Dale C. S. Destin |
Last week we had an extremely cold night (relative to our climate) and a few cool nights which led some persons to ask with “tongue-in-cheek” if we going to have snow. Are cold extremes becoming more or less frequent? What can we expect as our climate changes?
When I was growing up, I remember it was very common place to see our breaths (as mist) in the mornings, due to extremely low temperatures, at this time of the year. It was fun for us as we would pretend to be blowing smoke from our mouths and also blow mist onto the mirrors and then draw or write on them.
The fact is, such low temperature extremes, are decreasing fairly rapidly. So, the cold nights we had last week, are becoming more a thing of the past or a once in a “blue moon” event. 2015 had a record low number of extremely cold nights – 6 or 2% of the number of nights for the year; the next fewest is 2002 with 14 or 4%.
Data at the V. C. Bird International Airport (VCBIA), where the Met Office is located, show a significant decline in extremely cold nights, while extremely warn nights are on the increase but not yet considered to be rising significantly.
Extremely cold nights here mean nights with the minimum temperature in the bottom 10-percentile based on the climate period 1971-2000. Extremely warm nights are those with minimum temperature in the top 10-percentile.
This year in particular, nighttime lows are expected to be much higher than normal due mainly to the ongoing El Nino or warmer than usual sea surface temperatures (SSTs) across the equatorial Pacific.
El Nino causes higher than normal surface pressure across the equatorial Atlantic, which acts to weaken the trade winds. Weakened trade winds then translate into warmer than normal SSTs and the air in contact with it; hence the warmer than normal nights.
As our climate changes, cold extremes will continue to decrease and warm extremes are expected to increase. Thus, the drop in temperature to cold extremes will become fewer and the spikes to warm extremes will become more and more common place
Weather extremes are generally undesirable. Cold extremes cost us nothing as it is fairly easy to warm ourselves. On the other hand, warm extremes have negative implications for our health, economy and ecosystem.
So far for the year, there have been fewer than normal extremely cold nights at the VCBIA – one, and more than normal warm nights – nine or 23% of nights to date for 2016.