Without a radical transformation of energy, transportation and agriculture systems, the world will hurtle past the 1.5 degree Celsius target of the Paris climate agreement by the middle of the century, according to a new report from the Intergovernmental Panel on Climate Change.
Failing to cap global warming near that threshold dramatically increases risks to human civilization and the ecosystems that sustain life on Earth, according to the documents and summaries released Oct. 8.
To keep warming under 1.5°C, countries will have to cut global CO2 emissions 45 percent below 2010 levels by 2030 and reach net zero by around 2050, the report found, re-affirming previous conclusions about the need to end fossil fuel burning. Short-lived climate pollutants, such as methane, will have to be significantly reduced as well.
More than 1.5°C warming means nearly all of the planet's coral reefs will die, droughts and heat waves will continue to intensify, and an additional 10 million people will face greater risks from rising sea level, including deadly storm surges and flooded coastal zones. Most at risk are millions of people in less developed parts of the world, the panel warned.
The report is a follow-up to the 2015 Paris Agreement and shows how climate risks to society will dramatically increase if the average global temperature rises more than 1.5°C above pre-industrial levels. Through 2017, the buildup of greenhouse gases in the atmosphere had already warmed the world by about 1°C.
"Currently, we are on pace to blow past 1.5 degrees Celsius in a couple decades," said Pennsylvania State University climate scientist Michael Mann. Even under the current base-case scenario, with the emissions cuts pledged in Paris, the world is on track to warm between 3 and 4 degrees Celsius, he said.
"Every half-degree matters, and 2 degrees Celsius and 1.5C warming shouldn't be thought of as cliffs we walk off. A better analogy is a minefield. The further out on to that minefield we go, the more explosions we are likely to set off," he said.
In particular, the new report spells out the difference between warming 1.5°C and 2°C, based on thousands of new scientific research papers published during the past few years.
The scientific research underlying the report is more certain than ever that the risk of extreme and deadly heat waves increases. The increase from 1.5°C to 2°C pushes extreme heat events past the upper limit of variability and a new climate regime, particularly in tropical regions. It also suggests that:
- Risks from extreme precipitation events would increase dramatically with 2°C warming, especially in eastern Asia and eastern North America.
- Sea level would rise about 4 inches more with 2°C of warming than with 1.5°C, affecting 10 million more people.
- An extra 580,000 to 1 million square miles of permafrost would thaw at 2°C compared to 1.5°C.
- At 1.5°C of warming, the Arctic is forecast to be ice-free once per century; at 2°C warming, that would happen once every 10 years.
What's Missing from the IPCC Report?
Despite these projections, some groups closely watching the process say the final version of the report—which had to be approved by all 195 IPCC member nations—doesn't do enough to warn world leaders about the grim consequences of reaching potential climate tipping points that could trigger conflicts over resources and mass migration.
"I was a reviewer on an earlier draft and was concerned that it left out some of the most important risks governments need to be aware of," said Bob Ward, policy and communications director for the Grantham Research Institute on Climate Change and the Environment.
"There was no mention of the potential for conflicts and mass displacement of people, which is of huge concern to governments. There wasn't much mention of tipping points. The IPCC has a reputation of not describing high-impact, low-probability events. There is evidence we may have already passed some key climate thresholds, including a meltdown of the West Antarctic Ice Sheet, which would raise sea level several meters in the next few centuries," he said.
There's also a growing risk that warming will disrupt key ocean circulations, including currents that keep Europe mild despite its relatively high latitude, Ward said. That could have dramatic consequences, including a Scandinavian-like climate for temperate parts of Western Europe.
"Those concerns have been documented very clearly the last few years. It would be inexplicable if you don't talk about some of these biggest risks in the summary for policymakers," he said.
Numbers from the International Federation of Red Cross and Red Crescent Societies provide a solid foundation for those concerns: weather-related events displaced 23.5 million people in 2016. IFRC President Francesco Rocca said half of the organization's operations are in response to weather-related disasters, which are compounded by "climate shocks and stresses."
"It is difficult to comprehend the scale of crises confronting vulnerable communities in a world that is 1.5°C or 2.0°C hotter," he said in a statement reacting to the IPCC report.
Half a Degree Can Have Devastating Effects
University of Florida sea level rise expert Andrea Dutton said she hopes the new report will help clarify global warming threats for the public, especially the risk of sea level rise in coastal areas.
"What sounds like small increments in temperature can have devastating effects in terms of climate impacts on growing human populations," she said. "This report is not about whether the planet can withstand another half-degree increase in temperature. It is about understanding whether we can withstand it. Small temperature changes can have far-reaching impacts on our ability to survive on this planet."
Satellite measurements from recent years show sea level rising faster than expected, and new data from ancient ice layers, tree rings and other sources suggest the polar ice sheets are more vulnerable to extensive melting at 1.5°C warming than previously believed.
"So, it is all doom and gloom? No, because every increment of progress we can make to keep the temperature from climbing even higher will make a difference," Dutton said. "The steps that need to be taken to abate the worst outcomes require leadership at every level. My hope is that this report will encourage and empower that leadership."
What Countries Pledged, and What's Needed
Existing pledges to cut greenhouse gas emissions submitted under the Paris Agreement don't come close to limiting global warming to 1.5°C, or even 2°C; scientists say they would result in closer to 3 or 4°C of warming. To stay under 1.5°C warming without relying on unproven CO2 removal technology means CO2 emissions must be cut in half by 2030, according to the report.
The report should be a wakeup call to the world to start acting now, said Bill Hare, CEO of Climate Analytics, a climate science and policy think tank.
"This report shows that dealing with climate change will become more dangerous and more expensive the longer we wait. Governments must get ready to commit to much more aggressive climate targets by 2020 at the latest, and they have to ditch coal," he said.
According to the IPCC, renewable energy must make up more than half the global energy mix by 2050, and coal needs to be almost completely phased out by then.
Failing that, the world will have to remove large quantities of CO2 from the atmosphere in the second half of the century. If the average global temperature overshoots 1.5°C warming by just 0.2 degrees, CO2 removal would have to be deployed at a scale "that might not be achievable given considerable implementation challenges," the report says.
The new IPCC report will be key to discussions in Katowice, Poland, in December, when the world meets for the annual UN climate talks to try to finalize the rules for implementing the Paris Agreement.
Christopher Weber, global lead scientist for climate and energy for the World Wildlife Fund, said negotiators in Poland should focus on the underlying science.
"This is not a political negotiation, it's a science report. We're already seeing impacts like super storms, wildfires and heat waves from 1 degree of warming," he said. "This report underscores that many of the impacts we thought we would see at 2 degrees we will see sooner, and they may be unstoppable above that."