Despite the inclination to don fewer layers in the summer some, such as the neckerchief, are proven to combat the oppressive heat. Like much of traditional menswear, this isn't a new accessory or approach, just one that's stylish and makes sense. That should satisfy both the dandy and the pragmatist.
This one, in green with a faint white windowpane was an old scarf of my mother's. The green gives the white shirt a necessary lift as well as compliments the high blue of the blazer.
A small scarf or triangle piece of fabric loosely tied around the neck serves to absorb sweat as well as protect the neck from the sun's rays. That's the practical end. The less pragmatic point is that it looks pretty damn good. The open shirt gets tiring, yet a tie is too much of a commitment during heat waves. Enter the neckerchief. It adds the visual interest where a tie would go, with a less formal feel, but still dressed.
Imagery of the legendary Cary Grant in To Catch A Thief, has been used over and again to emphasize this stylish choice. So, in a momentary dearth of creativity, here's the photo again.
The colors are complimentary, enough for you and a retired cat burglar. The idea is pretty simple though. The scarf may be wrapped, knotted or just kind of arranged around the neck. There are no bonus points for intricate knots, just a sense of relaxed confidence.
I know, I know, despite it's practicality, this may be a more daring choice for some men. I still encourage it. As with any sartorial step, make it once and see how it goes.