Greenhouse pedantry?

In a recent issue of the American Geophysical Union’s house journal Eos is a letter that nicely illustrates the importance with which scientists view the use of technical language, and the implications of using incorrect terms that propagate into the public domain.

Responding to an opinion piece by Tucson-based physicist Xubin Zeng on the effect of the atmosphere on the Earth’s surface temperature, the Israeli agricultural scientist Gerry Stanhill objects to what he describes as Zeng’s inaccurate and misleading use of the terms “greenhouse effect” and “greenhouse gases”. The problem here is that Zeng’s focus is on the effect of solar radiation on heat exchange through the atmosphere, whereas the greenhouse effect has to do with heat transfer through a process of convection. The distinction is rather important.

Perhaps I should point out that Stanhill is famous for being the originator of the term “global dimming”, which describes an observed 4% reduction in solar radiation during the latter part of the 20th century. Global dimming is likely to have been due to the presence in the atmosphere of sulphate aerosols of industrial origin. The level of this pollution began to reduce from around 1990, and this coincided with a reversal in the dimming trend. What is particularly interesting about global dimming is that it should have a cooling effect. If it did, however, any cooling was swamped by warming due to “greenhouse gases” such as carbon dioxide.

But that’s by the bye. When it comes to global warming, Stanhill objects to the use of the greenhouse analogy on the grounds that, in physical terms, the greenhouse effect describes something quite different from the radiative heat exchange that is of special interest to scientists studying global climate change.

According to Stanhill…

“The importance of convective rather than radiative heat exchange in controlling the air temperature of a greenhouse can be demonstrated by opening its doors and side vents during a hot summer day; air temperature will drop rapidly due to enhanced convective exchange although the radiative exchange characteristics have not changed.”

In response, Zeng agrees with Stanhill that the terms “greenhouse effect” and “greenhouse gases” are inaccurate. But how in practical terms should we describe the processes involved? Zeng’s “more moderate suggestion” is to drop the related and confusing phrase “greenhouse effect of clouds”. That is certainly a start, but it may not be enough to satisfy everyone.

Further reading

Zubin Zeng, “What is the atmosphere’s effect on the Earth’s surface temperature?”, Eos 91(15), 134 (2010)

Gerald Stanhill, “Comment on ‘What is the atmosphere’s effect on the Earth’s surface temperature?'”, Eos 91(46), 431 (2010)