Met Office in the Media: 14 October 2012

An article by David Rose appears today in the Mail on Sunday under the title: ‘Global warming stopped 16 years ago, reveals Met Office report quietly released… and here is the chart to prove it’

It is the second article Mr Rose has written which contains some misleading information, after he wrote an article earlier this year on the same theme – you see our response to that one here.

To address some of the points in the article published today:

Firstly, the Met Office has not issued a report on this issue. We can only assume the article is referring to the completion of work to update the HadCRUT4 global temperature dataset compiled by ourselves and the University of East Anglia’s Climate Research Unit.

We announced that this work was going on in March and it was finished this week. You can see the HadCRUT4 website here.

Secondly, Mr Rose says the Met Office made no comment about its decadal climate predictions. This is because he did not ask us to make a comment about them.

You can see our full response to all of the questions Mr Rose did ask us below:

Hi David,

Here’s a response to your questions. I’ve kept them as concise as possible but the issues you raise require considerable explanation.

Q.1 “First, please confirm that they do indeed reveal no warming trend since 1997.”

The linear trend from August 1997 (in the middle of an exceptionally strong El Nino) to August 2012 (coming at the tail end of a double-dip La Nina) is about 0.03°C/decade, amounting to a temperature increase of 0.05°C over that period, but equally we could calculate the linear trend from 1999, during the subsequent La Nina, and show a more substantial warming.

As we’ve stressed before, choosing a starting or end point on short-term scales can be very misleading. Climate change can only be detected from multi-decadal timescales due to the inherent variability in the climate system. If you use a longer period from HadCRUT4 the trend looks very different. For example, 1979 to 2011 shows 0.16°C/decade (or 0.15°C/decade in the NCDC dataset, 0.16°C/decade in GISS). Looking at successive decades over this period, each decade was warmer than the previous – so the 1990s were warmer than the 1980s, and the 2000s were warmer than both. Eight of the top ten warmest years have occurred in the last decade.

Over the last 140 years global surface temperatures have risen by about 0.8ºC. However, within this record there have been several periods lasting a decade or more during which temperatures have risen very slowly or cooled. The current period of reduced warming is not unprecedented and 15 year long periods are not unusual.

Q.2 “Second, tell me what this says about the models used by the IPCC and others which have predicted a rise of 0.2 degrees celsius per decade for the 21st century. I accept that there will always be periods when a rising gradient may be interrupted. But this flat period has now gone on for about the same time as the 1980 – 1996 warming.”

The models exhibit large variations in the rate of warming from year to year and over a decade, owing to climate variations such as ENSO, the Atlantic Multi-Decadal Oscillation and Pacific Decadal Oscillation. So in that sense, such a period is not unexpected. It is not uncommon in the simulations for these periods to last up to 15 years, but longer periods are unlikely.

Q.3 “Finally, do these data suggest that factors other than CO2 – such as multi-decadal oceanic cycles – may exert a greater influence on climate than previously realised?”

We have limited observations on multi-decadal oceanic cycles but we have known for some time that they may act to slow down or accelerate the observed warming trend. In addition, we also know that changes in the surface temperature occur not just due to internal variability, but are also influenced by “external forcings”, such as changes in solar activity, volcanic eruptions or aerosol emissions. Combined, several of these factors could account for some or all of the reduced warming trend seen over the last decade – but this is an area of ongoing research.

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The below graph which shows years ranked in order of global temperature was not included in the response to Mr Rose, but is useful in this context as it illustrates the point made above that eight of the warmest years on record have occurred in the past decade.

Graph showing years ranked in order of global temperature.

Met Office in the Media: The Sunday Times – ‘So, do we freeze or fry’

Figures showing temperatures flatlining have given the climate debate fresh ferocity. Jonathan Leake, Science Editor of The Sunday Times, unpicks the row in ‘So, do we freeze or fry‘

John Prescott was apocalyptic. “Our polar ice caps are melting,” the then deputy prime minister thundered. “Only this weekend Mexico was hit by freak snowstorms . . . a world of drought and crop failures, rising seas, mass migration and disease . . . rising greenhouse grasses [sic] . . .”

The year was 1997 and Prescott had just come back from Kyoto in Japan to give the House of Commons his account of the latest climate talks.

Prescott’s terrifying warnings were backed by Britain’s leading climate scientists. Just before Kyoto a Met Office report warned that climate-related floods would put 50m people at risk of death from starvation in the coming decades. Whole island nations would disappear, it added, while the American Midwest, which helps to feed 100 nations, was likely to face drought and the North Pole might melt.

That was 15 years ago — what has happened to world temperatures since then? Last month came the suggestion that the answer was, embarrassingly, nothing. Research based on Met Office figures pointed to temperatures having been flat since 1997.

It was the kind of admission that those who doubt climate science pounce on. “Forget global warming,” trumpeted The Mail on Sunday, because “the planet has not warmed in 15 years”. It then cited other research, into the declining energy output of the sun, to suggest the real danger was from a big freeze, raising the prospect of a reprise of the frost fairs held on the frozen Thames in the 17th century.

Two days earlier The Wall Street Journal had published a letter from 16 scientists advancing similar arguments. It said: “The lack of warming for more than a decade . . . suggests that computer models have greatly exaggerated how much warming additional CO2 can cause.”

Since then the same cry has been taken up by innumerable bloggers, exemplified by David Whitehouse, formerly the BBC’s science editor, now an adviser to the Global Warming Policy Foundation, which frequently challenges the views of climate-change scientists. He, it turns out, was a source of the research that sparked the whole row.

“We set out to see how long it had been since the temperature had risen, and 15 years was what emerged from the data set,” he said. “It raises serious questions about how the Met Office models future climate.”
It seemed a strong argument but the climate scientists came out fighting, starting with a furious blog posted by the Met Office itself, which attacked the Mail on Sunday article as “entirely misleading”.

That was followed by another letter in The Wall Street Journal, this time signed by 35 leading climate scientists, who pointed out that few of the signatories to its sceptical predecessor were actually involved in climate research.

“Do you consult your dentist about your heart condition?” it asked, adding: “Climate experts know that the long-term warming trend has not abated in the past decade. In fact, it was the warmest on record.”

What were the rest of us meant to make of this? Some scientists appear to be warning we will fry, while other sources fear we will freeze. For the public the outcome is, increasingly, confusion. Where might the truth lie?

Perhaps the simplest first step is to put aside the arguments and get back to the data. Is it really true that global temperatures have not risen since 1997?

The simple answer is: they have risen, but not by very much. “Our records for the past 15 years suggest the world has warmed by about 0.051C over that period,” said the Met Office. In layman’s terms that is 51 thousandths of a degree.

These figures come from the Met Office HadCruT3 database, which takes readings from 3,000 land stations around the world, along with oceanic readings from a similar number of ships and buoys.

However, HadCruT3 is just one of several global temperature databases, each overseen by different scientists and calculated in slightly different ways. This allows each group to cross-check results, confirming findings or spotting errors.

One, held at the National Climate Data Centre (NCDC), run by America’s National Oceanic and Atmospheric Administration, suggests that global temperatures rose by an average of 0.074C since 1997. That’s small, too — but it is another rise.

A third and very different data set is overseen by John Christy, professor of atmospheric science at the University of Alabama in Huntsville. He gathers figures from three satellites that orbit the Earth 14 times a day. They measure the average temperature of the air from ground level to a height of 35,000ft, a method completely different from those of the Met Office and NCDC. Oddly, given his reputation as a climate sceptic, he found the biggest rise of all.

“From 1997-2011 our data show a global temperature rise of 0.15C,” he said. “What’s more, our satellites have been taking this data since 1979, and over that period [the] global temperature has risen 0.46C, so the world has been getting warmer.”

Overall, then, the world has got slightly warmer since 1997. Perhaps the real question is: why has it warmed so much less than was predicted by the climate models?

For most climate scientists the answer is simple. “Fifteen years is just too short a period over which to measure climate change,” said Peter Stott, head of climate monitoring at the Met Office. “The world undergoes natural temperature changes on all kinds of time scales from daily variations to seasonal ones. It also varies naturally from year to year and decade to decade.”

Whitehouse accepts this point. “The records do show that global temperatures have risen by about 0.4C over the past three decades, most of it in the 1990s,” he said.

“I accept that CO2 is a greenhouse gas that might warm the world but the key issue is how strong the effect is and how the data compare with the models used to predict the future.”

This is an interesting admission, turning what had appeared to be an attack on the keystones of climate science — that greenhouse gases cause global warming — into a “shades of grey” debate over whether global warming will happen slowly and steadily or in jerks, accelerating in some decades but then slowing or even reversing a little in others.

For the critics of climate science this is a crucial point — but why? The answer goes back to the 2001 and 2007 science reports from the Intergovernmental Panel on Climate Change that had predicted the world was likely to warm by an average of about 0.2C a decade. The implication was that temperatures would rise steadily, not with 15-year gaps. The existence of such gaps, the critics argue, implies the climate models themselves are too flawed to be relied on.

Other leading climate scientists have raised similar issues. One is Judith Curry, professor of atmospheric sciences at the Georgia Institute of Technology. She argues that global climate is affected by so many factors, ranging from solar output to volcanic eruptions, that predicting how the world will warm is impossible.

Crucially, however, Curry accepts that greenhouse gas emissions are likely to lead to long-term warming. She wrote on her blog: “We don’t know what the climate will be for the next several decades. In terms of when global warming will come ‘roaring back’, it is possible this may not happen for the first half of the 21st century.”

For Curry and many others one of the key unresolved issues lies in the behaviour of the sun, whose output appears to be undergoing a steady but small decline. Most scientists accept that this will reduce global warming. The debate is over just how strong this effect will be, with people such as Curry suggesting it could be powerful while others see it as small.

Among the latter is Mike Lockwood, professor of space physics at Reading University’s meteorology department, who believes the sun has been in a “grand solar maximum” since the 1960s, thought to be the longest-lived peak in its output for more than 9,000 years.

“A decline in activity is long overdue,” he said. “How deep will it go? We think there is about an 8% chance that it will drop below the famous Maunder minimum.”

This was a 60-year period, starting in about 1645, when the sun had very few sunspots; it was marked by an unusually high proportion of cold winters in Europe.

That sounds ominous but Lockwood calculates that even a decline in activity on that scale would now have little effect because the impact would be far smaller than the opposing effects of surging greenhouse gas emissions.

What about the most evocative image of all — the prediction that the Thames might freeze over? This did happen in 1963, but far upstream in the stretches around Windsor. The idea that the lower tidal reaches might be in similar danger generates little but scorn from all sides.

Lockwood said: “The disappearance of frost fairs is nothing to do with climate. It is because the old London Bridge — really more of a weir — was pulled down and the embankments were put in. So the river now flows much too fast to freeze and is also a lot saltier. Even a return to Maunder minimum solar conditions would not cause the Thames to freeze again so far downstream.”

This article first appeared in The Sunday Times on Sunday 5 February 2012.

Met Office in the Media: 29 January 2012

Today the Mail on Sunday published a story written by David Rose entitled “Forget global warming – it’s Cycle 25 we need to worry about”.

This article includes numerous errors in the reporting of published peer reviewed science undertaken by the Met Office Hadley Centre and for Mr. Rose to suggest that the latest global temperatures available show no warming in the last 15 years is entirely misleading.

Despite the Met Office having spoken to David Rose ahead of the publication of the story, he has chosen to not fully include the answers we gave him to questions around decadal projections produced by the Met Office or his belief that we have seen no warming since 1997.

For clarity I have included our full response to David Rose below:A spokesman for the Met Office said: “The ten year projection remains groundbreaking science. The complete period for the original projection is not over yet and these projections are regularly updated to take account of the most recent data.

“The projections are probabilistic in nature, and no individual forecast should be taken in isolation. Instead, several decades of data will be needed to assess the robustness of the projections.

“However, what is absolutely clear is that we have continued to see a trend of warming, with the decade of 2000-2009 being clearly the warmest in the instrumental record going back to 1850. Depending on which temperature records you use, 2010 was the warmest year on record  for NOAA NCDC and NASA GISS, and the second warmest on record in HadCRUT3.”

Global average temperatures from 1850 to 2011 from the three individual global temperature datasets (Met Office/UEA HadCRUT3, NASA GISS and NOAA NCDC

Furthermore despite criticism of a paper published by the Met Office he chose not to ask us to respond to his misconceptions. The study in question, supported by many others, provides an insight into the sensitivity of our climate to changes in the output of the sun.

It confirmed that although solar output is likely to reduce over the next 90 years this will not substantially delay expected increases in global temperatures caused by greenhouse gases. The study found that the expected decrease in solar activity would only most likely cause a reduction in global temperatures of 0.08 °C. This compares to an expected warming of about 2.5 °C over the same period due to greenhouse gases (according to the IPCC’s B2 scenario for greenhouse gas emissions that does not involve efforts to mitigate emissions).  In addition the study also showed that if solar output reduced below that seen in the Maunder Minimum – a period between 1645 and 1715 when solar activity was at its lowest observed level – the global temperature reduction would be 0.13C.