Good news! Global temperatures have stabilized, at least for now.

Summary:  This is the second in a series of posts examining what we know about global temperature trends.  The first discussed the strong consensus about the warming of the past two centuries.  This post shows that global temperatures have leveled off during the past decade.  Both sides of the public debate (among laymen) try to obscure these simple facts in order to advance their own interests.

Contents

This post shows the statements about recent global temperature trends by a few of the many experts working on climate science issues.  They represent a broad range of perspectives in the climate science field.  Jones and Hanson are mainstream figures; Whitehouse is a skeptic; the Berkeley project is a new attempt to resolves some of these issues.  Also shown is the satellite record, left to speak for itself.

1. Phil Jones, director of UEA’s Climate Research Unit
2. James Hanson, NASA
3. David Whitehouse, Global Warming Policy Foundation
4. The Berkeley Earth Surface Temperature project
5. Global Sea Surface temperatures
6. The satellite temperature record
7. Early articles noting the “pause”
8. Update:  Is this cherry-picking the historical data?
9. When will this “pause” become significant?
10. Chapters in this series
11. Other posts about climate science

These references will be updated as more are found.  See the follow-ups Still good news: global temperatures remain stable, at least for now and The IPCC sees the pause in global warming!

(1)   Richard Lindzen (Prof Meteorology, MIT)

“There has been no warming since 1997 and no statistically significant warming since 1995. Why bother with the arguments about an El Nino anomaly in 1998?”
— Email to Anthony Watts, 11 March 2008 (source)

(1)  Phil Jones, UK’s Climatic Research Unit

“Q&A: Professor Phil Jones“, BBC, 13 February 2010 –BBC’s environment analyst Roger Harrabin interviews Phil Jones, then director of the Climatic Research Unit (CRU) at the University of East Anglia (UEA).

Question: Do you agree that from 1995 to the present there has been no statistically-significant global warming

Dr. Jones:  Yes, but only just. I also calculated the trend for the period 1995 to 2009.  This trend (0.12C per decade) is positive, but not significant at the 95% significance level.  The positive trend is quite close to the significance level.  Achieving statistical significance in scientific terms is much more likely for longer periods, and much less likely for shorter periods.

Question:  Do you agree that from January 2002 to the present there has been statistically significant global cooling?

Dr. Jones:  No. This period is even shorter than 1995-2009.  The trend this time is negative (-0.12C per decade), but this trend is not statistically significant.

Update:  based on 2010 data, Jones has revised is evaluation of the trend since 1995:  “Global warming since 1995 ‘now significant’“, BBC, 10 June 2011.  Jones evaluation of the leveling was among the most aggressive among mainstream climate scientists, going back to 1995 rather than since 2000.  That was significant since most scientists consider climate trends significant only over periods of 15+ years.  One major study says that 17+ years are necessary:  “Separating signal and noise in atmospheric temperature changes: The importance of timescale“, Ben Santer et al, Geophysical Research Letters, 18 November 2011 — Free copy here.

(3)  Global Warming Policy Foundation

David Whitehouse (former Science correspondence of the BBC, PhD Astrophysics from U Manchester), Global Warming Policy Foundation, 31 December 2011 (red emphasis added):

It showed no increase in temperature. It has been often stated that there has been no statistically significant warming in the various temperature datasets since the start of this century, and this is now generally accepted. Pushing it back a few more years is possible. The years 1999 and 2000 were slightly cooler than the post-2001 data but since 1998, a strong El Nino year, is higher they provide compensation for each other. Thus if you look at the trend since 1997 you can easily see, and calculate, that it is negligible.

It is also possible to push it back a few more years still, according to the brief calculations made by Prof Phil Jones. It seems that 1995 – 2009 is flat, but 1995 – 2010 has a slight positive trend, though not at any impressive significance. It should be noted that 1995 – 2011 is back to no significant increase.

Statistically speaking it is accurate to say that according to HadCrut3 the world’s temperature has not increased for the 16 years between 1995 and 2011, though many prefer the more conservative ten years post-2001. This is not a ‘sceptical’ claim just a straightforward description of the data.

… The world has warmed since the start of the current warming spell that started around 1980 and each decade has been warmer than the previous one. … It is curious that the small data set of the recent warming spell (only thirty numbers or so if annual data is used) has been argued about, analysed and misrepresented for so long by climatologists and activists.

(2)  “Global Temperature in 2011, Trends, and Prospects“, James Hansen et al, NASA’s Goddard Institute for Space Sciences, 18 January 2012

Thus, although the current global warming graphs (Figs. 2, 3 and the upper part of Fig. 7) are suggestive of a slowdown in global warming, this apparent slowdown may largely disappear as a few more years of data are added.  In particular we need to see how high global temperature rises in response to the next El Niño, and we also need to consider the effect of the 10-12 year cycle of solar irradiance.  This raises the question of when the next El Niño will occur and the status of the solar cycle.

(4)  The Berkeley Earth Surface Temperature project, from the Frequently Asked Questions page of their website.  (red emphasis added).

Has Global Warming Stopped?

Some people have suggested that there has been no global warming over the past 13 years, and they ask whether our land-only analysis verifies that. The graph shows the results of our analysis with 1-year averaging (to smooth it) for the last 6 decades so you can better see the period in question. The blue curve is the result of our analysis, and the grey lines represent our 95% confidence limit.

The large fluctuations up and down that take place every few years correlate very strongly with the North Atlantic temperatures (the AMO index) and with El Nino (ENSO index 3.4). See our paper on “Decadal Variations in the Global Atmospheric Land Temperatures” for analysis of that. The presence of these fluctuations makes any strong extrapolations from short-term behavior uncertain.

Some people draw a line segment covering the period 1998 to 2010 and argue that we confirm no temperature change in that period. However, if you did that same exercise back in 1995, and drew a horizontal line through the data for 1980 to 1995, you might have falsely concluded that global warming had stopped back then. This exercise simply shows that the decadal fluctuations are too large to allow us to make decisive conclusions about long term trends based on close examination of periods as short as 13 to 15 years.

Do Judith Curry and Richard Muller disagree?

Below is a joint statement by Judith Curry (Professor and Chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology ) and Richard Muller (Prof of Physics at Berkeley, Scientific Director of the project):

In recent days, statements we’ve made to the media and on blogs have been characterized as contradictory. They are not.

We have both said that the global temperature record of the last 13 years shows evidence suggesting that the warming has slowed. Our new analysis of the land-based data neither confirms nor denies this contention. If you look at our new land temperature estimates, you can see a flattening of the rise, or a continuation of the rise, depending on the statistical approach you take.

Continued global warming “skepticism” is a proper and a necessary part of the scientific process. The Wall St. Journal Op-Ed by one of us (Muller) seemed to take the opposite view with its title and subtitle: “The Case Against Global-Warming Skepticism — There were good reasons for doubt, until now.” But those words were not written by Muller. The title and the subtitle of the submitted Op-Ed were “Cooling the Warming Debate – Are you a global warming skeptic? If not, perhaps you should be. Let me explain why.” The title and subtitle were changed by the editors without consulting or seeking permission from the author. Readers are encouraged to ignore the title and read the content of the Op-Ed.

We do not agree with each other on every feature of climate change. We have had vigorous discussions, for example, on the proper way to analyze hurricane records. Such disagreements are an essential part of the scientific process.

Update:  Judith Curry has more about this here.

(5)  Global Sea Surface temperatures (SST)

The temperature datasets that get the most attention measure land surface temperatures. Not only are the seas 70% of the Earth’s surface, but the oceans are the primary reservoir of heat for the coupled sea-air system in which we live. Unfortunately we don’t have good historical data (for this purpose) before roughly 1982.  There are several datasets of accurate global SST data after the early 1980s; for details see Bob Tisdale’s “An Overview Of Sea Surface Temperature Datasets Used In Global Temperature Products“.

Here is a graph of NOAA Sea Surface Temperature data from Bob Tisdale’s website, which combines both direct measurements (ie, ships and buoys) and satellite data)  Again, no warming this decade.  SST’s show the effect of the large decadal-scale cycles (eg, La Nina – El Nino in the tropical Pacific), which effect global temperatures.

The Argo project, a network of high-tech buoys fully deployed in 2007, now provides high quality data of global ocean temperatures at various depths.  This will answer many questions about climate dynamics, and allow development of better models.  For more information see:

• Argo.net Home page
• Argo at the Scripps Institution of Oceanography

(6)  The satellite temperature record

Satellite data is often described by non-experts as the definitive source of global temperatures.

For more about satellite climate data see this article by the National Institute of Standards and Technology (NIST), 6 February 2012

Satellites do not measure temperature directly; instead they measure the amount of radiation incident on their sensors at various key wavelengths and sometimes polarizations associated with different meteorological phenomena and different sections of the atmosphere or surface. Those data are then processed by different groups using various methods to yield temperature equivalents.

It gets even more complex.  Adjustments must be made for sensor decay, change of satellite orbits, and replacement of satellites.

There are three major datasets:  the National Oceanic and Atmospheric Administration (NOAA), Remote Sensing Systems (RSS, data from NASA satellites), and the University of Alabama at Huntsville (UAH).  This graph from the NIST article shows the recent temperature plateau.

Here is the UAH data through January 2012 (source: Roy Spencer, co-developer of the data series)

(7)  Early articles noting the stabilization of global temperatures

• “What happened to global warming?“, BBC, 9 October 2009
• “World will ‘cool for the next decade’“, New Scientist, 9 September 2009 — Summary of forecasts about decadal cooling (e.g., “Advancing decadal-scale climate prediction in the North Atlantic sector“, Mojib Latif et al, Nature, 1 May 2008
• “Climatologists Baffled by Global Warming Time-Out“, Der Spiegel, 19 November 2009
• “World may not be warming, say scientists“, The Times, 14 February 2010

(8)  Update:  Is this cherry-picking the historical data?

No, it’s not.  See “Trends, change points & hypotheses“, Judith Curry posted at Climate Etc, 7 February 2012 — Excerpt:

Back to the issue of cherry picking data, and interpreting the temperature time series for the past two decades.

Is the first decade+ of the 21st century the warmest in the past 100 years (as per Peter Gleick’s argument)? Yes, but the very small positive trend is not consistent with the expectation of 0.2C/decade provided by the IPCC AR4. In terms of anticipating temperature change in the coming decades, the AGW dominated prediction of 0.2C/decade does not seem like a good bet, particularly with the prospect of reduced solar radiation.

Has there been any warming since 1997 (Jonathan Leake’s question)? There has been slight warming during the past 15 years. Is it “cherry picking” to start a trend analysis at 1998? No, not if you are looking for a long period of time where there is little or no warming, in efforts to refute Hypothesis I.

… And none of this data analysis is very satisfying or definitive owing to deficiencies in the data sets, particularly over the ocean.

(9)   How long must the pause continue to become significant? 

(a)   Email from Phil Jones (UK’s Climatic Research Unit) to Mike Lockwood, 5 July 2009

“… The box is on page S20-21 of the bigger pdf. This is part of a much bigger article on the State of the Climate System 2008 which will appear later in the year. Bottom line – the no upward trend has to continue for a total of 15 years before we get worried.”

(b)  “Do global temperature trends over the last decade falsify climate predictions?”, J Knight et al. Part of  “State of the Climate in 2008“, Editors T C Peterson and M O Baringer, Bulletin of the American Meteorological Society, August 2009:

Observations indicate that global temperature rise has slowed in the last decade. The least squares trend for January 1999 to December 2008 calculated from the HadCRUT3 dataset is +0.07±0.07°C decade — much less than the 0.18°C decade recorded between 1979 and 2005 and the 0.2°C decade expected in the next decade. This is despite a steady increase in radiative forcing as a result of human activities and has led some to question climate predictions of substantial twenty-first century warming.

… ENSO-adjusted warming in the three surface temperature datasets over the last 2–25 yr continually lies within the 90% range of all similar-length ENSO-adjusted temperature changes in these simulations. Near-zero and even negative trends are common for intervals of a decade or less in the simulations, due to the model’s internal climate variability.

The simulations rule out (at the 95% level) zero trends for intervals of 15 yr or more, suggesting that an observed absence of warming of this duration is needed to create a discrepancy with the expected present-day warming rate.

(c)  “Does the Global Warming Pause in the Last Decade: 1999-2008?“, Shaowu Wang et al, Advances in Climate Change Research, issue #1 2010 — Abstract:

Issues related to the pause of global warming in the last decade are reviewed. It is indicated that:

1. The decade of 1999-2008 is still the warmest of the last 30 years, though the global temperature increment is near zero;
2. Natural factors such as volcanism, solar radiation, ENSO, and thermohaline circulation can have impact on the inter-annual and inter-decadal variability of global mean temperatures. However, it will not mask the global warming trend for a long time;
3. Temperatures of China continue to increase in 1999-2008 with an increment of 0.4-0.5°C per 10 years.

(d)  “Climate science: Decadal predictions in demand“, Mark A. Cane, Nature Geoscience, 21 March 2010 — Free copy here.  Red emphasis added.

Over the past decade, the mean global temperature did not rise much, if at all. This pause in global warming cannot be attributed to cutbacks in greenhouse-gas emissions by the planet’s human population, so it must be nature taking a turn towards colder temperatures. The extent to which such natural climate variability can be predicted on decadal timescales is not known.

Creating useful climate predictions is not straightforward. … The Miami workshop turned the attention of both climate scientists and stakeholders to decadal predictions of climate, a field that is still in its infancy (if not prenatal). Decadal climate predictions aim to cover the gap between seasonal to interannual prediction with lead times of two years or less and projections of climate change a century ahead.

… Therefore, the hope for useful skill in predicting natural variability is far from assured. The climate system is chaotic and it is not known how predictable decadal variations are, even if we had perfect models and sufficient observations to determine the initial state with high precision.

Perhaps there is something special about a decadal timescale that affords predictability, but perhaps not: decadal variability may just be the part of a featureless spectrum of frequencies that we happen to pick out of our instrumental records because they are only about 150 years long. Several valuable efforts to extend the record with palaeoproxy data were reported (L. Stott, Univ. Southern California, USA; B. Horton, Univ. Pennsylvania, USA; P. Swart and H. Wanless, Univ. Miami, USA), but these data are still too sparse and uncertain to allow a firm assessment.

As one example, according to the current leading idea, the Atlantic Multidecadal Oscillation is generated by atmospheric noise (E. Schneider, Center for Ocean, Land, Atmosphere/George Mason Univ., USA). If indeed random processes are at the heart of decadal variability, as strongly supported by the talk of C. Deser (National Center for Atmospheric Research, USA), this might seem to doom hopes for decadal predictability. However, the possibility remains that, once underway, the evolution of important patterns of variability could be projected forward.

… Demand for accurate decadal prediction is running ahead of supply. This imbalance challenges us to determine how much of the natural climate variability that will contribute substantially to global climate in the next few decades is predictable. Even if it turns out that climate is essentially not predictable at a decadal scale, projections of future climate will be misleading unless we gain a fuller understanding of the range of natural variability in store for us in a warmer world.

(e)  “Reconciling anthropogenic climate change with observed temperature 1998–2008“, Robert K. Kaufmann et at, Proceedings of the National Academy of Science, 19 July 2011 — Abstract:

Given the widely noted increase in the warming effects of rising greenhouse gas concentrations, it has been unclear why global surface temperatures did not rise between 1998 and 2008. We find that this hiatus in warming coincides with a period of little increase in the sum of anthropogenic and natural forcings. Declining solar insolation as part of a normal eleven-year cycle, and a cyclical change from an El Nino to a La Nina dominate our measure of anthropogenic effects because rapid growth in short-lived sulfur emissions partially offsets rising greenhouse gas concentrations.

As such, we find that recent global temperature records are consistent with the existing understanding of the relationship among global surface temperature, internal variability, and radiative forcing, which includes anthropogenic factors with well known warming and cooling effects.

(f)  “Global warming, human-induced carbon emissions, and their uncertainties“, JingYun Fang et al, Science China – Earth Science, October 2011 — Free copy here. Abstract:

In recent decades, there have been a number of debates on climate warming and its driving forces. Based on an extensive literature review, we suggest that

1. climate warming occurs with great uncertainty in the magnitude of the temperature increase;
2. both human activities and natural forces contribute to climate change, but their relative contributions are difficult to quantify; and
3. the dominant role of the increase in the atmospheric concentration of greenhouse gases (including CO₂) in the global warming claimed by the Intergovernmental Panel on Climate Change (IPCC) is questioned by the scientific communities because of large uncertainties in the mechanisms of natural factors and anthropogenic activities and in the sources of the increased atmospheric CO₂ concentration.

More efforts should be made in order to clarify these uncertainties.

(g)  Update:  “Separating signal and noise in atmospheric temperature changes: The importance of timescale“, Ben Santer et al, Journal of Geophysical Research (Atmospheres), 18 November 2011:

Because of the pronounced effect of interannual noise on decadal trends, a multi‐model ensemble of anthropogenically‐forced simulations displays many 10‐year periods with little warming. A single decade of observational TLT {temperature of the lower troposphere} data is therefore inadequate for identifying a slowly evolving anthropogenic warming signal. Our results show that temperature records of at least 17 years in length are required for identifying human effects on global‐mean tropospheric temperature.

(10)  Other chapters in this series

1. What we know about our past climate, and its causes
2. Good news!  Global temperatures have stabilized, at least for now.
3. Is it possible to debate climate change with true believers? See the replies to Thursday’s post.  Comments welcomed!
4. What can climate scientists tell about the drivers of future warming?
5. What can climate scientists tell us about the drivers of future warming?  – part two of two
6. The slow solar cycle is getting a lot of attention. What are its effect on us?
7. What we’re learning about climate, and recommendations

(11)  Other posts about climate science

(a)  For more information see the other FM Reference Pages:

• Science and Nature – my articles.
• Science & nature – studies & reports
• Science & Nature – general media articles
• Articles from the 1970′s about global cooling/warming

Posts about melting polar ice and rising sea levels:

1. An example of important climate change research hidden, lest it spoil the media’s narrative, 22 May 2009
2. About that melting arctic ice cap, 17 April 2010
3. Fear or Fail: about the melting Greenland ice sheet, 24 May 2010
4. Today’s good news, about rising sea levels, 3 June 2010 — Esp note the links to articles and studies!
5. It’s time to worry (again) about disappearing arctic ice, 8 June 2010
6. Climate Armageddon postponed (again): the melting polar ice, 9 October 2010
7. Looking into the past for guidance about warnings of future climate apocalypses, 17 October 2010

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