Final answer:
Glaciers worldwide have faced a negative mass balance since the 1960s, mainly due to global warming, leading to a significant reduction in size and number, with notable impacts on local ecosystems and a contribution to rising sea levels.
Step-by-step explanation:
Since the 1960s, glaciers worldwide have experienced a negative mass balance, indicating a general trend of mass loss over several decades. This is largely due to global warming, which causes glaciers to melt more rapidly than they accumulate new snow and ice. Glacier National Park, once home to around 150 glaciers in 1850, saw a dramatic reduction to approximately 24 glaciers by 2010. The Grinnell Glacier, for example, has shrunk by 40 percent between 1966 and 2005. The retreat of glaciers not only impacts local ecosystems by reducing summer meltwaters but also contributes to the rising of global sea levels, currently averaging 1.8 mm per year.