Carbon dioxide, the gas largely blamed for global warming, has reached record-high levels in the atmosphere after growing at an accelerated pace in the past year, say scientists monitoring the sky from this 2-mile-high station atop a Hawaiian volcano. Carbon dioxide, mostly from burning of coal, gasoline and other fossil fuels, traps heat that otherwise would radiate into space. A leading climatologist, Ralph Keeling, whose father, Charles D. Keeling, developed methods for measuring carbon dioxide, noted that the rate “does fluctuate up and down a bit,” and said it was too early to reach conclusions. But he added: “People are worried about ‘feedbacks.’ We are moving into a warmer world.” He explained that warming itself releases carbon dioxide from the ocean and soil. By raising the gas’s level in the atmosphere, that in turn could increase warming, in a “positive feedback,” said Keeling, of San Diego’s Scripps Institution of Oceanography.