Document, "Reconciling Earth's growing energy imbalance with ocean warming" by Richard P. Allan and Christopher J. Merchant, published in Environmental Research Letters in 2025, looks at Earth's growing energy imbalance and its link to ocean warming over the period 1985 to 2024. The authors combine satellite observations of Earth's energy balance and ocean surface temperature with the ERA5 atmospheric reanalysis to improve the physical understanding of changes in Earth's net energy imbalance and subsequent ocean surface warming.

Main findings and conclusions of the study:

• Earth's growing energy imbalance: The study found that Earth's net energy imbalance (N) doubled from 0.6 ± 0.2 Wm⁻² in 2001–2014 to 1.2 ± 0.2 Wm⁻² in 2015–2023This increase is primarily explained by an increase in absorbed solar radiation related to the radiative effects of clouds over the oceans.
• Differences between observations and reanalysis: The observed increase in absorbed solar radiation is not fully captured by the ERA5 reanalysis. Differences between the CERES and ERA5 satellite observations suggest that The main cause of the divergence in the net radiation balance is the coverage and brightness of clouds over the oceans.ERA5 underestimates the reduction in reflected solar radiation by marine clouds, particularly in stratocumulus regions off the coast of California and Namibia, as well as due to the loss of Antarctic sea ice in the Weddell and Ross Seas.
• Impact of aerosols: While ERA5 can accurately represent changes in absorbed solar radiation under clear skies over most oceans, this is not the case for eastern China, where aerosol emissions are likely to have decreased more than predicted in ERA5. The study suggests that Aerosol interactions with clouds over the oceans play a significant role in increasing absorbed solar radiationThe decline in global aerosol emissions since 2000 is considered an important factor in the growth of the Earth's energy imbalance.
• Link to ocean warming: The study identified increase in annual warming of the near-global ocean by 0.1 °C per year for every 1 Wm⁻² increase in the Earth's energy imbalance on an interannual timescale (2000–2023). This finding is consistent with a simple ocean mixed layer energy budget assuming no simultaneous change in heat flux beneath the mixed layer.
• Rapid warming in 2022-2023: Extraordinary rapid warming of ocean surface by 0.27°C from 2022 to 2023 is physically consistent with a large energy imbalance of 1.85 ± 0.2 Wm⁻² from August 2022 to July 2023, but only if (1) the reduced mixed layer depth (approximately 50 m) is warming or (2) there is reversal in the direction of heat flow under the mixed layer in connection with the transition from La Niña to El Niño conditions. The second explanation seems more likely given the transition to El Niño, which is associated with the outflow of warm water from the subsurface layers of the eastern Pacific.
• A simple energy balance model: The study uses a simple energy balance framework to illustrate the link between the Earth's energy imbalance and ocean warming. The model suggests that a short-term (interannual) increase in energy imbalance of 1 Wm⁻² leads to an additional warming of the ocean surface of about 0.1°C per year, with the impact being distributed to deeper ocean layers on longer time scales.
• The importance of continuous monitoring: The authors emphasize the critical importance of the continuity of global Earth observation systems, including radiation balance records, to maintain the ability to monitor and accurately predict short-term climate change.

Overall, this study provides new insights into the causes of Earth's growing energy imbalance, highlighting the key role of cloud cover over the oceans and the potential impact of declining aerosol emissions. It also clarifies the link between this imbalance and ocean warming, particularly in the context of record-breaking warming in 2023, and highlights the complex interactions between the surface and deep ocean layers in absorbing Earth's excess energy. Spring

Glossary of key terms

• Energy imbalance of the Earth (Net Energy Imbalance – N): The difference between the solar radiation absorbed by the Earth and the infrared radiation radiated back into space. A positive imbalance means that energy is accumulating in the climate system, leading to warming.
• Top of Atmosphere Radiation Budget: The sum of incoming and outgoing radiation at the top of the Earth's atmosphere, which determines the Earth's energy imbalance.
• CERES (Clouds and the Earth's Radiant Energy System): A suite of NASA satellite instruments to measure the Earth's radiation balance, including reflected solar radiation and emitted infrared radiation.
• ERA5: The fifth generation of the ECMWF (European Centre for Medium-Range Weather Forecasts) global atmospheric reanalysis, which combines extensive observations with an atmospheric model to create a comprehensive record of the state of the atmosphere over time.
• Absorbed Shortwave Radiation (ASR): The amount of solar radiation that the Earth absorbs after some is reflected from the surface and atmosphere (including clouds and aerosols).
• Outgoing Longwave Radiation (OLR): Infrared radiation that the Earth and its atmosphere emit into space.
• Stratocumulus: Low-altitude stratiform clouds that cover large areas of ocean, especially in subtropical regions off the western coasts of continents. They have a significant effect on the reflection of solar radiation.
• Antarctic sea ice: Ice that forms on the surface of the Southern Ocean around Antarctica. Its extent and thickness affect the Earth's albedo and the exchange of heat between the ocean and the atmosphere.
• Ocean Mixed Layer: The upper layer of the ocean where water is well mixed by wind and surface heat, resulting in a relatively homogeneous temperature and salinity. Its depth can vary depending on the season and location.
• Heat Flux: The transfer of thermal energy between different components of the climate system (e.g. between the atmosphere and the ocean, between the ocean surface and deeper layers).
• La Niña and El Niño: Phases of the large-scale Equatorial Pacific Ocean Surface Temperature Oscillation (ENSO). La Niña is characterized by cooler than average temperatures, while El Niño is characterized by warmer than average temperatures. These phenomena have global impacts on weather and climate.
• Aerosols: Tiny particles suspended in the atmosphere that can affect climate by directly reflecting and absorbing solar radiation (direct effect) and indirectly by influencing cloud formation and properties (indirect effect).
• Albedo: The degree of reflectivity of a surface. High albedo (e.g., snow and ice) reflects more sunlight, while low albedo (e.g., dark ocean) absorbs more.