Recently I have encountered what I consider to be surprising doubts about the reality of anthropogenic climate change. Perhaps this is a sign of the times, where authorities such as scientists are no longer trusted and assumed to be operating with some kind of political agenda. What are we to believe in the face of apparent disagreement over the issue?
The mainstream view of climate science is that mankind is causing the warming of our atmosphere through burning hydrocarbons, and that unless some action is taken to limit the temperature increase to 1.5°, we are on course for serious and unpredictable effects on humanity and other life on earth. The aim of this article is to explore a few of the ideas which have gained currency and are used to dispute the mainstream view.
Here is a list of some climate objections which I have heard expressed of late:
- The climate varies due to natural causes (and life has survived just fine)
- The science is not settled
- CO2 is not a pollutant (it makes plants grow, so more is better)
- Correlation is not causation
- The economy will collapse if we stop using oil and gas
- Solar and wind are too intermittent to meet energy needs
The climate varies due to natural causes (and life has survived just fine)
This is true. Over geological timescales there is huge variation in climate. The causes are manifold.
Over millions of years, changes in the position of continents have a strong effect on climate. There are causes related to the earth’s motion such as variation in the tilt of its spin axis, precession of the spin axis and the eccentricity of its orbit around the sun. These three can be lumped together under something called Milankovitch theory. The effect operates on a scale measured in 10s to 100s of thousand years. Events like volcanic eruptions can occur and generally have a cooling effect which may last for months or years. It is also true that CO2 concentrations have varied widely. High CO2 concentrations have been associated with high temperatures over geological timescales. It is also true that earth has been much hotter in the past and life did just fine. In recent history (i.e. the last few 100,000 years) earth has been much colder than present, since we are currently in an interglacial period. If all we care about is that life will survive, then there is probably little cause for concern. Global warming will not wipe life out. However, this does not mean that all species will survive just fine. Climate change has been responsible for some of the major extinction events in geological history. More relevantly, it also is no guarantee that conditions which are comfortable for human civilization will persist. Furthermore, geologically speaking CO2 concentrations change over periods measured in thousands of years, not decades. It is the speed with which CO2 is being cranked up by human activity which is a cause for concern.
The science is not settled
The claim that the science is not settled, is usually based on the acknowledged uncertainties around modelling a complex system such as the climate. It is important to distinguish between uncertainties related to the fact of climate change and the details as to how it will manifest. Climate prediction is fraught because of non-linear responses and feedback. For example, water vapour is a stronger contributor to climate change than CO2, and one criticism I have come across is that the effect of warming on water vapour and cloud formation is poorly understood. In general terms, we know that it can be a negative feedback (i.e. reduce the effect of warming) via clouds which may reflect sunlight back to space, but it can also serve as a positive feedback (i.e. amplify the effect of warming) by trapping energy within the atmosphere.
The presence of feedbacks such as water vapour does not lead logically to a climate change denial position however: the fact is that the feedback effects could potentially make climate change more extreme, rather than less. Meanwhile, ongoing measurements are by and large confirming that the models do a reasonable job of prediction. This suggests the feedback effects though not fully understood are well enough understood to make climate models useful as input to climate policy.
CO2 is not a pollutant (it makes plants grow, so more is better)
This strawman argument attributes those who are concerned about climate change with saying “CO2 is polluting our atmosphere”, as if it was similar to smog. It is easy to ridicule such eco fanatics, pointing out that life depends on CO2, since photosynthesis requires it and so on! In fact, without the blanked of CO2 (and other greenhouse gases) which our atmosphere already contains, the average surface temperature would be -18C and life would be impossible. Does the fact that some of a thing is good always mean that more of it is better? No, obviously not.
We can agree, CO2 is not a pollutant in the conventional sense, harming life directly: scientists are not suggesting that it is. However, the atmospheric concentration matters. The earth is warming due to additional CO2 generated by human activity, taking place over a relatively short time period – rising from under 350ppm to over 400ppm during the last 50 years, as seen in the Keeling Curve. This rapid increase is harmful to some plant and animal species, and very likely to human civilization.
Correlation is not Causation
This argument is all about the relationship between CO2 levels and temperature. It goes like this: “OK it is true that over geological time there is a correlation between CO2 levels and temperature indicators. But, so what? This doesn’t prove that CO2 causes temperature change, it could just as easily be the reverse”.
If we had nothing to go on except the fact that two variables appear to have correlation this argument would hold (some) water. But this is not the case. We have a clear physical basis for the expectation that CO2 should cause temperature increases, due to the trapping of infrared radiation. In fact, the effect goes both ways – a temperature increase also causes the release of CO2 from the oceans, thus creating a positive (reinforcing) feedback effect.
It is true that ice core measurements covering the last 400,000 years appear to indicate that the net release of CO2 lags the increase in temperature. In these long timescale observations, the initial temperature increase is known to be caused by changes in the earth’s orbit. However, the total effect was then amplified by the resulting release of CO2 into the atmosphere. The orbital effect is also well understood and is not sufficient on its own to explain observed temperature changes.
So, rather than allowing us to be less concerned about CO2 levels, this feedback loop should make us more concerned.
The economy will collapse if we stop using oil and gas
Several studies have shown that economies can grow while converting to renewable energy. During recent years, some countries have taken steps based on their climate commitments to reduce greenhouse emissions, and their economies have not shuddered to a halt. In 2017 CO2 emissions in the UK reached a level 38% below 1990 and not seen since 1890, largely as a result of reduced coal power generation. In a recent UK government ONS report Dr Amina Syed states that “The UK has shown evidence of absolute decoupling between 1985 and 2016, as gross domestic product (GDP) per head grew by 70.7%, while CO2 emissions fell by 34.2%.” Obviously for countries with economies based on export of oil and gas or coal, such as Saudi, Canada or Australia, a move away from these forms of energy could be economically difficult, unless these industries are replaced by renewable equivalents. However, for countries which have mixed economies, and are primarily consumers of oil and gas, switching to renewables can be neutral or beneficial to the economies.
Solar and wind are too intermittent to meet energy needs
This used to be a stronger argument against the viability of renewables, but advances in battery technology and other forms of storage such as pumped hydroelectric, as well as smart grid management are making this concern obsolete.