ATM 623: Climate Modeling

Brian E. J. Rose, University at Albany

Lecture 1: Planetary energy budget

About these notes:

This document uses the interactive IPython notebook format (now also called Jupyter). The notes can be accessed in several different ways:

Many of these notes make use of the climlab package, available at https://github.com/brian-rose/climlab


1. What is a Climate Model?


Let's be a little pedantic and decompose that question:

  • what is Climate?
  • what is a Model?

Climate is

  • statistics of weather, e.g. space and time averages of temperature and precip.
  • (statistics might also mean higher-order stats: variability etc)

A model is

  • not easy to define!

Wikipedia: http://en.wikipedia.org/wiki/Conceptual_model

In the most general sense, a model is anything used in any way to represent anything else. Some models are physical objects, for instance, a toy model which may be assembled, and may even be made to work like the object it represents. Whereas, a conceptual model is a model made of the composition of concepts, that thus exists only in the mind. Conceptual models are used to help us know, understand, or simulate the subject matter they represent.

George E. P. Box (statistician):

Essentially, all models are wrong, but some are useful.”

What is a Climate Model?

A minimal definition: A representation of the exchange of energy between the Earth system and space, and its effects on average surface temperature.

(what average?)

Note the focus on planetary energy budget. That’s the key to all climate modeling.

Back to Wikipedia: http://en.wikipedia.org/wiki/Climate_model

Climate models use quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice. They are used for a variety of purposes from study of the dynamics of the climate system to projections of future climate. The most talked-about use of climate models in recent years has been to project temperature changes resulting from increases in atmospheric concentrations of greenhouse gases. All climate models take account of incoming energy from the sun as short wave electromagnetic radiation, chiefly visible and short-wave (near) infrared, as well as outgoing energy as long wave (far) infrared electromagnetic radiation from the earth. Any imbalance results in a change in temperature. Models can range from relatively simple to quite complex:

  • A simple radiant heat transfer model that treats the earth as a single point and averages outgoing energy
  • this can be expanded vertically (radiative-convective models), or horizontally
  • finally, (coupled) atmosphere–ocean–sea ice global climate models discretise and solve the full equations for mass and >energy transfer and radiant exchange.

This is not a full list; for example "box models" can be written to treat flows across and within ocean basins. Furthermore, other types of modelling can be interlinked, such as land use, allowing researchers to predict the interaction between climate and ecosystems.


2. The observed global energy budget


The figure below shows current best estimates of the global, annual mean energy fluxes through the climate system.

We will look at many of these processes in detail throughout the course.

In [1]:
from IPython.display import Image
Image('../images/GlobalEnergyBudget.png')
Out[1]: