Global Warming, page-180

Most climate scientists are too frightened to speak up against global warming because they would lose their job if they did and never get another one. Things have not changed much since Galileo tried to tell everybody that earth is not at the center of the universe and almost got burnt at the stake for it.

There is overwhelming evidence showing that earth's temperature (ie ice ages and warmer interglacial periods) are caused mostly by variations in earth's eccentricity and has nothing whatsoever to do with atmospheric CO2 - which remains at a historic low over a geological timescale (i.e. millions of years). Milankovitch cycles are explained here:

http://www.indiana.edu/~geol105/images/gaia_chapter_4/milankovitch.htm

No planet has a perfectly circular orbit because they get pulled around by each other, especially by the gas giant Jupiter. Earth's eccentricity varies from being almost perfectly concentric (circular) to being 5% elliptical. When earth's orbit is elliptical it cools down, because it spends more time in the slow part of its orbit that is further away from the sun. When earth's orbit is circular it heats up, because it spends more time being closer to the sun than when it is in an elliptical orbit. This is shown here:



Now there is evidence that the eccentricity of earth's orbit is not only responsibly for the 100,000 year climate cycle, but also likely responsible for major extinction events and magnetic pole reversal. See here:

https://www.universetoday.com/139198/jupiter-and-venus-change-earths-orbit-every-405000-years/