Earth's millennial climate cycle has been studied by scientists for
decades, but its cause has been lacking. It warms the Earth for several
hundred years and melts some of the ice sheets in Greenland and
Antarctica. My analysis discovered that it is caused by the astronomical
conjunction of the planets Jupiter, Saturn and Neptune. This paper
describes the observations that led to its discovery and explains how
its 1,470-year spin-orbit resonance cycle warms the Earth with
geothermal heat. The current cycle started warming the Earth in the year
1791 and will probably reach peak temperature in year 2060 at the next
Jupiter, Saturn and Neptune conjunction. Then it will cause cooling
oscillations for the rest of the cycle.