Greenhouse effect
Model the greenhouse effect by comparing the heating of a CO₂-enriched atmosphere (carbonated soda) and a normal atmosphere (flat soda) under a lamp.
Learning objectives:
The student compares the temperature evolution in two chambers — one with CO₂-enriched air, one with normal air — under the same lamp, measuring with SCD40 sensors.
Level:
Author:
High school
Serge Paupy
Duration (minutes) :
90
What students will do :
- Design and perform a model experiment with a control
- Measure temperature and CO₂ concentration simultaneously in two chambers
- Observe the enhanced warming of a CO₂-enriched atmosphere
- Critically discuss the limitations of the classroom model
- Understand the difference between the radiative greenhouse effect and convective confinement
Scientific concepts:
- Greenhouse effect
- Infrared radiation
- Absorption and thermal emission
- Convection and confinement
- Greenhouse gases (CO₂)
- Experimental modeling and limitations
Sensors:
- SCD40 sensor (CO₂ in ppm, temperature in °C) × 2
What is required:
- Smartphone or tablet with FizziQ Connect
- Two M5 Stack modules with SCD40 sensors
- Two identical transparent containers
- Two bottles of the same soda (one degassed overnight)
- A powerful lamp (halogen preferred)
- Plastic wrap
Experimental procedure:
The day before, open a bottle of soda and leave it open overnight to let the gas escape completely.
On the day of the experiment, prepare a second identical bottle, freshly opened and still carbonated.
Equip each M5 Stack module with an SCD40 sensor. Turn them on and verify they display CO₂ (ppm) and temperature (°C).
Pour the flat soda into the first container and the carbonated soda into the second. Use identical volumes.
Place an SCD40 sensor in each container, above the liquid (not submerged). Cover with plastic wrap to seal.
Note the initial CO₂ and temperature values for both chambers. The CO₂ in the carbonated chamber should be much higher.
Place both containers side by side, at the same distance from the lamp. Start recording on both modules.
Turn on the lamp (halogen preferred for strong infrared emission). Record for 60 to 90 minutes.
Stop the recording and export the data from each module in FizziQ Connect.
Compare the temperature and CO₂ curves for both chambers. Discuss the results, taking into account the model's limitations.
Expected results:
With carbonated soda, the CO₂ in the enriched chamber quickly reaches 40,000+ ppm (sensor saturation), while the flat soda chamber stays at a few hundred ppm. The temperature in the CO₂-enriched chamber rises 1-3°C more than the control after 60-90 minutes. The difference is small but reproducible.
Scientific questions:
- Can we conclude that the observed temperature difference is solely due to infrared absorption by CO₂?
- Why are results more convincing with a halogen lamp (more infrared) than an LED lamp?
- What are the limitations of this model compared to the real atmospheric greenhouse effect?
- Why is the term 'greenhouse effect' somewhat misleading?
- How does the enhanced greenhouse effect from human activities differ from the natural greenhouse effect?
- What evidence from satellite data confirms the atmospheric greenhouse effect?
Scientific explanations:
The atmospheric greenhouse effect is a radiative phenomenon: certain gases (CO₂, H₂O, CH₄) absorb infrared radiation emitted by the Earth's surface and re-emit it in all directions, including back toward the surface, causing additional warming.
In this experiment, the CO₂-enriched chamber does warm more, but the mechanisms involved are not purely radiative. In a container filled with dense CO₂, the air must be hotter to begin escaping, reducing convective cooling.
In a crystallizer filled with dense CO₂, the air must be hotter to start escaping and being replaced by fresh air. This confinement effect adds to any radiative effect.
The term 'greenhouse effect' is itself misleading: in a horticultural greenhouse, warming is primarily due to convective confinement (blocking wind and mixing), not infrared absorption by the glass.
There is no simple classroom experiment that faithfully reproduces the radiative mechanism of the atmospheric greenhouse effect. This experiment is a model with significant limitations that should be discussed critically.
The real atmospheric greenhouse effect is measured by satellite: without the natural greenhouse effect, Earth's average temperature would be about -18°C instead of +15°C. The enhanced greenhouse effect from human CO₂ emissions is causing the observed global warming.
Extension activities:
- Can we conclude that the observed temperature difference is solely due to infrared absorption by CO₂?
- Why are results more convincing with a halogen lamp (more infrared) than an LED lamp?
- What are the limitations of this model compared to the real atmospheric greenhouse effect?
- Why is the term 'greenhouse effect' somewhat misleading?
- How does the enhanced greenhouse effect from human activities differ from the natural greenhouse effect?
- What evidence from satellite data confirms the atmospheric greenhouse effect?
Frequently asked questions:
Q: The SCD40 sensor saturates at 40,000 ppm. Is this a problem?
R: The SCD40 range goes up to 40,000 ppm. If the concentration exceeds this, the readings plateau. This does not affect the temperature measurement.
Q: The temperature difference is very small (< 1°C). Is the experiment valid?
R: Yes, the effect is real but small in a classroom setting. Use precise sensors and long recording times. The difference should be reproducible.
Q: Why does the flat soda chamber also warm up?
R: Both chambers absorb light from the lamp and warm up. The CO₂ chamber warms slightly more. The relevant quantity is the temperature difference between the two.
Q: Is this experiment proof of the greenhouse effect?
R: It is a simplified model with significant limitations. It demonstrates that CO₂-enriched air warms more under irradiation, but the mechanisms are not purely radiative. Use it as a starting point for critical discussion.