, is found to be strongest at high latitudes, associated with strengthened mid-latitude westerlies. Summer warmth, by contrast, is found to be greatest in southern Europe and the Mediterranean Sea, associated with reduced westerlies and strengthened southerly winds off North Africa. The results of our analysis thus underscore the complexity of the spatial and seasonal structure of the MCA in Europe.” Hugues Goosse, Joel Guiot, Michael E. Mann, Svetlana Dubinkina and Yoann Sallaz-Damaz, Global and Planetary Change, doi:10.1016/j.gloplacha.2011.07.002.

Red Sea is warming rapidly

Abrupt warming of the Red Sea – Raitsos et al. (2011) “Coral reef ecosystems, often referred to as “marine rainforests,” concentrate the most diverse life in the oceans. Red Sea reef dwellers are adapted in a very warm environment, fact that makes them vulnerable to further and rapid warming. The detection and understanding of abrupt temperature changes is an important task, as ecosystems have more chances to adapt in a slowly rather than in a rapid changing environment. Using satellite derived sea surface and ground based air temperatures, it is shown that the Red Sea is going through an intense warming initiated in the mid-90s, with evidence for an abrupt increase after 1994 (0.7°C difference pre and post the shift). The air temperature is found to be a key parameter that influences the Red Sea marine temperature. The comparisons with Northern Hemisphere temperatures revealed that the observed warming is part of global climate change trends. The hitherto results also raise additional questions regarding other broader climatic impacts over the area.” Raitsos, D. E., I. Hoteit, P. K. Prihartato, T. Chronis, G. Triantafyllou, and Y. Abualnaja (2011), Geophys. Res. Lett., 38, L14601, doi:10.1029/2011GL047984.

Atmospheric methane changes over western Pacific

Interannual variability and trends in atmospheric methane over the western Pacific from 1994 to 2010 – Terao et al. (2011) “We present an analysis of interannual variability (IAV) and trends in atmospheric methane (CH4) mixing ratios over the western Pacific between 55°N and 35°S from 1994 to 2010. Observations were made by the Center for Global Environmental Research (CGER) of the National Institute for Environmental Studies (NIES), using voluntary observation ships sailing between Japan and Australia/New Zealand and between Japan and North America, sampling background maritime air quasi-monthly (∼10 times per year) with high latitudinal resolution. In addition, simulations of CH4 were performed using NIES atmospheric transport model. A large CH4 increase was observed in the tropics (10°N–5°S) during 1997 (between 15 ± 3 and 19 ± 3 ppb yr−1) and during 1998 for other regions (40°N–50°N: 10 ± 2–16 ± 1 ppb yr−1; 10°S–25°S: 12 ± 2–22 ± 4 ppb yr−1). The CH4 increase leveled off from 1999 to 2006 at all latitudes. The CH4 growth rate was enhanced in 2007 (25°N–50°N: 10 ± 1–12 ± 3 ppb yr−1; 15°S–35°S: 7 ± 1–8 ± 1 ppb yr−1) but diminished thereafter; however, a large CH4 growth (10 ± 1–17 ± 1 ppb yr−1) was observed in 2009 over the northern tropics (0°–15°N). These observations, combined with the simulation results, suggest that to explain the CH4 increase in 2007 would require an increase in surface emissions of ∼20 ± 3 Tg-CH4 yr−1 globally and an increase in the Northern Hemisphere (NH) of 4–7 ± 3 Tg-CH4 yr−1 more than that in the Southern Hemisphere (SH), assuming no change in OH concentrations; alternatively, a decrease in OH concentrations of 4.5 ± 0.6%–5.5 ± 0.5% yr−1 globally would be required if we assume no change in surface emissions. Over the western Pacific, the IAV in CH4 within the northern tropics was characterized by a high growth rate in mid-1997 and a reduced growth in 2007. The present data indicate that these events were strongly influenced by the IAV in atmospheric circulation associated with El Niño and La Niña events. Our observations captured the CH4 anomaly in 1997 associated with forest fires in Indonesia. The IAV and trends in CH4 as seen by our data sets capture the global features of background CH4 levels in the northern midlatitudes and the SH, and regional features of CH4 variations in the western tropical Pacific.” Terao, Y., H. Mukai, Y. Nojiri, T. Machida, Y. Tohjima, T. Saeki, and S. Maksyutov (2011), J. Geophys. Res., 116, D14303, doi:10.1029/2010JD015467.

In-situ SST measurement biases and uncertainties, paper 1

Reassessing biases and other uncertainties in sea surface temperature observations measured in situ since 1850: 1. Measurement and sampling uncertainties – Kennedy et al. (2011) “New estimates of measurement and sampling uncertainties of gridded in situ sea surface temperature anomalies are calculated for 1850 to 2006. The measurement uncertainties account for correlations between errors in observations made by the same ship or buoy due, for example, to miscalibration of the thermometer. Correlations between the errors increase the estimated uncertainties on grid box averages. In grid boxes where there are many observations from only a few ships or drifting buoys, this increase can be large. The correlations also increase uncertainties of regional, hemispheric, and global averages above and beyond the increase arising solely from the inflation of the grid box uncertainties. This is due to correlations in the errors between grid boxes visited by the same ship or drifting buoy. At times when reliable estimates can be made, the uncertainties in global average, Southern Hemisphere, and tropical sea surface temperature anomalies are between 2 and 3 times as large as when calculated assuming the errors are uncorrelated. Uncertainties of Northern Hemisphere averages are approximately double. A new estimate is also made of sampling uncertainties. They are largest in regions of high sea surface temperature variability such as the western boundary currents and along the northern boundary of the Southern Ocean. The sampling uncertainties are generally smaller in the tropics and in the ocean gyres.” Kennedy, J. J., N. A. Rayner, R. O. Smith, D. E. Parker, and M. Saunby (2011), J. Geophys. Res., 116, D14103, doi:10.1029/2010JD015218. [Full text]

In-situ SST measurement biases and uncertainties, paper 2

Reassessing biases and other uncertainties in sea surface temperature observations measured in situ since 1850: 2. Biases and homogenization – Kennedy et al. (2011) “Changes in instrumentation and data availability have caused time-varying biases in estimates of global and regional average sea surface temperature. The size of the biases arising from these changes are estimated and their uncertainties evaluated. The estimated biases and their associated uncertainties are largest during the period immediately following the Second World War, reflecting the rapid and incompletely documented changes in shipping and data availability at the time. Adjustments have been applied to reduce these effects in gridded data sets of sea surface temperature and the results are presented as a set of interchangeable realizations. Uncertainties of estimated trends in global and regional average sea surface temperature due to bias adjustments since the Second World War are found to be larger than uncertainties arising from the choice of analysis technique, indicating that this is an important source of uncertainty in analyses of historical sea surface temperatures. Despite this, trends over the twentieth century remain qualitatively consistent.” Kennedy, J. J., N. A. Rayner, R. O. Smith, D. E. Parker, and M. Saunby (2011), J. Geophys. Res., 116, D14104, doi:10.1029/2010JD015220. [Full text]

Methane feedbacks in atmosphere might double methane warming effect

Large methane releases lead to strong aerosol forcing and reduced cloudiness – Kurtén et al. (2011) “The release of vast quantities of methane into the atmosphere as a result of clathrate destabilization is a potential mechanism for rapid amplification of global warming. Previous studies have calculated the enhanced warming based mainly on the radiative effect of the methane itself, with smaller contributions from the associated carbon dioxide or ozone increases. Here, we study the effect of strongly elevated methane (CH4) levels on oxidant and aerosol particle concentrations using a combination of chemistry-transport and general circulation models. A 10-fold increase in methane concentrations is predicted to significantly decrease hydroxyl radical (OH) concentrations, while moderately increasing ozone (O3). These changes lead to a 70 % increase in the atmospheric lifetime of methane, and an 18 % decrease in global mean cloud droplet number concentrations (CDNC). The CDNC change causes a radiative forcing that is comparable in magnitude to the longwave radiative forcing (“enhanced greenhouse effect”) of the added methane. Together, the indirect CH4-O3 and CH4-OH-aerosol forcings could more than double the warming effect of large methane increases. Our findings may help explain the anomalously large temperature changes associated with historic methane releases.” Kurtén, T., Zhou, L., Makkonen, R., Merikanto, J., Räisänen, P., Boy, M., Richards, N., Rap, A., Smolander, S., Sogachev, A., Guenther, A., Mann, G. W., Carslaw, K., and Kulmala, M., Atmos. Chem. Phys., 11, 6961-6969, doi:10.5194/acp-11-6961-2011, 2011. [Full text]

Feedbacks causing polar amplification during Mid-Holocene

Polar amplification in the mid-Holocene derived from dynamical vegetation change with a GCM – O’ishi & Abe-Ouchi (2011) “AOGCM simulations of the mid-Holocene tend to largely underestimate annual mean temperature over land in northern hemisphere compared to that of paleodata reconstruction. While the vegetation feedback has not been yet quantitatively reported, its neglect is suggested to be one of the cause of this underestimation. Here, we perform several experiments using an atmosphere-ocean-vegetation coupled model and quantify a vegetation-induced feedback in the mid-Holocene climate using MIROC GCM. Our result indicates an annual warming of +1.3K over land north of 40°N in the mid-Holocene, much larger than the previous GCM results. This warming is due to direct amplification of warming over high latitude land through increases in vegetation and reduced albedo during the summer and indirect amplification through sea-ice feedback in autumn and winter and snow albedo feedback in spring. These feedback were not properly represented in previous GCM analysis.” O’ishi, R., and A. Abe-Ouchi (2011), Geophys. Res. Lett., 38, L14702, doi:10.1029/2011GL048001.

Contributors to last interglacial sea level rise

The role of ocean thermal expansion in Last Interglacial sea level rise – McKay et al. (2011) “A compilation of paleoceanographic data and a coupled atmosphere-ocean climate model were used to examine global ocean surface temperatures of the Last Interglacial (LIG) period, and to produce the first quantitative estimate of the role that ocean thermal expansion likely played in driving sea level rise above present day during the LIG. Our analysis of the paleoclimatic data suggests a peak LIG global sea surface temperature (SST) warming of 0.7 ± 0.6°C compared to the late Holocene. Our LIG climate model simulation suggests a slight cooling of global average SST relative to preindustrial conditions (ΔSST = −0.4°C), with a reduction in atmospheric water vapor in the Southern Hemisphere driven by a northward shift of the Intertropical Convergence Zone, and substantially reduced seasonality in the Southern Hemisphere. Taken together, the model and paleoceanographic data imply a minimal contribution of ocean thermal expansion to LIG sea level rise above present day. Uncertainty remains, but it seems unlikely that thermosteric sea level rise exceeded 0.4 ± 0.3 m during the LIG. This constraint, along with estimates of the sea level contributions from the Greenland Ice Sheet, glaciers and ice caps, implies that 4.1 to 5.8 m of sea level rise during the Last Interglacial period was derived from the Antarctic Ice Sheet. These results reemphasize the concern that both the Antarctic and Greenland Ice Sheets may be more sensitive to temperature than widely thought.” McKay, N. P., J. T. Overpeck, and B. L. Otto-Bliesner (2011), Geophys. Res. Lett., 38, L14605, doi:10.1029/2011GL048280.

Reducing uncertainty in Holocene carbon dioxide estimates

Observational constraints on the causes of Holocene CO2 change – Goodwin et al. (2011) “The mechanisms that controlled past atmospheric CO2 levels are not directly measurable, hence many proxy data sources are combined when reconstructing past carbon cycling. The accuracy of Holocene modeling reconstructions is checked by seeking consistency between data-based observables and their numerically simulated counterparts. A new framework is presented to evaluate which combinations of observables can best constrain carbon cycle mechanisms with the minimum of uncertainty. We show that when previous studies have combined ocean temperatures, ocean [CO32−], and the δ13C of atmospheric CO2 as observables, uncertainties in the data sources are amplified by over 2 orders of magnitude when reconstructing the mechanisms responsible for CO2 increase. However, incorporating mean δ13C of ocean DIC since 8000 years ago as an additional data source reduces the uncertainties by more than a factor of 5, making this observable a priority for future research. Our analysis indicates that the 20 ppm increase in CO2 between 8000 years BP and preindustrial was caused by significant CaCO3 precipitation and a reduction in the ocean soft tissue pump. Meanwhile, an increase in terrestrial carbon storage opposed the CO2 increase. The methods presented here are useful for investigating a range of paleoclimate events.” Goodwin, P., K. I. C. Oliver, and T. M. Lenton (2011), Global Biogeochem. Cycles, 25, GB3011, doi:10.1029/2010GB003888.

Early Eocene perhaps was not super-hot

Warm, not super-hot, temperatures in the early Eocene subtropics – Keating-Bitonti et al. (2011) “The early Eocene (ca. 55–48 Ma) encompasses one of the warmest intervals of the past 65 m.y. and is characterized by an unusually low equator-to-pole thermal gradient. Recent proxy studies suggest temperatures well in excess of 30 °C even at high latitudes, but conflicting interpretations derived from different types of data leave considerable uncertainty about actual early Eocene temperatures. A robust comparison among new paleotemperature proxies may provide insight into possible biases in their temperature estimates, and additional detail on the spatial distribution of temperatures will further resolve the early Eocene meridional temperature gradient. We use a suite of paleotemperature proxies based on the chemistry of bivalve shell carbonate and associated sedimentary organic matter from the United States Gulf Coastal Plain to constrain climate at a subtropical site during this key interval of Earth history. Oxygen isotope and clumped isotope analyses of shell carbonate and two tetraether lipid analyses of sedimentary organic carbon all yield temperatures of ∼27 °C. High-resolution, intraannual oxygen isotope data reveal a consistent, large range of seasonal variation, but clumped isotope data suggest that seasonality is due primarily to precipitation, not to temperature. These paleotemperature estimates are 2–3 °C warmer than the northern Gulf of Mexico today, and generally consistent with early Eocene temperature estimates from other low and mid-latitude locations, but are significantly cooler than contemporaneous estimates from high southern latitudes.” Caitlin R. Keating-Bitonti, Linda C. Ivany, Hagit P. Affek, Peter Douglas and Scott D. Samson, Geology, v. 39 no. 8 p. 771-774, doi: 10.1130/G32054.1.

Climate change increases fish species richness of Baltic Sea by increasing salinity

What is the effect of climate change on marine fish biodiversity in an area of low connectivity, the Baltic Sea? – Hiddink & Coleby (2011) “Aim: Climate change could result in an increase in species richness because large-scale biogeography suggests that more species could be gained from equatorial regions than may be lost pole-ward. However, the colonization of newly available habitat may lag behind the rate dictated by climatic warming if there exists of a lack of connectivity between ‘donor’ and receiving areas. The objective of this study was to compare how regional warming affected the biodiversity of marine fish in areas that differed in their connectivity in the Baltic Sea. Location: North-east Atlantic, Kattegat and Baltic Sea. Methods: The total species richness and the mean species richness from scientific surveys were related to changes in temperature and salinity. Changes in the extent of the distribution of individual fish species were related to the latitudinal distribution, salinity tolerance, maximum body size and exploitation status to assess to what extent climate change and fishing impacts could explain changes in species richness in the Baltic. Results: Rising temperatures in the well-connected Kattegat correlated to an increase in the species richness of fish, due to an increase in low-latitude species. Unexpectedly, species richness in the poorly connected Baltic Sea also increased. However, the increase seems to be related to higher salinity rather than temperature and there was no influx of low-latitude species. Main conclusions: These results do not support the hypothesis that low-connectivity areas are less likely to see increases in species richness in response to warming. This indicates that the effect of climate change on biodiversity may be more difficult to predict in areas of low connectivity than in well-connected areas.” Jan Geert Hiddink, Chris Coleby, Global Ecology and Biogeography, DOI: 10.1111/j.1466-8238.2011.00696.x.

Anthropogenic soils define the Anthropocene

Anthropogenic soils are the golden spikes for the Anthropocene – Certini & Scalenghe (2011) “We propose that the Anthropocene be defined as the last c. 2000 years of the late Holocene and characterized on the basis of anthropogenic soils. This contrasts with the original definition of the Anthropocene as the last c. 250 years (since the Industrial Revolution) and more recent proposals that the Anthropocene began some 5000 to 8000 years ago in the early to mid Holocene (the early-Anthropocene hypothesis). Anthropogenic soil horizons, of which several types are recognized, provide extensive terrestrial stratigraphic markers for defining the start of the Anthropocene. The pedosphere is regarded as the best indicator of the rise to dominance of human impacts on the total environment because it reflects strongly the growing impact of early civilisations over much of the Earth’s surface. Hence, the composition of anthropogenic soils is deemed more appropriate than atmospheric composition in providing ‘golden spikes’ for the Anthropocene.” Giacomo Certini, Riccardo Scalenghe, Anthropogenic soils are the golden spikes for the Anthropocene, The Holocene July 19, 2011 0959683611408454, doi: 10.1177/0959683611408454.

Greenhouse gas emissions from cereals

An agronomic assessment of greenhouse gas emissions from major cereal crops – Linquist et al. (2011) “Agricultural greenhouse gas (GHG) emissions contribute approximately 12% to total global anthropogenic GHG emissions. Cereals (rice, wheat and maize) are the largest source of human calories, and it is estimated that world cereal production must increase 1.3% annually to 2025 in order to meet growing demand. Sustainable intensification of cereal production systems requires maintaining high yields while reducing environmental costs. We conducted a meta-analysis (57 published studies consisting of 62 study sites and 328 observations) to test the hypothesis that the Global Warming Potential (GWP) of CH4 and N2O emissions from rice, wheat, and maize, when expressed per ton of grain (yield-scaled GWP), is similar, and that lowest value for each cereal is achieved at near optimal yields. Results show that the GWP of CH4 and N2O emissions from rice (3757 kg CO2 eq ha−1 season−1) was higher than wheat (662 kg CO2 eq ha−1 season−1) and maize (1399 kg CO2 eq ha−1 season−1). The yield-scaled GWP of rice was about four times higher (657 kg CO2 eq Mg−1) than wheat (166 kg CO2 eq Mg−1) and maize (185 kg CO2 eq Mg−1). Across cereals, the lowest yield-scaled GWP values were achieved at 92% of maximal yield and was about twice as high for rice (279 kg CO2 eq Mg−1) than wheat (102 kg CO2 eq Mg−1) or maize (140 kg CO2 eq Mg−1), suggesting greater mitigation opportunities for rice systems. In rice, wheat and maize, 0.68%, 1.21% and 1.06% of N applied was emitted as N2O, respectively. In rice systems, there was no correlation between CH4 emissions and N rate. Finally, when evaluating issues related to food security and environmental sustainability other factors including cultural significance, the provisioning of ecosystem services, food security, and human health and well-being must also be considered.” Bruce Linquist, Kees Jan van Groenigen, Maria Arlene Adviento-Borbe, Cameron Pittelkow, Chris van Kessel, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02502.x.

Norwegian peat cores tell the climate of the past 7500 years

Climate changes during the last c. 7500 years as recorded by the degree of peat humification in the Lofoten region, Norway – Vorren et al. (2011) “Two peat cores from two neighbouring bogs in Lofoten, northern Norway were densely AMS dated and analysed for humification. The two cores have been influenced by human agricultural impact, especially c. 1600 cal. a BP, which may have affected the local hydrology of the bogs. From 7400 cal. a BP onwards, 19 distinct wet-shifts are recorded in the two cores. Eight or nine of these correspond chronologically to periods of low solar activity. This correlation is most convincing during the last 2000 years. Some wet-shifts are connected with a solar low-activity period during the Subboreal/Subatlantic transition, which in central Europe is dated at 2750–2565 cal. a BP. For Lofoten, the corresponding Subboreal/Subatlantic transition – or the wet-shift marking this transition – is dated at c. 2600 cal. a BP. Some wet-shifts occur just before or just after solar low-activity periods, but only four of the nineteen wet-shifts are clearly not temporally connected with periods of low solar activity. Compared with the wet-shifts in NW European (mainly British Isles) bogs, there are more frequent wet-shifts in northern Norway. Compared with other peat cores in northern Norway, especially for the interval 6500–5000 cal. a BP, Lofoten deviates by its lack of wet-shifts. As in England, Scotland and Ireland, there is regional variability in the temporal formation of wet-shifts in northern Norway.” Karl-Dag Vorren, Christin Eldegard Jensen, Eilif Nilssen, Boreas, DOI: 10.1111/j.1502-3885.2011.00220.x.


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