Wednesday, December 04, 2013

Let's Stop Comparing Global Warming to the Hiroshima Bomb

Skeptical Science has a widget that claims to show how much additional heat is being trapped on the Earth by anthropogenic factors: 4 Hiroshima bombs per second, or 4 Hiros/s.

The Hiro is an useful energy unit when discussing global warming, and I've certainly used it in the past, but a recent mailing list post I read has convinced me it's unnecessarily alarmist, and probably insensitive too.

It's useful because an energy imbalance of 1 W/m2 over the Earth's entire surface = 8.1 Hiros/second -- the yield of the Hiroshima bomb being 63 terajoules (TJ), or 15 kilotons of TNT.

But a couple of months ago, Alan Robock, who's done a lot of work on nuclear winter scenarios, wrote on a geoengineering mailing list:
I think this is a terrible comparison to make and should not be used.  I heard someone this summer who was trained by Al Gore use this and she did not distinguish between all the effects of atomic bombs and the energy equivalent of the atomic explosions.

Equating nuclear war and global warming is a false comparison.  Nuclear war is a much worse fate for our planet, and is a scare tactic.  The number is correct (I did the calculation myself when I first heard of this), but trapping energy has completely different effects from dropping nuclear bombs on people.  Using this is distracting, sensational, and easy to refute if the speaker does not carefully explain that it is the energy released by the bombs, with no other effects including radioactivity, fires, and blast.

I told John Cook this at the AGU Chapman Conference on Climate Communication this summer, and he said he would consider this recommendation, but I don't know if he plans to continue to feature this idea on Skeptical Science.

But see for another point of view.
He convinced me: the "Hiro" is inappropriate -- a scare tactic. And a false equivalence that neither captures the essence of global warming (since the energy is spread over the entire planet and not just a city), nor captures or respects the tragedy of the bombs dropped on Japan.

As someone who in his late twenties often had nightmares about nuclear war and woke up screaming (much to the fright of a few girlfriends), and who when younger thought there would certainly be a global nuclear war in my lifetime, I'm not going to use the "Hiro" any more.

So what is a better unit? I asked Alan via the list, and he responded:
I think an array of incandescent light bulbs around the world would work much better.  If you have 100 W bulbs, and want to model an imbalance at the surface of 1 W/m2, then you will need one light bulb every 100 m2, multiplied by 1 over the fraction of energy emitted by each bulb that is heat rather than light.  Light bulbs in an array separated by 5-10 m on a side would not perhaps seem dramatic, but if you would zoom out and see them everywhere on Earth, it could be.
It isn't as dramatic, which underscores the point: the "Hiro" is used for its incendiary nature, purposely trying to elicit fear. While global warming is, in some sense, scary, it's sloooooooow long-term scary, unfolding over decades, centuries, and millennia, and not wake-up-screaming scary.

Another option is to compare it to sunlight. At the top of its atmosphere, the Earth receives 1,376.6 W/m2 from the Sun, or 2,768 Hiros/second (as the Earth's intercepting area is only πR2). So global warming's 4 Hiros/second is equivalent to 0.1% more sunlight at the TOA.

Or, an energy imbalance of 4 Hiros/s is, over an entire year, an extra 8 billion terajoules, or 13 extra hours of sunlight at the TOA. That sounds impressive, but not in the way something terrifying is impressive.

Or, 4 Hiros/s = 252 terawatts, or about 14 times the power consumption of the entire Earth.


John Fleck said...

Alex Wellerstein has written a handy "Hiroshima-equivalents" calculator that shows the absurdity of the measure. My favorite: Bic Macs. Maybe we need to translate global warming into Big Macs?

Anonymous said...

Dr Warren Pearce a social scientist at Nottingham University, wrote an article about the Hiroshima bomb framing, thinking it problematic a few months back..

Both John Cook and Dana Nucittelli joined in, in the comments. It looks like they took nothing on board.

Anonymous said...

Back in August Dr Paul Matthews (or is it Prof) made this comment, about an earlier reaction.. (from Warren's articles comments)

Paul Matthews -
"As far as I can see, it started with an article in the Sydney Morning Herald, which incorrectly attributed it to ‘climate scientists’, when in fact it came from Mr Cook.

Here’s a selection of tweets about it from climate scientists, that can be added to the opinion of Victor above.

Andreas Schmittner ‏@ASchmittner These are the sort of catastrophic messages I don’t
like. Just don’t compare climate change to A-bombs, will you? Its not!

Doug McNeall ‏@dougmcneall Comparing climate change to A-bombs like this is utterly

O. Bothe ‏@geschichtenpost Dear scientists, we don’t have to use big scary metaphors “to market”
research, really, that’s not necessary (and reduces trust? oops.)

O. Bothe ‏@geschichtenpost framing as A-bombs is much too emotionally loaded

As I think I have said before, cheerleaders like Dana and John damage the credibility of climate science and give fuel to the sceptics." - Paul Matthews

Unknown said...

Hi David,
I completely agree. I also suggested the 'half day energy per year' metric on twitter.

which I also think is much better.

Dana and John still maintain that Hiroshimas are a good visualisation, no matter how many people say otherwise.


Paul S said...

"Hiroshima bombs" is a very common quantitative reference used in popular science communication. I've heard it frequently with regards the energy involved in earthquakes, volcanoes and recently Typhoon Haiyan.

I'm not sure how much people really take from this. I guess the idea is that it's a well-known reference for something which was very powerful, so the comparison emphasises a massive abundance of energy.

People have tabled some minor scientific rationales for rejecting the use of this comparison with global warming, but the main objections appear to about sensitivity and perception of alarmism. Yet I've never seen such an objection raised when the same metric has been applied to other phenomena.

Is the desire for sensitivity and moderation in this particular case due to unease about us being the cause?

Vinny Burgoo said...

The extra heat retained each second is enough to heat every house in the UK for a day. Probably. I have thrown away the calculation. It might even be a week.

Useful? Probably not.

Dano said...

I understand the need for it, but I can't think of what would replace it to be more useful.

It shouldn't be replaced because some denialist had a sad.



David Appell said...

Dano, except Alan Robock is hardly a denier. Moreso, he's studied the effects of nuclear bombs far more than most.

I just can't see how equating global warming so far to 2 billion Hiroshima bombs is in any way a useful comparison.

Dano said...

David, I'm just agreeing with the need for a good visual for understanding.

I just don't know what the visual would be - a billion puppy-tail wags? A trillion cellphone angry bird games?



citizenschallenge said...

Seems to me,
considering the inaction of our political and business leaders.
And considering the dedication of 'climate science denialists' to focus on increasing misunderstanding and divisiveness rather than any sort of sincere learning process.

The future that is barreling down on us *unopposed* is going to dwarf the horrors of Hiroshima. So, all this hand wringing about the naughty SkS HiroshimaBomb Widget feels meaningless.

David Appell said...

The future that is barreling down on us *unopposed* is going to dwarf the horrors of Hiroshima.

You can't be serious.

You think that in 100 or 200 or 300 years the planet is going to be the site of utter destruction (of EVERYTHING) with the death of about 1/3rd of the people on the planet (the percentage who died in Hiroshima)?

Jon said...

You think that in 100 or 200 or 300 years the planet is going to be the site of utter destruction (of EVERYTHING) with the death of about 1/3rd of the people on the planet (the percentage who died in Hiroshima)?

1/3 of global population 100 or 200 or 300 years from now would be many more deaths (unless something other than global warming substantially depopulates the planet first) than died at Hiroshima due to the bomb. Even 1/1000 of current global population would be many more than died at Hiroshima. And presumably if natural disasters or famine kill that many (which certainly doesn't strike me as unreasonable in a scenario of severe future warming), a large fraction of the other 999/1000 would be suffering considerable hardship. I fail to understand why you apparently think dwarfing the horrors of Hiroshima can't be merely a matter of much larger absolute amounts of death and suffering. A hurricane many not be as intense as a tornado per unit area but nevertheless, the energy content of a hurricane dwarfs that of a tornado.