Future increases in Arctic precipitation linked to local evaporation and sea-ice retreat
Abstract:Precipitation changes projected for the end of the twenty-first century
show an increase of more than 50 per cent in the Arctic regions.
This marked increase, which is among the highest globally, has previously
been attributed primarily to enhanced poleward moisture
transport from lower latitudes. Here we use state-of-the-art global
climate models to show that the projected increases in Arctic precipitation
over the twenty-first century, which peak in late autumn
and winter, are instead due mainly to strongly intensified local surface
evaporation (maximum in winter), and only to a lesser degree
due to enhanced moisture inflow from lower latitudes (maximumin
late summer and autumn). Moreover, we show that the enhanced surface
evaporation results mainly from retreating winter sea ice, signalling
an amplified Arctic hydrological cycle. This demonstrates
that increases in Arctic precipitation are firmly linked to Arctic warming
and sea-ice decline. As a result, the Arctic mean precipitation sensitivity
(4.5 per cent increase per degree of temperature warming) is
much larger than the global value (1.6 to 1.9 per cent per kelvin).
The associated seasonally varying increase in Arctic precipitation
is likely to increase river discharge and snowfall over ice sheets
(thereby affecting global sea level), and can even affect global climate
through freshening of the Arctic Ocean and subsequent modulations
of the Atlantic meridional overturning circulation (AMOC). The reasons behind
the AMOC changes and its consequences will be discussed and quantified.