I assume if there's a massive volcanic eruption and the average is 1.7 - they'll [cough] cook the books and say there's no breach because the eruption was a natural fluctuation in the climate.

Not that it affects your overall point, but a large volcanic eruption would generally lower the temperature because the ash and chemicals it puts out increase the amount of light reflected back out of the atmosphere instead of being absorbed. It's basically the natural equivalent of the sorts of hairbrained geoengineering schemes techbros like to promise as a miracle cure. AFAIK there have even been what are basically miniature ice ages because of volcanic activity in recorded history.

So if, say, the Yellowstone volcano blew that would drop the global temperature back down for a year or two, as well as decreasing carbon emissions by shutting down the US and its coal mines and oil fields.