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 as if the famous line that marked the presidential campaign between Bill Clinton and George H. W. Bush in 1992: “It’s the economy, you fool!”.
The greenhouse effect
It is a natural phenomenon that helps retain some of the heat emitted by the sun on the Earth’s surface. 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
This was the concentration of CO2 in Earth’s atmosphere in 1750. The unit of measurement “parts per million” (ppm) indicates the number of molecules of CO2 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 must not exceed 400 ppm if global warming is to be limited to less than 2.4 ° C.
The carbon budget
The equation is relatively simple. 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, you have to respect a carbon budget, just as you would respect an expenditure budget, if you 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 lifespan 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.
Future risks and impacts of climate change
The influence of humans on the climate system is clearly established. The main risks in the various sectors and regions can be associated with five reasons for concern with an additional level of risk, undetectable to very high, as much as the average global warming will be.
They include: unique and threatened systems, in particular arctic sea ice and coral reefs; extreme weather events, for example heat waves, extreme precipitation and flooding in coastal areas; the distribution of impacts with generally greater risks for disadvantaged populations and communities in all countries; so-called “cumulative” risks which, for example, concern the loss of biodiversity and the disappearance of associated goods and services;
large-scale phenomena that are likely to undergo sudden and irreversible changes (the precise levels of climate change to reach a threshold or a tipping point remain uncertain but the risks generated increase with increasing temperatures).
Some risks are particularly relevant at the regional level while others are global. These risks can be reduced by limiting the rate and extent of climate change and ocean acidification. More specifically:
A large portion of species face an increased risk of extinction due to projected climate change over the twenty-first century and beyond and its interactions with other stressors such as habitat modification, overexploitation, pollution and proliferation of invasive species.
CLIMATE CHANGE AND MAJOR WEATHER EVENTS
The term “meteorological extreme” refers to the most visible manifestations of climate variability. In fact, ecosystems and we are more sensitive to devastating, often brief weather events than to a rise in temperature of a few tenths of a degree over several decades.
In addition, the speed and systematization of the dissemination of information by the media give us the feeling that extreme phenomena are identified: it suffices for an anomaly to be perceived locally by a person for it to be relayed to the planetary scale in a few hours. This real inflation in the number of phenomena identified raises the question of the relevance of their relationship with climate change, which has been observed since the beginning of the twentieth century.
What are extremes?
It is important to define the terms you use as precisely as possible. It is observed that scientific communities often use the expression “meteorological extreme” to designate quite different phenomena.
There are three categories of definitions for extremes; each depends on the scientific discipline that studies them [Jeandel and Mossery, 2011]. For statisticians, the extreme is indicated by very large values of a measured quantity, that is, values that deviate considerably from the mean and values that revolve around the mean.
We speak of the “tail of the statistical distribution” to speak of extremes, and therefore very large (or very small) values, which are however rarely reached.
For example, if we are interested in the daily temperature variations in Paris in summer, hot extremes occur when the thermometer exceeds 35 ° C.
