U.S. Steel Corp. /zigman2/quotes/200069642/composite X +3.78% said Wednesday it plans to reduce greenhouse-gas-emissions intensity across its global footprint by 20% by 2030. The reduction will be measured by the rate of carbon-dioxide equivalents emitted per ton of finished steel shipped, based on 2018 baseline levels. The steel sector is facing significant financial losses from future climate regulation, with the top 20 steel manufacturers at risk of a potential loss of 14% of their value by 2040, according to a report earlier this year from CDP, a sustainable-investing advocate. Existing steel-production techniques are already close to the limits of their efficiency, so meeting the goals of the Paris climate agreement, from which President Donald Trump is withdrawing the U.S., will require a radical change by the industry, the CDP alleges after analyzing the 20 top companies, worth a combined $259 billion. U.S. Steel shares fell about 2% in Wednesday trading; they're down 26.4% in 2019 to date. The S&P 500 /zigman2/quotes/210599714/realtime SPX +0.36% is up 23% in 2019.