Earth’s Changing Climate
| Apr |
| 21 |
| 7:00 pm |
Lecture Three
At the Elgin Public Museum
Ice Ages and Beyond
Thermometer-based temperature records go back only 150 years. This lecture explores the techniques scientists use to push global temperatures back thousands, millions, and billions of years. In particular, we’ll explore the cyclic pattern office ages punctuated by brief warmer spells. Our understanding of this pattern involves a complex interaction among astronomical effects on Earth’s orbit and axis, along with feedback effects that drive changes in the levels of atmospheric carbon dioxide and other gases. The picture of past climates developed in this lecture will be important in the next few lectures, where we seek to understand the scientific principles that establish climate, and in later lectures where we show why recent climate change is largely attributable to human activities.
Lecture Four
In the Greenhouse
What determines a planet’s temperature and, thus, establishes its overall climate? Ultimately, stable climate results form a balance between incoming solar energy and heat that a planet radiates to space. Well-established fundamental principles of physics govern that balance. But a planetary atmosphere complicates the picture, absorbing outgoing energy and, thereby, altering the energy balance. The result is the greenhouse effect, which can keep a planet significantly warmer than it would otherwise be. For Earth, the naturally occurring greenhouse effect – mostly the result of atmospheric water vapor and, to a lesser extent, carbon-dioxide – warms our planet by nearly 60°F (33°C) over what it would be absent these gases. Changes in atmospheric composition will alter the quantitative value of this greenhouse effect, and that’s the primary reason for concern about human-caused climate change.
