The Montreal Protocol: who had stopped by 1996?

Find your issue, and check it is measured

An environmental issue: something happening, to something, because of something, with proof that somebody measures it.

CFCs released at the surface drift up to the stratosphere and destroy ozone for decades. In 1987 every country agreed to stop using them, and developing countries were given fourteen more years to do it than everybody else.

Proof it is measured

Ozone-depleting substances, country by country, opened: every party's own annual return to the UN since 1986.

In the news

UN News, 9 January 2023: nearly 99% of banned ozone-depleting substances phased out, and the ozone layer on track to recover over the Antarctic by around 2066.

The system

Input: CFCs consumed, then released. Store: chlorine in the stratosphere, for decades. Effect: less ozone, more ultraviolet at the surface, damaging DNA and phytoplankton. The treaty can act only on the input.

Write your research question

One sentence naming the indicator and its units, the years and the places. No strategy in it.

A comparison of CFC consumption in 1996, as a percentage of each party's own highest year, between Article 5 and non-Article 5 parties to the Montreal Protocol.

Independent variable

Treaty group: Article 5 (developing) or non-Article 5 (developed).

Dependent variable

1996 CFC consumption as a percentage of the country's own highest year.

Why 1996

It is the treaty's deadline for non-Article 5 parties to reach zero, not a year chosen for its answer.

Find a real-world strategy and its tensions

One real-world strategy people are genuinely arguing about, two named positions, and what the tension does.

The Montreal Protocol, and its two phase-out schedules: 1996 for developed countries, 2010 for developing ones.

The strategy

The Montreal Protocol, agreed 16 September 1987 and in force from 1 January 1989. Every party reports its consumption each year, as the treaty's Article 7 requires, and those reports are this file.

Position 1 · social, political

Maneka Gandhi, India's environment minister, at London (UPI, 30 June 1990): "You have made the mess, and now you can pay to clean it up." The countries that had caused the problem should stop first, and pay.

Position 2 · economic, political

The United States, in William Reilly's opening statement at London (June 1990): it would pay its share, on condition that the cost was limited and predictable.

The tension

Speed against getting every country to agree. With a single deadline, the countries whose CFC use was still growing would not have joined.

What it does

Delay, written into the treaty as two deadlines fourteen years apart. Uneven costs, which the Multilateral Fund was set up to meet.

For the environment

The cost of the grace period (the extra fourteen years) was more chlorine: more CFCs released into a store that holds them for decades.

Link to the question

The treaty's two deadlines are the two groups being compared, and 1996 is the first of them. The question measures what the gap between the deadlines looked like in the data.

Select and document your data

A dataset you can defend: counted, documented, and cut to a rule fixed before you looked.

Source

Consumption of ozone-depleting substances, UNEP via Our World in Data. To download it, add .csv to the end of the chart address. Downloaded 18 September 2026: 5,642 rows, 177 entities.

The grouping

Article 5 status is not in the file. The Handbook for the Montreal Protocol (12th edition) defines the two groups, and the Ozone Secretariat's list of parties says which group each country is in. Check every country: Azerbaijan and Kazakhstan are on the developed side. Cite both in the method, not only the bibliography.

Derived quantity

For each party: 1996 CFC consumption divided by its own highest year, times 100. Measuring each country against itself lets a small party like Monaco and a large one like the United States be compared in the same test.

Inclusion rule

Drop the eight aggregates (blank code or OWID_: both rules are needed). Drop Andorra, Palestine and San Marino, which have no 1996 row, and the Vatican, which never reports a positive figure.

Missing without a word

No EU member state is in the file as a country. They report through one EU row, so only eighteen of the fifty developed parties can be compared.

How the numbers were made

Each government's own report. Consumption is production plus imports minus exports, so a few values are negative. Every value is in ODP tonnes: tonnes weighted by how much ozone the chemical destroys.

Treat your data

Run a statistical test, leading to figures you built and a statistical result.

A t-test, the version that does not assume equal variances.

Why this test

A difference between two independent groups on interval data. The groups differ in spread (standard deviations 23.6 and 31.0) and in size (18 and 147), so use the unequal-variance version.

The result

Medians of 0.5% (non-Article 5) and 73.9% (Article 5). Means 11.8% and 65.6%, a difference of 53.8 percentage points, t = 8.78.

The check

At 2010, the Article 5 deadline, both medians are 0.0%. So the 1996 gap is the treaty's schedule doing what it said.