The president said his advisers would devise new tariff levels reflecting countries’ tariffs, taxes, subsidies and other policies affecting trade with the United States.

Amid warnings of price increases, Canada moved quickly to retaliate, China said it had planned countermeasures and Mexico said it would soon unveil its response.

C.E.O.s, policymakers and billionaires at the World Economic Forum’s conference have long pledged to fight climate change. Has it done any good?