The Intergovernmental Panel on Climate Change made the pronouncement as part of its assessment of climate change and efforts to mitigate its negative impact. The study came as a response to the more than 190 signatory nations to the 2015 Paris climate accord, which at the time included the U.S. The Trump administration announced last year its intent to pull out of the accord.
A failure by countries to meet voluntary targets to limit global warming to “well below” two degrees Celsius, or 3.6 degrees Fahrenheit, would be devastating for some ecosystems and raise sea levels to flood many major cities and some entire countries, among other risks, the report says.
The IPCC’s process brings together several scientists as lead authors to assess the scientific, technical and economic data available on whatever climate-change-related topic they’re covering. Some of that is peer-reviewed research, but the work also includes some non-peer-reviewed work by governments and industry.
Typically, hundreds of scientists review the drafts IPCC authors put together, and government negotiators also have a say in their conclusions, a practice that has drawn criticism from scientists in the past. While a large body of scientific work concludes emissions cause global warming, some dispute those conclusions.
The IPCC report finds meeting the carbon-reduction goals would require dramatic changes in how citizens get energy, how industries make everyday products, and how cities are designed. It would put governments in the middle of routine decisions like how people use land.
Renewable energy and improved efficiency are catching on, but avoiding catastrophic climate change would require much more effort, including unproven and risky attempts to extract carbon already in the atmosphere, the report says.
The report, released after being completed in recent days during sessions in South Korea, comes in a year which has seen historic heat waves that have turned deadly and disasters and rising sea levels affecting markets like insurance and real estate.
To meet the goals of the Paris agreement and reduce other risks, 2010 levels of global carbon dioxide emissions would need to be halved by 2030, and effectively end by around 2050, the IPCC report says. Global emissions are not shrinking, and rose last year to record levels after several years of remaining flat—despite emissions cuts in the U.S., U.K. and some other countries, according to the International Energy Agency.
“Limiting warming to 1.5ºC is possible within the laws of chemistry and physics but doing so would require unprecedented changes,” said Jim Skea, co-chairman of an IPCC working group.
International diplomats will be meeting in Poland later this year, followed by other meetings in the years to come, on how to enact and refine the goals of the Paris accord. The IPCC assessment is supposed to help that.
Key to success will be extracting carbon from the atmosphere, the IPCC said. The buildup of emissions over time means either limiting or ending emissions is not enough. Carbon already existing in the atmosphere would have to be captured to stop global warming from becoming more severe.
Options include the restoration of forests and technology to lower the amount of acid in oceans or pull carbon directly from the air. But all are unproven, the report says, adding there are few obvious ways to make this work profitable, putting the costs of existing carbon reduction on governments.
“Climate change is one of those generational challenges that simply cannot be solved without diplomacy—without international cooperation,” former Secretary of State John Kerry said in a statement about the report. “This needs to be an action-forcing moment for renewed global focus.”
The IPCC was the subject of controversy in a 2009 dispute, after the release of hacked emails led to questions over its methodology. A series of independent investigations following the hack, allowed the institution to claim vindication.
Under former President Barack Obama, Mr. Kerry led the negotiations that produced the Paris agreement, the first to require all developed and developing nations to help slow global warming by limiting their greenhouse-gas emissions.
Since then, Mr. Obama’s successor Donald Trump pledged to remove from the accord the U.S., the world’s largest economy, raising questions about the effectiveness of international efforts to tackle such an expensive, complicated problem.
A weakness of the Paris accord is its failure to address how nations might invest in the technologies needed to capture carbon emissions, said George David Banks, a former adviser to Mr. Trump on climate issues who supports the U.S. remaining in the accord.
“We have some of those discussions now, but they’re not focused enough,” he added. “Just deploying wind farms and solar farms in developing countries is not going to solve the problem.”
The challenges are so great that every country and business sector will need to do more and act more quickly to slow global warming, said Lou Leonard, senior vice president for climate change and energy at the World Wildlife Fund.
“The reality is that the technology is there, we do know what to do,” Mr. Leonard said. “But will we? That’s a political question, not a technical question.”