In 2014, the United Nations Intergovernmental Panel on Climate Change (IPCC) published its fifth assessment report (AR5). As in previous reports, AR5 included the latest insights from climate change experts across all relevant disciplines, as well as forecasts for the near future. In short, the AR5 and its predecessors were assessments of the effects of anthropogenic climate change on the planet and how we can avoid worst-case scenarios.
On August 9, 2021, the IPCC published a report entitled Climate Change 2021: the Physical Science Basis. Combining the latest advances in climate science and multiple lines of evidence, this first report paints a rather bleak picture of the rest of the 21st century. At the same time, it is a call to action and shows how abatement strategies and the reduction of greenhouse gas emissions ensure a better future for all.
The Working Group I report is the first edition of the IPCC’s Sixth Assessment Report (AR6), which will be completed and made available to the public by 2022 in the region. This time, however, the report focuses more on recommendations for reducing carbon dioxide (CO2) and other greenhouse gases.
Given the predictions made in this latest report, especially positive feedback mechanisms, this should come as no surprise. “This report reflects extraordinary efforts in extraordinary circumstances,” said Hoesung Lee, chairman of the IPCC, in a press release accompanying the release of AR6. “The innovations in this report and the advances in climate science it contains make an invaluable contribution to climate negotiations and decisions.”
A total of 234 authors from 66 countries (31 coordinating authors, 167 first-time authors and 36 review editors) and 517 contributing authors contributed to the creation of the Working Group I report. Originally slated for release in April 2021, the COVID-19 pandemic delayed the report for several months, making the AR6 the only report that was the subject of a virtual approval meeting. IPCC Working Group I Co-Chair Valérie Masson-Delmotte stated:
“For decades it has been clear that the earth’s climate is changing and the role of human influence on the climate system is undisputed … This report is a reality check. We now have a much clearer picture of past, present and future climates, which is critical to understanding where we are going, what can be done and how we can prepare. “
Consistent with previous assessment reports, the AR6 is based on improved observational datasets that assess historical warming and progress in the scientific community in the Earth’s climate response to anthropogenic greenhouse gas emissions. Like its predecessors, the AR6 finds that an average global increase of 1.5 ° C (2.7 ° F) between now and 2100 is the best scenario.
Meanwhile, she again states that a 2 ° C (3.6 ° F) increase is the scenario to avoid. However, this is not the worst case scenario as every scenario boils down to the greenhouse gas (GHG) emissions produced each year by (or as a result of) human activities. While this may not sound like big changes, it’s important to understand that the average represents all variations, depending on the region, time of year, and even day and night cycles.
With a rise of 1.5 ° C, the hottest days in the mid-latitudes of the earth will be up to 3 ° C (5.4 ° F). At higher latitudes, the coldest nights are 4.5 ° C (8.1 ° F) warmer; In the Arctic, temperatures are getting 5.5 ° C (9.9 ° F) warmer and cold spells are getting shorter. Even in the “best case” scenario, the resulting impact is significant, ranging from increased forest fires and drought to severe flooding and sea level rise (all of which have already been observed).
First, the report explains how the average global temperature has already risen by around 1.1 ° C (~ 2 ° F) since 1850-1900, directly due to human activity and rising greenhouse gas emissions. The report then provides new estimates of the chances of exceeding 1.5 ° C in the decades to come, and concludes that this goal will be unattainable without immediate, rapid and sweeping reductions in greenhouse gas emissions.
In fact, she estimates that even an average rise of 2 ° C will be inevitable, with more serious ecological consequences. In this scenario, temperatures will rise up to 4 ° C (7.2 ° F) closer to the equator, while the higher elevations and the Arctic will warm up to 6 ° C (10.8 ° F) and 8 ° C ( 14.4 ° F). respectively. The resulting positive feedbacks, in which Arctic ice sheets and permafrost floors are depleted, triggering the release of large pockets of methane, will also be more significant.
To summarize the results, the AR6 indicates that an average increase of 1.5 ° C leads to increased heat waves, longer warm seasons, and shorter cold seasons. With an average increase of 2 ° C, however, heat extremes will more often reach critical tolerance levels for agriculture and health. In short, the first scenario is not nice, but at least sustainable. In the latter and all other worse scenarios, life in certain parts of the planet becomes untenable.
Impact by region
The AR6 also provides a detailed breakdown of the impact of this warming by region. For example, further warming trends will further intensify the planet’s water cycle, leading to more intense droughts and heat waves in many regions and to heavier rainfall and associated flooding in others. Precipitation patterns are also still being influenced, with increasing rainfall in the higher latitudes and lower rainfall (especially during monsoons) in large parts of the tropics.
It is expected that sea levels in coastal areas will continue to rise on average over the 21st century in both scenarios. This will lead to more frequent “nuisance floods”, with storms regularly infiltrating coastal waters, causing property damage and the overflow of drainage systems. It will also mean that there will be more extreme sea level events each year that happened once in a century.
The increasing loss of ice sheets and permafrost, as well as decreased seasonal snow cover, will increase the solar energy that the polar tundra and the Arctic sea absorb. This will release methane deposits in both areas, a “super greenhouse gas” that will exacerbate the problem. Rise in sea temperatures, sea heat waves, ocean acidification and decreased oxygen levels will also have serious effects on ocean ecosystems and fisheries.
Another point of the report is how this impact will differ for people in urban and rural areas. Major demographic change is expected this century, with most of the world’s population living in large cities. The effects of climate change are amplified here in a number of ways, as urban areas are generally warmer than their surroundings and coastal cities are prone to flooding and sea level rise.
Fortunately, the report wasn’t all doom and gloom. Not only does it show the likely effects of climate change in the coming century, but it also shows how strong and sustainable reductions in greenhouse gas emissions would limit climate change. While the air quality benefits (and associated public health concerns) would be felt quickly, it would take 20 to 30 years for global temperatures to begin to stabilize.
In addition, the AR6 provides (for the first time) a detailed overview of the regional impact and information that can feed into risk assessment, adaptation and other decision-making in the coming years. It also provides a new framework that helps users understand what physical changes in climate – increased heat waves, drought, forest fires, rainfall, floods, cold spells, etc. – could mean for society and ecosystems.
Finally, the new report also reflects major advances in our understanding of the role of climate change in intensifying certain weather and climatic events – the so-called “mapping science”. The report also emphasizes that human action is a double-edged sword, where our actions have the potential to positively (as well as negatively) change the climate.
The regional effects of climate change can be examined in detail with a new tool developed by the IPCC, the so-called Interactive Atlas. The Policy Makers Executive Summary, Technical Summary (TS), FAQ Sheet, Media Essentials, and the full AR6 report are all available on the IPCC AR6 website. The Co-Chair of IPCC Working Group I, Panmao Zhai, summarized:
“Climate change is already affecting every region of the world in many ways. The changes we are experiencing will increase with additional warming. Stabilizing the climate requires a strong, rapid and sustainable reduction in greenhouse gas emissions and the achievement of net zero CO2 emissions. Limiting other greenhouse gases and air pollutants, particularly methane, could be beneficial for both health and the climate. “
Avoid scenarios by 2050 and the end of 21. At this point, it’s not just about significantly reducing our emissions; it will likely also require large-scale carbon sequestration and perhaps ecological engineering as well. It’s a big mountain to climb, but much more pleasant (and cheaper) than the alternative!
Further reading: IPCC