Is it safe to double atmospheric Carbon Dioxide over a 200 year period?

We are on track to double pre-industrial atmospheric carbon dioxide concentrations. In assessing the risk, the above question is much more fundamental than asking how much the climate warmed over the 20th century. So what’s the answer?

Society has standard approaches for assessing risk and safety. When it comes to assessing risk for major intervention, this approach entails a null hypothesis, or base assumption, that things are unsafe until proven safe.  Examples occur in medicine, engineering and just about every human activity. In medicine, a drug company can not assume that a new vaccine is safe, with the burden of proof on others to prove it is unsafe. Note that this is different to determining whether the vaccine is effective, where the null hypothesis could be that there is no association between the vaccine and immunity. Rather, the null hypothesis for the risk assessment relates to the question, can I use this vaccine for a major public vaccination program?

When it comes to carbon pollution, the normal convention for risk assessment goes right out the window. The scientific null hypothesis that there is no association between carbon dioxide and climate change is easily broken. But the public risk question really relates to doubling the atmospheric carbon dioxide concentration in 200 years. In other words, is altering atmospheric chemistry in that manner safe?  In the weird world of greenhouse policy, we would like everyone to assume that putting 3.6 billion tons of carbon into the atmosphere is entirely safe, with the onus on climatologists to prove otherwise.

Taking the wrong null hypothesis has serious implications for the way the science is assessed. Going back to our medical analogy, even a relatively small amount of evidence that the vaccine is unsafe is enough to inform a risk assessment. In other words, the null hypothesis stands. You need to produce a great deal of evidence to satisfy authorities that the vaccine is safe.

In the assessment of carbon pollution, we have this the wrong way around. Small uncertainties in the conventional science are used to reinforce the notion that doubling atmospheric carbon dioxide is entirely safe. Most importantly, and somewhat amazingly when you stop to think about it, major polluters and proponents of continued carbon pollution have never proved that their product is safe. Not only that, they haven’t even been asked, by governments and the public alike, to prove that their product is safe.

This means that, to date, we have no studies demonstrating that the climate system is insensitive to such increases in carbon dioxide, and a mountain of evidence indicating that doubling atmospheric carbon dioxide will result in dramatic climate change. Yet still, we refuse to really accept the risks. One of the biggest reasons for this is that the skeptics have been successful in limiting public discussion to 20th century global mean temperature. In reality, the case against doubling atmospheric carbon dioxide is well established before we look at the 20th century climate record.

One of the most certain things in climate science is that increasing carbon dioxide warms the climate system. Doubling atmospheric concentrations is sure to cause significant warming of the climate system. And doubling a over a 200 year period represents one of the most rapid changes in atmospheric carbon dioxide in the history of the Earth.

The certainty that carbon dioxide warms the climate system does not rely on any 20th century climate observations, such as employed in fingerprinting studies. These studies seek to determine how much the 40% increase in carbon dioxide over the 20th century has already affected the climate. Rather, the evidence against increasing carbon dioxide is much more fundamental.

The first place to look is of course the paleoclimate record. Over the last several decades of research, the sensitivity of the climate system to changes in carbon dioxide has been established through ice core samples and other proxy climate indicators. In short, past climates with high atmospheric carbon dioxide concentrations were very warm, unless incoming solar radiation was low. Rapid changes in carbon dioxide (such as due to planetary volcanic activity or asteroid strikes) resulted in rapid changes in the climate system. The literature on this topic remains unchallenged; in the Earth’s geological history, if carbon dioxide concentrations increased, the planet warmed.

The second and more important place to look is the fundamental physics and chemistry- using mathematical modelling. Models used in climate come in different shapes and sizes. Some of the most basic models, such as the behaviour of gases exposed to radiation of different wavelengths, are well established physical models.

Far from being controversial, numerical models are used in all modern fields of science. Mathematical models are implicit in our understanding of the universe. For example, the governing equation for the gravitational effect is also 'just a model'.  In fact, it’s the very definition of a model, since we do not actually understand how gravity works. However our mathematical model of the nature of gravity has been verified through countless observations. We are quite certain that our mathematical model of gravity accurately describes the Newtonian universe. These principles are not negotiable like the tenets of social sciences or economics. They are fundamental laws. The universe doesn't fudge fundamental laws of scale.

Similarly, the mathematical model of the organisation of an atom; neutrons, protons, electrons, is just a model. We cannot actually look inside an atom. But the model has been verified and it holds as a fundamental certainty.

The mathematical model of how atoms absorb and re-emit radiation in discrete energy packets and in discrete wavelengths is also a model. It also faithfully describes the universe. A whole heap of technology is built on the certainty of this model. If these models did not work, then most of the appliances in your house would also not work, including the microwave oven and the television.

Therefore we can faithfully model how radiation passing through layers of radiative gas will be absorbed and re-emitted. There is nothing speculative about this either. This is fundamental physics and chemistry, text book material rather than brand new science.

(Image created by Robert A. Rohde / Global Warming Art)

If anyone seriously thinks that our understanding of radiation is wrong, then could they please publish that alternative theory in a proper scientific journal so we can all absorb a new reality? You will need to overturn more than 100 years of physics in the process. You will also likely win a Nobel Prize for your efforts. The incentive is there.

You see, you can't just say you don't agree with the fundamental laws of physics, or that you are not convinced by them, and leave it at that. At least, not if you want to be taken seriously in the scientific community (as opposed to simply confusing the public with red herrings). As an aside, I suspect that being taken seriously by the science community has never been a key priority for the skeptics.  By publishing almost exclusively on blogs and in the opinion sections of newspapers, and eschewing peer-reviewed scientific journals, they have staked out their real audience. Contributing to science has nothing to do with it.

Now where were we? Oh yes, we understand entirely how radiative gases like carbon dioxide absorb and re-emit radiation from physics, quantum physics and chemistry. We also understand the physics of radiation (for example the Stephan Boltzmann relationship). We understand entirely that if you increase the concentrations of carbon dioxide in the atmosphere, you will warm the surface of the planet. This result is repeatable (you get the same answer) using a simple model of radiation physics alone (just a couple of lines of code) or using a fully coupled atmosphere-ocean-sea-ice model with turbulent mixing. People have been trying to break this result for fifty years and have not. That’s how science works.

The sensitivity of the atmosphere to greenhouse gases can also be observed on nearby planets (Mars and Venus) and is consistent with the maths. The maths is also supported by the observed feedback mechanism between temperature and carbon dioxide in the ice-core record and other paleo indicators. If you double or even triple atmospheric carbon dioxide, which we will do sometime this century or early next, you will significantly warm the climate system. This is well above a 95% probability, and is hence a near certainty. No one has disproved any of this in the literature. No drug would make it onto the market with that kind of evidence running against it.

The climate system is complex, so the fundamental physics operates over many interacting variables. As such, many things can act to slow down the rate of warming or amplify it, such as the warming-water vapour feedback mechanism. But the system is not that complex, and is certainly far less complex than the human body. And the complexity of the system cannot change the radiative properties of carbon dioxide. Hence, over time, and given the rate of carbon dioxide increases that are proposed, warming will be set in train and is assured from the fundamental physics. Hence we are certain from all the science that the mean trajectory we are now on is a warming trajectory. Small uncertainties in the rate of future warming are irrelevant to the risk assessment. That’s like pinning the risk assessment associated with childhood exposure to UV radiation to uncertainty in the exact age that skin cancer is most likely to occur.

The climate of the deep past has shown that we are nowhere near the natural limits of warming for planet Earth. In other words, the current state of the climate has more things that can amplify warming than it does things that will keep a lid on the warming. There are mechanisms that limit warming, but we have plenty of room to warm given that the level of pre-industrial carbon dioxide was very low in relation to extremely warm climates in the distant past. This level of warming is more than enough to elevate sea level and change the predominant patterns of global climate. The uncertainties in the context of the enhanced greenhouse effect are actually more worrying than they are reassuring. This is a concept that the public does not understand very well.

Guess what? I haven’t even talked about a 20th century thermometer reading, and we already have heaps of evidence against the safety of rapidly doubling atmospheric carbon dioxide. The matching greenhouse fingerprints in the 20th century climate record are really the final nail of evidence.  If there is some study that contradicts the fundamental science, then where is it? No one has managed to find an alternative solution after decades of trying. While the skeptics will throw up the occasional vaguely set-out paper from fringe (and mostly non peer-reviewed) journals, they can not produce a set of key papers which demonstrate that doubling atmospheric chemistry has no significant effect on the climate system. And that is what they wish to prove is it not? It is certainly what they should be required to do.

So people should ask the skeptics their own set of questions. Why have they never produced a repeatable formulation of the physics as they see it? Why have they never developed their own climate models, and performed their own model experiments? Why have they never produced their own paleoclimate reconstructions? Why have they never compiled their own record of surface temperature?  Apparently, the lack of published research showing the inert nature of atmospheric carbon dioxide changes is the result of a long running, worldwide scientific conspiracy.

But that too doesn't stand up. With all the money supposedly at stake, the complete lack of credible research by the skeptics points to a complete inability to successfully argue their case in scientific circles. If destroying the conventional science was as easy as they suggest, the major polluters would have funded such research twenty years ago, and moved on. Again, the incentive is there, and large companies are more than capable of funding and producing credible research. But, importantly, they have not attempted to do so.

Posted by fingerprinter on Friday, 24 December, 2010

Creative Commons License The Skeptical Science website by Skeptical Science is licensed under a Creative Commons Attribution 3.0 Unported License.