10 | New Scientist | 21 September 2019
getting worse because of a lack
of data, she says, but it feels worse
than in the past. “I think there’s
more rockfall, without a doubt.”
The heatwave was made more
probable by climate change.
The retreat of the glaciers is
affecting flora and fauna too, says
Hillary Gerardi of the Research
Centre for Alpine Ecosystems
in Chamonix. “We are seeing the
productivity of vegetation going
way up, plants are moving up the
slope and the growing season is
getting longer,” she says, citing
the example of a large tree that
was found growing above
Chamonix where a glacier had
been situated just a decade ago.
Another example comes from
the keeper of the Vignettes hut,
a stop on a popular walking route
in the area. A local plant known as
génépi, used to make an alcoholic
drink, is usually picked at about
2400 metres above sea level.
This year, the keeper picked it at
3100 metres, the highest so far.
Meanwhile, some species will lose
out, like the rock ptarmigan, a bird
whose Alps habitat is shrinking.
The world is currently on the
path to dangerous warming, but
on 23 September, some 60 heads
of state are expected to present
new climate change plans at a
UN summit in New York. The UN
special climate envoy, Luis Alfonso
de Alba, says the European Union’s
contribution will be fundamental
to the meeting’s success.
Unless global action is taken
to curb carbon emissions, France’s
two greatest glaciers are doomed.
A recent study by Vincent shows
that on the current emissions
trajectory, Argentière will be
gone by 2080 and Mer de Glace
by the end of the century.
“Almost nothing” can be done
locally to stop their decline, he
says. Their future rests on the
course the world takes. ❚Steps lead down to
the Mer de Glace
glacier (above). An ice
cave (left) is dug in the
glacier every yearGreenlandMeltwater could
raise sea level an
extra 7 centimetresMELTING and refreezing is turning
the absorbent surface snow of
Greenland into solid ice. This means
more water is draining straight into
the sea instead of soaking into the
snow and refreezing deeper down.
Now a study suggests that this will
cause an extra sea level rise by
2100 of at least a few centimetres.
“As a human and a father
of three, it’s a little terrifying,”
says Michael MacFerrin at the
University of Colorado, whose
team discovered the effect.
The Greenland ice sheet is
made of snow. Deeper layers
gradually turn to ice, but the surface
used to consist almost entirely
of porous snow. When parts of it
melted, the water sank through
the snow and refroze deeper
down, forming chunks of ice.Extracted ice cores and radar
observations show that surface
melting is becoming so common
and widespread in Greenland
that these bits of ice are getting
larger and joining up to form
extensive solid slabs.
“This process really is
transforming the surface
of the ice sheet in the interior
of Greenland,” says MacFerrin.
At present, almost all ice loss
from Greenland is a result of
glaciers flowing faster into the sea.According to a recent survey of
climate scientists, Greenland ice
loss alone could add 33 centimetres,
or maybe even 100 centimetres,
to global sea level by 2100.
In parts of Greenland, however,
meltwater now runs over thesurface of this ice rather than
sinking into snow. This was first
observed in 2012, when there
was extensive surface melting
across Greenland.
Now computer modelling by
MacFerrin’s team suggests that
meltwater runoff from the interior
could add somewhere between
2 and 7 additional centimetres to
sea level by 2100 (Nature, DOI:
10.1038/s41586-019-1550-3).
That is roughly double previous
estimates that don’t take this
slab-forming effect into account.
The good news is that it isn’t
a runaway process that can’t be
reversed, such as the now-
inevitable collapse of the West
Antarctic ice sheet. If surface
melting was reduced, a porous
snow layer would build up again.
“This is completely dependent
on atmospheric temperatures,”
says MacFerrin. “If you stop the
warming, you stop this effect.” ❚
Michael Le PageSpecial report Ice loss
2-7cm
The predicted extra rise in sea level
caused by surface snow turning to iceThe melt of Mer de Glace
In 1988, it took just three steps to reach
the Mer de Glace glacier from a lift stop.
Today, it takes 580 to reach the glacier
and the ice cave carved into it1988: 3 steps
1990: 12 steps2000: 118 steps2010: 321 steps2015: 370 stepsICE CAVE2019: 580 stepsSOURCE: COMPAGNIE DU MONT-BLANCAdam Vaughan is
chief reporter at New
Scientist and tweets as
@adamvaughan_ukK ATIE MOORE FOR NEW SCIENTIST