An interpreter gets distracted by every rustle in the hall, and a one-hour meeting stretches into two. The atmosphere is like such an interpreter: it hears not only the biosphere's words but also its tone. When plants change the pace at which they absorb carbon dioxide, the air responds not to the gas itself but to how quickly and how abruptly its amount changes.

Since 1960, the Hawaiian observatory at Mauna Loa has measured CO₂ concentration every month. If you take not the level itself but its rate of change, the first derivative, it matches tropical temperatures almost perfectly. But the most interesting part begins with the second derivative, that is, the acceleration. It turns out that the acceleration of CO₂ change leads the Southern Oscillation by two months. The Southern Oscillation is the pressure difference between the eastern and western Pacific, the atmospheric part of El Niño.

Previously, El Niño was explained as an independent ocean mode, but now it appears that it may be a response of the biosphere to the acceleration of CO₂ change. This ties together the carbon cycle, vegetation, and large-scale atmospheric circulation. An interpreter who hears the tone does not need to wait for the biosphere to finish its sentence.