The concept of Occam’s Razor, also known as the principle of parsimony, is a motivating force in science. Galileo’s experiment of dropping objects of different weights from atop the Leaning Tower of Pisa to show that they fall at the same rate is an illustration of this principle. But the application of Occam’s Razor to climate modeling is less straightforward. Simple models of the kind used by Manabe provide qualitative insights, but they are not well-suited for quantitative predictions. To understand this, we can make an analogy between the hierarchy of climate models and the hierarchy of biological models, from fruit fly to mouse. Simple models are used to explore “climate tipping points,” where amplifying feedbacks lead to abrupt climate change, but they may not consider all the stabilizing feedbacks. It is therefore important to use a hierarchy of models, with varying degrees of complexity, to study climate phenomena.

The Geophysical Fluid Dynamics Laboratory (GFDL) is a pioneering institution in the field of climate modeling. Its founding director, Joseph Smagorinsky, was a member of the Princeton Meteorology Group. He hired a Japanese scientist, Syukuro Manabe, who formulated a one-dimensional model of climate, known as the radiative–convective model, that was able to calculate the amplifying climate feedback due to water vapor. This model provided one of the first reliable estimates of global warming. Manabe worked with other scientists to build three-dimensional climate models, including the first model that coupled an atmospheric model to an ocean model. The concepts of reductionism and emergentism, which provide the philosophical context for these scientific developments, are introduced.