The human impact on Earth’s climate is suggested by the close correlation between rapidly increasing temperatures and the recent increase in atmospheric carbon dioxide concentration as shown in the Keeling Curve. Also, collisional de-excitation—the mechanism by which greenhouse gases absorb IR radiation and contribute to atmospheric warming—is well understood.

Why Should We Care?

Humanity’s alteration of Earth’s energy balance and atmospheric warming are causing profound changes to the planetary climate, with important consequences for human society, such as increased severity of extreme weather events and rising sea levels. These topics are addressed more fully throughout the lesson.

What can be done to address this issue? The common answer is to reduce greenhouse gas emissions, but how might this goal be achieved? Examine the graph below, displaying the percentage of world greenhouse gas emissions in 2004 by sector, and answer the following question.

Your Turn

1. What sector is responsible for the largest percentage of the world’s emissions of greenhouse gases?
2. Suggest two strategies for reducing greenhouse gas emissions which target the sector identified in part A.