UK scientists are warning that a staggering loss” of 28 trillion tonnes of Earth’s ice could see sea level rise reach a metre by the end of the century, triggered by melting glaciers and ice sheets.

Photo: Mer De Glace, Chamonix, France

The level of ice loss revealed in their new analysis matches the worst-case-scenario predictions outlined by the Intergovernmental Panel on Climate Change (IPCC).

The research has been undertaken by scientists at the Centre for Polar Observation and Modelling, School of Earth and Environment, University of Leeds, the School of GeoSciences, University of Edinburgh and the Mullard Space Science Laboratory, Department of Space & Climate Physics, University College London.

The researchers combined satellite observations and numerical models to show that Earth lost 28 trillion tonnes of ice between 1994 and 2017.

Arctic sea ice (7.6 trillion tonnes), Antarctic ice shelves (6.5 trillion tonnes), mountain glaciers (6.2 trillion tonnes), the Greenland ice sheet (3.8 trillion tonnes), the Antarctic ice sheet (2.5 trillion tonnes), and Southern Ocean sea ice (0.9 trillion tonnes) have all decreased in mass.

Just over half (60 %) of the ice loss was from the northern hemisphere, and the remainder (40 %) was from the southern hemisphere. The rate of ice loss has risen by 57 % since the 1990s – from 0.8 to 1.2 trillion tonnes per year – owing to increased losses from mountain glaciers, Antarctica, Greenland, and from Antarctic ice shelves.

During the same period, the loss of grounded ice from the Antarctic and Greenland ice sheets and mountain glaciers raised the global sea level by 35.0 ± 3.2 mm.

There are over 215 thousand glaciers worldwide containing 160 thousand km3 of ice - their retreat has accounted for 21 % of global sea-level rise between 1993 and 2017.

The majority of all ice losses from were driven by atmospheric melting (68 % from Arctic sea ice, mountain glaciers ice shelf calving and ice sheet surface mass balance), with the remaining losses (32 % from ice sheet discharge and ice shelf thinning) being driven by oceanic melting.

Altogether, ice losses from Antarctica and Greenland have caused global sea levels to rise by 17.8 ± 1.8 mm between 1992 and 2017.

The paper - Earth’s ice imbalance - published in The Cryosphere Discussions says there is now “widespread evidence that climate change has caused reductions in Earth’s ice.”

On average, the planetary surface temperature has risen by 0.85 °C since 1880 and this signal has been amplified in the polar regions.

Although this warming has led to higher snowfall in winter, it has also driven larger increases in summertime surface melting. The global oceans have also warmed with significant impacts on

tidewater glaciers, on floating ice shelves and on the ice streams which have relied on their buttressing . Atmospheric warming – anthropogenic or otherwise – is responsible for the recent and long-term reductions in mountain glacier ice, while ocean-driven melting of outlet glaciers has caused the vast majority of the observed ice losses from Antarctica.

The overall rate of ice loss has increased by 49 % over the past 24 years compared to the 1990s - in situ measurements of changes in glacier mass and satellite records of ice shelf which pre-date the complete survey confirm this trend.

The scientists conclude:

“Even though Earth’s cryosphere has absorbed only a small fraction of the global energy imbalance, it has lost a staggering 28 trillion tonnes of ice between 1994 and 2017.

“Although a small fraction of mountain glacier losses are associated with retreat since the little ice age, there can be little doubt that the vast majority of Earth’s ice loss is a direct consequence of climate warming.”

Click here to read the research paper Earth’s ice imbalance in full

Slater, T., Lawrence, I. R., Otosaka, I. N., Shepherd, A., Gourmelen, N., Jakob, L., Tepes, P., and Gilbert, L.: Review Article: Earth's ice imbalance, The Cryosphere Discussions - in review, 2020.