Greenhouse Effect: Does Water Vapor Increase or Decrease the Lapse Rate?

April 9, 2014

(PRINCIPIA SCIENTIFIC) – At first glance this simple question appears to be lifted from a first year, undergraduate class in meteorology, because everyone who has even a rudimentary understanding of the thermodynamics of the atmosphere knows that water vapor decreases the lapse rate, i.e., the rate at which the air temperature changes with altitude—ascending air cools at a certain rate as it “does work” against its progressively less dense surroundings and descending air warms at a certain rate as its progressively more dense surroundings “does work” on it.

Written by Carl Brehmer

images-1As countless weather balloon soundings have shown water vapor decreases this lapse rate and it has even been observed that this attenuation becomes more acute as both the temperature and the humidity increase.  One wonders then why the country’s most prestigious universities in classes across the hall are teaching their students that water vapor increases the lapse rate via a hypothetical “greenhouse effect”.


“The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere. As a result, the temperature there is higher than it would be if direct heating by solar radiation were the only warming mechanism.”

University of California, Riverside

“What is the greenhouse effect?  “This refers to the retention of the sun’s warmth in the Earth’s lower atmosphere by greenhouse gases. These gases (primarily carbon dioxide, methane and nitrous oxide) act as a thermal blanket for the planet, warming the surface to a life-supporting average of 59 degrees Fahrenheit (15 degrees Celcius).”

Texas A&M University

“55% of the heat that warms the atmosphere is quickly re-radiated radiated back to the earth (324 W/m2). This warms the earth and the lower atmosphere.”

Columbia University 

“Some of the emitted radiation [from the surface] passes through the atmosphere and travels back to space, but some is absorbed by greenhouse gas molecules and then re-emitted in all directions. The effect of this is to warm the Earth’s surface and the lower atmosphere. Water vapor (H2O) and carbon dioxide (CO2) are the two largest contributors to the greenhouse effect.”

Boston University 

“We have demonstrated how the ‘natural’ greenhouse effect (e.g. H2O, natural CO2) elevated surface temperature.  Next time we will extend this simple model to show how the addition of greenhouse gases increases surface temperature.”  

Now, you might be saying, “What are you talking about?  None of these definitions mentions a ‘lapse rate’,” but notice that each one of these definitions of the “greenhouse effect” hypothesis asserts that “greenhouse gases” only warm the “surface and the lower atmosphere.”  Not one of them asserts that “greenhouse gases” warm the entire troposphere or the upper troposphere.  Doing so, of course, would be foolish since the upper troposphere in the mid-latitudes is commonly as cold as -60 °C and can be as cold as -80 °C!  By default then, when one asserts that there exists a thermodynamic process within the atmosphere that only warms the lower troposphere and not the upper troposphere one is asserting that that process increases the lapse rate—the temperature differential between lower tropospheric air and upper tropospheric air that is quantified in °C/km.  Indeed, it has even been suggested by some that if there were no “greenhouse gases” in the atmosphere there wouldn’t even be a lapse rate.

            “Without the destabilization provided by the greenhouse effect, convective overturning would slow and quite possible cease altogether. The atmosphere would eventually become isothermal, as the full depth of the atmosphere would achieve the same temperature as the surface through thermal conduction; without IR emission, the middle and upper troposphere would have no way to cool itself in the face of this heating.” Roy Spencer.

For complete article go to Principia Scientific.