Climate experts described the report as the most dire assessment of the effects of climate change ever issued by the United Nations Intergovernmental Panel on Climate Change, which has been issuing climate assessments for more than three decades.
"The new contribution of this report shows how much faster these things are happening than we originally thought," said Sherilee Harper, a climate scientist at the University of Alberta and the report's lead author.
According to the report, severe weather events exacerbated by global warming caused by the use of fossil fuels and other human activities have resulted in "widespread, pervasive impacts to ecosystems, people, settlements, and infrastructure." The report cites the extreme wildfires that ravaged Alaska in 2015, as well as the severe rainfall brought on by Hurricane Harvey in Texas in 2017. It comes months after the Pacific Northwest was hit by a deadly heat wave.
Some governments' efforts to adapt to climate change, such as the implementation of systems that warn the public of impending heat waves, have helped to mitigate the effects of such events, according to the report. However, the report warns that current global preparedness will be insufficient to avoid the costly and far-reaching consequences of extreme weather events in the coming decades.
"People are suffering and dying right now as a result of climate change, and we're not seeing an investment to ensure that we're prepared for an even warmer future," said Kristie Ebi, a professor of global health at the University of Washington and the report's lead author.
The report, the most comprehensive assessment of climate change impacts since 2014, is based on over 34,000 studies and was compiled by 270 scientists from 67 countries. The reports are meant to assist government leaders in developing science-based climate policies.
"We've seen graphic, compelling evidence of the impacts of climate change on people and nature all over the world," said Jane Lubchenco, deputy director for climate and environment at the White House Office of Science and Technology Policy, who was not involved with the report. "The report documents what we already know about what is happening and how it is causing real problems for people."
The scientists who prepared the report used recent advances in attribution science, as well as new data on extreme weather events over the last decade. This emerging subfield of climate research seeks to better understand the role of climate change in extreme weather events and to forecast the growing health consequences of a warming climate, such as foodborne and waterborne illnesses and insect-borne infections.
"What you see here is an overwhelming and unfortunately confident attribution of current damages and current impacts to anthropogenic climate change," said Gavin Schmidt, a climate scientist at NASA.
As part of the Paris Agreement, nearly 200 countries agreed in 2015 to take steps to limit the rise in global average surface temperature from preindustrial levels to "well below" 2 degrees Celsius—ideally, no more than 1.5 degrees Celsius.
According to an IPCC assessment published in 2018, human activities have already resulted in global warming of about 1 degree Celsius above preindustrial levels. If warming continues at its current rate, temperatures will rise by 1.5 degrees Celsius above preindustrial levels between 2030 and 2052, according to the report.
According to the new report, between 3.3 billion and 3.6 billion people, or nearly half of the world's population, live in circumstances that make them especially vulnerable to the effects of climate change. People in poverty, those with limited access to healthcare, and those living in low-lying, flood-prone areas or in the path of recurring storms are especially vulnerable.
According to the report, parts of Africa, South Asia, and Central and South America will bear the brunt of the consequences. And, because they are so closely linked to the land and are so directly affected by environmental impacts, indigenous people are already experiencing irreversible changes in their ways of life and are expected to bear the brunt of the consequences, according to the report.
Nations updated their pledges to take action to combat climate change at a major climate meeting last year in Glasgow. According to a United Nations report released in October, many countries are falling short of their targets.
In the United States, proposed legislation backed by President Biden aimed at shifting the country away from fossil fuels and toward renewable energy sources has failed in Congress.
However, "widespread action is really urgently needed, even more urgently than previously thought, and that window for action is rapidly closing," according to Dr. Harper. "Every decision we make now has the potential to move us closer or further away from a climate-resilient future."