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Over 99.9% of Studies Agree: Humans Have Caused Climate Change on Earth

21 OCTOBER 2021

If you're wondering just how much scientific consensus there is that humans have caused the climate of our planet to change, we can now put a number on it: 99.9 percent.

That doesn't leave much room for doubt. To get to that figure, researchers looked in detail at a total of 3,000 peer-reviewed studies randomly selected from a list of 88,125 climate related papers published since 2012, finding that just four of them expressed any doubt that human activity is leading to shifts in Earth's climate.

 

The last time a similar study was done, looking at papers published between 1991 and 2012, there was 97 percent certainty – so it would appear that the small level of skepticism is continuing to shrink over time.

"We are virtually certain that the consensus is well over 99 percent now and that it's pretty much case closed for any meaningful public conversation about the reality of human-caused climate change," says Mark Lynas, the climate lead of the Alliance for Science at Cornell University in New York.

Despite the almost universal agreement among the scientific community, more than 1 in 3 people in the US don't think that global warming – one of the main symptoms of climate change – is mainly attributable to human activity. There is also doubt among certain political circles.

Besides the detailed look at 3,000 papers, the team also used an algorithm based on keywords to rank the entire database of 88,125 papers in order of anthropogenic climate-change skepticism, resulting in 28 labeled as being implicitly or explicitly 'skeptical'.

That's similar to the level of consensus on plate tectonics or evolution, the team says – and the sheer number of studies that have been analyzed leave little room for argument when it comes to debating the science of climate change.

 

"To understand where a consensus exists, you have to be able to quantify it," says Lynas.

"That means surveying the literature in a coherent and non-arbitrary way in order to avoid trading cherry-picked papers, which is often how these arguments are carried out in the public sphere."

However, it's not clear that this weight of scientific opinion is actually being noticed by the public: only 27 percent of people in the US think that experts are mostly all agreed on the cause of climate change (by comparison, 55 percent think almost all scientists are agreed that the MMR vaccine is safe).

This particular study doesn't try to answer the question of why there is a discrepancy between what scientists think and what the public thinks they think, but other researchers have offered some ideas – the spread of disinformation, for example.

There's also no doubt about how human activity is causing global warming: through greenhouse gas emissions. With the COP26 global climate summit getting underway in the UK at the end of this month, world leaders have another chance to implement the drastic measures required to slow down the warming of the planet.

"It's critical to acknowledge the principal role of greenhouse gas emissions so that we can rapidly mobilize new solutions, since we are already witnessing in real time the devastating impacts of climate related disasters on businesses, people and the economy," says environmental scientist Benjamin Houlton, from Cornell University.

The research has been published in Environmental Research Letters.