Climate change | A matter of mathematics

Concluding a new international agreement to limit global warming is a complex affair, which requires a global response. The problem to be solved is much simpler. A matter of numbers and mathematics, in a way. A bit like the famous line that marked the presidential campaign between Bill Clinton and George H. W. Bush in 1992: “It’s the economy, you idiot! ”

Eric-Pierre Champagne
Press

The greenhouse effect

It is a natural phenomenon which makes it possible to retain part of the heat emitted by the sun on the surface of the Earth. It is obtained thanks to the famous greenhouse gases (GHG) that we talk about so much. Without this greenhouse effect, the average temperature on the planet would be -18 ° C.

Greenhouse gases (GHGs)

The two best known are carbon dioxide (CO₂) and methane (CH₄). There are also water vapors (H₂O), ozone (O₃) and nitrous oxide (N₂O). These GHGs exist naturally and are therefore not a human invention.

The impact of human activities

For a very long time, GHG emissions have remained relatively stable. They began to increase significantly from the industrial revolution in 1750 due to human activities and the use of coal, oil and natural gas, which release CO₂. This gas remains in the atmosphere for up to 100 years.

277 parts per million

It was the concentration of CO₂ in the Earth’s atmosphere in 1750. The unit of measurement “parts per million” (ppm) indicates the number of CO molecules₂ for every million molecules of air.

414.26 ppm

This is the most recent measurement of the concentration of CO₂ in the atmosphere, dated October 30, 2021. You have to go back to about 3 million years ago to find such high concentrations.

400 ppm

According to the Intergovernmental Panel on Climate Change (IPCC), the concentration of CO₂ in the atmosphere should not exceed 400 ppm if global warming is to be limited to less than 2.4 ° C.

The carbon budget

The equation is relatively straightforward. To limit global warming to less than 2 ° C above the pre-industrial level and if possible not to exceed 1.5 ° C, it is necessary to reduce GHG emissions caused by human activities. To achieve this, we must respect a carbon budget, just as we would respect an expenditure budget, if we want to eventually avoid bankruptcy. The Global Carbon Project has calculated how much we have left to spend to meet the targets set by the Paris Agreement.

1.5 ° C target

To limit global warming to 1.5 ° C, the world has 420 billion tonnes of GHGs to spend, with a 50% chance of achieving this goal. At the rate of global emissions in 2021, this budget would be exhausted in 11 years. To increase our chances of success to 66%, the limit is 360 billion tonnes. At the current rate, it will take us nine years before we fall into the red.

Target of 2 ° C

To limit global warming to 2 ° C, the world has 1270 billion tonnes of GHGs to spend, with a 50% chance of success. At the current rate, this budget would be exhausted in 33 years. To increase our chances of success to 66%, the limit is 1110 billion tonnes, a budget that would be exhausted in 26 years at the current rate.

2.7 ° C

According to the latest forecasts, the world is heading towards a global warming of 2.7 ° C with the commitments that have been made so far by the various nations. To date, the planet has already warmed by 1.2 degrees compared to the pre-industrial era.

Watch out for methane

Methane (CH₄) is a greenhouse gas 28 times more potent than CO₂, but its lifetime in the atmosphere does not exceed 10 years. The main sources of methane pollution are natural gas, agriculture, warming oceans and melting permafrost. To limit warming to less than 2 ° C, it will necessarily be necessary to reduce methane emissions.

Sources: IPCC, Carbon Brief, Global Carbon Project, World Bank, NOAA