Atomic Tea

There is at least one complaint made by my climate denialism curious friend, JP, that is valid.  Some elements of the media are guilty of catastrophising.

 

I can understand why they do it, to a certain extent – they are selling papers, or magazines, or advertising airtime, or clicks, or eyeballs, or bums on seats etc etc.  The complete and accurate truth is, in at least one sense, not primary.  If the complete and accurate truth got them the outcome there are after, then they would be all for it, but still only as a means to an end, not as the end itself.  Even non-commercial media has to report viewer numbers, or levels of engagement, making them more and more like the commercial outlets with their click-baity headlines and sensational content.

 

The most recent example that I have read, at time of writing, is a piece by the Australian ABC, talking about how bad 2020 was.  I think we call all agree that 2020 was pretty bad but this article was focussed on something that has not been foremost in our concerns for a while – the climate.  The climate is still there, even if it’s largely outside and many of us have been locked inside more than usual.  And it’s still on a bit of a slide.

 

The article in question did highlight something of considerable concern, namely that the “world's oceans absorbed 20 sextillion joules of heat due to climate change in 2020 and warmed to record levels” (referencing a paper that has “temperature” in the title, but not so much in the text).  For context, it’s worth considering what NOAA have to report.  They talk about this in terms of a “heat content anomaly” measured against the average for the period 1955-2006 in the top 700m of (ocean) water:

Note that a sextillion (or zetta) is 10²¹, so don’t let the fact that this is sitting just under 20x10²² confuse you.  Things are a little more clear in another chart (lower on the same page).

It does seem like 20 zettajoules in a year is a bit of a spike, but there are ups and downs, so we really should be thinking about the trend, which is a bit over 160/27 = ~6 zettajoules per year.  Still not great.

 

The most egregious statement, in my view, is that 20 zettajoules is equivalent to the release of 10 Hiroshima grade atomic bombs each second.  That’s more than 300 million bombs, or slightly over two bombs for every square kilometre of land surface on the planet which, even if it happened only once in a year, would be enough to make that a worse year than 2020.

 

(For those keeping score, the Hiroshima bomb, “Little Boy”, is calculated to have released between 50 and 75 terajoules.  If we say it was 63 terajoules [15 kilotons], then you would indeed need very close to 10 bombs per second for a year to reach 20 zettajoules.)

 

It’s very scary to think of so many atomic bombs going off and one could well imagine that this was intention of the writer.  It’s also probably pretty scary to imagine that amount of energy being added to the oceans, since it’s the heat in oceans that cause the sort of storms that can do so much damage to coastal regions and it’s simple to imagine that more energy equals either more storms or stronger storms (or perhaps both).  Whether there is such a simple link? … perhaps, perhaps not.  Oil extraction companies have upgraded their drilling platforms, so perhaps they think there might be.

 

I wondered, however, how much energy we expend each year on hot drinks?  To make it easier, I am going to limit it to tea and assume that for tea, one boils fresh water from room temperature (293K) to boiling (373K) without markedly affecting the density of said water.  I am also going to assume one drinks from a standard cup at 0.24 litres.  So, a litre of fresh water weighs one kilogram and the heat capacity of water is 4.2kJ per kg per K.  Conveniently, this is very close to 1kJ per cup of water per K and since the temperature difference is 80K, we expend 80kJ on boiling water for each cup of tea (assuming no wastage).

 

The question then is how many cups of tea do we, as humans, drink?  World Tea News (yes, there is such a thing) has the answer, conveniently in terms of cups per second – 25,000 cups.  That means that we expend about 2 million kilojoules per second on tea.  This is somewhat short of a sextillion, but we are thinking in terms of Hiroshima grade atomic bombs, each at 63 terajoules.   A terajoule is 10¹² joules, so one bomb is equivalent to 31437 seconds of tea preparation, which is one bomb every 8.7 hours, or very close to 1,000 bombs a year.

 

I am reasonably certain that the average English person would be willing to accept 1,000 bombs a year in order to have a good cup of tea.  What, on the other hand, would be patently ridiculous is to express the energy used to prepare tea in terms of atomic bombs.  I have a nagging feeling that the same applies to the amount of energy absorbed by the oceans.

 

Perhaps the author of the article (and the original paper) could have assisted by expressing the temperature change that would be caused by the 20 zettajoules being absorbed by the oceans.  If we make some assumptions, we can get a rough idea.  The ocean surface is about 360 million square kilometres.  The paper was referring to a depth of water of 2,000 metres, but not all the ocean is that deep, and beyond a certain depth (the epipelagic zone) there really isn’t much variation in the temperature, so we could make a rough calculation using an average of 600 metres depth, which is in the middle of the mesopelagic zone, so we have an ocean volume of 2.17x10¹⁷ m³ and given that there are 1000 litres in a cubic metre and it takes 3850J to raise a litre of seawater by 1K, that’s about 0.024K a year or 0.24 degrees per decade.  Note that this is very rough calculation, but it’s in the same order as what NOAA are reporting (at climate.gov) where they say that temperatures have been rising at 0.18 degrees per decade since 1981.  If we use 800m, which is towards the bottom of the mesopelagic zone, the result is very close to 0.18K per decade.  I doubt that that figure is right though, since that’s the average since 1981, and today’s figure is likely to be higher (although maybe not as much as a full third higher).

 

If anyone knows what the actual average temperature increase of the ocean was, please let me know.  Looking at the heat content chart (1955 through to 2020) overlaid on the temperature chart (1880 through to 2016), it looks like it’s probably gone up: