Negative values of b may in fact be statistically significant for sufficient temporal degrees of freedom. (deepclimate.org)
It often takes years to build up these credentials on your own, meaning you'll probably be operating with negative value until you cross a certain threshold of experience. (audiencebloom.com)
Positive values indicate that the region is a source and negative values indicate that the region is a sink for the given gas. (climate.copernicus.eu)