claim: Because oxygen in the global ocean is not evenly distributed, the 2 percent overall decline means there is a much larger decline in some areas of the ocean than others.
evidence: Ozone depletion consists of two related events observed since the late 1970s : a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere ( the ozone layer ), and a much larger springtime decrease in stratospheric ozone around Earth's polar regions.