The Impact of the GRACE Mission on Glaciology and Climate Science

Science and technology have come a long way. We continue to learn more and more about our planet and its complex dynamics each and every day, and much of this new data is attained through cutting-edge tools and Earth monitoring systems.

One of the most revolutionary advances for physical sciences in recent decades is GRACE, (short for Gravity Recovery and Climate Experiment) mission. Launched by NASA and the German Aerospace Center in 2002, GRACE was a satellite mission aimed towards better understanding the mass changes of the planet’s hydrosphere and cryosphere.

Byron D. Tapley and colleagues recently published a review of the GRACE mission in Nature Climate Change. The researchers examined the contributions of GRACE to our current observations and understanding of mass transport of water, whether liquid, solid ice, or vapor in the atmosphere.

Some additions from this mission include observations of terrestrial water cycles, ice sheet melting and glacier retreat, and a first look at groundwater resources from up above. Check out this video below on GRACE and it’s effects by the NASA Jet Propulsion Laboratory.

An Overview of GRACE

Unlike previous single satellite approaches, the GRACE mission utilized two satellites orbiting one behind the other. As they orbit, they shift a miniscule The measurements are produced by tracking of the distance between the satellites, which varies depending on the gravitational attractions as they circle the globe. Measurements are collected after each month and estimates of the mass balance of the Earth’s surface are then composed through changes in its gravity field.

Battery failures resulted in the end of the GRACE mission on October 15, 2017. However the over 15 years of data collected has been monumental in perceiving quantifiable changes on the Earth’s surface.

“For the first time, GRACE enabled the quantification of mass trends and mass fluctuations of terrestrial water storage, continental aquifers, and glaciers and ice sheets, and enlightened our view of large-scale mass redistribution associated with glacial-isostatic adjustment and earthquakes” the authors state. GRACE was able to measure global and regional changes, and also capture both natural variability and anthropogenic influences on the planet’s water storage.

A diagram of satellite separation (Source: NASA Jet Propulsion Laboratory)

Major Contributions to Glaciology and Climate Science

One way in which GRACE was different from previous satellite observations was  that it provided direct measurements of the net mass change of ice sheets and glaciers. The measurements include precipitation, evaporation, runoff, and ice discharge. Without GRACE, satellite altimetry is limited to just surface mass change, and it is also limited by sampling errors and multi-annual trends. GRACE has fewer sampling errors for ice sheet measurements, which are obtained monthly. This makes the data obtained through GRACE relatively more robust.

According to the authors, GRACE was able to reveal a clear signal of ice-mass loss in Greenland and Antarctica after just two years from the launch date. Throughout the lifespan of GRACE, ice-mass loss encompassed the entire ice sheet in Greenland, while in Antarctica the mass lost came mostly from the Amundsen Sea Embayment, which was found to be influenced by ocean conditions. The satellites continued to build more robust mass trends over time, as well as develop higher quality gravity field solutions.

The GRACE mission has also been impactful in providing a robust survey of terrestrial water storage, groundwater and the anthropogenic influences on depletion, and also sea level rise and ocean dynamic changes. It has been able to produce annual zonal mean plots of terrestrial water storage and groundwater variability, which can be representative of such events as floods and droughts. It’s identified hot spots for water loss among some of the world’s major aquifer systems, in which studies confirmed excessive groundwater extraction.

Artist’s concept of GRACE (Source: NASA Jet Propulsion Laboratory)

Scientists continue to produce analyses of global sea levels with data from GRACE, altimetry readings, and Argo floats, which drift on the surface of the oceans to measure temperature and salinity. Respectively, these different tools provide measurements of total sea-level trend, mass inflow, and thermal expansion.The combined use of GRACE and temperature measurements from Argo also produced reliable measurements on ocean heat content. Although Argo floats are unable to measure temperatures 2,000 meters below sea level, other observations are applied for an indirect approach to the oceans’ heat budget.  

As a follow-on to GRACE, NASA recently launched the GRACE-FO mission on May 22, 2018. This mission will continue to monitor the planet’s water storage, and the authors are hopeful that this project will bring us one step closer to achieving a multi-decadal record of mass variability on Earth’s hydrological systems.

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Roundup: Chemistry, Dams and Elevations

Roundup: Meltwater Chemistry, Hydroelectric Dams and Glacier Elevation

 

Diurnal Changes in the Chemistry of Glacier Meltwater

From Chemosphere: “An evaluation of glacial meltwater chemistry is needed under recent dramatic glacier melting when water resources might be significantly impacted. This study investigated trace elements variation in the meltwater stream, and its related aquatic environmental information, at the Laohugou glacier basin (4260 m a.s.l.) at a remote location in northeast Tibetan Plateau… Results showed evident elements spatial difference on the glacier surface meltwater, as most of the elements showed increased concentration at the terminus compared to higher elevations sites… The accelerated diurnal and temporal snow-ice melting (with high runoff level) were correlated to increased elemental concentration, pH, EF (enrichment factor,the minimum factor by which the weight percent of mineral in is greater than the average occurrence of that mineral in the Earth’s crust) and elemental change mode, and thus this work is of great importance for evaluating the impacts of accelerated glacier melting to meltwater chemistry and downstream ecosystem in the northeast Tibetan Plateau.”

Read more about it here.

Accelerated melting affects the chemistry of glacier meltwater streams (Source: Shayon Ghosh/Creative Commons)
Accelerated melting affects the chemistry of glacier meltwater streams (Source: Shayon Ghosh/Creative Commons)

 

Locals Oppose Dam Construction in the North Western Himalayas

From the International Journal of Interdisciplinary and Multidisciplinary Studies: “Since early 1970s dam development projects witnessed severe opposition in India. The remote tribal groups and rural population rejected the idea of large scale displacement, land alienation, economic insecurity and endless suffering that came along with ‘development’ projects… In recent past the construction of hydroelectricity projects has faced severe opposition in the tribal regions in Himachal Pradesh. The locals in Kinnaur are facing numerous socio-economic and environmental consequences of these constructions in fragile Himalayan ecology… More than 30 hydro projects proposed in Lahaul & Spiti are also being challenged by the people in Chenab valley… The paper summarises the ongoing struggle and diverse implications added with climate change in the rural structures.”

Read more about local opposition to these projects here.

Karcham Wangtoo Hydroelectric Plant in Kinnaur (Source: Sumit Mahar/Creative Commons).
Karcham Wangtoo Hydroelectric Plant in Kinnaur (Source: Sumit Mahar/Creative Commons).

 

Uneven Changes in Ice Sheet Elevation in West Antarctica

From Geophysical Research Letters: “We combine measurements acquired by five satellite altimeter missions to obtain an uninterrupted record of ice sheet elevation change over the Amundsen Sea Embayment, West Antarctica, since 1992… Surface lowering has spread slowest (<6 km/yr) along the Pope, Smith, and Kohler (PSK) Glaciers, due to their small extent. Pine Island Glacier (PIG) is characterized by a continuous inland spreading of surface lowering, notably fast at rates of 13 to 15 km/yr along tributaries draining the southeastern lobe, possibly due to basal conditions or tributary geometry… Ice-dynamical imbalance across the sector has therefore been uneven during the satellite record.”

Read more about the changes in ice sheet elevation here.

The calving front of Pine Island Glacier (Source: NASA/Creative Commons).
The calving front of Pine Island Glacier (Source: NASA/Creative Commons).

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Photo Friday: Tibetan Plateau From Space

55 million years ago, a major collision took place between two of the large blocks that form the Earth’s crust. The Indian Plate pushed into the Eurasian Plate, creating what is known as the Tibetan Plateau. The region, also known as the “Third Pole,” spans a million square miles and contains the largest amount of glacier ice outside of the poles. A photograph of the southern Tibetan Plateau taken from space was released June 17th, showing the dramatic topography in false color. The photograph, taken by the Sentinel-2A, was captured near Nepal and Sikkim, a northern state of India, on February 1st. According to the European Space Agency (ESA), “From their vantage point 800 km high, satellites can monitor changes in glacier mass, melting and other effects that climate change has on our planet.” This week, enjoy stunning satellite pictures of the Tibetan Plateau over time.

Tibetan Plateau taken from Sentinel-2A, released June 17, 2016 (Credit: ESA)
Tibetan Plateau taken from Sentinel-2A, released June 17, 2016 (Credit: ESA)

NASA also has taken photographs of the same plate collision from space, showing the snow-capped Himalayas, which are still rising.

Tibetan Plateau Plate T-48 from Space (NASA)
Tibetan Plateau Plate T-48 from Space (NASA)

A true-color image of the Tibetan Plateau, taken in 2003 by NASA’S MODIS Rapid Response Team, shows the region’s lakes as dark patches against the sand-colored mountains.

True-color photograph of Tibetan Plateau lakes (NASA--MODIS)
True-color photograph of Tibetan Plateau lakes (NASA–MODIS)

Prior to the true-color photograph, a spaceborne radar image of the Himalayan Mountains was taken in 1994 in southeast Tibet. Each color is assigned to a different radar frequency that depends of the direction that the radar was transmitted.

Spaceborne Radar image of Southeast Tibet, 1994 (NASA, JPL)
Spaceborne Radar image of Southeast Tibet, 1994 (NASA, JPL)

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Satellite Images Offer Clues to Causes of Glacial Lake Flooding

(from journal article: Field observations for glacial lakes: (a) the rapidly expanding Lake Longbasaba in 2012; (b) an areally increasing glacial lake at the Middle Rongbu Glacier near Mount Qomolangma (Everest) in 2008.)
(from journal article: Field observations for glacial lakes: (a) the rapidly expanding Lake Longbasaba in 2012; (b) an areally increasing glacial lake at the Middle Rongbu Glacier near Mount Qomolangma (Everest) in 2008.)

Satellites are now allowing us to track the behavior of icy glacial lakes on the Himalayan Mountains–in particular the conditions that lead to glacial lake outburst floods (GLOFs), which have become increasingly frequent in the region over the past 20 years.

Researchers from the Institute of Mountain Hazards and Environment and the State Key Laboratory of Cryosphere Sciences in China published a study in PLOS One in December of last year that catalogued data from lakes in the central Himalayas between 1990 to 2010.

The scientists, Drs. Yong Nie, Qiao Liu, and Shiyin Liu, used images from Landsat scientific satellites to count and measure glacial lakes in the region. As the longest running remote sensing project, Landsat has over 40 years of images available across the globe.

(from journal article: Distribution of glacial lakes in the central Himalayas)
(from journal article: Distribution of glacial lakes in the central Himalayas)

GLOFs – floods that occur when a lake dammed by a glacier or glacial moraine is released – are hazardous to communities located at elevations below the burst lake. Flooding and debris flows damage infrastructure, cause property loss, and can take lives, as GlacierHub has reported in prior posts. It is widely believed that rising temperatures due to climate change and reduced albedo of the ice from cryoconite (also known as carbon dust particles) are melting the glaciers at higher rates and causing lake volumes to rise, which in turn increases the risk of GLOF events. But the specific processes that lead to GLOF outbursts are not well understood.

By looking at lakes at four time points (1990, 2000, 2005 and 2010), at different elevations (from 3,500 to 6,100 meters), of different types (pro-glacial and supraglacial), and of varying sizes, the researchers were able to identify which lakes expanded faster and burst more frequently to understand which ones pose the greatest risk of GLOFs.

A GLOF from above in Alaska’s Kennai Peninsula (Travis S./Flickr, some rights reserved)
A GLOF from above in Alaska’s Kennai Peninsula (Travis S./Flickr, some rights reserved)

Overall, it was found that total lake surface area for the 1,314 lakes in the central Himalayas had increased over the 20-year period. Drs. Nie, Liu and Liu found that more lakes on the northern side of the central Himalayan range were expanding rapidly. They also found that pro-glacial lakes (lakes at the terminus of a glacier) grew faster than supraglacial lakes (lakes on the surface of the glacier). Some pro-glacial lakes are connected directly to glaciers while others are not, but those that were connected grew far faster. Additionally, larger pro-glacial lakes were likely to flood sooner than smaller ones and more changes to glacial lakes occurred at the altitudes between 4,500 and 5,600 meters.

The dynamics of alpine glacial lakes are complex, but this study could help communities monitor lakes at high risk of flooding and to create early-warning systems and disaster preparedness plans.

PAPER DOI: 10.1371/journal.pone.0083973.g002

GLOF aftermath in Peru ( Will McElwain/Flickr, some rights reserved)
GLOF aftermath in Peru (Will McElwain/Flickr, some rights reserved)

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