How can there possibly be a link between a modestly cool month in Reigate and the earliest start to the melt-season in Greenland, the devastating wild fires in Canada and the seventh hottest-ever global month in succession?
April summary weather statistics for Reigate
- Average Temp 8.2C
- Tmax 17.7C
- Tmin 0.1C
- precipitation 43.4mm (local Reigate) SE PPT 55mm
- sunshine 140.4 hours
- Max wind gust 30mph
- average wind bearing 199 degrees
Reigate, like the UK as a whole, had a cooler than average April at 8.2C. The town even experienced some unusual snow showers on 26 April in a cool northerly air flow.
The cool month for the UK is in stark contrast to the bulk of the planet which experienced a much much warmer month than average, at over 1.1C warmer than any previously measured April.
Astonishingly, this is the seventh month straight that has brought record breaking global temperature anomalies. This continuing succession of warm months globally should be of concern to everyone. More on this below.
— Stefan Rahmstorf (@rahmstorf) May 15, 2016
Back to the UK… The Central England Temperature came out at 7.5C, 0.4C below average, and the UK mean was even lower at 6.5C, 0.9C below the long term average.
Rainfall was about average in Reigate with around 40mm of rainfall. The MetOffice SE figure came out at 55mm.
April was sunnier than usual with a total of 140 hours of sunshine.
This continues the trend of drier and sunnier Aprils in the UK in recent years.
The first half of April was unsettled with most of the rain falling associated with low pressure systems and fronts. The second half of April saw an unusual cool period as northern blocking over the Arctic sent cool northerly winds south with attendant sunshine and showers.
Globally April was the warmest ever April on record. An anomaly of 1.1C sent the Paris target of keeping global temperatures below 1.5C into grave doubt as this is the 7th month in succession to yield much higher temperatures than ever. This is now being dubbed a “Climate Emergency” because of the sudden and rapid increase in global temperature to levels not expected to occur so soon.
The UK / NW Europe was about the only part of the planet, with NE Canada, to record below average temperatures.
The cool spot over the UK was due to northern blocking (high pressure) over the Arctic. As pressure rose over the Arctic, cold air pushed out into mid-latitudes.
It is a matter of chance where high pressure and low pressure set up that determines where cold polar air penetrates in these northern blocking scenarios. This time the pattern sent the cold air to the UK and N Europe. The Northern Hemisphere as a whole saw anomalously low snow cover as a result of incredibly high temperatures elsewhere.
Arctic Amplification, where the northern latitudes experience highest rates of warming, is well documented and of increasing concern to climate change. It is acting as both a response and a further driving force behind rapid climate change.
Temperatures rocketed over the Arctic this cold season with temperature departures over 3C widely across the Polar regions. The Greenland ice sheet experienced one of the earliest starts to the ice melt season on record.
Arctic Sea cover also recorded another record low maximum winter extent.
“On March 24, Arctic sea ice extent peaked at 5.607 million square miles (14.52 million square kilometers), a new record low winter maximum extent in the satellite record that started in 1979. It is slightly smaller than the previous record low maximum extent of 5.612 million square miles (14.54 million square kilometers) that occurred last year. The 13 smallest maximum extents on the satellite record have happened in the last 13 years.” NASA
This is both a response and a further catastrophe for climate change. As snow and ice melt in the Polar regions there are connections with further warming as darker sea and land surfaces heat up more readily.
This Polar warming itself is connected with a weaker jetstream as latitudinal temperature gradients in the atmosphere decline. It is temperature gradient, especially in Mid-Latitudes, that generates the driving force behind the jetstream. A weaker jetstream is said to cause more blocked atmospheric conditions as it meanders with greater amplitude in a meridional pattern that locks in swoops of northerly and southerly winds. More extreme weather is caused as these pressure patterns persist for longer. Sweeps of warmer air penetrate into the Arctic, melting more ice over Greenland and, for mid-latitudes, cooler dry Polar air leaks out causing damaging late frosts and wild fires.
So, whilst it seems tenuous to connect these far-off events to our own rather benignly cool April, it is still important to think globally when considering how our own weather links to increasingly extreme weather elsewhere.