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OPINION: Let this sink in for a second. The world's population is increasing the size of Wellington, each day. And that's after you account for daily deaths.

I'm telling you this because I was recently flight shamed. Someone went to quite some effort to track down my details - and get in touch - telling me I needed to watch my carbon footprint.

Flight shaming in a New Zealand context can't be applied with the same broad brush as it is in Europe. We don't have cities connected by high-speed train. We're also surrounded by water.

I'm a travel journalist - so I'm an easy target. But, I'm also covering important stories about the climate. For example, I've just come off a carbon-neutral cruise to South Georgia, where scientists told us the glaciers there are melting by two metres, a day.

ISTOCK The world population is growing by around 155 people a minute. Why aren't we talking about it?

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I also think travel is vitally important; most of the people I know who deny climate change have travelled very little. I think people should travel more widely; with education, comes action, and seeing Earth is the greatest classroom.

Lastly, we all need a break - I think it's important we occasionally go on holiday and don't feel guilty about it.

So, back to the person who flight shamed me. I had a quick look into them, and found they had a large number of children; and an even greater number of grandchildren.

I'm perplexed why there is so much discussion on flying, yet little talk on a bigger issue: too many people on the planet.

By 1800 the human population hit one billion people. It took all of human history to reach this point, right back to the caveman. It took just 130 years to add the second billion. The next billion just 30 years. Now, we're up to a rate of one billion extra people in just 12 years.

So, what does that mean? The world population is growing by around 155 people a minute. Or 220,000 a day. That's roughly the size of Wellington. Google the World Population clock. You may need to adopt meditative breathing as you watch it whizz up.

We can try and make all the incremental changes we want to our carbon footprint, but it's never going to offset the enormous carbon impact of a world population that continues to explode. A recent study found that one of the worst things we can do for the environment is to have children.

The study, by researchers at Lund University in Sweden, found "a US family who chooses to have one (less) child would provide the same level of emissions reductions as 684 teenagers who choose to adopt comprehensive recycling for the rest of their lives."

By any measure, the Earth isn't coping with so many humans. The atmosphere has more carbon in it than at any point in the past three million years. There is so much plastic in our oceans it has been detected in seafood. It's estimated up to 150-200 species of plants, inspects, birds and mammals become extinct every 24 hours. Our rainforests are disappearing. Poor air quality led to an estimated 4.2 million premature deaths in 2016 alone. There is no end to these kinds of statistics.

Sadly, our economic and political systems aren't designed to encourage sensible discussion about population growth. Put simply; countries need more humans to grow GDP, pay tax, and importantly, fund programmes to look after older people who are now living longer than ever.

Yes, population growth rates are projected to decline - but the world is still expected to reach 11 billion people by 2100.

As Sir David Attenborough points out, " it is very alarming at the rate we're going, and although people will say, 'In the long run, we are going to stabilize', they're going to stabilize - as far as I can see - at a rather higher level than the Earth can really accommodate."

Yes, we all need to make incremental changes in our lives. I've just started using toothpaste tablets, instead of tubes. It's estimated that about 1.5 billion tubes of toothpaste are thrown away each year. I don't go around toothpaste shaming the vast majority of people that still use tubes. Nor do I think child shaming should become a thing. Because, we're never going to make progress if we blame, and shame each other. Tell me a conflict in the world that has been solved by that.

The simple truth is, we can try and reduce our personal carbon footprint all we want, but we're never going to truly address the issue unless population growth is part of the discussion.

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