evidence: Scientists can track these earlier natural changes in climate by examining ice cores drilled from Greenland and Antarctica, which provide evidence about conditions as far back as 800,000 years ago. The ice cores have shown that rising CO2 levels and rising temperatures are closely linked. [...] The number of record-breaking hot temperatures in the U.S. is on the rise. Oceans are the warmest they have been in a half-century; the top layer is warming about 0.2˚F per decade. The oceans are also 30 percent more acidic than they were at the start of the Industrial Revolution because they are absorbing more CO2. Global sea levels rose an average of 6.7 inches in the last century, and in the last 10 years, have risen almost twice as fast. [...] "There are lot of things that we’re absolutely certain about," said de Menocal. "We’re absolutely certain carbon dioxide is rising in the atmosphere. We’re absolutely certain it’s warming the planet and we’re absolutely certain that it’s acidifying the oceans."