This chapter’s title reflects both the profound climactic disruptions and the exponential increase in scientific understanding that have occurred since the first Earth Day in 1970. Schneider begins with a personal anecdote, recalling a childhood spent skiing in the Harz mountains of Germany, now no longer possible, due to the dramatic shortening of winter and the loss of snow cover. In contrast, his present home of Los Angeles now experiences an extra two weeks of above average hot days compared to 1970. This change is paralleled by the development of climate science, pioneered by Swedish chemist and Nobel Laureate Svante Arrhenius, whose often inaccurate measurements first connected rising and falling CO2 levels to global warming and cooling. Today, a combination of fossil fuels and deforestation have resulted in CO2 levels of 415 ppm (parts per million) compared to 320 ppm in 1970 – 20% above pre-industrial levels. Industrialized nations have therefore added twice as much carbon dioxide to the atmosphere since 1970 as in all of previous human history before. The chapter emphasizes the continuing need for more accurate data and modeling to predict the effects on incredibly complex global systems. By dividing the earth into manageable grids, scientists are more accurately able to predict atmospheric variations, using supercomputers to break down the impossibly large variables. The chapter ends on a stark note: even if all greenhouse emissions were to be halted today (virtually impossible given the nature of our global energy economy), temperatures would still rise by 0.4–1.7°C, as a new baseline would take centuries, if not millennia, to establish. The conclusion is simple: every facet of human activity will be impacted, and we will have to adapt.