Editing Greenhouse effect (section)

== Misconceptions ==
[[File:Earth's Overall Heat Flow.svg|thumb|upright=1.35|Earth's overall heat flow. Heat (net energy) ''always flows from warmer to cooler'', honoring the [[second law of thermodynamics]].<ref name="2ndlawviol" /> (This heat flow diagram is equivalent to NASA's [[:File:The-NASA-Earth's-Energy-Budget-Poster-Radiant-Energy-System-satellite-infrared-radiation-fluxes.jpg|earth energy budget]] diagram. Data is from 2009.)]]

There are sometimes misunderstandings about how the greenhouse effect functions and raises temperatures.

The ''surface budget fallacy'' is a common error in thinking.<ref name="PierrehumbertTextbook" />{{rp|413}} It involves thinking that an increased {{CO2}} concentration could only cause warming by increasing the downward thermal radiation to the surface, as a result of making the atmosphere a better emitter. If the atmosphere near the surface is already nearly opaque to thermal radiation, this would mean that increasing {{CO2}} could not lead to higher temperatures. However, it is a mistake to focus on the surface energy budget rather than the top-of-atmosphere energy budget. Regardless of what happens at the surface, increasing the concentration of {{CO2}} tends to reduce the thermal radiation reaching space (OLR), leading to a TOA energy imbalance that leads to warming. Earlier researchers like [[Guy Stewart Callendar|Callendar]] (1938) and [[Gilbert Plass|Plass]] (1959) focused on the surface budget, but the work of [[Syukuro Manabe|Manabe]] in the 1960s clarified the importance of the top-of-atmosphere energy budget.<ref name="PierrehumbertTextbook">{{cite book |last1=Pierrehumbert |first1=Raymond T. |title=Principles of Planetary Climate |date=2010 |publisher=Cambridge University Press |isbn=978-0-521-86556-2}}</ref>{{rp|414}}

Among those who do not believe in the greenhouse effect, there is a fallacy that the greenhouse effect involves greenhouse gases sending heat from the cool atmosphere to the planet's warm surface, in violation of the [[second law of thermodynamics]].<ref name="2ndlawviol">{{cite web |title=Global Warming Violates the Second Law of Thermodynamics: Brief Responses to Climate Change Denialism Statements |url=https://www.geol.umd.edu/sgc/elevator/elevator34.html |publisher=University of Maryland |access-date=13 June 2023}}</ref><ref name="Halpern2010">{{cite journal |last1=Halpern |first1=J. B. |last2=Close |first2=C. M. |last3=Ho-Stuart |first3=C. |last4=Shore |first4=J. D. |last5=Smith |first5=A. P. |last6=Zimmermann |first6=J. |title=Comment on "falsification of the Atmospheric CO2 Greenhouse Effects Within the Frame of Physics" |journal=International Journal of Modern Physics B |date=2010 |volume=24 |issue=10 |pages=1309–1332 |doi=10.1142/S021797921005555X}}</ref> However, this idea reflects a misunderstanding. Radiation heat flow is the ''net energy flow'' after the flows of radiation in both directions have been taken into account.<ref name="Modest2021">{{cite book |last1=Modest |first1=Michael F. |title=Radiative Heat Transfer |date=2021 |publisher=Academic Press |isbn=978-0323984065 |edition=4}}</ref> Radiation heat flow occurs in the direction from the surface to the atmosphere and space,<ref name="budget" /> as is to be [[Second law of thermodynamics|expected]] given that the surface is warmer than the atmosphere and space. While greenhouse gases emit thermal radiation downward to the surface, this is part of the normal process of [[Heat transfer#Radiation|radiation heat transfer]].<ref name="Siegel1971">{{cite web |last1=Siegel |first1=R. |last2=Howell |first2=J. R. |title=Thermal Radiation Heat Transfer |url=https://ntrs.nasa.gov/api/citations/19710021465/downloads/19710021465.pdf |publisher=NASA |access-date=28 May 2023 |date=1971}}</ref> The downward thermal radiation simply reduces the upward thermal radiation net energy flow (radiation heat flow), i.e., it reduces cooling.<ref name="uaATMO336eeb">{{cite web |title=The Earth's Energy Budget II -- Radiation Emitted by the Earth, the Greenhouse Effect, and the Overall Energy Balance |url=http://www.atmo.arizona.edu/students/courselinks/spring17/atmo336s2/lectures/sec3/energybudget2.html |publisher=University of Arizona, Hydrology & Atmospheric Sciences |access-date=28 May 2023 |date=2017}}</ref>