What does global cooling look like?
In popular culture, an ice age is often shown as a realm of perpetual winter — endless snowy plains from pole to pole, with Siberian frost present year round. Scientists, however, refer to a far more modest set of changes when they talk about global cooling. At the peak of the last glaciation about 18,000 years ago, when global temperatures were roughly 6.5 degrees Celsius cooler, glaciers did not blanket the entire Earth. They reached the modern northern borders of the United States, covering parts of Scandinavia, the Baltic region, and the northern parts of modern Russia. The mid-latitudes hosted steppe and tundra across Central Europe, France, and Ukraine, while forest-steppes pushed further south.
During the Little Ice Age spanning the 14th to the 19th centuries, Western Europe often experienced harsh winters and cooler, cloudier summers. This climate pattern contributed to crop shortages and periodic famine, with Europe seeing a drop in temperatures by about 1–2 degrees at the height of the cold period, even bringing on a winter ice cover in places like the Adriatic. If a modern shift toward cooler conditions replaced ongoing warming, it would strain economies but would not pose an existential threat to civilization.
In the era of systematic climate observation, scientists also explored the idea of a smaller-scale nuclear winter experiment. The Tambora eruption in 1815 was one of the most powerful volcanic events in recorded history and produced a vast veil of ash and sulfur compounds high in the atmosphere. This volcanic shoot blocked sunlight and lowered temperatures in many regions for years. As a result, global temperatures fell by about 0.4–0.7 degrees Celsius, frost and snowfall affected crops, and 1816 became known as the year without a summer.
Only once in Earth’s long history did temperatures swing toward a near-snowball state, around 700–600 million years ago, when glaciers advanced into tropical latitudes. Modern interpretations vary: oceanic heat storage and coastal differences likely tempered extreme drops, and the ice sheet’s reach may have varied from a polar projection to land masses retreating well above the equator.
Who came up with the concept of nuclear winter?
The idea that nuclear explosions could alter climate first gained serious attention during the early Cold War. In 1952, the United States tested a hydrogen bomb with a yield around 10 megatons during the Ivy Mike test, and some scientists worried about possible cooling effects. Reports from the period suggested that large yields could loft dust into the stratosphere, potentially dimming sunlight if tests occurred repeatedly.
Since then, debate has continued about whether nuclear detonations could trigger deep cooling. The discussion sharpened in the early 1980s when astronomer Carl Sagan popularized the concept. Sagan’s public influence in the space program helped bring attention to potential climate effects from nuclear conflict. His work, and collaborations with colleagues, explored how atmospheric particles from multiple detonations could reflect sunlight and cool the surface.
In 1983, a landmark article titled Nuclear Winter: The Global Consequences of Multiple Nuclear Explosions laid out models for dust behavior, particulate matter, and radiative heat transfer to estimate possible surface cooling. The scenario suggested dramatic drops in average hemispheric temperatures following massive nuclear exchanges, with contrasts among regions due to ocean heat capacity and storm tracks.
Simulations indicated that a large-scale release of aerosols could reduce heat reaching the surface, leading to significant cooling within weeks and lasting for months. In some models, the Stone Age climate description seems almost apocalyptic, with subfreezing temperatures persisting for extended periods before recovery.
However, these projections came with caveats. They assumed continental-scale fires and idealized atmospheric conditions. The ocean acts as a large heat reservoir, dampening some effects of cooling along coastlines and leaving other areas more exposed to temperature shifts. Early Soviet researchers also explored similar ideas, albeit with less certainty in their conclusions.
Oil Winter and Desert Storm
The world quickly moved from theory to testable scenarios. In 1990, a geopolitical crisis unfolded as Saddam Hussein threatened to ignite oil wells in Kuwait during the Gulf War. The discussion focused on whether such fires could produce the soot plumes necessary to trigger a global downturn in sunlight. The collective concern was that widespread fires would loft smoke into the upper atmosphere, potentially mimicking a nuclear winter effect.
As the conflict unfolded, it did not produce a global climate catastrophe. The fires did not deliver the expected amount of smoke to the stratosphere, and the overall climatic impact remained limited to regional scales. Later analyses attributed this to several factors: fewer particles released than anticipated, smoke that was less black than modeled, limited ascent into the stratosphere, and rapid cleanup of smoke when it did rise. The takeaway is that a large, sustained plume would be required to drive a global cooling event, and oil well fires alone did not meet that threshold.
Physicist Peter Hobbs summarized the key results: emissions were below expectations, the smoke did not rise high enough or stay aloft long enough, and atmospheric dynamics dispersed the aerosols faster than anticipated. The cooling observed was localized and minor, and some early estimates that suggested broad, catastrophic cooling were later revised downward.
Is it possible to predict the effect of an atomic explosion?
Modeling the climatic impact of a nuclear conflict relies on assumptions. Modern climate models for aerosols and soot are robust, but their accuracy depends on correctly estimating how much soot would reach the stratosphere and from where. This requires understanding how many targets would burn and how intensely they would burn in a real conflict.
In practice, cities are typically seen as vulnerable sites, but the most consequential fires in climate terms would come from large-scale infrastructure and industrial targets. The likelihood of a single event causing sustained, global effects remains uncertain. Some researchers argue that any realistic nuclear exchange would not produce the massive, planet-wide cooling once imagined, while others contend that certain attack scenarios could still drive noticeable regional climate shifts for years.
Experts also point to the complexity of urban fire dynamics. The structure of cities, the distribution of combustible materials, and the way buildings respond to heat all influence whether a large firestorm could form. Some observers question whether modern cities could generate a single sustained firestorm, given construction practices and suppression capabilities. Different viewpoints exist within the climate science community, reflecting ongoing debates about model assumptions and urban fire behavior.
What do modern scientists think?
Over time, the field has moved away from the most alarming Sagan–Turco scenario of continuous 20–30 degree cooling. A recent line of research explores multiple targeted nuclear strikes, particularly across densely populated corridors, and estimates more modest, though still significant, global effects. Some studies suggest average global land temperature could fall around 4–8 degrees Celsius, with the entire planet cooling by 2–5 degrees for a period that might last roughly a decade. This would resemble a Stone Age-like climate for a while but not doom the planet to a permanent ice age.
At the same time, prominent researchers challenge these extremes. Scientists from leading labs argue that actual climate response might be more nuanced. Modern modeling includes an array of environmental processes, from fire-driven smoke to atmospheric chemistry, and simulations often show far less dramatic outcomes when tested against varied scenarios. In some discussions, a climate model comparison emphasizes how much of the initial particle mass fails to reach the upper atmosphere, and how storms and rainfall remove much of the soot. In those viewpoints, global cooling is limited and temporary, with regional effects fading within a few years.
Overall, the consensus leans toward a cautious view: while a nuclear exchange could alter climate on regional scales and for a limited time, a true, planet-wide ice-age-type outcome is unlikely under most realistic scenarios. The science stresses the importance of understanding atmospheric transport, aerosol lifetime, and the role of oceans in moderating heat. The debate continues as researchers refine models and test new assumptions about fire behavior, urban dynamics, and global climate responses.