A new study warns that in the Arctic, ice-nucleating particles (INPs) are far more prevalent than has been previously thought and calls for more research into how they interact with clouds to drive up temperatures. The surprise results fly in the face of conventional thinking about how cloud composition should change with warming in the Arctic.
Changes in the Cloudscape of the Arctic
The Arctic has been a center of climate study for some time because it is warming rapidly and especially vulnerable to shifts in the composition of clouds. Historically, climate models have projected that with Arctic warming we’d see more liquid water in the clouds of the region and less ice, since warmer temperatures should suppress the formation of ice crystals.
But the new study, headed by Associate Professor Yutaka Tobo at Japan’s National Institute of Polar Research, says there is a catch. The team had previously identified that the area of the polar ice and snow is decreasing as it warms (warmer than -5 C), providing more opportunities for active INPs to be released into the atmosphere from soil. Under certain conditions, these INPs promote ice crystal formation in clouds to decrease the liquid water content in mixed-phase clouds and potentially accelerate warming in the region.
The Role of Ice Nucleation in The Environment
The relationship between surface air temperature and the abundance of ice-forming particles known as ice-nucleating particles (INPs) was examined in the study. INPs are recognized as the accelerating cores in cloud ice nucleation process, which linkage to energy balance in regional and climate system.
The researchers also collected year-round measurements of INPs at the Zeppelin Observatory in Svalbard, where warming was proceeding at a rate five to seven times higher than the global mean. What they discovered was an extraordinary proliferation of INPs in the warmer months, when surface air temperatures leapfrogged above zero degrees Celsius, and further investigation uncovered that these particles were mostly mineral dust and carbonaceous species — sediment from the snow-free barren soil and vegetation plain that swelled along with the thawing.
The researchers are especially concerned about this finding because winter temperatures at Svalbard have been warming even faster — more than 2° C per decade. They predict that the increase in highly efficient INPs will indeed drive higher emissions under snow and ice-free Arctic winter conditions, with potential ramifications for mixed-phase clouds composition.
Conclusion
These surprising findings from the bumpy boundary layer suggest a new paradigm for how cloud composition may evolve with Arctic warming. Rather than the expected jump in liquid water content, though, the investigators discovered that greater quantity of ice-nucleating particles (INPs) from newly snow-covered and ice-free areas could trigger more cloud ice formation, potentially speeding up warming in the region. These findings underscore the intricate, coupled processes that dictate Arctic climate and the necessity of accounting for aerosol effects on clouds in climate models.
