Forget human activity, forget the sun, the main cause of global warming is under our feet, or probably more accurately under the oceans. The crust thickness is far from being equal. Especially under the seas, it is very thin. There are numerous hot springs at the bottom of the seas and underwater volcanoes. The oceans are probably warming much faster than what we believe as seen in northern Greenland which could be the canary in the ocean mine. Marine animals know it and terrestrial ones also must feel it.
This could be the real reason of the planet heating and I'm afraid there is nothing we could do about it. All the carbon tax, the so-called geoengineering are useful distraction to cash in some more on people dumbness' backs.
Scientists Discover that Heat From INSIDE the Earth is Melting some Areas of Arctic Ice
Hundreds of Methane Plumes Spotted on Sea Floor
"An estimated two-thirds of the emissions emanate from sediments at depths where methane-rich ices may be decomposing due to warming waters along the ocean bottom"