  For a given carbon budget over several decades, different transformation
rates for the energy system yield starkly different results. Here we consider a
budget of 33 GtCO2 for the cumulative carbon dioxide emissions from the
European electricity, heating, and transport sectors between 2020 and 2050,
which represents Europe's contribution to the Paris Agreement. We have found
that following an early and steady path in which emissions are strongly reduced
in the first decade is more cost-effective than following a late and rapid path
in which low initial reduction targets quickly deplete the carbon budget and
require a sharp reduction later. We show that solar photovoltaic, onshore and
offshore wind can become the cornerstone of a fully decarbonised energy system
and that installation rates similar to historical maxima are required to
achieve timely decarbonisation. Key to those results is a proper representation
of existing balancing strategies through an open, hourly-resolved, networked
model of the sector-coupled European energy system.
