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Dust aerosols affect the radiative and energy balance at local and global scales by scattering and absorbing sunlight and infrared light. A previous study suggests that dust size distribution is one of the major sources of uncertainty in modeling the dust global distribution. Climate models overestimate the fine dust (≤5 µm) by an order of magnitude, while underestimates of the coarse dust (≥5 µm) range between 0.5 to 1.5 orders of magnitude compared with the global observations. Here we improved the simulated size distribution of dust aerosol using a sectional aerosol model (Community Aerosol and Radiation Model for Atmospheres) coupled with the Community Earth System Model (CESM1/CARMA). Simulated dust mass size distributions peak at around 2–3 µm in diameter and increase by 4 orders of magnitude from 0.1 to 2 µm. Our model demonstrates that North African, Middle Eastern, and Asian dust accounts for ∼ 59.7 %, 12.5 %, and 13.3 % of the global annual mean dust emissions, with the remaining 14.5 % originating from scattered smaller dust sources. The model dust vertical distributions are validated against the NASA Atmospheric Tomography (ATom) field campaign datasets. Both simulations and ATom in situ measurements during the ATom field campaign suggest that dust mass concentrations over the remote ocean drop by 2 to 3 orders of magnitude from the surface to the upper troposphere (200 hPa). Our model suggests that Asian dust contributes to more than 40 % of annual mean dust mass abundances in the global upper troposphere and lower stratosphere (UTLS). The model suggests that Asian dust dominates the dust mass budget in the UTLS of the Asian summer monsoon (ASM) region, with a relative contribution 1–2 orders of magnitude higher than the dust originating from the North African and Middle Eastern deserts.

The direct effects of nuclear war would be horrific, with blast, fires, and radiation killing and injuring many people. But in 1983, United States and Soviet Union scientists showed that a nuclear war could also produce a nuclear winter, with catastrophic consequences for global food supplies for people far removed from the conflict. Smoke from fires ignited by nuclear weapons exploded on cities and industrial targets would block out sunlight, causing dark, cold, and dry surface conditions, producing a nuclear winter, with surface temperatures below freezing even in summer for years. Nuclear winter theory helped to end the nuclear arms race in the 1980s and to produce the Treaty on the Prohibition of Nuclear Weapons in 2017, which led to the 2017 Nobel Peace Prize. Because awareness of nuclear winter is now widespread, nuclear nations have so far not used nuclear weapons. But the mere existence of nuclear weapons means that they can be used, by unstable leaders or because of an accident, computer malfunction, sensor malfunction, human error, or terrorism. Because they cannot be used without the danger of escalation and a global humanitarian catastrophe, and because of recent threats to use them by Russia, it is even more urgent for scientists to broadly communicate their results and work for the elimination of nuclear weapons.

The tropospheric and stratospheric nitrate aerosol is simulated by a sectional aerosol model coupled to the Community Earth System Model. The simulated nitrate mass fractional contribution to aerosols is significantly higher in the upper troposphere and lower stratosphere (UTLS) than that at the surface. Both in situ measurements and simulations show that nitrate aerosol accounts for about 30%-40% of the aerosol mass at the tropopause of the Asian summer monsoon (ASM) region. Furthermore, simulated condensed nitric acid particles account for ∼20% of the annual mean aerosol mass at the tropical tropopause, and over 95% in the UTLS at the South Pole in June-July-August. Our study suggests that the extremely cold ambient conditions in the UTLS of the tropics, ASM and polar regions thermodynamically favor the condensation of ammonia and nitric acid. The widely distributed nitrate aerosol in the global UTLS may be overlooked by climate models.

Dust aerosols affect the radiative and energy balance at local and global scales by scattering and absorbing sunlight and infrared light. Parameterizations of dust lifting, microphysics, as well as physical and radiative properties of dust in climate models are still subject to large uncertainty. Here we use a sectional aerosol model (CARMA) coupled with a climate model (CESM1) to investigate the global distribution of dust aerosols, with an emphasis on the vertical distribution of dust. Consistent with observations at locations remote from source regions, simulated dust mass size distributions peak at around 2–3 micrometres in diameter and increase by 4 orders of magnitude from 0.1 μm to 2 µm. The size distribution above 2 µm is highly variable depending on distance from the source, and subject to uncertainty due to possible size dependent changes in physical properties such as shape and density. Simulated annual mean dust mass concentrations are within one order of magnitude of those found by the surface measurement network around the globe. Simulated annual mean aerosol optical depths are ~10 % lower than AERONET observations near the dust source regions. Both simulations and in-situ measurements during the NASA ATom field campaign suggest that dust mass concentrations over the remote ocean drop by two to three orders of magnitude from the surface to the upper troposphere (200 hPa). The model suggests that Saharan, Middle Eastern, and Asian dust accounts for ~59.7 %, 12.5 %, and 13.3 % of the global annual mean dust emissions, with the remaining 14.5 % originating from scattered smaller dust sources. Although Saharan dust dominates global dust mass loading at the surface, the relative contribution of Asian dust increases with altitude and becomes dominant in the upper troposphere. The simulations show that Asian dust contributes ~60.9 % to the global and annual mean dust concentration between 266 hPa and 160 hPa. Asian dust is mostly lifted in the spring by mid-latitude frontal systems. However, deep convection during the Asian summer monsoon (ASM) favours the vertical transport of local dust to the upper atmosphere. Simulated dust accumulates in the ASM anticyclone and forms a local maximum; however, the simulated dust mass concentration is only ~0.04 % of the total aerosols in the Asian Tropopause Aerosol Layer (ATAL), which are dominated by organics, sulfates and nitrates.

Significance Nuclear conflict poses the chilling prospect of triggering abrupt global cooling, and consequently, severely reduced crop production. However, the impacts on marine fisheries are unknown. If agricultural yields fall on land, could we turn to the sea instead? Here, we show that agricultural losses could not be offset by the world’s fisheries, especially given widespread overfishing. Cold temperatures and reduced sunlight would decrease the growth of fish biomass, at worst as much as under unmitigated climate change. Although intensified postwar fishing could yield a small catch increase, dramatic declines would ensue due to overharvesting. However, effective prewar fisheries management would create a substantial buffer of fish in the ocean, greatly increasing the oceans’ potential contribution during a global food emergency., Nuclear war, beyond its devastating direct impacts, is expected to cause global climatic perturbations through injections of soot into the upper atmosphere. Reduced temperature and sunlight could drive unprecedented reductions in agricultural production, endangering global food security. However, the effects of nuclear war on marine wild-capture fisheries, which significantly contribute to the global animal protein and micronutrient supply, remain unexplored. We simulate the climatic effects of six war scenarios on fish biomass and catch globally, using a state-of-the-art Earth system model and global process-based fisheries model. We also simulate how either rapidly increased fish demand (driven by food shortages) or decreased ability to fish (due to infrastructure disruptions), would affect global catches, and test the benefits of strong prewar fisheries management. We find a decade-long negative climatic impact that intensifies with soot emissions, with global biomass and catch falling by up to 18 ± 3% and 29 ± 7% after a US–Russia war under business-as-usual fishing—similar in magnitude to the end-of-century declines under unmitigated global warming. When war occurs in an overfished state, increasing demand increases short-term (1 to 2 y) catch by at most ∼30% followed by precipitous declines of up to ∼70%, thus offsetting only a minor fraction of agricultural losses. However, effective prewar management that rebuilds fish biomass could ensure a short-term catch buffer large enough to replace ∼43 ± 35% of today’s global animal protein production. This buffering function in the event of a global food emergency adds to the many previously known economic and ecological benefits of effective and precautionary fisheries management.

This article describes how an India-Pakistan nuclear war might come to pass, and what the local and global effects of such a war might be. The direct effects of this nuclear exchange would be horri...

In a nuclear war, bombs targeted on cities and industrial areas would start firestorms, injecting large amounts of soot into the upper atmosphere, which would spread globally and rapidly cool the planet. The soot loadings would cause decadal disruptions in Earth’s climate, which would impact food production systems on land and in the oceans. In 1980s, investigations of nuclear winter impacts on global agricultural production and food availability for 15 nations, but new information now allows us to update those estimates. Recently, several studies analyzed changes of major grain crops and marine wild-catch fisheries for different scenarios of regional nuclear war using sophisticated models. However, the impact on the total food supply available to humans is more complex. Here we show that considering all food sources and potential adaptation measures, such as using animal feed directly for humans, famine would result for most of Earth even from a war between India and Pakistan using less than 3% of the global nuclear arsenal. We look at the climate impacts from a range of scales from regional to global nuclear war, and estimate the total amount of food calories available in each nation, including crops, livestock, and fisheries, for each year following a nuclear holocaust. Our findings quantify the global indirect impacts of nuclear war away from target areas, and demonstrate the need to prevent any scale of nuclear war.

Solar-powered lofting makes stratospheric aerosol injection viable with the existing aircraft fleet., Many climate intervention (CI) methods have been proposed to offset greenhouse gas–induced global warming, but the practicalities regarding implementation have not received sufficient attention. Stratospheric aerosol injection (SAI) involves introducing large amounts of CI material well within the stratosphere to enhance the aerosol loading, thereby increasing reflection of solar radiation. We explore a delivery method termed solar-powered lofting (SPL) that uses solar energy to loft CI material injected at lower altitudes accessible by conventional aircraft. Particles that absorb solar radiation are dispersed with the CI material and heat the surrounding air. The heated air rises, carrying the CI material to the stratosphere. Global model simulations show that black carbon aerosol (10 microgram per cubic meter) is sufficient to quickly loft CI material well into the stratosphere. SPL could make SAI viable at present, is also more energy efficient, and disperses CI material faster than direct stratospheric injection.

Submicrometre-size meteoric smoke aggregates form when interplanetary dust particles ablate and re-coagulate in the Martian atmosphere. The MAVEN (Mars Atmosphere and Volatile Evolution) satellite has detected pervasive ionized metallic layers due to meteor ablation at an 80–90 km altitude, which suggests a continuous supply of meteoric smoke particles that settle to lower altitudes. Until now, meteoric smoke has been neglected in general circulation model studies of the formation of Martian water ice clouds. Here we show that when meteoric smoke is included in simulations of the atmospheric circulation on Mars, mesospheric water ice clouds form at low pressures and in discrete layers, polar hood clouds extend to higher altitudes and the seasonal Hadley cell is weakened. Furthermore, we find that the middle atmosphere water ice clouds respond to and influence the diurnal and semidiurnal migrating thermal tides. We conclude that Mars atmospheric simulations that neglect meteoric smoke do not reproduce the observed spatial distribution of water ice clouds and miss crucial radiative impacts on the overall atmospheric dynamics. Particles from interplanetary dust ablating in Mars’ atmosphere control high-altitude water ice cloud formation, according to numerical simulations of the Martian atmosphere.

The climate impacts of smoke from fires ignited by nuclear war would include global cooling and crop failure. Facing increased reliance on ocean-based food sources, it is critical to understand the physical and biological state of the post-war oceans. Here we use an Earth system model to simulate six nuclear war scenarios. We show that global cooling can generate a large, sustained response in the equatorial Pacific, resembling an El Nino but persisting for up to seven years. The El Nino following nuclear war, or Nuclear Nino, would be characterized by westerly trade wind anomalies and a shutdown of equatorial Pacific upwelling, caused primarily by cooling of the Maritime Continent and tropical Africa. Reduced incident sunlight and ocean circulation changes would cause a 40% reduction in equatorial Pacific phytoplankton productivity. These results indicate nuclear war could trigger extreme climate change and compromise food security beyond the impacts of crop failure. A nuclear conflict could lead to global cooling followed by a large and sustained El Nino-like response in the tropical Pacific region, according to an evaluation of six scenarios for nuclear conflict with an Earth system model.

Significance Impacts of global warming on agricultural productivity have been evaluated extensively. The implications of sudden cooling for global crop growth, however, are as yet little understood. While crop failures after historic volcanic eruptions are documented, a nuclear conflict can cause even more severe and longer-lasting climate anomalies. India and Pakistan are contributing to a de facto Asian arms race and the political instability in South Asia increasingly imposes a global threat. Based on comprehensive climate and crop model ensemble simulations, we provide critical quantitative information on how sudden cooling and perturbations of precipitation and solar radiation could disrupt food production and trade worldwide for about a decade—more than the impact from anthropogenic climate change by late century., A limited nuclear war between India and Pakistan could ignite fires large enough to emit more than 5 Tg of soot into the stratosphere. Climate model simulations have shown severe resulting climate perturbations with declines in global mean temperature by 1.8 °C and precipitation by 8%, for at least 5 y. Here we evaluate impacts for the global food system. Six harmonized state-of-the-art crop models show that global caloric production from maize, wheat, rice, and soybean falls by 13 (±1)%, 11 (±8)%, 3 (±5)%, and 17 (±2)% over 5 y. Total single-year losses of 12 (±4)% quadruple the largest observed historical anomaly and exceed impacts caused by historic droughts and volcanic eruptions. Colder temperatures drive losses more than changes in precipitation and solar radiation, leading to strongest impacts in temperate regions poleward of 30°N, including the United States, Europe, and China for 10 to 15 y. Integrated food trade network analyses show that domestic reserves and global trade can largely buffer the production anomaly in the first year. Persistent multiyear losses, however, would constrain domestic food availability and propagate to the Global South, especially to food-insecure countries. By year 5, maize and wheat availability would decrease by 13% globally and by more than 20% in 71 countries with a cumulative population of 1.3 billion people. In view of increasing instability in South Asia, this study shows that a regional conflict using

Large fires can inject smoke into the upper troposphere and lower stratosphere. Detailed fire simulations allow for assessment of how local weather interacts with these fires and affects smoke lofting. In this study, we employ the fire simulation package in the Weather Research and Forecasting model (WRF-Fire), Version 4.0.1, to explore how smoke lofting from a fire burning a homogeneous fuel bed changes with varying local winds, relative humidity, and atmospheric boundary-layer stability for two different-sized areal fires. We find that the presence of moisture has the greatest influence on the results by raising the altitude of lofting, while faster winds speeds dampen lofting and lower the injection height. Stably stratified conditions further inhibit plume propagation compared with neutrally stratified conditions.

Volcanic ash is often neglected in climate simulations because ash particles are assumed to have a short atmospheric lifetime, and to not participate in sulfur chemistry. After the Mt. Kelut eruption in 2014, stratospheric ash-rich aerosols were observed for months. Here we show that the persistence of super-micron ash is consistent with a density near 0.5 g cm−3, close to pumice. Ash-rich particles dominate the volcanic cloud optical properties for the first 60 days. We also find that the initial SO2 lifetime is determined by SO2 uptake on ash, rather than by reaction with OH as commonly assumed. About 43% more volcanic sulfur is removed from the stratosphere in 2 months with the SO2 heterogeneous chemistry on ash particles than without. This research suggests the need for re-evaluation of factors controlling SO2 lifetime in climate model simulations, and of the impact of volcanic ash on stratospheric chemistry and radiation., Volcanic ash is often neglected in climate simulations as it is assumed to have a short atmospheric lifetime. Here, the authors show a persistent super-micron ash layer after the Mt. Kelut eruption in 2014 that impacts the stratospheric sulfur burden and chemistry for over the first months after the eruption.

Deep convective transport of gaseous precursors to ozone (O(3)) and aerosols to the upper troposphere is affected by liquid phase and mixed-phase scavenging, entrainment of free tropospheric air and aqueous chemistry. The contributions of these processes are examined using aircraft measurements obtained in storm inflow and outflow during the 2012 Deep Convective Clouds and Chemistry (DC3) experiment combined with high-resolution (dx ≤ 3 km) WRF-Chem simulations of a severe storm, an air mass storm, and a mesoscale convective system (MCS). The simulation results for the MCS suggest that formaldehyde (CH(2)O) is not retained in ice when cloud water freezes, in agreement with previous studies of the severe storm. By analyzing WRF-Chem trajectories, the effects of scavenging, entrainment, and aqueous chemistry on outflow mixing ratios of CH(2)O, methyl hydroperoxide (CH(3)OOH), and hydrogen peroxide (H(2)O(2)) are quantified. Liquid phase microphysical scavenging was the dominant process reducing CH(2)O and H(2)O(2) outflow mixing ratios in all three storms. Aqueous chemistry did not significantly affect outflow mixing ratios of all three species. In the severe storm and MCS, the higher than expected reductions in CH(3)OOH mixing ratios in the storm cores were primarily due to entrainment of low-background CH(3)OOH. In the air mass storm, lower CH(3)OOH and H(2)O(2) scavenging efficiencies (SEs) than in the MCS were partly due to entrainment of higher background CH(3)OOH and H(2)O(2). Overestimated rain and hail production in WRF-Chem reduces the confidence in ice retention fraction values determined for the peroxides and CH(2)O.

Of the nine countries known to have nuclear weapons, six are located in Asia and another, the United States, borders the Pacific Ocean. Russia and China were the first Asian nations with nuclear weapons, followed by Israel, India, Pakistan, and North Korea. Most of the world's nuclear powers are reducing their arsenals or maintaining them at historic levels, but several of those in Asia—India, Pakistan, and North Korea—continue to pursue relentless and expensive programs of nuclear weapons development and production. Hopefully, the nuclear agreement reached in July 2015 between Iran, the European Union, and the five permanent members of the United Nations Security Council will be a step toward eliminating nuclear weapons throughout Asia and the rest of the world. As we will discuss below, any country possessing a nuclear arsenal is on a path leading toward self-assured destruction, and is a threat to people everywhere on Earth.