ON TOPIC: The global climate has been cyclical for the entirety of earth's history. The Holocene Warm Period stretched on for 5000-9000 years and was much warmer than anything which has been predicted by modern science, without any interference from humans. As well, we can't predict next weeks weather with any accuracy, let alone climate trends.
Problem one: it doesn't usually change this quickly. The halocene changed over periods of thousands of years, not decades.
Problem two: the sea levels around that time were pretty goddamn different from the ones we have now. If we did return to the sea levels we had then, we'd quite clearly be plunged into chaos.
Problem three: your final sentence shows a pretty basic mistake.
"Weather" and "climate" are two entirely different things. Day to day weather is harder to predict than an overall trend in climate and temperature ranges. In the same way we can't predict whether a coin will be heads or tails on its next flip, but we can predict a rough estimate of how many tails we expect if we flip it 100,000 times.
Incidentally, "The earth's climate is cyclical" is a very obvious statement. We know about that from ice ages and stuff. It's like saying "Things fall downwards!" and using that as proof that the earth isn't round.