Seven billion is a big number. It doesn't seem quite so big, however, if you think that 7 billion of us could fit into the state of Texas and live there with a population density enjoyed by the residents of New York City.

But a major concern is the impact yet more humans will have on the health of the planet – and it's for this reason that population anxiety has become a concern for people already worried about climate change and resource scarcity.

The United Nations, in its latest revision is projecting 9 billion by 2050 – and even 10 billion by 2100 – before world population stabilises and starts to decline. That's the "medium fertility variant" projection – it would be 8 billion by 2050 declining to 6 billion by 2100 if you used the low fertility variant, and up to 16 billion if you used a high one. Which should serve as a bit of a warning about the nature of projections.

Much hangs on the question of the "total fertility rate" – or the number of children a woman has on average during her lifetime.

What the more alarmist news reports often fail to mention is that since the 1970s fertility has been declining in almost all nations and that once the trend to smaller family size begins it is hard to reverse – as policy makers in Japan, Korea and Italy have found.

Today, according to the UN's population division, 42% of the world's population lives in countries with fertility at below replacement level. Another 40% are in intermediate fertility countries, where people are replacing themselves. And the remaining 18% are living in countries with high fertility, mostly in sub-Saharan Africa, where women may be having five or more children on average.

The places with largest family size are the poorest, where per capita consumption and energy use is low. The places where families are smallest are some of the richest, with high consumption and energy use, such as Japan and much of Europe.

And this is where an almighty hole appears in the argument of those who suggest that if we care about climate change we should worry about women having lots of children in the countries with high fertility rates.

Although low-income countries were responsible for more than 52% of population growth between 1980 and 2005, they were responsible for only 12.8% of the growth in global carbon emissions, according to David Satterthwaite, director of London's International Institute of Environment and Development. High-income nations, meanwhile, provided only 7% of population growth but 29% of growth in emissions.

The reason is simple: so unequal are global consumption levels that one European or North American may be responsible for more emissions than an entire village of Africans.

So how about people in rich countries with high consumption, high pollution, habits doing the decent thing and abstaining from having children? That's what some, including the radical US-based Voluntary Human Extinction Movement, are advocating. But even that would not be enough to get us out of trouble.

Researchers at the National Centre for Atmospheric Research at Boulder, Colorado have found that if population were to reach, say, 7.4 billion in 2050 instead of 9 billion, it would reduce emissions by 15% – not nearly enough to meet the most modest current targets advocated by the G8 of between 50 and 80% reductions by 2050.

But surely, any reduction in population growth is better for the environment than none?

Population is certainly a multiplier, but that does not make it the cause of the problem. As the Australian writer Simon Butler puts it: "People are not pollution. Blaming too many people for driving climate change is like blaming too many trees for causing bushfires."

The real cause of climate change is an economy locked into burning fossil fuels for energy. Massive fossil fuel use in industrialised countries cannot be countered by handing out condoms.

The excessive focus on population is a dangerous distraction from the core problem, which is not how many of us there are but how we use the planet and share its resources.

There's no dodging it. We need an energy revolution – away from fossil fuels and towards renewables and energy conservation – which is as radical and more rapid than the industrial revolution that laid the basis for our carbon economies. And we need it regardless of how big the population gets.

So, instead of a fanfare of orchestrated fear and panic, let us welcome baby 7 billion with a resolution to tackle the real issues facing humanity – climate change, inequality and poverty – and stop obsessing about human numbers.

• Vanessa Baird is the author of The No-Nonsense Guide to World Population, recently published by New Internationalist

Facts and figures

• Fertility is declining. The global average is now 2.5 children per woman. In the developing world the rate fell from six children to about three between 1950 and 2000. (Source: UN population division)

• Between 2010 and 2050, 45 countries are expected to decrease in population size. China's population should start shrinking in 2023. (Source: UN population division)

• The CO2 emissions of the average US citizen are 19.9 tonnes per year, and of the average African citizen 1.2 tonnes per year. (Source: IEA, 2009)

• Industrialized countries with 20% of the world's population are responsible for 80% of the accumulated carbon dioxide in the atmosphere.

• The world is already growing enough grain to feed a population of 10 billion on a vegetarian diet. (Source: Fred Pearce, Peoplequake, 2010)

• Of the 2bn tonnes of grain grown in the world in 2008, under half was eaten directly by people. (Source: Fred Pearce, Peoplequake, 2010)

• Americans throw away 50% of the food they buy, and Britons 30%. Farmers grow 25% more than needed to meet the aesthetic standards of supermarkets. In economically booming India, large amounts of food rots in warehouses and gets thrown away while the poor go hungry because they cannot afford to buy it. (Source: Tristram Stuart, Waste, 2009.)

• Land sold to speculators increased from 4 million hectares in 2006 to 60 million (the size of France) in 2009.