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.





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.





Met Office in the Media: 20 March 2012

20 03 2012

There has been widespread coverage of a scientific paper detailing an update to the joint Met Office Hadley Centre and University of East Anglia, HadCRUT global temperature dataset. The paper is published in the Journal of Geophysical Research.

Compiled from temperature observations obtained over land and sea, HadCRUT is used as a basis for a global temperature record going back to 1850. The latest version of the dataset, called HadCRUT4, includes newly available data – notably adding much more information from the sparsely observed northern higher latitude region. Differences in the way sea surface temperature observations have been collected have been taken account of and the new version also provides much more detail on uncertainty.

The amendments do not change the long-term trend. Annual global mean temperature record under HadCRUT3 and HadCRUT4 can be found on the Met Office website.

The BBC reported on the ‘Update for world temperature data‘, while the Telegraph reported ‘World warmed even more in last ten years than previously thought when Arctic data added’. Elsewhere the Mail Online reported that ‘New temperature record confirms world HAS warmed 0.75C since 1900‘. Other reports included the Herald, Scotsman, ClickGreen and the New York Times.

The Telegraph and CCRMagazine.com have written about the Government publication of the Terms of Reference for the Data Strategy Board & the Public Data Group. The Met Office, as part of the Public Data Group, with Ordnance Survey, Land Registry and Companies House is already making data available allowing the public and businesses access to our data that will allow it to be re-used and repackaged.

Real-time weather observation and forecast datasets made available for the first time by the Met Office in November are an example of the kind of data that will promote the creation of high-value businesses, while widening the marketplace and empowering the individual citizen. Following this Golfmagic.com reports on how Marriot Golf has launched a new app which has Met Office weather forecasts embedded into the App.

In other news the BBC reports on the British team that is developing a car that will capable of reaching 1,000mph. The Met Office is supporting Bloodhound SSC (SuperSonic Car), by providing scientific monitoring of the weather ahead of any record attempt. The Mail Online and the Observer both report on the inclusion of Space Weather in the National Risk Register. The Met Office is working with partners in the UK and the US on developing an operational space weather service.








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