Reanalysis Models Expose Global Energy And Mass Imbalances

Andy May (May 2025) publishes a paper examining weather reanalysis systems ERA5 and MERRA-2, arguing they are model outputs rather than observations and discussing their assimilation-induced errors. The paper quantifies imbalances—ERA5 TOA mean radiative imbalance 0.68 ± 0.6 Wm-2 (2000–2020) and MERRA-2 TOA flux bias ≈ -4 Wm-2 (2001–2015)—and highlights impacts on precipitation, clouds, and radiation studies.