Why do researchers tune climate models? (Choose the best answer.)

The correct answer is (a) To achieve a stable control climate.

In a process akin to calibrating laboratory instruments to reduce measurement errors, modelers "tune" the model to achieve a steady state under constant boundary conditions. Once a stable control is established, only then can they design experiments to answer questions about the effects of changing those boundary conditions.

Which of the following are characteristics of a good candidate for being a tunable parameter? (Choose all that apply.)

The correct answers are (c) and (d).

To tune a climate model, the developers usually find a parameterization that has a large effect on the energy budget within the range of observational uncertainty. Tuning is done to achieve a stable control climate, not to reduce biases in model simulations.