The simulations all show that it is not
possible to explain the
anomalous late 20th century warmth without including the contribution
from anthropogenic
forcing factors,
and, in particular, modern greenhouse gas concentration increases. A
healthy, vigorous debate can be found in the legitimate peer-reviewed
climate research literature with regard to the precise details of
empirically and model-based estimates of climate changes in past
centuries, and it remains a challenge to reduce the substantial
uncertainties that currently exist. Despite current uncertainties, it
nonetheless remains a widespread view among paleoclimate researchers
that late 20th century hemispheric-scale warmth is anomalous in a
long-term (at least millennial) context, and that anthropogenic factors
likely play an important role in explaining the anomalous recent warmth.
The pattern is broadly compatible with retreat
driven by atmospheric warming, but the rapidity of the
migration suggests that this may not be the sole driver of
glacier retreat in this region.
The movie talks about the shrinking Greenland and
Antarctic ice sheets, but I heard somewhere that scientists have found
that the ice is actually gaining mass. Which is correct?
WALT: It is true that both Greenland and
Antarctica have gained mass, but only at the high elevations in their
interior. This is because of increased snowfall, which even though it
may seem counterintuitive, is actually expected under warmer
conditions. However, both have been losing ice at the coast at
increasing rates in recent years. In Greenland, it is becoming apparent
that there is a net loss of ice. In Antarctica, the data are
inconclusive, although the most recent results point to a loss. Under
continued warming conditions, a net loss of ice is assured and rising
sea levels would follow.