The Human and Climatic Effects of an India-Pakistan Nuclear Conflict

By Christine Parthemore

On October 2, a team of researchers published the results of extensive work to model the effects of nuclear war between Pakistan and India. The scenario, posited for the year 2025, features a high-casualty terrorist attack on Indian government officials resulting in widespread conflict between these countries.

In “Rapidly expanding nuclear arsenals in Pakistan and India portend regional and global catastrophe,” published in Science Advances, the authors chose a scenario in which India and Pakistan successfully use 300 strategic nuclear weapons against one another’s urban targets. Their chosen scenario entails further conflict, but with some weapons failing to detonate and some being targeted at remote military sites for which damage was not included.

The article presents stark human and climatic results of such a conflict. It estimates that 50 to 125 million people could die in the immediate conflict. Global surface temperatures could decline 2° to 5°C with precipitation declining by 15 to 30%. Effects would spread globally but vary by region, and “net primary productivity declines 15 to 30% on land and 5 to 15% in oceans threatening mass starvation and additional worldwide collateral fatalities.”

Behind this work, there is a long and interesting history of nuclear weapons and climate work intertwining. The methods and tech developed in the early decades of the nuclear age to better understand the potential effects of nuclear weapon detonations later contributed to scientists identifying that Earth’s climate was changing due to human influences. Many personalities overlap in this history as well: numerous scientists from the United States, the Soviet Union, and elsewhere have played key roles in understanding atmospheric effects of both nuclear weapons and the changing climate.   

Over the past few decades, this nuclear-climate relationship has extended into the social sciences and medicine as well. For example, psychologists have found that people instinctively equate nuclear destruction and environmental devastation even when they have little specific knowledge about either set of issues. (Think about the tendency to equate these issues every time you hear someone say that climate change and nuclear weapons use are two of the world’s greatest threats.) In an edited volume published in March based on a workshop held by the Nobel Institute, Nuclear Disarmament: A Critical Assessment, I contributed a chapter on this intermingled history.    

We at CSR have been working at this intersection as well, operating a multidisciplinary Working Group since 2016 that works to more deeply understand the links between nuclear and climate issues as they affect and are affected by national and international security dynamics. CSR’s podcast network explores these issues together as well, including in recent episodes on Pakistan and China.

Turning back to the study, the specific scenario used warrants special thought. The article is thorough in explaining its approach. It outlines a range of potential conflict scenarios their modeling did and did not cover and numerous important variables: yields of the weapons, where and how they are used, failure rates of the nuclear weapons employed, whether specific weapons are targeted to urban or unpopulated areas, potential fuel for fires, what calculations are made regarding China’s potential backing of Pakistan in wartime, and others. The scenario the researchers finally used for their modeling work is well-backed by research and expert views on how a large-scale India-Pakistan conflict may unfold. 

Particularly important is the study’s detailed exploration of how conflict escalation could occur. The size of the nuclear arsenals used—100s of nuclear weapons—may give some readers pause, as it has become fashionable among some experts to believe that nuclear escalation can be controlled and carried forward in a logical, predictable matter as conflicts play out. Indeed, some modeling work has been used to support this idea, in some cases downplaying the potential effects of nuclear weapons in some scenarios (though this work is at times done with more basic decision-support modeling systems, not the sophisticated models used at top universities and national labs). 

Building on the scenario used in this study of large-scale nuclear conflict, it would be important to test the assumptions and results behind various scenarios in which low-yield nuclear weapons are used and escalation is (hypothetically) more limited. Climate effect modeling can be used to argue contradictory ideas, contributing to important debates but potentially leaving the public and policy makers a bit confused about which results are more accurate. As I wrote in the Nuclear Disarmament chapter: 

“Deeper understanding of climate questions related to nuclear weapons may have particularly strong implications for concepts such as limited nuclear war and escalation control, as they did late in the twentieth century. Policymakers and experts in countries such as Pakistan, Russia, and the United States are actively debating or advancing these concepts and their implications for effective deterrence, credibility, and the desirability of nuclear weapons investments designed to build relevant capabilities—low-yield options in particular.

The exact role the nuclear-climate link will play is unclear. Updated models of the climate effects of nuclear weapons use are making their way into current nuclear weapons discourse, and some experts are developing new, easy-to-understand tools to convey the impacts to the general public. Some of this work is overtly designed to mobilize support for arms limitations and disarmament. However, the deeper knowledge we have today of the environmental and health effects of nuclear weapons use is simultaneously being used to help justify investments in lower-yield nuclear weapons and doctrines designed with the intention of limiting the scope and scale of nuclear warfare, should it occur.

No matter the policy implications, it remains important to run and rerun current models to help game out the specific nuclear weapons use scenarios that reflect new thinking on the prospects of limited nuclear war, escalate-to-deescalate concepts, and use of newer, lower-yield nuclear weapons.”

Such work could play an important role in nuclear policy discourse. There is a growing schism between the long-held, bipartisan assumption by U.S. presidents, NATO leaders, and countless defense experts that escalation in nuclear warfare cannot be predicted and we cannot expect that it would remain constrained; and newer concepts that take the opposing view, especially if specific types of nuclear weapons that they perceive as less destructive are the ones used early in conflict.  

The Science Advances article is sure to provoke responses, including similar scenarios modeled by other scholars in efforts to replicate or refute the results. However such back-and-forth proceeds, it will be a worthy addition to discourse on nuclear war. 

Whatever plays out, this article is an important contribution. Nuclear weapon policies are too often discussed in highly abstract terms, normally focused on their effects on nation-state political behavior. With the world having entered a new nuclear arms race, it is important to increase attention paid to the potential effects of their use on people and the physical environment.


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