the idea that human activities will cause global warming is well over a century old now. the united nations has been sponsoring studies of this idea for almost two decades. the assembled scientists have concluded, with high confidence, that: group of answer choices co2 levels in the atmosphere have been rising, warming the planet a small fraction of a degree, and if we burn all the remaining fossil fuels, we may raise the temperature another small fraction of a degree. co2 levels in the atmosp