ZANDI SHABALALA and HELEN REID Glencore boss Ivan Glasenberg is to step down next year and Gary Nagle, head of coal assets at the mining and trading group, will become the new CEO. Ivan Glasenberg Glasenberg's departure will mark a shift to a new, younger leadership for the business, which, along with other mining companies, has faced increasing pressure from investors to cut carbon emissions. Glasenberg, 63, has been chief executive since 2002 and investors have been expecting a succession plan after several senior members of management retired in the last few years. He said his goal during his 18-year…