What: Shares of Freeport-McMoRan (FCX -2.21%) jumped more than 16% by 2:45 p.m. EST on Thursday. Driving today's buying was a rise in the price of copper, which rose almost 2% to $2.13 per pound. Copper is now up 9.8% since mid-January and is at its highest point in 2016.

So what: Copper is moving higher today as a result of a positive economic growth forecast out of China and a weaker dollar, which makes copper appear cheaper and drives both investment and commercial demand for the metal. That said, the more important driver of the copper price is China. It had some good economic news after the head of its economic planning agency said that the country's economic growth target remains in a range between 6.5% and 7%. That's great news for copper producers like Freeport-McMoRan and Teck Resources (TECK -1.38%), because that country accounts for 45% of global copper demand.  

Strong demand from China should lead to continued strength in the copper price, which is important for both companies. That's because every $0.10 per pound change in the price of copper over the course of a year impact's Teck Resources  EBITDA by $80 million while a similar change in the copper price would have $500 million change on Freeport-McMoRan's EBITDA. That's why Freeport-McMoRan and Teck Resources tend to move when the price of copper moving.

Now what: Despite the strength in the copper price over the past few weeks, it's still at levels not seen since 2009. That's putting a lot of pressure on the cash flow of copper producers, especially Freeport-McMoRan given its out-sized leverage to copper. Needless to say, it will really benefit if the price of copper continues to rebound.