http://science.howstuffworks.com/nature/climate-weather/atmospheric/question566.htm
BTW, there are plenty of trees all over the world yet it isn't by chance the the hammock originated in countries with hot humid nights.
Try this : the next windy day , lay down on the ground for 5 minutes or so then lay across two chairs for the same time .
Is it colder on the ground or 2 feet up ?
(if you have an anemometer with wind chill display, measure the temperature at ground level and 2 feet up)

Again if a hammock is more comfortable for you the difference in tot weight or cost or whatever is irrelevant.