There are plenty of baby carriages on the streets of London, but Britain's birth-rate is low - just 1.8 children for every woman of child-bearing age.
The world's population, however, is soaring. It is currently 6.8 billion, according to the U.S Census Bureau, and the U.N. estimates it will reach 9 billion by 2050.
And that growth rate, according to Simon Ross of Britain's Optimum Population Trust, is unsustainable.
"If we have one or two children, then we're really just replacing ourselves," he said. "Two parents and two children - of course some people don't have children at all. So if most people said, 'Yes, I'll have one or two children and that's enough, that's me with my family,' then the population will gradually decline and we'll get back to a number that's sustainable."
The Optimum Population Trust wants the world to prioritize family planning. It estimates that 200 million women - mainly in sub-Saharan Africa and parts of Asia - don't have access to birth control. Given the opportunity, the Trust believes many people would choose to have fewer children.
"We are talking about voluntary methods here," he added. "There's no implication from us that this is something that people will be made to do. It's something that people actually do want to do. If they have access to those methods they tend to have one or two children, that's our experience worldwide."
Mainstream climate experts continue to see renewable energies like solar power as the solution. Derry Newman, the CEO of Solar Century, Britain's largest solar energy company, doesn't believe population control is the answer.
"Who are we to dictate whether you should or should not have the next generation? And there are many, many more things to do before we consider such draconian objectives," he said.
The world's population can be supported, he says, but developed countries with large carbon footprints need to change the way they generate and use energy.
"Most people want to do the right thing," he added. "Very few people want to be wasteful. Very few people want to spend more on energy than they really need to. So if you can give people options which are cost-effective, long term value-adding to their property or business, and help them do what they believe to be the right thing, then it is win-win all around."
How to cut energy consumption, switch to cleaner technologies and find funding for it all - these are issues that delegates, government ministers and world leaders are discussing in Copenhagen this week. And they are being reminded that what they do will determine the lives of the world's future generations.