This image of Earth was compiled using 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 intricacies of our planet, particularly in relation to global change. Credit: Contains modified Copernicus Sentinel data (2019-20), processed by ESA and NASA’s cloud layer.
Warming oceans cause fewer bright clouds to reflect sunlight back into space, allowing more energy to enter Earth’s climate system.
A new study has revealed that rising ocean water temperatures have caused Earth’s brightness to decrease.
The researchers used decades of measurements of Earth’s brightness — the light reflected from Earth that illuminates the moon’s surface — as well as satellite measurements to see that there has been a significant decrease in Earth’s reflectance, or albedo, over the past two decades.
Earth now reflects about half a watt of light per square meter than it did 20 years ago, with most of the decline in bright Earth data occurring in the last three years, according to the new study in the journal AGU. Geophysical Research Letters, which publishes high-impact, short-form reports with immediate implications across all Earth and space sciences.
This equates to a 0.5% reduction in Earth’s reflection. The Earth reflects about 30% of the sunlight that shines on it.
Earth’s annual mean albedo 1998-2017 expressed in watts per square meter (W/m2). Albedo CERES annual 2001-2019 is shown in blue. The best fit line for CERES data (2001-2019) is shown by a dashed blue line. The average error bars for CERES measurements are 0.2 W/m2. Credit: Goode et al. (2021), Geophysical Research Letters
Philip Goode, researcher at New Jersey Institute of Technology and lead author of the new study, referring to Earth data from 1998 to 2017 that he collected Big Bear Solar Observatory in Southern California. When the most recent data was added to previous years, the opacity trend became apparent.
Two things affect the clear sunlight that reaches Earth: the brightness of the sun and the reflection of the planet. The changes in Earth’s albedo that the researchers observed were not associated with periodic changes in the sun’s brightness, meaning that changes in Earth’s reflectance are caused by something on Earth.
Specifically, there has been a decrease in low, bright and reflective clouds over the eastern Pacific Ocean in recent years, according to satellite measurements made as part of the NASAThe Clouds and Earth’s Radiant Energy System (CERES) Project.
This is the same region, off the western coasts of North and South America, where increases in sea surface temperatures have been recorded due to the reversal of a climate condition called the Pacific Decadal Oscillation, with its possible link to global climate change.
Earth dimming can also be seen in terms of how much solar energy is captured by the Earth’s climate system. Once this significant additional solar energy is in the Earth’s atmosphere and oceans, it may contribute to global warming, since the additional sunlight is about the same size as the total impact of anthropogenic climate over the past two decades.
“It’s really concerning,” said Edward Schwitterman, a planetary scientist at the University of California, Riverside, who was not involved in the new study. For some time, he said, many scientists had hoped that a warmer Earth would lead to more clouds and more albedo, which would then help mitigate global warming and balance the climate system. “But this shows that the opposite is true.”
Reference: “Earth’s Albedo 1998-2017 as measured from Earth’s brightness” by P.R. Goode, E. Pallé, A. Shoumko, S. Shoumko, P. Montañes-Rodriguez, and S.E. Koonin, August 29, 2021, Geophysical Research Letters.
They: 10.1029 / 2021GL094888