The universe is quiet, and Earth is dark.
That light, supposedly the color of hope, is now fading.
Earth is Quietly Darkening: New NASA research reveals that Earth's ability to reflect sunlight has steadily declined over the past 20 years, with a particularly noticeable decrease in the Northern Hemisphere. Melting sea ice and reduced cloud cover are absorbing more heat, potentially accelerating global warming and making summers in the Northern Hemisphere even hotter and longer.
The US Discovery magazine website reported on October 7 that researchers analyzing 24 years of data from NASA's Cloud and Earth Radiant Energy System (CERES) have found that Earth's gradual dimming is due to a decrease in reflected sunlight, with the dimming being more pronounced in the Northern Hemisphere.
Scientists first discovered the phenomenon of global dimming in the 1990s, initially believing that the primary factor was a gradual decrease in solar radiation. However, a new NASA report reveals that the current global dimming is more complex. The study, published in the Proceedings of the National Academy of Sciences, highlights an imbalance in Earth's radiation budget. Data show that the Northern Hemisphere receives approximately 0.34 watts more solar energy per square meter per decade than the Southern Hemisphere, enough to upset Earth's energy balance.
The study attributes this difference between the Northern and Southern Hemispheres to changes in atmospheric water vapor and cloud cover, as well as changes in Earth's surface reflectivity. As the climate warms, sea ice and snow cover in the Northern Hemisphere are gradually disappearing, absorbing more sunlight and causing the Earth to darken. Aerosols also play a significant role. Pollution control measures in the Northern Hemisphere have reduced aerosol particles, leading to fewer sunlight-reflecting clouds. Meanwhile, the Australian bushfires and volcanic eruptions in the Southern Hemisphere have increased aerosols, increasing cloud cover and reflecting more sunlight.
Dr. Norman G. Loeb, a climate scientist at NASA's Langley Research Center, stated that energy imbalances at Earth's surface drive air and ocean circulation, while the Earth's increasing dimming will absorb more heat, accelerating global warming. If this trend persists, the Northern Hemisphere's warming rate could continue to exceed the global average, leading to more intense and longer summers there.
However, scientists noted that this study has limitations. For example, the statistically significant differences in Earth's solar absorption are small, and disentangling the specific effects of aerosols, reflectivity, water vapor, and clouds remains challenging. Loeb's team stated that the next step will be to add more satellite records and incorporate new observations into climate models to further investigate whether this imbalance represents a temporary fluctuation in Earth's energy system or a long-term adjustment.