4 ms·

The point wasn't not only hitting that limit, but not hitting it before some date (end of century originally). The planet will continue warming up as long as we

The point wasn't not only hitting that limit, but not hitting it before some date (end of century originally). The planet will continue warming up as long as we have an excess of greenhouse gases, even if we reach some kind of cooked up "net zero" of emissions. If we warm faster, feedback loops will have more effect earlier, tipping points may be reached in shorter time, biodiversity will drop a lot, and our ability to react and do something about it will be compromised because we will have more urgent things to do like i.e. figuring out new food sources in scale after agriculture becomes unreliable enough. It is not if we will hit a mark, but how fast we will leave it behind. There is no possible adaptation to fast enough change, for us and the world we depend on.

hn_throwaway_99 4y ago
Thanks for your answer, but to be clear, I understand all that. My question is what, specifically, the 1.5 degree budget signifies, and why it seems like there will be such a discontinuous amount of harmful effects if we blow past it. What is the significance of 1.5 vs 1 or 3? Also, I'm not some sort of "climate skeptic" - I totally understand there will be severe negative consequences for continuing to pump carbon into the atmosphere. I'm just genuinely curious on why scientists landed on the 1.5 number.
- tito 4y ago
  Discontinuous effects, yes. A stable climate functions more like a light switch than a dimmer switch. There is an "off", and once we go there getting back is really hard. It's almost like a one way switch. As one example of a feedback loop, when polar ice melts, the area effectively turns from white (ice) to black (ocean). This area then absorbs more heat, driving more heating. So that's one feedback loop. I think the feedback loops are kind of cool to study. Methane emissions in the tundra. Greenland melting causes more melting. Higher temps cause more water vapor that absorbs heat. That doesn't give you specifics on where the line is. But wanted to give you an idea about the discontinuity, that there is a threshold vs dimmer switch. P.S. I plugged your question into ChatGPT but the response was vague.
- gmuslera 4y ago
  I think it was a compromise between achievability and limiting damage what made it to be accepted decades ago. It was unrealistic to ask to not reach 1.5ºC back then, but the increase should be as low as possible to avoid reaching tipping points and triggering positive feedback loops that could put things beyond our possibility of control. Things are not binary, we are talking about global average temperatures, not the temperature you reach some day or season in a region. So you have to deal with uncertainty and that with higher global average temperature you will have the smaller version of the loops, even if you didn't reach the budget yet. But when you surpass enough them, then you will have more players that are changing the climate, influencing each other, and things will change faster. And there the decimal resolution may lose its meaning, your range of confidence will be much wider.
- WorldMaker 4y ago
  A) We've already passed the expected point of no return for 0.5 (warned about as early as the 1960s as I recall) and 1.0. As of 2023 we have already experienced years at as much as 1.2 degrees (above pre-industrial average). B) The 1.5 degree budget, as I recall is the "best wish" case of the 2015 Paris agreement. C) The 2 degree budget is the "worst case" allowable by the 2015 Paris agreement. D) The Paris agreement was based on previous IPCC reports on some of the expected outcomes at 1.5 degree and 2 degree budgets. The Paris agreement was largely trying to pick the smallest number that still seemed feasible in 2015.

hn_throwaway_99 4y ago

Thanks for your answer, but to be clear, I understand all that. My question is what, specifically, the 1.5 degree budget signifies, and why it seems like there will be such a discontinuous amount of harmful effects if we blow past it. What is the significance of 1.5 vs 1 or 3? Also, I'm not some sort of "climate skeptic" - I totally understand there will be severe negative consequences for continuing to pump carbon into the atmosphere. I'm just genuinely curious on why scientists landed on the 1.5 number.

tito 4y ago
Discontinuous effects, yes. A stable climate functions more like a light switch than a dimmer switch. There is an "off", and once we go there getting back is really hard. It's almost like a one way switch. As one example of a feedback loop, when polar ice melts, the area effectively turns from white (ice) to black (ocean). This area then absorbs more heat, driving more heating. So that's one feedback loop. I think the feedback loops are kind of cool to study. Methane emissions in the tundra. Greenland melting causes more melting. Higher temps cause more water vapor that absorbs heat. That doesn't give you specifics on where the line is. But wanted to give you an idea about the discontinuity, that there is a threshold vs dimmer switch. P.S. I plugged your question into ChatGPT but the response was vague.
gmuslera 4y ago
I think it was a compromise between achievability and limiting damage what made it to be accepted decades ago. It was unrealistic to ask to not reach 1.5ºC back then, but the increase should be as low as possible to avoid reaching tipping points and triggering positive feedback loops that could put things beyond our possibility of control. Things are not binary, we are talking about global average temperatures, not the temperature you reach some day or season in a region. So you have to deal with uncertainty and that with higher global average temperature you will have the smaller version of the loops, even if you didn't reach the budget yet. But when you surpass enough them, then you will have more players that are changing the climate, influencing each other, and things will change faster. And there the decimal resolution may lose its meaning, your range of confidence will be much wider.
WorldMaker 4y ago
A) We've already passed the expected point of no return for 0.5 (warned about as early as the 1960s as I recall) and 1.0. As of 2023 we have already experienced years at as much as 1.2 degrees (above pre-industrial average). B) The 1.5 degree budget, as I recall is the "best wish" case of the 2015 Paris agreement. C) The 2 degree budget is the "worst case" allowable by the 2015 Paris agreement. D) The Paris agreement was based on previous IPCC reports on some of the expected outcomes at 1.5 degree and 2 degree budgets. The Paris agreement was largely trying to pick the smallest number that still seemed feasible in 2015.