Statement from Professor Phil Jones, Head of the Climatic Research Unit, University of East Anglia.
In the frenzy of the past few days, the most vital issue is being overshadowed: we face enormous challenges ahead if we are to continue to live on this planet.
One has to wonder if it is a coincidence that this email correspondence has been stolen and published at this time. This may be a concerted attempt to put a question mark over the science of climate change in the run-up to the Copenhagen talks.
That the world is warming is based on a range of sources: not only temperature records but other indicators such as sea level rise, glacier retreat and less Arctic sea ice.
Our global temperature series tallies with those of other, completely independent, groups of scientists working for NASA and the National Climate Data Center in the United States, among others. Even if you were to ignore our findings, theirs show the same results. The facts speak for themselves; there is no need for anyone to manipulate them.
We have been bombarded by Freedom of Information requests to release the temperature data that are provided to us by meteorological services around the world via a large network of weather stations. This information is not ours to give without the permission of the meteorological services involved.
We have responded to these Freedom of Information requests appropriately and with the knowledge and guidance of the Information Commissioner.We have stated that we hope to gain permission from each of these services to publish their data in the future and we are in the process of doing so.
My colleagues and I accept that some of the published emails do not read well. I regret any upset or confusion caused as a result. Some were clearly written in the heat of the moment, others use colloquialisms frequently used between close colleagues.
We are, and have always been, scrupulous in ensuring that our science publications are robust and honest.
Recently thousands of files and emails illegally obtained from a research server at the University of East Anglia (UEA) have been posted on various sites on the web. The emails relate to messages received or sent by the Climatic Research Unit (CRU) over the period 1996-2009.
A selection of these emails have been taken out of context and misinterpreted as evidence that CRU has manipulated climate data to present an unrealistic picture of global warming.
This conclusion is entirely unfounded and the evidence from CRU research is entirely consistent with independent evidence assembled by various research groups around the world.
There is excellent agreement on the course of temperature change since 1881 between the data set that we contribute to (HadCRUT3) and two other, independent analyses of worldwide temperature measurements. There are no statistically significant differences between the warming trends in the three series since the start of the 20th century. The three independent global temperature data series have been assembled by:
• CRU and the Met Office Hadley Centre (HadCRUT3) in the UK.
• The National Climatic Data Center (NCDC) of the National Oceanographic and Atmospheric Administration (NOAA) in Asheville, NC, USA.
• The Goddard Institute of Space Studies (GISS), part of the National Aeronautic and Space Administration (NASA) in New York.
The warming shown by the HadCRUT3 series between the averages of the two periods (1850-99 and 2001-2005) was 0.76±0.19°C, and this is corroborated by the other two data sets.
The Intergovernmental Panel on Climate Change (IPCC) in its 4th Assessment Report (AR4) published in 2007 concluded that the warming of the climate system was unequivocal. This conclusion was based not only on the observational temperature record, although this is the key piece of evidence, but on multiple strands of evidence. These factors include: long-term retreat of glaciers in most alpine regions of the world; reductions in the area of the Northern Hemisphere (NH) snow cover during the spring season; reductions in the length of the freeze season in many NH rivers and lakes; reduction in Arctic sea-ice extent in all seasons, but especially in the summer; increases in global average sea level since the 19th century; increases in the heat content of the ocean and warming of temperatures in the lower part of the atmosphere since the late 1950s.
CRU has also been involved in reconstructions of temperature (primarily for the Northern Hemisphere) from proxy data (non-instrumental sources such as tree rings, ice cores, corals and documentary records). Similar temperature reconstructions have been developed by numerous other groups around the world. The level of uncertainty in this indirect evidence for temperature change is much greater than for the picture of temperature change shown by the instrumental data. But different reconstructions of temperature change over a longer period, produced by different researchers using different methods, show essentially the same picture of highly unusual warmth across the NH during the 20th century. The principal conclusion from these studies (summarized in IPCC AR4) is that the second half of the 20th century was very likely (90% probable) warmer than any other 50-year period in the last 500 years and likely (66% probable) the warmest in the past 1300 years.
One particular, illegally obtained, email relates to the preparation of a figure for the WMO Statement on the Status of the Global Climate in 1999. This email referred to a “trick” of adding recent instrumental data to the end of temperature reconstructions that were based on proxy data. The requirement for the WMO Statement was for up-to-date evidence showing how temperatures may have changed over the last 1000 years. To produce temperature series that were completely up-to-date (i.e. through to 1999) it was necessary to combine the temperature reconstructions with the instrumental record, because the temperature reconstructions from proxy data ended many years earlier whereas the instrumental record is updated every month. The use of the word “trick” was not intended to imply any deception.
Phil Jones comments further: “One of the three temperature reconstructions was based entirely on a particular set of tree-ring data that shows a strong correlation with temperature from the 19th century through to the mid-20th century, but does not show a realistic trend of temperature after 1960. This is well known and is called the ‘decline’ or ‘divergence’. The use of the term ‘hiding the decline’ was in an email written in haste. CRU has not sought to hide the decline. Indeed, CRU has published a number of articles that both illustrate, and discuss the implications of, this recent tree-ring decline, including the article that is listed in the legend of the WMO Statement figure. It is because of this trend in these tree-ring data that we know does not represent temperature change that I only show this series up to 1960 in the WMO Statement.”
The ‘decline’ in this set of tree-ring data should not be taken to mean that there is any problem with the instrumental temperature data. As for the tree-ring decline, various manifestations of this phenomenon have been discussed by numerous authors, and its implications are clearly signposted in Chapter 6 of the IPCC AR4 report.
Included here is a copy of the figure used in the WMO statement, together with an alternative version where the climate reconstructions and the instrumental temperatures are shown separately.
The WMO1999 figure (top) with climate reconstructions and instrumental temperatures merged, and a version (bottom) with the climate reconstructions (coloured) and instrumental temperatures (annual & summer in black) shown separately.