Each day, an estimated 350,000 babies are born worldwide, outnumbering the number deaths, and adding to a growing population.

And while it may not be an obvious link, this overpopulation could be increasing the pace of climate change.

Dr Travis Rieder, a moral philosophy professor and bioethicist at Johns Hopkins University, explains why the key to stopping climate change is reducing the number of babies born each year.

Each day, an estimated 350,000 babies are born worldwide, outnumbering the number deaths, and adding to a growing population. And while it may not be an obvious link, it appears that this overpopulation could be increasing the pace of climate change

THE KAYA IDENTITY The Kaya identity is an equation relating factors that determine the level of human impact on the climate, in the form of emissions of the greenhouse gas, carbon dioxide. The Kaya identity says the pace of climate pollution is related to four factors: 1) Carbon dioxide emissions 2) Energy consumption 3) World GDP 4) Global population The equation says that as the number of people in the world increases, the pace of climate pollution also rises. Advertisement

Earlier this summer, I found myself in the middle of a lively debate because of my work on climate change and the ethics of having children.

NPR correspondent Jennifer Ludden profiled some of my work in procreative ethics with an article entitled, 'Should we be having kids in the age of climate change?,' which summarised my published views that we ought to consider adopting a 'small family ethic' and even pursuing fertility reduction efforts in response to the threat from climate change.

Although environmentalists for decades have worried about overpopulation for many good reasons, I suggest the fast-upcoming thresholds in climate change provide uniquely powerful reasons to consider taking real action to slow population growth.

Clearly, this idea struck a nerve: I was overwhelmed by the response in my personal email inbox as well as op-eds in other media outlets and over 70,000 shares on Facebook.

I am gratified that so many people took the time to read and reflect on the piece.

Having read and digested that discussion, I want to continue it by responding to some of the most vocal criticisms of my own work, which includes research on 'population engineering' – the intentional manipulation of human population size and structure – I've done with my colleagues, Jake Earl and Colin Hickey.

In short, the varied arguments against my views – that I'm overreacting, that the economy will tank and others – haven't changed my conviction that we need to discuss the ethics of having children in this era of climate change.

Although environmentalists for decades have worried about overpopulation for many good reasons, Dr Rieder suggests the fast-upcoming thresholds in climate change provide uniquely powerful reasons to consider taking real action to slow population growth

FOUR DEGREE WARMING COULD BE 'CATASTROPHIC' A report prepared for the Word Bank provides snapshots of the latest climate science. It warns that without concerted action, temperatures are on pace to rise to 4°C above pre-industrial times by the end of this century. At 4°C warming, the World Bank predicts that every summer month will be hotter than any current record heat wave, making the Middle East, North Africa and the Mediterranean deadly during the summer months. Many coastal cities will be completely under water, and all low-lying island nations will likely have to be abandoned. Hundreds of millions, if not billions of people could become climate refugees, as their homelands become uninhabitable. Advertisement

HOW BAD WILL THINGS GET?

Some comments – those claiming climate change is a hoax, devised by those who wish to control the world's resources – are not worth responding to.

Since 97 percent of all relevant experts cannot convince climate change skeptics of the basic scientific facts, then nothing I say will change their minds.

Other concerns, however, do require a response.

Many people reacted to my work on procreation ethics by saying climate change will not be so bad, and so curbing individual desires, such as having children, in its name is unnecessary fear-mongering.

In my work, I suggest that 1.5-2°C warming over pre-industrial levels will be 'dangerous' and 'very bad,' while 4°C will be 'catastrophic' and will leave large segments of the Earth 'largely uninhabitable by humans.'

Here is a very brief survey of the evidence for those claims based on what I consider reputable sources.

At 1.5-2°C, a World Bank report predicts an increase in extreme weather events, deadly heat waves and severe water stress.

Food production will decrease, and changing disease vectors will create unpredictable infectious disease outbreaks.

At 4°C warming, the World Bank predicts that every summer month will be hotter than any current record heat wave, making the Middle East, North Africa and the Mediterranean deadly during the summer months (stock image)

Sea levels will rise, combining with increased storm severity to place coastal cities at risk.

The World Health Organization (WHO) estimates that from the years 2030-2050 – as we reach this level of warming – at least 250,000 people will die every year from just some of the climate-related harms.

Perhaps many of us in rich countries (the 'us' who might be reading this) will be largely protected from these early harms; but that doesn't make them less real to the vulnerable citizens of, say, Bangladesh, Kiribati or the Maldives.

In fact, it escalates the injustice, as the global wealthy have benefited from and contributed to climate change the most, while the global poor will be hurt first and worst.

At 4°C warming, the World Bank predicts that every summer month will be hotter than any current record heat wave, making the Middle East, North Africa and the Mediterranean deadly during the summer months.

Many coastal cities will be completely under water, and all low-lying island nations will likely have to be abandoned.

If temperatures rise by 4°C, many coastal cities will be completely under water, and all low-lying island nations will likely have to be abandoned. Pictured are people affected by flooding in India

Hundreds of millions, if not billions of people could become climate refugees, as their homelands become uninhabitable.

Based on these descriptions, I stand by my predictions.

NO, ENVIRONMENTALISTS DON'T HATE BABIES

Other critics have argued that advocating for a lower birth rate = hating babies or being 'anti-life.'

Obviously I don't hate babies! I'm pretty wild about my own kid, and small humans in general.

This anti-life charge is more interesting, but equally wrong.

The premise seems to be that those who wish to lower fertility rates must be misanthropic, or fail to see the value of humans.

But that gets things exactly backwards: A radical concern for climate change is precisely motivated by a concern for human life – in particular, the human lives that will be affected by climate disruptions.

A valuable philosophical contribution here is the distinction between 'making people happy' and 'making happy people.'

When I feed a hungry person, or prevent a harm from befalling someone, I improve a person's well-being.

But when I create a person whom I will then feed and prevent from harm, I make a person who will predictably be well off.

In the first case, I added happiness to the world by helping an existing person; whereas in the second case, I added happiness by creating a person who will be happy. See the difference?

I, like many philosophers, believe that it's morally better to make people happy than to make happy people.

Those who exist already have needs and wants, and protecting and providing for them is motivated by respect for human life. It is not a harm to someone not to be created.

In fact, I would argue that it is more 'anti-life' to prioritize creating new life over caring for, or even not harming, those who already exist.

CAN THE ECONOMY GROW WITH LOWER POPULATION GROWTH?

Another opposing argument: People are not only consumers – they are also producers, and so will make the world better.

Yes, humans are producers, and many wonderful things have come from human genius.

But each person, whatever else they are (genius or dunce, producer or drag on the economy) is also a consumer.

And this is the only claim needed in order to be worried about climate change.

The problem here is that we have a finite resource – the ability of the Earth's atmosphere to absorb greenhouse gases without violently disrupting the climate – and each additional person contributes to the total amount of greenhouse gas in the atmosphere.

So although humans will hopefully save us (we do, in fact, desperately need brilliant people to develop scaleable technology to remove carbon from the air, for instance), the solution to this cannot be to have as many babies as possible, with the hope that this raises our probability of solving the problem.

Several people point to low-fertility countries like Japan, Italy and Germany, and argue that problems experienced by such countries are proof that the 'real' population crisis is our dropping fertility rate (stock image)

Because each baby is also an emitter, whether a genius or not.

Lastly, there's the view that lowering fertility rates will kill the economy.

Several commenters point to low-fertility countries like Japan, Italy and Germany, and argue that problems experienced by such countries are proof that the 'real' population crisis is our dropping fertility rate.

We need more babies to grow into healthy young producers to keep our economic engine humming.

The truth in this objection is the following: An economy that requires infinite growth to be healthy will be harmed in a world of finite resources.

But if it's true that our economies can't survive slowing or even reversing population growth, then we're in some trouble no matter what.

Why? It's simple logic that we cannot grow our population forever.

We can either reflect now on how to protect our economy while working toward a sustainable population, or we can ignore the problem until nature forces it on us, perhaps violently and unexpectedly.

I'll conclude with one, final thought: I don't enjoy arguing for a small family ethic, or a population engineering scheme.

Despite snide accusations to the contrary, I get no research funds or any other incentive for making this case.