I'm glad to see that there are still some people who keep their sanity when it comes to global warming which was invented by american politicians in the early 60s and taken to a full run in the 80s by so called environmentalists which had no technical or scientific credentials whatsoever.
in order to control people, leaders need to give them a common cause.
many thing (which I wouldn't want to get into) have been tried for thousands of years, some better some worse.
so off they went and find something new to give their subjects a reason to unite and voila, global warming sounds good and everybody should just agree to save the environment and the planet we live on.
the fact as mostly described correctly by voltekker (but there is also methane released by volcanic eruptions and dust particles) is that the earth has a wobble in its axis which causes dramatic climatic changes every 50k years.
to say it in simple words.
we're at the end of an ice age, this means everything is warming up and ice will melt and the planet will get hot.
after that the planet will cool down, water will freeze and half of the planet will be covered in ice and the people alive at that time will be blamed for global cooling.
it happened before and will happen again, with or without us.
this planet had many events where 30-40% of all life was wiped out, there were events where more then 90% of all life was wiped out, were there once were rainforest are now desserts and were there once where oceans are now mountains and all that without us ever being involved.
this planet is 5 billion years old, life exists for only 500 million years and has gone through some dramatic changes.
a lot more changes within the next 5 billion years will come, with us or (but most likely) without us.
btw, "they" just found that the polar caps on mars are thinning, who's to blame for that ohh, hold on a minute, haven't we send a remote control car over there? here we go.