Some of the hottest weather on record is lifting natural-gas prices, reversing last month’s plunge and reviving a key driver of inflation. Natural-gas futures have jumped 48% this month—including 10% on Wednesday—to $8.007 per million British thermal units. That is still more than $1 off the 14-year high hit just before a Texas natural-gas export facility caught fire in early June and sent prices tumbling along with the outlook for exports. Yet the power-plant and manufacturing fuel has bounced back to more than twice the price of a year ago, adding cost pressure across the economy.