<What 'if' they (scientists) are right?>
Well, those scientists and talking heads who believe in man-made global warming have pretty much had sway in policy and law in many developed nations for some time now. Not all. But if the tide can be turned, they are on the right track to do so.
What if they are wrong? They received tons of money to fund research. They made a career of a lie (whether genuinely believed by them or not). Some people built companies and fortunes selling a lie to a public that wanted to believe what they were fed. Governments of developed nations needlessly impeded or stopped the production of coal energy and the development of oil production/refinement in order to save the environment from a non-threat. Prices increased for everyone. Hundreds of thousands of jobs lost or never created in the name of junk science. But this is all hypothetical. If the world endures another 500 years, no matter what the weather does, there will still be smart people on both sides of this issue. Neither side can claim 100% certainty with credibility.
The Mayan (long count) calendar thought is interesting. I do not believe the Mayan's did "know" when the world would end. According to the Bible, which I believe to be true, that information is only known by the Creator and Sustainer of life. He didn't tell His son Jesus, while he was on this earth, so I doubt He told the Mayans. Others on here surely have a different opinion, and are welcome to it. According to Genesis 8:22, God promised Noah that as long as the earth endures, there will be summer and winter, cold and heat, seedtime and harvest. Doesn't say where the summer and heat and harvest will be on the earth. It could be that everything flips around. But this earth will always have hot and cold as long as there is an earth.
For those who keep bees in the northern hemisphere, it appears that we are entering into a colder winter season, for whatever reason. Whether it lasts a decade, or a hundred years, we probably need to look at better ways to over-winter bees in colder climate. 5 years from now, North Carolina's easy winter climate might look more like today's Maine. Who knows??? So...insulated hives? Small bee huts with heat sources inside? Electric blankets? Or it could go the other way. 5 years from now, Maine's winter could look like Southern Florida today. Good thing we can talk to people on the internet and see how to work in different climates.