This is the inquiry on the BBC World Service with me Ruth Alexander each week one question

four expert witnesses and an answer. It was a blisteringly hot June day in 1988 in Washington, D.C.

In fact, much of the United States had been suffering from abnormally high temperatures,

drought and forest fires.

On Capitol Hill, Dr James E. Hansen leaned forward to the microphone and began to address the

Senate Committee, whose members were about to witness history being made. The greenhouse effect has been detected and is changing our

climate now, he said.

This was the speech that introduced the world to climate change. A few months later, the Intergovernmental Panel on Climate Change was set up.

The world was waking up to the huge new challenge of man-made global warming.

In the years since, climate models have been a key tool to project what could happen in the future.

But some scientists are saying, too much emphasis has been put on the worst case scenarios

and it's harming our efforts to fix the planet.

So this week we're asking, have our climate models been wrong? Part 1. Business as usual.

Business as usual. Testing, testing. My name is Chelsea Harvey. I'm a reporter with E&E News. Does that help you?

It does.

Chelsea, whose US publication focuses on energy and environmental news, is going to tell us the story

of how one climate scenario became chief among all others.

It's one of a series of visions of our climate future,

which have been given the acronym RCP.

Right, so RCP stands for representative concentration pathways.

You can think of them as like hypothetical climate scenarios.

So what would the world look like if carbon dioxide concentrations in the

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