In December 2022, the United Nations General Assembly formally adopted a resolution to establish March 21st as World Glacier Day, starting in 2025.

Although we're still a year away from celebrating glaciers' special day, a recent study in Science Advances brings these icy giants back into focus: 40% of Antarctic ice shelves have significantly reduced in size over the last 25 years, demonstrating the substantial impact of human activities on polar environments.

Notably, 48 glaciers lost more than 30% of their mass, releasing 7.5 trillion tons of meltwater into the ocean. This meltwater could have a domino effect by influencing ocean circulation patterns.

How do we know glaciers' "weight"?

How do scientists gauge the changing area, thickness, and mass of glaciers?

Glacier area: This can be calculated by drawing a glacier distribution map, placing a grid over it, and counting the squares. Today, drones and satellite imagery can capture glacier boundaries, and computers can calculate the area.

Glacier thickness: This can be measured directly at a cross-section or by drilling. For steep cross-sections, a rope or measuring device can be used to determine the vertical height of the glacier. Drilling is more complex, as the borehole must be vertical and reach the glacier's base.

Specialized instruments like gravimeters and ground-penetrating radar can also provide thickness information. For example, scientists used a gravimeter in 1968 to measure the thickness of two cross-sections of Rongbuk Glacier at the foot of Mount Everest. In 2009, ground-penetrating radar was used to map the entire thickness of East Rongbuk Glacier.

The distribution of GPR thickness measurement lines (black lines L1-L8) on the East Rongbuk Glacier of Mount Everest, the distribution of glacier trough cross-sections (red lines C1-C5), the main flow line of the glacier (blue line), and the glacier terminus near C1, where GPR wave velocity measurements were carried out at P1 and P2. [1]

Radar measurements of wave velocity at sites P1 and P2 show a clear ice-bedrock interface. The bright spots correspond to a velocity of 0.13 meters per nanosecond, which is the average wave velocity between the glacier surface and the ice-bedrock interface. Multiplying this velocity by a time of 400 nanoseconds gives an ice thickness of approximately 52 meters at both sites P1 and P2. [1]

Ice Thickness Measurement Using Radar

These radar images of the East Rongbuk Glacier's L1-L8 sections clearly display ice thickness and subglacial topography.

Calculating Glacier Thickness and Volume

Multiple measurements of ice thickness enable the use of computer models to determine the glacier's average and maximum thickness. The more data points and the more evenly distributed they are, the more accurate the results.

For instance, ice thickness measurements indicate that the East Rongbuk Glacier has an average thickness of approximately 190 meters and a maximum thickness of around 320 meters.

Glacier volume can be calculated using the glacier's area and average thickness. Multiplying this volume by the glacier's average density provides an estimate of its weight. Comparing data from different periods can reveal changes in glacier weight.

Impact of Glacial Meltwater Influx into the Ocean

Glaciers store vast amounts of terrestrial freshwater. A rapid influx of this freshwater into the ocean can significantly reduce seawater salinity, disrupting the delicate balance and influencing ocean currents.

Ocean currents can be generated by various factors, including prevailing winds such as trade winds and westerlies. As ocean water moves, some areas experience an influx of water while others experience a reduction. Water flows from areas of high concentration to areas of low concentration, creating compensatory currents.

Density differences can also drive ocean currents. For example, the differing densities of seawater on either side of the Strait of Gibraltar lead to a surface current flowing from the Atlantic into the Mediterranean and a subsurface current flowing in the opposite direction.

The Impacts of Freshwater Flow into the Sea on Ocean Currents and Climate

Ocean Currents and Heat Exchange Ocean currents transport warm or cold water to different parts of the ocean, facilitating heat exchange. The Gulf Stream, for instance, brings warm water to Western Europe, resulting in mild, humid winters with average temperatures above freezing, despite its high latitude.

Disruption of Ocean Currents by Freshwater Influx When seawater density is reduced by freshwater melting, established ocean currents can be disrupted. This has significant implications for regional climate and ecosystems. During the Quaternary period, melting glaciers in North America altered the composition of seawater and disrupted the Gulf Stream, plunging Western Europe into a frigid, arid environment.

Can We Prevent Freshwater from Entering the Sea? Given the profound effects of freshwater inflow on ocean currents, climate, and vegetation, one may wonder if humans can prevent it. The answer is no. Glacial volumes are immense; just 48 Antarctic glaciers contributed 7.5 trillion tons of meltwater to the ocean over 25 years. Blocking such a colossal inflow is currently beyond human capabilities.

Harnessing Glacial Meltwater Some argue that glacial meltwater, being freshwater, could be utilized to address water scarcity. While the concept is promising, its implementation is fraught with challenges. Antarctica's remoteness necessitates massive containers and transportation systems, making it prohibitively expensive.

Addressing the Root Cause: Climate Change The fundamental driver of glacial melting is global warming, caused by greenhouse gas emissions. To halt this process, we must mitigate carbon emissions.

Global Carbon Reduction Efforts Many countries have set net-zero carbon targets, aiming to balance emissions and removals by 2060. This requires a concerted effort to increase renewable energy and energy efficiency, reduce fossil fuel use, and enhance carbon sequestration.

Reforestation Planting trees increases carbon absorption. By stabilizing emissions, we can slow the pace of global warming and potentially curb glacial retreat.