Global warming results from man-made greenhouse gas (GHG) emissions that have doubled the heating effect from incoming sunlight, which is now more than the heat radiated by earth into space in the last decade, according to research paper in AGU Advances published this month.

The dramatic increase in the energy imbalance between incoming sunlight and outgoing radiation comes at a time when governments are decommissioning the satellites used to measure the effect. Scientists complain this will stymie their ability to understand what is going on.

Known as the Earth Energy Imbalance (EEI), it is a measure of the difference between the sun’s radiation absorbed by the surface in terms of watts per square metre (W/m²) and the heat radiated by the planet, a cooling effect. As the imbalance climbs, the earth heats up, and over the last decade, the heating effect has doubled, according to a team lead by Professor Thorsten Mauritsen of the Department of Meteorology and Bolin Centre for Climate Research, Stockholm University, Sweden.

“The imbalance leads to energy accumulation in the atmosphere, oceans and land, and melting of the cryosphere, resulting in increasing temperatures, rising sea levels and more extreme weather around the globe,” the paper says.

The increased accumulation of heat from sunlight is due to “carbon forcing” – the effect that man-made CO₂ emissions and other GHGs have on the Earth's energy balance. In simple terms: carbon forcing means increases in atmospheric CO₂ traps more heat in the Earth’s atmosphere, contributing to global warming. For example, if carbon forcing is 2 W/m², it means there is an additional 2 watts of energy per square metre being retained in the Earth’s system due to elevated CO₂ levels, rather than escaping into space.

Professor Mauritsen says that the Earth’s energy imbalance has reached unprecedented levels, doubling over the past two decades and far exceeding climate model projections, according to scientists citing satellite data.

In 2023, the imbalance peaked at 1.8 W/m², twice the best estimate provided by the United Nations Intergovernmental Panel on Climate Change (IPCC), prompting renewed calls for improved climate monitoring infrastructure.

While the EEI imbalance is a well-established concept, dating back to Joseph Fourier’s 1822 findings, current observational capacity is under strain. “Our capacity to observe it is rapidly deteriorating as satellites are being decommissioned,” according to the paper. The [long-running NASA Clouds and the Earth’s Radiant Energy System, or CERES programme] instruments aboard several NASA satellites currently track radiation trends, while the [Total and Spectral Solar Irradiance Sensor-1] instrument on the International Space Station monitors total solar irradiance. However, the planned decommissioning of existing satellites and reliance on a single future mission, Libera, scheduled for 2027, would create a critical single point of failure,” the scientists say.

The observed acceleration in energy imbalance, even after accounting for GHG emissions, exceeds all of the IPCC forecasting models. Researchers suggest that a decrease in Earth’s solar reflectivity – possibly due to sea surface temperature anomalies, aerosol emission changes, or cloud effects – may explain the discrepancy.

Surface temperatures reached record levels each year for the last three disaster seasons, with a new record breaking the old record set only a year previously. Scientists caution against equating annual temperature anomalies directly with energy imbalance in the same year. Temperature increases typically lag behind accumulated energy and are also influenced by feedback and internal climate variability such as El Niño events. As a result of these effects, the energy imbalance began to decline somewhat in the latter half of 2023, continuing into 2024, potentially reflecting stabilising feedback mechanisms. Nevertheless, despite the fluctuations, the overall trend is clearly for the EEI to continue rising over the long term.

Annual global mean energy imbalance observed from space during 2001-2024. The imbalance is derived from the CERES-EBAF Edition 4.2.1 data set (Loeb et al., 2018). The blue line shows the linear trend over the 2001-2024 period when full annual means are available. Grey shading shows years affected by major El Niño events.

Climate model global mean temperature and energy imbalance under a strong mitigation scenario meeting the 2° target (SSP1-2.6). Time series are estimated from the IPCC AR6 Earth system emulator (IPCC, 2021, Chapter 7 supplementary material). Displayed data are from (Meyssignac et al., 2023). Uncertainty ranges indicate the 90 per cent confidence interval of the spread caused by uncertainties in forcing, the climate response, and the carbon cycle. The displayed uncertainty range therefore excludes internal variability. The dots mark the peak year on each time series.