How much warning would there be before a nuclear attack?

Warning time depends on the type of attack. An intercontinental ballistic missile (ICBM) launched from Russia gives approximately 25–30 minutes of warning. A submarine-launched ballistic missile (SLBM) fired from close to the target coast could reduce warning time to 6 minutes or less. Hypersonic glide vehicles, which maneuver unpredictably, may give 5–10 minutes. Cruise missiles flying at low altitude to evade radar could provide little to no warning.

Would going underground protect you from a nuclear bomb?

Underground shelter significantly improves survival chances, but the protection depends on the weapon's size and how close you are to the detonation. Within the fireball and severe blast zones (roughly 0–3 km from a 300 kt burst), nothing survives. At moderate distances (5–15 km), a basement or underground facility reduces blast and fallout exposure substantially. For fallout specifically, sheltering underground or in the interior of a solid building for 24–48 hours dramatically reduces radiation exposure because most fallout radiation decays quickly.

What is nuclear winter and how long would it last?

Nuclear winter is the cooling of Earth's climate caused by soot from nuclear firestorms blocking sunlight in the upper stratosphere. Unlike low-altitude smoke, stratospheric soot cannot be washed out by rain, and can persist for years. Climate models suggest a full-scale nuclear exchange could reduce global temperatures by 8–10°C for a decade or more, collapsing agriculture worldwide. Even a 'limited' regional nuclear war using around 100 bombs could cause 1–2°C of cooling for 10 years — enough to cause severe agricultural disruption and mass famine.

How many nuclear weapons are there in the world?

As of 2025, the nine nuclear-armed states collectively possess approximately 12,100 nuclear warheads. Russia has the largest arsenal at approximately 5,580 warheads, followed by the United States at approximately 5,044. China is expanding its arsenal rapidly, currently estimated at around 500 warheads. France, the United Kingdom, Pakistan, India, Israel, and North Korea account for the remaining warheads.

Could a nuclear war be 'limited'?

Whether nuclear war can be limited is one of the most debated questions in nuclear strategy. The theory of limited nuclear war holds that small numbers of low-yield nuclear weapons could be used for specific military objectives without triggering full escalation. Critics argue that once nuclear weapons are used, the psychological and political pressure to escalate is enormous, and that no actual historical evidence exists for successful 'escalation control' once nuclear thresholds have been crossed. Most independent analysts consider the concept of 'limited nuclear war' as historically untested and operationally dangerous.

What should you do if a nuclear attack is announced?

Official guidance from FEMA and most civil defense agencies is: Get inside a solid building immediately, stay inside, and stay tuned to emergency broadcasts. The most important protective action is reducing exposure to fallout radiation. Basements and the interior rooms of multi-story concrete or brick buildings provide the best protection. Do not attempt to drive out of the area — traffic gridlock makes car evacuation slower and more dangerous than sheltering in place. If you are outdoors at the time of detonation, lie face-down with your head away from the blast, with your hands under your body.

What Would Happen If Nuclear War Started? A Step-by-Step Guide

What would happen if nuclear war started? From the first launch to nuclear winter: blast radii, fallout zones, infrastructure collapse, and long-term survival timelines based on current scientific research.

March 3, 20265 min readNuclear Risk Nuclear Weapons Survival Nuclear Winter Fallout Doomsday Clock History

Firestorm cloud over Hiroshima, August 6, 1945 — the only use of nuclear weapons in war, and the basis for modern models of nuclear war consequences

If nuclear war started today, the first missile would arrive before most people knew it had been launched. The physical effects — blast, heat, radiation — would be followed by cascading failures in food, power, water, and medicine that could kill more people than the bombs themselves. This is what the science says would happen, step by step.

The First 30 Minutes: Launch, Warning, and Impact

Nuclear war does not begin with a bang most people hear. It begins with a data point on a radar screen.

Launch detection

The United States operates a layered early warning system. Space-based infrared satellites (SBIRS) detect the heat signature of a ballistic missile within seconds of launch. Ground-based radar stations track the missile's trajectory and calculate a predicted impact point. This data flows to NORAD's command center in Colorado within minutes.

The President is notified. The nuclear football — a briefcase carried by a military aide that travels with the President at all times — contains the decision tools. The President has authenticated codes and can order a launch in minutes, with no requirement for Congressional approval or secondary confirmation.

Warning time by scenario:

| Launch type | Distance | Warning time | |-------------|----------|--------------| | ICBM from Russia/China | 5,500–8,000 miles | 25–30 minutes | | SLBM from Atlantic submarine | ~1,500 miles | 8–12 minutes | | SLBM from close-in submarine | 300–600 miles | 3–6 minutes | | Hypersonic glide vehicle | Variable | 5–10 minutes | | Cruise missile (low-observable) | 500–1,000 miles | 0–15 minutes |

A President facing a confirmed incoming strike has, at most, ten minutes to make a decision. Advisors recommend. The President decides alone.

Launch under attack

US nuclear doctrine permits "launch under attack" — launching American missiles before incoming warheads detonate, to prevent them from destroying land-based ICBMs. This means nuclear war can be initiated and cannot be recalled. Once missiles are in the air, no code retracts them.

The first detonation

A 300-kiloton warhead — roughly representative of a modern Russian SS-18 reentry vehicle — detonating above a city produces four distinct lethal zones simultaneously.

Fireball zone (radius ~0.5 km from ground zero): The fireball reaches temperatures of several million degrees Celsius — hotter than the surface of the sun. Everything within this zone is vaporized instantaneously. There are no survivors.

Severe blast zone (radius ~2–3 km): Overpressures of 20 psi or more collapse reinforced concrete buildings. Air pressure equivalent to 140 mph winds carries building debris at lethal velocities. Most people in this zone die from blast, crush injury, or flying debris within seconds.

Moderate blast zone (radius ~5–8 km): Overpressures of 5–10 psi shatter windows, collapse residential buildings, and cause severe burns. Mortality in this zone is high but survivable with shelter.

Thermal radiation zone (radius ~10–15 km): The fireball emits an intense pulse of thermal radiation lasting several seconds. Exposed skin ignites at distances of 7–10 km. Fires start in buildings and vegetation across this entire zone simultaneously, potentially merging into a firestorm — a self-sustaining inferno that creates its own wind system and cannot be extinguished.

A single 300-kt detonation over New York City, for example, would kill an estimated 1.1 million people immediately and injure another 1.7 million.

The First 24 Hours: Fallout and Infrastructure Collapse

The immediate deaths are not the worst part.

Radioactive fallout

A ground burst — a weapon detonated at surface level, designed to destroy hardened military targets — sucks enormous quantities of soil and debris into the fireball. This material becomes highly radioactive and rises into the mushroom cloud, then falls back to earth downwind as fallout.

Fallout deposition:

Within 1–2 hours of detonation: heavy fallout begins falling 15–20 miles downwind
Within 6 hours: fallout reaches 50–100 miles downwind
Within 24 hours: fallout has spread 200–400 miles downwind, depending on winds

Fallout radiation is measured in rem (radiation equivalent man). Doses above 600 rem in a short period are fatal to most people without medical treatment. Doses of 100–300 rem cause acute radiation syndrome — vomiting, hair loss, immune suppression, and potentially death weeks later.

The good news, such as it is: most fallout radiation decays rapidly. The rule of seven applies: for every sevenfold increase in time after detonation, radiation intensity drops by a factor of ten. By 49 hours (7²), radiation has dropped to 1% of its initial level. Most fallout areas become survivable within two weeks if people shelter in basements or interior rooms during the acute phase.

reduction in fallout radiation for every sevenfold increase in time — the 'rule of seven'

US Federal Emergency Management Agency (FEMA)

Infrastructure collapse

Nuclear detonations at altitude generate an electromagnetic pulse (EMP) — a burst of electromagnetic energy that can damage or destroy electronics over a wide area without direct blast effects. A single high-altitude nuclear burst over the continental United States could theoretically disable power grids, communications networks, and transportation systems across millions of square miles.

Even without EMP, nuclear strikes on cities would overwhelm emergency response systems immediately:

Hospitals are destroyed or cut off from supplies
Water treatment plants lose power
Food distribution systems halt as transportation infrastructure is destroyed
Emergency services are unable to reach victims due to rubble and radiation

Within 24 hours of a major nuclear exchange, healthcare for the injured effectively ceases. The majority of casualties from blast and radiation injuries would die not from the initial effects but from the absence of treatment.

The First Month: Radiation Sickness and Secondary Deaths

Acute radiation syndrome (ARS) develops over days to weeks in people who received high radiation doses but survived the immediate blast effects. Symptoms progress through four stages:

Prodromal phase (hours to days): Nausea, vomiting, diarrhea, fatigue. Severity varies by dose.
Latent phase (days to weeks): Apparent recovery while bone marrow is being destroyed
Manifest illness phase (2–4 weeks after exposure): Immune system collapses; infection, bleeding, and organ failure
Recovery or death: Those who received doses below 300–400 rem and receive supportive care may recover; those above 600 rem without treatment face near-certain death

Without functioning hospitals, blood transfusions, or antibiotics — all of which would be unavailable in most affected areas — the mortality rate from ARS is far higher than in controlled medical settings.

The Long Term: Nuclear Winter and Global Famine

The effects of a large nuclear exchange would not be confined to the countries that were attacked. The mechanism is atmospheric.

What causes nuclear winter

Nuclear explosions ignite enormous fires. Cities burn for days. These fires inject millions of tons of black carbon soot into the upper stratosphere — high enough that rain cannot wash it out. The soot absorbs solar radiation, blocking sunlight from reaching Earth's surface.

Climate effects of different scenarios:

| Scenario | Warheads | Soot injected | Temp drop | Duration | Famine deaths | |----------|----------|---------------|-----------|----------|---------------| | India-Pakistan war | ~100 × 15 kt | 5 million tons | 1–2°C | 10 years | ~2 billion | | Regional exchange | ~500 × 50 kt | 50 million tons | 3–4°C | 15 years | ~4 billion | | Full US-Russia war | 4,000+ × 300 kt | 150 million tons | 8–10°C | 20+ years | ~5 billion |

A temperature drop of even 1–2°C for several growing seasons would collapse agricultural yields globally. Rice, wheat, and corn — which feed most of the world's population — are highly sensitive to temperature and growing season length. A country like China or India, which already operates at minimal food reserve margins, would face mass famine within 1–2 years of a nuclear exchange it was never directly involved in.

Nuclear weapons are not just weapons of mass destruction — they are weapons of mass starvation. The people who would die from nuclear winter would live nowhere near the bombs that killed them.

— Alan Robock, Professor of Climatology, Rutgers University

Who survives?

Population survival in a full-scale nuclear exchange depends heavily on location. Rural populations in the southern hemisphere — below the main fallout patterns and most fire zones — have the highest survival probability. Dense urban populations in the northern hemisphere face the worst outcomes.

Within the United States, FEMA estimates that roughly 140 million people would die immediately or within the first month from a full-scale Russian nuclear attack. The remaining 200+ million survivors would face collapsed infrastructure, contaminated water, radiation-tainted food supplies, and complete absence of functioning government in most areas.

The realistic picture of long-term survival is not romantic survivalism — it is years of subsistence agriculture in areas with functioning soil, water sources, and some remaining social organization.

How Likely Is Nuclear War?

Nuclear war is not inevitable. It has not happened in 80 years despite dozens of close calls. The mechanisms that have prevented it — deterrence, arms control, back-channel diplomacy, pure luck — remain partly functional.

But the current risk level is genuinely elevated. The Doomsday Clock stands at 89 seconds. Arms control architecture has been systematically dismantled. New nuclear states have emerged. AI is beginning to penetrate command-and-control systems. The Iran crisis of 2026 represents the most acute nuclear flashpoint since the Cuban Missile Crisis.

Understanding what nuclear war would actually look like is not defeatism. It is the necessary starting point for the political and policy work required to prevent it.