I read this book in the mid-nineties, probably written in the 80s or 90s. It’s set in the near future, where the world has experienced a sudden glaciation. Most of the United States and Europe is now covered with ice. Civilization has collapsed for the most part.
The protagonist is a drifter with strange-colored eyes (yellow, I think). Because of his weird eyes, he’s never really fit in anywhere. He moves from place to place just trying to survive, but somehow he discovers that the new ice-age did not occur naturally. It was engineered by extraterrestrials, to make their work easier. They’re looking for the plans for a super-weapon - a weapon that can cause any star to go nova. A rival group of aliens hid the plans for this weapon by encoding the information in the human genome millions of years ago. The marker to identify humans who carry this gene is - you guessed it - yellow-colored eyes.