Consensus or Contentious? How scientists come to an agreement…or don’t

97% of climate scientists agree that humans are the cause of global warming.’ This statistic, that at first seemed to be the definitive proof the world needed to take climate action, has done little to end social and political division on the matter. In fact, it’s become void of meaning for me after hearing it repeatedly in every environmental course I’ve ever taken or taught. I honestly stopped thinking about this statistic until concerns over COVID-19 sparked a number of scientific questions, such as: how long should quarantine last? or, does wearing a face mask even do anything? These questions made me wonder, is it really something special that 97% of climate scientists can agree on a single fact? Can scientists in other disciplines come to such a level of agreement in their respective fields?

Teacher looking at laptop
Attending my weekly teaching team meeting for the course, Intro to Environmental Studies. As a teaching assistant for the course, I guide students through discussions on a variety of modern environmental challenges, including climate change. (Photo Credit: Megan McKeown)


Before I delve into this question, let’s backtrack a bit and talk about where this 97% came from. In 2004, science historian Naomi Oreskes, conducted the first systematic review of all peer-reviewed literature on “global climate change” between 1993 and 2003. In short, a study of studies. She actually found that 100% of scientists that had published papers on the topic AND took a position on the cause, agreed that humans are causing global warming. This coalescence around a single fact is what is known as scientific consensus. Since Oreskes, six other consensus studies have been conducted surveying slightly different concepts and populations. There’s even a consensus on consensus paper (this is getting too meta now). In general, all these studies have converged around the statistic of 97% agreement.

Chart displaying percent of agreement on global warming
Percentage of agreement on the question of human-caused global warming found from the seven different consensus studies conducted in published scientific literature. (Source: Skeptical Science)


So back to the original question at hand, is this 97% agreement rare, or is it commonplace in the science realm? While this is by no means a comprehensive review (it’s a blog, after all), here are a few cases I looked into.


I’m referring specifically to the slew of vaccines many of us receive during childhood for measles, mumps and rubella (MMR). The modern day fear that these vaccines cause autism in children was started by a single study from 1998. Hundreds of studies followed to test the claims of this paper. A comprehensive review found that NONE of them could find an association between MMR vaccines and autism. The original 1998 study has since been debunked for an alarming number of reasons including a lack of statistical significance (it only assessed 12 kids), conflicts of interest, and ethical violations. The scientific consensus on this one is clear as day: vaccines do not cause autism.  

What’s concerning is how a single study was able to influence an entire movement of parents who choose not to vaccinate their children. In 2019, a lack of vaccinations led to the largest outbreak of measles in the U.S. since 1992. In response to the outbreak, states such as New York are overturning the right to refuse vaccines for religious and philosophical reasons, requiring that all students enrolled in schools be vaccinated. In this case, it’s refreshing to see consensus in a science community influence action in the policy realm.

Is there scientific consensus? Definitely!

Baby receiving a vaccine
A baby receiving one of the many vaccines it will need over the next few years to keep both it and society immune from what were once rampant and deadly viruses. (Source)


Genetically Modified Organisms (GMOs)

Many worry about the impact GMOs have on their health and the environment. In an attempt to clear away these concerns, the National Academies of Sciences published a systematic review of current research on GMOs analyzing over 1,000 studies. The authors concluded that there is no evidence of a health difference between consuming GMOs versus conventional crops. They also found no evidence that GMOs harm the environment. Sounds like a consensus, right? Well, a group of 300 scientists fired back arguing that there is not enough independent or long-term epidemiological studies to claim such consensus. The opposing scientists fear that accepting the notion of consensus will lead to complacency in research and regulations. However, it’s hard to assess if this small opposition should be held on an equal platform to the numerous institutions that support the claim of consensus.

Consensus or not, policymakers and the public are still asked to vote on new GMO regulations. A requirement to label foods as GMO has been introduced to Congress and has previously appeared on ballots in Washington and California. Without a consistent answer from the scientific community, people – including myself – often remain undecided on the matter. Yet concerningly, we’re still being asked to make voting decisions regarding their use. 

Is there scientific consensus? It’s complicated.

Papaya, corn, milk and soybeans
Papaya (Source), soybeans (Source), milk (Source) and corn (Source) are some of the most commonly produced GMOs.



The International Astronomical Union (IAU) demoted Pluto from its planetary status in 2006. The IAU is an accredited scientific organization, so you’d think the decision would have been the result of a significant consensus in the field, right? Not quite. Turns out, planetary experts were totally split on the matter. 

The underlying question to Pluto’s status was establishing what criteria defines a planet. The Planet Definition Committee had been stalled on this question for years. The discovery of another celestial body rather similar to Pluto, Eris, finally forced the IAU to decide on a definition. The decision was put to an IAU membership vote at their 2006 conference. However, at the conference, a secret committee made last minute changes to the proposed definition. With little time for the international community to comment and discuss the changes, a vote was cast by only 424 conference attendees out of the entire 9,000 IAU membership body. While 90% of those in attendance voted for a definition that dethroned Pluto, they represented only a fraction of the scientific community as a whole.

Many on #teamPluto, scientists included, were unhappy about this. Some felt the new definition was sloppy and arbitrary. However, a recent resurgence of the debate means there is hope yet for this big rock that wears its heart on its sleeve.

Is there scientific consensus? Far from it!

An image of Pluto
Pluto and its newly discovered “heart” as imaged by NASA’s New Horizons spacecraft. (Source: NASA)


Wrapping Up 

While vaccine experts are in wide agreement, debates continue regarding the safety of GMOs, and Pluto’s fate was decided by a minority at the last minute. It seems achieving scientific consensus is a mixed bag. For me, this adds new meaning to how truly telling it is that the large majority of climate experts agree on the cause of climate change.   

However, looking at how consensus can influence spheres beyond science, it’s rare for a scientific consensus to induce policy changes. It’s even more rare for the public to mirror the same agreement as experts. In writing this blog post, I realized that there are bigger questions to ask than ‘how often do scientists agree?’. What we should really be asking is: What action should we take with the current knowledge we have, even if it’s incomplete, as in the case on GMOs? And who should be given the authority to decide on a matter if a scientific community can’t agree on a controversy, as with Pluto? 

The debate shouldn’t just be about the science; it should be about the decision-making process, too. Nowhere is a continued debate on the process more needed than in the climate conversation, where scientists agree yet decision-makers are as divided as ever. We’re running out of time to flatten this climate curve. As was the case with vaccines, here’s hoping that climate policy starts reflecting the scientific consensus.