Thread by @mark_lynas

With each new Russian atrocity in Ukraine, calls for NATO intervention increase. Are we sleepwalking towards nuclear war? The appetite for risk is increasing with the horror of civilian casualties. Putin is cornered and may escalate. What's the worst that can happen? Thread: 1/12

With memories of the Cold War fading, some seem to suggest that nuclear war is worth risking. That is not what the science says. Nuclear war scenarios have been thoroughly evaluated using climate models - the same ones used by the IPCC to project global warming. 2/12

The US and Russia have deployable nuclear weapons inventories of roughly 4,000 warheads each, with many thousands more held in reserve. Over the last decade, scientists have studied a scenario where roughly half the inventories are detonated, involving 4,400 nuclear blasts. 3/12

This would cause an estimated 770 million direct deaths. These people are vaporised, incinerated, buried in flattened buildings or die within days from acute radiation sickness. In the US about a fifth of the population is killed outright. They are the lucky ones. 4/12

Firestorms from the explosions pour 150 Tg (teragrams) of soot into the atmosphere from burning cities and forests. Rising to the stratosphere, these black carbon particles block 60-70% of incoming sunlight, causing worldwide gloom. They also destroy most of the ozone layer. 5/12

Surface temperatures plummet. The weather stays below freezing throughout the Northern Hemisphere summer. e.g. in Iowa temps remain below 0°C for 730 days straight. There is no growing season. This is what my generation used to call a 'nuclear winter'. 6/12

By years 3 & 4 after the nuclear exchange, global rainfall has fallen by half. It takes over a decade for anything like climatic normality to return to the planet. This is why radiation is unimportant. Long before any cancers show up, most people will already be dead. 7/12

This is because almost all those who survive the initial bomb blasts die in the subsequent global famine. Food stocks are quickly exhausted, and less than a quarter of the population of most countries even lives past year 1. Dying from starvation is horrible. 8/12

The models are eerily specific. Averaged over 5 years, China sees a reduction in food calories of 97.2 percent, France by 97.5 percent, Russia by 99.7 percent, the UK by 99.5 percent and the US by 98.9 percent. In all these countries, virtually everyone starves to death. 9/12

The good news is that this probably does not cause a species-level extinction of Homo sapiens. It's also not as bad as the end-Cretaceous mass extinction that killed the dinosaurs 65 million years ago. Some humans survive to eke out a living on a devastated, barren planet. 10/12

But this is why cool heads MUST ultimately prevail, even as emotions run high. The price of nuclear war is planetary suicide. No-one wins. Neither Zelensky nor Putin. It won’t save lives in Ukraine - it simply takes the death toll from the thousands into the billions. 11/12

Here's the full article published by @ScienceAlly with all the above facts together with important context and sources from the peer-reviewed literature. Please do read and share - the word count is only 1,500. 12/12. END

allianceforscience.cornell.edu/blog/2022/03/w…