Germans go to the polls on Sunday for federal elections, in which the economy has dominated campaigning.<br /> <br />But global warming will be a key policy challenge for whoever wins.<br /> <br />Germany has already agreed to cut at least 20 percent of its carbon dioxide emissions by the year 2020.<br /> <br />That will leave some difficult decisions on how to fulfill its future energy needs. <br />Al Jazeera's Barnaby Phillips reports.
