Lesson 2 Summary

In this lesson, we reviewed key observations that detail how our atmosphere and climate are changing. We have seen that:

• Greenhouse gas concentrations, including atmospheric CO₂ and methane, are increasing dramatically, and these increases are associated with human activity;
• The surface of the Earth is warming and certain regions (e.g., the Arctic) are warming faster than others, consistent, as we will see, with expectations from climate model projections;
• The vertical pattern of the warming indicates that the surface and lower atmosphere (troposphere) are warming, while the atmosphere is cooling at altitude (in the stratosphere), a pattern that is consistent with greenhouse warming, but not with the natural factors such as solar output changes;
• There is a complicated pattern of changes in rainfall patterns around the globe, with some regions becoming wetter while other regions become drier;
• Despite the heterogeneous pattern of changes in rainfall, there is a trend towards more widespread drought, consistent with the additional impact of warming on evaporation from the soil.

We also learned how to analyze basic relationships in observational data, including:

• How to assess whether or not there is a statistically significant trend over time in a data series;
• How to assess whether or not there is a statistically significant relationship between two distinct data series.

In our next lesson, we will look at some additional types and sources of observational climate data, and we will explore some additional tools for analyzing data.

Reminder - Complete all of the lesson tasks!

You have finished Lesson 2. 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.