Conversation

Many scientists point - rightfully - to the fact that we cannot state with certainty that climate would suddenly go berserk in 12 years if we weren’t doing any climate mitigation. But who can state with certainty that we would be safe beyond that stage or even before that? (3/n)
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Turns out that we know how to deal with this type of dilemma in our everyday life: Take tobacco… Many of us don’t indulge even in 1 single cigarette for years, not because this one cigarette would kill us but because we know that once we would get into the habit of smoking (6/n)
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... we’d get into more risks of poor health and possibly cancer. Should we fight about establishing the exact number of cigarettes at which our “health breakdown” would happen? Probably not very useful. We know some might be more vulnerable or unlucky than others… (7/n)
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There is wind and people can fall down. At 1 meter (e.g. 1°C such as present global warming), risks are still limited: You might twist your ankle, though already at that level a baby could die or an older person could seriously be harmed. (10/n)
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At 4m most people falling down would die. Of course some might argue that you don’t need to fall down, even if the platform is at 4m, the wealthy people could build barriers and strap themselves to the platform. (12/n)
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But how about those who cannot afford a barrier? And how about those who are vulnerable & could be affected even at lower levels (babies, elderly)? And if you get a tornado coming by, even the best barriers or straps won’t stop you from falling down. (13/n)
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Finally, we know that at a given height, the platform becomes unstable and all of us would fall down. We don’t know for sure at what height this would be, but we have evidence showing that risks of this happening would increase above 1.5m. (14/n)
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It’s hard to say exactly when these tipping points would be triggered, but the chances get higher as the world gets hotter theconversation.com/hothouse-earth
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The SR15 concludes that we'd reach +1.5°C in 2030 if CO2 emissions continue as now. If we want to buy time, we should decrease our CO2 emissions by at least 50% until then - starting with what is easiest - bc some emissions will take longer to get rid of (e.g. aviation). (16/n)
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As scientists, none of us are saying that we are all going to die beyond +1.5°C. But I'd say that we are not guaranteeing that we could live safely beyond +1.5°C of global warming. And in fact, even at +1°C already too many people are dying… (17/n)
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NEW - Limiting warming to 1.5C could prevent ‘thousands’ of heat deaths in US cities | @rtmcswee @EuniceLoClimate @ScienceAdvances @vlimaye j.mp/2JZABWQ
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Namely, we should shift from avoiding Type I errors to avoiding Type II errors (i.e. missing a risk that potentially is there - since we have already established that climate change is happening). See also following paper on a similar topic twitter.com/nature/status/ (21/n)
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Comment: @vamrhein, @Lester_Domes, Blake McShane and more than 800 signatories call for “a stop to the use of P values in the conventional, dichotomous way — to decide whether a result refutes or supports a scientific hypothesis.” go.nature.com/2YfQ6h7
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Thinking of that question (What's still safe?) shows that the only responsible answer is: We should do all what is in our power to reduce CO2 emissions immediately & drastically. Because we're poisoning our world, as tobacco would be poisoning our body if we were smoking. (22/n)
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Finally, and this is not negligible: Many solutions to shifting to a low-CO2 society are available now. Life with low CO2 could be a nice life, it is not necessary to assume that this would imply huge sacrifices…. (/end)
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Following #cop24, check the storylines we derived in the @IPCC_CH #SR15 report for possible futures at a) +1.5°C without overshoot, b) +2°C, and c) +3°C. They start in 2020, when the #ParisAgreement comes into force. We have 2 critical years ahead. iacweb.ethz.ch/staff//sonia/d
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