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This image of Earth was compiled from tens of thousands of images from the Copernicus Sentinel-2 mission. Thanks to the age of satellites, we are in a better position to understand the complexities of our planet, especially when it comes to global change. Credit: Contains modified Copernicus Sentinel data (2019-20), processed by ESA and NASA cloud layer
Warming oceans cause fewer bright clouds to reflect sunlight back into space, admitting even more energy into Earth’s climate system.
Warming ocean waters have caused the Earth’s luminosity to drop, according to a new study.
The researchers used decades of measurements of the Earth’s brightness – the light reflected from the Earth that illuminates the surface of the Moon – as well as satellite measurements to find that there has been a significant drop in reflectance. Earth, or albedo, over the past two decades.
The Earth now reflects about half a watt of light per square meter less than it did 20 years ago, with most of the decline having occurred in the past three years of Earth’s glow data, according to the new study published in the journal AGU. Geophysical research letters, which publishes high-impact, short reports with immediate implications covering all Earth and space sciences.
This is the equivalent of a 0.5% decrease in the Earth’s reflectance. The Earth reflects about 30% of the sunlight that shines on it.
Earthshine annual mean albedo 1998-2017 expressed in watts per square meter (W / m2). The annual CERES 2001-2019 albedo is shown in blue. A line of best fit to CERES data (2001-2019) is shown with a blue dotted line. The average error bars for CERES measurements are of the order of 0.2 W / m2. Credit: Goode et al. (2021), Geophysical research letters
“The decline in albedo surprised us so much when we analyzed data from the past three years after 17 years of near-flat albedo,” said Philip Goode, researcher at New Jersey Institute of Technology and the lead author of the new study, referring to data on earth luster from 1998 to 2017 collected by the Big Bear Solar Observatory in Southern California. When the latest data was added to previous years, the tendency towards obscurity became clear.
Two things affect the net sunlight reaching the Earth: the brightness of the Sun and the reflectivity of the planet. The changes in Earth’s albedo observed by the researchers did not correlate with periodic changes in the Sun’s brightness, meaning that the changes in Earth’s reflectivity are caused by something on Earth.
Specifically, there has been a reduction in bright, reflective low clouds over the eastern Pacific Ocean in recent years, according to satellite measurements made as part of Nasa‘s Clouds and the Earth’s Radiant Energy System (CERES).
This is the same area, off the western coasts of North and South America, where increases in sea surface temperatures have been recorded due to the reversal of a climatic condition called the decadal oscillation of the sea. Pacific, with likely links to global climate change.
The darkening of the Earth can also be seen in terms of how much more solar energy is being captured by the Earth’s climate system. Once this important additional solar energy is in the Earth’s atmosphere and oceans, it can contribute to global warming, as the additional sunlight is of the same magnitude as the total anthropogenic climate forcing over the past two decades.
“It’s actually quite concerning,” said Edward Schwieterman, a planetary scientist at the University of California at Riverside who was not involved in the new study. For a while, many scientists hoped that a warmer Earth could lead to more clouds and higher albedo, which in turn would help moderate warming and balance the climate system, he said. declared. “But it shows that the opposite is true.”
Reference: “Earth’s Albedo 1998-2017 as Measured From Earthshine” by PR Goode, E. Pallé, A. Shoumko, S. Shoumko, P. Montañes-Rodriguez and SE Koonin, August 29, 2021, Geophysical research letters.
DOI: 10.1029 / 2021GL094888
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