@puck61: Krakatoa's eruption in 1883 indeed had an abrupt effect, resulting in global cooling that lasted until 1888. Mount Tambora's eruption in 1815 was even larger, resulting in what was called the "year without summer" in 1816, when frosts were reported in New Hampshire in every month, including June, July, and August. But where these eruptions differ from the current global climate change is that they were over after a few years, and temperatures returned to normal, whereas the current increase in greenhouse gases such as carbon dioxide and methane will continue to impact the climate for generations. This is true even if we stopped emitted carbon dioxide, which isn't going to happen.
There are always short-term fluctuations in climate, but that doesn't mean that we should accept long-term drastic changes as something normal. It isn't. In geologic time, the warming we've experienced is both abrupt and unprecedented in human history. And it is only going to get worse. We can choose to do something, or do nothing and watch it and try to deal with the effects. I don't see that as alarmism. It is making a decision based on the best science that is available.