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.