Par Kenny Chicate-Moibert, André Naegely-Hofstetter, Florian Girardot, Maria Smetanina, Julien Brocard, Paul Frere, Manon Lombardet, étudiants ESTA Belfort, 05/2022

Mots clés: #IPCC #climate change #global warming

What is the IPCC?

The IPCC prepares a comprehensive assessment of the current state of scientific, technical and socioeconomic knowledge on climate change, its impacts and future risks, and options for reducing climate change. It also produces reports on issues agreed by member governments, as well as methodological reports that provide guidance for the preparation of greenhouse gas inventories. The IPCC is preparing the Sixth Assessment Report, which consists of three working group papers and a synthesis report. The WG1 contribution was completed in August 2021, and the WG2 contribution was completed in February 2022.

IPCC 1 group : Impact

Definition of the environmental impact, how to calculate it with the carbon footprint, how does the IPCC calculate it with their data (digging in their previous reports to find the most accurate parts and global stats that we can add in order to make our article the clearest it can be.

Give a brief first glance on how the IPCC predicts our future in the coming years (the 5 different scenarios regarding the climate in the coming years), so that we can develop each single scenario individually afterwards.

Current climate conditions and the IPCC Scénarios

Current climate conditions

There is no doubt that human influence has warmed the atmosphere, ocean and land. Rapid and significant changes have occurred in the atmosphere, ocean, cryosphere and biosphere.

100% of global warming is due to human activity. This is a certain and unequivocal fact (to understand what radiative forcing is, read this article).

The magnitude of recent changes in the overall climate system and the current state of many aspects of the climate system are unprecedented, ranging from hundreds to thousands of years.

Over the past three thousand years, sea level has not risen as rapidly as it has since 1900

Since the first IPCC report was published in 1990, 1,000 billion tons of carbon dioxide have been emitted. That’s almost half of our emissions since the beginning of the entire industrial era.

Human activity is warming the climate at a rate not seen in at least 2,000 years. Recent climate change has been widespread, rapid and intensified. Compared to 1850-1900, temperatures have increased by 1.1°C in the last 10 years.

Human-induced climate change has affected many extreme weather and climate events in all regions of the world. Evidence of changes in extreme events such as heat waves, heavy rainfall, droughts, and tropical cyclones, especially their attribution to human influence, has increased since AR5.

We will develop the different scenarios.

The IPCC Scénarios (Intergovernmental Panel on Climate Change)

SSP1-1.9 : The addition of the CO2 concentration in the atmosphere of from -18 Gita Tons of CO2 per year, -9 Megatons of Methane per year, 8 Megatons of Nitrous oxide per year and 4 Megatons of Sulphur dioxide per year will lead to a global surface temperature increase from 1,2°C to 1,9°C

SSP1-2.6 : The addition of the CO2 concentration in the atmosphere of from -9 Gita Tons of CO2 per year, -9 Megatons of Methane per year, 8 Megatons of Nitrous oxide per year and 4 Megatons of Sulphur dioxide per year will lead to a global surface temperature increase from 1,4°C to 2,6°C

SSP2-4.5 : The addition of the CO2 concentration in the atmosphere of from 5 Gita Tons of CO2 per year, 8 Mega Tons of Methane per year, 240 Megatons of Nitrous oxide per year and 31 Megatons of Sulphur dioxide per year will lead to a global surface temperature increase from 2°C to 3,5°C

SSP3-7.0 : The addition of the CO2 concentration in the atmosphere of from 82 Gita Tons of CO2 per year, 790 Mega Tons of Methane per year, 21 Megatons of Nitrous oxide per year and 79 Megatons of Sulphur dioxide per year will lead to a global surface temperature increase from 2,6°C to 4,6°C

SSP5-8.5 : The addition of the CO2 concentration in the atmosphere of from 125 Gita Tons of CO2 per year, 490 Mega Tons of Methane per year, 16 Megatons of Nitrous oxide per year and 35 Megatons of Sulphur dioxide per year will lead to a global surface temperature increase from 3,2°C to 5,7°C

Average estimations from the following graphics :

From IPCC’s AR6 WGI full report

The IPCC’s Average estimations of temperatures evolution on Near term, Mid-term and Long-terme :

Near-term : 2021 – 2040

Mid-term : 2041 – 2060

Long-term : 2081 – 2100

From the best estimation to the worst one.

Note : Best estimation is the average temperature between the best one and the worst one.

All SSP scenarios predict that the Earth will warm by 1.5°C. The most ambitious emission projections predict that we will reach 1.5°C in the 2030s, then peak at +1.6°C, before falling back to 1.4°C by the end of the century.

The problem is that we know that the technology needed to achieve negative emissions at these orders of magnitude does not exist or has never been tested at this scale.

Information on future climate change and its consequences

Under scenarios of increasing CO2 emissions, oceanic and terrestrial carbon sinks will be less effective in slowing the accumulation of CO2 in the atmosphere

The IPCC describes the evolution of future temperatures according to 5 different socio-economic pathways (SSP)

In all emission scenarios (except the lowest one, SSP1-1.9), we will exceed the global warming threshold of +1.5°C in the near future (between 2021 and 2040) and remain above +1.5°C until the end of the century.

With continued warming, each region could experience more extreme weather events, sometimes in combination, and with multiple consequences. This is more likely to happen with +2°C warming than 1.5°C (and even more so with additional warming levels). Translate « combined » as « several at once » (heatwave, followed by megafires for example, as in Canada in June 2021).

Tipping points are included in the report because, although they have a lower probability of occurring, they could have devastating consequences. Low-probability events, such as ice sheet melt, abrupt changes in ocean currents (e.g., AMOC), some cumulative extreme events, and warming significantly greater than the range of warming estimated to be very likely, cannot be excluded and are included in the risk assessment.

The glaciers in the mountains and at the poles are doomed to melt for decades or even centuries to come, while the release of carbon from the permafrost by thawing, considered over a period of more than 1000 years, is irreversible.

Limiting climate change in the future

In order to limit global warming, strong, rapid and sustainable actions will be needed to reduce CO2, methane and other greenhouse gas emissions. This would not only reduce the consequences of climate change but also improve air quality.

Limiting global warming to +1.5°C will no longer be possible without an immediate and large-scale reduction of GHG emissions (see the different scenarios).

If we reach carbon neutrality, global warming should stop (with more certainty than in the previous report).

Many changes due to past and future greenhouse gas emissions are irreversible for centuries or even millennia, including changes in the oceans, ice caps, and global sea level. However, some changes can be slowed and some stopped by limiting global warming.

Estimates of the remaining carbon budget – a simplified way of assessing how much CO2 can be released before a given level of warming is reached – have been improved since previous reports, but the carbon budget remains broadly unchanged.

Change projection :

Projected changes are shown at global warming levels of 1°C, 1.5°C, 2°C, and 4°C and are relative to 1850-1900 representing a climate without human influence. The figure depicts frequencies and increases in intensity of 10-year or 50-year extreme events from the base period (1850-1900) under different global warming levels. (Too change and explain properly)

Attribution of extreme events

Very significant progress has been made since the last IPCC attribution report. It is science that tells us whether we can attribute extreme weather events to climate change. Here is what the IPCC told us:

« Human-induced climate change has affected many extreme weather and climate events in all regions of the world. Since AR5, evidence of changes in extreme events such as heat waves, heavy rainfall, droughts, and tropical cyclones, particularly their impact on the attribution of human influence, has been strengthened. »

The global proportion of major tropical cyclones (categories 3 to 5) may have increased over the past four years.

It is no longer necessary to talk about the effects of climate change on all events in general; for example, we can estimate how much human activity has exacerbated a given heat wave (see also the work on global weather attribution)

The IPCC is the first to describe the observed increase in extreme hurricanes. Previously, these changes were too uncertain to have international consensus. Extreme weather events are now becoming more severe in all regions of all continents (with the exception of southern South America, where data is too sparse).

Here is an excellent infographic that expresses the probability of different extreme events based on possible warming:

Regionality of climate change

The IPCC also points out that « natural factors and internal variability will moderate anthropogenic changes, particularly on a regional scale and in the short term, with little effect on centennial climate warming ». These adjustments are important when planning for any possible changes, especially for risk management.

Based on the 2 temperatures proposed by the IPCC (+2°C and +4°C), it is clear how differently things are warming on Earth.

The second diagram shows the rise in water levels caused by global warming. We therefore notice that the more the climate changes, the more the consequences on our lives (rising sea levels, temperature increases) the more difficult our living conditions will be.

Proportion of CO2 emissions

The graph above shows the division of CO2 emissions between 3 different spaces (ocean, land, atmosphere) according to the 5 scenarios from 1850 to 2100. From this graph, we can observe that it is in the atmosphere that global warming will have the most impact. Indeed, it is in the atmosphere that there is the biggest difference according to the scenarios. However, we must not forget that the oceans and the land will also be affected by these changes.

Global surface temperature changes in °C (referral : 1850-1900)

In all scenarios the global temperature increases however we observe a high delta (about 3.5°C).

Arctic ice evolution and projections in 10^6 km²

The global warming of the surface temperature leads to a melting of the ice. From the graph above, we can see that the ice melt is important. In 3 of the 5 scenarios, we can see that by 2100 we will be below the practically ice-free limit.

Sea level increasing projections in metters

Due to global warming and melting ice, the sea level is rising between 0.2 and 0.7 metters depending on the different scenarios until 2100.

Ocean acidity (pH) projections

This graph shows us that the ocean acidity increase more and more strongly according to the different scenarios.

Synthesis and conclusion

According to climate scientists, our world is likely to continue to warm this century and beyond. The conclusion is based on scientists’ understanding of how the climate system works and computer models developed to simulate Earth’s climate. Results from various climate model simulations suggest that Earth’s average temperature in 2100 could be 1.1 to 5.4°C (2 to 9.7°F) warmer than it is today.

The main cause of the temperature increase is carbon dioxide and other heat-trapping « greenhouse gases » produced by human activities. The biggest source of extra carbon dioxide is people burning coal and other fossil fuels.

The exact amount of warming that will occur in the coming century depends largely on the energy choices that we make now and in the next few decades, particularly since those choices directly influence how fast we put heat-trapping gases into the atmosphere. And so we have to take care about the different consequences of this warming. These risks include sea level rise, leading to coastal flooding and erosion; changes to the salinity of coastal groundwater supplies, resulting in freshwater stress; risks to marine ecosystems, such as mass coral bleaching and die-offs; and more intense tropical cyclones. Limiting warming to 1.5 degrees Celsius will mean 40,000 less people will see their land inundated by 2150.

Références

IPCC AR6 WG (2021), Climate Change 2021 The Physical Science Basis, available from: https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Full_Report.pdf