Parts per million and why they matter

“Parts per million” (ppm) refer to the number of CO2 molecules per million molecules of dry air. As we have seen, Carbon dioxide (CO2) and other greenhouse gases (GHGs) act like a blanket, preventing the heat from escaping Earth into space. Since the Industrial Revolution, human activities have been spewing out GHGs and making this blanket “thicker”. 

In March 2024, NASA recorded 425 parts per million of CO2. While this may not sound like much, it is substantially more than the preindustrial level of 280 ppm. It is also over the “Goldilocks” range of 300-350 ppm of CO2 needed to keep temperatures comfortable for humans as well as for most plants and animals, but also to ensure that our societies, food system and infrastructures aren’t overwhelmed by the inevitable storms, floods, droughts, wildfires and rising sea levels that result from higher temperatures. 

If we are to avoid the most catastrophic consequences of climate change and stick to the Paris Agreement’s benchmark 1.5°C, we have to stay below 421 ppm. We are fast approaching this limit and in 2023, the world hit an average of 419.3 ppm, a new record high.

At the current rate, it is debatable whether we will manage to keep below 2°C, never mind 1.5°C. The Global Carbon Budget estimates that we have a 50% chance that global warming will exceed 1.5°C consistently in about 7 years. Policies and pledges in place now put the world on track for a rise of between 2.4°C and 2.6°C, without taking into account the consequences of passing climate “tipping points” (self-reinforcing and irreversible negative planetary changes). The Earth is already “well outside the safe operating space for humanity” in that 6 out of 9 planetary boundaries have been broken due to human-induced pollution and destruction of the natural world.

But there is still hope, though we must act fast and decisively.