16:8And the fourth angel poured out his bowl upon the sun; and it was given to it to scorch men with fire.

And the FOURTH ANGEL poured out his BOWL upon the SUN;

This is most often interpreted literally. The symbolic interpretation is that "the SUN" is a great leader (probably military) who directs a scorched earth campaign. A parallel to Joseph's dream in Genesis 37:1-11 is used to explain this position. What is difficult to understand with this symbolic view is why this great leader would want to torture/destroy his own constituents (verse 2)?

The literal interpretation, on the other hand, is not without its difficulties too. Unlike the fourth trumpet, where the darkening of the sun, moon, and stars probably is an earth generated event, this bowl requires an increase in the SUN's energy output. Now the earth only receives about one two billionth of the sun's total energy output. It is believed that the energy is derived from the conversion of mass following the Einstein's energy = mass (converted) times the speed of light squared formula. Estimates are that about 4 million tons of solar matter per second are turned into energy. But this implies that the mass and thus energy output of the sun is slowly decreasing (not increasing as this bowl indicates).

Thus, something in the fourth bowl causes an increase in the SUN's energy which is directed toward the earth. It is well known that solar flares generate immense heat but the flare usually lasts a half hour or less. So this bowl event must be a sustained set of flares with the possibility of holes in the earth's ozone layer augmenting the heating effect.a

An update: recent understanding in astrophysics indicates this is a type of nova (recurrent macronova, most likelyb). There is the increase of heat without the total destruction of earth. That does not say there will not be major impact on modern infrastructure and control electronics.

and it was given to it to SCORCH MEN with FIRE.

Numerous scholars believe the following Old Testament prophesies are fulfilled with the pouring of this bowl:

The use of fire to convince is not new in the Revelation. The false prophet confirmed the beast by "making fire come down out of heaven" (Revelation 13:13). In contrast, the tribulation saints are specifically protected from the heat of the SUN (Revelation 7:16).

Economic impact: The SUN is the light source for the whole earth. If MEN are scorched this severely, a person can assume that plants will wither quickly and a world-wide famine will set in. Furthermore, the polar ice caps will melt rapidly into the sea (blood- verse 3). Since it is assumed that blood doesn't evaporate as quickly as water, the so called "greenhouse effect" probably won't come into play. Any clouds which do form would be burned away.

aASTRONOMY, Franklyn M. Branley, Mark R. Chartrand III, and Helmut K. Wimmer, Thomas Y. Crowell Publishing, p. 108-113, 278
bWeatherman's Guide to the Sun, Third Edition, Davidson, Ben, Chapter 8,p. 240-241