Climate Change: Isn’t it natural?

Over the last few years, I have spent a lot of time on the internet arguing with sceptical Republicans about climate change. I often do it in the Facebook comment sections of right-leaning American news outlets, such as The Daily wire and Breitbart, because it gives me the opportunity to practice debating people who are different to me politically.

In 2017, President Donald Trump pulled America out of the Paris Climate Accords, describing it as “an agreement that disadvantages the United States to the exclusive benefit of other countries”. His main reason for pulling out was because he campaigned on it, as did the rest of the Republicans in 2016 presidential elections. Trump, Ted Cruz, and Marco Rubio, the Republicans with 1st, 2nd, and 4th largest popular vote shares in the Republican Primaries (collectively 81.3%), have all stated that “the climate has always changed” at some point. Why did they campaign on such a fallacy?

There are two possible reasons. Either these presidential candidates don’t believe that current warming is human-induced, or they are simply appealing to their voter base. A 2018 YouGov Poll found that 47% of Republican voters believe climate change is occurring naturally, and 10% don’t believe the climate is changing at all. Less than 30% believe it is human-induced. It is therefore understandable why Republican politicians don’t run with this message on their ticket – it is political suicide.

So if you ever find yourself in the position debating a sceptic who says “the climate has always changed”, how do you respond? Simple. You say, ‘what do you mean?’

As a scientist, I am a sceptic. Science is about observation and inference, not hard truths, and it is important to not take sweeping statements at face value. I want to see evidence for their claim. What do you mean when you say the climate has always changed? Do you have any sources to back your claims up?

When pressing for an answer, the argument I hear most frequently is that the person does not accept current climate change is due to Carbon Dioxide (CO2). They either state that CO2 doesn’t cause temperature increases, or that whilst CO2 can cause temperature increases, the sun is the main cause of temperature increases today. In the rest of this article, I’ll tackle these two claims and I’ll show you how a healthy dose of scepticism and source checking can debunk them thoroughly.

Claim 1: CO2 doesn’t cause global warming!

The first claim is that CO2 doesn’t affect global temperatures. To prove this point, I have often been shown this graph by sceptics of temperatures and CO2 levels over the last 500 million years (Figure 1).


Figure 1 CO2 + T

Figure 1. A comparison of atmospheric carbon dioxide concentration and global temperatures in the Phanerozoic. Sourced from a climate change sceptic’s blog entitled “”. Clearly this is a reputable scientific source.


At first glance, there appears to be no correlation here. However, we need to take a closer look. For starters, the graph ends at 0, to represent the present. This is misleading – when creating reconstructions, scientists almost always use a baseline of 1950 to avoid confusion. So this graph actually ends at 1950, not 2018. Secondly, this graph is actually two graphs from different sources: One was another blog that compiled a graph showing temperatures, however it provided no sources. The second was a paper published in 2001 that compiled a graph showing CO2 levels (1). In the discussion, the paper states “over the long term there is indeed a correlation between CO2 and Paleotemperature”. So the main scientific source from which Figure 1 gets its data from actually concludes that CO2 correlates with temperature increases, the very thing that Figure 1 is trying to disprove.

The hypothesis that CO­2 could be a possible regulator of the earth’s temperature was first addressed in 1896 (2). In a landmark study, physicist Svante Arrhenius worked out a relationship between CO2 and temperature, noting that CO2 molecules are adept at retaining heat energy. He predicted that a 2.5-3 fold increase in atmospheric CO2 levels (280ppm to 700/840ppm) could result in a temperature rise of 8-9 Celsius in the Northern Hemisphere. So we’ve known for over 100 years that CO2 could be a possible driver of global temperatures, and increases in atmospheric CO2 could certainly affect global temperatures today.

Claim 2: It’s the sun, stupid!

The next line of argument I hear is that CO2 isn’t causing current warming, it’s actually the sun. The sun is definitely a main driver of the Earth’s climate. Heat energy from the sun (known as solar irradiance) has kept the Earth warm since it formed 4.6 bya. This heat energy is absorbed in the atmosphere by greenhouse gases like CO2.

When correlating the sun and CO2 individually against temperature, the correlations are very weak. However, a geological study by Royer (3) combined CO2 and solar irradiance together and compared them with temperatures over the last 500 million years. His results found an extremely good correlation (Figure 2).


Figure 2 - CO2 + SI

Figure 2. Correlations of carbon dioxide + solar irradiance (GEOCARD III line) and temperature (Proxies (LOESS) line) over the last 500 million years. Sourced from Royer 2006 (3).


So now we know that the sun and CO2 are the two main driving forces of the world’s climate. So which factor is causing warming today? Well, since 1860 there has been a 46% increase in atmospheric CO2 (Figure 3). During the same period of time, solar irradiance has been more erratic, and has actually been significantly declining since 1980 (4), during the period of greatest warming (Figure 3).


Figure 3 - SI, T, CO2

Figure 3. A comparison of atmospheric carbon dioxide, solar irradiance, and temperature (from three independent monitoring locations) between 1980-2010. Source:


With the knowledge that these two factors have the greatest influence on global temperatures and the decline in solar irradiance since 1980, the current temperature increases must be due to the increases in atmospheric CO2 concentration.

So what can you take from this? Well, for starters, don’t believe everything you read on the internet! Treat everything with a healthy dose of scepticism and make sure you find original sources for claims. Secondly, if you ever get in an argument with a climate change “sceptic”, keep it cool! I’ve now armed you with the tools you need to debunk a climate change sceptic in the future. Knowledge is our strongest asset, and we have a duty to share it. Good luck!


  1. Berner RA, Kothavala Z (2001). GEOCARB III: a revised model of atmospheric CO2 over Phanerozoic time. American Journal of Science301(2), 182-204.
  2. Arrhenius S (1896). On the influence of carbonic acid in the air upon the temperature on the ground. Philosophical Magazine and Journal of Science 41, 237–275.
  3. Royer DL (2006). CO2-forced climate thresholds during the Phanerozoic. Geochimica et Cosmochimica Acta 70(23), 5665-5675.
  4. Krivova NA, Solanki SK (2008). Models of solar irradiance variations: Current status. Journal of Astrophysics and Astronomy 29(1-2), 151-158.

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