Comment by hn_throwaway_99 | Hacker News Reader

Comment by hn_throwaway_99 | Hacker News Reader

hn_throwaway_99

To start, yes, I agree with all the rest of the comments. Of course if you look at the action needed to start within the 1.5 degree carbon budget, it's simply impossible. It's kind of like saying how much better humanity would be if there were no wars - a nice thought, but also not going to happen.

I'm curious, though, and I admit I haven't read the report, but what is it about 1.5 degrees that the scientific community sees as so critical. Is that the temp after which positive feedback loops take over and it becomes a "runaway train", so to speak (e.g. less ice results in less albedo and more warming, which causes less ice). I just want to understand why that number was chosen to represent such a critical point.

And since it's obvious we are not going to make that limit, what are the additional consequences of hitting 2 or 3 degrees of warming?

Edit: To the downvoters, please take a look at https://ourworldindata.org/co2-emissions. Global CO2 emissions have simply skyrocketed since 1950. The only year they didn't go up was 2020 - remember that year we had a pandemic that shut down much of the world for months and months on end. And still, despite all the stoppage of activity, there was just a small blip down in CO2 emissions. I don't understand how any sane person can look at this graph and believe that 1.5 is attainable. Remember, we don't just have to flatten this graph, we need to bring it all the way back down to 0. I do think alternative energy technology will eventually get us there, but certainly not in 15 years, all across the world.

1.5 degrees is commonly talked about because almost every country on earth pledged to "pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels" [0] in the Paris agreement. We won't hit that anymore, but it makes sense for scientists to compare the taken measures with the original goal. Every degree matters and aiming for 1.5 and missing by 0.5 degrees is better than aiming for a "realistic" 2.5 degrees and missing by 0.2 degrees.

[0] https://unfccc.int/process-and-meetings/the-paris-agreement

Thanks very much for your response, I think it makes the most sense - that is, 1.5 degrees isn't some "magic number", but every .1 degree makes things disproportionally worse, and we want to limit the damage as much as possible.

In that case, I think still harping on the 1.5 degree number is a communications mistake. It is obviously impossible at this point (see the edit in my original comment), and so I think focusing it risks encouraging a "well, this is obviously too late, might as well enjoy our bread and circuses while they last" attitude. I think it would be much better if scientists said "Remember when we warned you about that 1.5 degree limit? Well, y'all f'd that up, so now a lot of these dire predictions are going to come true. Oh, and here is a whole host of even more dire predictions that will occur for every .1 degree you miss the limit, so you better try to limit carbon emissions as much as you can to prevent things from becoming more screwed than they are already guaranteed to be."

I just think that any messaging that talks about things eventually being "too late" is bad from a public motivation standpoint.

Well what you are criticizing is mainly a problem of the media. Look at the actual IPCC report [0], there multiple scenarios are outlined, with 1.5 degrees being the most optimistic one, which makes sense. I did not read through it yet, but from a quick glance they do describe the impact of different scenarios, while also presenting measures to reach those, just like you asked for. You sadly can not expect that kind of nuance from the media though, most articles (just like the linked The Guardian article) seem to focus exclusively on the 1.5 degrees scenario.

[0] https://report.ipcc.ch/ar6syr/pdf/IPCC_AR6_SYR_SPM.pdf

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.

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.

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.

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.

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.

I suggest watching a Kevin Anderson lecture, basically, the 1.5C and 2C come from the political world, scientists then create research around that to get published, get their research into IPCC reports, etc. It is a farce and purely a political one. They are obsessed with "good news" and "hope".

The assumptions for how 1.5C is "possible" amount to futurism.

The goalposts keep moving too - once it was a 66% chance of staying under 2C, now it's common to talk about exceeding 2C and lowering the temperature later, which is about as plausible as running a car into reverse while the gas pedal is down.

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