evidence: If you could travel back in time five centuries, you'd encounter an Aztec empire nearly at the end of its run, fresh paintings from Raphael, Titian and Durer, and cooler temperatures across the Northern Hemisphere. This was a world in the midst of the Little Ice Age (1300 to 1850 C.E.) and a period of vast European exploration now known as the Age of Discovery. If we looked 500 years into the future and glimpse the Earth of the 26th century, we might find that the planet is as different to us as it would have seemed to residents of the 16th century. But this largely depends on the relationship between human civilization and our natural environment — its past, its present and, of course, its future. [...] According to NASA, carbon dioxide levels are up to 412 parts per million (ppm) as of December 2019, up from 316 ppm in 1958 when scientists first started tracking CO2. Global temperature was up 2.07 degrees Fahrenheit (1.15 degrees Celsius) since 1880, according to the National Oceanic and Atmospheric Administration. Meanwhile, Arctic ice declines 12.85 percent per decade, and sea levels rise 3.3 millimeters per year, says NASA.