Fred Pearce is an environmentalist. It’s not just the ruffled hair, greying beard and checked shirt – he is a passionate campaigner on behalf of our planet.

Pearce was UK environment journalist of the year in 2001 and has been described as "one of Britain’s finest science writers". As well as his job at The Guardian, he is environment consultant for New Scientist and contributes regularly to the Daily Telegraph, the Independent and Times Higher Education.

I ask him how he first became interested in journalism. "I began in student journalism. In Cambridge, as it happens," he says. Initially he worked as a photographer for Stop Press (a rival publication to Varsity in the early 1970s before they merged) but he soon began writing. He explains why journalism suits him: "I am inquisitive, like questioning everything and hate hierarchies. A born outsider. Journalism allows me to be the perpetual outsider," he says.

Pearce specialises in reporting on global environmental issues, including water supply, climate change and population.

He recalls how the issue of overpopulation first gripped him: "Population was a big issue when I was at school in the 1960s. A biologist called Paul Ehrlich wrote a book called The Population Bomb, saying we had lost the battle to feed the world. And with population set to double in a generation it did seem impossible to double food production. I remember that vividly."

In February 2010 he released his own book on population under the title Peoplequake. However, in the United States, the book is called The Coming Population Crash.

"My American publishers decided Peoplequake did not convey enough information. Right now I see Amazon says that people who buy Peoplequake also buy The Coming Population Crash. If so, they are in for a disappointment!" he chuckles.

The book dives straight in at the deep end: "It’s Armageddon. We fear an overpopulated world teeming with the dispossessed and the alienated, the fanatical and the fascist, the wetbacks and the snakeheads, the Humvee-driving super-polluters and the dirt-poor deforesters. Surely, we are racing to demographic disaster."

Pearce doesn’t mince his words, but he doesn’t actually believe these ones either. "If I lived in sub-Saharan Africa or parts of the Middle East I would still be very worried by rising numbers of people. But globally, environmental damage is mostly the result of rising consumption, not numbers of people" he tells me. As he says later in the book, "we can expect peak population by mid-century and a decline after that."

In his opinion, we’ve done as much as we need to do to address overpopulation and now the emphasis must shift. "Addressing environmental problems purely through population policies is wrong," he argues.

So what should we be doing to tackle our environmental problems? I ask him if he thinks that scientific innovation offers a way out. He replies, "I’m a technological optimist. But we need dramatic changes, orders of magnitude in the way we consume. We need to run the economy without carbon, we need to produce food in a much more efficient way and we need to use energy much more efficiently."

I press him on the specifics: how should we be producing our energy? "Nuclear power," he responds hesitantly, "but ultimately solar power". It is refreshing to hear him say this. He’s a realist as well as an optimist.

The trouble is the problem is only going to get bigger: as the less developed world catches up, our global carbon footprint will rocket. Pearce thinks that the onus is still very much on the West.

"It is ethically unsound to deny them development. We are the big consumers now. The trouble is that developing countries are following the Western development model. We need to change the model," he says.

I turn to the sticky question of climate change. Pearce is an expert on matters climate-related. Another of his recent books, The Climate Files, investigates the ‘Climategate’ scandal, which involved leaked emails suggesting that climate scientists had been manipulating and hiding data to prevent climate sceptics from getting hold of it.

He writes: "None of the 1,073 emails… upsets the 200-year-old science behind the ‘greenhouse effect’ We might wish it weren’t so, but the world still has a problem. A big problem."

I ask him what he sees as the biggest barrier to action on climate change. "Politics," he says. "We know how to curb CO2 emissions dramatically. The technology is basically there. We know it is not cripplingly expensive. What we lack is the ability to organise ourselves to do what most see as necessary."

Climate change is no longer in the science, but in the communication of science. We can be thankful that we have people as intelligent and sensitive as Pearce doing just that.