IB Biology Experiment
Modelling the Greenhouse Effect
Environmental Science Published for Everybody
Round the Earth
The energy of light is transported in the air as electromagnetic radiation. Only a small
fraction of this energy spectrum (visible light) is seen by our eyes. Other parts are
invisible and damage our skin (ultraviolet light) or we can feel it as warm radiation
(infrared radiation).
The temperature in the atmosphere is considerably governed by the capability of the
different air molecules (Carbon Dioxide, Argon, Nitrogen, Oxygen) to absorb this
radiation.
An important fraction of the sunlight reaching the earth’s surface is absorbed,
transformed into thermal energy and emitted again as infrared radiation.
Greenhouse gases (methane, carbon dioxide, oxides of nitrogen) in the atmosphere are
gases who efficiently absorb this infrared radiation emitted by the earth in order to keep
the heat in the atmosphere, like in a greenhouse.
To investigate the greenhouse effect carry out the following experiment:
Apparatus: - per group
2 x 250ml glass beakers containing air (right) and CO2 (left)
two lights of identical output (or the sun)
two petri dishes with water
black cardboard
2 x Temperature sensors ( linked to a computer)
Stopwatch
Method:
A The lamp represents
the sun.
B A petri dish filled 1cm deep with water
absorbs the thermal energy emitted by the lights,.
Normal bulbs emit a major fraction of their
energy as heat but only the radiation should pass.
C1 The left hand side beaker is filled with pure
carbon dioxide. (made using bicarbonate and HCl
C2 The right hand beaker is filled with normal
air containing only about 0,03% of carbon
dioxide.
Therefore the heat absorbing effect of CO2 should
be greater in the left vessel.
D Below the glass vessels is a layer of black
card, representing the dark surface of the earth.
After switching on the light, the temperature is measured in both vessels and plotted on
the computer screen as a function of the time. Readings every minute for 15 minutes.
left: carbon dioxide
the infrared radiation emitted by the
cardboard, is absorbed by the CO2
and causes an increase of heat in the
vessel.
right: air
the infrared radiation emitted by the
cardboard leaves the vessel without
any significant absorption. The
increase in tempearture is less.
How it works?
1) The lights are switched on
2) Infrared light (heat) is absorbed by the water in the pan above the vessel and does not
reach the air or the CO2 below.
3) The visible light emitted by the bulbs passes the water and reaches the black
cardboard.
4) The cardboard becomes warmer and emits infrared radiation.
5) The infrared light is absorbed by the pure carbon dioxide (left) much stronger than by
the air (right).
6) In the vessel with carbon dioxide the gas is heated due the absorption.
Result:
Temperature as a function of time:
Time
T (air)
T (CO2)
[min]
[°C]
[°C]
0
22
22
5
32
37
10
35
40
15
40
45
20
44
50
Diagram:
The blue series in front shows the course of temperatures in the right vessel.
The violet series behind shows the temperature course in the left vessel containing carbon
dioxide.
Conclusions:
Due to the infrared radiation absorbed by the pure carbon dioxide this gas is
heated by far stronger than the air consisting mainly from nitrogen and oxygen.
The fraction of carbon dioxide in the air is acting as a greenhouse gas.