NASA climate scientists are playing with fire… from a nuclear war, to be precise…in a computer simulation, that is. The computer simulations are an attempt to determine the effects of a limited or regional nuclear war on the planet’s climate system.
Lead researchers Luke Oman at NASA’s Goddard Space Flight Center actually conceived of the idea five years ago at a meeting of the American Geophysical Union (AGU). He had been presenting his research on the impact of volcanoes (sulfur dioxide gas) on the climate, using a computer simulation. Several other colleagues approach him wanting to know the impact of black soot aerosols resulting from a nuclear conflict.
The two “ingredients” or inputs (sulfur dioxide and soot) are different in their impacts. They differ principally in the amount of sunlight they absorb or reflect (or let pass through to reach the surface). Volcanic aerosols can warm the upper atmosphere somewhat, but generally produce a cooling effect on near-surface atmospheric temperatures. Initially, nuclear-borne fires would produce a dramatic heating effect, but the massive injection of black soot into the upper atmosphere that follows this would tend to counteract that by blocking incoming radiation.
The initial input for the simulation was 5 teragrams (megatons) of black carbon particles injected into Earth’s upper troposphere. This is the estimated result of the surface detonation of 100 Hiroshima-size bombs (each equivalent to 15K tons of TNT).
Although inferior to H-bombs and today’s nuclear arsenal (The US/Russia have primarily hydrogen bombs, designated by mega-tonnage), even this relatively modest exchange could have a dramatic climate impact that would last years.
But it could also “revert” years of global warming impacts.
The scientists used a general circulation model known as ModelE (developed at NASA’s Goddard Institute for Space Studies, New York). The model calculates ocean-atmosphere coupling effects in addition to allowing varying aerosol inputs.
Running their simulation, the team found that global temperatures would fall by a little over 1 °C (1.8 °F) over the first three years (3 times more cooling, for 3 times longer, than from the Mt. Pinatubo explosion). Also, because black soot is smaller/lighter that the sulfur particles, they can be carried higher into the upper troposphere. Once in this atmospheric band, impacts can last up to a decade or more.
Here is one typical scenario:
In a theoretical regional war, as in one between India And Pakistan, widespread fires would result sending thick clouds of dust, ash and smoke into the troposphere. Acting as a gigantic black soot sun screen, the layer of black carbon aerosols would absorb a good deal of heat radiation (making it rise up higher like a hot-air balloon), warming the upper atmosphere, where it would continue to block some quantity of the in-coming solar radiation.
On the surface, apart from suffering the effects of nuclear radiation, the short to medium-term impacts of this effect would be:
1] A decrease in global temperatures (up to 1.5° Celsius [2.7° F] drop in average global temperatures) over three years.
This would be a slighter version of the “nuclear winter” that was so chillingly described by Carl Sagan in a televised panel discussion, following the broadcast of the film The Day After (early 198o’s).
2] A decrease in rainfall (up to 10%), two to four years after the event
Since heat (input) is the driver of precipitation cycles, a decrease in heat input (insolation) would disrupt growing seasons and have a devastating effect on world agriculture. Fresh water will become scarce, millions will starve, mass migrations will lead to more suffering and conflict…
Although the simulation shows a recovery after about ten years, the impact of such a “limited” nuclear scenario would be highly disruptive to life as we know it, and the impact on human civilization would be long-term (for example, through a protracted, global conflict, or series).
According to colleagues at the National Center for Atmospheric Research (NCAR), the nuclear scenario also results in loss of ozone in the stratosphere, which would then allow more solar input/radiation, countering any cooling impact (as the black carbon layer dissipates), and possibly reverting the Earth to its previous, warming state, or, sending it into a hothouse state.
The simulated scenario was never conceived of as any sort of radical geo-engineering method, but to perhaps serve as a cautionary tale concerning impacts from a nuclear exchange.
In an NASA website news article by Kathryn Hansen, the team was asked about the relevance of this simulation to policy makers:
“A primary goal of this work is to get the information revealed by our study into the hands of decision makers as well as to get other groups interested in this problem and to be aware of the potential impacts. Before we did this study, we didn’t know what the climate anomalies would be or how long they would last. This is critical information that needs to be known in advance along with knowledge that the consequences of such a scenario would be global.”
Some source material for this article came from the NASA news article : How would nuclear war affect the climate? by Kathryn Hansen
