On the face of it, without researching the weather patterns further it does appear a linked coincident that many parts of Britain had a great Spring with long spells of clear blue skies and now a pretty consistent cold winter period so far. And there was and is minimal aircraft traffic/traffic volumes across some parts the world.
Edited 1 times. Last edit at 20.55hrs Sat 6 Feb 21 by raddays.
A key scientific motto is "correlation does not necessarily indicate causation".
As Geoffers states, aviation is "only" 2.1% of global CO2 Emissions, and it has not totally ground to a halt. Yes, the euro short haul passenger market is way down, but the big polluter long-haul is still surprisingly active, with many "heavy" passenger aircraft being used solely as freight flights. Also have a look at [www.bgs.ac.uk] and you may be surprised at some of the big emmitters - eg cement manufacturing industry between 5% and 8% of global emmissions. Big construction projects have been kept going so far through the pandemic, so cement co2 emmissions are unlikely to have reduced much.
Undoubtedly, there was a drop in emissions worldwide in March-April last year, but very short term, and now the politicos are pushing for more inrastructure big builds to kick start economies, giving a consequent boost to all emmitting industries.