Page 29 - Earth's Climate Past and Future

CHAPTER 1 • Overview of Climate Science 5

BOX 1-1 TOOLS OF CLIMATE SCIENCE
Temperature Scales

hree temperature scales are in common use in the developed by the German physicist Gabriel Fahrenheit. It
Tworld today. For day-to-day nonscientific purposes, measures temperature in degrees Fahrenheit (°F), with
most people in the United States use the Fahrenheit scale, the freezing point of water at sea level set at 32°F and the
boiling point at 212°F.
Fahrenheit Kelvin Celsius Most other countries in the world and most scientists,
as well, routinely use the Celsius (or centigrade) scale
9981˚ 5773˚ 5500˚ developed by the Swedish astronomer Anders Celsius. It
Sun’s surface temperature
measures temperature in degrees Celsius (°C), with the
scale set so that the freezing point of water is 0°C and the
boiling point of water is 100°C.
212˚ 373˚ 100˚
Boiling point of water These equations convert temperature values between
the two scales:
T = 0.55 (T – 32) T = 1.8T + 32
F
C
C
F
32˚ 273˚ 0˚ Freezing point Earth’s
of water climate where T is the temperature in degrees Fahrenheit and T is the
F C
temperature in degrees Celsius.
Many scientific calculations make use of a third tem-
perature scale developed by the British physicist Lord
Kelvin (William Thomson) and known as the Kelvin scale.
This scale is divided into units of Kelvins, rather than
degrees Kelvin. The lowest point on the Kelvin scale
(absolute zero, or 0K) is the coldest temperature possible,
-460˚ 0˚ -273˚ Absolute zero the temperature at which motions of atomic particles
effectively cease. The Kelvin scale does not have negative
temperatures, because no temperature colder than 0K is
possible.
Temperatures above absolute zero on the Kelvin
Temperature scales Scientists use the Celsius and the Kelvin scale increase at the same rate as the Celsius scale, but
temperature scales to measure climate changes. Temperatures
at Earth’s surface vary mainly within a small range of 50°C with a constant offset. Absolute zero (0K) is equivalent
to +30°C, just below and above the freezing point of water. to 273°C, and each 1K increase on the Kelvin scale
(Adapted from W. F. Kaufman III and N. F. Comins, Discovering the above absolute zero is equivalent to a 1°C increase on the
Universe, 7th ed., © 2006 by W. H. Freeman and Company.) Celsius scale. As a result, 0°C is equivalent to 273K.

action of air and water on Earth’s surface has eroded away Even the last 10% of Earth’s history covers time
many of the early deposits that might have helped us spans beyond imagining. The climate scientists who
reconstruct and understand more of this history. study records spanning hundreds of thousands to hun-
This book focuses mainly on the last several hun- dreds of millions of years understand time only in a tech-
dred million years of Earth’s history, equivalent to less nical way, in effect as a means for cataloging and filing
than 10% of its total age. Our focus is limited because information. Geologists often refer to these unimagin-
many aspects of Earth’s history are only vaguely known ably old and long intervals as “deep time,” hinting at
far back in the past, and as scientists investigate further their remoteness from real understanding. Like the sci-
and further back, they are forced to speculate more and entists who study climate change, you will learn in this
more about fewer and fewer hard facts. But more infor- book to catalog deep time in your own mental file, even if
mation is available in the younger part of the climatic you cannot comprehend it in a literal sense.
record, and our chances of measuring and understand- The plot of time on the left in Figure 1-2 (page 6)
ing climate change increase. shows that much of this book (Parts III through V)