I think it’s long enough, there are lots of atmospheric science papers finding significant trends over such timeframes (or even shorter). There is the question of interdecadal variability and whether we’re just seeing certain long-term cycles…but I’d think 80 years would be enough to even avoid many of those.

Seconding this! It's not "in the year 2050, all the shit will hit the fan." It's "everywhere will be getting a little more extreme every decade, on average." There are various extreme thresholds (too hot or cold, wet or dry) beyond which human life cannot thrive. The point of "fcked" in a given region would occur when the conditions move beyond that threshold. This is why regions where humans already live close to that climatological threshold - deserts, vulnerable coastlines, dangerous monsoon regions - will be some of the first to go.

Oh good! Hopefully if this continues and accelerates we’ll at least be able to avoid the worst-case scenario of constant/increasing fossil fuel use throughout the 21st century

I'm not an expert on that, but huge climate migration is expected by mid-century already - I've seen estimates of anywhere from ~150 million to ~1 billion. In general, the frequency of extremes will be increasing gradually but consistently. These changes would typically include more intense and/or frequent extreme precipitation and heat waves; and even if overall precipitation totals stay the same or increase, it being delivered in these very intense extreme events with less light and moderate rain in between will increase the likelihood of drought. Rapid intensification of hurricanes/typhoons has increased as well, and will likely continue to do so in the future. So that would be an influence in many tropical and subtropical regions. I would worry about the greatest danger for short-term catastrophic changes being in regions that already experience extreme drought, fire, life-threatening heat, or monsoons, all of which stand to be intensified by climate change. Anyway, as for a specific time frame - I don't have an answer beyond...it's already becoming a problem, and will only get worse over the next few decades.

Meanwhile, as expected, we're failing to take the drastic action that would be necessary to actually meet emissions goals. It is now inevitable (barring some miraculous scientific discovery) that the future will be several degrees warmer, with more intense precipitation and drought. I do atmospheric science research, and looking at the high-end RCP8.5 and SSP5-8.5 scenarios is...disturbing.