Phones and other devices seem the least of our power worries — but that cloud could burst. The electricity demands of global information and communications technology now generate only about 2 percent of the world’s carbon emissions. But with digital demand growing exponentially, that could increase to 20 percent in little over a decade. That includes the proliferation of power-hungry, cavernous data centers and cryptocurrencies’ seemingly endless demand for computing capacity. While technology is also becoming more power-thrifty, experts doubt the efficiency curve can stay ahead of humankind’s voracious data appetite.