In the simplest description of the greenhouse effect, incident solar
radiation passes through transparent glass windows and heats the floor
inside a greenhouse. The warmed floor emits infrared radiation, which
cannot pass out of the greenhouse because the glass windows are opaque
to infrared. The infrared is therefore reflected back to the floor,
where the temperature increases because the infrared cannot be radiated
away.

But in 1909, Prof. R. W. Wood, an experimental physicist at Johns
Hopkins University, reported that the greenhouse effect had no
measurable influence on the temperature inside a glass greenhouse. (R.

In the simplest description of the greenhouse effect, incident solar
radiation passes through transparent glass windows and heats the floor
inside a greenhouse. The warmed floor emits infrared radiation, which
cannot pass out of the greenhouse because the glass windows are opaque
to infrared. The infrared is therefore reflected back to the floor, where the
temperature increases because the infrared cannot be radiated away.

But in 1909, Prof. R. W. Wood, an experimental physicist at Johns
Hopkins University, reported that the greenhouse effect had no
measurable influence on the temperature inside a glass greenhouse. (R.
W. Wood, "Note on the Theory of the Greenhouse," Philosophical
Magazine, 1909, vol. 17, pp. 319-320.) Prof. Wood built two identical
greenhouse models made of black cardboard enclosures that were covered
with cotton for insulation and fitted with thermometers. A glass window
was placed on top of one enclosure, and a window made of rock salt,
which is transparent to infrared radiation, was placed on top of the
other.

When the models were allowed to heat up in the sun, their temperatures
rose gradually to about 65 C, but the model with the rock salt window
was consistently warmer than the one with the glass window, because the
glass window prevented solar infrared from entering the model. To
ensure that identical radiation entered the two models, Prof. Wood
placed an additional glass window above both model greenhouses. The two
models then performed almost identically, rising in temperature to
about 55 C.

Prof. Wood concluded that when the floor of a greenhouse is warmed by
sunlight, convection currents carry heat away from the floor and mix
with the cooler air inside the greenhouse.

While Prof. Wood was satisfied that no warming greenhouse effect had
been detected, he may have overlooked the fact that he had detected an
opposing, cooling greenhouse effect. At the beginning of the
experiment, the model with the rock salt window was consistently warmer
than the model with the glass window, because glass is just as opaque
to incident solar IR as it is to IR radiated by a greenhouse floor. It
is difficult to imagine why this possibility seems never to be
considered.

In summary, when there is a warming greenhouse effect inside a glass
greenhouse, there must also be a cooling greenhouse effect on the
outside. In Prof. Wood's experiment, the cooling effect was the only
one actually detected, and the result was a greenhouse that was cooled
rather than warmed.

The implications for the idea that the greenhouse effect warms the
Earth's atmosphere seem obvious. A greenhouse gas that is opaque to IR
radiated from the Earth's surface must also be opaque to the IR
component of sunlight. What is the net effect?

Gene Ledbetter / ledbettergene at yahoo dot com

The implications for the idea that the greenhouse effect warms the
Earth's atmosphere seem obvious. A greenhouse gas that is opaque to IR
radiated from the Earth's surface must also be opaque to the IR
component of sunlight. What is the net effect?

In the simplest description of the greenhouse effect, incident solar
radiation passes through transparent glass windows and heats the floor
inside a greenhouse. The warmed floor emits infrared radiation, which
cannot pass out of the greenhouse because the glass windows are opaque
to infrared. The infrared is therefore reflected back to the floor,
where the temperature increases because the infrared cannot be radiated
away.

But in 1909, Prof. R. W. Wood, an experimental physicist at Johns
Hopkins University, reported that the greenhouse effect had no
measurable influence on the temperature inside a glass greenhouse. (R.
W. Wood, "Note on the Theory of the Greenhouse," Philosophical
Magazine, 1909, vol. 17, pp. 319-320.) Prof. Wood built two identical
greenhouse models made of black cardboard enclosures that were covered
with cotton for insulation and fitted with thermometers. A glass window
was placed on top of one enclosure, and a window made of rock salt,
which is transparent to infrared radiation, was placed on top of the
other.

When the models were allowed to heat up in the sun, their temperatures
rose gradually to about 65 C, but the model with the rock salt window
was consistently warmer than the one with the glass window, because the
glass window prevented solar infrared from entering the model. To
ensure that identical radiation entered the two models, Prof. Wood
placed an additional glass window above both model greenhouses. The two
models then performed almost identically, rising in temperature to
about 55 C.

Prof. Wood concluded that when the floor of a greenhouse is warmed by
sunlight, convection currents carry heat away from the floor and mix
with the cooler air inside the greenhouse.

While Prof. Wood was satisfied that no warming greenhouse effect had
been detected, he may have overlooked the fact that he had detected an
opposing, cooling greenhouse effect. At the beginning of the
experiment, the model with the rock salt window was consistently warmer
than the model with the glass window, because glass is just as opaque
to incident solar IR as it is to IR radiated by a greenhouse floor. It
is difficult to imagine why this possibility seems never to be
considered.

In summary, when there is a warming greenhouse effect inside a glass
greenhouse, there must also be a cooling greenhouse effect on the
outside. In Prof. Wood's experiment, the cooling effect was the only
one actually detected, and the result was a greenhouse that was cooled
rather than warmed.

The implications for the idea that the greenhouse effect warms the
Earth's atmosphere seem obvious. A greenhouse gas that is opaque to IR
radiated from the Earth's surface must also be opaque to the IR
component of sunlight. What is the net effect?

Gene Ledbetter / ledbettergene at yahoo dot com