The ten warmest years of the 20th century have occurred since 1980 . . the snow cover in the northern hemisphere and floating ice in the arctic ocean have decreased. globally, sea level has risen 4-10 inches.
—environmental protection agency

to what do scientists believe the types of changes noted in the quotation are most closely related? a. decreasing water quality b. increasing concentrations of greenhouse gases c. depletion of soil nutrients d. failure to recycle metals, glass, and paper