Global warming is undoubtedly real. So it global cooling. There's tons of evidence that shows that our planet has gone through tons and tons of change over the past billions of years. Some of the data we have from the past thousands of years is moderately accurate and can paint some pictures.

The problem is, there is data, but not a lot of it. It's also not incontrovertible. It sometimes does and sometimes doesn't line up with other data. Ice core samples. Rock samples. Archeological evidence. Geographical evidence. We've only had very real, SOLID temperature data for the past 100 years or so. Some of it's suspect anyway, due to potentially bad or faulty equipment, skill or human error. 100 years in the scope of the life of this planet is a tiny speck of a fart and drawing far ranging conclusions based on that is ridiculous.

In short, we don't know, and what conclusions we can draw are highly tenuous at best.

That said:

I unconditionally agree that humanity needs to get a hell of a lot better at taking care of spaceship earth. Heavy emphasis on recycling. Using greener energy methods. Cleaning up existing pollution. Educating people in all regards. Using more environmentally friendly products, and methods for producing these products. These are all very good, very solid things that we should all be moving towards. Using fear or bunk science as a method to push that is not the right way.