‘Earthshine’ is dimming and that’s bad news for the climate
Earthshine is one of the most spectacular sights in our night sky. Yet, this astronomical phenomenon is slowly vanishing, and this is providing us with a new warning sign for the climate.
Gaze up at a thin Crescent Moon as it hangs above the horizon, and you will often be able to dimly make out the features that are immersed in the shadow of the Moon’s dark side. This phenomenon is known as Earthshine.
Earthshine – Science@NASA
Sunlight reflected from Earth shines upon the Moon’s dark side, in a phenomenon called Earthshine. Credit: Science@NASA
Earthshine results from Earth’s albedo. Of all the incoming sunlight that reaches Earth, roughly one-third gets directly reflected back into space by bright cloud tops and icy surfaces.
Some of this reflected sunlight shines onto the Moon’s surface. This effect is best seen just before and just after a New Moon. That’s when the greatest amount of dark lunar surface is lit by the greatest amount of reflected light from Earth. Anyone looking up at the Moon on those nights will be able to pick out the most prominent features of the lunar surface, even though they are not lit by the direct light of the Sun.
Earth, Moon & Earthshine – NASA
Viewing the Moon from Earth and Earth from the Moon during any month reveals how their phases are complementary. As shown in this image, anyone standing on the lunar surface during a thin Crescent Moon would see a brightly lit “nearly full” Earth. Credit: NASA
However, according to a new study, this phenomenon is slowly disappearing.
Researchers gathered two decades worth of observations of Earthshine, from 1998 to 2017, taken at the Big Bear Solar Observatory, in San Bernardino National Forest, east of Los Angeles, California. The data they collected revealed that Earthshine had dimmed over that time, by about 0.5 per cent. Since the dimming they observed did not match up with changes in the Sun’s brightness during that same time period, that means the dimming is being caused by Earth.
In other words, Earth’s albedo is decreasing, thus the planet is now reflecting less sunlight back into space than it was 20 years ago.
“The albedo drop was such a surprise to us when we analyzed the last three years of data after 17 years of nearly flat albedo,” Philip Goode, the lead researcher on the study from the New Jersey Institute of Technology, said in a press release from the American Geophysical Union (AGU).
This graph shows two decades worth of Earthshine data (black points), alongside data from NASA’s Clouds and the Earth’s Radiant Energy System (CERES) instruments in orbit (blue points). Both reveal that Earth’s albedo is decreasing. CERES detected a significant drop in albedo in 2019. Credit: Goode et al. (2021), Geophysical Research Letters.
While the slow disappearance of Earthshine would be terrible for stargazers, there is a much more significant and troubling impact from this discovery.
Over the years, one of the uncertainties in Earth’s climate system has been whether rising ocean temperatures would increase or decrease cloud cover.
If it increased cloud cover, it could create a self-limiting effect on climate change. Greater cloud cover would increase the amount of sunlight being reflected back into space. As a result, with less sunlight reaching the surface, it would reduce the amount of heat being added to the climate system.
On the other hand, if warming oceans resulted in less cloud cover, it would lower the planet’s albedo. More sunlight would reach the ground, which would result in more heat being added to the climate system. Over time, this would increase the rate of global warming and make the impacts of climate change worse.
Earthshine – ISS028-E-20073 – NASA
Photographed from the International Space Station on July 31, 2011, this image shows the Crescent Moon shining above the limb of Earth, along with the different layers of the atmosphere (troposphere in orange, stratosphere in blue, fading into the mesosphere). The dark side of the Moon is dimly illuminated by the phenomenon of Earthshine. Credit: NASA
This new study found that, along with the detected decrease in Earthshine from their observations, NASA’s Clouds and the Earth’s Radiant Energy System (CERES) project also saw a reduction in the amount of cloud cover over the eastern Pacific Ocean. The CERES instruments, carried by NASA’s Terra and Aqua satellites, found fewer bright, low-lying clouds over a region of the Pacific Ocean off the west coasts of North and South America.
This reduction in clouds is over a region of the ocean where previous studies have shown sea surface temperatures to be on the rise. The increase in temperatures is likely due to changes in a large-scale climate pattern known as the Pacific Decadal Oscillation (PDO).
Thus, based on the findings of this study, it would appear that warmer oceans are reducing the amount of cloud cover, which is very bad news.
Also, although the drop in albedo is only 0.5 per cent, the amount of extra heat it adds to our climate system is nearly the same as what human activity added over the same time period.
“The two-decade decrease in earthshine-derived albedo corresponds to an increase in radiative forcing of about 0.5 Watts per square metre, which is climatologically significant,” the researchers wrote. “For comparison, total anthropogenic forcing increased by about 0.6 Watts per square metre over the same period.”
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
