Magnitude of upcoming climate change

Scientific summary

Astronoo's article analyzes the projections of the 6^th IPCC report concerning the magnitude of upcoming global warming. It highlights the quasi-linear relationship between anthropogenic CO₂ emissions and global temperature increase. Five scenarios (SSP) are detailed, ranging from moderate warming of +1.5°C to extreme warming of +4.4°C by 2100. The article emphasizes the irreversibility of certain changes (oceans, ice sheets) and the crucial importance of actions to be taken in the next two decades to limit impacts. It also addresses individual and collective levers for action.

What is the magnitude of upcoming climate change and what can we do about it?

This article is devoted to the magnitude of upcoming climate change, a central question of the 6^th IPCC report (2021-2022). The answer is clear: regardless of the scenario considered, a warming of 2°C above pre-industrial levels will be exceeded during the 21st century. But the exact magnitude – between +1.5°C and +4.4°C in 2100 – will directly depend on our greenhouse gas emissions. The five IPCC scenarios, from the most optimistic (SSP1-1.9) to the most pessimistic (SSP5-8.5), illustrate this range. The article deciphers these trajectories and their consequences: multiplication of extreme events, sea level rise, erosion, etc. It emphasizes that the next twenty years are decisive for bending the curve. Beyond the diagnosis, it offers concrete action paths, both individual and collective, to reduce emissions, promote innovation and raise public awareness, in order to limit damage and adapt to inevitable changes.

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Climate change is irreversible

Warming directly linked to CO₂ emissions

The 6th IPCC report 2021-2022 reaffirms with high confidence the conclusion of the previous report that there is a quasi-linear relationship between anthropogenic CO2 emissions and the global warming they cause. The IPCC has developed 5 scenarios for 2100 concerning greenhouse gas emissions (CO2, CH4 and NO2). Global average surface temperature differences are calculated relative to the 1850–1900 period.

Projections ranging from +1.5°C to +4.4°C by 2100

Regardless of the scenario, a global warming of 2 °C would be exceeded during the 21st century. Since the 1850–1900 period, global average temperature has increased by 1.1 °C. Since the 1970s, an amplification has appeared with a rate of 0.15 to 0.20 °C per decade. According to the scenarios (from the most optimistic to the most pessimistic), the temperature will have increased from +1.5°C to 1.6°C by 2040, from 1.6°C to 2.4°C between 2041 and 2060 and from 1.4°C to 4.4°C between 2081 and 2100.

The 5 IPCC scenarios

Scenario SSP1-1.9 (very low emissions)

+1.5°C compared to 1850–1900 (Paris Agreement). In this scenario, global CO2 emissions fall to zero around 2050. Societies adopt more environmentally friendly practices, with the focus no longer on economic growth but on general well-being. Investments in education and health increase and inequalities decrease. Violent weather events are more frequent but the world has avoided the worst consequences of climate change.

Scenario SSP1-2.6 (low emissions)

+1.8°C compared to 1850–1900 at the end of the century. In this scenario, global CO2 emissions fall to zero after 2050.

Scenario SSP2-4.5 (intermediate emissions)

+2.7°C compared to 1850–1900 at the end of the century. In this scenario, CO2 emissions oscillate around current levels and begin to decline in the middle of the century. No sudden change in our behaviors.

Scenario SSP3-7.0 (high emissions)

+3.6°C compared to 1850–1900 at the end of the century. In this scenario, CO2 emissions are almost doubled compared to current levels by 2100.

Scenario SSP5-8.5 (very high emissions)

+4.4°C compared to 1850–1900 at the end of the century. In this scenario, CO2 emissions are almost doubled by 2050. The global economy grows rapidly but this growth is fueled by the exploitation of fossil fuels and very energy-intensive lifestyles.

Probability of IPCC scenarios

Already tangible impacts and programmed irreversibility

The global thermometer does not lie: each additional tenth of a degree amplifies the violence of cyclones, accelerates sea level rise, intensifies coastal erosion and lengthens heatwaves at an alarming rate. Extreme scenarios (SSP1 and SSP5) are the least likely, but irreversibility is a certainty. The oceans, which have absorbed 90% of the excess heat, will continue to warm for centuries. The Greenland and Antarctic ice sheets, weakened, will continue their inexorable decline. Yet not everything is lost: every fraction of a degree avoided is a victory. Concerted actions, from individual gestures to international diplomacy, can still slow the pace and limit the damage. Urgency does not exclude hope, but it demands a response equal to the challenge.

Decarbonizing the economy: the heart of the matter

Fossil fuels — oil, gas, coal — are the main culprits of global emissions, alongside intensive agriculture and heavy industry. The solution? An unprecedented energy transformation: replacing black with green, fossil with renewable. Solar, wind, hydro, geothermal… alternatives exist and their cost continues to fall. But producing clean energy is not enough: we must rethink our mobility, rethink our agriculture, rethink our relationship with energy. Each megawatt-hour saved is a step towards a world where the air is breathable and the climate livable. The transition is not an option, it is a vital necessity.

Eco-gestures: small steps, big waves

They are often called "small gestures", but their accumulation creates waves of change. On an individual level, the power is real: turn off rather than leave on, insulate rather than waste, cycle rather than pollute. Public transport, cycling, energy sobriety, waste reduction, local and seasonal food… these daily choices, seemingly trivial, form a silent army of committed citizens. They send a clear signal to industries and governments: we are ready to change. And when millions of people act, margins become movements.

Innovation: the spark that can change everything

Technology is not a magic wand, but it is an indispensable ally. Energy storage, energy efficiency, renewable production, regenerative agriculture, intelligent waste management… innovation is everywhere, but it needs to be encouraged, funded and deployed. Startups, research laboratories, visionary companies invent solutions every day to decarbonize our world. The challenge is to bring them out of the laboratories and integrate them into our lives. The future belongs to those who dare to innovate, and this future is being built today, in urgency and creativity.

Strong policies and binding agreements

Good intentions are not enough: we need ambitious legislative frameworks and binding international commitments. The Paris Agreement is a compass, but its implementation remains insufficient. States must move from words to actions: tax carbon, subsidize green, ban the worst. Climate policies are not a brake on the economy, they are an investment in our survival. International cooperation is more essential than ever: climate knows no borders, and only a planetary response can save the planet. Every summit, every treaty, every regulation is a brick laid on the path to a livable future.

References

FAQ: Everything you need to know about the magnitude of global warming

What is meant by "magnitude of global warming"?

The magnitude of global warming refers to the increase in the global average temperature at the Earth's surface, measured in degrees Celsius (°C) relative to a reference period. The IPCC uses the 1850–1900 period, which corresponds to the beginning of the industrial era, before human emissions of greenhouse gases significantly disrupted the climate. This magnitude directly depends on the total amount of CO₂ and other greenhouse gases we continue to emit into the atmosphere. The higher the emissions, the greater the warming will be.

What are the IPCC scenarios?

The IPCC has defined five scenarios (called SSPs, for Shared Socioeconomic Pathways) that project climate evolution until 2100. They range from the most optimistic to the most pessimistic:

SSP1-1.9 (very low): +1.5°C — zero emissions around 2050, sustainable and inclusive society.
SSP1-2.6 (low): +1.8°C — zero emissions after 2050, progressive transition.
SSP2-4.5 (intermediate): +2.7°C — no abrupt change, emissions stagnating then declining.
SSP3-7.0 (high): +3.6°C — doubled emissions, economic growth at the expense of the environment.
SSP5-8.5 (very high): +4.4°C — economy based on fossil fuels, very energy-intensive lifestyles.

These scenarios are not predictions, but possible trajectories that depend on our collective choices.

Why is warming irreversible?

Global warming is considered irreversible on a human timescale for several reasons. First, the oceans absorb a large part of the excess heat, and their thermal inertia is such that they will continue to warm for centuries, even if emissions stopped immediately. Second, the melting of ice sheets and glaciers is a self-sustaining process: as ice melts, it exposes darker surfaces (ocean or land) that absorb more solar radiation, accelerating melting further. Finally, emitted carbon remains in the atmosphere for hundreds to thousands of years, prolonging the greenhouse effect. So we cannot "stop" warming, but we can limit its magnitude and slow its effects.

What are the main impacts of global warming?

The impacts are multiple and already visible:

Extreme events: more frequent and intense heatwaves, prolonged droughts, floods, storms and cyclones.
Sea level rise: due to ice melt and thermal expansion of oceans, threatening coastal areas and small islands.
Ecosystems and biodiversity: habitat destruction (corals, forests, wetlands), forced species migration, accelerated extinction.
Agriculture and food security: declining yields in already fragile regions, rising prices, famine risks.
Human health: increase in heat-related illnesses, spread of vector-borne diseases (such as malaria), worsened air pollution.

The magnitude of these impacts will directly depend on the extent of warming we allow to occur.

What can I do at my level?

Every citizen can act on their own scale. Here are some concrete suggestions:

Reduce energy consumption: insulate your home, lower heating, use LED bulbs, turn off appliances on standby.
Choose sustainable transport: walk, cycle, use public transport, carpool, and limit flying.
Adopt a sustainable diet: reduce red meat consumption, choose local and seasonal products, limit food waste.
Reduce waste: promote recycling, composting, and avoid single-use products (plastics, packaging).
Inform and raise awareness: talk about climate around you, support associations, and exercise your right to vote for ambitious climate policies.

These gestures, multiplied by millions of people, have a significant impact and send a strong signal to decision-makers.

What is the role of the Paris Agreement?

The Paris Agreement, adopted in 2015 at COP21, is a legally binding international treaty on climate. Its main objective is to keep the increase in global temperature well below 2°C above pre-industrial levels, and to pursue efforts to limit it to 1.5°C. To achieve this, each signatory country must submit nationally determined contributions (NDCs), i.e. action plans to reduce their greenhouse gas emissions. The agreement also provides for a five-year review mechanism of commitments, to increase ambition over time. It also encourages international cooperation, technology transfer and financing for developing countries to help them adapt to the impacts of climate change.

What is the difference between an optimistic scenario and a pessimistic scenario?

The difference is considerable, both in terms of temperature and consequences. In an optimistic scenario (SSP1-1.9), warming is limited to +1.5°C. Impacts remain manageable: extreme events are more frequent, but societies have time to adapt, ecosystems are partially preserved and sea level rise remains moderate. In a pessimistic scenario (SSP5-8.5), warming reaches +4.4°C. The consequences are catastrophic: deadly heatwaves, rising waters submerging entire cities, collapse of biodiversity, massive food and migration crises. It is a world where conflicts over resources intensify and living conditions become extremely difficult for a large part of humanity. The choice between these two futures is still in our hands.