(CNN)Almost a quarter of the West Antarctic ice sheet is now affected by ice thinning, according to a new study.
It found that the ice sheet has thinned by as much as 122 meters in some places, and thinning has left glaciers unstable, according to scientists at the University of Leeds in England.
Affected glaciers are unstable because melting and calving (the breaking off of ice chunks) is reducing their mass faster than it can be replenished by snowfall, and thinning has spread across 24% of West Antarctica since 1992.
The largest ice streams in the region -- the Pine Island and Thwaites glaciers -- are losing ice five times faster than they were when the measurements began.
A team of researchers from the UK Centre for Polar Observation and Modelling (CPOM), which is based at the university, used 25 years of satellite observations and climate models to track the evolution of snow and ice cover in the area.
The measurements distinguish between short-term changes due to weather patterns and long-term trends.
"In parts of Antarctica the ice sheet has thinned by extraordinary amounts, and so we set out to show how much was due to changes in climate and how much was due to weather," said Andy Shepherd, lead study author and CPOM Director.
And ice losses are driving up sea levels around the globe, Shepherd added.
"Altogether, ice losses from East and West Antarctica have contributed 4.6mm to global sea level rise since 1992," he said.