There’s no doubt on CO2’s role in climate change, despite Jordan Peterson and Joe Rogan’s claims

On 22 April 2025, Jordan Peterson appeared on episode 2309 of the Joe Rogan Experience. In one extended section of the episode, Rogan and Peterson – a repeat guest on Rogan’s podcast – shared debunked claims about climate science and global warming.

Peterson claimed that it isn’t clear whether human activity had in fact increased carbon dioxide (CO2) levels in Earth’s atmosphere. Moreover, Peterson asserted that increased CO2 is actually a good thing by allowing plants to grow better. Rogan and Peterson – without providing any evidence – also portrayed climate scientists as making inaccurate predictions, trying to suppress dissent, and using climate science as a means of control.

The episode has collected more than 4 million views on YouTube and has been widely shared elsewhere. For instance, a post on X quoting this section of the podcast has gained more than 900,000 views.

Peterson has a track record of minimizing climate change, stating that carbon dioxide in the atmosphere isn’t a threat to humanity and treating climate action supporters with hostility. He has done so in prior appearances on Rogan’s podcast, and Rogan has spread similar climate misinformation. Rogan’s podcast has also spread health misinformation, especially related to Covid-19 treatments, some of which Science Feedback has debunked.

Likewise, we’ve previously reviewed – and debunked – many of Rogan and Peterson’s latest climate-related claims, as we’ll show below.

Claim 1 (Misleading):

Rogan: “We’re in a cooling period” […]
Peterson: “The conclusion you draw about climate and carbon dioxide is entirely dependent on where you put the origin point of your graph”

It is true that Earth is cooler today than in the distant past, but it’s misleading to imply this means modern-day climate change isn’t a serious problem.

Rogan cites a Washington Post article, which actually covered a 2024 study charting Earth’s temperature through the last 485 million years^[1]. Neither this study, nor others plotting how temperatures have risen and fallen throughout Earth’s geological history, minimizes modern-day climate change – in reality, the opposite is the case^[1,2]. 

It actually does matter where we place the ‘origin point of our graph’, because humans did not exist at any point on that graph. Humans did not evolve in the hot, humid climates of past Earths. Human civilization developed more recently, in cooler conditions matching those prior to the Industrial Revolution. If the climate continues to warm, many of us will need to drastically adapt.

As we’ve said in a past review, what matters is that we are causing Earth’s climate to warm at rates unprecedented in our planet’s known history (Figure 1)^[3]. Our planet’s surface has warmed about 1.4°C (2.5°F) on average since 1900, and scientists project between 2.2 and 3.7°C (4.0 and 6.7°F) of total warming by 2100. For comparison, without human intervention, temperatures change by 1°C over many thousands of years^[2]. 

The geological record tells us that the last time Earth had temperatures 3°C (5.4°F) higher than pre-industrial levels was about 3 million years ago, during what scientists call the Pliocene epoch^[5]. During the Pliocene, sea levels were about 17 meters (56 feet) higher than pre-industrial levels^[6]. Today, hundreds of millions of people live on seaboards less than 17 meters above sea level, in land that was underwater during the Pliocene.

We don’t need to wait for sea levels to rise 56 feet to see what such drastic climate change will do – a warmer world increases the risks from floods, natural disasters, extreme heat, drought, tropical diseases, and more, counteracting our efforts to make humans safer from these^[3].

Claim 2 (Incorrect):

Peterson: “Whether all that additional carbon dioxide is a function of human activity, that’s still debatable”

Peterson, as he has done in the past, tries to cast doubt on the idea that greenhouse gases like CO2 are warming the planet. In reality, this is a well-understood relationship supported by several lines of evidence^[3,7]. 

Although Earth’s climate is very complex, the relationship between CO2 and the climate today is straightforward – Earth’s climate will continue warming as more CO2 enters the atmosphere. 

CO2 levels have risen from about 280 parts per million (ppm) prior to the Industrial Revolution to about 420 ppm today. In that time, temperatures have also risen – as we’ve said, our planet’s surface has warmed about 1.4°C (2.5°F) on average since 1900.

Scientists have many ways of knowing that the CO2 from humans burning fossil fuels is responsible for recent global warming. For one, the increase of CO2 levels in the atmosphere matches what the increase we’d expect from the amount of fossil fuels we’ve burned. 

Additionally, as we’ve said in a past review, carbon atoms from fossil fuels come in different varieties (known as isotopes) from carbon atoms that are naturally in the atmosphere. By studying this makeup, scientists can tell which portion of CO2 that we’re adding to the atmosphere comes from fossil fuels.

What’s more, climate science isn’t new – scientists have used mathematical and computer models for many decades to predict how Earth’s temperatures would change in response to rising CO2. In fact, scientists’ predictions from the 1970s and 1980s have generally tracked well with later temperature observations^[8]. 

Although Peterson ridicules climate models, and although Rogan and Peterson accuse climate scientists of making false predictions, the reality is that climate science has correctly predicted – for decades – that the planet’s temperatures would warm as more CO2 entered the atmosphere (Figure 2)^[3,7].

Claim 3 (Unsupported):

Peterson: “The planet is 20% greener than it was 30 years ago [thanks to CO2]”

It’s unclear what Peterson means by “greener”, but he claims the 20% figure comes from“NASA data”.

Science Feedback identified several studies using satellite data to measure how much of the Earth’s surface is covered by greenery and how that area has changed over time. A 2018 study found that the amount of land covered by trees increased about 7% from 1982 to 2016^[9]. A similar 2019 study examined both forests and cropland and found that Earth’s surface area covered by leaves increased about 5% between 2000 and 2018^[10].

So the numbers don’t match Peterson’s claim of “20%”. More importantly, while CO2 can play a role in greening, these studies suggest it’s misleading to credit this increase to CO2 alone when humans are directly playing a role in increasing Earth’s green area^[9,10].

It is true that some plants can grow better in the presence of more CO2 – a phenomenon that scientists call the CO2 fertilization effect – but both studies credit Earth’s ‘greening’ primarily to human activity, such as tree-planting and the expansion of agriculture. The 2018 study found that human activity was responsible for 60% of tree expansion^[9].

It’s certainly good news that we’re able to increase forest coverage in many parts of the world, but it doesn’t change the reality that global warming is a threat to human society.

Moreover, it’s important to note the increased green area isn’t evenly distributed throughout the world. Some areas closer to the tropics, such as the Amazon, Sub-Saharan Africa, and Southeast Asia, are continuing to lose greenery as a result of deforestation, largely due to conversion of forests into land for beef cattle and for growing crops.

Peterson also claims that more CO2 means that ‘agricultural production is more effective’. The amount of food we get from the same land area has increased around the world, and there is evidence that the CO2 fertilization effect helped, but it’s misleading to attribute increased productivity to CO2 alone. Human technology, such as higher-yield crops and mechanization, also plays a role. 

And the effect isn’t the same around the world – the types of crops grown nearer the tropics are less likely to see increased yields from CO2 fertilization^[11].

Claim 4 (Lacks context):

Peterson: “Well, how about a world where there’s so much energy that poor people can afford?”

This is one line Peterson uses to argue that we shouldn’t build renewables – that solar and wind are more expensive than other electrical sources, such as fossil fuels. However, Peterson ignores several important details.

As we’ve shown in a past review, fossil fuels aren’t necessarily more affordable. Solar and wind are generally cheaper to build than other energy sources. Solar and wind are also far less susceptible to fossil fuel price spikes, such as the one many countries experienced in 2022 and 2023 after natural gas prices soared due to the Russian invasion of Ukraine.

Fossil fuels also bear costs that can’t directly be measured in money. For one, as we’ve covered in another previous review, burning fossil fuels generate other air pollutants like particulate matter and ozone, which we know can harm people’s respiratory and heart health. A 2023 study estimated that the air pollution from all fossil fuel use killed 3 to 6 million people in 2019^[12].

For another, as we’ve said, we know that fossil fuels are a contributor to climate change. Peterson accuses climate action advocates of “sacrificing” the poor, but in reality, it is likely the world’s most impoverished who bear the worst consequences of climate change. 

For example, climate change exacerbates the risks of diseases like dengue and malaria that disproportionately impact less wealthy parts of the world^[13]. Less wealthy regions are also more likely to see heat and drought that cancel out any gains in agricultural productivity, cause food shortages, and increase food insecurity^[11,14].

Peterson and Rogan aren’t climate scientists

It’s important to note that Jordan Peterson, by his own admission in the podcast, is not a climate scientist. He does not appear to have any background in climate science. His page on the website of the University of Toronto, his former institution, describes him as “a professor emeritus of psychology” and “a clinical psychologist” who has delivered lectures on “mythology and the psychology of religion”.

Rogan, who has a background in comedy, acting, and sports broadcasting, also has no climate science experience.

Climate scientists have analyzed data which shows that greenhouse gas emissions cause climate change. They have collected and analyzed this data for decades^[3]. To dismiss climate science as Peterson does is to say that the data isn’t important.

Furthermore, contrary to Peterson and Rogan’s claims that climate science leaves no room for dissent, there is actually a great deal of debate and uncertainty within the climate science community. 

For example, climate scientists are certain that humans are driving climate change, but they debate the extent to which ongoing policies will mitigate that change. They also note that the anticipated amount of warming is only forecast with a degree of confidence, using ranges like between 2.2 and 3.7°C (4.0 and 6.7°F) instead of as a single figure.

There is no evidence that climate science is about seeking power – on the contrary, many climate scientists are merely academics who are passionate about studying Earth’s climate. They are simply reporting what the data shows and trying to come to the best conclusions they can draw from it. 

If anyone is seeking attention, it is people like Rogan and Peterson, whose claims make it more difficult for climate scientists to do their work.

References:

• 1 – Judd et al. (2024) A 485-million-year history of Earth’s surface temperature. Science.
• 2 – Westerhold et al. (2020) An astronomically dated record of Earth’s climate and its predictability over the last 66 million years. Science.
• 3 – IPCC (2021) Sixth Assessment Report.
• 4 – Rae et al. (2021) Atmospheric CO2 over the Past 66 Million Years from Marine Archives. The Annual Review of Earth and Planetary Science.
• 5 – Burke et al. (2018) Pliocene and Eocene provide best analogs for near-future climates. PNAS.
• 6 – Dumitru et al. (2019) Constraints on global mean sea level during Pliocene warmth. Nature.
• 7 – Zhong and Haigh (2013) The greenhouse effect and carbon dioxide. Royal Meteorological Society Weather.
• 8 – Hausfather et al. (2019) Evaluating the Performance of Past Climate Model Projections. Geophysical Research Letters.
• 9 – Song et al. (2018) Global land change from 1982 to 2016. Nature.
• 10 – Chen et al. (2019) China and India lead in greening of the world through land-use management. Nature Sustainability.
• 11 – Rezeai et al. (2023) Climate change impacts on crop yields. Nature Reviews Earth & Environment.
• 12 – Lelieveld et al. (2023) Air pollution deaths attributable to fossil fuels: observational and modelling study. The British Medical Journal.
• 13 – Mora et al. (2022) Over half of known human pathogenic diseases can be aggravated by climate change. Nature Climate Change.
• 14 – Smith and Meyers (2018) Impact of anthropogenic CO2 emissions on global human nutrition. Nature Climate Change.