Nuclear War and Climate Change: The Urgency for Action

Christine Parthemore speaks on nuclear war and climate change at a COP26 side event hosted by the International Forum for Understanding, Nov 1, 2021. Source: International Forum for Understanding

By Christine Parthemore

I had the honor of delivering a keynote speech at a COP26 side event hosted by the International Forum for Understanding on November 1, 2021, on the subject of nuclear war and climate change. My remarks were followed by a panel of talented, cross-discipline emerging leaders. The evening was capped with a dinner during which actors played out an allegory about climate change and nuclear war. Within this play, Asle Toje, the deputy leader of the Norwegian Nobel Committee, delivered a striking monologue as a reminder of the catastrophic risks to humanity these issues pose.

The following are my remarks as prepared and delivered.


Thank you to the International Forum for Understanding for holding this event and for exploring this subject. It is an honor to be here. I’d also like to give a special thanks to my colleagues at the Council on Strategic Risks, who I believe are at the forefront of working on the issues this event is addressing.

And thank you to everyone who is joining us here in this incredible setting.  

Today I will speak about two of the gravest risks to humanity: nuclear war and climate change — and how these threats are intertwined in countless ways. And while we now see regularly that climate change effects include influencing weather patterns and disrupting agricultural production, among others, it is far too seldom that we consider that such effects could stem from the use of nuclear weapons as well.  

The climate crisis

To begin, everyone who is here for COP, travelling during a pandemic, is likely committed to addressing the ongoing climate crisis. Numerous effects of climate change are reshaping our world — extreme droughts, deep freezes, severe storms, melting glaciers, rising seas inundating coasts, and much more. These events are devastating humanity in countless ways, such as leaving populations without sufficient food and water, forcing people to move, at times at great risk, to raising tensions among nations. 

Though the effects of climate change are taking many shapes, the regular occurrence of record-setting heat and wildfires in many parts of the world send an especially clear signal — one that is impossible to ignore. 

Each year, new record levels of heat strike different countries across the entire world – the Middle East, Asia, Europe, and the Americas. In 2019, India endured its worst heatwave ever. Canada reached its highest temperature ever this year. This July was the hottest month ever recorded. 

This heat alone is becoming severe enough that some scientists now project that in future decades, large parts of South Asia, the Middle East, and elsewhere will no longer be habitable year-round. But this projection masks the fact that these effects are already beginning and affecting the world now — in dramatic fashion. 

Horrific wildfires in Australia that began in 2019 killed an estimated 3 billion animals. The western part of the United States is still reeling from extensive wildfires this year on top of record-setting seasons each of the prior two years. In August, Russia was contending with more than 190 wildfires across Siberia that sent smoke billowing across the North Pole. Millions of acres of land, homes, and infrastructure are burning each year right before our eyes.

There is urgency in this Conference’s proceedings. The urgency is greater because the world’s leaders, to date, have not yet taken the climate crisis seriously enough. Not even close. Yet this echoes a shared challenge: across the most catastrophic risks facing humanity, whether climate change, biological risks, or the risk of nuclear war, we have historically underestimated these threats. 

Nuclear weapons  – shared history of underestimating effects

What happens when our policies and plans do not fully account for the damage they may cause to the world?

Just as we are witnessing the answers to this question unfolding regarding the climate crisis, there is a similar and in many ways shared history of underestimating the catastrophic effects that could come from nuclear weapons. 

During World War II, in the surge by the United States to ready nuclear weapons for potential use in the war, most estimates of damage focused on immediate blast effects of the use of these weapons — not secondary or enduring damage that may come after. And our knowledge of those effects was not robust. 

Those who created nuclear weapons largely seemed to believe that everyone within the area hit by these weapons would die from the nuclear blast itself — that everything would be obliterated quickly. That, it would be learned, was not necessarily the case. 

The first evidence came from the U.S. atomic bombings of Hiroshima and Nagasaki. The full human toll will never truly be known — estimates are between 110,000 and 210,000 people killed. 

Yet those who lost their lives directly from the attacks were just one aspect. The degree to which the use of atomic bombs in conflict caused serious, lasting, devastating injuries was underestimated. For those who were not immediately lost, thousands suffered ghastly burns, loss of skin, and shrapnel embedded in their bodies that caused excruciating pain for as long as they lived. This is in addition to extreme suffering beyond injuries and sickness, in years and in some cases lifetimes of economic hardship, social stigma, and psychological damage. 

These events also began to show the extreme health effects that could come from surviving such significant radiation exposure. This was another way in which the risks of using nuclear weapons were severely underestimated for many years.

In fact, even with the evidence gained from these first detonations of nuclear weapons in war and earlier tests, their actual effects continued to not be fully understood for decades, fueled by the censoring and classification of evidence being collected in Hiroshima and Nagasaki. 

Just as we are seeing with regard to climate change risks today, heat and fire are also central to this history.  

One landmark analysis of the effects of nuclear weapons use is a 2003 book called Whole World on Fire by Lynn Eden. It describes how — much like the world used to experience regarding the effects of climate change — for decades defense planners underestimated the effects of nuclear weapons. In particular, they calculated damages from the original nuclear blasts but left out the firestorms that would result from those blasts, and other short-term and long-term consequences. 

Under-estimating the damage of nuclear weapons contributed to the United States and Soviet Union producing astronomical numbers of them — tens of thousands — in part driven by the belief that they needed tens of thousands of nuclear warheads in order to effectively deter one another from war—or to effectively wipe out the other nation.

Along with these growing nuclear arsenals came increasing nuclear tests. Soviet and U.S. citizens  – and those of other nations – were subject to radiation effects from the detonation sites. 

Some of the early U.S. nuclear tests were carried out in the Marshall Islands. Others, in the desert of the U.S. southwest. 

Almost one quarter of all nuclear tests in history were conducted at one test site in what is now Kazakhstan from 1949 to 1989. The citizens of nearby villages that were exposed now tell the story of the radiation damage caused, including significant genetic effects that crossed generations. 

// On these terrible legacies of nuclear weapons tests was built significant knowledge of their effects. Before the international community united to ban them, mostly ending the practice, this included more than 2,000 nuclear tests. 

Though results were classified in their earliest decades, extensive data from these tests revealed that the use of nuclear weapons could cause major disruptions to temperature patterns, sunlight, and precipitation. Into the 1970s and 80s, it became clearer that such nuclear weapons effects could cause more geographically dispersed and longer-enduring harm than previously realized. 

With such data, the world was able to create mathematical and computer models of ever-increasing sophistication. 

Importantly, the results of modeling potential effects of nuclear war started becoming public in the last decades of the 20th Century. Citizens of the world began to learn more about how the use of nuclear weapons could cause dramatic changes in weather patterns, and how this could drive severe changes in the availability of food and water, and how it would affect peoples’ health and their ability to care for their families. One such initiative labeled the potential damages of nuclear war as a “nuclear winter” that would befall the planet in some scenarios.  

As a side effect, the world began to learn more about climate change as well. These decades of work to understand nuclear weapons effects contributed to broader understanding of atmospheric physics and other areas of science and modeling. Such advances contributed to the early warnings by scientists that the world was warming in the alarming ways that we now see every day.   

This open, public knowledge empowered civil society and normal citizens to better understand the risks of nuclear weapons. Heads of state and other national leaders spoke of nuclear winter and nuclear and environmental linkages. It also empowered countries to bring this lens to grander discussions of peace and security, even nations that did not themselves possess nuclear weapons.  

There is no agreement regarding the exact role of this work in driving more responsible pathways regarding nuclear weapons in those decades. Yet deepening classified knowledge of more extensive effects of nuclear weapons use from more-advanced models, and the public emergence of discourse on this topic, coincided with increasing movements toward arms control, mutual restraints, and the countries possessing most of the world’s nuclear weapons decreasing their arsenals substantially.    

Arms race today / Inflection Point

Unfortunately, this momentum has not been sustained. In the earliest decades of this Century, we have begun moving back in the wrong direction. 

During this time, the risk of nuclear war has begun rising again. Most nuclear-armed nations are trying to expand the types of nuclear capabilities they possess, adding even more scenarios for how these weapons might be used in conflict. 

Unfortunately, several nations — including my own — are reigniting interest in types of nuclear weapons that are envisioned to be more usable in conflict. These include increasing focus on the horrifically mis-labeled, so-called low-yield nuclear weapon options.  

Even more dangerous than the mere presence of such weapons is the mindset that, in the heat of a conflict, it may be feasible to use one nuclear weapon without it being reciprocated. This is a fallacy, and we should not accept it as an assumption steering policy. 

While this wasn’t the case early in the Cold War, this time, under-estimating the effects of using such nuclear weapons is not an excuse. We have to assume that the use of even one nuclear weapon would be followed by another, and potentially lead to a broader nuclear exchange and the catastrophic damage that would follow. Today, we know in great detail what that could look like.

A study from 2014 — which used different models and incorporated new ocean and sea ice dynamics — focused on an exchange between India and Pakistan in which each detonates 50 nuclear weapons of 15 kilotons each. These would be around the size of the nuclear weapons used on Hiroshima and Nagasaki.

The scenario of conflict envisioned for such a war is unfortunately highly feasible. The study found that effects of such a nuclear exchange on temperatures and precipitation could extend globally, and though they would vary in severity and longevity by continent, the corresponding reductions in growing seasons could strain world food supplies well beyond South Asia for years. 

Similarly, the author of the book Whole World on Fire projected the effects of the use of one nuclear weapon detonated about 1500 ft above Washington DC, envisioning the use of a 300 kiloton weapon. As she described the damage: 

“The blast wave in the winds would crush many structures and tear them apart….Within minutes of a detonation fire would be everywhere…This fire would cover a ground area of tens of square miles and begin to heat enormous volumes of air that would rise up while cool air from the periphery of the fire was pulled in to replace it. Within tens of minutes after detonation the pumping action from rising hot air would generate superheated ground winds of hurricane force in the fire zone, further intensifying the fire. Virtually no one who was in the area would survive.”

The effects, she wrote, would “transform the targeted area into a huge hurricane of fire.”


If the intersection of nuclear weapons use and climate change is rooted in work to understand how our atmosphere and our world may be altered by both, today we have an even more daunting task. We have to consider how these threats may actually manifest together. 

Some effects of climate change are reigniting attention to past nuclear weapons damages. The Marshall Islands are a central case: at one atoll where the United States conducted nuclear weapon tests, a concrete dome that was designed to encase debris contaminated by these tests is now being inundated by rising seas. We don’t have to model this damage — it has been measured, and we have drone footage recording this occurring.

We also have a deeper understanding than ever about how the effects of climate change are contributing to instability, fragility, and geopolitical changes — including for nations that possess nuclear weapons. Extreme heat, extensive droughts, terrible disasters, and rising seas are creating wave after wave of challenge to societies around the world. This influences where and how people can viably live, thus affecting the social, economic, and political domains of nations — and thereby influencing relations among nations.  

Let’s consider again the example above of a conflict in South Asia. All countries in this region are heavily affected by climate change already, and the projections indicate even more dramatic challenges in the future if they are not prevented effectively. For India and Pakistan, there is already major concern regarding the future of their freshwater systems that begin in China. 

All 3 nations possess nuclear weapons, and all 3 are working to expand those arsenals to incorporate new nuclear capabilities. In some cases, those capabilities are viewed by myself and many other experts as more likely to be used in conflict. 

Such circumstances may just as likely stem from misunderstanding as much as planning — for example if one side in a conflict misreads the actions of others as escalating the conflict. One way this could happen is by a nation using nuclear signaling, such as moving nuclear-armed assets in alarming ways. Such miscalculations may lead to the use of a nuclear weapon that is then reciprocated, triggering further escalation. 

We know that in addition to the immediate death and destruction, such a nuclear conflict also risks significant damage to agricultural production through contamination or disruptions in weather patterns. Now combine this with a scenario in which such conflict occurs when extreme weather exacerbated by climate change has already spent years devastating the world’s food supplies. 

How many more millions of people could starve? How many millions of people will try to move in order to save themselves and their families, and how many communities could descend into instability or internal conflict if pressure is not relieved any other way? 

This is the reality of the world that we live in today — in which several catastrophic risks to humanity are occurring simultaneously, and they are not isolated from one another in time or space. 


I do not paint this picture to seem overwhelming, but simply to recognize the scale of the threats we all face — and the urgency for mitigating them.  

And as grim as this may sound, there is significant hope — otherwise I’m sure none of us would be here today working on these issues. In fact, we have more capabilities than ever before to address these grave risks to humanity if we can summon the will to do so.

It is perhaps not surprising that one of the greatest awakenings regarding the risks of climate change has come from young citizens of the world. The world should have acted earlier commensurate with the threat. Instead, we drove children to carry out strikes from their school days to push for change. We owe it to them to act with urgency, including at this conference but certainly not ending with pledges made in the coming weeks.

We have greater knowledge than ever before about the types of damages that climate change is already creating and the extreme risks facing the world if bold action is further delayed. That unprecedented foresight means that we have a responsibility to prepare accordingly, and prevent the worst outcomes where we can. 

As I’ve sought to demonstrate, we also have significant knowledge regarding the catastrophic risks of nuclear war. We have the histories of the destruction and humanitarian impacts of the nuclear bombings of Hiroshima and Nagasaki, and of later nuclear weapons tests. We have further evidence of potential effects from the same kinds of advanced modeling that can tell us the range of effects that climate change is likely to bring. 

Yet unlike for climate change, the risks of nuclear war are no longer discussed in public dialogue as commonly. It is time to change that, and to do so before such effects are unfolding before us in the same manner.  

Put simply – underestimating the risks we face is no longer an excuse. 

Nobel Prize winner Paul Crutzen co-authored one of the earliest public articles on nuclear weapons effects on the climate, called “The Atmosphere after a Nuclear War: Twilight at Noon.”  He is also credited with popularizing the terminology that we now live in an era called the Anthropocene. 

This epoch is loosely defined as uniquely characterized by human activity being the dominant force in shaping the planet. The Anthropocene term is now commonly evoked in climate change discourse as a reminder that we are the main drivers — and it is up to us to pursue solutions.

As concurrence surrounding this concept has spread globally, one key debate has been what date or phenomenon should mark the beginning of this epoch. In 2015, a 25-member international working group presented a singular event as the start of the Anthropocene: the first test of a nuclear weapon.

I urge the leaders of our nations to commit to serious progress in addressing the climate crisis in the days ahead. We must then also act with urgency, expanding those efforts to rally similar momentum to reduce the risks of nuclear war as well. 

And I hope the world’s leaders can find motivation in the historical and present ways that these catastrophic risks are linked. 

Thank you.


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