Reacción a "Antarctica loses 12,800 km² of coastline over 30 years"

The study, published in Proceedings of the National Academy of Sciences (PNAS) and based on more than 30 years of satellite synthetic aperture radar (SAR) observations, highlights a marked retreat of Antarctica’s grounding line and a consequent reduction in the area of the floating ice shelves fringing parts of the Antarctic coastline. The grounding line is the point at which the ice sheet loses contact with the bedrock and begins to float, at which stage it is referred to as an ice shelf. The significance of the study lies in the fact that ice shelves, being laterally confined by the sides of large embayments of the Antarctic continent, tend to buttress the flow of ice from the continent’s interior. Consequently, if the grounding line retreats and the area of the ice shelves diminishes, the rate at which the Antarctic ice sheet discharges ice into the ocean in the form of icebergs increases.

These findings are consistent with a wide range of evidence showing that the so-called Amundsen Sea sector of Antarctica, together with the Antarctic Peninsula, are the two Antarctic regions that have lost the greatest mass in recent decades as a result of submarine melting and the acceleration of solid ice discharge into the ocean. The release of continental ice into the ocean contributes to sea-level rise. Recent estimates place sea-level rise at around 4 mm per year, but the rate has been increasing for almost a century and is expected to continue to do so in the coming decades. Accordingly, projections by the Intergovernmental Panel on Climate Change (IPCC) for sea-level rise by the end of the twenty-first century range from 40 to 80 cm under low greenhouse gas emission scenarios to between 60 cm and 1 metre under high-emission scenarios. Only about half of this rise is attributed to the loss of mass from glaciers and ice sheets; the other half is due to the thermal expansion of the oceans (as seawater warms, it expands).

Despite this, satellite gravimetry data over the past three years indicate that increased snowfall has led to net mass gains for Antarctica as a whole during that period, notwithstanding substantial regional losses in certain areas. This is not incompatible with climate warming; indeed, warming leads to greater evaporation over tropical oceans, which in turn results in increased snowfall in the polar regions.

In summary, this is a thorough and significant study. The use of SAR data acquired from different satellite platforms over a 33-year period means that sensor resolution has varied (and improved) over time, but the lower precision of the earlier data has been duly taken into account in the error estimates.

There are also certain sources of uncertainty for which insufficient data were available for full assessment, but conservative error bounds have been assigned in such cases. The study’s results are therefore entirely credible within the stated margins of error.