Increased CO2 can indeed trigger cold blasts such as for example by disrupting ocean currents due to the ice melt.

As far as the Arctic ice cover goes, to my understanding they keep track of it every day and they note the lowest ice cover of the year, whatever day it may be on.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL