A double dose of climate science from the BBC's Today Programme
- 17 May 2013, 14:30
- Roz Pidcock
The BBC's Today programme has seven million listeners, so how it
covers climate science is quite important. This morning's programme
saw a report on climate change and recent temperature rise,
followed by an interview with the well-known climate scientist Dr
Broadly speaking, the programme did a good job of navigating
what has become an entangled web of scientific issues, although it
perhaps inevitably lacked clarity on a few points.
BBC environment correspondent Roger Harrabin posed the question
"what kind of risk are we taking with the climate?" With greenhouse
gases in the atmosphere rising, earth's surface temperature -
that's the air over the land and ocean - has risen more slowly over
the past decade and a half than in previous decades.
The Today programme report explored why this might be, while Dr
Hansen was on hand to explain why despite the recent slow pace of
surface warming, the science of climate change isn't really in
Warming still happening
Harrabin suggested that after being "largely ignored by
mainstream science for a while" climate skeptic voices questioning
the pace of global warming are now being heard. He suggested that
"the scientific establishment agrees that global warming appears to
have stalled", and that while "scientists thought temperatures
would be driven steadily upward", surface temperature hasn't risen
appreciably since 1998.
But this is a simplification, as Harrabin unpacked throughout
his report. The word "stalled" suggests surface temperature rise
has stopped - and might also imply it's expected to remain static.
In the second segment, Dr James Hansen took this point head on,
telling the programme that's not what scientists think at all. In
response to Sarah Montague's opening statement that "global average
will have been roughly the same for two decades", Hansen said:
"Well, I should correct what you just
said. It's not true that temperature has not changed in the last
two decades. In the last decade, it's warmed only by a tenth of a
degree as opposed to two tenths of a degree in the preceding
decade. But that's just natural variability - there's no reason to
be surprised by that at all."
Scientists have told us they don't expect a steady year-on-year
or decade-on-decade increase in warming. Natural climate cycles,
like the El Nino that
caused 1998 to be exceptionally warm, causes global temperatures to
jump around from year to year. The long term trend is
still one of warming.
Incidentally, Hansen's tenth of a degree figure refers to the five-year
running average surface temperature over the decade 2000 to
2010. Some reaction to his interview online has suggested a
different figure - of 0.01 degrees. That's the trend in monthly
temperature between 2003 to 2013, and
this really just illustrates the difficulties of measuring
temperature over such short timescales. As scientists have
repeatedly stressed, these are effectively temperature
snapshots that need to be looked at in the context of previous
On the Today programme Sir John Houghton, former chief scientist
of the Intergovernmental Panel on Climate Change (IPCC), explained
"If you look at the average, [the
temperature] is still going up. You see a bump at 1998 and beyond,
but the steady rise of about 0.1 degree per 10 years is still
The Today report explained that rising greenhouse gas emissions
must result in more warming - "That carbon dioxide warms the
climate is not in doubt."
So if there's more carbon dioxide, and the warming isn't staying
in the atmosphere,
where is it going?
Surface temperature is only a small (but important) part of the
climate system. In fact,
most of the extra heat the planet absorbs goes into the oceans,
climate scientist at the University of Reading Dr Richard Allan
"The vast ocean has a huge capacity to
store heat … To balance the books you need to be measuring the
energy coming in at the top of the atmosphere and all the places
where it's going to really understand how the climate is
Over the last decade or so when surface warming has slowed,
evidence that the amount of heat going into the deep ocean has
Sir Brian Hoskins, head of the Grantham Institute for Climate
Change at Imperial College, explained to Roger Harrabin:
"You can have a decade or so where the
ocean is storing up heat, but the atmosphere is not warming up
Scientists think the most likely reason for more heat entering
the oceans rather than staying in the atmosphere is due to
natural climate cycles that fluctuate slowly over timescales of
a few decades.
Allan explains to us why this makes looking at temperature
changes over short timescales a bad idea:
"[I]f you're measuring for a period of
ten, 20 or even 30 years, you might just be measuring part of that
natural cycle. You need to have a longer term perspective so you
can put these bumps and troughs in context of longer timescale
Importantly, the oceans absorbing more heat doesn't mean that
the planet is "adapting" to extra warming, as Hansen's interviewer
Sarah Montague seemed to imply at one point.
Decades in which atmospheric temperature rise slows down only to
speed up again afterwards have occurred throughout the temperature
record. With plenty of carbon dioxide in the atmosphere trapping
heat, what we're seeing now is a temporary situation - atmospheric
temperature will continue to rise when natural variability cycles
turn in the other direction.
The scientists in Harrabin's piece discuss natural variability
as the most likely driver of the surface warming slowdown.
Nevertheless, he examined an alternative idea - is the surface
warming slowdown happening because the earth is less sensitive to
greenhouse gases than previously thought?
The quick answer is no. We've written
more about this - but here's a brief summary.
Scientists define climate sensitivity as how much the planet
will warm with a doubling of carbon dioxide. The IPCC suggest that
climate sensitivity is most likely between
two and 4.5 degrees Celsius.
Harrabin referred to
some recent research based on observational estimates of
climate sensitivity that support of lower values. But as we've
highlighted before, other estimates of climate sensitivity using
climate models still support the higher end of the IPCC's likely
The Today programme actually did a pretty good job of unpacking
this complicated area:
"[Mainstream scientists] have concluded
that the top extreme [above 4.5 degrees Celsius] of the temperature
range forecast for a doubling of carbon dioxide is less likely than
ever. But the main projection remains about the same - something
between two and 4.5 degrees Celsius."
Allan tells us the surface warming slowdown "doesn't add much
physical insight" into scientists' estimates of climate
sensitivity, adding that it tells us more about variability than
long term warming. Hansen echoed this view extremely strongly on
the Today programme, saying that a decade of surface warming
slowdown provides "no change at all in our understanding of climate
sensitivity and where the climate is headed."
Other scientists have told us basically the same thing.
Professor Reto Knutti from the Institute for Atmospheric and
Climate Science in Zurich
told us recently:
"My personal view is that our overall
assessment [of the value of climate sensitivity] hasn't changed
While the recent surface warming slowdown doesn't challenge the
fundamentals of climate science, there are some interesting
questions about what's driving it. And the Today Programme gave a
pretty good rundown of what is a complicated area.
It's also good that Hansen did a particularly good job of
explaining why - although these are interesting questions - they
are "details" that "shouldn't distract from the main message."
Hansen ended his interview with a strongly worded statement on
those who use this period of slower surface temperature rise to
cast doubt on climate science:
"Deniers want the public to be confused,
they raise these minor issues which are something between experts
and then we forget about what is the main story: The main story is
carbon dioxide is going up, it's going to produce a climate which
is going to have dramatic changes if we don't begin to reduce our