As parts of the Southern Hemisphere in Australasia swelter, the mid-west has been plunged into a frigid cold snap.
And I witnessed both as I left Auckland on Wednesday at near 30C heat and arrived at State College, Pennsylvania, last night and this morning at -20C, a 50C personal "climate" change.
My travel was caught out as extreme wind chill closed Chicago's O'Hare Airport yesterday for several days.
The reason: the extremely cold temperatures were freezing the de-icing fluid so aircraft could not be de-iced. This was a new one for me.
As I sit in the Penn State University's Weather Centre I am watching denialists, including Donald Trump trumpeting "where's the global warming?"
But alas, Trump and his global warming denialists were looking at a very local picture – that over the mid-west and north east of the US.
Closer examination of the University of Maine's Climate Reanalyzer shown above displays the dramatic cold pool with mean temperatures 10C to 15C below average clearly for yesterday.
There is another similar cold pool over Siberia.
However, looking at the global picture below reveals mean temperatures 10C to 15C above average over parts of the Arctic, north-eastern Canada, and parts of the western US and Canada.
In fact, most land areas for the planet are above average.
The world, Northern Hemisphere and Southern Hemisphere were +0.3, +0.4 and +0.2C respectively above average.
Extrapolating global temperatures on any day for one region is such folly.
For our Australasian heatwave the main contributor to this heat was a persistent high-pressure system in the Tasman Sea which was blocking any cold fronts and cooler air from impacting the south of the country.
At the same time, there was a delayed onset to the monsoon in the north of the country so the cooler, moister air was not being injected into the north.
And in New Zealand the Southern Annular Mode was in action again squeezing the Southern Ocean storm tracks towards Antarctica.
Some of the statistics emerging are spectacular: on Wednesday Chicago recorded a bone-chilling -30.6C, the 14th lowest January temperature on record.
And the National Weather Service in Chicago has just released the following figures: last night the temperature plunged to -34.4C in Cedar Rapids IL, a new record.
A temperature of -38.9C was recorded at the Mt Carroll weather station.
This will be checked by the Illinois climate extremes committee and if deemed correct will be an all-time record for that state.
However, the cold snap is not expected to last with the mercury rising by 20C or more by the weekend.
So what is causing these topsy-turvy patterns over the Northern Hemisphere middle and high latitudes?
The answer is global warming.
In recent decades the Arctic and frigid areas of the Northern Hemisphere have warmed at a faster rate than the subtropical and tropical latitudes further south.
This means the temperature difference between the equator and North Pole decreases and the westerly jet streams at about 10km decreases.
This is a winding river strong westerly winds circulating around the North Hemisphere.
The pressure differences between the North Pole and mid-latitudes decreases, resulting in a weakened jet stream and its winds.
As slow-moving rivers typically meander, so to the slower-flowing jet stream tends to undulate more. And below these the cold pool or polar vortex occurs.
Normally this sits over the North Pole.
In terms of impacts then oddly these icy cold snaps over parts of the Northern Hemisphere are a consequence of a warming planet.
This latest one is effecting about 90 million people from the mid-west and New England, with 25 million experiencing temperatures below minus -29C.
This is yet another dire warning that we must hasten our action on reducing emissions as the clock ticks.
• Professor Jim Salinger is a research associate at University of Tasmania and a visiting professor at the University of Florence.