  We search for physically consistent realizations of evolving dark energy
suggested by the cosmological fit of DESI, Planck and Supernovae data. First we
note that any lagrangian description of the standard Chevallier-Polarski-Linder
(CPL) parametrization for the dark energy equation of state $w_{\rm eff}$,
allows for the addition of a cosmological constant. We perform the cosmological
fit finding new regions of parameter space that however continue to favour dark
energy with $w_{\rm eff}<-1$ at early times, that is challenging to realize in
consistent theories. Next, in the spirit of effective field theories, we
consider the effect of higher order terms in the Taylor expansion of the
equation of state of dark energy around the present epoch. We find that
non-linear corrections of the equation of state are weakly constrained, thus
opening the way to scenarios that differ from CPL at early times, possibly with
$w_{\rm eff}>-1$ at all times. We present indeed scenarios where evolving dark
energy can be realized through quintessence models. We introduce in particular
the ramp model where dark energy coincides with CPL at late times and
approximates to a cosmological constant at early times. The latter model
provides a much better fit than $\Lambda$CDM, and only slightly worse than
$w_0w_a$CDM, but with the notable advantage of being described by a simple and
theoretically consistent lagrangian of a canonical quintessence model.
