> ...ice cores show some pretty dramatic changes over just a few years.
I don't deny that the scientific record shows evidence of dramatic temperature changes. That's different from overall global trends. For example, a radical cooling could be from a huge volcanic explosion, or a large meteorite, creating a lot of atmospheric dust. A radical heating could be a change in the sun's output or the radiation bands around the Earth.
Point being that such punctuation does not necessarily presage a lasting change. And unless Yellowstone blows up or a big meteorite hits, or the VanAllen belts suddenly lose their structure, we're not likely to see any such example in our lifetimes.
As a vaguely related aside:
The scientific record gives us only some RESULTS of temperature changes. It cannot give us the CAUSES -- we modern humans have to interpret and apply scientific methodology to make the inferences and deductions required to say WHY something happened. And in my (limited) research, there are darn few PREDICTIONS that work out -- things like "Our interpretation shows that if you drill a core in this other location to this depth, it will show the following...". Merely making up plausible reasons for what you see is not science. You have to come up with predictions and verifiable hypotheses too. Otherwise science devolves into mere tealeaf reading.
I personally think that we humans can make small-scale localized changes in atmospheric/surface temperatures, enough to make ourselves uncomfortable -- but they are still just noise on the overall curve of whatever the Earth is doing at the scale of thousands of years.