alt Hacker NewsIts not a "risk".
Water vapor (clouds) is a stonger greenhouse gas than carbon dioxide. We already got measurably higher temperatures, so we also have higher water evaporation, and from the last 5 years it looks like it happens every year.
So the runaway is already happening, until something stops it near hothouse conditions or hopefully earlier than that.
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Water vapor (clouds) also reflects sunlight. So it's complicated. We know the planet has had higher CO2 and higher temperatures in the past, and it did not "run away"
True runaway (i.e. oceans boiling / Venus) cannot happen on Earth unless you significantly increase incoming radiation stream (or alternatively halve the planet's albedo).
The runaway effect is scary b/c at certain temperature (~400K) atmosphere consisting predominantly of water vapor looses its ability to radiate out more heat up until 1600K.
[0] https://www.nature.com/articles/ngeo1892 (see fig. 2b) (edit: the figure: https://imgur.com/a/ytoEXzd)
edit #2: I've measured some pixels and the starting runaway temp is closer to 315K / 42C, damn
And that's just one of the many positive feedback loops.
Thank you for saying this. If you want to know the answer to what causes climate problems, you need to go back to the era of dinosaurs, where CO2 levels were multiple times higher than today. Trees could thrive because they could breathe in a lot of CO2. Dinosaurs got so big because there were plenty of food. How could dinosaurs happily live with such high CO2 levels? The key is that there were plenty of forests. Peter Wohlleben's book "The Power of Trees: How Ancient Forests Can Save Us if We Let Them" explains how forests naturally circulate water.