Lesson 5 Summary

In this lesson, we further explored the use of theoretical models of the climate system. We found that:

• A generalization of the zero-dimensional EBM known as the one-layer EBM can be used to provide a more realistic description of the greenhouse effect. This model can be used to estimate both surface temperatures and temperatures of the mid-troposphere. It is also possible to study the effect of feedbacks using a simple model of this sort;
• A further generalization known as the one-dimensional EBM can be used to study the latitudinal dependence of energy balance and temperature distributions. The one-dimensional EBM can be used, among other applications, to try to understand the processes that drive climate into and out of Ice Ages;
• Full three-dimensional general circulation models (GCMs) and coupled Atmosphere-Ocean (AOGCM) versions of the GCM can be used to model the more detailed patterns of climate variability and climate change, and the study not just of temperature changes but other key fields such as precipitation, wind patterns, etc.;
• Theoretical climate models have been validated in numerous ways. Predictions of warming made back in the late 1980s have been borne out, and experiments simulating the response to natural events, such as volcanic eruptions, have demonstrated that climate models have the ability to make accurate predictions of the responses of the climate to both natural and human forcings;
• Comparisons of model simulations and observations, including so-called "fingerprint detection" studies, indicate that natural factors alone cannot explain the observed trends of the past century; only a combination of natural and human factors can explain these trends;
• By comparing model simulations and observations on a variety of timescales, scientists have constrained climate sensitivity—the equilibrium warming expected in response to a doubling of ${\text{CO}}_{\text{2}}$ concentrations—to lie somewhere within the range of 1.5 to 4.5°C, with a most likely estimate of around 3°C warming.

Reminder - Complete all of the lesson tasks!

You have finished Lesson 5. Double-check the list of requirements on the first page of this lesson to make sure you have completed all of the activities listed there before beginning the next lesson.