The more CO2 we emit from burning coal and oil and gas, the more we heat our climate — this sounds simple, and it is. Different analyzes have come up with different estimates of how much CO2 humankind can still emit if we want to hold global warming to the internationally agreed 1.5 and well below 2 degrees Celsius limits, but a lack of clarity of the reasons causing these variations has created unnecessary confusion, a new study shows.