20130517_R4

Source: BBC Radio 4: Today Programme

URL: N/A

Date: 17/05/2013

Event: "Mainstream scientists have been puzzled by the recent standstill in warming"

Attribution: BBC Radio 4

People:

Evan Davis: Presenter, BBC Radio 4: Today Programme
Roger Harrabin: BBC's Environment Analyst
Sir Brian Hoskins: Head of the Grantham Institute for Climate Change
Sir John Houghton: Former co-chair of the IPCC's scientific assessment working group
Sarah Montague: Presenter, BBC Radio 4: Today Programme
Andrew Montford: Blogger (Bishop Hill) and author, The Hockey Stick Illusion

Evan Davis: On Thursday last week, a measurement of daily average atmospheric carbon dioxide exceeded 400 parts per million. Last time CO2 was this high was 3-5 million years ago, before humans, when it was so hot that crocodiles roamed the Arctic. So what kind of risk are we taking with the climate? There's a puzzle here. Scientists thought temperatures would be driven steadily upwards by rising CO2. But they've been at a standstill since 1998, and climate sceptics are saying they were right. So what is going on? Our Environment Analyst Roger Harrabin has this special report.

Roger Harrabin: For several years climate sceptics having been pointing out that the atmosphere hasn't warmed much since 1998, a year superheated by an exceptionally strong episode of the warming ocean current El Nino. The sceptics were largely ignored by mainstream science for a while. But now the scientific establishment agrees that global warming appears to have stalled. The admission's welcomed by sceptics like the libertarian blogger and author Andrew Montford.

Andrew Montford: It was about time that they admitted that it hasn't warmed. Sceptics have been talking about this for at least the last five or six years, and we've been told that we're talking nonsense.

Roger Harrabin: Mainstream scientists had predicted that the climate would warm in fits and starts, at an average of 0.2 Celsius a decade. This was the expectation of Professor Sir John Houghton, first Scientific Chair of the Intergovernmental Panel on Climate Change. When I visit him at home in rural Wales - a home, incidentally, heated by renewable energy - he insists that the climate is still warming. It depends on when you start to measure the change.

Sir John Houghton: If you look at the average, it is still going up. You see a bump at 1998 and beyond, but the steady rise of about 0.1 degree per ten years is still there.

Roger Harrabin: The early projections suggested that the rise would be 0.2 degrees a decade.

Sir John Houghton: We gave a range, I think in 1990, of 0.1 - 0.3. But further, if we carry on puffing carbon dioxide in at the present rate into the atmosphere, we will be heading for 0.2 degrees per decade, before very long.

[Music plays: Tom Lehrer's Periodic Table Song.]

Roger Harrabin: Some things in science are not arguable, like the periodic table, for instance. Lehrer's song greets schoolchildren visiting London's historic Royal Institution. It's here that John Tyndall first measured the heating properties of CO2, in the mid 19th century. That CO2 warms the climate is not in doubt. But Tyndall's successors are wondering why, as CO2 in the atmosphere increased, warming shot up in the 1990s, then stalled since 1998. Changes in the Sun are partly responsible, but not wholly. Clouds are a mystery - were they to blame for blocking out heat? Professor Sir Brian Hoskins, a leading climate scientist at the Royal Society, thinks the answer lies in the sea.

Sir Brian Hoskins: The top two and a half metres of the ocean can hold as much heat as the atmosphere, and so - if we're thinking about "Where does this imbalance in energy, associated with our greenhouse gases, go?", then most of it will go into the ocean. And so you can have a period of a decade or so where the ocean is storing up heat but the atmosphere is not warming up much.

[Sounds of seagulls and breaking waves on a beach.]

Roger Harrabin: So, are we heating the seas? Some recent reports say there's evidence that we are. And it's hard to see where else the projected warmth has gone. There is another possibility, though, that the Earth's sensitivity to the warming potential of CO2 is less than scientists thought. A few recent studies suggest that the likely temperature rise, for doubling CO2, lies around one and a half Celsius, which we could probably live with. The studies are very optimistic, compared with official estimates of 2 - 4.5 degrees. But sceptics like Andrew Montford see implications for policy, if they prove accurate.

Andrew Montford: What it looks as if will happen is we will get a lot less global warming, at the end of the day, than previously thought. These numbers of climate sensitivity feed straight into the economic models. If you have a lower climate sensitivity, you get a lower cost of the damage of global warming. Therefore, the more expensive policy responses are no longer cost-effective.

Roger Harrabin: Mainstream scientists have been puzzled by the recent standstill in warming. They've concluded that the top extreme of the temperature range forecast for a doubling of CO2 is less likely than ever. But the main projection remains about the same, something between two and four and a half degrees Celsius, and there is little reassuring about that. What's more, temperatures may not be rising much now, but we've just had the 27th consecutive year above the long-term average. We've seen a startling melt of sea ice in the Arctic. Increasing CO2 will continue to change the chemistry of the oceans - that's something that sceptics rarely mention. We've also had weather disrupted round the globe, including in the UK.

Man 1: We're still very, very short of water, here. It's obviously the crops and the amount the grass will grow.

Man 2: We were hoping for sunshine, yeah.

Male interviewer: And all you've got is bobbly hats.

Woman 1: Bobbly hats that I've had on most of the weekend, yes.

Roger Harrabin: The science ascribing an increase in extreme weather events to climate change is not conclusive. But what's notable about the UK's drought followed by flood followed by cold was not so much each individual extreme but the fact that all the extremes stacked up together. So it is possible that the climate may warm less than predicted, but the effects of the warming, at a low level, may be greater than predicted. That's another possibility that Professors John Houghton and Brian Hoskins didn't anticipate.

Sir John Houghton: We didn't realise, I think, the impact it was likely to have on droughts and storms and heatwaves and floods, in the way that we've now seen.

Roger Harrabin: Do you think it's a problem for people to accept scientific uncertainty but still see the need for action?

Sir John Houghton: Economists are much more uncertain about the future, and yet we have to go along with them because that's the best we've got. And this is the best we've got, for the world at large. The whole thing has got more certain and the predictions have got stronger, in terms of the damage which is likely to occur.

* * *

Sir Brian Hoskins: We've performing a very dangerous experiment, but we don't know what the details of that experiment are.

Roger Harrabin: Some people will say "Well look, it's an experiment, it's under way, it's hard to cut greenhouse gases, the scientists don't really know what the future holds. We're committed to an experiment, let's just get on with it."

Sir Brian Hoskins [laughs]: I wouldn't want to risk the future of my children and grandchildren on the results of that experiment, and just let it go ahead. I'm like: it is incredibly dangerous. We're taking the greenhouse gases to a level which is way above what it's been in the last million years. And we know those greenhouse gases have been very important in the past, in changing the temperature. Now we're taking the whole Earth system, at a time when the room is incredibly warm, we're turning up the radiator. And we don't know what's going to happen. I don't want to risk it. I hope you don't.

[Sounds of breaking waves on a beach.]

Roger Harrabin: The Intergovernmental Panel on Climate Change will give its latest verdict in the autumn. I predict that scientists will be even more careful than before, explaining what's known and what's uncertain. There is a possibility that the recent slowdown in warming may prompt them to recalibrate their temperature range projections down just a tad. But will they delight the sceptics and say we can stop worrying about our experiment with the climate? They certainly will not.

Sarah Montague: Roger Harrabin, reporting there.