Climate Change Is Lengthening Days on Earth – Knowledge

A day is 24 hours long—even if those who are stressed sometimes wish there were more. Now, a team of researchers reports that climate change is having exactly that effect, albeit to a lesser extent: It’s making the days longer. As the researchers write in the journal Proceedings of the National Academy of Sciences (People) The melting of polar ice spreads across the world’s oceans. This causes a different distribution of mass on Earth, away from the poles and toward the equator, which slows the Earth’s rotation. However, the effect is hardly noticeable: the climate-related lengthening of the day is about 1.33 milliseconds per century.

If climate change is left unchecked, the impact will be greater than that of the Moon, explains the group led by Mostafa Kiani Shahvandi of ETH Zurich. The Moon is known to influence the Earth’s rotation: its gravity creates tidal forces on the Earth, which manifest themselves mainly in tides. The Moon’s pull on the Earth slows down its rotation. This lengthens the Earth’s day.

The impact of climate change on Earth’s rotation can be measured using modern satellites. In addition to satellite data, Shahvandi and his team also used computer models to quantify the impact since 1900 and project it out to 2100. The researchers consider different scenarios for the evolution of climate change.

The decisive factor was the melting of ice in Greenland and Antarctica.

Their calculations showed that the climate-related increase in day length fluctuated dramatically over the 20th century: between 0.31 milliseconds per century (1960 to 1980) and exactly one millisecond per century (1920 to 1940). “These fluctuations reflect the varying contributions of global surface temperature change, ice melt, changes in terrestrial water storage, and sea-level rise that occurred during the 20th century,” the authors wrote. Over the first two decades of the 21st century, the researchers calculated an average climate-related increase in day length of 1.33 milliseconds per century. According to computer models, the increase was mainly due to ice melt in Greenland and Antarctica. “These results show that, through their effect on day length, the mass transport from the poles to the equator due to climate change in the last two decades has been unprecedented compared to the previous 100 years,” the scientists explained.

The researchers also took into account the opposite effect of climate change. The kilometer-thick ice in Greenland and Antarctica pushes land masses into the viscous part of the mantle where the Earth’s plates move. When the ice melts, the land masses rise. This effect speeds up the Earth’s rotation; according to calculations, it is currently shortening the length of the day by 0.8 milliseconds per century.

When forecasting for 2100, Shahvandi’s team used a favorable scenario with a sharp decline in greenhouse gas emissions. This resulted in almost no change in day length due to climate change. In the case of the RCP 8.5 scenario, or the IPCC’s so-called “business as usual” scenario, there were significant changes: If further increases in greenhouse gas emissions led to the climate warming and the polar ice caps melting even more, the day would be lengthened by 2.62 milliseconds per century due to climate change.

This would also be barely noticeable at first: it would take more than 137 million years for the 2.62 milliseconds per century to add up to about an hour. But the effect would be at least as large as that caused by tidal forces from the moon, which lengthen the day by 2.40 milliseconds per century.