Oxygen-isotope proxies for air temperature in Greenland ice cores, with time resolutions of years to decades, document 25 periods from 120,000 to 14,000 BP when air temperatures warmed 5 to 16 oC within decades and cooled slowly, incrementally, over millennia back down into ice-age conditions. These clearly-observed Dansgaard--Oeschger events averaged 4000 years in length but were highly erratic in time of onset, intensity, and duration. They were typically associated with volcanic sulfate deposits and floods of fresh water into the North Atlantic. They appear to be caused primarily by sub-glacial basaltic eruptions in Iceland, the most intense of which lasted from 12,000 to 9500 BP, long enough to warm the oceans out of the last ice age. Similar sequences of current and warmer temperatures are observed in fine-layered sediments in the Eocene Green River Formation where erratic sequences averaged 5000 years. The most rapid and intense changes in sedimentation and fossils in the geologic time scale are contemporaneous with massive basaltic lava flows covering millions of square kilometers of continental rifts at the end of the Paleozoic, Carnian, Triassic, Pliensbachian, Albian, Mesozoic, Paleocene, Eocene, etc. Large, explosive, subduction-related volcanic eruptions form aerosols in the lower stratosphere cooling the globe 0.5 oC for a few years. Modelling shows that such short-term cooling of the whole ocean surface affects ocean temperatures for as long as a century. In this way, several major explosive eruptions per century over millennia cause slow, incremental cooling down into ice-age conditions as clearly resolved in deep ocean cores. It is very hard to explain these well-observed footprints of climate change using greenhouse gases. While Pinatubo erupted as much as 234 megatons of CO2 in 1991, concentrations at Mauna Loa slowed their rise due to cooling of the ocean surface. A set of 16 short videos, numerous papers, a book, and dozens of web pages all referenced at WhyClimateChanges.com document evidence for major effusive basaltic lava flows being the primary cause of fast global warming and sequences of major explosive volcanic eruptions being the major cause of slow incremental global cooling. Furthermore, they explain why greenhouse-warming theory is not only mistaken, it is Physically-Impossible.com.