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March Blizzard

Warming/cooling trends by month?

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We have seen a general warming trend in the CET series, especially so when you compare the long term average (1659-2012) to the most recent (1981-2010).

 

1659-2012 Average CET:

 

Jan:   3.2C

Feb:   3.9C

Mar:   5.3C

Apr: 7.9C

May: 11.2C

Jun:   14.3C

Jul:  16.0C

Aug:   15.6C

Sep:   13.3C

Oct: 9.7C

Nov:   6.1C

Dec: 4.1C

 

1981-2010 Average CET, with difference highlighted afterwards:

 

Jan:   4.4C +1.2C

Feb:   4.4C +0.5C

Mar:   6.6C +1.3C

Apr: 8.5C   +0.6C

May:  11.7C   +0.5C

Jun:   14.5C   +0.2C

Jul:  16.7C   +0.7C

Aug:   16.4C  +0.8C

Sep:   14.0C   +0.7C

Oct: 10.7C +1.0C

Nov:   7.1C +1.0C

Dec: 4.6C   +0.5C

 

The above shows that all months are warmer in the latest 30 year average compared to the overall one. The middle 6 "warmer" months (Apr thru Sep) have all warmed by less than 1C, whereas the other 6 "colder" months (Oct thru Mar) have seen an overall stronger warming.

 

I wondered if this could be attributed, in part, to the natural variability of a month i.e. the difference between the coldest and warmest monthly CET figures:

 

Jan: 10.6C (-3.1C to 7.5C)

Feb: 9.8C  (-1.9C to 7.9C) 

Mar: 8.2C  (1.0C to 9.2C)

Apr: 7.1C (4.7C to 11.8C)

May:  6.6C (8.5C to 15.1C)

Jun: 6.7C (11.5C to 18.2C)

Jul:   6.3C (13.4C to 19.7C)

Aug:  6.3C (12.9C to 19.2C)

Sep:  6.3C (10.5C to 16.8C)

Oct: 8.0C (5.3C to 13.3C)

Nov:  7.8C (2.3C to 10.1C)

Dec:  8.9C (-0.8C to 8.1C)

 

As you can see, the warmer middle months are less variable than the colder months, which generally see a greater disparity in temperatures in any given year to another. It appears that there is some kind of link between how variable a month is and it's tendency to show a warming (or cooling) trend from one rolling average to the next.

 

An example of this "cold month" variability is evidenced by the fact December has seen a 0.5C drop in temperature from the 1971-2000 to 1981-2010 average (5.1C to 4.6C). Similarly, March has seen a massive 0.9C rise between the 1961-1990 to 1981-2010 averages. (5.7C to 6.6C).

 

When looking at trends, do the more "reliable" and consistent middle months paint a truer picture than the other more "volatile" months?

As you can see, this is far from scientific. Just wondering what your take is on it?

Edited by March Blizzard

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If we look at the CET warming trends since 1659, we get the following (in degress celsius/century)

 

Posted Image

 

 

Winter (Oct-March) warming rate = +0.37C/century

Summer (Apr-Sept) warming rate = +0.15C/century

 

 

While 1850 to 2013 gives this

Posted Image

 

Winter (Oct-March) warming rate = +0.73C/century

Summer (Apr-Sept) warming rate = +0.50C/century

 

 

I could offer a possible partial explanation, but it does involve CO2 and thus the associated risk of this thread descending into chaos...

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If we look at the CET warming trends since 1659, we get the following (in degress celsius/century)

 

Posted Image

 

 

Winter (Oct-March) warming rate = +0.37C/century

Summer (Apr-Sept) warming rate = +0.15C/century

 

 

While 1850 to 2013 gives this

Posted Image

 

Winter (Oct-March) warming rate = +0.73C/century

Summer (Apr-Sept) warming rate = +0.50C/century

 

 

I could offer a possible partial explanation, but it does involve CO2 and thus the associated risk of this thread descending into chaos...

 

Thanks for the reply, BFTV.

 

I'd be interested to hear your partial explanation, although I understand your reservations.

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I really do apologise if this ends up ruining the thread!

 

Basically, during daylight hours, the surface is warmed largely by visible shortwave light. In the night, it cools by releasing longwave light or heat. Greenhouse gasses (GHGs) absorb some of this heat, and re-radiate it back to the surface, thus slowing the cooling and preventing us from freezing solid each time the sun sets. This is why humid tropical areas see little temperature variation (lots of water vapour preventing nights from cooling much) while deserts can get hot during the day and quite cool at night (very little water vapour, lots of temperature variation). As we increase the amount of GHGs, this effect will increase, causing nights to warm faster than days.

This is also expected to be a feature of summer vs winter warming rates. Cooling during winter results from an energy imbalance, causing the surface to release heat. The additional GHGs will absorb more of the heat and re-radiate it back to the surface, slowing the cooling rate. This means that while all months and seasons will continue to warm, the difference between summer and winter may become reduced overtime.

 

Of course, for a small region like the CET zone right next to an ocean, these trends can be quite variable and influence by many other factors. But increased GHGs could certainly be contributing to the long term pattern seen in the monthly warming trends.

 

Northern Hemisphere Land Surface Temperature for Summer (red) and Winter (blue)

Posted Image

Edited by BornFromTheVoid

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