  In 2023, the global mean temperature soared to 1.48K above the pre-industrial
level, surpassing the previous record by 0.17K. Previous best-guess estimates
of known drivers including anthropogenic warming and the El Nino onset fall
short by about 0.2K in explaining the temperature rise. Utilizing satellite and
reanalysis data, we identify a record-low planetary albedo as the primary
factor bridging this gap. The decline is caused largely by a reduced low-cloud
cover in the northern mid-latitudes and tropics, in continuation of a
multi-annual trend. Understanding how much of the low-cloud trend is due to
internal variability, reduced aerosol concentrations, or a possibly emerging
low-cloud feedback will be crucial for assessing the current and expected
future warming.
