Often, we can tend to examine global crises in isolation – however, they can have surprising feedback effects on one another. The COVID-19 pandemic, for instance, has led to a small global decrease in emissions, and climate experts are examining the effects that prolonged work-from-home practices might have on emissions trajectories. Now, researchers at Lawrence Livermore National Laboratory (LLNL) are using supercomputing to examine the effects that a limited nuclear war might have on climate change.
The researchers examined a scenario involving an exchange of a hundred 15-kiloton nuclear weapons (each roughly the tonnage of the “Little Boy” bomb that was dropped on Hiroshima) between India and Pakistan. Military tensions between India and Pakistan – which both possess nuclear weapons – have several times brought the two countries perilously close to nuclear war.
Using two high-fidelity models, the researchers took a variety of novel factors into account, including the prevalence of fuel at the site of a given nuclear blast, the characteristics of smoke plumes from resulting fires, aerosol properties and more. This allowed the researchers to develop an improved understanding of how the fires that would follow such a nuclear exchange might affect the global climate.
“One of the new aspects of our work is that we examined the dependence of the climate effects on different amounts of fuel available at the location of the detonation and subsequent fire,” said LLNL mechanical engineer Katie Lundquist, who led the study.
“Previous research has been inconclusive about what the consequences might be for the global climate from a regional nuclear weapons exchange,” added Lee Glascoe, a co-author of the study and the leader of LLNL’s National Atmospheric Release Advisory Center (NARAC).
To run the simulations, the researchers first used the Weather Research and Forecasting (WRF) model to simulate black carbon emissions from the nuclear fires. The results of the WRF model were then plugged into the Energy Exascale Earth System Model (E3SM), a fully coupled, high-resolution climate system introduced in 2018 with the intent of scaling to forthcoming exascale supercomputers.
“Our simulations show that the smoke from 100 simultaneous firestorms would block sunlight for about four years, instead of the eight to fifteen years predicted in other models,” the researchers wrote in their paper. “Additionally, we show that the global effects of the fires are sensitive to fuel availability and consumption, factors which are uncertain for cities in India and Pakistan.”
In addition to the study’s conclusions, the structure of the study itself bore special significance.
“This paper highlights that many localized processes, such as fuel density and fire intensity, could drive the global results,” Glascoe said. “There is a significance to this joint effort. We combined local weather-driven events, which is something in which NARAC specializes, with global climate-driven events, which is something in which the Climate Program specializes.”