So we have already surpassed 1.5C by this measure, and will pass 2C earlier than predicted. Does that mean the various events predicted to occur around 2C will also occur earlier? Or not, because this paper measures from an early date?
What are the risks is really more about climate sensitivity than a specific temperature, think of it as how much can change given a warming of X degrees. Recently there is growing scientific evidence that dangers we thought were only possible at high temp scenarios, say 3-4C, are possible at 2C or might even be underway. Meaning that the climate is more sensitive than had been projected. This means that not only according to the study linked above are we closer 1.5C + 2C, but we also have more to fear from passing those temps because more can go wrong at lower levels of warming.
Every tenth of a degree matters and we should stop obsessing over 1.5C or 2C and work on mitigating as much as possible and preparing for whats coming and slow emissions and pollution as much as possible
We were in an ice age 300 years ago.
The climate has changed a lot compared to an ice age. Is it really going to change even more in the next 0.5C?
Worse yet, we're exiting the stable climactic conditions that civilization assumes is present. Assumptions regarding maximum temperatures, precipitation, ground water are baked into our reservoirs, power transmission lines, asphalt roads, train tracks, et cetera. Increased extreme weather compromises our ability to maintain society; look no further than the heat domes in the Pacific Northwest or the cold snaps in Texas to see how those assumptions compromise basic societal functions.
0.5C doesn't imply slightly worse weather, it means the additions of staggering amounts of heat to our land, water, and seas -- and the resulting amplifications of storms.
For the same reason that -2°C + 1.5°C is below freezing and -1°C + 1.5°C isn't.
> We were in an ice age 300 years ago.
No, we weren't. Not unless you're using the term in a way that includes the Late Cenozoic Ice Age that began 34 million years ago and which is ongoing. Mostly people use the term to refer to glacial periods, the last of which ended between 19000 and 12000 years ago — that's not the date being vague, it's how long it took — when the area now called Boston lost its roughly one mile deep ice sheet.
That was a 4.3°C temperature difference.
What did happen from roughly the 16th to the 19th centuries that's sometimes called the "Little Ice Age" only affected the North Atlantic region; locally by about 1°C, but even given the size of the North Atlantic, the global difference was less than 0.16-0.25°C, small enough that year-to-year differences exceeded this.
Parent might have been referring to the Little Ice Age [2], which according to the IPCC was
> ...a multi-centennial period of relatively low temperature beginning around the 15th century, with GMST averaging –0.03 [–0.30 to 0.06] °C between 1450 and 1850 relative to 1850–1900.
GMST = global mean surface temperature
Hardly, counts as valid given that we are talking about 1.5C/0.03 = 50x bigger change right now.
Earth is currently in the ice age called Quaternary glaciation.
Ice ages occur when the various Milankovitch cycles[1] and the locations of the Earth’s various tectonic plates line up just so. There needs to be a large polar continent on which large ice sheets can form to create a positive feedback loop where the ice increases the Earth’s albedo resulting in further cooling, and even more ice, &c. There also need to be at least two oceans to slow heat transfer. So even with a polar supercontinent there’s no ice age.
As you can see, currently all the conditions necessary for an ice age obtain, which is why geologists say we’re in one. Currently a glaciation is theoretically possible, but we don’t really know what gets that particular snowball rolling.
[1] https://en.m.wikipedia.org/wiki/Milankovitch_cycles
[2] Note the complete lack of Shannon entropy in the first child. Followed by dismissing scientific knowledge about the Earth’s climate as “moot” no less!
What's relevant in this discussion, is when was the last time temperature and climate were significantly lower on the Earth, coupled with much larger amounts of ice on the planet. This was over 10k years ago.
Of course, this whole discussion is moot, because natural causes have never in scientifically measurably history, caused GMST to change at the rate it is now - about 2C in 150 years, caused by humans dumping CO2 into the atmosphere.
Meanwhile, emitting another 37GT of carbon to the atmosphere is preapproved.
That is how inaction is enforced.
You've probably put on a couple hundred pounds of weight over your lifetime. Do you think it would be negligible to put on another couple hundred pounds?
Besides that, temperature just doesn't rise without affecting everything else. There are multiple (positive) feedback loops that increase the rate of warming directly (like ice melting reflecting less sunlight) or indirectly (i.e. permafrost thawing do their own carbon emissions) that get triggered once we get past some limits. Once the ball gets rolling things will get much faster, even without our intervention.