Advancing the Clocks

On the early hours of Sunday 14 March 2021, most of the United States will put their clocks forward an hour and Daylight Saving Time (DST) will commence.

Two weeks later on 28 March most countries in Europe (including the UK) will follow, switching to  summer time. In this post I’ll talk about the practice of advancing our clocks by an hour during the spring and summer months and why it may be coming to an end.


The Early years of DST

The first place in the world to practise DST was the town of Port Arthur, Ontario. In 1908, a local businessman, John Hewitson petitioned the town council to adjust the clocks one hour forward in the summer months so the locals could enjoy an extra hour of summer sunshine. The council agreed and the town moved its clocks ahead one hour from May to September.

DST became established in Europe and North America during the first world war. The first countries to adopt it were two of the Central Powers (Germany and Austria-Hungary) in April 1916, followed by many European countries later that year. The US and Canada both adopted it in 1918. The main justification for its use was that by having an extra hour of daylight in the evening, it reduced the need for energy for heating and lighting in the stretched wartime economies.

After the end of the war its use was patchy. Many European countries abandoned the practice for a period of time only to reinstate it later. In the UK, where it is called British Summer Time,  DST has been used almost continuously since 1916 with two brief exceptions.  During the years 1941 to1945 and again in 1947, the clocks were two hours ahead of UTC in spring and summer and one hour ahead in autumn and winter. As an experiment, in 1968 the  twice yearly clock changes were ablolished and the UK was in a time zone one hour ahead of UTC* all year round. were. This proved unpopular with many in the northern part of the UK and was abandoned in October 1971 when the twice-yearly clock change was reinstated. Many of my older readers who live in the UK may remember the dark mornings during  this period. On the December solstice the Sun didn’t rise in Manchester until 9:22 am

* In the UK the term Greenwich Mean Time (GMT) is often used a synonym for UTC


Pros and Cons of DST

Applying DST shifts the day.  People lose an hour of daylight in the morning and gain an hour of daylight in the evening. Advocates of DST believe that the extra hour of daylight in the evening can be put to good use – allowing people to do outdoor activities in the evening without as much need for artificial light.  People are more inclined to do exercise outdoors (e.g.  walking, running, cycling) if it is daylight outside, with beneficial consequences for their health. In contrast, the hour of daylight lost in the early morning is of little importance, as it occurs before most people have started their daily activities. For example, on 20 June 2020, the Sun rose in London at 4:43 AM and set at 9:21 PM (data from If the UK didn’t observe DST it would have risen at 3:43 AM and set at 8:21 PM.

Supporters of DST also claim it reduces energy usage for heating and lighting. Although this may have been true in the past, this benefit is now debatable. Modern fluorescent and LED lights are much more efficient than older incandescent light bulbs.  In many southern states of the US, DST causes energy consumption to rise because it is slightly warmer in the evening – increasing the energy used on air conditioning.

One disadvantage of DST is that the twice-yearly clock shifts are disruptive to sleep patterns and need to be manually applied in many clocks, watches and some central heating timers. On the day of the change there can be disturbance to plans and people can arrive an hour late or early for appointments.

Another issue is that countries which observe DST do not change their clocks at the same time. For example, New York, like most of the US, puts its clocks forward at 2 AM (local time) on the second Sunday in March and back at 2 AM (local time) on the first Sunday in November. Whereas the UK, which aligns its clock changes with the EU, put its clocks forward at 1 AM (UTC) on the last Sunday in March and back at 1 AM (UTC) on the last Sunday in October. So, although for most of the year New York is five hours behind London, there are two periods when the time difference is four hours. This can cause confusion e.g. when people try to arrange a transatlantic online meeting in either of these periods.

Another complexity is that the small number of countries in the Southern Hemisphere which use DST put their clocks forward at the start of their spring (which corresponds to the Northern Hemisphere autumn) and back at the start of their autumn (which corresponds to the Northern Hemisphere spring). If we take last year (2020) as an example and consider the time difference between Santiago, Chile and New York

  • On 5 April Chile put its by one hour when it moved into winter time.
  • On 6 September, it put  them forward by one hour when it moved to summer time.

This meant that for five months of the year Chile was on the same time as New York. For roughly four and a half months it was two hours ahead and at other times one hour ahead. A recipe for confusion.


Data from


To avoid having a  non-standard difference between two areas over a short period of time the solution would be for all countries  which use DST to coordinate their clock changes at the same time. For example:

  • On a particular day in March, all countries in the Northern Hemisphere which use DST would put their clocks forward an hour and all countries in the Southern Hemisphere which use DST would put their clocks back an hour.
  • On a particular day in September, all countries in the Northern Hemisphere which use DST would put their clocks back an hour and all countries in the Southern Hemisphere which use DST would put their clocks forward an hour.

If this were adopted, London would always be five hours ahead of New York. Santiago and New York would be on the same time zone for six months and Santiago would be two hours ahead of New York for six months.

Obviously, to do this  would require a fair amount of international cooperation. To completely eliminate short non-standard time differences, clock changes would have to occur at the same time in all countries. This creates an interesting challenge because, currently,  clock changes always occur at night to minimise disruption . For example in the EU, the clocks go forward at 1:00 AM UTC in March and back at 1:00 AM UTC  in October. If it were decided to implement the clock changes at 01:00 AM UTC worldwide then this would be during the daytime in many countries.

The gradual move away from DST

DST has been declining over the past few decades. In the map below:

  • the areas shaded in blue observe Northern Hemisphere DST
  • the areas in orange Southern Hemisphere DST
  • the areas in dark grey have never observed DST
  • the areas in light grey used to observe DST (or permanent daylight saving where the clocks are advanced by one hour all year round) but no longer do so.



Image from Wikimedia commons.


In 2011 Russia switched to permanent summer time 

This was announced amid research claiming that changing the clocks caused Russians ‘stress and illness’.  However, many Russians didn’t like the dark mornings in the winter months caused by having the clocks permanently advanced. For example, in Moscow, the Sun didn’t rise until 9:57 AM on the date of the winter solstice. So, in 2014 Russia switched to permanent winter time to bring the civil time more in step with the solar time. Belarus, which has close political and economic ties with Russia also stopped the twice-yearly clock changes in 2011, but unlike Russia remains on permanent summer time (UTC+3).

Turkey (population 85 million) abolished DST in 2018 and remains on permanent summer time.

Other populous countries which have recently abolished DST include:

  • Argentina (population 45 million) in 2009.
  • China (population 1.44 billion) in 1991.
  • Iraq (population 40 million) in 2007.
  • South Korea (population 52 million) in 1988.
  • Egypt (population 104 million) in 2014

For more details see ( )

Attempt to abandon  DST in the EU

On March 26, 2019, the European Parliament voted in favour of backing the EU Committee draft directive to stop the one-hour clock change in the European Union. This was widely reported in the press at the time e.g. and was supposed to be implemented in 2021. It followed an EU-wide public consultation in 2018 which showed 84% of respondents wanting to scrap the biannual clock changes.  However, the public consultation was poorly publicised and I, like the vast majority of EU citizens, was unaware it was taking place. In total only 4.6 million people (less than 1% of EU population) expressed an opinion.  If the proposal had been adopted each country in the EU would have to have decided whether to remain on permanent summer time or permanent winter time. However, it required agreement of all EU member states and it is unclear if it will ever be implemented

One main stumbling block was that the  abolition of DST is opposed by most people in the Republic of Ireland. Shortly after the announcement the Irish government said they would oppose the change.  The Irish objection is because the UK (which includes Northern Ireland) has no plans to abolish the twice-yearly clock changes. This would mean that, regardless of whether Ireland opted to remain on permanent winter time or permanent summer time, Northern Ireland and the Republic of Ireland would be on different time zones for approximately half the year. To many in Ireland this is unacceptable.

The  Future of DST in the USA.

At present the US has no plan to abolish DST. Although individual states are allowed to opt out and remain on permanent winter time. At the moment, Hawaii and Arizona are the only states which do so. Oddly, states are not permitted to remain on permanent year-round summer time. In 2014 a poll of around 1000 American adults found that only a minority (33%) were in favour of the clock changes, 48% were against and the remainder unsure.

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However, at the moment, there is no strong nationwide push to abolish DST and even if the majority of people are against it, I suspect abolition of DST is relatively low on their list of priorities. It will be interesting to see if this changes over the coming decades!



The term Greenwich Mean Time is no longer used by astronomers.    Instead, they use two different times which agree with each other to within 1 second.

  • Universal Time, often abbreviated to UT1, is the mean solar time, the time determined by the rising and setting of the Sun at the Greenwich Meridian, zero degrees longitude.
  • Co-ordinated Universal Time, usually abbreviated to UTC, is the time measured by atomic clocks and is kept to within 1 second of UT1 by the addition of leap seconds.

In common use, Greenwich Mean Time (GMT) is often taken to be the  same as UTC, which is the approach I have taken for this post. However, it can also be taken to mean UT1. Owing to the ambiguity of whether UTC or UT1 is meant, and because timekeeping laws usually refer to UTC, GMT is normally avoided in precise writing.

8 thoughts on “Advancing the Clocks”

    1. Yes,
      Broadly speaking I am against DST. The twice yearly clock changes are a nuisance but, to be honest, it not something I feel strongly about.

      It will interesting to see if it gets abolished in the EU over the next decade. I suspect the discussions will rumble on for a while !

      Liked by 1 person

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