What did Jonas learn about the sun?

The Giver wanted to show Jonas how the same thing can cause both pleasure and pain, "Before Sameness. Before Climate Control." He gives Jonas the memory of warmth and pleasure from the sun.

It was not as exciting as the ride through the snowy air; but it was pleasurable and comforting.

Then the Giver shares a memory that involved sunburn,

He opened his eyes, wincing with discomfort. "It hurt," he told the man, "and I couldn't get the word for it."

"It was sunburn," the old man told him.