Research, Science & environment

U.N. climate report underscores urgency of cutting carbon emissions

Global warming is already driving rampant wildfire and the extinction of plant and animal species, said UC Berkeley professor Patrick Gonzalez

Smoke billows above a wildfire, which is burning through a large open field in the Amazon.

The latest report from the United Nations Intergovernmental Panel on Climate change (IPCC) is the first to find that warming temperatures are driving increased wildfire across the globe. (Photo by Vinicius Mendonca/Ibama via AP)

Today, the United Nations Intergovernmental Panel on Climate Change (IPCC) released a major report detailing our current scientific understanding of the social and ecological impacts of climate change. It is the second report in the panel’s sixth assessment cycle. The first report of the cycle, released in August 2021, was called  a “code red for humanity” by the U.N.

To learn about the new report, Berkeley News spoke with Patrick Gonzalez, an associate adjunct professor at UC Berkeley who served as a lead author of the chapter on terrestrial ecosystems. Gonzalez was first invited as an author of the 2001 IPCC report because of his extensive fieldwork documenting how human-caused climate change was killing trees in Africa. He went on to serve as a lead author of four IPCC reports, including two of the reports for which the IPCC shared the 2007 Nobel Peace Prize.

Gonzalez said that he considers IPCC service “the most important scientific work of my life” because the reports are providing the foundation for global action on climate change.

A headshot of Patrick Gonzalez in the woods

Patrick Gonzalez is an associate adjunct professor at UC Berkeley and a lead author of the new IPCC report. (Photo by Adam Sings)

What are the most important takeaways from the new IPCC report?

This new report provides strengthened evidence that human-caused climate change has damaged ecosystems and people. Most importantly, the scientific results increase the urgency of cutting carbon pollution to net zero by 2050 to avoid the most severe consequences of climate change.

Scientific evidence shows that human-caused climate change has driven two animal species to extinction, doubled the area burned by wildfire over natural levels in western North America, increased tree death up to 20% in Africa and North America, contributed to carbon loss from tropical rainforests and Arctic permafrost, and shifted major vegetation zones around the world. Analyses attribute these impacts to human-caused climate change more than agricultural expansion, urbanization or other factors.

These impacts have occurred at a global temperature increase of 0.9 degrees Celsius (1.6 degrees Fahrenheit) above the pre-industrial period, acting through increases in heat, aridity and drought. By 2020, the increase reached 1.1 C (2 F). At a temperature increase of 4 C (7.2 F), continued climate change could drive additional plant and animal species to extinction, double the burned area in the Amazon, and release the equivalent of over 15 years of global carbon emissions from burning tropical forests and thawing Arctic permafrost.

Cutting carbon emissions to net zero by 2050 would limit the temperature increase to 1.5 to 2 C (2.7 to 3.6 F), mostly averting these risks or reducing them by half.

Could you describe your role in authoring the IPCC 2022 report?

I served as a lead author of the IPCC 2022 chapter on terrestrial ecosystems, on a team of 12 authors. I led sections examining climate change and wildfire, tree death, biome shifts, ecosystem carbon and protected areas and brought together an assessment of key risks. We have been working on this since August 2018 — three and a half years of work.

During this time, I have been a U.S. government employee, but managers during the past administration attempted to block me from working on IPCC. I stood up for scientific integrity, as reported in the New York Times, and worked on IPCC on my own time, under my UC Berkeley affiliation. The College of Natural Resources and the Institute of International Studies made my work possible.

Were there any findings that particularly surprised you?

A photo of a bright orange frog sitting on a leaf

The Golden toad (Incilius periglenes) from Monteverde cloud forest, Costa Rica, is one of two animal species that have been driven to extinction by the impacts of climate change. (Photo courtesy of U.S. Fish and Wildlife Service, via Wikimedia Commons)

While not surprising, increased wildfire emerged for the first time in a major IPCC assessment as a key risk for the world.

Human-caused climate change has doubled the area burned by wildfire in the western U.S. above natural levels since 1984 and increased burned area seven to 11 times natural levels in the extreme fire year of 2017 in British Columbia, Canada. Deforestation, agriculture, peat draining and El Niño have exerted an even stronger influence than climate change in increasing wildfire in other regions, including the Amazon, the Arctic, Australia and Indonesia.

At a temperature increase of 4 C, continued climate change could increase wildfire frequency on up to two-thirds of global land, doubling the burned area in the Amazon and tripling the burned area in parts of the Arctic — regions where fire has been absent or rare. Cutting carbon pollution could limit heating to 2 C and reduce the projected increase in burned area to one-third of global land.

Another important and concerning key risk is the extinction of plant and animal species. Sadly, human-caused climate change has driven two animal species to extinction: the Golden toad (Incilius periglenes) from Monteverde cloud forest, Costa Rica, and the Bramble Cay melomys (Melomys rubicola), a small rodent, from its last island in the Torres Strait, Australia.

Climate change has also driven local disappearances (extirpation) in over 400 plant and animal species. These include birds in the southwestern U.S. and bumblebees in North America and Europe.

At a temperature increase of 4 C, continued climate change puts 4% to 39% of plant and animal species at risk of extinction. Limiting heating to 2 C decreases extinction risk to 3% to 18%. Still, climate change at 2 C could cause the same number of extinctions as habitat destruction and exploitation by humans in the past 12,000 years.


Patrick Gonzalez describes how reducing carbon pollution will be a necessary step towards scaling back catastrophic wildfire. (Credit: Clare Major and Roxanne Makasdjian)

How would you describe the state of climate change mitigation/adaptation? Are we “past the point of no return”? Are there reasons to hope?

The IPCC analyses show that we can limit the temperature increase to 1.5 to 2 C with concerted global action, using existing technologies and practices.

The challenge is substantial — at current rates, IPCC projections indicate temperature could increase 1.5 C above the pre-industrial period by 2032 to 2034 and 2 C by 2047 to 2051. Nevertheless, if all countries enacted and implemented their Paris Agreement pledges, analyses indicate the world could limit heating to 1.9 C above pre-industrial levels.

Recent progress shows that this is possible. From 2009 to 2018, the world doubled renewable energy capacity globally, adding solar, wind and other renewable energy equivalent to 3,200 coal plants. In 2019 in the U.S., renewable energy sources exceeded coal for the first time since the 1800s. Consequently, the U.S. cut carbon emissions 13% from 2005 to 2019. California has cut its emissions below 1990 levels. These data make me optimistic — a science-based optimism.

What do you think are the most important actions that need to be taken?

A photo of a small rodent

The Bramble Cay melomys (Melomys rubicola), from the Torres Strait, Australia, has also gone extinct as a result of climate change. (Photo by Ian Bell, via Wikimedia commons)

First, replacing fossil fuels with renewable energy and personal energy is essential. For example, transportation generates more carbon pollution that any other sector. So, you can take action by walking, biking and taking public transit. Published research shows that this can reduce your personal emissions up to 99%. I live a car-free life and encourage you to also.

Currently, each person in the U.S. emits 4.2 tons of carbon per person per year — over three times the global average of 1.2 tons. For comparison, the average in France is 1.3 tons of carbon per person per year. This shows that it is entirely possible to reduce our carbon pollution and maintain a healthy lifestyle.

Second, halting tropical deforestation would reduce climate change and conserve species. Deforestation through intentional burning in the Amazon, Congo and Southeast Asia rainforests is driving the most extensive and severe wildfire increases in the world, in ecosystems where fire had been rare. Halting tropical deforestation would cut global carbon emissions 15% and protect globally unique biodiversity.