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FactCheck: Was damage to the ozone layer caused by nuclear testing?

Independent TD Danny Healy-Rae made the extraordinary claim during a debate on climate change last week.


THE DÁIL RATIFIED the Paris Agreement on climate change last Thursday, but not before some lively debate by TDs on all sides.

In particular, Independent deputy Danny Healy-Rae made some extraordinary statements about the causes of climate change and damage to the ozone layer, claiming:

It was nuclear testing.

(Send your FactCheck requests to factcheck@thejournal.ie, tweet @TJ_FactCheck, or send us a DM).

Claim: Nuclear testing, not emissions from human activity, caused ozone depletion
Verdict: FALSE

What was said:

Source: TheJournal.ie/YouTube

You can watch a video of Healy-Rae’s claims, above.

Our focus is on these statements:

They told us about the ozone layer, that it was greenhouse gases and that it was cans of hairspray or whatever. But they never told us that it was nuclear testing.
…They never told us that nuclear testing in the pacific ocean, 50 years ago, actually caused the serious damage to the ozone layer.
Thankfully now, it’s mending and it’s curing and it’s not anything to do with policies in any countries in recent times, but the damage was caused by nuclear testing in the pacific ocean.


The Basics

  • Ozone layer – a region of the earth’s stratosphere containing a high density of a gas called ozone (O3), which absorbs some UV (ultraviolet) light from the sun, and protects life on the planet
  • Stratosphere – the second layer of the earth’s atmosphere, between 10 and 50 km (6 and 30 miles) above the earth’s surface

According to the EPA – the US federal government’s Environmental Protection Agency – and a joint report produced by NOAA, NASA, the European Commission, the UN and the World Meteorological Organisation, the ozone layer is, in brief, damaged in the following way:

  • Two chemical elements called chlorine (Cl) and bromine (Br) destroy ozone when they contact it in the stratosphere
  • Chemical compounds that release chlorine and bromine into the atmosphere therefore contribute to ozone depletion, and are known as “halogen source gases
  • Some halogen source gases occur naturally, but a large subset of them are caused by human activity – these are known as “ozone-depleting substances” (ODS)
  • Halogen source gases are released into the air near the earth’s surface and accumulate
  • They are then transported beyond the troposphere (the closest layer of the atmosphere to the earth’s surface, and what we all live in) and upwards into the stratosphere
  • A chemical reaction between the chlorine and bromine in halogen sources gases, and ozone, causes the destruction of the ozone, and the depletion of the ozone layer


OZONE_D2016-10-30_G^348X348.IOMI_PAURA_V8F_MGEOS5FP_LSH The ozone layer over the Antarctic on Sunday 30 October. Blue indicates the least ozone, while green and yellow indicate the most. Source: NASA


Natural ecosystems on land and in the oceans contribute to the halogen source gases that enter the stratosphere.

According to NOAA, in 2012 natural sources accounted for 17% of chlorine and 30% of bromine in the stratosphere, where the depletion of the ozone layer occurs.

Cycles in solar radiation also cause temporary changes in the ozone layer, but not long term, progressive depletion.

Similarly, volcanic eruptions can have a very small but measurable impact on ozone levels.


Some of the major ODS (ozone-depleting substances) which release chlorine are: hydrochlorofluorocarbons (HCFCs), carbon tetrachloride and methyl chloroform.

Of all ODS, the one with the most damaging impact on the ozone layer is chlorofluorocarbons (CFCs).

Some of the ODS which release bromine include halons and methyl bromide.

Many of these ODS are (or were historically) used in fridges, freezers, ice machines, air conditioners, water coolers, aerosol products, fire extinguishers, insulation and pipe covers.

The landmark 1987 Montreal Protocol, a treaty signed by every UN member state, defined the nature and causes of ozone depletion, and listed specific ODS to be phased out of use throughout the world, which you can find here.

Nuclear testing

The only thing we haven’t mentioned so far is what Danny Healy-Rae pointed to as the true cause of ozone depletion – nuclear tests in the Pacific Ocean.

It is not mentioned as a cause by NOAA, the UN, NASA, the World Meteorological Organisation, European Commission, nor the EPA, nor anywhere in the Montreal Protocol, which is akin to the Bible of ozone depletion reversal.

In response to our queries, NOAA told FactCheck:

Nuclear testing is not the cause of the ozone layer depletion we have experienced….Human emissions of long-lived chlorine and bromine compounds, including CFCs and halons, have led to the observed ozone depletion.

FactCheck asked Danny Healy-Rae for evidence to support his claim, but he did not respond.

However, there is at least some scientific research on this issue, though relatively little.

Studies on a possible nuclear link

Nuclear 09 Test Ban II The aftermath of a nuclear bomb test in Nevada in 1952. Source: AP/Press Association Images

One major study in 1975 analysed the possible effects of the 1961-1962 series of nuclear tests by the US and Russian governments, and a 1970 test by France.

The theory with nuclear testing is that it produces nitrous oxide, which is an ozone-depleting substance.

The 1975 study observed an association between the nuclear tests and a very small depletion in ozone (a few percent), but crucially found that that depletion “lies within the probable error of available ozone measurements”.

Which is to say, it wasn’t statistically significant.

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An earlier significant study, in 1973, speculated that the 5% increase in ozone between 1963 and 1970 may have been caused by the cessation of nuclear testing in 1962.

However, this is obviously speculation rather than positive proof, and it was challenged by yet another study in 1976, which looked for an effect on ozone depletion from nuclear testing and concluded “there is little evidence of such an effect”.

Finally, a high-profile 2008 study used scientific models to predict massive depletion of the ozone layer in the event of a nuclear war.

This is clearly an entirely different scenario to the occasional nuclear testing pointed to by Danny Healy-Rae – the study based its conclusions on a war involving 100 nuclear explosions, each with the force of the bomb that destroyed Hiroshima at the end of World War II.

And secondly, it’s also ultimately speculation.


Sequence 22.00_00_19_02.Still001 Source: Oireachtas.ie

There is some evidence which suggests a possible very small correlation between nuclear testing in the 1960s and ozone levels at that time.

However, there is no evidence that nuclear testing played a role in the progressive, long-term depletion of the ozone layer which was observed from the early 1980s until around five years ago, when a recovery began.

On the other hand, there is abundant evidence that exponentially increased ozone depletion during that period was caused by human commercial and industrial products emitting ozone-depleting substances.

And despite Danny Healy-Rae’s somewhat mocking reference, this includes products such as hairspray.

Healy-Rae’s claim was that ozone depletion was caused by nuclear testing, and that it was not caused by human emissions of gases.

We rate this claim FALSE.

TheJournal.ie’s FactCheck is a signatory to the International Fact-Checking Network’s Code of Principles. You can read it here.

For information on how FactCheck works, what the verdicts mean, and how you can take part, check out our Reader’s Guide here

About the author:

Dan MacGuill

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