4th paragraph
The 4th paragraph is wrong. 

The black body temperature of the Earth is 5.5 °C.[4] Since the Earth reflects about 28% of incoming sunlight[5], in the absence of the greenhouse effect the planet's mean temperature would be far lower - about -18 or -19 °C [6][7] instead of the much higher current mean temperature, about 14 °C.

The black body temperature of the Earth is -18 or -19 °C, not 5.5 °C (which is the temperature of an ideal blackbody the same distance from the Sun as the Earth). It was correct before it was changed on Dec 9,2009. Also, reference [4] does not support that statement. I suggest the following as a possible replacement paragraph and even as a possible first paragraph since it actually defines what Greenhouse Effect really refers to.

If an ideal thermally conductive blackbody was the same distance from the Sun as the Earth, it would have an expected blackbody temperature of 5.3 °C. However, since the Earth reflects about 30%NASA Earth Fact Sheet (or 28%Introduction to Atmospheric Chemistry, by Daniel J. Jacob, Princeton University Press, 1999. Chapter 7, "The Greenhouse Effect".) of the incoming sunlight, the planet's actual blackbody temperature is about -18 or -19 °C Solar Radiation and the Earth's Energy BalanceIntergovernmental Panel on Climate Change Fourth Assessment Report. Chapter 1: Historical overview of climate change science page 97, about 33°C below the actual surface temperature of about 14 °C or 15 °C.The elusive "absolute surface air temperature," see GISS discussion The mechanism that produces this difference between the actual temperature and the blackbody temperature is due to the atmosphere and is known as the Greenhouse Effect.

Note that I also modified the expected temperature and albedo based on NASA data. If the values in the current paragraph are used in Stephan's equation, 5.5°C with no reflection is associated with -16.5°C with 28% reflection and -18°C with 30%.