Source: BBC Radio 4: More or Less
URL: http://www.bbc.co.uk/programmes/b006qshd
Date: 13/01/2012
Event: A four year-old bet between David Whitehouse and James Annan is resolved
Attribution: BBC Radio 4
People:
Tim Harford: You're listening to More or Less. And four years ago, this programme was the catalyst for a bet on climate change. The debate still rages about whether global warming is continuing or whether the last ten years show that the temperature rises seen in the 1980s and 1990s have stopped. At the time, we spoke to David Whitehouse, an astrophysicist and former BBC Science Editor, and James Annan, a climate scientist. They made this bet.
James Annan: We're not certain to see another record in the next few years, but I think it's more likely than not. Looking at the numbers, I think probably by about 2011 we should see a new record, if not before.
Tim Harford: So would you put money on that?
James Annan: Yes, certainly, yes.
Tim Harford: Excellent - I'm delighted to be furthering the BBC's duty to promote gambling. And will David Whitehouse take the bet?
We've spoken to the climate scientist James Annan. He's willing to bet that the peak of 1998 will be exceeded on or by 2011 - we'll see a hotter year for average global temperature. Are you willing to take the other side of that bet?
David Whitehouse: Certainly am. I don't think anybody really knows what's going to happen in the future.
Tim Harford: Shall we say £100?
David Whitehouse: That sounds fine to me. I look forward to it, and I can't wait to see the outcome.
Tim Harford: There's little dispute that in the last 100 years, the globe has warmed by about 3 quarters of a degree Celsius. But what provoked concern about global warming was a dramatic increase in the last few decades, especially the 1980s and the 1990s. The record for average global temperature was broken in 1983, 1988, 1990, 1995 and, most recently, in 1998. So have we seen another record year since the bet in 2008? It was agreed that the bet would be based on data from the Met Office's Hadley Centre. 2008, 2009 and 2010 didn't break the record, by this measure, and the figure for 2011 should be known next week but it's already clear, with 11 months' data available, no record will be broken for 2011,either. Well, I called David Whitehouse and James Annan.
David, congratulations, you've won the bet. What does this tell you?
David Whitehouse: Thank you very much. I think it shows that we did enter a warm spell 30 years ago and I think it shows that the rate of warming of that spell is not constant. The '80s and the '90s, it was warming, but I think that it is - structure in this data that shows in this past ten years the temperature's remained constant.
Tim Harford: And you think that goes beyond just looking at record years? Because I think we can agree that's not the only way to look at temperature data, right?
David Whitehouse: Oh yes, that's by far not the only way to look for the temperature data. We live in the warmest decade of the instrumental era. The Noughties were warmer than the '90s, which were warmer than the '80s. But that's not to say that you should only look at this just over a long time period, say 30 years, which is the standard time scale for climate change. There is structure within this 30-year period. There is no change in the global average temperature for the past ten years, and possibly longer than that.
Tim Harford: So James, you both agree that the most recent decade is the warmest decade on measure. But do you agree with David's analysis that over the last decade there's no sign of warming?
James Annan: I'd say there's absolutely no sign of any change in the warming rate, is still - the trend is still upwards. There's obviously some variability, that means if you look at a very short period of time, you can't tell very precisely what the underlying trend is, but there's no sign of any reduction in trend.
Tim Harford: So why did you lose the bet, then?
James Annan: Um, just bad luck, really.
David Whitehouse: I don't think it's bad luck at all.
James Annan: If we had chosen either of the other two datasets, then I'd have won it.
Tim Harford: But after you took the bet, James, you did write a blog post that said that, according to the models, you were pretty confident that there should be another record year. I mean - is the model wrong? Or...
James Annan: No, I'm still fairly confident that we're due another record year quite soon. There's some interannual variability, which means that you can't guarantee that any specific year is going to be warmer than the one before -
David Whitehouse: But surely, James, we're talking about global warming here, and the fundamental parameter of global warming is warming. And if you look at the past 30 years, you have two decades in which the temperature was warming, but not at a great deal in the 1980s. You have the last decade where it hasn't warmed. And I think you made the mistake of drawing a straight line between the beginning and end of that period, and projecting it forward.
Tim Harford: James? Made a simple mistake? Just drew a straight line through data, where you should have been fitting a curve?
James Annan: The trend is robustly positive. The trend is positive over the last ten years -
Tim Harford: I hesitate to leap in at this point, but there is of course an obvious way to resolve this disagreement. We could go double or quits. Will we have a record year in the next four years? James, are you tempted?
James Annan: I think there's every possibility that'll happen, yes.
Tim Harford: David, would you be tempted?
David Whitehouse: There is a possibility, but remember, if we extend the bet to nine or ten years, there is a chance - due to statistical fluctuations - that one of the years might be high, just to fluke. So I would say yes, I'm up for double or quits, but I would like to see evidence of sustained warming, which means more than one year, more than one standard deviation above the straight line of the past ten years.
Tim Harford: We'll nail you down, over email, about exactly what you are or are not going to agree to. James, if you lost this bet again, would that start to make you question what you believe about climate change?
James Annan: I think it would start - yes, if the record temperature in 1998 isn't beaten in the next four years, then it would certainly start to point towards a slightly lower warming trend. It wouldn't, however, change the fundamental fact that carbon dioxide warms the atmosphere, which I think even David Whitehouse would agree.
David Whitehouse: Yes, "even David Whitehouse" would agree, because I'm not a sceptic - it's not a question of whether carbon dioxide warms the atmosphere. It's a question of the greenhouse effect in the real world, and the only way you determine that is not by models, but by measurement, and measurement shows that the temperature of the last ten years is flat. But I'll let the data do the talking.
Tim Harford: David Whitehouse there, and James Annan. You're listening to More or Less.