The world’s top climate scientists today released their first major review in eight years on the physical science of climate change, in a report approved by 195 countries. Here are 13 things we learned from the , about 3000 pages of which are simply a list of citations for the 14,000 scientific papers assessed.
1. The world has warmed by 0.1°C more than previously thought
The amount the world has already warmed has been revised upwards compared with the last version of the IPCC’s report, released in 2013. This shift is due to improved observational records and a series of very warm years in the past decade. Earth’s global average surface temperature is now 1.09°C above 1850-1900 levels. The rate of warming since the industrial revolution is unprecedented in at least 2000 years.
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2. We have even greater certainty that our fossil fuel burning and activities are to blame
“It [the report] tells us that it is indisputable that human activities are causing climate change,” says Hoesung Lee, chair of the IPCC. The report itself says: “It is unequivocal that human influence has warmed the atmosphere, ocean and land.” In 2013, the IPCC said human influence was only “clear”.
3. Earth is expected to reach or breach 1.5°C of warming within two decades
All five emissions scenarios evaluated by the IPCC suggest we will miss the Paris Agreement’s toughest target, of holding warming to 1.5°C, within the next 20 years. The central estimate is for the early 2030s. Even in the very lowest of scenarios for future greenhouse gas emissions, the threshold is “more likely than not” to be hit.
4. Staying below 1.5°C in the longer term is still possible
In the very lowest emissions scenario, temperatures are expected to fall back to 1.4°C by 2100 after reaching 1.5°C. “If we rapidly reduce greenhouse gas emissions, if we can reach global net zero carbon dioxide emissions by around 2050, it is extremely likely we can keep global warming well below 2°C,” says Valérie Masson-Delmotte of the IPCC. That will require much stronger policies and measures than governments have in place now, though.
5. We have already locked in climate changes that will last thousands of years
Emissions to date mean some changes to the environment are now unavoidable, but we can slow them by cutting emissions faster. “Deep ocean warming, acidification and sea level rise are committed to ongoing change for millennia after global surface temperatures initially stabilize and are irreversible on human time scales,” the report says.
6. Some air pollution cuts are likely to increase climate change
Some of the warming to date has been masked by the aerosols, or pollution, we have put into the air. The IPCC estimates a cooling effect of 0-0.8°C so far. Cleaning up air pollution in the short term is good idea for human health and often also addresses some of the root causes of climate change. Nonetheless, doing so is “very likely” to cause further warming in the next two decades, because pollution – aerosols – have a cooling effect on global warming.
7. Each fraction of warming and every extra tonne of CO2 matters
Every additional 0.5°C of global warming will cause “clearly discernible increases” in the intensity and frequency of heatwaves, heavy rainfall, and droughts in some regions. That means we will still feel the benefits of efforts to reduce emissions even if we breach 1.5°C or 2°C. Passing such thresholds doesn’t mean we should give up on net zero.
8. The pandemic has had little impact on climate change
The covid-19 pandemic led to a huge drop in global emissions last year but it hasn’t changed the big picture on climate change. The impact of reduced emissions caused by lockdowns and economic slowdowns were “undetectable” beyond natural variability due to their temporary nature, said the IPCC.
9. CO2 removals are going to be important
Using technology and tree-planting to remove CO2 from the atmosphere does work, and is a plausible way of stabilising global temperature rises. The report concludes that CO2 removal can work, and that it would actually reverse warming, says Joeri Rogelj at Imperial College London, an IPCC author. “So that is good news.” However, each tonne of CO2 removed could be 10 per cent less effective at cooling than each tonne of CO2 emitted is at warming – in other words, we can’t simply take CO2 out of the atmosphere and pretend we never emitted it.
10. We cannot rely on nature as an excuse for business as usual
Forests, oceans and other “carbon sinks” will get less efficient at absorbing CO2 if we continue with high emissions. “While natural land and ocean carbon sinks are projected to take up, in absolute terms, a progressively larger amount of CO2 under higher compared to lower CO2 emissions scenarios, they become less effective, that is, the proportion of emissions taken up by land and ocean decrease with increasing cumulative CO2 emissions,” says the report.
11. Geoengineering the planet is probably a bad idea
One proposed solution to climate change, putting particles in the atmosphere to reduce the amount of the sun’s energy reaching Earth, is probably a bad idea. The report says the approach, and other ones under a suite of “solar radiation modification” options, could offset global warming but is likely to cause abrupt changes to water cycles, could have regional climate impacts and poses a risk because suddenly stopping would cause “rapid climate change.” Amanda Maycock at the University of Leeds, UK, and an IPCC author, says such strategies “have a huge number of risks associated with them”.
12. There is no longer any doubt about the links between climate change and extreme weather
Heatwaves, floods and other events have all been blamed on climate change in recent years. In 2013, the IPCC said it had “detected changes in some climate extremes” due to human influences such as burning fossil fuels. Today the IPCC said “it is now an established fact” that the increased frequency and intensity of such events is due to humanity’s emissions.
13. The Arctic is likely be ice-free at points in coming decades
Even in a net zero world where emissions follow the lowest of the IPCC’s five scenarios, the Arctic is likely to fall to a “practically ice-free state” (meaning there are less than a million square kilometres of ice) at least once before 2050. Under the highest emission scenarios, that ice-free state will become the norm for late summer by the end of the century.
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