GREEN BAY, Wis. — In its most recent assessment released this fall, the Intergovernmental Panel on Climate Change said that warming of the Earth’s climate system is both unequivocal and unprecedented, a conclusion that rests on multiple and independent sources of data. The authoritative IPCC study also found that it was “extremely likely” that human influence, particularly our reliance on fossil fuels, has been the dominant cause of climate change. At the same time, international meetings — such as the Climate Change Conference just concluded in Warsaw, Poland — struggle to devise broadly acceptable agreements to reduce greenhouse gas emissions that pose grave risks to the world’s economy, its environment and public health and well-being.