The proof of climate change

Where is the proof that climate change is real and that humans are at fault? Climate sceptics love to pounce on the fact that scientists cannot prove that humans are the cause of climate change. Tony Abbott has said previously that climate science is “absolute crap”. More recently he has clarified that he meant to say the science of climate change is not yet “settled”. These comments presumably refer to climate scientists’ inability to prove that the climate is warming and that humans are contributing to it.

The concept of “proof” in science relates to the way in which scientists form and test hypotheses. But, as discussed by Massimo Pigliucci in his book Nonsense on Stilts, the way scientists go about testing these hypotheses depends on the complexity of the system they are trying to explain.

For example, a chemist in the laboratory may be trying to determine whether some compound “A” causes a particular reaction “B” to occur. To test this hypothesis, the chemist would probably set up an experiment to test whether reaction B occurred in the presence of A, and compare this with what happened in the absence of A. The chemist can follow this particular line of inquiry because they have the ability to manipulate and control most or all of the different factors that could affect the outcome of the lab experiment. An experiment is highly repeatable in controlled conditions, meaning that if the experiment is repeated over and over, the same results can be obtained consistently. Thus, predicting the behaviour of a system becomes very accurate when most of the variables are accounted for.

But imagine now that the chemist now has to perform their experiment out of the lab. The temperature and light intensity now fluctuates, and a little dust or dirt gets into the reaction. A little of compound A blows away in the wind before the chemist can add it to the reaction. Reaction B does not occur. The frustrated chemist repeats the process and this time reaction B does occur. Another repeat of the experiment produces a negative result. Once a system moves outside the lab and into the real world where some variables cannot be controlled, the system becomes less predictable.

Now consider an atmospheric scientist, who, like the chemist, wants to know whether compound A causes reaction B to occur in the atmosphere. In this situation, the atmospheric scientist cannot perform an experiment to change the concentration of compound A in the air - that would be impractical and irresponsible. Instead, the atmospheric scientist has observed that the concentration of compound A has increased in the atmosphere over the last few decades. Furthermore, the rate of reaction B has also increased during the same time period. Is the atmospheric scientist able to confirm or refute their hypothesis that compound A causes reaction B to occur in the atmosphere? Given that an experiment in the atmosphere is not feasible, is the current evidence sufficient to support the hypothesis? Or is the question just unanswerable? Is the science just “crap”?

Not all streams of science are able to test hypotheses by conducting a controlled experiment. While the outcome of a controlled experiment is highly repeatable, the results of the experiment have limited relevance in the real world, where conditions are impossible to standardise. On the other hand, it is difficult to conclusively demonstrate cause-and-effect relationships in natural systems because there are so often multiple factors that determine the outcome. Streams of science such as ecology and climate science often rely on making observations to identify trends and links between potential causes and effects. But scientists in these fields must report these results using sufficiently cautious language, using phrases such as “the evidence suggests…” and “our results may mean…”

Pigliucci argues that this does not make the science “crap” but instead reflects the limitations that scientists face in answering questions about complex systems. Unless we have a spare planet earth that we could observe, subject to exactly the same conditions as our own, except devoid of human life, proving in a scientific sense that climate change is human-induced is an impossible task and a foolish endeavour.

Scientists studying these complex systems are stuck between a rock and a hard place when it comes to communicating their work. The philosophy of science is such that definite conclusions are made only when hypotheses are tested in controlled experiments. The strict peer-review process, in which published science research is scrutinised by other experts in the field (I’ve discussed this in a previous post), effectively discourages scientists from making outlandish, unfounded claims. In contrast, those in business and politics want to see strong definitive results from science research, particularly when deciding whether to make a monetary investment in a discovery or when making government policies based on the results of a study.

But in some situations, as is the case with climate science and climate change, another aspect needs to be taken into account. With the climate data we have and the trends we have identified, we need to weigh up whether the price of inaction outweighs our need for a controlled experiment to prove our hypothesis. With this in mind, and considering that a controlled experiment to test the hypotheses is not feasible, I think we need accept that we are as close to proof as we are going to get, and we to act now.

Who are the real population experts?

A debate on the ABC program Q and A on Thursday followed the screening of Dick Smith’s Population Puzzle. The debate panel plus guests from the floor comprised a curious selection of “population experts”. These included four politicians, a professor of cultural studies, a chairman of an infrastructure company, a representative of the Minerals Council of NSW, a newspaper columnist and the mayor of a small town in South Australia.

Oh, and some biologist called Tim Flannery.

What a strange choice of panellists for a debate about population growth! Politicians, with one hand in developers’ back pockets while checking their poll results to make sure they don’t ruffle too many feathers with their policy decisions, are not the truly impartial judges we need when it comes to deciding whether we need to stem our population growth.

Neither are people with vested business interests in seeing our population grow. And neither are social commentators, whose simplistic solution to the problem seems to be to allow people to migrate from very overpopulated areas of the world to less-densely populated ones. Even if our planet's population was evenly distributed among countries, we would still be grossly overpopulated. According to the Worldwide Fund for Nature (WWF), our global ecological footprint exceeded the biological capacity of our planet in the mid 1980s. Population growth is an international issue requiring international solutions.

Unfortunately what this debate lacked completely was any real science about the factors that control the growth of populations. It seems to me that if people want to hear from real experts on population growth and sustainability, to get the hard facts and real data on the dynamics of populations, that we should be asking people who study this for their job – biologists.

So why are biologists the real authorities on population growth?

Well, as much as most people don’t like to admit, we are just another species on the earth. We are just another organism reproducing selfishly until something stops us. Population ecology describes the how populations swell and crash and how they interact with their environment. Theory says that populations will multiply exponentially until one of two things stops the increase: when resources become limited (food, water, space), or when a disease epidemic culls a significant percentage of the population.

Finite resources limiting population growth is an obvious concept that the majority of people (except property developers and most economists) can understand. No more food, no more water, no more space means no more growth.

But the threat of disease epidemics may sound more like science-fiction than science fact in a developed country like Australia. After all we have a decent healthcare system, we are educated in basic hygiene practices and medical research provides us with vaccinations for most of the communicable diseases that are responsible for epidemics in poorer parts of the world. But diseases, particularly those caused by viruses, can still ravage developed countries if they spread faster than we can quarantine infected people, or if they mutate more quickly than we can develop vaccines for them.

The most virulent viruses come from other animals, such as bird flu and swine flu. These viruses can persist in the host animal species asymptomatically, but they inflict incredible destruction when they move to another species, such as humans, that is immunologically naïve to the virus. A pertinent example of a virus that crossed the species barrier is HIV, which spread from chimps to humans in the early 1980s.

As the recent book Virolution by Frank Ryan explains, the ability of viruses to cross the species barrier is not unnatural and is in fact crucial to their evolutionary success. Viruses co-evolve over multiple generations with a particular species until the virus causes only very mild or no symptoms for the host. In some cases, the virus actually inserts its own DNA into the genetic code of the host species. In a strange twist, this results in a situation that is mutually beneficial for both the host and the virus. The virus has a place to live and has effectively become immortal, reproducing every time DNA replication occurs in the host species. In return, the virus acts as the host's secret attack arsenal. The virus lies latent until the habitat of the host species is under threat from a competitor, at which point the virus can reawaken and infect the immunologically-naïve invader. Not a bad evolutionary partnership really, and one that is, and may always be, one step ahead of our efforts to stop it.

Humans, with our rapidly growing population, are the immunologically-naïve invader in this story, encroaching on the habitat of other species as we expand our own territory. And as our population density increases, we will also live in closer and closer contact with the animals that we have domesticated for our food, increasing the potential for more viruses to jump the species divide. Additionally, a very dense population promotes the quick spread of these viral outbreaks and provides more human hosts in which the virus can mutate. All of this combines to impede our ability to quarantine infected individuals during an outbreak and develop vaccines before the virus mutates.

So the debate about population growth is not just a social, economic or environmental issue. We have to realise that we are not outside the laws of biology that keep populations of all species in check. Unlike other species, however, we have the advantage of being able to understand and acknowledge that these biological processes act on populations, including our own. We also have the ability to choose whether we limit our own population growth or allow these biological processes to do the job instead. Although it would be far from easy, I am sure that we could come up with an effective global plan to manage our own population. But at the moment, any effective action is hampered by an economic system that relies on population growth for economic prosperity, by religions that oppose all forms of contraception, and by a lack of basic education in many parts of the world. In light of what we know, if we still choose to take no action and face population control enforced by depleted resources and disease epidemics, instead of at our own hands, we will truly prove that we are no different and no better than all other selfishly-reproducing species on this planet.