Climate Change 2.0 – Part 2 : Seasons

By Tsahi Frankovits, January 14, 2018

In the previous article we've learned that the frequency of summery days over the years have grown while wintery days portion in recent years dropped to under 20%. But what does it mean in terms of seasons?

When thinking about seasons we refer to several manifestations of the season: We refer to its start and end day (or its length), to the intensity of the weather phenomenon during the season, to extreme weather events etc. Under the framework of the Global Warming discussion it is usually about extreme weather conditions and average temperatures.   But, in order to examine weather patterns during the seasons we first need to know when the seasons start and ends.  This is the object of this post.

When does the winter start and when does it end?

The arbitrary answer is given by the "official" dates of winter -  December 21^st (the shorter day of the year) is the first day of winter and March 20^th (the equilibrium day) is defined as the last day of winter/first day of spring. Summer, by this convention, start on June 21^st (the longest day) and ends on September 21^st (the second equilibrium day).

Unfortunately, climate conditions are not necessarily "obeying" to these rules, so we need a more objective, facts driven, measure. Using my daily weather patterns classifiers, we can define a new measure of start/end day of the seasons. For our purpose, I've defined the turning point of the two major seasons (Summer and Winter) as follows:

If the number of summery days during the last 21 days exceeds 10 (i.e. more than 50%) than we are at Summer, and when it drops to below 10 days, Summer is over. The same applies to Winter. The other two seasons are derived thereafter.

Using this method over the entire period of 50 years, and looking at 5-year periods (to avoid localities), I found that since the early 90' summer is getting longer on both sides (starts earlier and ends later) so that Summer duration is now approximately 155 days vs. 123 days during 1965-1970.  While summer is longer, Winter is getting shorter -  mainly by ending earlier. During 1965 through 1976 Winter usually lasted until day 80-87 of the year (~last 10 days of March), but in recent years winter ends some 18-25 days earlier. See in the next two charts.

These are not good news to a country who sits on the edge of the desert and strives for natural water resources, though Israel was smart enough to identify the growing gap between its water needs and its natural water resources and developed large water desalination facilities.

In my next post of this series I will use the definitions of start/end days of summers and winters over my 50 years sample to discover main weather characteristics changes along the years.    

Climate Change 2.0 – My Version of the True

By Tsahi Frankovits, January 2, 2018

POTUS D.J.T has three alternative ideas about Global Warming:

The first one is – there's no such thing as global warming. 

The second – even if there's global warming, it has nothing to do with human activities.

The third – even if there's global warming and humans are responsible, we (the US) shouldn’t be the one to pay the price.

I don't intend to judge the U.S president's internal logic, nor I'm able to proof any linkage between weather and human activities – that's not my goal. I'm here to offer a somewhat different view on the last 50 years weather phenomena and show that, well – something significant is happening in our lifetime and it's a bit disturbing….

In this first article I'll give you a single snapshot in to my findings. later I'll dive deeper into the phenomena and the new picture of the seasons as I see it through my data and analytical models. The last article in this short series I will describe some of the ideas I've been using to generate these results.

A word about the data I'm using: it's a data set on meteorological measurements in a single weather station here in central Israel. I'm using bi-hourly measures (12 data points a day) for a variety of weather features such as temperatures, wind speed, moisture etc. And a daily measure of precipitation. The data was taken from Israel Meteorological Service web site.    

 Let's go straight to business

When people are talking about global warming they talk about the rise of average temperatures during the last 50 years, the increase of extreme weather phenomenon, growing sea levels etc. But it's always start with average temp.

The focus on temperatures as the main measure or manifestation of climate changes has drown my attention for two reasons: First – how do you measure average temp. on a global scale.  Second – it’s a slow process that people can not refer to. You can't feel global warming….

On the other hand, if you ask people about the weather now they'll say that it's a wintry day, a nice and pleasant spring day or a very hot summer day. But wintry day refers to many different aspects of weather – it may feel wintry because it's rainy, or because it's cold outside and/or windy etc.  We perceive weather as a more complex experience as just temperature. This notion has led me to think that what I should look for is a way to characterize the days over the year based on their weather-related characteristics. That means – a day is a wintry day not because it's winter now (a fixed time window during the year or "the season") but because it has the features of a wintry day.

So now that I know what the days are really like, I can look back 50 years in to the past and reveal a new and more interesting view of our weather. Here is the first glimpse of it:  

In the following chart you see how days were distributes over the years based on their actual seasonal characteristics. And the somewhat disturbing true is obvious to the eye.

We're in the center of Israel and what we see is that the percentage of summer days in every year moved up from around 35% (until the early 90') to more then 40% of the year (i.e. from 127 days to 153 days a year) and wintry days, which were at their pick in the mid 80' around 30% of the year (109 days) are consistently dropping since then and are below 20% (~70 days) of the year during the last 10 years or so.

People who live in central Israel say that "we are not buying coats to our kids any more". It's not because summer are warmer but because winters are, well, not as wintery as we remember from our days as young kinds in the country.

In the next article we'll talk about measuring the actual length of seasons and see how climate changed our seasons, moving to 3 or even 2.5 seasons' world (at least to us in this small corner of the world).

Tsahi