Tag: Ice sheets

Satellites Reveal: Greenland and Antarctica Lost Over 11 Trillion Tons of Ice Since the 1970s — 84% Driven by Speeding Glaciers

Satellites show Earth lost more than 12 trillion tons of ice from Greenland and Antarctica over ~47 years (roughly 1979- 2023), according to a major study published in Scientific Data.

SMB models refer to Surface Mass Balance models (or, more precisely, the surface mass balance components derived from regional climate models).

A digital illustration showing glaciers and icebergs in Greenland and Antarctica, accompanied by text highlighting significant ice loss revealed by satellites since the 1970s.
AI generated by Grok

Satellites show Earth lost more than 12 trillion tons of ice from Greenland and Antarctica over ~47 years (roughly 1979- 2023), according to a major study published in Scientific Data.

Key findings from the international collaboration (led in part by the European Space Agency’s IMBIE initiative, incorporating NASA satellite data for a longer record):

Total ice loss: about 12.5 trillion tons (11.3 trillion metric tons). This is enough to cover the continental United States with ice roughly 5 feet (1.5 meters) deep.

Sea- level contribution: This melt alone raised global sea levels by about 1 inch (≈3.1 cm) since 1979 (on top of other factors). Greenland accounts for a somewhat larger share.

Main driver: ~5/6 (about 84%) of the loss comes from dynamic processes, warmer ocean water undercutting and melting ice sheets from below/sides, accelerating glacier flow into the ocean, rather than surface melting from warmer air.

Acceleration: Ice sheets were relatively stable in the 1970s-1990s; losses ramped up later, especially in the 2010s. A temporary slowdown around 2020- 2023 (partly due to heavy snowfall in East Antarctica offsetting West Antarctic losses) was viewed as short- term variability; the longer- term accelerating trend has resumed.

Methods: Combined data from dozens of independent surveys and 27 satellites (including earlier Landsat archives) for the longest continuous satellite- based mass- balance record of the two ice sheets.

Scientists involved (including Ines Otosaka of Northumbria University and Eric Rignot of UC Irvine) emphasize that the dynamical ice discharge raises concerns about potential tipping points or instability, particularly in parts of Antarctica, with implications for continued sea- level rise and coastal flooding risk even if warming stabilizes. Independent experts noted the multi- method approach increases confidence in the upward trend.

The article is an Associated Press report by Seth Borenstein (dated around mid- to- late September 2026 in various outlets).

This extends earlier satellite records (previously focused more on the 1990s onward) and aligns with the broader observed pattern of accelerating polar ice loss linked to climate change.

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SMB models refer to Surface Mass Balance models (or, more precisely, the surface mass balance components derived from regional climate models).

In the context of the Greenland and Antarctic ice- sheet mass- balance study we discussed:

What is Surface Mass Balance (SMB)?

SMB is the net gain or loss of mass at the surface of an ice sheet. It is calculated as:

SMB=snowfall accumulation−(meltwater runoff+sublimation+evaporation+blowing-snow erosion)\text{SMB} = \text{snowfall accumulation} – (\text{meltwater runoff} + \text{sublimation} + \text{evaporation} + \text{blowing-snow erosion})

Positive SMB means the ice sheet is gaining mass at the surface (mainly from snowfall). Negative SMB means net surface loss (mainly from melting and runoff).

Role of SMB models in the study

The paper uses regional climate models (RCMs) to estimate SMB. These models simulate the atmosphere– ice- sheet interactions at relatively high spatial resolution over the polar regions. Common examples used in ice- sheet research include:

  • MAR (Modèle Atmosphérique Régional)
  • RACMO (Regional Atmospheric Climate Model)
  • HIRHAM
  • Other similar atmospheric models forced by global reanalyses (e.g., ERA5) or climate models

These models provide the time- varying SMB fields that are combined with satellite observations in the input- output method (also called the mass- budget method):

  • Ice discharge (how much ice flows into the ocean) is measured from satellites (velocity + ice thickness).
  • SMB is taken from the regional climate models.
  • Mass balance = SMB − ice discharge (plus any basal melt terms where relevant).

Key finding from the paper related to SMB

Of the total 11,309 ± 565 Gt of ice lost from Greenland and Antarctica (1979- 2023):

  • 84% came from ice dynamical imbalance (accelerated glacier flow and discharge into the ocean, largely driven by warmer ocean water).
  • 16% came from reduced SMB (mainly increased surface melting and runoff, especially in Greenland).

In Greenland, the split was roughly 67% dynamics / 33% SMB. In Antarctica, nearly all the loss was dynamical; SMB changes were smaller or even positive in some periods due to increased snowfall.

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Mass balance of the Greenland and Antarctic ice sheets from the 1970s to 2023

The Greenland and Antarctic ice sheets are major contributors to global mean sea- level rise and the largest source of uncertainty in future projections. This data descriptor compares and combines 42 independent estimates of ice- sheet mass balance derived from satellite observations of changes in ice flow, volume, and gravitational attraction.

It covers:

  • Greenland Ice Sheet (GrIS): 1972- 2023
  • Antarctic Ice Sheet (AIS) and its sectors (West Antarctica/WAIS, East Antarctica/EAIS, Antarctic Peninsula/APIS): 1979- 2023

Regional climate models are used to partition total mass balance into surface mass balance (SMB) and ice dynamical imbalance.

Key result: The ice sheets lost 11,309 ± 565 billion tonnes (Gt) of ice between 1979 and 2023. Glacier dynamical imbalance drove 84% of the loss; reduced surface mass balance accounted for the remaining 16%. The dataset supports tracking ice-sheet contributions to sea- level rise and constraining future projections.

Main quantitative findings

  • Combined (1979- 2023): 11,309 ± 565 Gt lost → 31.4 ± 1.6 mm global sea- level rise.
  • Antarctica (1979- 2023): 4,780 ± 513 Gt lost → 13.3 ± 1.4 mm sea- level rise. Essentially all of Antarctica’s losses were driven by ice dynamics.
  • Greenland (1972- 2023): 6,215 ± 467 Gt lost (average rate 119 ± 9 Gt yr⁻¹). ~67% from increased ice discharge, ~33% from reduced SMB. Greenland was near balance in the 1970s; losses rose from ~60 Gt yr⁻¹ in the 1980s to much higher rates later (e.g., hundreds of Gt yr⁻¹ in the 2010s). nature.com

Losses accelerated from the 1990s onward. A temporary slowdown in overall loss rates around 2020- 2023 (linked to high snowfall in East Antarctica and milder Greenland summers) is described as short- term variability rather than a change in the long- term trend.

Methods overview

Techniques: Input- output method (ice discharge and SMB models), satellite altimetry (volume change), and satellite gravimetry (mass change from gravity).

Satellites: Data from 27 missions, including early Landsat archives for velocity back to the 1970s.

Standardization: Individual estimates converted to monthly rates of mass change; reconciled into consensus time series with uncertainties. Peripheral glaciers/ice caps are accounted for where relevant.

Only mass changes that contribute to sea level are included (ice- shelf thinning/retreat and grounded ice below sea level are excluded from the sea-level contribution figures).

Data availability

Reconciled mass- balance time series (rates and cumulative anomalies for total mass, SMB, and dynamics, with uncertainties) are freely available at:


https://doi.org/10.5285/128c5e33-5224-4197-82f0-19dcc95b80a0

Code for aggregation is also openly available.

This extends previous IMBIE assessments (which focused more on the post- 1992 period) and provides the longest continuous satellite- based consensus record of the two ice sheets. The paper is open access.

Published:  Scientific Data volume 13, Article number: 1301 (2026)

DOI: 10.1038/s41597-026-08088-0

Authors: Lead authors include Inès N. Otosaka, Andrew Shepherd, and a large international team (IMBIE – Ice Sheet Mass Balance Inter-comparison Exercise).

Abstract

The Greenland and Antarctic ice sheets are major drivers of global mean sea level rise and are predicted to continue to do so in the future. However, they also represent the largest source of uncertainty in projections of future sea level rise making robust estimates of observed ice sheet mass changes critical. Here, we compare and combine 42 independent estimates of ice sheet mass balance derived from satellite observations of temporal changes in ice sheet flow, volume, and gravitational attraction to determine the ice sheet mass balance from 1972 (Greenland) and 1979 (Antarctica) until 2023. We then use regional climate models to partition the total mass balance into contributions associated with surface mass balance and ice dynamical imbalance. The ice sheets lost 11,309 ± 565 billion tonnes of ice between 1979 and 2023, with glacier dynamical imbalance driving 84% of the ice loss and surface mass balance the remainder. This dataset can be used to track the contribution of the ice sheets to sea level rise and constrain projections of future sea level rise.

Heat transfer and meltwater flows in ice sheets

This post challenges the conventional framework for simulating meltwater flows on glaciers and ice sheets.

TOPSHOT – Meltwater flows from the Greenland ice sheet into the Baffin Bay near Pituffik, Greenland on July 17, 2022 as captured from the ground during a NASA mission along with University of texas scientists to measure melting Arctic sea ice. – New observations from ICESAT-2 show remarkable Arctic Sea ice thinning in just three years. Over the past two decades, the Arctic has lost about one-third of its winter sea ice volume, largely due to a decline in sea ice that persists over several years, called multiyear ice, according to a new study. The study also found sea ice is likely thinner than previous estimates. (Photo by Kerem Yücel / AFP) / The erroneous mention appearing in the metadata of this photo by Kerem Yücel has been modified in AFP systems in the following manner: [as captured from the ground] instead of [during an airborne mission]. Please immediately remove the erroneous mention from all your online services and delete it from your servers. If you have been authorized by AFP to distribute it to third parties, please ensure that the same actions are carried out by them. Failure to promptly comply with these instructions will entail liability on your part for any continued or post notification usage. Therefore we thank you very much for all your attention and prompt action. We are sorry for the inconvenience this notification may cause and remain at your disposal for any further information you may require. (Photo by KEREM YUCEL/AFP via Getty Images)

From Climate Etc.

by Dan Hughes

This post challenges the conventional framework for simulating meltwater flows on glaciers and ice sheets.

Increased melting rates due to potential increases in temperature would add liquid water directly into the oceans. An additional aspect is that the meltwater, on reaching the base of glaciers, might lead to increased sliding of the glaciers and the consequent calving at the terminus.

The World Resources Institute (WRI) has summarized the IPCC AR6 results regarding melting of Greenland and Antarctica ice:

Should warming reach between 2 degrees C (3.6 degrees F) and 3 degrees C (5.4 degrees F), for example, the West Antarctic and Greenland ice sheets could melt almost completely and irreversibly over many thousands of years, causing sea levels to rise by several meters.

Temperature Increase1.5 C (2.7 F)2.0 C (3.6 F)3.0 C (5.4 F)
Global mean sea level rise by 21000.28 – 0.55 m(0.92 – 1.80 ft)0.33 – 0.61 m(1.08 – 2.00 ft)0.44 – 0.76 m(1.44 – 2.40 ft)

Meltwater flows on the surface of and with glaciers and other ice sheets are important relative to the addition of liquid water into Earth’s oceans, and to bulk motions of the glaciers and ice sheets. Glacial meltwater might flow along the surface like a stream or river, accumulate in surface lakes, flow downward into open crevasses or moulins, accumulate as lakes interior to the ice mass, flow as a sheet of liquid between the ice bottom and bedrock, or flow enclosed in channels partially or completely embedded within the ice mass.

Flows that reach the boundary of the ice sheet deplete the ice mass balance and can contribute to sea level rise if the flow reaches the sea.  Meltwater remaining on the surface of the glacier or ice sheet can refreeze and have no impact on the glacier mass balance.  Flows reaching the base of the glaciers by way of crevasse and moulins are considered to provide potential lubrication and flotation that enhances bulk ice motions.

How solid is the foundation for simulating glacial meltwater flows that are included in projections of ice sheet melting?

Glacial meltwater flows have been modeled for more than four decades using thermal-hydraulic modeling.  The widely used Springer-Hutton formulation is based on principles of continuum mechanics, and detailed mathematical reduction to the standard 1-dimensional channel- average form for engineering applications. A steady-state energy balance equation is applied to flow of liquid water in ice channels embedded in large ice masses. The Spring-Hutter system considers the case of evolution in time and space of the flow area of the channel. Changes in flow area are caused by ice melting and dynamics of the ice in which channels are located. There have been numerous studies providing clarifications, modifications and applications of Spring-Sutter framework.

New paper

I have conducted a detailed analysis of the Spring-Sutter equations and their solutions in this paper [EDHmelt]

The paper clarifies and improves calculations of the role of viscous dissipation of kinetic energy into thermal energy as this physical process appears in models of meltwater flows embedded in and at the boundaries of glaciers and ice sheets.

Meltwater flows on the surface of and within glaciers and other ice sheets are important relative to the addition of liquid water into Earth’s oceans, and to bulk motions of the glaciers and ice sheets. Glacial meltwater might flow along the surface like a stream or river, accumulate in surface lakes, flow downward into open crevasses or moulins, accumulate as lakes interior to the ice mass, flow as a sheet of liquid between the ice bottom and bedrock, or flow enclosed in channels partially or completely embedded within the ice mass.

Flows that reach the boundary of the ice sheet deplete the ice mass balance and can contribute to sea level rise if the flow reaches the sea.  Meltwater remaining on the surface of the glacier or ice sheet can refreeze and have no impact on the glacier mass balance.  Flows reaching the base of the glaciers by way of crevasse and moulins are considered to provide potential lubrication and flotation that enhances bulk ice motions.

A dimensionless form for steady-state energy balance for the liquid, accounting for effects of meltwater on the bulk liquid, is developed and solved. Analytical solutions of the temperature distribution along the channel are developed. The solutions explicitly illustrate effects of viscous dissipation of kinetic energy into heat, and the consequence effects on melting ice at the liquid-ice interface.

The paper shows that:

  • Letting viscous dissipation of kinetic energy go directly into melting is not correct
  • The energy equations are not complete because they do not account for meltwater entering the bulk liquid
  • The Spring-Hutter accounting for meltwater entering the bulk liquid is not correct.

The Sahara Desert used to be a green savannah – new research explains why

Algeria’s Tassili N’Ajjer plateau is Africa’s largest national park. Among its vast sandstone formations is perhaps the world’s largest art museum. Over 15,000 etchings and paintings are exhibited there, some as much as 11,000 years old according to scientific dating techniques, representing a unique ethnological and climatological record of the region.

The-‘Eye-of-Sahara-by-ESA-3

 From The Conversation

By Edward Armstrong

Algeria’s Tassili N’Ajjer plateau is Africa’s largest national park. Among its vast sandstone formations is perhaps the world’s largest art museum. Over 15,000 etchings and paintings are exhibited there, some as much as 11,000 years old according to scientific dating techniques, representing a unique ethnological and climatological record of the region.

Curiously, however, these images do not depict the arid, barren landscape that is present in the Tassili N’Ajjer today. Instead, they portray a vibrant savannah inhabited by elephants, giraffes, rhinos and hippos. This rock art is an important record of the past environmental conditions that prevailed in the Sahara, the world’s largest hot desert.

These images depict a period approximately 6,000-11,000 years ago called the Green Sahara or North African Humid Period. There is widespread climatological evidence that during this period the Sahara supported wooded savannah ecosystems and numerous rivers and lakes in what are now Libya, Niger, Chad and Mali.

This greening of the Sahara didn’t happen once. Using marine and lake sediments, scientists have identified over 230 of these greenings occurring about every 21,000 years over the past eight million years. These greening events provided vegetated corridors which influenced species’ distribution and evolution, including the out-of-Africa migrations of ancient humans.

These dramatic greenings would have required a large-scale reorganisation of the atmospheric system to bring rains to this hyper arid region. But most climate models haven’t been able to simulate how dramatic these events were.

As a team of climate modellers and anthropologists, we have overcome this obstacle. We developed a climate model that more accurately simulates atmospheric circulation over the Sahara and the impacts of vegetation on rainfall.

We identified why north Africa greened approximately every 21,000 years over the past eight million years. It was caused by changes in the Earth’s orbital precession – the slight wobbling of the planet while rotating. This moves the Northern Hemisphere closer to the sun during the summer months.

Africa’s vegetation cycles. Author provided (no reuse)

This caused warmer summers in the Northern Hemisphere, and warmer air is able to hold more moisture. This intensified the strength of the West African Monsoon system and shifted the African rainbelt northwards. This increased Saharan rainfall, resulting in the spread of savannah and wooded grassland across the desert from the tropics to the Mediterranean, providing a vast habitat for plants and animals.

Our results demonstrate the sensitivity of the Sahara Desert to changes in past climate. They explain how this sensitivity affects rainfall across north Africa. This is important for understanding the implications of present-day climate change (driven by human activities). Warmer temperatures in the future may also enhance monsoon strength, with both local and global impacts.

Earth’s changing orbit

The fact that the wetter periods in north Africa have recurred every 21,000 years or so is a big clue about what causes them: variations in Earth’s orbit. Due to gravitational influences from the moon and other planets in our solar system, the orbit of the Earth around the sun is not constant. It has cyclic variations on multi-thousand year timescales. These orbital cycles are termed Milankovitch cycles; they influence the amount of energy the Earth receives from the sun.

On 100,000-year cycles, the shape of Earth’s orbit (or eccentricity) shifts between circular and oval, and on 41,000 year cycles the tilt of Earth’s axis varies (termed obliquity). Eccentricity and obliquity cycles are responsible for driving the ice ages of the past 2.4 million years.

The third Milankovitch cycle is precession. This concerns Earth’s wobble on its axis, which varies on a 21,000 year timescale. The similarity between the precession cycle and the timing of the humid periods indicates that precession is their dominant driver. Precession influences seasonal contrasts, increasing them in one hemisphere and reducing them in another. During warmer Northern Hemisphere summers, a consequent increase in north African summer rainfall would have initiated a humid phase, resulting in the spread of vegetation across the region.

Eccentricity and the ice sheets

In our study we also identified that the humid periods did not occur during the ice ages, when large glacial ice sheets covered much of the polar regions. This is because these vast ice sheets cooled the atmosphere. The cooling countered the influence of precession and suppressed the expansion of the African monsoon system.

The ice ages are driven by the eccentricity cycle, which determines how circular Earth’s orbit is around the sun. So our findings show that eccentricity indirectly influences the magnitude of the humid periods via its influence on the ice sheets. This highlights, for the first time, a major connection between these distant high latitude and tropical regions.

The Sahara acts as a gate. It controls the dispersal of species between north and sub-Saharan Africa, and in and out of the continent. The gate was open when the Sahara was green and closed when deserts prevailed. Our results reveal the sensitivity of this gate to Earth’s orbit around the sun. They also show that high latitude ice sheets may have restricted the dispersal of species during the glacial periods of the last 800,000 years.

The Sahara desert. Getty Images

Our ability to model the African humid periods helps us understand the alternation of humid and arid phases. This had major consequences for the dispersal and evolution of species, including humans, within and out of Africa. Furthermore, it provides a tool for understanding future greening in response to climate change and its environmental impact.

Refined models may, in the future, be able to identify how climate warming will influence rainfall and vegetation in the Sahara region, and the wider implications for society.