What will the planet’s climate be like by the end of this century? The answer may lie in really, really old rocks, according to a new report that urges a coordinated research effort to study them.

Scientists have already pieced together a comprehensive record of Earth’s changing climate from studies of rocks and ice that stretches back about 2 million years. The problem is that the amount of carbon dioxide already pumped into the atmosphere is 25 to 30 percent higher than at any point in that record.