Chapter 7.2 - Heat Transfer and the Natural Greenhouse Effect
Here is a summary of what you will learn in this section:
• The natural greenhouse effect is a natural process that occurs in Earth’s atmosphere and is
essential to life.
• Earth’s net radiation budget is the difference between the amount of incoming radiation
from the Sun and the outgoing energy from Earth.
• The amount of energy reflected from Earth is affected by the albedo of the area.
• Thermal energy is transferred by radiation, conduction, and convection.
• The transfer of thermal energy on Earth affects winds and ocean currents.
Trapping Heat
page 275
→ Describe in your own words how these situations “trap heat”
a) School bus on a warm day
b) Vegetable and Plant Greenhouses
Greenhouse operators rely on the sun to keep their greenhouses warm.
- Sunlight passes through the glass in the windows of the greenhouse
(Figure 7.16) on page 275
- Some of the solar radiation reflects off the tables, ground, and
plants inside and escapes back through the windows.
- Some of the solar radiation heats those tables, the ground, and the
plants.
- These heat the air in the greenhouse.
- However, this air cannot escape so the greenhouse becomes
warmer and warmer.
- While the glass lets the sunlight in, it does not let the warm air out.
Insolation and the Natural Greenhouse Effect
•
•
Virtually all the energy on Earth comes from the Sun →different regions receive different amounts of
solar radiation
Insolation is the amount of solar radiation received by a region of Earth’s surface
** Describe in your own words HOW the latitude and the specific characteristics of the lithosphere,
atmosphere, and hydrosphere in a specific region are related to the term Insolation. (page 276 in textbook)
The Natural Greenhouse Effect
•
A natural process whereby gases and clouds absorb infrared radiation emitted from
Earth’s surface and radiate it, heating the atmosphere and Earth’s surface.
Figure 7.17 The natural greenhouse effect keeps
Earth warm enough to support life by absorbing some
of the infrared radiation re-emitted from Earth’s
surface.
Some of the solar radiation that is
absorbed by Earth’s surface is re-emitted
into the atmosphere as infrared radiation
(Figure 7.17).
Most of this radiation is absorbed as
thermal energy in the atmosphere by
clouds and gases (such as water vapor,
carbon dioxide (CO2), and methane
(CH4).
Without the atmosphere, this thermal
energy would escape into space, and Earth would be significantly cooler.
The absorption of thermal energy by the atmosphere is known as the natural greenhouse
effect.
The natural greenhouse effect helps keep the temperature of our planet in the range that
supports life.
The average temperature at Earth’s surface in 2007 was 14.7°C. Without the natural
greenhouse effect, the average temperature on Earth would be about 20°C.
Water vapor, carbon dioxide, nitrous oxide, and methane are called greenhouse gases, gases that
contribute to the natural greenhouse effect
The Net Radiation Budget
•
•
•
We can live on Earth because Earth’s surface and the atmosphere absorb incoming
insolation.
However, not all the incoming solar radiation is absorbed.
Some is reflected out to space, and some is re-emitted as thermal energy by Earth’s
surface and atmosphere.
•
Figure 7.18 shows the different aspects of Earth’s average net radiation budget
Net radiation budget = incoming radiation − outgoing radiation