(ShareCast News) - The "very challenging" outlook for the price of copper and other metals and the resulting heightened volatility in Glencore´s earnings requires a more cautious approach by investors towards the company´s debt and financial leverage, Standard&Poor´s said.As a result, the ratings agency lowered its rating on the commodity trader´s long-term debt from BBB to BBB-.However, S&P kept a 'stable' outlook on the firm´s debt rating, as its free cash flow generation and strong liquidity meant downside risks should be limited.As of 13:22GMT shares in Glencore were trading up by 5.58% 90.75p.-- More to follow --