A 'snowball Earth' climate triggered by continental break-up through changes in runoff.

When the Marinoan snowball Earth deglaciated in response to high atmospheric carbon dioxide (CO2) concentrations, the planet warmed rapidly. It is commonly hypothesized that the ensuing supergreenhouse climate then declined slowly over hundreds of thousands of years through continental weathering. However, how the ocean affected atmospheric CO2 in the snowball Earth aftermath has never been quantified. Here we show that the ocean’s carbon cycle drives the supergreenhouse climate evolution via a set of different mechanisms, triggering scenarios ranging from a rapid decline to an intensification of the supergreenhouse climate. We further identify the rapid formation of carbonate sediments from pre-existing ocean alkalinity as a possible explanation for the enigmatic origin of Marinoan cap dolostones. This work demonstrates that a moderate and relatively short-lived supergreenhouse climate following the Marinoan snowball Earth is a plausible scenario that is in accordance with geological data, challenging the previous hypothesis.

The Cryogenian Period (717–635 Ma), or ‘Snowball Earth’, was an unusually cool period of Earth history when glaciers extended to low latitudes. Past ideas on causes of this widespread glaciation include increased consumption of atmospheric carbon dioxide by silicate weathering due to continental drift into tropical paleolatitudes, or by voluminous, easily weathered volcanic tuffs. Alternatively, carbon sequestration from the atmosphere may have been intensified by advances in biomass on land or at sea. These hypotheses are tested with a new study of red siltstones of the Johnnys Creek Formation (785–717 Ma) in central Australia, where paleosols have long been recognised. Although these dolomitic red siltstones look like shales, they lack lamination. Instead, they have the massive bedding and grainsize distribution of dolomitic and calcareous loess, which precede tillites of the Areyonga Formation. Paleomagnetic studies indicate little drift from a paleolatitude of 26.2° during accumulation of the Johnnys Creek Formation. Nor does the Johnnys Creek Formation contain easily weathered volcanic ash, only local basalt flows. Paleoproductivity of the paleosols increases up section, as estimated in ppm soil CO2 from depth in paleosols to gypsic (By) and then calcic (Bk) horizons. Deepening and intensification of soil respiration reflects greater terrestrial carbon sequestration, and increased chemical weathering up section, and both would have drawn down atmospheric CO2. Comparable transition from gypsic to calcic soils in modern deserts reflects change from cyanobacterial-gypsic to fungal–algal calcic ecosystems. Snowball Earth glaciation may have been induced by evolutionary advances to eukaryotic and multicellular life on land, in the same way as Ordovician glaciation was induced by land plants, Permo-Carboniferous glaciation by trees, and Pleistocene glaciation by grasslands. KEY POINTS Johnnys Creek Formation of central Australia has paleosols dated 785–717 Ma. Little drift from paleolatitude 26.2°, and no volcanic ash, only local basalt flows. Paleosol paleoproductivity and depth of weathering increased steadily up section. Glaciation may have been induced by eukaryotic and multicellular life on land.

<p>The climate is changing, not just where we live at ground level, but also where we fly in the upper troposphere and lower stratosphere. Climate change has important consequences for aviation, because the atmosphere’s meteorological characteristics strongly influence flight routes, journey times, and turbulence. This presentation will review the possible impacts of climate change on aviation, which have only recently begun to emerge (as opposed to the impacts of aviation on climate change, which have long been recognised).</p><p>Turbulence currently injures hundreds of air passengers each year worldwide, costing airlines hundreds of millions of dollars and occasionally causing structural damage to planes. To investigate the influence of climate change on turbulence, we diagnose an ensemble of 21 clear-air turbulence measures from climate model simulations. We find that turbulence strengthens significantly under climate change, all around the world, in all seasons, and at a wide range of aircraft cruising altitudes. For example, within the transatlantic flight corridor in winter at around 39,000 feet, the occurrence of light turbulence increases by an ensemble-mean value of 59% (with an intra-ensemble range of 43–68%), light-to-moderate by 75% (39–96%), moderate by 94% (37–118%), moderate-to-severe by 127% (30–170%), and severe by 149% (36–188%). These findings underline the urgent need to improve the skill of operational clear-air turbulence forecasts, to avoid increases in on-board discomfort and injuries in the coming decades.</p><p>To investigate the influence of climate change on flight routes and journey times, we feed atmospheric wind fields generated from climate model simulations into a routing algorithm of the type used operationally by flight planners. We focus on transatlantic flights between London and New York, and how they change when the atmospheric carbon dioxide (CO2) concentration is doubled. We find that a strengthening of the prevailing jet-stream winds causes eastbound flights to significantly shorten and westbound flights to significantly lengthen in all seasons. For example, eastbound and westbound crossings in winter become approximately twice as likely to take under 5 hours 20 minutes and over 7 hours, respectively. Even assuming no future growth in aviation, the extrapolation of our results to all transatlantic traffic suggests that aircraft will collectively be airborne for an extra 2,000 hours each year, burning an extra 7.2 million gallons of jet fuel at a cost of US$ 22 million, and emitting an extra 70 million kg CO2.</p><p>The above findings provide further evidence of the two-way interaction between aviation and climate change, which is an emerging research area that deserves further study.</p>

The standard industrial process for the purification of natural gas is to remove acid gases, mainly hydrogen sulfide and carbon dioxide, by the absorption and reaction of these gases with alkanolamines, but the lack of reliable and accurate vapor‐liquid equilibrium (VLE) data impedes the commercial application of more efficient alkanolamine systems. The objective of this research was to develop an FTIR apparatus and an in‐situ technique capable of making VLE measurements of acid‐gas–aqueous alkanolamine systems and to improve the accuracy of vapor–liquid equilibrium measurements at low hydrogen sulfide and carbon dioxide concentrations. The new FTIR apparatus and technique were tested in VLE measurements of low concentrations of carbon dioxide and hydrogen sulfide in aqueous mixtures of diethanolamine.

Abstract. Detecting the direction and strength of the causality signal in observed time series is becoming a popular tool for exploration of distributed systems such as Earth's climate system. Here, we suggest that in addition to reproducing observed time series of climate variables within required accuracy a model should also exhibit the causality relationship between variables found in nature. Specifically, we propose a novel framework for a comprehensive analysis of climate model responses to external natural and anthropogenic forcing based on the method of conditional dispersion. As an illustration, we assess the causal relationship between anthropogenic forcing (i.e., atmospheric carbon dioxide concentration) and surface temperature anomalies. We demonstrate a strong directional causality between global temperatures and carbon dioxide concentrations (meaning that carbon dioxide affects temperature more than temperature affects carbon dioxide) in both the observations and in (Coupled Model Intercomparison Project phase 5; CMIP5) climate model simulated temperatures.

Past work demonstrating an association between indoor air quality and cognitive performance brought attention to the benefits of increasing outdoor air ventilation rates beyond code minimums. These code minimums were scrutinized during the COVID-19 pandemic for insufficient ventilation and filtration specifications. As higher outdoor air ventilation was recommended in response, questions arose about potential benefits of enhanced ventilation beyond infection risk reduction. This was investigated by examining associations between indoor carbon dioxide concentrations, reflective of ventilation and building occupancy, and cognitive test scores among graduate students attending lectures in university classrooms with infection risk management strategies, namely increased ventilation. Post-class cognitive performance tests (Stroop, assessing inhibitory control and selective attention; Arithmetic, assessing cognitive speed and working memory) were administered through a smartphone application to participating students (54 included in analysis) over the 2022-2023 academic year in classrooms equipped with continuous indoor environmental quality monitors that provided real-time measurements of classroom carbon dioxide concentrations. Temporally and spatially paired exposure and outcome data was used to construct mixed effects statistical models that examined different carbon dioxide exposure metrics and cognitive test scores. Model estimates show directionally consistent evidence that higher central and peak classroom carbon dioxide concentrations, indicative of ventilation and occupancy, are associated with lower cognitive test scores over the measured range included in analysis ( ~ 440-1630 ppm). The effect estimates are strongest for 95th percentile class carbon dioxide concentrations, representing peak class carbon dioxide exposures. As the COVID-19 pandemic eased, questions emerged on the benefits of increased outdoor air ventilation beyond infection reduction. This work assesses associations between carbon dioxide concentrations, indicative of ventilation and occupancy, and cognitive test scores among students in university classrooms with increased outdoor air ventilation. Although not causal, models show statistically significant evidence of associations between lower carbon dioxide concentrations and higher cognitive test scores over the low range of carbon dioxide exposures in these classrooms. While the underlying mechanisms remain unknown, higher outdoor air ventilation appears to provide additional benefits by reducing indoor air exposure and supporting student performance.

In anticipation of the 2013 publication of the Intergovernmental Panel on Climate Change's fifth assessment report, many in the climate modeling community came together in 2008 under the banner of the Fifth Coupled Model Intercomparison Project (CMIP5). An international effort, this project sought to identify crucial research directions and laid down standardized parameters under which atmosphere‐ocean coupled general circulation models (AOGCMs) should be tested so that they can be compared on equal footing. Andrews et al. assessed 15 models participating in the CMIP5 to find the most up‐to‐date measure of climate sensitivity and the remaining sources of model uncertainty. To test the AOGCMs, the authors looked at how the modeled top‐of‐the‐atmosphere (TOA) radiative emissions from the Earth respond to an imposed change in atmospheric carbon dioxide concentration. Because TOA emissions depend on the global mean atmospheric and surface temperatures, this technique provides an effective way to investigate the feedback mechanisms built into each of the models. The authors assessed model runs for pre‐industrial atmospheric carbon dioxide levels as well as those that simulated a sudden quadrupling in the concentration of atmospheric carbon dioxide—the amount that could be reached given a “do nothing” approach to mitigating carbon emissions.

Human and natural physical caused climate change can affect climate extremes, as well as maximum temperatures. The variations of the interannual and interdecadal hot temperatures have been studied between 1960 and 2012 (53 years) based on Abadan annual maximum temperatures (AAMT) data. The decadal analysis of the time variations of AAMT showed a positive and ascending trend in 60d, 70d and 90d, the neutral trend in 80d, and the descending trend in the last decade of the twentieth century. The positive time variations of AAMT in the 60d and 70d are too severe and more significant than that of other decades. The analysis of relationship between the absolute AAMT and the factors such as the global annual mean land-ocean temperature index (GAMLOTI), the annual concentration of atmospheric carbon dioxide (ACD), and the summer June–July–August (JJA) index of North Atlantic Oscillation (NAO) teleconnection pattern in AAMT showed that there is a significant correlation between AAMT and the mentioned factors. Thus, the relationship between the AAMT and the GAMLOTI is significant with a correlation coefficient of 0.602 at the significant level of 0.01. ACD had a negative significant correlation (r = 0.60), and the JJA NAO index had a negative significant correlation (r = −0.34) with AAMT. The results of multiple regression analysis showed that the overall effect of the GAMLOTI, the annual concentration of ACD, and the JJA NAO index on the temporal variability of AAMT during a 53-year period is 46.2 %. The relationship between the AAMT and the GAMLOTI and the annual concentration of ACD represents the effects of global warming on the variability of the AAMT.

Siberia, the wandering northern terrane, and its changing geography through the Palaeozoic

The automatic determination of nitrate in sea water : Brewer P. G. and J. P. Riley, 1965. Deep-Sea Res., 12 (6): 765–772

This paper is concerned with the mathematical modeling of a severe and common congenital defect called hypoplastic left heart syndrome (HLHS). Surgical approaches are utilized for palliating this heart condition; however, a brain white matter injury called periventricular leukomalacia (PVL) occurs with high prevalence at or around the time of surgery, the exact cause of which is not known presently. Our main goal in this paper is to study the hemodynamic conditions under which HLHS physiology may lead to the occurrence of PVL. A lumped parameter model of the HLHS circulation has been developed integrating diffusion modeling of oxygen and carbon dioxide concentrations in order to study hemodynamic variables such as pressure, flow, and blood gas concentration. Results presented include calculations of blood pressures and flow rates in different parts of the circulation. Simulations also show changes in the ratio of pulmonary to systemic blood flow rates when the sizes of the patent ductus arteriosus and atrial septal defect are varied. These changes lead to unbalanced blood circulations and, when combined with low oxygen and carbon dioxide concentrations in arteries, result in poor oxygen delivery to the brain. We stipulate that PVL occurs as a consequence.

The Great Unconformity (GUn)-a widely recognized discontinuity and associated gap in the rock record between Precambrian and Cambrian rocks-represents a globally important interval of continental exposure and erosion that is notable also for the first appearance of all major animal phyla on Earth. However, its origin remains the subject of vigorous debate. Here, we present field relationships, and zircon and monazite U-Pb, biotite and muscovite Rb-Sr, and zircon (U-Th)/He thermochronology data for Precambrian crystalline basement rocks from North China to constrain the exhumation history below the unconformity. Dates from multichronometers and thermal history inversions show that the most substantial cooling of continental basement took place from ~2,100 to 1,600 Ma. Comparison with thermal history data from Laurentia, Baltica, and Amazonia suggests that protracted plate tectonics broadly modulated by supercontinent cycles, and not "snowball Earth" glaciation, is responsible for crustal exhumation below the unconformity. The most pronounced erosion evident in both the thermochronologic record and geochemical indicators of continental weathering is shown to correspond with development of Earth's first true supercontinent (Columbia), rather than with either the Cambrian explosion or the emergence of modern plate tectonics.

The concentration of atmospheric carbon dioxide in Antarctica at ground level is nearly constant, according to measurements obtained in 1958 at Little America and from 1960 through 1963 at the South Pole. Discernible, however, is a small seasonal variation superimposed on a small yearly increase. The increase is very nearly the same as observed at Mauna Loa Observatory, Hawaii, by Pales and Keeling in 1965. It is attributable to the burning of fossil fuels, which is causing the amount of CO2 in the atmosphere to rise on a world-wide scale.

A primary motivation for the development of future fuels is to halt the increasing concentration of atmospheric carbon dioxide. As such, a fuel that can potentially be produced from a feedstock of alcohols and atmospheric carbon dioxide is an attractive proposition. Symmetrical carbonate esters may thus offer a sustainable means of converting alcohols to larger molecules that are potentially better suited to use in compression ignition engines. This paper presents experimental investigations carried out on a compression ignition engine fuelled with a range of binary fuel mixtures to determine the effect of carbonate molecular structure on combustion and exhaust emissions. Six symmetrical carbonate esters, dimethyl carbonate, diethyl carbonate, di-n-butyl carbonate, di-1-methyl-propyl carbonate, di-2-methyl-propyl carbonate, and ditert-butyl carbonate, one ester, butyl valerate, and one ketone, 5-nonanone, were investigated so as to ascertain the way in which the alkyl chain length, branching in the alkyl chain, and molar oxygen content of similar molecules affects compression ignition combustion and emissions. The engine tests of the fuels were carried out as binary mixtures with 30% (w/w) n-decane, as they were found not to combust in a steady manner as single component fuels; dimethyl and diethyl carbonate were also tested as binary mixtures with n-decane at a range of proportions. All fuels were initially tested at constant injection and constant ignition timings and repeated at two constant ignition delay timings, which were achieved through the addition of small quantities of ignition improver (2-ethylhexyl nitrate). Relative to di-n-butyl carbonate, decreasing the alkyl chain length and also introducing methyl branches to the alkyl moiety increased the duration of ignition delay, while decreasing the molar oxygen content to form butyl valerate and 5-nonone decreased the ignition delay. The respective changes in ignition delay with molecular structure were attributed to the importance of the alkyl moieties of the fuels tested in determining low temperature reactivity. When the dimethyl carbonate or diethyl carbonate content of blends with n-decane was increased, levels of peak heat released increased linearly, suggesting an influence of ignition delay and the carbonate physical properties on the extent of fuel and air premixing. At constant ignition delay timings, an effect of decreasing particulate matter and CO emissions with an increasing level of fuel bound oxygen was observed, while at all conditions NOx emissions were most significantly influenced by in-cylinder thermal conditions.

BackgroundChanges in aboveground plant species diversity as well as variations of environmental conditions such as exposure of ecosystems to elevated concentrations of atmospheric carbon dioxide may lead to changes in metabolic activity, composition and diversity of belowground microbial communities, both bacterial and fungal.ResultsWe examined soil samples taken from a biodiversity × CO2 grassland experiment where replicate plots harboring 5, 12, or 31 different plant species had been exposed to ambient or elevated (600 ppm) levels of carbon dioxide for 5 years. Analysis of soil bacterial communities in these plots by temporal temperature gradient gel electrophoresis (TTGE) showed that dominant soil bacterial populations varied only very little between different experimental treatments. These populations seem to be ubiquitous. Likewise, screening of samples on a high-resolution level by terminal restriction fragment length polymorphism (T-RFLP) showed that increased levels of carbon dioxide had no significant influence on both soil bacterial community composition (appearance and frequency of operational taxonomic units, OTUs) and on bacterial richness (total number of different OTUs). In contrast, differences in plant diversity levels had a significant effect on bacterial composition but no influence on bacterial richness. Regarding species level, several bacterial species were found only in specific plots and were related to elevated carbon dioxide or varying plant diversity levels. For example, analysis of T-RFLP showed that the occurrence of Salmonella typhimurium was significantly increased in plots exposed to elevated CO2 (P < 0.05).ConclusionPlant diversity levels are affecting bacterial composition (bacterial types and their frequency of occurrence). Elevated carbon dioxide does not lead to quantitative alteration (bacterial richness), whereas plant diversity is responsible for qualitative changes (bacterial diversity).