The climates of tomorrow are decided today. And those we know after 2050 will depend on our emissions over the next two decades.
This is one of the major lessons of sixth assessment report published by the Intergovernmental Panel on Climate Change (IPCC) from 2021.
Climate scenarios: emission flows, stock and generations
As soon as very first report, in 1990, the IPCC produced scenarios as so many stylized representations describing the climates of the future and corresponding to our emission trajectories.
Based on the climate models of the time, these scenarios projected average warming between 2100 and 2°C (relative to the pre-industrial era) by 4,5.
For 2020, they projected a warming of between 1 and 1,5°C. Thirty years after this first IPCC report, the World Meteorological Office observed an increase in average temperature of 1,2°C for 2020. The projection of the first IPCC report thus proved to be surprisingly robust!
Since then, climate models have been perfected, but they operate according to the same approach: linking the annual flows of GHG emissions to the evolution of their stock in the atmosphere, which conditions the warming (or cooling) of the planet. .
In its Sixth Assessment Report, the IPCC identified three families of scenarios, identified by their colors on the graph below. They are distinguished by the date on which the CO emission peak2 is achieved and by that where carbon neutrality makes it possible to stabilize its stock in the atmosphere.
Given the inertia of the stock, it takes twenty to thirty years, the time of a generation, for the drop in emissions to have a significant impact on the stock. This is why global warming is a generational affair. Let's look at the case of the generation born in 2020, during the Covid epidemic.
In 2050, the Covid generation will be 30 years old. The climate it will experience will be largely determined by the stock of GHGs in the atmosphere it inherited in 2020. The average warming will have exceeded 1,5°C, regardless of the scenario considered. She will face more severe impacts than the 1,2°C world prevailing when she was born. It is after 2050 that the climatic conditions diverge strongly according to the emission trajectories and the color of the scenarios.
Red scenarios: the price of inaction!
In the most emitting scenarios (in red on the graph), the absence of any climate action leads to massive use of fossil fuels. In the best of cases, the peak of emissions is only reached towards the end of the century. The stock of CO2 in the atmosphere has no chance of stabilizing by 2100, suggesting continued warming in the XXIIe century.
In 2075, the Covid generation turns 55: the prime of life. In the red scenario, it faces an average warming that has exceeded 3°C. Agricultural production conditions have deteriorated, leading to the multiplication of hunger revolts and forced population displacements. The cost of climate extremes is becoming exorbitant.
Sea level rise has just reached 0,75 meters. The large delta areas are becoming uninhabitable, provoking violent conflicts, particularly in South Asia. Manhattan has given up protecting the lower part of the city deserted by its brokers and investment bankers.
In 2100, the rise in the thermometer approaches 4 to 5°C. The multiple troubles resulting from climate change have disrupted economies. Whole swathes of activity are collapsing, which will cause CO emissions to decline2. The melting of Antarctica threatens to dramatically accelerate the rise in water levels. In such climate chaos, it is hard to imagine how societies can still function. Protecting the survivors of the Covid generation, now in their eighties, becomes an impossible bet.
Blue scenarios: 1,5°C or 2°C?
Opposite red are the blue emission control scenarios. To be in the blue scenario, the world must pass the peak of CO emissions2 from 2020, then reduce emissions sufficiently to stabilize the stock (carbon neutrality) around 2070 at the latest.
In 2075, the Covid generation drastically reduced its fossil fuel consumption. At the same time, it managed to maintain the ability to absorb CO2 by the natural environment by protecting terrestrial and marine biodiversity. The average temperature stabilizes between 1,5 and 2°C.
The Covid generation then experiences the severity of the impacts of a world where warming exceeds 1,5°C. Climate extremes – heat waves, droughts and storms – hit hard. Agricultural yields suffer. Lower Manhattan is not directly threatened by the rising waters, but the balance sheets of its insurance companies have suffered a veritable tsunami. The great deltas of the world are affected by the scourge of submersion and soil salinization.
Despite the incredible upheaval in the energy landscape since 2020, time has also run out in the blue scenarios to put Earthlings completely protected from climate risk. The Covid generation then discovers that climate neutrality was only a point of passage. To limit climate risks, it is necessary to switch to a negative emissions regime to reduce the stock of CO2 in the atmosphere and bring warming well below 2°C.
The actions to be taken are complex, but not out of reach. Residual CO emissions2 are the most difficult to reduce. CO absorption capacities2 by the natural environment are not infinitely expandable and technologies for capturing by technology are expensive. In the best-case scenario, the strengthening of climate action will bring the rise of the thermometer back to +1,5°C in 2100, which will greatly facilitate the protection of the octogenarians of the Covid generation.
Yellow scenario: the world after Glasgow!
In the world in yellow, the peak of global CO emissions2 is reached around 2030 to stabilize on a plateau for two decades. The countries' commitments announced at COP26 in Glasgow (2021) under the Country Agreement have been fulfilled. But we do not go beyond these commitments. In this post-Glasgow world, the decline in emissions after 2050 does not make it possible to achieve neutrality by the end of the century. The warming is not stabilized.
In 2075, the Covid generation faces an average warming exceeding 2°C. Droughts and storms increasingly affect agricultural yields. The world food situation is deteriorating. Food riots are on the rise. The cost of damage caused by tropical cyclones has skyrocketed. Residents of affected areas can no longer insure their property with insurance companies.
Sea level rise has exceeded 0,5 meters. The IPCC has just recalled that it will increase and extend well beyond 2100. Manhattan is completing a five-foot protection dyke to protect its assets and its population. In the deltas, the evacuation of the most vulnerable areas has begun, because the rise in water levels will continue long after the thermometer has stabilized.
The Covid generation then realizes that temperature stabilization is still not in sight. She sets out to accelerate climate action. But the global "carbon budget" measuring the overall amount of CO emissions2 giving a two in three chance of stabilizing warming at 2°C was fully used before 2050.
Despite the acceleration of the decline in emissions, carbon neutrality will not be achieved before the end of the century. In 2100, the average warming exceeds 2,5°C. The old days of the Covid generation do not look auspicious, as the rise in the thermometer has not been stemmed.
Red, blue, yellow?
What world are we heading towards? Its color does not depend on a draw, as in the lottery. It will primarily result from the evolution of our emissions over the coming decades.
The scenarios in red have a low probability of occurring for economic reasons. The fall in the price of renewable energies and the cost of storing electricity makes the switch to low-carbon energies and the gradual abandonment of fossil fuels economically profitable. This shift will take place even in the absence of climate action. It will limit anthropogenic emissions of CO2 but will be too slow to bring us back to blue or yellow.
Committed climate action is not enough either. It passes on to future generations far too high a share of emission reduction commitments. It therefore directs us towards the yellow scenario, moving away from the blue as time passes. The challenge for the next stages of the climate negotiation will therefore be to move from yellow to blue, by accelerating the energy and agro-ecological transitions.
The COP27 which has just opened in Sharm el Sheikh against a background of dissension between rich countries and countries poor enable progress in this direction?