Explore the vast range of titles available.

In light of uncertainties regarding climate sensitivity and future anthropogenic greenhouse gas emissions, we explore the plausibility of global warming over the next millennium which is significantly higher than what is usually expected. Although efforts to decarbonize the global economy have significantly shifted global anthropogenic emissions away from the most extreme emission scenarios, intermediate emission scenarios are still plausible. Significant warming in these scenarios cannot be ruled out as uncertainties in equilibrium climate sensitivity (ECS) remain very large. Until now, long-term climate change projections and their uncertainties for such scenarios have not been investigated using Earth system models (ESMs) that account for all major carbon cycle feedbacks. Using the fast ESM CLIMBER-X with interactive CO2 and CH4 (the latter typically not included in most models), we performed simulations for the next millennium under extended SSP1-2.6, SSP4-3.4 and SSP2-4.5 scenarios. These scenarios are usually associated with peak global warming levels of 1.5 ∘C, 2 ∘C and 3 ∘C, respectively, for an ECS of ∼3 ∘C, considered the best estimate in the latest Intergovernmental Panel on Climate Change (IPCC) report. As ECS values lower or higher than this estimate cannot be ruled out, we emulate a wide range of ECS from 2 ∘C to 5 ∘C, defined as the ‘very likely’ range by the IPCC. Our results show that achieving the Paris Agreement goal of a 2 ∘C temperature increase is only feasible for low emission scenarios and if ECS is lower than 3.5 ∘C. With an ECS of 5 ∘C, peak warming in all considered scenarios more than doubles compared to an ECS of 3 ∘C. Approximately 50% of this additional warming is attributed to positive climate–carbon cycle feedbacks with comparable contributions from CO2 and CH4. The interplay between potentially high ECS and carbon cycle feedbacks could drastically enhance future warming, demonstrating the importance of properly accounting for all major climate feedbacks and associated uncertainties in projecting future climate change.

Hot and moist “hothouse” climates occurred in Earth's past and are expected in Earth's far future climate, driven by increasing solar luminosity. In hothouse climate regimes, precipitation transitions from a quasi‐steady state, as in present‐day tropical convection, to an “episodic deluge” or relaxation‐oscillator (RO) regime where precipitation occurs in intense bursts separated by multi‐day dry spells. Recent studies suggest that the transition to RO convection regimes is radiatively driven. However, the transition from steady state to RO convection has only been studied with radiative convective equilibrium (RCE) simulations with constant insolation, excluding the diurnal cycle. Precipitation and convection are strongly linked to the diurnal cycle in Earth's present climate over both land and ocean. We explore the impact of the diurnal cycle on the transition from steady state to RO convection using two sets of small‐domain RCE simulations with ocean and swamp‐like surface boundary conditions. Our RCE simulations with ocean boundary conditions show convection transitions to an episodic deluge regime at 322 K and the diurnal cycle modulates precipitation to occur during late‐night or near dawn, when convective inhibition is the weakest. Our RCE simulations with swamp‐like boundary conditions, which allow for mean surface temperature variations, show that as RO states emerge, the diurnal cycle modulates precipitation to primarily occur during the late‐afternoon to about dusk; but as the mean SST increases, precipitation occurs during the late‐night to dawn. These results show that the diurnal cycle strongly influences the timing of convection and precipitation patterns in extreme climates. In hot and wet “hothouse” climate conditions, rainfall transitions from a pattern that fluctuates from about a mean of 3 mm to more intense outbursts that are separated by multi‐day dry spells. Previous studies on hothouse climates did not consider the role of the diurnal cycle even though it strongly controls precipitation in Earth's current climate. This study uses radiative‐convective equilibrium simulations to investigate the impact of rising temperatures on the transition to hothouse conditions, incorporating the diurnal cycle with both swamp‐like and open ocean surface conditions. We find that episodic precipitation occurs at surface temperatures above 322 K even when accounting for the diurnal cycle. However, the diurnal cycle significantly influences the timing of convection and rainfall at high temperatures with precipitation primarily starting late at night or in the early morning. We study hothouse climates using radiative convective equilibrium simulations with a diurnal cycle over ocean and swamp‐like conditions A transition from steady state to episodic precipitation occurs when accounting for diurnal variability at high surface temperatures The diurnal cycle modulates the episodic precipitation events with precipitation occurring primarily during the dawn or dusk hours

In a “hothouse” climate, warm temperatures lead to a high tropospheric water vapor concentration. Sufficiently high water vapor levels lead to the closing of the water vapor infrared window, which prevents radiative cooling of the lower troposphere. Because water vapor also weakly absorbs solar radiation, hothouse climates feature radiative heating of the lower troposphere. In recent work, this radiative heating was shown to trigger a shift into a novel “episodic deluge” precipitation regime, where rainfall occurs in short, intense outbursts separated by multi‐day dry spells. Here, we further examine the role of the lower tropospheric radiative heating (LTRH) in the transition into the “episodic deluge” regime. We demonstrate that under high sea‐surface temperature the “episodic deluge” regime could be formed even before the LTRH turns positive. In addition, we examine whether these oscillations operate on larger scales and how these oscillations, which represent “temporal” convective self‐organization, would manifest in the presence of traditional “spatial” self‐ or forced‐aggregation in large‐domain convection‐permitting simulations. We find that the temporal oscillations become much less synchronized throughout a large domain (O$\\mathcal{O}$1,000 km) because gravity waves cannot propagate fast enough to synchronize convection. We also show that temporal oscillations still dominate the rainfall distribution even when there is tropical convective self‐aggregation or a large‐scale overturning circulation. These results could have important implications for extreme precipitation events under a warming climate. Plain Language Summary Water vapor is a strong greenhouse gas that closely follows surface temperature. Under very warm (“hothouse”) conditions, which are believed to have existed in the Earth's distant past, temperature and water vapor are sufficiently high that the greenhouse effect of water vapor prevents heat from escaping out of the lower part of the atmosphere. This trapped heat makes the lower atmosphere even hotter, causing some unusual weather patterns. For example, it was recently shown to lead to short but intense bursts of rain, followed by several days of dry weather. However, it is unclear whether these patterns occur on larger scales and what their characteristic scale is. In this study, computer simulations were conducted to address these uncertainties and to further elucidate the role of the lower tropospheric radiative heating in the transition into this “episodic deluge” regime. We show that these temporal oscillations dominate the rainfall distribution even in the presence of other atmospheric factors such as tropical convective self‐aggregation or large‐scale overturning circulation. Key Points We examine the temporal and spatial organization of convection in simulated hothouse conditions We demonstrate that lower tropospheric radiative heating is not necessary for the “episodic deluge” precipitation regime “Episodic deluge” precipitation regime occurs in self‐ or forced‐convective aggregated large domain simulations but is less synchronized

Malware detection is in a coevolutionary arms race where the attackers and defenders are constantly seeking advantage. This arms race is asymmetric: detection is harder and more expensive than evasion. White hats must be conservative to avoid false positives when searching for malicious behaviour. We seek to redress this imbalance. Most of the time, black hats need only make incremental changes to evade them. On occasion, white hats make a disruptive move and find a new technique that forces black hats to work harder. Examples include system calls, signatures and machine learning. We present a method, called Hothouse, that combines simulation and search to accelerate the white hat’s ability to counter the black hat’s incremental moves, thereby forcing black hats to perform disruptive moves more often. To realise Hothouse, we evolve EEE, an entropy-based polymorphic packer for Windows executables. Playing the role of a black hat, EEE uses evolutionary computation to disrupt the creation of malware signatures. We enter EEE into the detection arms race with VirusTotal, the most prominent cloud service for running anti-virus tools on software. During our 6 month study, we continually improved EEE in response to VirusTotal, eventually learning a packer that produces packed malware whose evasiveness goes from an initial 51.8% median to 19.6%. We report both how well VirusTotal learns to detect EEE-packed binaries and how well VirusTotal forgets in order to reduce false positives. VirusTotal’s tools learn and forget fast, actually in about 3 days. We also show where VirusTotal focuses its detection efforts, by analysing EEE’s variants.

Seeley and Wordsworth (2021, https://doi.org/10.1038/s41586‐021‐03919‐z) showed that in small‐domain cloud‐resolving simulations the temporal pattern of precipitation transforms in extremely hot climates (≥320 K) from quasi‐steady to organized episodic deluges, with outbursts of heavy rain alternating with several dry days. They proposed a mechanism for this transition involving increased water vapor greenhouse effect and solar radiation absorption leading to net lower‐tropospheric radiative heating. This heating inhibits lower‐tropospheric convection and decouples the boundary layer from the upper troposphere during the dry phase, allowing lower‐tropospheric moist static energy to build until it discharges, resulting in a deluge. We perform cloud‐resolving simulations in polar night and show that the same transition occurs, implying that some revision of their mechanism is necessary. We perform further tests to show that episodic deluges can occur even if the lower‐tropospheric radiative heating rate is negative, as long as the magnitude of the upper‐tropospheric radiative cooling is about twice as large. We find that in the episodic deluge regime the period can be predicted from the time for radiation and reevaporation to cool the lower atmosphere. Plain Language Summary Precipitation plays an important role in Earth's climate and habitability, and also influences important weathering processes such as the carbonate‐silicate cycle. In the distant future, Earth may experience a very hot and wet “hothouse” climate, just like it may have in the Archean. Modeling results show that in a hothouse climate, precipitation transforms into an “episodic deluge” pattern, with outbursts of heavy rain alternating with several dry days. In this study, we find that positive lower‐tropospheric heating is not the necessary cause for episodic deluges. Instead, vertical radiative cooling contrast is critical in triggering the episodic deluges in small‐domain hothouse climates. We also try to understand the underlying mechanism of episodic deluges through CIN and CAPE analyses. Key Points Episodic deluges can occur during polar night Lower‐tropospheric radiative heating is not necessary for the occurrence of episodic deluges A strong vertical gradient of radiative cooling is a key factor in triggering episodic deluges

Hothouse climates in Earth's geologic past, such as the Eocene epoch, are thought to have been caused by the release of large amounts of carbon dioxide and/or methane, which had been stored as carbon in biogenic gases and organic matter in sediments, to the ocean-atmosphere system. However, to avoid runaway temperatures, there must be long-term negative feedbacks that consume CO₂ on time scales longer than the ~ 100,000 years generally ascribed to ocean uptake of CO₂ and burial of marine organic carbon. Here, we argue that continental chemical weathering of silicate rocks, the ultimate long-term (multi-million year) sink for CO₂, must have been almost dormant during the late Paleocene and early Eocene, allowing buildup of atmospheric CO₂ to levels exceeding 1,000 ppm. This reduction in the strength of the CO₂ sink was the result of minimal global tectonic uplift of silicate rocks that did not produce mountains susceptible to physical and chemical weathering, an inversion of the Uplift-Weathering Hypothesis. There is lack of terrestrial evidence for absence of uplift; however, the δ⁷Li chemistry of the Paleogene ocean indicates that continental relief during this period of the Early Cenozoic was one of peneplained (flat) continents characterized by high chemical weathering intensity and slow physical and chemical weathering rates, yielding low river fluxes of suspended solids, dissolved cations, and clays delivered to the sea. Only upon re-initiation of mountain building in the Oligocene-Miocene (Himalayas, Andes, Rockies) and drifting of these continental blocks to low-latitude locations near the Inter-Tropical Convergence Zone and monsoonal climate belts did continental weathering take on modern characteristics of rivers with high suspended loads and incongruent weathering, with much of the cations released during weathering being sequestered into secondary clay minerals. The δ⁷Li record of the Cenozoic ocean provides another piece of circumstantial evidence in support of the Late Cenozoic Uplift-Weathering Hypothesis.

O emprego da mecanização na cafeicultura brasileira é essencial para otimização da produção, entretanto, a crescente exigência dos mercados internacionais em busca de uma cadeia produtiva de baixo carbono faz com que as propriedades cafeeiras busquem compreender como suas atividades contribuem para a emissão de gases de efeito estufa (GEE). O objetivo do presente estudo foi estimar a emissão de CO2 equivalente (CO2 eq) por hectare, nas principais operações mecanizadas realizadas na cultura do cafeeiro no Sul de Minas Gerais. A estimativa de CO2 eq foi realizada através de um estudo de caso, utilizando-se para os cálculos os parâmetros de emissão de GEE da metodologia do GHG Protocol Agricultura. Os resultados mostraram que nas operações de plantio de café em sistema agrícola convencional as atividades de aração, aplicação de matéria orgânica e de bater covas contribuíram com 73,92% das emissões estimadas de CO2 eq ha-1 nesta etapa, totalizando 178,61 kg CO2 eq ha-1. Nos tratos culturais as operações realizadas para colheita mecanizada apresentaram-se como as maiores fontes de emissão de GEE, estimadas em 123,81 kg CO2 eq ha-1.

Elevated surface paleobrine temperatures (average 85.6 °C) are reported here from Cretaceous marine halites in the Maha Sarakham Formation, Khorat Plateau, Thailand. Fluid inclusions in primary subaqueous “chevron” and “cumulate” halites associated with potash salts contain daughter crystals of sylvite (KCl) and carnallite (MgCl2·KCl·6H2O). Petrographic textures demonstrate that these fluid inclusions were trapped from the warm brines in which the halite crystallized. Later cooling produced supersaturated conditions leading to the precipitation of sylvite and carnallite daughter crystals within fluid inclusions. Dissolution temperatures of daughter crystals in fluid inclusions from the same halite bed vary over a large range (57.9 °C to 117.2 °C), suggesting that halite grew at different temperatures within and at the bottom of the water column. Consistency of daughter crystal dissolution temperatures within fluid inclusion bands and the absence of vapor bubbles at room temperature demonstrate that fluid inclusions have not stretched or leaked. Daughter crystal dissolution temperatures are reproducible to within 0.1 °C to 10.2 °C (average of 1.8 °C), and thus faithfully document paleobrine conditions. Microcrystalline hematite incorporated within halite crystals also indicate high paleobrine temperatures. We conclude that halite crystallized from warm brines rich in K-Mg-Na-Cl; sylvite and carnallite daughter crystals were nucleated during cooling of the warm brines sometime after deposition. Hothouse, hydrothermal, and solar-heating hypotheses are compared to explain the anomalously high surface paleobrine temperatures. Solar radiation stored in shallow density stratified brines is the most plausible explanation for the observed paleobrine temperatures and the progressively higher temperatures downward through the paleobrine column. The solar-heating hypothesis may also explain high paleobrine temperatures documented from fluid inclusions in other ancient halites.

A suinocultura é uma atividade econômica de destaque no agronegócio brasileiro. Entretanto, a geração de efluentes em grande quantidade com potencial de poluição elevado caracteriza um obstáculo para o crescimento desta atividade. Diante deste cenário, este trabalho objetivou contextualizar a importância ambiental, econômica e sanitária do tratamento das dejeções suinícolas e descrever a tecnologia da biodigestão anaeróbia aplicada neste âmbito. A adoção da biodigestão anaeróbia se apresenta como uma alternativa eficiente para o tratamento destes dejetos. O uso de biodigestores promove um ambiente com condições anaeróbias que possibilita o desenvolvimento de bactérias hidrolíticas, acidogênicas, acetogênicas e metanogênicas que promovem a degradação da matéria orgânica e a reciclagem de nutrientes culminando na geração de subprodutos de valor agregado: biogás e biofertilizante, com desdobramentos ambientais, sanitários, econômicos e sociais positivos.