Scientists have adopted basic rules of management, such as: "You can't manage what you can't measure." This is a truism in climate science. In order to understand where our climate is headed, we need to know where it has been in the past, and where it is now.

Understanding the state of the climate is an immense engineering challenge. Think of trying to measure the energy of the oceans, or the chemistry of the Earth's waters. How about temperatures or chemistry of the atmosphere? What about the extent of ice (including both area and thickness)? How about sea level?