Climate science: Greenland ice sheet to contribute over 270mm to sea-level rise

Nature Climate Change

The overall loss of ice from the Greenland ice sheet — alongside increasing precipitation, ice flow discharge and meltwater runoff — will lead to at least 274 mm in sea-level rise, regardless of future climate warming projections, according to a study published in Nature Climate Change.

The glaciologist team setting up an automatic weather station on the snowy surface above the snow line during the melt season. Credit: The Geological Survey of Denmark and Greenland, GEUS

Greenland’s ice budget deficit emerged after the 1980s when it began losing more ice, due to surface melt runoff and ice flow discharge, than it gained in the accumulation of precipitation. However, despite its importance to future sea-level rise, the ability to accurately predict Greenland’s response to climate change is hindered by the imprecise measurements of land, atmosphere and ocean boundaries in current models.

Professor Jason Box taking ice samples standing on exposed ice below the snow line of the Greenland Ice Sheet in West Greenland during the melt season. Credit: The Geological Survey of Denmark and Greenland, GEUS

Using climate data from 2000 to 2019, Jason Box and colleagues calculated the committed changes in ice-sheet volume and area incurred by Greenland’s ice imbalance. The authors reveal that surface ablation through meltwater runoff was the primary driver of the variability of the Greenland ice sheet mass budget from year to year. 

In the recent (2000–2019) climate, the Greenland ice has built up a disequilibrium which will inevitably correct itself by reducing total mass by at least 3.3 percent in order to regain equilibrium at a new average snow line in a higher alteration. Credit: The Geological Survey of Denmark and Greenland, GEUS

Losses from the ice sheet will already lead to a rise of at least 274 mm in sea level from 5,900 km2 of ice retreat — equivalent to a volume loss of 3.3% — regardless of future climate scenarios.

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The minimum global sea level rise and likely global sea level rise resulting from the committed mass loss from the Greenland Ice Sheet. Credit: The Geological Survey of Denmark and Greenland, GEUS

If the high melt year of 2012 is considered to be indicative of normal in the future, then ice loss and consequent sea-level rises could be committed to 782 mm, which the authors conclude should act as a warning for Greenland’s future, as temperatures rise in the twenty-first century.

North American boreal trees show a decline in the survival of saplings in response to warming or reduced rainfall.

Nature 

Four separate papers exploring how forests and tree species respond to global changes — such as rising temperatures — are published in Nature this week. The studies highlight some of the challenges forests in North America and the Amazon may face in response to climate change.

Temperate deciduous tree with a dendrometer band, of the type used in the study, in the ForestGEO plot at the Smithsonian Conservation Biology Institute in Front Royal, VA.

Credit: Kristina J. Anderson-Teixeira

A study of nine North American boreal tree species, including maples, firs, spruces and pines, shows a decline for all species in the survival of saplings in response to warming or reduced rainfall. In a five-year open-air field experiment, Peter Reich and colleagues found that fir, spruce and pine species abundant in southern boreal forests had the largest reductions in growth and survival due to changes in climate. 

Temperate deciduous tree with a dendrometer band, of the type used in the study, in the ForestGEO plot at the Smithsonian Conservation Biology Institute in Front Royal, VA.Credit: Kristina J. Anderson-Teixeira

However, the species that experienced lower rates of mortality and were more likely to experience growth in response to warming, such as maples, are rarer in southern boreal forests and are unlikely to expand their distribution in this region fast enough to compensate for regeneration failure of the current dominant species.

 An otherwise barren, unnamed valley in the west-central Brooks Range of Alaska, USA, supports a population of boreal white spruce that likely provides the seeds carried many kilometers away by winter wind to germinate in Arctic tundra. Credit: Roman Dial

In another paper, Roman Dial and colleagues describe the northward migration of a North American population of white spruce (Picea glauca) into the Arctic tundra, unoccupied by this species for millennia, at a rate of more than 4 km per decade. The authors found that increasing temperatures together with winter winds, deeper snowpack and increased soil nutrient availability have supported this treeline advance. They argue that increasing Arctic tree cover could lead to a decrease in the habitat available for migratory species and a redistribution of carbon stores.

Two white spruce trees, each probably under 30 years old, overlook a remote tundra valley in northwest Alaska, USA. Recent climate warming, winter winds, and an increasing deep snowpack are facilitating the colonization of Arctic tundra by this boreal species. The trekking pole is one meter long. Credit: Roman Dial

Kristina Anderson-Teixeira and colleagues paired dendrometer band measurements with 207 tree-ring chronologies from 108 forests across temperate deciduous forests of eastern North America. They found that warmer spring temperatures advance the timing of stem growth but have little effect on total annual stem growth. The authors suggest that barring rapid acclimation of these forests to warming conditions, they are unlikely to sequester increasing amounts of carbon as temperatures rise.

In this picture at the Ely site (one of two of the experiment) we see one of the ambient plot in the foreground and some heated plots in the background.  All plants are in the process of fall senescence with slowly developing differentiation in plant senescence between ambient (and the research plots surrounding vegetation) and warmed plots due to the effect warming has on plant phenology.

Finally, Hellen Fernanda Viana Cunha and colleagues show that limitations in the availability of phosphorous directly impact the productivity of the Amazon forest by restricting its responses to CO2 fertilization. This may potentially affect forest resilience to climate change.