The use of nuclear weapons by Russia would have severe consequences, including massive reputational damage for the Russian authorities, many deaths, and the destruction of infrastructure. The US and its allies would respond by leading a collective effort that would take out every Russian conventional force that they can see and identify on the battlefield in Ukraine and also in Crimea and every ship in the Black Sea. The risks of escalation and a nuclear response would be very high, and the use of nuclear weapons would not trigger the alliances Article 5, which calls for a collective defense. The decision to use nuclear weapons would be taken by the Russian president, and he would be informed and advised by a group of people that does not include the experts who took part in the recent discussion. There are at least three distinct scenarios for Russias use of a nuclear weapon, each of which differs in rationale and likely consequences. The environmental effects of tactical nuclear weapons use are difficult to calculate and would depend on warhead yield, detonation height, weather, and local conditions.