Science

The massive melting of the ice changes the axis of rotation of the Earth

One of the main consequences of climate change is the massive melting of sea ice and glaciers in the oceans. Beyond the gradual loss of land for different fauna and the gradual increase in sea level, this global melting causes an even deeper effect. Indeed, geophysicists have recently shown that these displacements of several hundreds of billions of tons of water per year have modified the axis of rotation of the planet for more than 30 years, causing a drift of the poles.

The massive melting of glaciers as a result of global warming has caused marked changes in the Earth’s axis of rotation since the 1990s. This demonstrates the profound impact humans have on the planet, according to a new study published in the journal Geophysical Research Letters. The planet’s geographic North and South poles are the points of intersection between the Earth’s axis of rotation and its surface, but they are not fixed. Changes in the distribution of land mass around the planet cause the axis to shift, and therefore the poles.

Melting ice: it causes the drift of geographic poles

In the past, only natural factors such as ocean currents and the convection of hot rocks in the depths of the Earth contributed to the drift position of the geographic poles. But new research shows that since the 1990s, the loss of hundreds of billions of tonnes of ice per year in the oceans as a result of the climate crisis has caused the poles to shift in new directions.

Graphs showing the drift of different polar components due to water displacements. The drift is measured in mas (milliseconds of arc). © S. Deng et al. 2021

Geophysicists discovered that the direction of the polar drift had shifted from south to east in 1995 and that the average drift speed from 1995 to 2020 was 17 times faster than from 1981 to 1995. Since 1980, the pole position shifted about 4 meters. ” The accelerated decline of the water stored on Earth resulting from the melting ice is the main driver of the rapid polar drift after the 1990s Concluded the team, led by Shanshan Deng, of the Institute of Geographic Sciences and Natural Resources of the Chinese Academy of Sciences.

Gravity data from the Grace satellite, launched in 2002, had been used to relate glacier melt to pole movements in 2005 and 2012, both as a result of increased ice loss. But Deng’s research breaks new ground by extending the link before the satellite’s launch, showing that human activities have shifted the poles since the 1990s, nearly three decades ago.

Massive water movements: a consequence of human activities

Research has shown that glacial loss accounted for most of the change, but it is likely that groundwater pumping also contributed to the movements. Groundwater is stored underground but, once pumped for consumption or agriculture, most of it eventually flows to the sea, redistributing its weight across the world. Over the past 50 years, humanity has removed 18 trillion tonnes of water from deep underground reservoirs without being replaced.

polar drift tipping point
Graphs showing the tipping point from which the polar components began to significantly drift (early 1990s). © S. Deng et al. 2021

Vincent Humphrey, of the University of Zurich (Switzerland), and not involved in the new research, says the study shows how human activities have redistributed huge amounts of water around the planet. ” This tells you the strength of this mass change; it is so important that it can change the axis of the Earth “. However, the movement of the Earth’s axis is not large enough to affect daily life: it could change the length of a day, but only by a few milliseconds.

Some scientists say the magnitude of this impact means that a new geological epoch – the Anthropocene – must be declared. Since the mid-twentieth century, there has been a marked acceleration in carbon dioxide emissions and sea level rise, destruction of wildlife and transformation of land through agriculture, deforestation and land use. development.

Sources: Geophysical Research Letters

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