  We study the energy and nuclear A dependence of the hadronic production of
heavy quarkonia. We review theoretical ideas which have been put forward,
seeking a consistent global picture reconciling the large effects in quarkonia
with the small nuclear effects observed in continuum Drell Yan production. The
data indicates that shadowing or leading twist modifications of parton
distributions can be ruled out as explanations, leaving higher twist energy
loss. {}From general principles the maximum allowed energy loss of partons
traversing the nuclear medium can be related to the parton transverse momenta.
We then show that the experimental data on nuclear suppression of charm- and
bottom- onium for large $x_F$ is consistent with this effect: using the
observed transverse momenta to bound the $x_F$ dependence in an almost model
independent manner generates a relation that practically reproduces the data.
Several prediction are discussed; the dependence on $x_F$ as $x_F\to 1$, and
large and small $k_T^2$ cuts, can be used to discriminate between quark and
gluon induced effects.
