Conveying abstract or hard-to-visualize ideas is always a challenge. That’s a core reason why the best communicators have always used metaphors.

As Aristotle wrote in his classic work Poetics, “the greatest thing by far is to be a master of metaphor.”

How can one convey the Earth’s staggering rate of heat build up from human-caused global warming — 250 trillion Watts (Joules per second)? The analogy to the energy released by the Hiroshima bomb has been used in recent years by a number of scientists, such as NOAA oceanographer John Lyman and Mike Sandiford, Director of the Melbourne Energy Institute. In his TED talk Climatologist James Hansen explained the current rate of increase in global warming is: “… equivalent to exploding 400,000 Hiroshima atomic bombs per day, 365 days per year. That’s how much extra energy Earth is gaining each day.”

That comes out to more than four Hiroshima bombs, which is a metric Skeptical Science has turned into a widget. I prefer the 400,000 Hiroshimas per day metric simply because the heat imbalance is occurring over a very large area, which four Hiroshimas don’t do justice to.

The deniers don’t like the metaphor because, they assert, it is inexact and sensationalistic. But the deniers don’t like the literal facts because they think those are inexact and sensationalistic, too, so we can safely ignore them.

Some climate scientists disagree with those scientists (and others) who use this metric “because climate change is nothing like atom bombs” and “my problem is that the association of death and destruction is also easy to grasp,” as Dr. Doug McNeal of the UK Met Office has tweeted.

Metaphors are not literal — by design — so if you don’t like non-literal comparisons, you won’t like metaphors. I have argued at great length that one of the major failings of science communication is the failure to use figurative language. For what it’s worth, Aristotle believed, “To be a master of metaphor is a sign of genius, since a good metaphor implies intuitive perception of the similarity in dissimilars.”

So I’ve been delighted to see scientists start to use metaphors, such as analogizing the effect of greenhouse gases on extreme weather, by saying it’s like the climate on steroids. But of course the climate isn’t literally on steroids. It is figuratively on steroids. It is literally on CO2, which is much worse.

Abraham Lincoln was a master of metaphors. He famously said of a nation split by slavery that, “A house divided against itself cannot stand.” But, of course, he was literally wrong: You could turn it into a duplex.

Ironically, a metaphor is the source of some of the most common terms in climate science: the greenhouse effect and greenhouse gases. And yet at least one expert has argued that the metaphor is fatally flawed: “By producing an illusion that the climate system will respond instantly at the moment when CO2 level is reduced, the greenhouse metaphor is ultimately responsible for the wait-and-see approach to climate change.”

So it is certainly the case that “Metaphors are double-edge swords,” which this amazing 1962 ad for Humble Oil makes clear:

Humble oil ad copy 


Yes, Humble Oil (which later consolidated with Standard and became Exxon) touted oil’s ability to melt glaciers!



Ultimately, metaphors need to be judged for whether they bring more light than heat, as it were.

In my quarter century communicating on climate change, I’ve found that many people in the media and the public have a visceral belief that “Humans are too insignificant to affect global climate.”

The anti-science CNBC anchor Joe Kernen voiced this conviction when he suggested that “as old as the planet is” there is no way “puny, gnawing little humans” could change the climate in “70 years.”

Certainly humans do seem tiny compared to the oceans or even a superstorm like Sandy. So I don’t see anything wrong with trying to find a quantitatively accurate metaphor that puts things in perspective.

The assertion that “climate change is nothing like atom bombs” isn’t quite true. Like global warming, atom bombs deliver a vast amount of energy in a very short period of time, which is the primary point of the metaphor. Indeed, when the first nuclear explosion in history occurred in July 1945, one observer said the fireball “rose from the desert like a second sun.” Also, climate change and atoms bombs are manmade — and highly destructive (more on that shortly). Like Frankenstein’s monster, both have become symbols of how our mastery of science and technology has had unintended consequences. The scientific community issued warning after warning about the dangers of both an unrestricted nuclear arms race and unrestricted CO2 emissions — warnings that were largely ignored for decades.

So it is a pretty good metaphor. Yes, the Hiroshima bomb has an element that goes beyond most nuclear bombs because it was dropped on a city and killed some 100,000 people. But is the metaphor flawed because “the association of death and destruction is also easy to grasp”?

Well, one of the whole points of the metaphor is that “puny humans” can in fact inflict catastrophic damage through human-caused global warming. On our current emissions path, Sandy-type storm surges will be an every year phenomenon for the New Jersey coast in a half-century! And then we have the warning of Harold Wanless, chair of University of Miami’s geological sciences: “Miami, as we know it today, is doomed. It’s not a question of if. It’s a question of when.”

Like the Hiroshima bomb, global warming is capable of destroying cities. So the “association of destruction” of the metaphor isn’t a bug, it’s a feature, as they say. Assuming we don’t end our self-destructive carbon feeding frenzy anytime soon, I do not think future generations will think this aspect of the metaphor is flawed in the least bit.

That leaves “the association of death” and all its implications. Hiroshima killed some 100,000 people in a flash. That is, arguably, the most problematic aspect of the metaphor. And if you are speaking to an audience you think might be sensitive to that, for instance, if you are speaking in Japan, you might want to use a different metaphor or at least be especially clear you are just talking about the energy released.

That said, while global warming doesn’t kill tens of thousands of people in a flash, it is on track to reduce the carrying capacity of the planet post-2050 far below the 9 billion people that we are projected to have. Again, where we are headed, I doubt future generations will think this aspect of the metaphor was somehow morally inappropriate. It’ll be our inaction — and everyone and everything that fed our inaction — that will be seen as morally inappropriate.

I do understand metaphors are not for everyone, but I do think that they are the perhaps the defining figure of speech of history’s greatest communicators. And as metaphors go, the Hiroshima bomb one seems to be better than most.

Last week, Skeptical Science reported that “Previous estimates put the amount of heat accumulated by the world’s oceans over the past decade equivalent to about four Hiroshima atomic bomb detonations per second, on average, but [Dr. Kevin] Trenberth’s research puts the estimate equivalent to more than six detonations per second.”

Skeptical Science’s John Cook reported at the American Geophysical Union (AGU) fall meeting, “For those who prefer a cuddlier comparison, Cook converted this to units of kitten sneezes — 7.4 quadrillion per second.” If Trenberth’s new paper is right, that is actually more than 10 quadrillion kitten sneezes per second.

Finally, the kitten metaphor brings us to some advice offered by a student of climate communications. She offers seven things that worked for her. Here are two of them:

Making jokes. Climate change is perceived as a serious, heavy, difficult topic. Which it can be — but that doesn’t mean that talking about it needs to be serious, heavy and difficult. Making appropriate, engaging jokes made people laugh and then think about whatever they were laughing about. It made the topic more accessible. They don’t have to be full jokes — just point out one of the many weird, quirky things that go on in the climate and alpine environments…

Metaphors. To explain how a glacier worked, I used the example of a glacier as a savings account. And And how rising temperatures and decreased snow pack affects the balance of the savings account. One of the most powerful climate-metaphors that Simon taught us is the extreme weather, steroids and baseball one.

Aristotle would be proud.


This Commentary was originally published on Climate Progress, 22 Dec 2013, with live links to all sources, at


Joe Romm, “The greatest thing by far is to be a master of metaphor”: How to be as persuasive as Lincoln, Part 3,  think progress (18 Feb 2009).

James Hansen: Why I must speak out about climate change

“4 Hiroshima bombs per second: a widget to raise awareness about global warming,” Skeptical Science (25 Nov 2013).

Joseph J Romm, Language Intelligence: Lessons on persuasion from Jesus, Shakespeare, Lincoln, and Lady Gaga (Kindle Book)

Must-See Video: Steroids, Baseball and Climate Change think progress (8 Feb 2012).

Xiang Chen, “The Greenhouse Metaphor and the Greenhouse Effect: A Case Study of a Flawed Analogous Model,” Springer (2012).

Joe Romm, “Uber-ironic 1962 ad touts oil’s ability to melt glaciers!”  think progress (19 Nov 2009).

“Are humans too insignificant to affect global climate?” Skeptical Science (26 Aug 2010).

Judd Legum, “CNBC Anchor Argues ‘Puny, Gnawing Little Humans’ Can’t Change The Climate” think progress (26 June 2006).

Joe Romm, “NOAA: Warming-Driven Sea Level Rise To Make Sandy-Type Storm Surges The Norm On East Coast,” think progress (5 Sept 2013).

Joe Romm, “Scientist: ‘Miami, As We Know It Today, Is Doomed. It’s Not A Question Of If. It’s A Question Of When.’” think progress (23 June 2013).

“Global warming is unpaused and stuck on fast forward, new research shows,” Skeptical Science (10 Dec 2013).

“In pictures: cutting edge climate science, communication, and kittens from the 2013 AGU conference,” Skeptical Science (17 Dec 2013).

Meghan Beamish, “Talking climate in the Canadian Rockies,” Maribo Blog (15 Dec 2013).




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