Showing papers by "Owen B. Toon published in 2019"

Black carbon lofts wildfire smoke high into the stratosphere to form a persistent plume.

Abstract: In 2017, western Canadian wildfires injected smoke into the stratosphere that was detectable by satellites for more than 8 months. The smoke plume rose from 12 to 23 kilometers within 2 months owing to solar heating of black carbon, extending the lifetime and latitudinal spread. Comparisons of model simulations to the rate of observed lofting indicate that 2% of the smoke mass was black carbon. The observed smoke lifetime in the stratosphere was 40% shorter than calculated with a standard model that does not consider photochemical loss of organic carbon. Photochemistry is represented by using an empirical ozone-organics reaction probability that matches the observed smoke decay. The observed rapid plume rise, latitudinal spread, and photochemical reactions provide new insights into potential global climate impacts from nuclear war.

Nuclear Winter Responses to Nuclear War Between the United States and Russia in the Whole Atmosphere Community Climate Model Version 4 and the Goddard Institute for Space Studies ModelE

Abstract: Current nuclear arsenals used in a war between the United States and Russia could inject 150 Tg of soot from fires ignited by nuclear explosions into the upper troposphere and lower stratosphere. We simulate the climate response using the Community Earth System Model‐Whole Atmosphere Community Climate Model version 4 (WACCM4), run at 2° horizontal resolution with 66 layers from the surface to 140 km, with full stratospheric chemistry and with aerosols from the Community Aerosol and Radiation Model for Atmospheres allowing for particle growth. We compare the results to an older simulation conducted in 2007 with the Goddard Institute for Space Studies ModelE run at 4° × 5° horizontal resolution with 23 levels up to 80 km and constant specified aerosol properties and ozone. These are the only two comprehensive climate model simulations of this scenario. Despite having different features and capabilities, both models produce similar results. Nuclear winter, with below freezing temperatures over much of the Northern Hemisphere during summer, occurs because of a reduction of surface solar radiation due to smoke lofted into the stratosphere. WACCM4's more sophisticated aerosol representation removes smoke more quickly, but the magnitude of the climate response is not reduced. In fact, the higher‐resolution WACCM4 simulates larger temperature and precipitation reductions than ModelE in the first few years following a 150‐Tg soot injection. A strengthening of the northern polar vortex occurs during winter in both simulations in the first year, contributing to above normal, but still below freezing, temperatures in the Arctic and northern Eurasia.

A Review of Ice Particle Shapes in Cirrus formed In Situ and in Anvils

Abstract: Results from 22 airborne field campaigns, including more than 10 million high‐resolution particle images collected in cirrus formed in situ and in convective anvils, are interpreted in terms of particle shapes and their potential impact on radiative transfer. Emphasis is placed on characterizing ice particle shapes in tropical maritime and midlatitude continental anvil cirrus, as well as in cirrus formed in situ in the upper troposphere, and subvisible cirrus in the upper tropical troposphere layer. There is a distinctive difference in cirrus ice particle shapes formed in situ compared to those in anvils that are generated in close proximity to convection. More than half the mass in cirrus formed in situ are rosette shapes (polycrystals and bullet rosettes). Cirrus formed from fresh convective anvils is mostly devoid of rosette‐shaped particles. However, small frozen drops may experience regrowth downwind of an aged anvil in a regime with RHice > ~120% and then grow into rosette shapes. Identifiable particle shapes in tropical maritime anvils that have not been impacted by continental influences typically contain mostly single plate‐like and columnar crystals and aggregates. Midlatitude continental anvils contain single‐rimed particles, more and larger aggregates with riming, and chains of small ice particles when in a highly electrified environment. The particles in subvisible cirrus are < ~100 μm and quasi‐spherical with some plates and rare trigonal shapes. Percentages of particle shapes and power laws relating mean particle area and mass to dimension are provided to improve parameterization of remote retrievals and numerical simulations.

Rapidly expanding nuclear arsenals in Pakistan and India portend regional and global catastrophe

Abstract: Pakistan and India may have 400 to 500 nuclear weapons by 2025 with yields from tested 12- to 45-kt values to a few hundred kilotons. If India uses 100 strategic weapons to attack urban centers and Pakistan uses 150, fatalities could reach 50 to 125 million people, and nuclear-ignited fires could release 16 to 36 Tg of black carbon in smoke, depending on yield. The smoke will rise into the upper troposphere, be self-lofted into the stratosphere, and spread globally within weeks. Surface sunlight will decline by 20 to 35%, cooling the global surface by 2° to 5°C and reducing precipitation by 15 to 30%, with larger regional impacts. Recovery takes more than 10 years. Net primary productivity declines 15 to 30% on land and 5 to 15% in oceans threatening mass starvation and additional worldwide collateral fatalities.

Efficient In-Cloud Removal of Aerosols by Deep Convection.

Abstract: Convective systems dominate the vertical transport of aerosols and trace gases. The most recent in situ aerosol measurements presented here show that the concentrations of primary aerosols including sea salt and black carbon drop by factors of 10 to 10,000 from the surface to the upper troposphere. In this study we show that the default convective transport scheme in the National Science Foundation/Department of Energy Community Earth System Model results in a high bias of 10-1,000 times the measured aerosol mass for black carbon and sea salt in the middle and upper troposphere. A modified transport scheme, which considers aerosol activation from entrained air above the cloud base and aerosol-cloud interaction associated with convection, dramatically improves model agreement with in situ measurements suggesting that deep convection can efficiently remove primary aerosols. We suggest that models that fail to consider secondary activation may overestimate black carbon's radiative forcing by a factor of 2.

High-altitude water ice cloud formation on Mars controlled by interplanetary dust particles

Abstract: 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.

How an India-Pakistan nuclear war could start—and have global consequences

Abstract: 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...

Comment on "Climate Impact of a Regional Nuclear Weapon Exchange: An Improved Assessment Based on Detailed Source Calculations" by Reisner et al.

Abstract: Reisner et al. revisited a study we had done modeling the climate impacts of a nuclear war between India and Pakistan, in which fires started by 100 15‐kt atomic bombs would produce 5 Tg of soot injected into the upper troposphere, and subsequently lofted into the lower stratosphere. Their claim that there would be much less smoke than in our results is wrong for several reasons. They chose a target area of suburban Atlanta that includes a golf course, playground, and individual houses with large yards, with little material to burn, which is not representative of densely populated cities in India and Pakistan. The fire they modeled is not typical of the type of mass fire likely to result from a nuclear attack on cities. They used winds that are stronger than typical winds. They did not allow moist convection, which would be important in convective lofting of the smoke. Their claim that if they included convection the resulting rain would wash out the smoke is not supported by observations of pyrocumulonimbus injection of smoke into the stratosphere from forest fires. And they used a fire model that they have not made available for other scientists to try to reproduce their work, and which has not been shown to accurately simulate firestorms observed in Hamburg, Dresden, and Hiroshima during World War II. They significantly underestimate the amount of smoke, and climate and agricultural impacts likely after a nuclear war. Reisner et al. (2019, hereafter Reisner et al.) revisit a study we had done (Mills et al., 2014) modeling the climate impacts of a nuclear war between India and Pakistan, in which fires started by 100 15‐kt atomic bombs would produce 5 Tg of soot injected into the upper troposphere. When Reisner et al. repeated our climate model simulations with a 5‐Tg soot injection, they reproduced the same climate response. Similar results have also been reported using different models (Mills et al., 2008; Pausata et al., 2016; Robock et al., 2007). However, using results from their simulation of a mass fire in suburban Atlanta with HIGRAD‐FIRETEC, a model which is not available from them preventing others from recreating their calculations, Reisner et al. calculate that much less soot would be injected into the upper troposphere because the plumes from fires would not rise as high in the atmosphere, and therefore there would be less climate response. While we agree that this reduced smoke input would result in a much smaller climate response, we have serious concerns that the fire theymodeled is not typical of the type ofmass fire likely to result from a nuclear attack on densely populated cities in India and Pakistan and therefore their smoke estimate may significantly underestimate the amount of smoke likely to rise into the upper troposphere and lower stratosphere during a nuclear war. Reisner et al. state that they are simulating a mass fire, presumably of the sort that would be expected in an urban area after a nuclear explosion. However, it is clear that they did not simulate a firestorm such as occurred in Hamburg, Dresden, and Hiroshima during World War II. Without them demonstrating that their model can accurately simulate these actual firestorms, it is difficult to interpret conclusions from their simulations. Firestorms have strong inflowing winds so that they have little spread, extremely tall convection columns or smoke plumes, and burn for long durations until all the fuel within their perimeter is consumed (e.g., Glasstone & Dolan, 1977). Numerous studies of firestorms (e.g., Badlan et al., 2017; Cotton, 1985; Penner et al., 1986; Small et al., 1989; Small & Heikes, 1988) show smoke rising into the stratosphere from simulated firestorms, and explore the dependence of smoke altitude on fire intensity, atmospheric stability, moisture, fire size, wind speed, and other parameters. In a nuclear conflict over a large country involving a large number of weapons many of the fires would be expected to develop into firestorms. Glasstone ©2019. American Geophysical Union. All Rights Reserved. COMMENT 10.1029/2019JD030777 This article is a comment on Reisner et al. (2019), https://doi.org/10.1002/ 2017JD027331. Key Points: • Reisner et al. chose an area that included a golf course, playground, and individual houses with large yards, with little material to burn • They made other assumptions that bring into question their conclusions, including not allowing moist convection and too strong winds • Reisner et al. significantly underestimated the amount of smoke, and climate and agricultural impacts, likely after a nuclear war Correspondence to: A. Robock, robock@envsci.rutgers.edu Citation: Robock, A., Toon, O. B., & Bardeen, C. G. (2019). Comment on “Climate impact of a regional nuclear weapon exchange: An improved assessment based on detailed source calculations” by Reisner et al.. Journal of Geophysical Research: Atmospheres, 124, 12,953–12,958. https://doi.org/10.1029/ 2019JD030777 Received 9 APR 2019 Accepted 25 SEP 2019 Accepted article online 19 OCT 2019 Published online 9 DEC 2019 Author Contributions: Conceptualization: Alan Robock Formal analysis: Alan Robock, Owen B. Toon, Charles G. Bardeen Funding acquisition: Alan Robock Investigation: Charles G. Bardeen Methodology: Charles G. Bardeen Writing ‐ original draft: Alan Robock Writing – review & editing: Alan Robock, Owen B. Toon, Charles G. Bardeen ROBOCK ET AL. 12,953 and Dolan (1977) suggested, based on the experience with 69 mass fires in Japan and many others in Germany during World War II, that firestorms occur when the following criteria are met: 1. a minimum burning area of about 1.3 km; 2. half the structures in the area are on fire simultaneously; 3. a fuel load of at least 4 g/cm; and 4. ambient winds less than 3.6 m/s. Glasstone and Dolan (1977) and results from Reisner et al. show that, assuming flat topography, a 15‐kt weapon would ignite fires in a ~13‐km area including a majority of the structures within that area, thus fulfilling the first two criteria. However, the second two criteria were not met in the Reisner et al. study. The fuel load in Reisner et al. is too small to generate a fire storm. Mills et al. (2014) used smoke estimates from Toon et al. (2007), who calculate fuel loads ranging from 12.6 to 94.5 g/cm for the top 50 urban targets in India and Pakistan. These values are all significantly above the 4 g/cm threshold value needed to support a firestorm. In their paper, Reisner et al. do not provide either the target location or the fuel loads used in their fire model. Rather they state that they visually examined Google images of Indian and Pakistani cities and chose a similar area of Atlanta. In personal communications, Jon Reisner did connect us with the provider of their fuel loads, Joseph Crepeau of Applied Research Associates, Inc., so that we could assess these critical data. Their ground zero is near the East Lake Golf Club in suburban Atlanta (33.750°N, 84.305°W), more than 5 km east of downtown Atlanta. A Google Earth map of this region (Figure 1) shows that this suburban region with a golf course looks nothing like a city in India or Pakistan (e.g., Figure 2). From their fuel loadmaps, we were able to calculate the average burnable fuel load in the 13 km target area to be 0.14 g/cm and in the 10‐km × 10‐km domain of their model to be 0.91 g/cm. Both of these values are well below the fuel load threshold for a firestorm, and the target area has 6 times less fuel density than the domain average. Figure 1. Google Earth image of the location in suburban Atlanta targeted by the simulation of Reisner et al. The red circle has an area of 13 km, the area of the firestorm produced by the atomic bombing of Hiroshima on 6 August 1945. It is clear that this area includes a golf course, lake, school grounds, and widely spaced suburban homes. 10.1029/2019JD030777 Journal of Geophysical Research: Atmospheres ROBOCK ET AL. 12,954 The fuel load for the target area is also well below the value calculated using maps of population density following Toon et al. (2007) of 0.87 g/cm. Fundamentally Reisner et al. simply chose a target with very little fuel. The 0.14 g/cm value for the Reisner et al. target area is 15 to 110 times smaller than the top 50 targets in India and Pakistan which were considered in the Mills et al. (2014) study. Reisner et al. assume a wind profile with 6–8 m/s winds in the boundary layer, which they call “very calm,” but which are significantly above the threshold of 3.6 m/s for a firestorm. Toon et al. (2007) did not consider the effects of surface winds in assuming firestorm conditions. For the top targets in India and Pakistan, during May our own numerical simulations with the version of the WACCM model used by Mills et al. (2014) suggest that surface winds for likely targets would be expected to be above the firestorm threshold about 50% of the time, so assuming sufficient fuel loads, about half of the targets should develop into firestorms and half into conflagrations. Because of the choice of target location and wind speed, Reisner et al. simulated a weak conflagration rather than a firestorm. Furthermore, for their climate simulation they assume that all 100 targets have the same smoke emissions as this case. In Toon et al. (2007), targets were identified and smoke production scaled by population density and thus each location injected a different amount of smoke proportional to the population. Figure 5 of Reisner et al. shows that their fire is blowing downwind. Conflagrations were observed in World War II mass fires, and indeed were desired in order to burn the largest possible area. They are also commonly observed in modern forest fires. Reisner et al. state “As indicated below, the simulations include various worst case assumptions with regard to the specification of the fuel, weather conditions, and height of burst of the device. Therefore, they serve as upper bounds with regard to the expecte