For the past nine years I had the privilege of being the science adviser to three New Zealand prime ministers. This involved dealing with domestic and international challenges about how science feeds into policymaking that affects the daily lives of every man, woman and child. Examples include vaccination and immunisations, tackling youth obesity and advising on legal and illicit drug use.

These "life and death" issues have resonance for countries worldwide. Yet my daily interactions were always flanked by awareness of progress in other countries, and among those were valuable relationships with the SA science system. As a leader in pan-African policy innovation, SA gets the importance of scientific evidence to support laws meeting the nation and its citizens’ needs.

I have shared multiple platforms with SA leaders and intellectuals. One of my career highlights was receiving the inaugural American Association for the Advancement of Science’s Science Diplomacy Award in 2015, to be followed by then science minister Naledi Pandor in 2016. We have all been impressed by the carrier-wave effect her creation of Science Forum SA (www.sfsa.co.za) has had in igniting conversations about science, society, education, youth, innovation and diplomacy across Africa.

I again saw the green shoots of this outward-looking vision in Pretoria earlier in August when meeting with the Academy of Science, the National Advisory Council on Innovation, and the Diplomatic Training and International School of the Department of International Relations and Co-operation Department of International Relations & Co-operation.

SA scientists are in global demand too. In June, Dr Albert S van Jaarsveld was appointed director-general and CEO of the Vienna-based International Institute for Applied Systems Analysis. In July, Prof Daya Reddy was elected as first president of the Paris-based International Science Council. In July also, Cape Town was announced as host of World Science Forum 2021.

These and other international recognitions showcase how SA’s scientific reputation is rising.

SOME COUNTRIES DEAL WITH INDIVIDUAL DRUG USE AS A HEALTH AND ADDICTION ISSUE…. OTHERS SEE DRUG USE AS A CRIMINAL MATTER

I am a strong believer in the value of independent science advice in complex decision-making. These are issues in which scientific evidence and public or political values do not necessarily align.

With about 50 ministers, 11 official languages and a dizzying array of public, private and civil society influencers, it is easy to see how SA’s elected representatives have particularly challenging roles. Policy-making is ultimately about choices between options that involve different tradeoffs affecting different stakeholders in different ways.

It is entirely proper that in choosing between possible options, policymakers weigh up societal and political values — fiscal, diplomatic, ideological and religious, to name but a few — and they will always have an imminent electoral risk in mind. But science has a critical role in providing the understandings that will underpin those policy choices.

People’s world views are too often reinforced by the information bubbles they now live in, which means many only listen to people and media whose views align with their own inherent biases and ideologies. People want categorical answers. Science can rarely provide them. And social media and other nonneutral media can be used to manipulate opinion, often by claiming "facts" and "truths" even when they are neither factual nor truthful. Such manipulation not only undermines democracy but also society’s ability to use knowledge to make progress. There is always a danger that even the best available science can be ignored in such an environment. When that happens, it is more likely that policy outcomes will not serve the citizen well.

But, as expectations on policy processes grow, science and robust evidence have increasingly essential roles to play. Science has multiple disciplines defined by a set of processes designed to find as reliable as possible knowledge about the world within and beyond us. When used to inform the policymaker and citizen, science can identify what options really exist and the likely consequences of each. Science is always provisional, but that should not be an excuse for ignoring it. Nor should it be dismissed simply because it does not fit with prior biases or fixed views. But science can reduce the heat in values-laden debates that can otherwise be drowned in polemical rhetoric and assist decision-makers to work through complex and seemingly irresolvable issues.

One of the most difficult areas of public policy is harm-reduction science, aimed at reducing the adverse health, social and economic consequences of the use of legal and illegal psychoactive drugs. The science is often cherry-picked or interpreted to advance opposing arguments. Civil society and industry actors are well drilled in this. In turn, this can reinforce firm convictions about the validity or otherwise of the science.

All countries recognise the importance of vaccination and immunisation. Yet the "antivax" movement seems impossible to eradicate — it is supported by false science, rejected by every robust health authority and scientific academy, and yet is promoted by celebrities and other nonexperts. There are side-effects to vaccination but the societal sense of precaution and risk assessment has balanced those risks as being small in relation to the consequences of the pandemic illnesses that vaccination is designed to eradicate. As a young paediatrician, I remember well dealing with young children with irreversible brain damage or pneumonias from measles. Diphtheria and polio are not diseases we want to face again. But for the policymakers having to weigh up such decisions, scientific support and evaluation is essential.

The harm from smoking tobacco is well understood. About 75% of smokers may die from related diseases. SA is losing about 1,000 citizens a week. It is universally accepted that smoking kills. But regarding vaping, the science is still evolving, hence the difficult policy debates worldwide. Vaping clearly reduces exposure to cancer-causing chemicals, and any reduction in carcinogen exposure is clearly beneficial to the individual. But some argue that it may create a gateway to smoking. The long-term safety of some of the chemicals used in vaping systems is unclear, and the variety of vaping systems creates further uncertainties.

Regulation is needed. It is a matter of concern that tobacco and alcohol companies are targeting Africa and Asia as their market opportunities decline elsewhere. A further confounder is that vaping manufacturers are often the very tobacco companies that created the problem in the first place. Policy dilemmas are apparent.

On balance, the arguments for vaping have been accepted by many reputable scientific authorities and governments are better informed. New Zealand reversed its outright ban, while Public Health England advocates that vaping technologies be given out free to smokers. Yet there remain too many unknowns that only truly independent science can resolve. Africa too must invest in and share this research in global partnerships.

Countries are debating whether to view drug addiction through a criminal or a health lens. Needle exchange, while it may facilitate intravenous drug use, reduces the rates of HIV/Aids and hepatitis in user communities. Some countries deal with individual drug use as a health and addiction issue, moving to legalise marijuana either broadly or for apparent medical reasons and restricting criminal approaches to dealers and importers. Others see drug use as a zero-tolerance criminal matter clogging their justice systems, while not tackling root issues.

But there are layers of complexity here. Opiates, methamphetamines and cannabinoids all have different market dynamics and biological effects. Science has documented the side-effects of heavy marijuana use on the adolescent brain, yet advocates of decriminalisation provide "evidence" minimising this. The dangers of synthetics, very high-potency leaves, contamination and the social costs of criminalisation are all powerful arguments. Science-informed and much more nuanced conversations are needed regarding drugs and those who use them, and why, with greater emphasis on justice, dignity and human rights.

My fundamental belief is that science alone cannot decide on such matters. "Evidence" is one among many types of advice that inform the decision-making process. Above all, the meaning of risk varies. Risk to a politician is very different than to a citizen. Key determinants such as information selection, confirmation bias and polarisation require greater understanding and attention. Others include ethical values, cultures, politics and the impact any decision can have on other areas of policy. How to balance risk and precaution is a recurrent theme for politicians and the leaders of their national science systems. The scientific community must, however, stand behind its evidence and speak up when policy-makers clearly get it wrong.

While I have used examples of harm reduction, the interaction between science, societal values, concepts of risk and precaution and politics pervade every aspect of a democratic society. Whether it is dealing with climate change, artificial intelligence or tackling obesity, in every case both the natural and social sciences working together have an important role to play.

Better decisions are more likely when science is properly used. In recent years, SA has understood and is embracing this. As the late Kofi Annan rightly said, "Drugs have killed many people, but bad policies have killed many more." The parallel rise in reputation of SA science has been impressive to see — 56-million South Africans and 1.2-billion other Africans have a stake in this continuing.

• Sir Peter chairs the International Network for Government Science Advice