The Kremlin’s response to the Luhansk strike is a calibrated act of geopolitical signalling, but one that carries the weight of existential consequence. President Putin’s pledge to retaliate, framed in language that deliberately echoes Cold War brinkmanship, is not merely rhetorical. It is a reminder that the threshold for nuclear use remains dangerously low when conventional deterrence fails.
Let us be precise. The strike on Luhansk, which Ukrainian forces claim targeted a command centre, is a tactical blow. But in the physics of escalation, a tactical strike can trigger a strategic reaction. Russia’s nuclear doctrine explicitly permits the use of non-strategic nuclear weapons when the state’s existence is threatened. Putin’s statement that Russia will use “all means available” is a direct invocation of this doctrine.
The risk is not an immediate detonation. But the probability of miscalculation rises with every such exchange. The war in Ukraine has already eroded the norms that have kept nuclear weapons unused for nearly 80 years. We are witnessing a slow, grinding normalisation of nuclear threats. Each time a leader invokes the arsenal, the taboo weakens.
What does this mean for the biosphere? A limited nuclear exchange would be catastrophic. Even a single 100-kiloton airburst over a city would cause firestorms, radioactive fallout, and a regional climate perturbation. But a broader exchange, even of so-called tactical weapons, could inject soot into the stratosphere, triggering a nuclear winter that collapses agriculture globally. This is not alarmism. Models from the 1980s have been refined with modern climate data and they confirm it: a regional nuclear war could reduce global temperatures by 1-2 °C for a decade, destroying harvests and causing mass famine.
But let us focus on the immediate reality. Putin’s vow is a pressure test for NATO’s resolve. The alliance’s response, measured and defensive so far, must now account for a leader who views nuclear threats as leverage. The energy transition, meanwhile, is caught in the crossfire. Europe’s dash for energy independence from Russian gas is accelerating renewables, but the transition itself is vulnerable to geopolitical shocks. A nuclear event would divert trillions from clean energy to militarisation.
There is a technical solution, though it is not a quick fix. Strengthened early warning systems and direct military-to-military communication channels between nuclear states could reduce the risk of accidental escalation. But such measures require political will, and that is in short supply. The scientific community can model the risks, but we cannot enforce the rational decisions needed to avoid them.
The atmosphere does not care about national borders or historical grievances. It responds only to the physical laws of radiative transfer. If we test those laws with a nuclear weapon, the biosphere will deliver its verdict without emotion. Putin’s vow is a reminder that our civilisational foundation is fragile. The calm urgency in my voice is because I have seen the data. The window for responsible action is narrowing.
