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Earth's current average global temperature (i.e. including hot deserts and cold polar caps) is reported be somewhere between 14°C and 16°C (depending on sources and methods).

This temperature varies on a long-term basis due to climate change.

But does it also vary (substantially) on a daily basis ?
I.e. are there hotter and colder days (worldwide) ?
Or is it exactly the opposite, namely a zero-sum game: A hotter-than-average day in – say – Australia inevitably goes along with a colder-than-usual day somewhere else on the planet to make up for the difference, so that the global temperature stays the same from one day to the next (because energy is not created but only transferred from one region to another) ?

As an example, below are the relative temperatures (i.e. colder/hotter than expected/average) for 3 Feb 2014. Would the hotter and colder temperature regions balance out (compensate one another), so that the global temperature on 3 feb 2014 is the same as on 2 feb 2014 and 4 feb 2014 ?

3feb2014 temperature anomalies source: https://robertscribbler.com/2014/02/03/arctic-heat-in-winter-february-2-temperature-anomaly-hits-13-f-for-entire-arctic

(Please note: The image doesn't exactly illustrate my question, because it doesn't depict the air temperature difference between 3 Feb 2014 and the previous day, but between 3 Feb 2014 and the average for [3 Feb, I assume] 1979-2000. So due to global warming, 3 Feb 2014 was obviously warmer than 3 Feb in previous decades – by 0.45°C to be precise, as the sum of northern hemisphere + southern hemisphere = -0.01°C + 0.45°C = +0.45 °C. But my question is not about global warming or long term trends, but daily variations. I just couldn't find a similar heat map depicting temperature differences between one day and the next, so I just took this image for illustration purposes, although it doesn't perfectly relate to the question asked.).  
 

As Earth surface temperatures don't necessarily correspond to the air temperature (see below), please distinguish both cases in your answer, i.e.:

  • Can global average Earth surface temperature vary from one day to the next ?
  • Can global average air temperature vary from one day to the next ?

Andreas Schmittner, Oregon State University: "It is not the average temperature of Earth that is reported but the average air temperature near the surface (2 m) of the Earth."
source: researchgate.net/post/It_it_misleading_to_report_the_average_temperature_of_the_Earth

I would appreciate if your answer included both a source for your claim AND an explanation (i.e. WHY the global temperature can or cannot vary on a daily basis).

The best answer would include a diagram or table of global average air and Earth surface temperatures for any given month, since this couldn't be argued with.

Example:

+-----------+--------------------------------+----------------------+
|           | avg. global Earth surface temp | avg. global air temp |
+-----------+--------------------------------+----------------------+
| 01 Feb 14 |           15.1 °C              |       15.2 °C        |
| 02 Feb 14 |           15.1 °C              |       15.3 °C        |
| 03 Feb 14 |           15.1 °C              |       15.7 °C        |
| 04 Feb 14 |           15.1 °C              |       15.2 °C        |
| 05 Feb 14 |           15.1 °C              |       15.1 °C        |
|   ...     |            ...                 |        ...           |
+-----------+--------------------------------+----------------------+

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1 Answer 1

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The site http://www.karstenhaustein.com/climate.php comes closer to answering your main question with a daily anomaly graph:

enter image description here

Indeed it's still not the actual average temperature... and I too was really interested to see if there are annual global fluctuations in global mean temperature itself. (Surprising how much focus is on anomalies, but how little most sites note the mean temperature itself.) But eventually I found NOAA's monthly global climate reports, and was able to piece together the combined "globally averaged temperature over land and ocean surfaces" for each month and put together this graph:

enter image description here

(One trouble to point out in global totals such as these is that they require the whole globe... so observation of the full far reaches... but we still have a somewhat limited surface observation networks in spots, and each satellite can only see a portion of the globe at one time [and even more, geostationary satellites can't see the Poles], and then all of it is put together by varying data assimilation methods, so there will be some limitations\variation in any global estimates of it [as you can see later down that Karsten Haustein's page in the section comparing CFSR-GFS, NCEP reanalysis, and GISS temperature results])

But Karsten's graph above and all the other plots from their site are useful in showing that in real-time and in the past that there are definitely some real oscillations day-to-day... but also that there is indeed quite a bit of overall stability, whereby large regions of hot temperatures will tend to be balanced quite a bit by reduced temperatures elsewhere.

This conceptually would seem to make sense to me, as in the end the guiding framework would be that the energy put into the Earth system (by solar radiation) must equal the energy coming out in the long run. (related example: if you put your food in the oven, it takes in some of the energy, radiating less than it receives, and thereby gaining temperature until it gets up to temp).
That balance in itself wouldn't prevent fluctuations in the radiating temperature/energy sent out to space.

This is one reason I should expect the global average temperature as a whole does shift some through the year: because water changes temperature more slowly than land, and the NH and SH have different coverage, there should probably be differences/lag in temperature and energy absorption/emission depending upon which portion of the Earth is receiving more sunlight. Additionally, while the sun's energy is very constant, and the tilt only changes which region receives the energy but not the total amount incoming, there will actually be some overall change in how much energy we get into the lower parts of the atmosphere/to Earth's surface globally day-to-day and over longer periods due to variation in how much snow, cloud cover, and aerosols absorb/reflect some of the energy before reaching to near the surface.

Overall, it seems it would make sense to see a global peak in July (NH summer), when both: more of the "warm Hemisphere" that is receiving increased energy is land to heat faster... and less of the "cold Hemisphere" is land prone to being temporarily covered with very reflective snow.

When it comes to any specific layers within the Earth system, be it the surface ground/water, or the atmosphere at 2 meters above the ground, or any other height for that matter, except at depth inside the Earth (which is insulated from those surface energy changes) I'd expect the answer would likely be the same: there is some fluctuation both daily and seasonally. It's indeed not a zero-sum game because of the variations in the makeup of the globe. But because the overriding principle is net energy balance of the Earth, those daily/seasonal changes are likely kept to a few degrees tenths of a degree in the short-term and a few degrees Celsius innerannually.
The ground/ocean are the primary heat source of air near the ground (air itself doesn't absorb much solar energy). So generally fluctuations in global average air temperature (at 2 meters) should connect very well to changes in global average near-surface ground/water temperatures... though differences in heat capacity and absorption spectra between air/soil/water/etc likely cause the sizes to be different, and probably small differences in the synchronization as well. But overall, they should have very similar patterns?

But the average anomalies they compute for the globe do their best to take a true global area average it appears. And while it's true that the same temperature of different substances equates to different amounts of stored energy, I believe radiatively those varying substances would still be emitting the same amount of energy at equal temperatures, so such global averages and anomalies of temperatures do have some fair use... and of course are very important to us.

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  • $\begingroup$ I thought your graph does indeed answer the question. Why is the black line ("global") in your first image "still not the actual average temperature" ? $\endgroup$
    – summerrain
    Mar 8 at 22:54
  • $\begingroup$ I would have expected cloud cover to play a significant role in daily global temperature oscillation. $\endgroup$
    – summerrain
    Mar 8 at 22:57

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