The 2013 global mean temperature

29 01 2014

In December 2013 we published an estimate of the global mean temperature up to the end of October 2013, based on an average of the three main global temperature datasets – Met Office and University of East Anglia (HadCRUT4), NOAA National Climatic Data Center (NOAA NCDC) and NASA Goddard Institute of Space Studies (NASA GISS).

The United Nations’ World Meteorological Organisation (WMO) and the IPCC’s provisional estimate global mean temperature for 2013 is 0.5 °C ± 0.1 °C above the long-term (1961-1990) average.

For HadCRUT4, the provisional estimate for the whole of 2013 is between 0.39 °C and 0.59 °C above the long-term (1961-1990) average of 14.0 °C, with a central estimate of 0.49 °C.

This means 2013 is in the top ten warmest years on record and we continue to see near record global temperatures like those which resulted in 2000-2009 being the warmest decade in the instrumental record.

As always the latest figure has generated interest in the media, which focuses on how it relates to previous forecasts from the Met Office.

The global mean temperature is just one of many indicators – including sea level rise, shrinking glaciers and reducing Arctic sea ice – that give even more confidence that the world is warming. Climate models are an invaluable tool in helping us to understand past changes and predict how temperatures may change in the future; they have provided overall good advice capturing and representing the warmer world we now live in.

We can see from the IPCC AR5 report figure below how global temperatures have risen since 1860 and how the latest provisional observational estimates still lie within the range of the forecast models. This figure also shows that, looking back over the entire observational record there are a number of occasions where the observations lie close to both the upper and lower bounds of the model simulations, so what we are seeing at the moment is nothing new.

Time series of global and annual-averaged surface temperature change from 1860 to 2012 showing results from two ensemble of climate models driven with natural forcings and human-induced changes in greenhouse gases and aerosols compared to observations of global mean temperature from three different datasets relative to 1880-1919. CMIP3 relates to the suite of climate models used in IPCC AR4 and CMIP5 those models used in IPCC AR5.*

Time series of global and annual-averaged surface temperature change from 1860 to 2012 showing results from two ensemble of climate models driven with natural forcings and human-induced changes in greenhouse gases and aerosols compared to observations of global mean temperature from three different datasets relative to 1880-1919. CMIP3 relates to the suite of climate models used in IPCC AR4 and CMIP5 those models used in IPCC AR5.*

So, why might the global mean temperature be different from forecasts? Well, we know that, due to the lack of long-term observing sites in polar latitudes, HadCRUT4 underestimates the contribution from Arctic warming which has accelerated in recent years.

There is also increasing scientific evidence that the current pause in surface warming is associated with natural variability in the global oceans, as they absorb heat from the atmosphere. Changes in the exchange of heat between the upper and deep ocean appear to have caused at least part of the pause in surface warming, and observations suggest that the Pacific Ocean may play a key role. You can find out more about the recent pause in warming here.

*Figure modified from Bindoff, N. L., P. A. Stott, K. M. AchutaRao, M. R. Allen, N. Gillett, D. Gutzler, K. Hansingo, G. Hegerl, Y. Hu, S. Jain, I. I. Mokhov, J. Overland, J. Perlwitz, R. Sebbari and X. Zhang, 2013: Detection and Attribution of Climate Change: from Global to Regional. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T. F., D. Qin, G.-K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, in press.





Should climate models have predicted the pause?

27 09 2013

Media coverage today of the launch of the 5th Assessment Report of the IPCC has again said that global warming is “unequivocal” and that the pause in warming over the past 15 years is too short to reflect long-term trends.

Over recent days some commentators have criticised climate models for not predicting the pause. It’s good to see this being addressed, and so begin to clarify the difference between climate model projections and predictions.

We should not confuse climate prediction with climate change projection. Climate prediction is about saying what the state of the climate will be in the next few years, and it depends absolutely on knowing what the state of the climate is today. And that requires a vast number of high quality observations, of the atmosphere and especially of the ocean.

Whilst the last decade has seen a rapid increase in good observations of the surface and upper ocean, thanks to Argo floats, we have very few for the deep ocean. Without these requisite observations to initialise, i.e. set running, a climate prediction, it is impossible to have predicted the current pause, however good the climate models.

On the other hand, climate change projections are concerned with the long view; the impact of the large and powerful influences on our climate, such as greenhouse gases. Projections capture the role of these overwhelming influences on climate and its variability, rather than predict the current state of the variability itself.

The IPCC model simulations are projections and not predictions; in other words the models do not start from the state of the climate system today or even 10 years ago. There is no mileage in a story about models being ‘flawed’ because they did not predict the pause; it’s merely a misunderstanding of the science and the difference between a prediction and a projection.

As the IPCC states in line with our three papers on the pause, the deep ocean is likely a key player in the current pause, effectively ‘hiding’ heat from the surface. Climate model projections simulate such pauses, a few every hundred years lasting a decade or more; and they replicate the influence of the modes of natural climate variability, like the Pacific Decadal Oscillation (PDO) that we think is at the centre of the current pause.

The Daily Telegraph today also covers the science of the pause.

Critically there is ever more confidence that the world is warming as a result of human actions, and limiting climate change would require substantial and sustained reductions in emissions of carbon dioxide (CO2) and other greenhouse gases.





Arctic sea ice reaches minimum extent for 2013

24 09 2013

Arctic sea ice has been in the media quite a bit this month and we looked at the issue in a blog a couple of weeks ago.

Late last week there was an update to the continuing story, as the National Snow and Ice Data Center (NSIDC) in the US announced that Arctic sea ice extent had reached its summer minimum.

Figures from the NSIDC show this year extent fell to 5.10 million square kilometres on 13 September, and the ice cover  is now increasing as we head into the northern hemisphere winter.

It’s possible that a shift in wind patterns or a late season melt could push ice extent lower, but – assuming the current figure remains – this year’s minimum extent is the sixth smallest since satellite records began in late 1970s.

The five lower seasonal minimum ice extents all happened from 2007 onwards, with the record set last year. That record low was just 3.41 million square kilometres, a notably low figure that was likely to have been influenced by weather conditions over the region which accelerated ice loss.

While a detailed analysis is required to understand the exact causes of the seasonal minimum this year, the weather conditions during the summer have been less conducive to ice loss than those experienced last year.

From late May to late June a stream of storms entered the Arctic Ocean, creating cloudy conditions at the time when the sun was at its strongest.

Relatively high ice cover during June and July (compared to recent years) was likely to have delayed the warming of the upper ocean and reduced melting at the base of the ice towards the end of the melt season.

We do expect a year to year variability in sea ice extent precisely because it can be so heavily influenced by weather patterns, but there is a long-term picture of decline – as you can see in the graph of August ice extents below.

August Arctic sea ice extent

August Arctic sea ice extent

New ice thickness data from the Cryosat satellite has also been released recently, and this shows a continuing shrinkage of winter ice volume.  This provides a timely reminder that despite the modest recovery in seasonal minimum ice extent this year, the ice continues to thin and the volume of sea ice continues to shrink.





A response on statistical models and global temperature

31 05 2013

Over a period of several months the Met Office has been involved in dialogue and answered a series of questions on the subject of the use of statistical models in relation to the global temperature record.

The Met Office’s Chief Scientist, Julia Slingo, has written a discussion paper on the subject – you can now view the Executive Summary and a link to the full paper in an article on our Research News pages.

Publication of this paper follows a guest article recently published on the Bishop Hill blog site, where one of the people with which the Met Office has been speaking with – Doug Keenan – makes a series of accusations about the Met Office and its science.

Professor Slingo’s paper answers many of the points Mr Keenan makes, and the Met Office has already directly addressed many of the points Mr Keenan raises through considerable previous correspondence we have had with him on this issue. However, here we directly address a few of the key points in Mr Keenan’s article:

1)       Mr Keenan says that there is “no basis” for the claim that the increase in global temperatures since the late 1800s is too large to be reasonably attributed to natural random variation. He goes on to argue that this is because we haven’t used the right statistical model.

However, the claim that the increase in global warming is larger than could be explained by natural variability has a clear and well understood grounding in fundamental physics and chemistry. There is very high confidence (using the IPCC’s definition) that the global average net effect of human activities since 1850 has been one of warming. The basis for this claim is not, and never has been, the sole use of statistical models to emulate a global temperature trend. Instead it is based on hundreds of years of scientific advancement, supported by the development of high-quality observations and computational modeling.

2)       Mr Keenan suggests that Met Office scientists have been ‘trying to cover it [point 1, above] up’.

The Met Office has entered into email discussion at the working scientific level and responded promptly and transparently on all parliamentary matters and questions. We have also responded to numerous emails from Mr Keenan and invited him to come to the Met Office to discuss statistical modeling in climate science. As he points out in his article, so far those invitations have been declined or unanswered. The invitation still stands.

3)       Mr Keenan then goes on to argue that you can only use a statistical model to determine whether the warming we have seen is statistically significant. He argues that the Met Office has used the wrong statistical model and, therefore, our science is flawed.

The study of climate variability and change is broader than the domain of statistics, most notably due to the importance of the underpinning science of the climate system. Our judgment that changes in temperature since 1850 are driven by human activity is based on information not just from the global temperature trend, or statistics, but also our knowledge of the way that the climate system works, how it responds to global fossil fuel emissions and observations of a wide range of other indicators, such as sea ice, glacier mass, sea level rise, etc.

Using statistical tests in the absence of this other information is inappropriate, particularly when it is not possible to know, definitively, which is the most appropriate statistical model to use. In particular, a key test of an appropriate statistical model is that it agrees with everything we know about the system. Neither of the models discussed by Mr Keenan is adequate in this regard. On that basis, this conversation on statistical modelling is of little scientific merit.

4)       Mr Keenan details his argument to say that various different statistical models can emulate the global temperature record better and worse than others.

This is something the Met Office has already spoken about and shown analysis on (such as in an answer to a parliamentary question (PQHL62)). However, this assessment of relative likelihood does not ensure that any of the statistical models are scientifically valid. Because the Met Office does not make an assessment of global warming solely on statistics – let alone the statistical models referred to in Mr Keenan’s article, this exercise is of very little, if any, scientific use.

5)       Mr Keenan also makes repeated accusations that the Met Office did not, or was not willing to respond to Parliamentary Questions.

This is not the case. The Met Office answered every request for input to Parliamentary Questions and answered them in the most scientifically appropriate way to the best of its knowledge. There has never been a refusal to provide information to answer a Parliamentary Question.





Addressing the Daily Mail and James Delingpole’s ‘crazy climate change obsession’ article

10 01 2013

An article by James Delingpole appears in the Daily Mail today under the headline The crazy climate change obsession that’s made the Met Office a menace’.

This article contains a series of factual inaccuracies about the Met Office and its science, as outlined below.

Firstly, he claims the Met Office failed to predict snow in 2010, but our 5-day forecasts accurately forecast 12 out of 13 snowfall events – as you can see in this article. In addition the Press Complaints Commission has also already addressed this fallacy with the Daily Telegraph in February of last year. As a result the newspaper published a clarification that highlighted that “the Met Office did warn the public of last winter’s [2010/11] cold weather from early November 2010.” 

Mr Delingpole also says we failed to predict flooding in November last year. Once again, our 5-day forecasts gave accurate guidance and warnings throughout the period. In just one example of feedback the Met Office has received for highly accurate forecasting and guidance throughout 2012, Assistant Chief Constable Paul Netherton, Chair for the Local Resilience Forum for Devon, Cornwall and the Isles of Scilly (which was one of the areas most affected by flooding in November), said: “[I] would like to formally thank and recognise the hard work of the Met Office over the past week. The information you provided was invaluable and enabled the responders in Devon, Cornwall and the Isles of Scilly to prepare and respond effectively to assist our communities.”

Mr Delingpole then inaccurately states that the Met Office has conceded ‘there is no evidence that ‘global warming’ is happening’. We have not said this at any point.

In fact, we explicitly say this was not the case in an article, posted on the home page of our website and widely circulated, which was written in response to articles about updates to our decadal forecast. Professor Julia Slingo, Met Office Chief Scientist, has also provided a more in depth feature on ‘Decadal Forecasting – What is it and what does it tell us?’.

Further on in the print version of the article (although amended online), Mr Delingpole says “According to the Met, Britain is apparently experiencing more rain by volume and intensity than at any time since records began.” Although he is right in saying the Met Office has published preliminary observations which show an increase in the intensity and volume of rain, we are clear that this relates to a period from 1960 onwards – not ‘since records began’ as he claims.

He also states that the Met Office was trying to defend a narrative that the “the past ten years have been the ‘wettest decade ever’”. Again, this is not something the Met Office has ever said.

Also he quotes David Whitehouse of the Global Warming Policy Foundation saying that the Met Office ‘thinks weather forecasting is beneath it’ and that ‘climate change… brings in more money’.

A cursory glance at our annual report and accounts (pdf) would reveal weather forecasting represents the vast majority of the Met Office’s contractual work on behalf of the public.

There are also a number of other accusations which cannot be substantiated.

Mr Delingpole does quote Dr Whitehouse saying “when it comes to four or five day weather forecasting, the Met Office is the best in the world.”

This supports the view of the World Meterological Organization (WMO) which consistently ranks the Met Office in the top two operational forecasters in the world.

Our reputation for forecasting accuracy is based on our commitment to provide the world’s best weather and climate service which helps protect lives and property here in the UK and around the world.





Met Office in the Media: 14 October 2012

14 10 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.

———–

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.





Citizen science looks at future warming uncertainty

26 03 2012

A project running almost 10,000 climate simulations on volunteers’ home computers has found that a global warming of 3 degrees Celsius by 2050 is ‘equally plausible’ as a rise of 1.4 degrees.

The study addresses some of the uncertainties that previous forecasts, using simpler models or only a few dozen simulations, may have over-looked.

Importantly, the forecast range is derived from using a complex Met Office model that accurately reproduces observed temperature changes over the last 50 years.

The results suggest that the world is very likely to cross the ‘2 degrees barrier’ at some point this century if emissions continue unabated.

It also suggests that those planning for the impacts of climate change need to consider the possibility of warming of up to 3 degrees (above the 1961-1990 average) by 2050, even on a mid-range emission scenario. This is a faster rate of warming than most other models predict.

The research was made possible because volunteers donated time to run the simulations on their home computers through climateprediction.net as part of the BBC Climate Change Experiment. A report of the research is published in Nature Geoscience.

“It’s only by running such a large number of simulations – with model versions deliberately chosen to display a range of behaviour – that you can get a handle on the uncertainty present in a complex system such as our climate,” said Dr Dan Rowlands of Oxford University’s Department of Physics, lead author of the paper. “Our work was only possible because thousands of people donated their home computer time to run these simulations.”

Dr Ben Booth, Senior Climate Scientist at the Met Office Hadley Centre, an author of the paper, said: “There have been substantial efforts within the international community to quantify and understand the consequence of climate uncertainties for future projections. Perhaps the most ambitious effort to date, this work illustrates how the citizen science movement is making an important contribution to this field.”

The model used in the project was supplied by the Met Office and the work was supported by the Natural Environment Research Council (NERC), the European Union FP6 WATCH and ENSEMBLES projects, the Oxford Martin School, the Smith School of Enterprise and the Environment, and Microsoft Research.

You can see this research covered here:

ABC Australia

USA Today

BBC





Climate Week gets underway with Met Office as science advisor

14 03 2012

Tyrone Dunbar, is a Met Office scientist currently seconded to Defra and DECC in support of our role in providing policy relevant science to Government. In this guest blog he talks about Climate Week.

This week is Climate Week, and there are thousands of climate week related events happening all over the UK. I’ve just had a quick look at the website and there are 2802 registered events shown on their interactive map, so there’s absolutely loads of stuff going on (I’ll be honest, I was surprised how many events have been organised!).

The week officially kicked off on Sunday with a launch event at Lancaster House in London. There was a wide range of inspiring projects on display, from innovative projects such as drought-resistant maize which helps farmers in Africa adapt to climate change, to campaigns such as the Sustainable Restaurant Association’s Too Good to Waste “doggy box” promotion. There was also the fantastic news that Defra and HR Wallingford won the award for Best Initiative by a Government or Statutory Body for their work on the Climate Change Risk Assessment (CCRA). The Met Office were also involved in the CCRA, providing scientific guidance on the latest climate projections (UKCP09) that underpin the study, leading on the risk assessment for the Energy Sector and provided further research on urban heat islands and rainfall runoff.

The Met Office is the official science advisor for Climate Week and we have a number of things going on as well. There was a Met Office stand at the launch event, and we have a poster display in the atrium at the Department for International Development (DfID) running throughout the week highlighting various climate change issues as well as Met Office research, such as forecasting of the onset of the rainy season in East Africa. This has been really well received and DfID will be sending this exhibition to posts around the world. We are also running a Climate Challenge competition in some local Tesco stores in Devon (Tesco are the main Climate Week sponsors), as you can see in the picture below.

You can find out more about the role of the Met Office as one of the worlds leading centres for climate science research in the climate change section of our website.

 





Met Office in the Media: 29 January 2012

29 01 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.





Met Office in the Media: 11 October 2011

11 10 2011

There has been continued interest in the research from the Met Office with  Imperial College London and the University of Oxford, that shows that low UV output from the sun can contribute to an increased risk of  cold winters over parts of the northern hemisphere, such as recently seen in the UK. Michael Hanlon of the Daily Mail posted an fascinating blog article on Mini ice-age or global warming: why can’t they make their minds up?. Elsewhere Jonathan Leake from the Sunday Times has clarified his article on this science in which he said:

Thanks to those who have commented on this article. However, there appears to be a common misunderstanding. This article is not about anthropogenic climate change. The phenomena mentioned in this article are natural and separate from climate change. They operate in parallel to climate change, in parallel to each other but, of course, each on very different time scales.
La Nina, for example, is really about weather. It’s part of a relatively short term natural cycle operating over periods of a few years. 
It’s just one of many factors which together mean that weather is constantly showing a high level of variability. In other words, getting a cold winter or two does not tell us anything about climate change. It just tells us that weather changes a lot – which we already know.
Similarly, the research in Nature Geoscience about the changes in solar radiation, is also nothing to do with climate change. It’s an entirely separate effect happening in parallel. Scientists think its part of a 3-400 year cycle of changes in UV radiation. There’s a good article here
and the original is here.
It’s interesting to wonder if it will mitigate or amplify the effects of greenhouse gas emissions but I suspect no-one really knows yet.
The key point is that short term changes in the weather and long term changes in the climate are both driven by a complex mix of variables. Working out the most likely future trends is hard and takes long-term dedicated science. Reducing it all to an argument to undermine climate change misses the real point which is that we should be trying to use the best science to assess just how much of a problem all these effects really present to an increasingly crowded and interconnected world.
The science suggesting that the Earth faces significant warming remains very strong. If you disagree then you need good science to back your case. These other phenomena (La Nina, UV radiation etc) are simply not relevant.
Jonathan Leake

 








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