"Atmospheric concentrations" refers to the amount or level of certain substances present in the air around us. It indicates the concentration or abundance of various gases, pollutants, or particles in the Earth's atmosphere. Full definition
Scientific predictions of the impacts of increasing atmospheric concentrations of greenhouse gases from fossil fuels and deforestation match observed changes. (aaas.org)
However, the rise in atmospheric concentration of CO2 driving the modern warming is NOT coming from the oceans, but from the human burning of fossil fuels. (skepticalscience.com)
Both of these trends are consistent with the influence of increasing atmospheric concentrations of greenhouse gases. (en.wikipedia.org)