Measured ice crystal number concentrations are often orders of magnitude
higher than the number concentrations of ice nucleating particles,
indicating the existence of secondary ice production (SIP) in clouds.
Here, we present the first study to examine the global impacts of SIP
through droplet shattering during freezing of rain, ice-ice collision
fragmentation, and rime splintering, using a global climate model. Our
results show that SIP happens pretty uniformly in the two hemispheres
and dominates the ice formation in the moderately cold clouds with
temperatures warmer than -15℃. SIP decreases the global averaged liquid
water path by –14.6 g m–2 (–22%), increases the
global averaged ice water path by 8.7 g m–2 (23%),
improving the model agreement with observations. SIP changes the
shortwave, longwave, and net cloud forcing by 2.1, –1.0, and 1.1 W
m–2, respectively, highlighting the importance of SIP
on cloud properties on the global scale.