Recently, the research team led by Academician Huang Jianping from the College of Atmospheric Sciences at Lanzhou University published a review titled "Planetary Albedo and Reflected Shortwave Flux: Basic Characteristics, Mechanisms of Change, and Future Projections" in the authoritative international journal *Earth-Science Reviews*. As a core parameter in Earth's energy balance, planetary albedo exhibits subtle variations that can significantly influence global temperatures through radiative forcing and trigger multi-layer feedback mechanisms. Its continuous decline has become a key factor exacerbating global energy imbalance, making precise quantification of its spatiotemporal variability and climate feedback crucial for understanding climate change. Based on the latest CERES EBAF Ed4.2 observational data from 2001 to 2023, this review systematically examines the spatiotemporal evolution, driving mechanisms, and future trends of Earth's planetary albedo and reflected shortwave radiation over the past two decades. The findings provide vital scientific foundations for optimizing climate prediction models, assessing future temperature changes, and developing effective climate mitigation strategies.
Figure 1. Schematic diagram of the planetary albedo influence factor and the hypothesis of hemispheric symmetry maintenance.
The albedo of the Earth's planets decreased significantly
The global average planetary albedo is declining at a rate of-0.0023 per decade, reaching a satellite-record low of 0.286 in 2023. This reduction has led to a continuous increase in Earth's absorption of solar radiation, exacerbating global warming. Notably, the Northern Hemisphere shows a faster albedo decrease than the Southern Hemisphere, revealing significant regional climate asymmetry. Research indicates that this change is primarily driven by three factors: reduced low cloud cover in tropical and subtropical oceans, melting polar ice and snow, and decreased aerosol emissions from pollution control measures and shipping industry emission reductions.
Figure 2. Decomposition of latitudinal and spatial trends in reflected solar radiation and its clear-sky atmospheric, surface and cloud components.
Surprising hemispheric symmetry of planetary albedo
Hemispheric symmetry refers to the near-equal reflection of solar radiation by the planet's northern and southern hemispheres at annual mean scales, a phenomenon known as hemispheric albedo symmetry. However, the maintenance mechanism of this symmetry remains a mystery, posing a significant challenge to climate model simulations. This paper comprehensively reviews the characteristics of hemispheric symmetry, existing hypotheses for its maintenance, and recent advancements in model simulations, emphasizing the complex compensatory interactions among clouds, aerosols, the Earth's surface, and large-scale atmospheric circulation (including tropical cloud systems and mid-latitude baroclinic activities).
Observation constraint: The downward trend will continue
The research team employed the "emergent constraint" method to significantly reduce uncertainties in predicting shortwave radiation reflection, revealing that Earth's reflected solar radiation will continue to decrease throughout this century, meaning more heat will be absorbed by the planet. Under the traditional development path scenario dominated by fossil fuels (SSP5-8.5), the rate of reflected radiation decline will accelerate, exacerbating global warming; whereas under the sustainable development path scenario (SSP1-2.6), this trend is expected to gradually slow down, highlighting the critical impact of sustainable development pathways on Earth's energy balance.
Figure 3. Global and hemispheric average atmospheric top reflection solar radiation anomalies from CMIP6 model ensemble simulations (2015-2099) relative to the 2001-2014 observation baseline period.
Article information: Ruixue Li, Bida Jian, Jiming Li, Jiayi Li, Zhenyu Cao, Yang Wang, Yuan Wang, Jianping Huang. Planetary albedo and reflected shortwave flux: Basic characteristics, mechanisms of change and future projections. Earth-Science Reviews, 2025,105274, ISSN 0012-8252,https://doi.org/10.1016/j.earscirev.2025.105274.
The corresponding author of this article is Professor Li Jiming from Lanzhou University, and the co-first authors are doctoral student Li Ruixue and young researcher Jian Bida. The research was supported by the National Natural Science Foundation of China (Key Project 42430601), the National Natural Science Foundation of China (42305072), the China Postdoctoral Science Foundation (2023M731454), and the "Innovation Star" Cultivation Program for Outstanding Graduate Students of the Gansu Provincial Department of Education (2025CXZX-075).
Welcome to read the team’s related work articles:
Jian, B., Li, J., Wang, G., He, Y., Han, Y., Zhang, M., Huang, J., 2018. The Impacts of Atmospheric and Surface Parameters on Long-Term Variations in the Planetary Albedo. J. Clim. 31(21): 8705-8718. https://doi.org/10.1175/jcli-d-17-0848.1 Jian, B., Li, J., Zhao, Y., He, Y., Wang, J., Huang, J., 2020. Evaluation of the CMIP6 planetary albedo climatology using satellite observations. Clim. Dyn. 54(11-12): 5145-5161.https://doi.org/10.1007/s00382-020-05277-4.
Li, R., Jian, B., Li, J., Wen, D., Zhang, L., Wang, Y., Wang, Y., 2024. Understanding the trends in reflected solar radiation: a latitude-and month-based perspective. Atmos. Chem. Phys. 24(17): 9777-9803. http://dx.doi.org/10.5194/acp-24-9777-2024.
