In a greenhouse effect lab experiment, why would a covered beaker with exhaled breath and soil heat slower?

Question

We did an experiment to simulate the greenhouse effect. One of the questions asks for a possible reason why when the lamp was on (simulating the sun) did the covered beaker, which had soil and an exhaled breath in it (CO2 and water vapor), heat slower than a beaker with soil in it but no cover or exhaled breath?

i am thinking that it is because the beaker with the cover on it reflected some of the heat, just like the earth, but this answer seems to easy.

Answer 1

Science teacher's first explanation is the correct one (the second part about water vapor is not correct).  The glass cover on top of the beaker blocks infrared radiation.  For an incandescent lamp, that is a significant source of energy since an incandescent lamp is much colder than the sun and generates more power in the IR relative to the visible.  Removing the infrared from the energy flux reduces the energy warming the soil in the covered beaker, so it heats slower than an uncovered beaker.

Your experiment is a classic example of why it is essentially impossible to do a correct laboratory-scale demonstration of the planetary atmospheric greenhouse effect.

Answer 2

Maybe the cover stopped some of the sunlight.

Answer 3

What kind of cover was it?  I assume it was transparent.  Even so, it might have blocked some of the infrared radiation from the lamp.

My main guess is that since water takes longer to heat than air, the water vapor contributed to the slower heating rate.  But I'm also guessing it wasn't that big an effect.  How much longer did it take the one to heat up?