Introduction

Introduction

CCSM3 Simulation of Water Vapor (white) and Precipitation (orange) for April

Weather forecasters depend on numerical weather prediction (NWP) models to produce timely, accurate forecasts. We depend on these forecasts to make all manner of decisions from recreation choice to emergency response. As a community, weather forecasters understand the strengths and weaknesses of NWP models better than just about any other group. Every forecaster knows, for example, that model skill drops sharply with time and that NWP models struggle to produce accurate and precise forecasts more than a week into the future.

Climate models share a common heritage with NWP models. For example, this animation shows water vapor and precipitation for a period of several days. We see the same weather patterns produced by NWP models and observed in satellite images. In a climate simulation, the model would run for decades or centuries, rather than days. As a result, forecasters frequently wonder how a climate model can produce an accurate projection decades or centuries in the future, when NWP models cannot produce an accurate forecast at 10 days. The answer lies in the questions the respective models seek to address.

This module explains how climate models work. Our intended audience is the weather forecasting community: those who are already familiar with NWP models. We explain not only how, but why climate models differ from weather models.

We have attempted to restrict the scope of this module to climate models, rather than climate science. We do however, draw upon climate science to illuminate the questions that climate models answer and to illustrate concepts with data from models and observations. For example, we do not attempt to explain the mechanics of El Nino-Southern Oscillation (ENSO), but we show examples of observations and model simulations of ENSO phenomena. There are many resources available that explain climate science, including several modules available at the MetEd website.

Non-forecasters with an interest in weather and climate should also find the module useful. The content is not overly technical and our goal is not to train people to develop climate models. Because we assume some familiarity with weather models, those unfamiliar with them may wish to view the short COMET module Model Fundamentals before starting this one.