As the regional war in Iran continues to spiral into a broader, seemingly intractable crisis, a chilling specter has returned to the forefront of global anxiety: the threat of nuclear weapons. Indeed, Iran doesn’t have nuclear weapons nor would the U.S. use them in this conflict, but it doesn’t take very much for a regional war to escalate into a world war. And at that point, all bets are off.
If the unthinkable happens and the conflict crosses the nuclear threshold, the immediate devastation of the blasts would merely be the prelude to a much larger, planet-wide catastrophe. This is because the most dangerous part of a nuclear war is not the devastating explosions, but what comes after.
Even a limited nuclear conflict could trigger a planet-wide climate disaster, often called a nuclear winter, which leads to the collapse of sunlight, agriculture, food supply chain, and ultimately, human survival itself. In fact, some well-studied scenarios suggest billions could die in such a case, not from blasts, but from the famine that follows nuclear winter.
“Agriculture would fail, and when agriculture fails, people just die. On top of that, you have the radiation poisoning because the ozone layer will be so damaged and destroyed that you couldn’t be outside in the sunlight – people will be forced to live underground,” Annie Jacobsen, a journalist and author of the book Nuclear War: A Scenario, said in a podcast.
However, in that dark, frozen aftermath, there are two countries, Australia and New Zealand, where agriculture and people could still survive, according to Jacobson, based on research she studied.
How the world looks in a nuclear winter
The roots of this idea go back to the Cold War, when scientists first tried to understand the environmental consequences of nuclear war. Early work led by American astronomer Carl Sagan introduced the concept of ‘nuclear winter’—a scenario where massive amounts of soot from burning cities rise into the atmosphere and block sunlight for many years.
At the time, the mathematical models were basic, but the conclusion was alarming. The climate effects could extend far beyond the blast zones.
For instance, a 2025 study suggests that “ten times more people could die (due to nuclear winter effects) in nations far removed from the conflict than would die from the direct, horrific blasts, fires, and radiation in the target nations.”
Since then, advances in climate modeling have allowed scientists to revisit nuclear winter scenarios with far greater precision. Modern studies have simulated what happens when multiple nuclear weapons ignite massive firestorms in urban areas. These fires release black carbon—fine soot particles—that rise into the upper atmosphere, where they can linger for years.
Once there, the soot spreads across the globe, driven by atmospheric currents, and acts like a shield, blocking sunlight globally. As a result, temperatures drop, the planet cools dramatically, and rainfall patterns are messed up, devastating agriculture.
“It doesn’t matter who is bombing whom. It can be India and Pakistan or NATO and Russia. Once the smoke is released into the upper atmosphere, it spreads globally and affects everyone,” said Cheryl Harrison, an Assistant Professor at the Louisiana State University Department of Oceanography & Coastal Sciences.
Studies suggest the damage could be extreme. In large-scale scenarios, food production in major agricultural powers like the US, China, and Russia could drop by as much as 90 percent or more, while global fisheries could decline sharply as ocean ecosystems are disrupted.
“We demonstrate that soot injections larger than 5 Tg (teragram or 109 kg) would lead to mass food shortages, and livestock and aquatic food production would be unable to compensate for reduced crop output, in almost all countries,” a 2022 study notes.
Another study modeled a nuclear exchange between the U.S. and Russia, which involved 4,400 100-kiloton nuclear weapons aimed primarily at population centers and industrial areas. This war resulted in 150 teragrams — over 330 billion pounds or 30 times more than the threshold estimated by the previously mentioned study for agricultural collapse — of smoke and soot being injected into the upper atmosphere.
In the first month after these exchanges, the team explains, the average global temperature would drop by around 13 degrees Fahrenheit (roughly 7 Celsius). This would be a more dramatic temperature change than the one experienced during the last Ice Age.
Ocean temperatures would drop quickly and would not return to their pre-war baseline even after the smoke and soot cleared. These lower temperatures would cause sea ice to expand by over 6 million square miles (roughly 16 million sq kilometers) worldwide, reaching thicknesses of up to 6 ft (1.8 m) in some major basins. This ice would completely block several of the world’s major ports including Tianjin, Copenhagen, and St. Petersburg. Since major port regions are normally ice-free, most ships today are not designed to contend with sea ice. Essentially, a nuclear war would quickly make it impossible for global trade as it is today to continue.
What sets the two countries apart
Against this global collapse, Australia and New Zealand stand out as relatively safe havens, according to a 2022 study. That doesn’t mean these countries are spared from disruption, but compared to other places, they would be the least worst.
Scientists reached this conclusion by comparing 38 island nations across multiple factors, including location, food production, energy resources, infrastructure, and social resilience. For instance, both countries benefit from their geographic isolation and position in the Southern Hemisphere. Most nuclear targets and, therefore, most soot-producing fires are concentrated in the Northern Hemisphere.
While atmospheric circulation would still spread soot globally, the Southern Hemisphere is likely to experience a less severe impact. But geography alone isn’t the full story. These countries also have unusually resilient food systems.
Australia, for instance, has a gigantic food supply buffer, “with potential to feed many tens of millions of extra people. Good-quality infrastructure, vast energy surplus, the second-highest health security in the world, and triple the defense spending of any other island in our analysis, all suggest that Australia has the potential to thrive,” the 2022 study notes.
New Zealand’s case is even more striking. Its agricultural sector produces far more food than its population needs. Between 90 and 95 percent of its crop, dairy, and meat production is exported. So even after a severe nuclear winter—where crop yields could fall by over 60 percent—the country could still theoretically feed its entire population.
At the same time, the oceans surrounding these countries act as climate stabilizers, absorbing and redistributing heat. This reduces temperature extremes compared to large continental regions, making the survival of agriculture more plausible.
No nuclear war is the best-case scenario
Australia and New Zealand’s resilience comes with serious caveats. For instance, both countries depend heavily on global trade for critical inputs like fuel, fertilizers, and machinery. So if global supply chains collapse, food production itself could be disrupted.
Besides, industrial breakdown and social instability could undermine even the most food-secure nations. In short, life would be far from normal in these places, although other countries would fare much worse.
The bottom line is that in the event of a nuclear world war, no place is really safe.