"Cities are major contributors to climate change," con-suming 78% of the world's energy and producing more than 60% of global greenhouse gas emissions, explains a United Nations website about cities, pollution, and climate change solutions. A key factor in this metropolitan problem is that most of the electricity that powers cities is still generated by burning fossil fuels: Only about 29% of the world's electricity currently comes from renewable sources, such as wind and solar, the U.N. notes. But "cleaner sources of energy are gaining ground," and the cost of renewable energy technologies "also keeps falling, making renewables the most affordable source of power today," the U.N. states.
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