Science: when global warming slows down the rotation of the Earth

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Global warming projects us towards an ever darker future and manifests itself in sometimes very surprising ways. Some of its impacts are now very well documented and the scientific consensus is well established regarding them. Disruptions in precipitation patterns, rising sea levels, impacts on food security, threats to natural ecosystems and melting of glaciers and ice caps. It is precisely this last point which has consequences that we did not yet suspect.

A recent study published in Natureon March 27, reveals that the melting of polar ice, by redistributing the Earth's mass, leads to a slowdown in its rotation. This might seem anecdotal, but in reality, we calculate the time that passes in relation to this same rotation, which could lead us to re-evaluate the very concept of time.

A global gravitational phenomenon

For Duncan Agnew, geophysicist at the Institute of ;oceanography Scripps and co-author of the study, the phenomenon is of unprecedented magnitude: “ < em>This is yet another new impact of climate change that has never been observed before “.

As it melts, huge quantities of water migrate from the poles towards the equator; these quantities are so large that the distribution of the earth's mass is completely disrupted. The speed of rotation of the Earth as well as its gravity are also affected by the phenomenon.

An easy example to understand how this phenomenon acts is that of a figure skater. Imagine her spinning around, her arms tightly around her head. Now imagine that she gradually kisses her arms while extending them outwards: naturally her rotation slows down. In physics, this phenomenon is called conservation of angular momentum. A property which is the basis of the functioning of the gyroscope (see video below).

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For Kylie Kinne, oceanographic physicist and specialist in the effects of ice caps on water circulation in fjords, this discovery is astonishing: “ It’s amazing how multi-faceted the melting ice is […] We continue to discover new ways that [ice melt] changes the climate and the planet, this study is proof “.

The implications for measuring time

This redistribution of land mass could potentially force us to adjust our time measurement system, Coordinated Universal Time (UTC ). Traditionally, a leap second is added to UTC in order to compensate for the slowing of the Earth's rotation and maintain alignment of civil time with mean solar time.

However, with this new phenomenon, this method of temporal adjustment could become insufficient. According to Agnew's estimates, these changes could lead to the need to eliminate a leap second by 2028 or 2029 to more accurately reflect the length of the Earth's day.

Actually, we might need to subtract a second rather than add it if we want to stay synchronized with astronomical time; this would be a first in the history of UTC, since its introduction in January 1960. An unprecedented event in the history of modern chronometry and further proof that the consequences of the change climate are multidimensional.

Over the last 50 years, our days have therefore become slightly shorter, d&amp ;#8217;approximately 0.0025 seconds. Jerry X. Mitrovica, a geophysicist at Harvard University, commented on this study: “Despite our perceptions as humans, Earth is not a perfect clock.” An assertion which perfectly illustrates to what extent the measurement of time is a complex, unpredictable affair and closely linked to the rotational variabilities of our planet.

Climate change, in addition to disrupt physically our planet and the life that is established there, also affects our relationship to time, intangible concept by excellence. The phenomenon described by the study therefore goes beyond the ecological and social consequences. While we took the measurement of time for granted, it turns out that it really wasn't. Perhaps humanity will have to, for the time it has left, redefine its relationship to time more regularlythan before.

• A study published on March 29 in Nature proved that the melting of the ice redistributed the general mass of the Earth.
• A phenomenon which modifies the speed of rotation of the planet as well as its gravity.
• This discovery could one day lead us to redefine the way we calculate time, which is based on planetary rotation.

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