This summer, something strange has been happening in the mesosphere. The mesosphere is a layer of the atmosphere so high that it almost touches space. In the rarefied air 83 km above Earth’s surface, summertime wisps of water vapor wrap themselves around specks of meteor smoke. The resulting swarms of ice crystals form noctilucent clouds (NLCs), which can be seen glowing in the night sky at high latitudes.
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During the first half of August 2018, reports of NLCs to Spaceweather.com have tripled compared to the same period in 2017. The clouds refuse to go away.
Researchers at the University of Colorado may have figured out why. “There has been an unexpected surge of water vapor in the mesosphere,” says Lynn Harvey of Colorado’s Laboratory for Atmospheric and Space Physics (LASP). This plot, which Harvey prepared using data from NASA’s satellite-based Microwave Limb Sounder (MLS) instrument, shows that the days of late July and August 2018 have been the wettest in the mesosphere for the past 11 years:
In addition to being extra wet, the mesosphere has also been a bit colder than usual, according to MLS data. The combination of wet and cold has created favorable conditions for icy noctilucent clouds.
Water vapor is the primary greenhouse gas, even in the mesosphere.
The Next Grand Minimum 
Are you sure this is a greenhouse effect? Seems NLCs would act to deflect sunlight before it enters the atmosphere to heat anything…ice is not equivalent to water.
Are you sure? Ice in the mesosphere would seem to act to reflect sunlight and not add to any greenhouse effect.
Agree, not greenhouse effect. I was noting that water vapor a greenhouse gas was reaching into space. Water vapor is the real climate control knob. Convection caused by ocean heating creates water vapor. The more water vapor in the atmosphere the warmer it gets. According to Joe Bastardi, it is polar water vapor that has elevated the polar temperatures, raising the global average temps, where between 80 South and 80 North the temps have been quite average.