Multidecadal global cooling and unprecedented ozone loss following a regional nuclear conflict

Abstract

We present the first study of the global impacts of a regional nuclear war with an Earth system model including atmospheric chemistry, ocean dynamics, and interactive sea ice and land components. A limited, regional nuclear war between India and Pakistan in which each side detonates 50 15 kt weapons could produce about 5 Tg of black carbon (BC). This would self-loft to the stratosphere, where it would spread globally, producing a sudden drop in surface temperatures and intense heating of the stratosphere. Using the Community Earth System Model with the Whole Atmosphere Community Climate Model, we calculate an e-folding time of 8.7 years for stratospheric BC compared to 4-6.5 years for previous studies. Our calculations show that global ozone losses of 20%-50% over populated areas, levels unprecedented in human history, would accompany the coldest average surface temperatures in the last 1000 years. We calculate summer enhancements in UV indices of 30%-80% over midlatitudes, suggesting widespread damage to human health, agriculture, and terrestrial and aquatic ecosystems. Killing frosts would reduce growing seasons by 10-40 days per year for 5 years. Surface temperatures would be reduced for more than 25 years due to thermal inertia and albedo effects in the ocean and expanded sea ice. The combined cooling and enhanced UV would put significant pressures on global food supplies and could trigger a global nuclear famine. Knowledge of the impacts of 100 small nuclear weapons should motivate the elimination of more than 17,000 nuclear weapons that exist today.

Climate effects of a hypothetical regional nuclear war: Sensitivity to emission duration and particle composition

“…In the 5BC 1d case, the mean global precipitation as well as cloud cover decreases compared to the reference climate (Figures 2e and 2f ), which is consistent with earlier studies [Robock et al, 2007;Mills et al, 2014]. However, given the smaller radiative imbalance simulated in our model and the consequently much weaker cooling of the ocean compared to the above-mentioned studies, the magnitude of the decrease in global Interestingly, while for temperature, the shorter-emission duration (1 day and 1 week) scenarios show the greatest globally averaged anomalies (Figures 2c and 2d), for precipitation the 1-month scenarios display the largest impacts with a decrease of up to 50% more (Figure 2e).…”

“…The maximum peak mass mixing ratio of about 20 kg (BC)/10 9 kg (air), reaches the top of the model at ∼40 km within 1 month and then sinks down to 25 km after 10-12 months ( Figure 1a). These values are notably lower compared to the values shown in a recent work by Mills et al [2014] where the BC peak is around 60 kg (BC)/10 9 kg (air) reaching heights of up to 60 km a.s.l. The maximum peak stays in the upper stratosphere (∼40 to 50 km) for the entire first year.…”

“…As mentioned above, such a difference may be related to several aspects such as the different vertical and horizontal model resolution, the height of top of the model, the size of the emission region as well as the transport and dispersion of particles. Furthermore, compared to the study by Mills et al [2014], the change in ocean temperature is substantially smaller in our study [cf. Figures 2d and 6 in Mills et al, 2014], indicating that the ocean model may also play an important part in explaining the different results.…”

“…The maximum temperature anomaly is larger in the study by Mills et al [2014] who also found the peak anomaly at a height above the model top in our experiments. However, there is little air at these heights so it is easily heated.…”

“…The selected year is characterized by a neutral ENSO state to avoid possible ENSO imprint on the simulated climate anomalies associated with the nuclear war [Pausata et al, 2015a]. The choice of the detonation date (January 1st) is arbitrary and follows [Mills et al, 2014]. The choice is further driven by the fact that the high concentrations of BC and POM tend to render the model unstable during the summer months.…”