evidence: On the whole, these and other studies find consistent results. While the Sun's influence is detectable in Earth's temperature records, the global-scale warming influence of human-produced greenhouse gases is likely to be far stronger than even a very strong Grand Solar Minimum. [...] For the past million years at least, Milankovitch cycles have coincided with 100,000-year-long ice ages punctuated by short intervals of rapid warming. Although there are pieces of the puzzle experts still don’t understand, the key climate influence seems to be changes in the amount of incoming sunlight, or insolation, reaching the high latitudes of the Northern Hemisphere during the summer. The Northern Hemisphere is key to the ice ages because massive ice sheets can only grow over land, not ocean, and most of Earth’s land area has been concentrated in the Northern Hemisphere for at least tens of millions of years.