Some world leaders, especially in developing countries like India, have long said it’s hard to reduce the emissions that are warming the planet because they need to use relatively inexpensive — but highly carbon-intensive — fuels like coal to keep energy affordable. That argument is losing its salience as the cost of renewable energy sources like wind and solar continues to fall.

Last year, for the first time, renewables accounted for a majority of new electricity-generating capacity added around the world, according to a recent United Nations report. More than half the $286 billion invested in wind, solar and other renewables occurred in emerging markets like China, India and Brazil — also for the first time. Excluding large hydroelectric plants, 10.3 percent of all electricity generated globally in 2015 came from renewables, roughly double the amount in 2007, according to the report.

The average global cost of generating electricity from solar panels fell 61 percent between 2009 and 2015 and 14 percent for land-based wind turbines. In sunny parts of the world like India and Dubai, developers of solar farms have recently offered to sell electricity for less than half the global average price. In November, the accounting firm KPMG predicted that by 2020 solar energy in India could be 10 percent cheaper than electricity generated by burning coal.

These are all hopeful signs. They suggest that reductions in carbon emissions can be achieved more quickly and more cheaply than widely believed. And they provide hope that nations will be able to achieve the ambitious goals they set for themselves at last December’s climate summit meeting in Paris — to keep warming below the threshold beyond which the world will be locked into a future of devastating consequences, including rising sea levels, severe droughts and flooding, widespread food and water shortages and more destructive storms.