## 2 Importance of ERB at TOA and EEI Measurements for the Next Decades
Combined satellite and OHC data reveal an average EEI of approximately +0.5 Wm\({}^{-2}\) between 1971 and 2020, rising to around +0.74 Wm\({}^{-2}\) during the 2006-2020 period [5]. Recent satellite data indicate that the EEI is rising at a rate much faster than climate models have projected, reaching approximately +1.8 Wm\({}^{-2}\) in 2023 [22]--nearly twice the best estimate presented in the IPCC AR6 [16]. This increase has more than doubled over the past two decades, challenging the ability of state-of-the-art climate models to fully reproduce the observed acceleration [23]. Several factors contribute to this rapid increase in EEI. First, [PERSON] et al. (2021) [24] attribute it to a reduction in Earth's reflectivity caused by decreased cloud cover and sea ice extent. At the same time, a reduction in OLR is driven by increased concentrations of trace GHGs and water vapor. Radiative forcing from GHGs has grown substantially, with [PERSON] et al. (2021) [25] reporting an increase in instantaneous radiative forcing from +0.42 to +0.64 Wm\({}^{-2}\) between 2003 and 2018. Meanwhile, the cooling effect of anthropogenic aerosols--caused by their reflection of sunlight and interactions with clouds--has diminished. This trend is reinforced by international regulations such as the International Maritime Organization (IMO)'s MARPOL Annex VI, which mandates reduced sulfur content in marine fuels. The global sulfur cap was lowered from 3.5% to 0.5% on 1 January 2020 (IMO 2020), following stricter limits already applied in Sulfur Emission Control Areas (SECAs) since 2015. As a result, marine sulfur dioxide (\(SO_{2}\)) emissions and consequently sulfate aerosol concentrations have significantly decreased--particularly impacting stratocumulus cloud formation in regions like the Peruvian coast. With fewer aerosols acting as cloud condensation nuclei, the frequency and optical thickness of marine stratiform clouds may decrease, allowing more solar radiation to reach the surface and thereby altering local atmospheric dynamics. These aerosol-related changes are supported by studies from [PERSON] et al. (2020) [26] and [PERSON] et al. (2022) [27], which noted an increase in TOA forcing by +0.17 Wm\({}^{-2}\) per decade from 2000 to 2017. The reduction in aerosols likely contributed to increased solar absorption, compounding the warming effects of GHGs. Additional indirect effects on clouds may also be involved. Moreover, recent Sea Surface Temperature (SST) patterns, such as reduced low-level cloud cover in the subtropical Pacific, appear to be amplifying solar absorption to levels exceeding model predictions [28]. Beyond these anthropogenic influences, natural factors also play a role. The notable temperature peak in 2023 coincides with the transition from La Nina to El Nino conditions, which increased global surface temperatures but paradoxically reduced the net EEI due to enhanced outgoing radiation, as we will show in this study. Additionally, the injection of water vapor into the stratosphere following the Hunga Tonga volcanic eruption may have contributed a transient warming effect of approximately +0.16 Wm\({}^{-2}\)[29; 30], although some studies suggest compensatory cooling effects in the upper atmosphere [31]. Another contributing factor is the solar cycle. Solar activity follows an approximately 11-year cycle that modulates TSI by about 0.1%. Solar Cycle 25, which began at the end of 2019, is showing a gradual increase in solar activity compared to the previous minimum. While the contribution of this cycle to global warming is real, its impact on Earth's global mean surface temperature remains minor--estimated at no more than 0.1 \({}^{\circ}\)C. The recent warming and record temperatures in 2023-2024 were primarily driven by anthropogenic forcing (e.g., \(CO_{2}\) and \(CH_{4}\)), with solar variability playing only a secondary role. Events such as the 2023-2024 El Nino further amplified surface temperatures but do not explain the long-term trend.