Smoke billows from a coal-fired power plant.
The increase in atmospheric CO2 since pre-industrial times is around 50%, an expert told AAP FactCheck.

Recycled letter’s dodgy maths on C02 rise is bad for the planet

Nik Dirga May 24, 2022

The amount of carbon dioxide in the air increased just .004 per cent in 50 years.


False. The real figure is an 11.7 per cent increase with the correct calculation.

A letter to the editor written to a regional Australian newspaper in 2009 is being recycled on social media as purported evidence against man-made climate change.

The letter, as seen in this Facebook post (screenshot here), is attributed to a former employee of the now-defunct Electricity Commission of NSW. It discusses the benefits of coal-fired power over other forms of energy, and claims the amount of carbon dioxide in the atmosphere has risen only .004 per cent in the past 50 years.

However, experts told AAP FactCheck the claim is wrong and misunderstands how to calculate percentage increases with the real figure almost 12 per cent. They say even a tiny rise in CO2 levels will prove disastrous for the planet’s ecosystems.

Near the end of the post, the author claims: “According to the ‘believers’ the CO2 in air has risen from .034% to .038% in air over the last 50 years,” and that “By (the government’s) own figures they state the CO2 in air has risen from .034% to .038% in 50 years. Assuming this is correct, the world CO2 has increased in 50 years by…004%.”

The Facebook post can be traced to a letter written to the Rockhampton Morning Bulletin in Queensland in 2009. Its content is frequently shared online (see here, here and here).

The problem is it confuses a percentage point change for a percentage change when comparing figures. A percentage change is proportional to the original quantity, whereas a percentage point change is the numerical difference between two percentages. For example, a rise from 10 per cent to 15 per cent is an increase of five percentage points, but a rise of 50 per cent on the original figure.

Therefore, a rise from .034 per cent to .038 per cent is not a .004 per cent increase. It is a .004 percentage point change, but that’s calculated as an increase of 11.7 per cent.

The information in the 2019 post is also more than a decade old, and doesn’t take into account current global average CO2 in the atmosphere, which has risen 12 per cent just since 2000, and about 25 per cent since 1970, according to the US government’s National Oceanic and Atmospheric Administration. Concentrations of CO2 have risen from 325 parts per million (ppm) in 1970 to 415ppm in 2021.

Experts told AAP FactCheck the post and original letter, is wrong on many levels.

“The statement is not accurate as the concentrations quoted are not correct,” said James Renwick, a climate scientist and professor at Victoria University of Wellington Te Herenga Waka, who has worked extensively in atmospheric physics.

“The increase in atmospheric CO2 since pre-industrial times (when the level was 280ppm) is around 50%. Most of the addition (two-thirds) of CO2 to the air since the 1700s has occurred in the last 50 years,” Prof Renwick said in an email.

Manfred Lenzen, a professor of sustainability research at the University of Sydney’s School of Physics, says it’s also important to know how CO2 is measured.

“Atmospheric concentrations are actually not measured in per cent,” he told AAP FactCheck in an email.

“They’re measured in ppm (parts per million) so that is a 90 part per million increase between 1970 and 2020. You can express by a percentage value and it could be very small.”

Carbon dioxide represents a small portion of the atmosphere, just 0.04 per cent, but a tiny rise has an impact. It has been steadily rising for decades, according to measurements taken at Mauna Loa Observatory in Hawaii since 1958.

“CO2 has an outsize effect on global temperatures and the radiation budget of the planet, as it is so good at absorbing heat and re-radiating it back to the earth’s surface,” said Prof Renwick. “A little bit of greenhouse gas goes a long way.”

He says a temperature rise of one degree Celsius can have a major impact on the planet.

“It matters because if you look at biological systems, the biomes that exist on earth, most of them live in a very narrow temperature range. Other biomes you cannot put them in a temperature that’s two degrees warmer or colder and expect them to thrive.”

The Verdict

The post’s claim that carbon dioxide levels have risen only .004 per cent in 50 years is false. It is taken from a 2009 letter relying on old figures and misunderstands basic maths on how to calculate percentage increases, making it wildly inaccurate. The real increase based on the figures used is 11.7 per cent. Climate scientists told AAP FactCheck there has been a large increase of CO2 parts per million since 1970.

False – The claim is inaccurate.

* AAP FactCheck is an accredited member of the International Fact-Checking Network. To keep up with our latest fact checks, follow us on Facebook, Twitter and Instagram.

All information, text and images included on the AAP Websites is for personal use only and may not be re-written, copied, re-sold or re-distributed, framed, linked, shared onto social media or otherwise used whether for compensation of any kind or not, unless you have the prior written permission of AAP. For more information, please refer to our standard terms and conditions.