How do you measure ice loss in Antarctica?

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by Emil Morhardt

In a new paper about accelerated ice loss in Antarctica, Rignot et al. (2019) list the three ways: 1. the component method in which whatever data on ice and snow amounts are available at the finest resolution possible, from the smallest areas studied areas (as little as 100 meters, ranging up to 1km) are collected then added up for as many years as they are available, and the trend plotted; 2. The altimetry method which, I presume, uses satellite altimetry to figure out how much ice and snow are present based on the height above ground and sea is measured…this has a spatial resolution of 1-10km; and 3.  The gravity method (probably using the Grace satellite pairs to measure gravity changes over time owing to ice loss. The latter method can resolve centimeter-level losses but at a low resolution of 333 km. The latter two methods are relatively easy…just process satellite data…or maybe not so easy but relatively so. The component method is labor intensive, but better at pinpointing areas of loss which facilitates trying to understand what is causing the loss. Rignot used the component method.

Their results, reported widely in the news media, should be chilling.  The climate-change enhanced westerly winds in the southern hemisphere are evidently pushing relatively warm circumpolar deep water (CDW) up against the edges of the ice sheets over much of the continent and increasing their melting and calving of icebergs at much higher rates than in previous decades. The loss of ice not only increases sea level faster than anyone had thought, it allows glaciers to flow into the sea faster as well, speeding the whole process.

Not that this comes as too much of a surprise to those of us who have been following global warming, but considering the exacerbated coastal flooding that is becoming commonplace, it might be good to point out to the climate change deniers inhabiting the higher levels of our government.

Rignot et al. 2019, http://www.pnas.org/cgi/doi/10.1073/pnas.1812883116

Rising Seas

by Owen Dubeck

Coral Davenport summarizes the effects of rising sea levels across Kiribati, Greenland, Panama, Fiji and the United States. Kiribati, a chain of islands northwest of Australia, will see some of the worst consequences. Given the island’s low elevation, it could be completely underwater by 2100. Fortunately, the government has urgently responded, buying over 6,000 acres of land in Fiji. This land can function both as a source of crops and possibly a new home. Continue reading

Past Polar Ice-Sheet Mass Loss Contributes to Sea-Level Rise

by Grace Stewart

Understanding of global mean sea level during past interglacial periods has greatly improved, but many challenges remain. By using coastal records and oxygen-18 proxy data, Dutton et al. (2015) determined global mean sea level and the contribution from polar ice sheets during three past interglacial periods. Although the results were uncertain, it was determined that global mean sea level was higher than modern day levels in every interglacial period studied—the mid-Pliocene warm period 3,000,000 years ago, the marine isotope stage (MIS) 11 400,000 years ago, and MIS 5e 125,000 years ago. Previous findings were corrected by taking glacial isostatic adjustment (the adjustment of the earth for a long time after a period of deglaciation), dynamic topography, and ice sheet reconstructions into account. Continue reading

Protecting Island Biodiversity

by Alexander Birk

Island biodiversity is of paramount importance on a global scale. The islands of the world contain twenty percent of all terrestrial plant and animal species. In addition the rate of endemic species on islands is much greater than on main lands, and island species are facing many threats. Over half of the most recent extinctions on the planet come from species inhabiting islands. In addition one third of all terrestrial species that are currently threatened with extinction are island-dwelling species (Couchamp et al. 2014). Continue reading