Climate Change: The Evidence

Posted on July 9, 2013 at 10:37 am,

This is the latest in a series of posts critiquing Wayne Grudem’s book Politics According to the Bible. Today, we’re in the middle of the chapter on the Environment, looking at what he says about climate change. Grudem claims that it isn’t happening. In this post, we’ll be looking at the evidence he presents. The next post in the series will examine the political and theological implications of climate change.

Grudem begins with a brief introduction to the issue of climate. He explains the greenhouse effect, and the fact that there are other things that affect climate. He then talks about carbon dioxide. He mentions that atmospheric concentrations of carbon dioxide have risen from about 270ppm to about 385ppm, but disputes that this is the result of human activity, though he does not mention any other possible source. He then claims that predictions about the dangers of an increase in the average global temperature are solely the result of computer models and the assumption that other factors will increase the impact of carbon emissions in raising the temperature. He argues that the climate has a low sensitivity to increases in carbon levels (i.e. that temperature rises will be at the lower end of the predictions).

He then makes several claims that the scientific evidence does not back up the claims that are being made about climate change. Addressing this fully would take an entire series of posts, so we’ll only really skim the surface, though each section contains links to more detailed information.

Is computer modelling reliable?

Grudem says that climate change theory is based on computer models, that these models are hypotheses, and are not based on empirical observations of the real world. In actual fact, before any computer model is accepted as a potential prediction of the future, it is tested against empirical measurements of the past – the modellers take a starting point in the past, put in the data from that and see if the model correctly predicts climate trends from that date up until the present. If a model cannot predict the past correctly, then it is rejected out of hand. And many of the older climate models have continued to be correct for decades after they were first created. (more info)

Are scientists “strongly divided” on the issue?

Grudem claims that more scientists reject the existence of man-made climate change than embrace it. He cites a list compiled by a US senate panel of more than 700 scientists who have published rejections of the whole, or significant parts, of the global warming hypothesis. However, it turns out that fewer than 10% of the people cited are climate scientists, only 15% had had anything published in journals related in any way to climate science, around 80% had no published scientific papers at all, and about 4% had no disagreements with the consensus view that climate change is happening and is man-made. Furthermore, some of the people cited were basically just weathermen. (debunking here).

He also cites a petition of 31,000 people with science degrees claiming that climate change is not happening. There are a number of problems with this. Firstly, only 0.1% (39) of the people signing are said to have any background in climatology, though another 0.4% have a background in Atmospheric Science. Secondly, there is no way to check the claimed scientific credentials of the people on the list. Thirdly, the wording of the petition actually specifies “catastrophic” heating of the Earth’s atmosphere, wording which could be considered consistent with current climate change theory. So it’s a few thousand people with no particular expertise signing to a petition say that there is no evidence that “catastrophic” climate change is happening. Hardly convincing evidence of a scientific split. (debunking here and here).

He also cites a book called The Deniers by Lawrence Solomon which claims that many of the top experts reject the climate change consensus. The problem with this claim is that the scientists cited in the book all accept said hypothesis, and Solomon’s book actually admits the fact. (debunking here and here)

Finally, Grudem claims that scientific literature is divided on the issue. In actual fact, 97% of climate scientists and climate science articles support the consensus. Grudem claims that a 2004 study by Naomi Oreskes showing the consensus was flawed, citing a refutation by Benny Peiser. But Peiser has withdrawn his initial criticism, and agrees that Oreskes’ data was correct. (debunking here).

Has the Earth’s temperature fallen or remained steady?

Grudem claims that the temperature has fallen or remained steady for the last 15 years (up to his publication date of 2010). To examine that, let’s look at the list of the ten warmest years on record. They are (up to my publication date partway through 2013), in order:


The earliest year in that list is 1998. If the planet was not warming over the long term, the list should be dominated by years from the 20th century (since we’ve only had global direct measurements since 1880). Instead, it’s almost entirely years from the 21st Century. Given that a number of these years were in the cool (La Niña) years of the El Niño/La Niña cycle (a natural cycle that significantly increases or decreases the global average temperature), it is pretty clear evidence that the planet is warming over the longer term, and strongly suggests that it has warmed even in the shorter period since 1995. Also, earlier in the chapter Grudem stressed the importance of relying on long-term trends over short-term, local evidence – which pretty much undercuts his use of this argument.

Grudem also claims that temperature changes might be a result of the “urban heat island” effect – where the growth of urban areas causes the local area near a weather station to increase. The problem with this theory is that urban and rural temperature monitoring stations show the exact same warming trend. (evidence).

He also says that ocean currents and solar flares might produce alternative explanations for any warming trend. The argument for it being ocean currents requires either that the oceans are cooling, or that the laws of thermodynamics (which are the most fundamental part of physics) are wrong. But as the oceans are warming, the argument is clearly wrong (evidence). When it comes to solar flares, the trend over the last 35 years has been that temperature has been increasing whilst solar flares have been flatlining or declining. (evidence)

Can the scientists be trusted?

Grudem points out that the IPCC (Intergovernmental Panel on Climate Change) is considered the world’s most authoritative body on climate change. Grudem begins by claiming that the IPCC summary for policymakers exaggerates the scientific conclusions. His citation for this points out one dissenting scientist and one “expert reviewer” (which means somebody who asked to see the report and commented on it) who has no climate change credentials. And claims that some more sceptical language was omitted. In response to this, it is worth noting that there is reason to believe that the IPCC reports are overly cautious.

Grudem also claims that the IPCC are highly politicised, and biased because they are expected to study human, rather than natural causes of climate change. However, there is evidence that there is significant political pressure being put on them to underestimate the evidence for climate change..

Finally, he mentions Climategate. This was something that happened whilst Grudem wrote his book. Basically, some climate change deniers hacked into the computers of the Climate Research Unit at the University of East Anglia, stole all their files and emails, and posted them on the internet. A number of charges were levelled at the climate scientists at the CRU by various climate change sceptics/deniers regarding the way they used the evidence. Grudem claimed that the charges completely undermined confidence in their research. As I am writing this quite some time after the events, I know (which Grudem couldn’t have) that there have been eight separate enquiries into the CRU and the allegations, all of which have found no evidence of wrongdoing. The accusations against the CRU were basically people taking comments in the emails out of context. To date, the criminal or criminals who hacked into the computers have not been caught.

Glaciers and Sea Ice

Grudem claims that, contrary to claims about climate change melting glaciers, glacier coverage has been expanding. However, the evidence suggests that such claims rely on cherry-picking.. He also claims that sea levels are, at worst, only going to rise by a tiny amount. In fact, the evidence shows that sea levels are rising, and the rate of change is accelerating. They may only rise by a tiny amount, but the trend is not looking good.

Is severe weather increasing?

Grudem points out that climate change is predicted to increase the number and severity of severe weather events such as hurricanes, droughts, and floods. He claims that there is no evidence that they have increased. Whilst the jury is still out on whether the number of tropical storms such as hurricanes have increased (there has been an increase, but it could be due to increased monitoring), there is reason to believe that they have increased in intensity. As for severe weather events in general, this is a subject that has not been looked into as much as other areas of climatology. The studies are beginning to be done, but the jury is still out.

Are carbon emissions actually a good thing?

Grudem makes two final claims about the science. Firstly, he says that that carbon emissions could be beneficial. He says that carbon dioxide helps plants to grow, and that previous geological eras with high levels of carbon dioxide had abundant plant life. He also says that the evidence suggests that previous naturally occurring periods of global warming were caused by other factors – and that there was little correlation between carbon dioxide levels and temperatures in previous warming periods.

The second claim is, of course, utterly irrelevant. The fact that a previous instance of global warming was not caused by industrial carbon emissions does not mean that global warming cannot be triggered by carbon emissions. As to the first claim, carbon dioxide is not the only thing that plants need to grow – if carbon dioxide causes increased plant growth, those plants will use other nutrients faster, degrading soil quality. Secondly, experiments on plant growth in an atmosphere with more carbon dioxide have mostly been done in isolation. There is some evidence that these plants might be more vulnerable to insects. And, of course, climate change driven by the increased levels of carbon dioxide is likely to increase the amount of desert, and decrease the amount of arable land for plants to grow in. (more info here)

In Conclusion

Grudem claims that the scientific evidence is strongly against the idea that human activity is causing the planet to warm up and, therefore, changing the climate. As we have seen, his claims do not stand up to scrutiny, and the scientific evidence is robust (and rather stronger than we’ve shown here, because we’ve just been rebutting Grudem’s claims).

In the next post, looking at the theology and politics, we’ll see that Grudem has a theological framework that rules out the possibility that human beings could affect the climate in any significant way. Given the weakness of his scientific arguments, I am left with the impression that this theology gave him a strong confirmation bias* on the issue, making him think that the claims of the climate change denial lobby are a lot stronger than in reality. The fact that this lobby is closely connected to the political party he supports would only have reinforced that.

*confirmation bias is when our minds subconsciously give more credibility to evidence that supports our existing opinions, and finds ways to discount evidence that contradicts them. Psychologists have proven that confirmation bias is pretty universal amongst human beings.

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