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Adjusting for humanity’s fingerprints

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Six years ago, Professors Gabi Hegerl and Simon Tett’s work to prove human-caused greenhouse gasses are warming our planet underpinned the 2015 Paris Agreement. Today they argue we still aren’t doing enough to adapt to climate change.

The 2015 Paris Agreement was a watershed moment. Signed by 195 states and the European Union at the United Nations’ 21st Climate Change Conference of the Parties (COP21), the legally binding treaty committed almost every nation on Earth to take steps to limit global warming to well below 2C, and preferably below 1.5C, this century compared to pre-industrial levels.

With some notable exceptions, such as the Trump administration theatrically withdrawing the United States from the agreement in 2017 – a move later overturned by President Biden in 2021 –  there have been promising signs that the treaty has made the world wake up to climate change. Thirty-four national governments and many more local jurisdictions have since declared a climate emergency.

Still, it’s impossible to escape the all too frequent impact of humanity on our changing climate. 2021 alone has seen record droughts in the US, deadly flooding in Germany, Belgium and China, a heatwave of temperatures exceeding 49C in Canada and wildfires rage in Greece.

Making our mark

University of Edinburgh researchers have played a pivotal role in informing global climate change mitigation policy for nearly two decades. Among the first to unequivocally demonstrate the link between human-caused greenhouse gas emissions and climate change, their research formed the scientific foundation of the Paris Agreement.

“We’ve known our climate is warming for decades, but Edinburgh research was able to separate the signature of warming related to human activity from the Earth’s natural cycle of heating and cooling,” explains Professor of Climate System Science Gabi Hegerl, who led critical sections of the Intergovernmental Panel on Climate Change (IPCC) reports that would go on to underpin the 2015 treaty.

Hegerl and colleagues’ technique involves analysing available data on temperatures before and after the industrial revolution against emissions and natural climatic events, such as solar warming and volcanic eruptions, to isolate those climate changes that only humans could cause – the human ‘fingerprint’. This finding means it is undisputable that humans are driving highly unusual global warming compared to the long-term record. Using these results, Edinburgh researchers can predict how much warming different future scenarios will cause.

Cooling towers

“These methods also enable us to attribute extreme weather events to human influence,” adds Simon Tett, Hegerl’s collaborator and Professor of Earth System Dynamics. “For example, they have demonstrated that human actions have already caused a five to 10 percent increase in the risk of extreme rainfall and two to 10 times increase in the risk of extreme temperatures.”

“Code red for humanity”

Six years after the Paris Agreement, the latest IPCC report, which was published in August 2021, didn’t offer much cause for celebration. Described by its authors as a “code red for humanity”, the report said a 1.5C rise in temperatures and, along with it, more flooding, droughts and wildfires, is now inevitable by 2040. Unless we slash carbon emissions within the next few years, it will happen much sooner.

This latest assessment did not surprise Hegerl. Edinburgh research contributed to the IPCC’s 2018 landmark special report that showed humanity’s wriggle room was being squeezed. It said that the level of carbon emissions the world could withstand during the next century without temperatures rising beyond 1.5C threshold was 40 per cent less than originally estimated. This work also showed that this temperature rise started earlier than often recognised.

“The 2018 report did seem to have a galvanising effect on policymakers and led countries such as the UK to accelerate their commitments to achieving net-zero CO2 emissions by transitioning to a post-carbon economy,” Hegerl notes.

Nonetheless, with the stage set for some challenging negotiations when world leaders gather at COP26 in Glasgow this November, she has mixed feelings about what’s to come.

“The scientific community has unequivocally proved that humans influence climate change, and most policymakers are listening. Still, I don’t feel we’ve focused enough on the dangers. Whether we meet the 1.5C target or not, climate change is here, it is irreversible on human timescales, and we are already feeling its effects,” she says.

Flooded village in Germany
The River Elz flooded the village of Monreal, Germany, in July 2021

“It frustrates me that we’ve known extreme weather events would become more frequent, but we’ve taken little action to adapt to them and avoid tragedies such as the awful loss of life during the floods in Germany and Belgium. It’s increasingly difficult to separate our scientific findings from this feeling that we are heading for huge problems if we don’t start to also focus efforts on mitigating the real impacts of climate change today.”

Strengthening the message

Tett welcomes the IPCC’s recent efforts to strengthen its language around climate, albeit he says the scientific community must still do more to get its message across.

“We’re moving in the right direction, and keeping warming below 2C this century feels achievable, but I think there may be just too many actors to expect the rapid change necessary to stay below 1.5C,” he says.

“There is always a balance to strike between environmental and economic concerns. The ongoing conversation about new oil exploration of Shetland is good evidence of this.  Nonetheless, I feel more governments now understand the existential threat of climate change is as much economic as environmental. As scientists, we must ensure policymakers hear our voice as loudly as businesses that may, unfortunately, lose out in the transition to a low-carbon economy.

“We must get the message across that we are living through climate change, and no matter what action we take now, the carbon we’ve already put into the atmosphere won’t go away. The best-case scenario is that climate we have now is the one we’ll have forever.”

Picture credits: lake bed – namcheolukla/Getty; cooling towers – enviromantic/Getty; floods – Markus Volk/Getty