I have a story to tell. It’s a story you might not have heard. A story about how, back in 1995, scientists first identified human fingerprints on global climate, and what happened in the media when they reported those findings. I lived through this 30-year history.

Here are a few notes of preamble. My parents moved from suburban Maryland to Dortmund in 1966. They put me in a British Army school in Dortmund. I was 11 years old. The only “damn Yank” in the school. The only kid whose parents were not in the military. The only kid who had never seen a soccer, rugby or cricket ball. I spoke differently. I embodied “otherness”. Learning to play soccer was my meal ticket to peer acceptance.

I wasn’t a science nerd at school. I gravitated towards language, poetry, literature and amateur dramatics. I can still recite the lines I learned playing the third witch in Macbeth, Puck in A Midsummer Night’s Dream, and Feste the jester in Twelfth Night. My army school education gave me a lasting appreciation of the power of words.

I was also interested in understanding the physical world. After finishing A-levels, I went to the University of East Anglia in 1973 to study environmental sciences. UEA gave me a solid foundation for looking at climate change and other interdisciplinary global problems. In 1983, I went back to East Anglia to do a PhD at the Climatic Research Unit. In the final year of my PhD, I attended a scientific conference in Sicily. The conference lunch breaks were long. I played tennis during one break. Professor Klaus Hasselmann – director of the Max Planck Institute for Meteorology in Hamburg, who would later receive the 2021 Nobel Prize for Physics – happened to walk by the tennis courts and challenged me to a game.

That one game of tennis changed my life. After our match, Hasselmann invited me to Hamburg to give a talk about my PhD research. This eventually led to the offer of a post-doc position at the Max Planck Institute. I arrived in Hamburg in 1987. I was initially unsure how I’d fit in there. Klaus Hasselmann kindly took me under his wing, asking me to read an old paper he had written back in 1979. The paper outlined a statistical method for identifying human effects on climate. Its basic premise was that each of the many factors influencing Earth’s climate has a distinctive fingerprint. Human-caused changes in heat-trapping greenhouse gases have one type of fingerprint. Purely natural changes in the sun’s energy output or in volcanic activity have completely different fingerprints. By looking at large-scale patterns of climate change – geographical patterns at Earth’s surface, or vertical slices through layers of the ocean or atmosphere – one might be able to disentangle human and natural influences on climate.

My job as a post-doc in Hamburg was to do this disentangling. I was tasked with identifying the climate equivalent of “canaries in the coal mine”. Where might scientists have the best chance of finding human-caused warming signals? In the tropics? In polar regions? On land, or in the oceans? And of the many dozens of climate properties that could be interrogated by climate scientists, which properties might offer the most promising early warning signs of human influence? Temperature? Rainfall? Surface pressure? Atmospheric circulation patterns?

It was a good time to be a young scientist. A time of intellectual innocence. A time before the political implications of climate fingerprinting became painfully obvious. I moved from Hamburg to Lawrence Livermore National Lab (LLNL) in California in 1992. At LLNL, I continued my work in climate fingerprinting. This work eventually led to another life-changing event: an invitation from the Intergovernmental Panel on Climate Change to participate in the 1995 IPCC Second Report. The IPCC’s role was (and still is) to advise the governments of the world on the physical science of climate change, as well as on climate change impacts and response strategies.

I was asked to serve as convening lead author of Chapter 8 of the 1995 report. This was the chapter dealing with Detection of Climate Change and Attribution of Causes. A senior colleague and friend strongly encouraged me to accept the IPCC’s offer. I followed his advice and signed up for the Chapter 8 role in April 1994.

For the next one-and-a-half years, Chapter 8’s international team of experts assessed the relevant scientific literature. We had different skill sets. Some members of the team developed observational climate data sets or used supercomputers to model the climate system. Others tried to understand natural climate variability, applied statistical methods for detecting unusual changes in climate, or used so-called tree rings, ice cores and sediment records to study changes in climate over millennia.

We evaluated more than 130 research papers. We wrote and rewrote many drafts of Chapter 8, responding to review comments from experts not directly involved in the chapter, from the member countries of the IPCC, from NGOs, and from the authors of other IPCC chapters. It was peer review on steroids, exhausting and exhaustive. Our bottom-line finding was that human activities had changed Earth’s climate, primarily through the release of greenhouse gases from fossil-fuel burning. A human-caused global warming signal had risen out of the “noise” of natural climate variability. Humans were no longer innocent bystanders in Earth’s climate system.

My job was safe but what about my life?

The process of working on the IPCC Second Assessment Report came to a preliminary conclusion at an IPCC plenary meeting in Madrid in November 1995. The protagonists “included 177 delegates from 96 countries, representatives from 14 NGOs and 28 lead authors”. Chapter 8’s finding of human fingerprints on climate received extraordinary attention, particularly from representatives of oil-rich Saudi Arabia and Kuwait, as well as from NGOs with business interests aligned with fossil-fuel production.

The Madrid plenary proceedings were dramatic – a drama that was recently reenacted in the play Kyoto, which premiered in Stratford-upon- Avon in July 2024. The high point of the Madrid meeting was captured in 12 simple yet powerful words: “The balance of evidence suggests a discernible human influence on global climate.” All government delegates signed off on this finding. Even the Saudis and Kuwaitis.

After Madrid, I thought my job was over. I could return to normal family life. I wouldn’t have to travel as much. I could spend more time with my son and wife in the mountains of California, far from the public arena. I wouldn’t have to wade through hundreds and hundreds of Chapter 8 review comments. I could pick up the threads of neglected research projects.

But “normal life” proved to be elusive. It never returned. The 12 words from Madrid fundamentally changed my life. The reaction to the IPCC’s 1995 “discernible human influence on global climate” was swift and harsh. Powerful individuals, companies, and countries did not like it. It was bad for business. The recognition that fossil-fuel burning was altering Earth’s climate in concerning ways could throw a spanner in the works of business as usual. The scientific underpinning of the “discernible human influence” finding had to be discredited, along with the scientists responsible for the finding, and the assessment process by which the finding was reached. Organisations such as the Climate Council – a consortium of energy interests – tried to achieve these goals by engaging in a deliberate “scorched Earth” strategy.

As convening lead author of Chapter 8, I was an obvious target. After publication of the Second Assessment Report in early 1996, at a time of ethnic cleansing in Bosnia, I was publicly accused of “scientific cleansing” – of purging all discussion of scientific uncertainty from Chapter 8. This charge was absurd. Nearly 20 per cent of Chapter 8 was specifically devoted to the discussion of scientific uncertainties in climate models, in observational climate change estimates, and in the statistical methods used to make inferences about the causes of climate change. Other charges were equally absurd. There was the charge that Chapter 8 had been subject to political tampering. That in the process of finalising the chapter, the peer-review system had been abused. That the chapter’s findings were solely based on two of my own papers.

The attacks on Chapter 8 snowballed, accreting new layers, new adherents, and new column space in the press. In June 1996, a former president of the US National Academy of Sciences, Frederick Seitz, wrote the following in an op-ed in The Wall Street Journal: “In my more than 60 years as a member of the American scientific community, including service as president of both the National Academy of Sciences and the American Physical Society, I have never witnessed a more disturbing corruption of the peer-review process than the events that led to this IPCC report… I am in no position to know who made the major changes in Chapter 8; but the report’s lead author, Benjamin D. Santer, must presumably take the major responsibility”.

Prof Seitz had not attended the critical November 1995 Madrid IPCC meeting at which changes to Chapter 8 were thoroughly discussed in plenary. As the IPCC chairman and co-chairs subsequently replied in The Wall Street Journal, the error made by Seitz (and others who echoed his criticisms) was in assuming “that the draft version of the chapter of Oct. 9 was accepted unmodified at the Madrid meeting. This is not the case. The changes made followed the clear decision at Madrid to accept the draft chapter subject to its modification to improve its presentation, clarity and consistency in accordance with the views both of scientists and delegates expressed at length during the meeting. The rules of procedure were strictly followed and none of the 96 countries represented at Madrid have challenged either the changes or the procedures”.

It’s unpleasant to be unjustly accused of serious professional misconduct in a major national newspaper read by hundreds of thousands. For some fraction of the readership, accusation equals guilt. And to use climate parlance, the forcing and the response have different timescales – it’s easy and quick to disseminate untruths, but a much slower process to try to correct them.

Now it is difficult to deny the reality of global warming

The snowball kept rolling downhill. Former US congressman Dana Rohrabacher (aka “Putin’s favourite congressman”) decided to investigate my funding sources and why the US Department of Energy had allowed me to work on Chapter 8. In a newsletter circulated on Capitol Hill, Senator Dr Arthur Robinson called for my dismissal “with prejudice” from my position as a climate scientist at Lawrence Livermore National Lab. A German electrical engineer and climate consultant, Peter Dietze, distributed an email claiming that an action had been filed against me at the International Court in The Hague “for falsification of international scientific relevant documents”. My wife disappeared to a foreign country with our son; I had to file papers under the Hague Convention on International Child Abduction to secure his return to the US. The summer of 1996 was a real bummer.

I spent years trying to address criticism to the IPCC’s 1995 “discernible human influence” finding. I was a representative of an entire scientific community. I had to explain the evidentiary basis for Chapter 8’s key finding, and the process by which it had been reached. I needed to figure out how to publish responses to specious and to scientifically reasonable criticism. How to give interviews. How to write my own op-eds. And most importantly, how to remain an integral part of my young son’s life.

Much has changed since 1996. The planet has continued to warm, now by more than 1.5°C since the second half of the 19th century. In 2024, it’s difficult to deny the reality and seriousness of global warming with a straight face. It’s equally difficult to deny significant human culpability in warming. All four IPCC reports published since 1995 have affirmed and strengthened our cautious “discernible human influence” conclusion. As the headline of the IPCC’s 2021 Sixth Assessment Report tersely stated: “It is unequivocal that human influence has warmed the atmosphere, ocean, and land.”

The media landscape has also changed. False balance in climate reporting, so prevalent in 1996, is now rare (“Scientist A claims that warming is real and serious; Scientist B claims warming is not real and, even if it were, it would never be serious.”) There is more in-depth reporting on the substance of the science. There is detailed, rapid-response fact-checking. Powerful politicians who make demonstrably incorrect claims about the size and causes of warming are held publicly accountable. Entities and individuals responsible for misleading the public on climate change are receiving unfavourable press. And the reluctance many scientists once felt about speaking to the media is fading, particularly among younger researchers. Many younger colleagues are both willing and able to explain what they’ve learned and why it matters.

In July, I spent four days kayaking on the beautiful Rogue River in Oregon. The highlight of the trip was Mule Creek Canyon – a half-mile section of narrow canyon framed by steep rock walls, with swirling, turbulent “boils” and eddies. My kayak got temporarily caught up in the “Coffee Pot”, a whirlpool-like feature at the end of Mule Creek Canyon. Getting safely through the canyon was a wild ride.

In the United States, we face an equally wild and turbulent ride in the run-up to the November 2024 election of the next president. Voting for one candidate risks trapping the United States and the planet in an eddy of ignorance. I hope voters leave that candidate behind in the eddy, spinning around endlessly in his conspiracy theories and climate change denial. And I hope the rest of us move out of the dark canyon and into the light of reality, embracing the hard work that needs to be done to protect our planetary life-support system.