- The greenhouse gases humans have released into the atmosphere over the past 100 to 150 years has led to a 1.1°C (2°F) rise in global temperatures, according to the Intergovernmental Panel on Climate Change, or IPCC.
- The authors of the IPCC’s latest report use the strongest language yet to connect human activity to climate change, calling the link “unequivocal.”
- The report draws on the findings of thousands of studies, pointing to the need to cut CO2 emissions immediately while also suggesting that many of the impacts of climate change are irreversible.
- This report focuses on the science behind climate change and will be combined with two subsequent reports on the adaptation and vulnerability to the impacts of climate change and ways to mitigate its effects to produce the IPCC’s sixth assessment, scheduled for publication in September 2022.
The greenhouse gases humans have released into the atmosphere over the past 100 to 150 years, mostly in the form of carbon dioxide, have led to a 1.1° Celsius (2° Fahrenheit) rise in global temperatures, according to the Intergovernmental Panel on Climate Change, or IPCC.
More than 200 scientists from around the world contributed to an IPCC report released Aug. 9 that looks back at past changes to climate, assesses the current state of the planet, and projects the changes that Earth’s life may face in the future. In the strongest language yet, it ties the role of humans to climate change, describing the link as “unequivocal.”
“It has been clear for decades that the Earth’s climate is changing, and the role of human influence on the climate system is undisputed,” Valérie Masson-Delmotte, co-chair of the working group that produced the findings and a senior scientist at the University of Paris-Saclay, said in a statement. The report also connects the surge in extreme weather to human-caused changes to the climate, which the authors describe as “widespread, rapid and intensifying.”
This publication, focused on the science of climate change, is actually just a piece of the sixth “assessment report” that will have been produced by the IPCC since the Switzerland-based panel was founded in 1988. Two other reports, focused on adaptation and vulnerability to the impacts of climate change and ways to mitigate its effects, are set to be released in 2022. The IPCC will then compile these three parts, along with findings from three special reports on the implications of a 1.5°C (2.7°F) temperature rise, climate change’s impact on land, and the ramifications for the ocean and ice on Earth, in a summary scheduled for publication in September 2022.
The authors of the report are scientists who have volunteered their time to work with the IPCC, which is itself a group of governments formed by the World Meteorological Association and the United Nations Environment Programme. All 195 members must approve each report before it is released.
Its publication comes ahead of the U.N. climate change conference (COP26) beginning Oct. 31 in Glasgow, Scotland.
The IPCC published its fifth assessment report in 2014, and it served as the foundation for the global agreements aimed at keeping human-caused warming under a 1.5°C rise above pre-industrial levels that were part of the Paris climate accords.
Studies of ancient climate conditions on Earth cited in the report reveal that average global temperatures haven’t risen this fast in at least 2,000 years, and the concentration of CO2 hasn’t been this high in 2 million years. The authors predict that Earth will probably reach — or escalate beyond — that 1.5°C threshold in the next 20 years.
“This report is a reality check,” Masson-Delmotte said.
Since the 2014 report, ongoing research has improved scientists’ understanding of the effects of increasing levels of carbon in the atmosphere.
“We now have a much clearer picture of the past, present and future climate, which is essential for understanding where we are headed, what can be done, and how we can prepare,” Masson-Delmotte added.
The authors have narrowed the range of the warming caused by doubling the amount of carbon in the atmosphere compared to what it was about two centuries ago — what’s known as equilibrium climate sensitivity — to somewhere between 2.5°C and 4°C (4.5°F and 7.2°F). The authors’ “best estimate” is that the climate will begin to stabilize when it has warmed by 3°C (5.4°F).
CO2, a byproduct of burning fossil fuels for energy, clearing forests for agriculture, and other human activity, has been, and continues to be, the biggest climate-warming culprit. There are other “greenhouse gases” that we humans produce and that contribute to climate change, including methane, ozone and chlorofluorocarbons. But these chemicals only hang around in the atmosphere for at most a few decades. Other chemicals used or produced by humans, such as nitrates and aerosols, can actually have a cooling effect, but they typically only linger for a matter of days, and today’s climate models account for their impacts. By contrast, CO2 emitted today will be part of the atmosphere for hundreds of years, if not longer, leading to its pronounced effect on the changing climate.
The authors point out that reducing our emissions of many of these compounds could slow warming while providing cleaner air.
“Limiting other greenhouse gases and air pollutants, especially methane, could have benefits both for health and the climate,” Panmao Zhai, co-chair of the working group and a research professor at the Chinese Academy of Meteorological Sciences, said in the statement.
Still, they emphasize the need to reduce CO2 in the atmosphere immediately, with the goal of reaching net-zero emissions as soon as possible. The takeaway from the thousands of studies that anchor the IPCC’s conclusions is that many of climate change’s effects are “irreversible” through the end of the century. Immediate, drastic cuts in the release of CO2 probably won’t be enough to stave off the melting of the ice sheets like the one that covers much of Greenland and the resulting rise in sea levels. As a result, sea levels could still rise by 50 centimeters (20 inches), even under a scenario with relatively low emissions. Higher emissions could more than double that figure, which could lead to catastrophic flooding in coastal areas.
Shifts in the ocean, which has absorbed more than 90% of the excess heat from climate change, are likely to play out over the decades to come. With more CO2, waters have become more acidic, putting pressure on ecosystems that ultimately provide food to millions of people.
The scientists note that rising average temperatures globally are only part of the story. Evidence has shown that the impacts of the overall changing climate are much more localized. Increasing volatility in the weather has already led to an uptick in stronger storms, sweeping heat waves and droughts in parts of the world. These changes could alter farming conditions, trigger more frequent fires, and make parts of the world, such as low-lying islands, uninhabitable.
Substantial changes in rainfall patterns are also likely, the authors predict, with more precipitation closer to the poles and in the tropics, while declining in the regions between. However, there is some evidence to suggest that droughts could increase in the Amazon, the world’s largest tropical forest.
Along with the report’s release, the IPCC has produced an interactive atlas that allows users to see how different scenarios might affect certain spots around the globe.
The authors say that reducing the likelihood of extreme events — or minimizing the chances that their likelihood increases, at least — demands immediate action.
“Stabilizing the climate will require strong, rapid, and sustained reductions in greenhouse gas emissions, and reaching net zero CO2 emissions,” Zhai said.
In the starkest relief yet, the current report shows that ignoring such warnings and allowing a continuous stream of carbon to flow into the atmosphere will only exacerbate the challenges that have come at an increasing clip in recent decades.
“Climate change is already affecting every region on Earth, in multiple ways,” Zhai said. “The changes we experience will increase with additional warming.”
Banner image: Glacier in Antarctica. Photo credit: N. Butler
John Cannon is a staff features writer with Mongabay. Find him on Twitter: @johnccannon
Citation:
IPCC, 2021: Frequently Asked questions. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. In Press.
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