It has a profound impact on all life on Earth, yet for decades it has been conspicuously absent from public debate.

Most natural scientists agree our growing numbers and our unchecked impact on the natural environment move us inexorably toward global calamities of unthinkable severity.

They agree the need to address population has become desperate.

Yet many environmentalists avoid the subject, a few objecting strongly to any focus on our numbers.

Some activists insist acting to influence population growth infringes on human rights; they maintain that it is best to leave the problem alone.

Let's dispense with this confused notion right now.

Yes, there have been past abuses in the name of "population control".

There have been abuses of health care and education too, but the idea of reacting by abandoning any of these causes is absurd.

We can learn from past abuses, reducing the likelihood of fresh problems arising in the future.

In fact, those working on population issues have done so. Today, they recognise that the methods with the best track records of reducing population growth are, by their nature, respectful and promoting of human rights.

They include educating girls and women in developing countries to help empower them.

This is achieved by providing more options, using media strategies to make them aware of alternatives regarding family sizes and family planning.

Those who oppose talking about the world's population are obstructing the further provision of such services and resources.

Last chance saloon

Fundamentally, we need to ask what is the greater threat to human welfare: the possibility that humane efforts to address population growth might be abused, or our ongoing failure to act to prevent hundreds of millions, even billions, dying as a result of global ecological collapse?

Many now recognise the urgency with which we need to halt the human-caused degradation of Earth's natural environment

It's no far fetched possibility. Increasingly, environmental scientists insist we have overshot the Earth's carrying capacity.

I believe they are right; the proof is everywhere. Our inability to live as we do, at our current numbers, without causing pervasive environmental degradation is the very definition of carrying capacity overshoot.

Overshoot, we know, is followed by population decline. As we have learned form other species, this manifests itself initially with a crash.

For humanity, this portends a potential cataclysm exceeding anything in our history.

Our chance to avert such an outcome depends on our ability to address our numbers before nature reduces them for us.

There's no other way out. Merely reducing per capita consumption, for instance, won't do it.

After all, per capita consumption levels multiply with population size to determine our total resource consumption.

Just look at the data from the Global Footprint Network group. They estimate that we'll remain in overshoot unless we also address population.

Solutions do not spring from silence. We must bring population back to the centre of public discussion.

We need to break through the taboo to encourage not just a few voices but all those with relevant expertise to speak out on the subject loudly and often.

Recently I wondered what would happen if all the scientists - and everyone else considered a scholar of the population issue - spoke out all at once.

Would it help to weaken the taboo now shackling the subject, pushing it closer to centre stage?

Would it bring the matter enough attention to begin generating new or more widespread solutions?

Might it prompt a deeper examination of our ecological plight?

The Global Population Speak Out campaign has brought together over 100 voices from 19 countries, all pledging to speak out publicly on the population issue throughout the month of February, 2009.

Many now recognise the urgency with which we need to halt the human-caused degradation of Earth's natural environment.