The PPM: a crucial indicator for measuring the impact of human activities on the climate

On their arms, a number and an acronym: PPM, carried like a banner. But what exactly do these three letters mean?

It is the acronym for “parts per million“, the unit of measurement used to evaluate the concentration of CO2 in the atmosphere.

This rate continues to increase year after year. The starting point of this acceleration: 1850, date of the second industrial revolution, when fossil fuels such as oil and coal started to be used en masse to run our economy. The consequence: a rise in the global average temperature.

Measuring CO2 in PPM is therefore a tangible marker of the human origin of climate change. And the consequences for each of us.

More information on PPM?

Why is CO2 in PPM increasing at an ever increasing rate?

CO2 remains in the atmosphere for a very long time: it takes about 100 years for a large part of the excess CO2 to be absorbed by the oceans or the soil and it will take more than 10,000 years for it to leave the atmosphere completely. The CO2 particles therefore accumulate over the years. This phenomenon is natural and essential to our life on earth because the greenhouse effect thus produced allows us to live in a world at +15 degrees Celsius on average against -18°C if this effect did not exist.

Where it starts to go wrong is from the second industrial revolution, that of electricity, steamships, oil, the chemical industry and the automobile. For it is indeed the combustion of fossil fuels that emits (still today), most of the CO2 emissions of human origin.

Until 1850, the concentration of CO2 in the atmosphere only varied by a few tens of ppm over the last thousands of years. At the beginning of the first industrial revolution (that of the railroad), in 1750, this figure was 227 ppm. In 1850, it rose to 280 ppm.

Then it went into overdrive. From 1950 onwards, this accumulation takes on a new magnitude, at an unprecedented rate: 317 ppm in 1960, 338 in 1980, 354 in 1990, 370 in 2000, 390 in 2010, 415 in 2020… This is due to the ever-increasing volume of fossil fuels burned to ensure our economic development.

In 2022, the concentration of CO2 in the atmosphere has risen to 417 ppm, with occasional peaks of 420 ppm. These figures have not been observed for 3 to 4 million years.

Why is this measure important?

CO2 is the greenhouse gas that has contributed the most to global warming and it emanates from our human activities (fossil fuel use and deforestation). The monitoring of CO2 levels in ppm in the atmosphere is therefore a crucial indicator to measure the impact of human activities on the climate and to evaluate the progress of global warming. This is the indicator that the Stockholm Resilience Center has chosen to monitor the exceeding of the global limit of climate change.

What are the consequences?

This increasing concentration risks causing “dangerous human interference” with the climate system and causing irreversible disasters In a scientific article published in 2013*, several researchers including NASA climatologist James Hansen and paleoclimatologist believe that to avoid this destabilization, the concentration of CO2 in the atmosphere must remain below 350 ppm.

This is the origin of the name of the NGO which fights against climate change, notably through campaigns of divestment from fossil fuels. However, it has not escaped your attention that we have exceeded this limit…since 1988.

Because if this limit is not dangerous in the short term, it is dangerous in the long term. “If CO2 is maintained for a long time at a level higher than this limit, there is a risk of being placed on a trajectory leading to a dangerous and irreversible climatic disruption”, explained climatologist Valérie Masson-Delmotte to Le Monde ten years ago. And we can already observe the first consequences: multiplication and increase in the intensity and or duration of heat waves, droughts, floods, hurricanes…

Follow the increase of the CO2 rate in ppm to predict the future

CO2 concentration rates in the atmosphere in ppm are also used for climate scenarios such as those of the IPCC or the International Energy Agency. Thus, scenarios based on a concentration of 450 ppm at the end of the century would have a significant probability (66%) of maintaining global warming at 2°C in 2100. But it would require very proactive measures to hope to achieve this… A “business as usual” scenario would lead us to a concentration of more than 1200 ppm and a warming of more than 4°C by the end of the century.

Source: IPCC, Volume 1 of the AR6 report on the physical aspects of climate change (2021)

We must also add the atmospheric concentration of methane (1866 ppb – “parts per trillion” – in 2019), 220 times lower than that of C02 but responsible for more than a quarter of the warming because of its stronger warming power. “The amplitude of the variations for CO2 and CH4 far exceeds that of the natural variations between ice ages and interglacial periods over the last 800,000 years,” estimates The Shift Project. If we add up all the greenhouse gases, we will be at 510 ppm C02 equivalent in 2023.

The ppm, a marker of commitment to the fight against climate change.

“I was born at 375 PPM,” writes Swedish activist Greta Thunberg in her twitter bio rather than mentioning her year of birth (2003). Like her, many scientists or people involved in climate issues mention this figure on social networks, or even in their email signature. A display notably borrowed from the action of environmental activists in November 2015. Two days before the opening of the climate negotiations of the COP21 where the Paris Agreement was signed, 35 activists settle in the gallery dedicated to the 1840s of the Tate Britain, in London. They then tattooed the figures of the concentration of CO2 in the atmosphere of the year of their birth. A way to denounce the impact of oil on climate negotiations, culture (the oil company BP is a patron of the London museum), society and the economy in general, explains the group Liberate Tate at the origin of the event.

Today, displaying the concentration rate of CO2 in ppm has gone beyond the militant framework. This figure is thus updated every day on the website of the British newspaper The Guardian but also of Bloomberg Green and other media, in the manner of the weather or stock exchange data that usually punctuate the daily life of general or economic newspapers. Just to show that it is necessary to change the indicator…

And you… how many ppm were you born with?

A big thank you to Béatrice Héraud, journalist, author of the newsletter Le Grand Ecart who wrote this article.