Copper prices jumped more than 5.5 percent to a four-week high on Wednesday on a wave of short-covering after global central banks' surprise intervention to provide needed liquidity to the financial system. In the United States, benchmark December copper futures finished up 5.54 percent at $3.563 per lb, their highest level since November 2. Soon-to-be-benchmark March copper ended up 5.5 percent at $3.5755 a lb.