On August 9, the IPCC published its 6th report . Everyone has heard of it; we know the news is not good. Let's try to see things more clearly and to begin with, let's take a moment to focus on the IPCC.
What is the IPCC?
Here is what we can read on the organization's website:
“The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 to provide detailed assessments of the state of scientific, technical and socio-economic knowledge on climate change, its causes, potential repercussions and coping strategies. »
In other words, the IPCC compiles, studies and evaluates scientific literature relating to climate to produce summaries, updated periodically. Its authors do not make recommendations, they do not give orders to decision-makers, they report recent discoveries and model scenarios, based on available data, to anticipate the climate future.
This time, the 234 authors – handpicked AND volunteers – combed through 14,000 publications to produce a first version of the report. This was shared with reviewers who were able to provide 78,000 comments , all of which were taken into account to obtain the second version. The revised version, which runs to some 4,000 pages , as well as the technical summary and that intended for political decision-makers, was finally submitted to all the representatives of the IPCC member states, who validated it, line by line.
This “repeat” publication system minimizes the risk of error and indicates that the 195 nations represented – including China and the United States – have read and validated the report's findings.
Finally, let us remember that this report is the fruit of the work of group 1 of the IPCC, which has three.
- Group 1 studies the physical functioning of the climate and models its evolution.
- Group 2 is interested in the vulnerability of our societies to climate change, by evaluating the positive and negative consequences they can have as well as the possibility of adapting to them.
- Group 3 evaluates existing solutions to reduce greenhouse gas emissions or otherwise mitigate climate change.
The reports of groups 2 and 3, which complement the one that interests us today, were respectively published in February and March 2022. A summary of the 3 reports is due to appear in September 2022.
Now that we have presented the IPCC and explained why its work deserves to be taken seriously, let's move on to the content of the report itself, which includes a certain number of new features compared to the previous ones (the 5th dated from 2014).
Overview
Here are some key points to remember about the current state of the climate:
- It is indisputable that human activities are the cause of climate change.
- Recent climate changes, whether affecting the atmosphere, oceans, cryosphere or biosphere, are widespread, rapid and intensifying. They are unprecedented in thousands of years.
- Global warming makes extreme events, including heat waves, heavy precipitation and droughts, more frequent and more severe.
- The increase in surface temperature accelerates the rise of sea levels and causes warming, loss of oxygen and acidification of the oceans.
- Unless there is an immediate, rapid and large-scale reduction in greenhouse gas emissions, limiting warming to 1.5°C will be out of reach.
Now let's try to clarify some things.
“It is indisputable that human influence has warmed the atmosphere, oceans and land. »
The 6th report in some way puts an end to the debate on the origin, anthropogenic or not, of global warming. It is now “unequivocal” that human activity – through the greenhouse gas emissions it generates – is warming the planet, whereas this was “only” extremely probable in the 5th report , which left room for contestation, more or less scientific, for skeptics.
Instead, let's look at the diagram presented in the summary for policy makers (all the legends of the diagrams which follow have been translated by Le Bon Pote ).
The figure on the left shows that the increase in temperature since 1850 is unprecedented for at least 2,000 years. The report indicates that it is very likely without precedent for at least 100,000 years.
The figure on the right compares three curves:
- The black curve corresponds to the observed temperatures
- The green curve corresponds to a modeling of the evolution of temperature, on which only natural factors (solar irradiance and volcanic eruptions) would influence.
- The brown curve corresponds to a second modeling, this time integrating human factors, first and foremost CO emissions.2.
We notice that the green curve is approximately constant, which means that the influence of natural factors is almost zero over this period. On the other hand, the brown curve is superimposed on the observed temperatures.
Conclusion ? It is human factors that cause the curve to drop.
The following diagram shows the same thing, in another way:
The last ten years have been 1.1°C warmer than at the start of the industrial era (1850-1900). Human influence is evident.
In this regard, it must be remembered that the land is warming more than the oceans. Thus, an average increase of 1.5°C corresponds in certain regions of the world to an increase of 3°C... And as we all live on emerged territories, we must expect that the warming felt will be higher than the temperatures announced.
A diagram from the report illustrates this point:
Each additional ton of CO 2 released into the atmosphere increases warming.
Warming is almost proportional to cumulative CO 2 into the atmosphere . If each ton of CO2 released amplifies warming, by contrast, all avoided emissions reduce warming .
This is clearly seen in the following graph:
Let's open a parenthesis to explain what the scenarios retained by the IPCC in this report correspond to, indicated in 5 different colors:
- SP1-1.9
- SSP1-2.6
- SSP2-4.5
- SSP3-7.0
- SSP5-8.5
Let's take the example of the yellow scenario, SSP2-4.5.
SSP stands for Shared Socio-economic Pathway and designates a scenario which takes into account several parameters such as the evolution of the world population, the pace of growth or the degree of international cooperation in the face of the climate emergency. SSP2 therefore refers to a defined socio-economic scenario, nicknamed “the middle way”. For details of the five scenarios, go to the corresponding Wikipedia page .
4.5 designates the level of radiative forcing associated with the SSP2 scenario. This notion, which is essential to fully understand the phenomenon of global warming, is explained very clearly by Le bon pote here . Today the radiative forcing is 2.3 W/m². Remember that it increases each time CO 2 is emitted and stored in the atmosphere. And the more it increases, the more the temperature on the surface of the globe increases.
To put it simply, the light blue scenario corresponds to the best of all worlds, in which the energy transition would take place at high speed, in a concerted manner at the national and international levels; the dark red curve models the disaster scenario, with galloping growth, increased use of fossil fuels and no measures taken to reduce emissions. Both are equally improbable.
In the following table, the IPCC indicates how the temperature will evolve, in the short, medium and long term, depending on the scenario chosen.
Remember that very likely range means that the given interval is more than 90% certain.
For the moment we are rather following the yellow curve, SSP2-4.5, which leads to an increase of 2°C around 2050, and of 2.7°C by 2100.
Climate change is already affecting all inhabited regions of the planet.
Let's start by taking a look at the following diagrams:
The first diagram indicates that extreme heatwaves will increase throughout the world , with a high degree of certainty in most cases.
The next two show that intense precipitation will increase in regions colored green while droughts will increase in those colored yellow. However, these forecasts are less reliable, due to a lack of consensus or a limited data panel.
Warming amplifies extreme climatic phenomena (heat waves, heavy precipitation, droughts, cyclones) – or the snowball effect.
If we take the example of heatwaves occurring once every ten years before the industrial era, we observe that today, due to an increase of 1°C in the average temperature, they will occur probably 2.8 times per decade.
If warming reaches 2°C (which is likely to be the case) they will occur on average 5.6 times per decade, and their intensity, which was around +1.2°C with a warming of 1° C, will increase to +2.6°C.
Intense precipitation and droughts will be subject to a comparable surge, although to a lesser extent.
What should we conclude from this? Well, the more the average temperature increases on the surface of the globe, the more violent and frequent will be heatwaves, droughts, floods, precipitation...
In other words, and as climatologist Christophe Cassou, author of the report, says:
“Each fraction of a degree counts because it conditions the risk associated with extreme events. If we cannot contain global warming to +1.5°C, we must do everything to limit it to +1.6°C. »
Carbon budgets:
Since the publication of the first IPCC report in 1990, that is to say in thirty years, 1,000 billion tonnes of CO 2 (GtCO 2 ) have been emitted. This is almost half of our cumulative emissions (2,390 GtCO 2 ) since the start of the industrial era in 1850.
Taking into account the almost proportional relationship between cumulative emissions and the increase in the average temperature on the surface of the globe, it is possible to calculate what margin we have left depending on a temperature objective to be achieved, or not to be achieved. exceed.
This is where carbon budgets come from. The following table indicates the quantity of CO 2 which can still be released into the atmosphere before reaching a certain level, at different degrees of certainty.
Let's try to decipher what we have before our eyes. If we do not want to exceed +1.5°C compared to the pre-industrial era, knowing that we are already at +1.07, this implies sticking to +0.43°C in the future, i.e. a carbon budget of 300 GtCO 2 to maximize our chances (83%), and up to 500 if we are players and we agree to toss a coin on the coming catastrophe. A release of an additional 900 gigatons would most likely put us close to +2°C, with the consequences that we have seen.
Given that global emissions are currently around 40 GtCO 2 /year, this budget is likely to shrink dramatically, or melt like snow in the sun... Hence the rapid, widespread and sustained changes over time that the IPCC calls for his wishes. Political decision-makers, but not only that, businesses and citizens too, now have the cards in hand, the situation is clear: there is an urgent need to act.
The final word
“Unequivocally”: this formula is a big step for the IPCC. The responsibility of human activity has now been demonstrated. Energy production, industry, transport, residential, tertiary, agriculture, waste treatment, all these sectors, because they emit greenhouse gases in excessive quantities on a global scale, contribute to warming the planet.
If the consequences of business as usual as described in this report – the red scenarios – send chills down your spine, the worst can still be avoided. To do this, it is about being aware of the threat that weighs, taking note of it and reacting accordingly.
The avenues are known: energy efficiency of buildings, renewable energies, sustainable mobility, creation of carbon sinks… All of this contributes to the reduction, avoidance or compensation of carbon dioxide and equivalent emissions – which in turn slow down global warming. and mitigate its consequences.
The fact remains that ambitious public policies, massive investments, increased awareness and responsibility of all economic actors, as well as effective collaboration on an international scale, constitute all decisive factors for a successful transition. energy that is required.
