Even decades of warnings couldn’t buffer the sobering wake-up call issued by the United Nations Intergovernmental Panel on Climate Change (IPCC)’s Sixth Assessment Report in August.
“We are no longer referring to climate change in the future tense. The headline message from the IPCC report is ‘climate change is now,’” says William Collins, director of Berkeley Lab’s Climate and Ecosystem Sciences Division and a lead author of the Sixth Assessment’s chapter on short-lived climate forcers, such as methane and ozone, that don’t persist in the atmosphere nearly as long as CO2. “We are now saying it is indisputable that humankind has had a measurable impact on the climate system. We’re no longer leaving wiggle room.”
Since 1990, the UN panel has produced scientific assessments of climate change that set the standards for scientists and policymakers worldwide. In 2007, the body was awarded the Nobel Peace Prize, along with former Vice President Al Gore, who was credited for amplifying the alarm inherent in the science.
The first of the Sixth Assessment’s four parts, which covers the physical science of climate change, was released after a four-month pandemic-related delay. It documents the increase in the number and intensity of wildfires, which has compromised ecosystems and population health, and the role of fire as a feedback to climate change. Subsequent analyses are due next year.
More than 700 authors and editors from 90 countries contributed to the Sixth Assessment, among them several Berkeley faculty and alumni. In addition to Collins, they include Berkeley Lab scientists Charles Koven, Ph.D. ’06, Michael Wehner, Chaincy Kuo, Ph.D. ’99, Nan Zhou, and Stephane de la Rue du Can; Berkeley assistant project scientist Polly Buotte; and the Breakthrough Institute’s Zeke Hausfather, Ph.D. ’19. Another contributor, Berkeley Associate Adjunct Professor Patrick Gonzalez, Ph.D. ’97, now advises the Biden administration on climate change and biodiversity.
The latest analysis offers more precise data than past reports by including a more detailed regional assessment of climate change and increased vetting of both the data and programming code. It also boasts a more diverse and inclusive author team.
With aspects of climate change irreversible, the authors focused on ways to keep the global mean temperature in check. The 2015 Paris Agreement, an international treaty on climate change, pledged to limit warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial levels. Since the late 19th century, the global temperature has risen roughly 1.1°C (nearly 2°F). On our current trajectory, we will cross the Paris threshold in 10 to 20 years.
“That’s why this is being correctly described in the media as a climate emergency,” says Koven, one of the lead authors of the chapter on global carbon cycles.
If the warning is dire, it’s not apocalyptic, stresses Koven.
“We’re not doomed. We can choose to act in a way that limits climate change. When and if we’re able to stop emitting CO2 into the atmosphere, we expect the climate system to stabilize at that point and stop getting worse. To reverse it, we’d have to pull CO2 out of the atmosphere, and that technology doesn’t exist at scale yet.”
It’s a daunting goal, given that the COVID-related economic slowdown decreased global carbon dioxide emissions by only 6.4 percent in 2020. For perspective, the UN Environment Programme estimates that emissions will have to decrease by 7.6 percent annually for the next decade if we are to meet the 1.5°C target in the Paris Agreement.
“We should be worried because it’s already happening and it’s not going to get better; it can really only get worse,” says Koven. “The question is, how much worse are we going to allow it to get?”