Summarizing the previous 5 synthesis reports, that have progressively sounded the alarm louder and louder
Many of you are likely aware that the Intergovernmental Panel on Climate Change (IPCC) has been the world’s foremost authority on the science and assessment of climate change since their inception back in 1988. They have been guiding us in understanding what the research is telling us and how bad things can get if we don’t take action. Their reports of what different levels of global warming can mean for the planet, and the concentration of greenhouse gas emissions that can lead there, have been the building blocks of climate policy formulation since the 1990’s. A common misconception is that the IPCC itself carries out research, but really it is a body of around 796 sector experts, who have parsed over 100,000 peer-reviewed climate change studies to give us the definitive answers on climate change.
Our Avengers-like group of scientists from across the world (who largely volunteer their time for this work) recently released the last part to their 6th Assessment Report (The AR6 Synthesis Report), on March 20th this week. This report synthesizes 6 previous climate change reports, and gives us the latest picture on climate change science, effects, vulnerability, as well as mitigation and adaptation. So in light of this final AR6 report, we at The Decarbonomics Initiative wanted to take a look back in time, and do our best to give you the key takeaways of all the previous IPCC assessment reports to date. Reports that amalgamate the lessons from the three IPCC working groups:
The Physical Science of Climate Change;
The Impacts, Adaptation and Vulnerability; and
The Mitigation of Climate Change.
These reports are famously technical, and maybe too much so for the layperson to fully comprehend the message. Hence, here is our attempt at closing that gap:
[Full disclosure, I have not reviewed the AR6 synthesis report as of the time of writing. So take this piece as more of a background and primer, a sort of Climate Assessments 101 to prepare you for reading into what the new report might have.]
 | First Assessment Report (FAR, 1990): “Yup we probably have a role in what’s happening, probably because of oil, and we’re probably going to have to collaborate to fix it.”
The FAR provided an initial assessment of the scientific basis for understanding climate change (greenhouse gases → global warming → changed climate patterns), its potential impacts, and options for response. It confirmed the role of human activities, particularly the burning of fossil fuels, and highlighted the uncertainties in predicting future scenarios. The FAR also emphasized the need for international cooperation in addressing the issue. What this assessment report lacked was on the economic impacts, technical feasibility, and any sort of concrete pathway to tackle climate change. A lot of “we don’t know for certain, but this is what’s probably happening.” |
 | Second Assessment Report (SAR, 1995): “We’ve reviewed more evidence, are now more sure of our projections for emissions growth, and let’s all commit to do something about it? See you all in Kyoto!”
The SAR strengthened the evidence for human-induced climate change, concluding that the balance of evidence suggested a discernible human influence on global climate. It provided clearer regional-based projections of future climatic patterns, potential impacts on various sectors, and spent more real estate on the economic impact of climate change, as well as strategies for adaptation and mitigation. The SAR played a critical role in the negotiations leading to the Kyoto Protocol—which eventually failed since it did not include the world’s largest economies, did not hold developing countries to any binding targets, and the US did not sign up entirely. |
 | Third Assessment Report (TAR, 2001): “Ok we are really really sure that we are causing climate change, if we were not scientists we’d probably bet on it now. Also since you don’t seem to care about the environment alone, here’s more on what it could mean for human health”
The TAR further increased confidence in human influence on climate change, stating that there was a 66-90% probability that most of the warming observed over the past 50 years was attributable to human activities. The report refined climate projections, estimating a global mean temperature increase of 1.4°C to 5.8°C by 2100 (increased from SAR), and projected sea-level rise between 9 cm and 88 cm during the same period. The discussion on incorporating both adaptation and mitigation strategies was richened by highlighting the need to incorporate climate policies for sustainable development. |
 | Fourth Assessment Report (AR4, 2007): “Ok we are officially sounding the alarm! WE the humans are for sure for sure (“as much as scientists can be”) causing this. Please we need to do something together. Thank you for backing us up Al Gore, the Nobel Peace Prize is the next best thing to the presidency”
The AR4 concluded that it was unequivocal that the Earth's climate was warming, and more than 90% likely that human activities were the primary cause since the mid-20th century. The report projected a global mean temperature rise of 1.1°C to 6.4°C by 2100, depending on emissions scenarios, and estimated a sea-level rise of 18 cm to 59 cm within the same timeframe (a closing gap from the previous assessment). AR4 underscored the severe consequences of climate change, such as increased frequency |
 | Fifth Assessment Report (AR5, 2013-2014): “We’ve reached hand sanitizer level, essentially 99% confident that we are at fault. All of these severe effects will happen now unless we take rapid action. We might get locked into a climate change pathway. Also, I think we’ve settled on a logo…” AR5 presented even stronger evidence of human influence on climate change, stating that it was "extremely likely" (with a 95-100% probability) that human activities were the dominant cause of the observed warming since the mid-20th century. The report projected a global mean temperature increase of 0.3°C to 4.8°C by 2100, depending on the emissions scenarios, and estimated a sea-level rise of 26 cm to 98 cm within the same timeframe, emphasizing that continued emissions would increase the likelihood of severe and irreversible impacts on humans and ecosystems (now including more frequent and intense heat waves, extreme precipitation events). The story on coordination on mitigation and adaptation was still there but with a further emphasis on the need to rapidly decarbonize to avoid the worst effects of what was to come. |
The sixth assessment synthesis report released on Monday now synthesizes the following special and working group reports:
Special report on Global Warming of 1.5C (SR15), 2018
Special report on Climate Change and Land (SRCCL), 2019
Ocean & Cryosphere in Changing Climate (SROCC), 2019
Climate Change 2021: The physical science basis of climate change, 2021
Climate Change 2022: Impacts, Adaptation & Vulnerability
Climate Change 2022: Mitigation of Climate Change
As such, the AR6 is probably now the latest authoritative guidelines on climate change, its effects, who is most vulnerable, and what we can do to further mitigate it and adapt to it. It will also now take into account the 2016 Paris Agreement, which superseded the 1997 Kyoto Protocol, as well as the progress (or lack thereof) we have collectively made towards those targets.
Now that we are for sure locked into a +1.0°C world; and limiting warming to 1.5°C seems less and less doable, I am hoping that this synthesis report might have a completely different tone than the previous ones. We probably don’t need to leave room for uncertainty now on the scale of the issue and the urgency to act drastically and rapidly. Otherwise, the next time the IPCC publishes an assessment, we might be talking more about how to contain the damage than to mitigate it.
We hope that this synthesis report becomes a turning point, as it leverages the fact that we are nearing the locking-in point for some of the effects of climate change. A turn towards immediately adopting solutions that both continue enabling economic growth, and help to mitigate climate change through decarbonization.
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