Abstract
Changes in atmospheric composition, such as increasing greenhouse gases,
cause an initial radiative imbalance to the climate system, quantified
as the instantaneous radiative forcing. This fundamental metric has not
been directly observed globally and previous estimates have come from
models. In part, this is because current space‐based instruments cannot
distinguish the instantaneous radiative forcing from the climate’s
radiative response. We apply radiative kernels to satellite observations
to disentangle these components and find all‐sky instantaneous radiative
forcing has increased 0.53±0.11 W/m2 from 2003 through 2018, accounting
for positive trends in the total planetary radiative imbalance. This
increase has been due to a combination of rising concentrations of
well‐mixed greenhouse gases and recent reductions in aerosol emissions.
These results highlight distinct fingerprints of anthropogenic activity
in Earth’s changing energy budget, which we find observations can detect
within 4 years.