The event hankmorgan refers to was probably a large volcanic event. That was not an extinction level event. The largest volcanic events we know of generally only cause a major disruption over a few years, and then it is back to business as usual. It was “the year without a summer” not “the century without summers.”
When two such events happen within a few years, you can get prolonged effects as happened in the decade of the 530AD.
The difference in time scale between those isolated volcanic events and the present situation is that CO2 levels will remain high for centuries, not a few years. Such a time scale means that the occasional and short-lived changes to patterns of atmospheric and oceanic flows will become long-term changes, affecting all aspects of life. Places like the SouthEast US may find themselves constantly dealing with floods they have never seen before, with wetlands expanding far beyond what they were in early colonial America. From the point of view of humanity, change will persist over lifetimes, not a few years.
Time scales matter. The increase in CO2 from just 1959 until now exceeds the increases from previous ice age lows (when ice was at maximum, near enough, and temperatures lowest) to interglacial peak values. The shortest such natural time was more than 7000 years. We’ve done the same increase in a mere 60 years. We have no way to undo that in the short term, so we can expect centuries of changed climate.
BTW, as I have repeatedly stressed, planting trees is not likely to work. Because they won’t be allowed to compete with farm plantings. They’ll be planted in regions with low water supplies, so they won’t grow fast (see the Chinese planting in a desert). You want coast redwoods, not Bristlecone pines.
We will see sea level rises and climate changes that displace millions of people. Such displacements are the breeding ground for disease and disorder not in just a few locations, but around the world, from pole to pole.