Still good news: global temperatures remain stable, at least for now.

Summary:  Today we look at good news (rarely seen here), the stabilization of global temperatures. The long rise during the past two centuries, which produced many forecasts of imminent doom, has leveled off since the late 1990s — as shown by all the major temperature datasets.  It’s not something the mainstream wants us to know, as it spoils the narrative set by alarmists.  This pause might not last, but it is unexpected — and should spark some reflection on our handling of this — and other shockwave threats.

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Update: much of this post is dated. The debate has evolved since this was posted in October 2012. I suggest skipping to section 9. This gives links to research about the pause, and has been updated — showing gradual recognition of the pause by climate scientists, including the IPCC and UK Met Office. Now discussion has moved to implications of the pause:

1. One of the most important questions we face: when will the pause in global warming end?, 25 August 2013 – It’s a “pause”, not a “stop”
2. Scientists explore causes of the pause in warming, perhaps the most important research of the decade, 17 January 2014

Contents

This post will be updated as new research is published.

1. The Globe & Mail breaks the story!
2. The new UK Met Office dataset
3. A prominent climate scientists comments
4. The Met Office replies
5. Global Sea Surface temperatures
6. The satellite temperature record
7. Early articles about the warming pause
8. Is this cherry-picking the historical data?
9. For more information: other studies
10. Other chapters in this series
11. Other posts about climate science

This article has been extensively updated as new information has become available.  Changes have been marked.

(1)  The Globe & Mail breaks the story!

“Global warming stopped 16 years ago, reveals Met Office report quietly released, and here is the chart to prove it“, Globe & Mail (“Canada’s newspaper”), 13 October 2012 — Opening and closing:

The figures reveal that from the beginning of 1997 until August 2012 there was no discernible rise in aggregate global temperatures. This means that the ‘pause’ in global warming has now lasted for about the same time as the previous period when temperatures rose, 1980 to 1996.

… So let’s be clear. Yes: global warming is real, and some of it at least has been caused by the CO2 emitted by fossil fuels. But the evidence is beginning to suggest that it may be happening much slower than the catastrophists have claimed – a conclusion with enormous policy implications.

Please click to read the full story. It quotes two climate scientists.  First Professor Judith Curry, Chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology:

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{deleted; see her remarks in section #3}

And Professor Phil Jones, director of the Climate Research Unit at the University of East Anglia:

{He} would not normally be expected to agree with her. Yet on two important points, he did. The data does suggest a plateau, he admitted, and without a major El Nino event – the sudden, dramatic warming of the southern Pacific which takes place unpredictably and always has a huge effect on global weather – ‘it could go on for a while’.

Like Prof Curry, Prof Jones also admitted that the climate models were imperfect: ‘We don’t fully understand how to input things like changes in the oceans, and because we don’t fully understand it you could say that natural variability is now working to suppress the warming. We don’t know what natural variability is doing.’

He insisted that 15 or 16 years is not a significant period: pauses of such length had always been expected, he said. Yet in 2009, when the plateau was already becoming apparent and being discussed by scientists, he told a colleague in one of the Climategate emails: ‘Bottom  line: the “no upward trend” has to  continue for a total of 15 years before we get worried.’

But although that point has now been passed, he said that he hadn’t changed his mind about the  models’ gloomy predictions:  ‘I still think that the current decade which began in 2010 will be warmer by about 0.17 degrees than the previous one, which was warmer than the Nineties.’

Only if that did not happen would he seriously begin to  wonder whether something more profound might be happening. In other words, though five years ago he seemed to be saying that 15 years without warming would make him ‘worried’, that period has now become 20 years.

Jones said something similar to the BBC on 13 February 2010.

(2)  The new UK Met Office dataset

The UK Met Office released the HadCRUT.4.1.1.0 aprox 3 September 2012.  This is probably the basis for the Daily News story.

Here is a graph using this, the latest long-term data, from “Quantifying uncertainties in global and regional temperature change using an ensemble of observational estimates: the HadCRUT4 data set“.  Looking back further into history, data shows temperatures substantially rising in the 19th century, but the case for attributing that to the small anthropogenic release in CO2 is quite weak.  Most studies date substantial anthropogenic effects after WWII: 1950 for the BEST project, 1960 for the IPCC.

For more information see this page about Global-average temperature records by Dr Peter Stott at the Met Office.

Update: see the large July 2013 report by the UK Met Office about the pause — links in item k of section 9 below.

(3)  A prominent climate scientists comments on the article

A reply to the article posted at her website, Climate Etc, by Professor Judith Curry (Chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology). She didn’t agree with the aspects of the quote attributed to her in the article.

… I agree that 16 years is too short,  given the timescales of the PDO and AMO, to separate out natural versus anthropogenic variability (but this cuts both ways:  the warming period between 1980 and 1998 was arguably amped by the PDO and AMO).   … Here is the text I emailed Rose, in response to his questions:

The data confirms the existence of a ‘pause’ in the warming. The impact of this pause within the climate dynamic community has been to focus increased attention on the impact of natural variability, particularly the impact of internal multi-decadal oscillations in the ocean.  The new climate model calculations for the AR5 have focused on trying to assess what it would take to accurately simulate these multi-decadal ocean oscillations and how predictable they might be.  These new observations and climate modeling results will hopefully impact the the IPCC AR5 deliberations so that we do not see the same overly confident consensus statements that we saw in the AR4.

You might be interested in my recent blog post: RS Workshop on Handling Uncertainty in Weather & Climate Prediction. Part I.

The flawed assumption behind the orthodoxy was that natural variability is merely ‘noise’ superimposed on the long term trend.  The natural variability has been shown over the past two decades to have a magnitude that dominates the greenhouse warming signal.  It is becoming increasingly apparent that our attribution of warming since 1980 and future projections of climate change needs to consider natural internal variability as a factor of fundamental importance.  I sincerely hope that the AR5 provides an assessment of what we know and what we don’t know and areas of disagreement, rather than trying to manufacture a consensus.

Climate models are very complex, but they are imperfect and incomplete.  In that context the problem is how people interpret the simulations from climate models in view of the uncertainties and imperfections.

For context on this issue, see these other Climate Etc. posts:

• Pause(?), 4 November 2011
• Trends, change points, and hypotheses, 7 February 2012
• ‘Pause’ discussion thread, 14 October 2012 — Analysis of the Mail article
• ‘Pause’ discussion thread: Part II, 16 October 2012 — Analysis of the Guardian rebuttal of the Mail article
• ‘Pause’ : Waving the Italian Flag, 17 October 2012 — The three-valued logic approach of the “Italian flag analysis”

(4)  The Met Office replies

On October 14 the UK Met Office issued a reply on their blog to the Mail.  Here is the money paragraph:

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.

Repeat: “during the past 140 years the global surface temperatures have risen by about 0.8ºC” (1.4ºF).  Not yet the disaster commonly described in the news media; as yet not an unusual temperature variation in terms of the past few thousand years of history.  Also, it’s difficult to assess the seriousness of this without know the precision of the estimates. Measuring global temperature (especially sea surfaces) for 140 must have quite large error bars.

Also, the Met Office response is technically correct, but raises a severe operational problem: scientific theories must be falsifiable. We should know in advance what data will disprove a model’s forecast.  This pause is significant because the major models failed to predict it, and because it’s duration has reached the durations some prominent climate scientists previously said would be significant.  With no boundary conditions, or ones that are extended as they’re reached, forecasts of catastrophic anthropogenic global warming become a matter of faith — not science.

From the comments to this article on the Met Office Blog:

We agree with Mr Rose that there has been only a very small amount of warming in the 21st Century. As stated in our response, this is 0.05 degrees Celsius since 1997 equivalent to 0.03 degrees Celsius per decade.

Update: a July 2013 report by the Met Office full acknowledges the pause, and discusses possible causes. See item (k) in Section 9 below.

(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 since the late 1990s.  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. It’s not that simple, as explained in 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.

Also, 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 that the recent temperature plateau appears in all three datasets.

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

(7)  Early articles noting the stabilization of global temperatures

1. “There IS a problem with global warming… it stopped in 1998“,  Bob Carter (retired professor and head of the School of Earth Science at James Cook U), op-ed in The Telegraph, 9 Apr 2006
2. “Next decade ‘may see no warming’“, Richard Black, BBC, 1 May 2008
3. “An inconvenient truth about global warming“, Tom Feilden, BBC, 16 September 2009 — “”Far from suggesting the planet will get warmer, one of the world’s leading climate modellers says the latest data indicates we could be in for a significant period of steady temperatures and possibly even a little global cooling.” {refers to Professor Mojib Latif, from the Leibniz Institute of Marine Sciences at Kiel University}”
4. “What happened to global warming?“, BBC, 9 October 2009
5. “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
6. “Climatologists Baffled by Global Warming Time-Out“, Der Spiegel, 19 November 2009
7. “World may not be warming, say scientists“, The Times, 14 February 2010

(8)   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)  For more information: other studies (this will be updated as more appear)

Note the surge of articles about the pause starting in 2010.  They come in two kinds.  Once assesses the statistical significance of the pause.  The second attempt to explain the pause in terms of known climate models.  While significant, these are exercises in fitting — matching the models to new data — and do not validate the models as would successful predictions.

(a)  “Advancing decadal-scale climate prediction in the North Atlantic sector“, N. S. Keenlyside, M. Latif, J. Jungclaus, L. Kornblueh & E. Roeckner, Nature, 1 May 2008 — Conclusion of the abstract:

Our results suggest that global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.

Note they say “temporarily”. In the paper they show warming resuming, then continuing through the end of their forecast period in 2030.

(b) “Is the climate warming or cooling?“, Daid R. Easterling and Michael F. Wehner, Geophysical Research Letters, April 2009 — One of the earliest articles, waving the pause away as insignificant. Excerpt:

It is true that if we fit a linear trend line to the annual global land-ocean surface air temperature (Smith et al. 2005) shown in Figure 1 for the period 1998 to 2008 there is no real trend, even though global temperatures remain well above the long-term average. The unusually strong 1997-1998 El Niño contributed to unusual warmth in the global temperature for 1998 at the start of this period resulting in only a small, statistically insignificant positive trend. However, if we fit a trend line to the same annual global land-ocean temperatures for the 1977-1985 period or the 1981-1989 period we also get no trend, even though these periods are em bedded in the 1975-2008 period showing a substantial overall warming.

(c)  “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:

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.

(d)  “An imperative for climate change planning : tracking Earth’s global energy“, Kevin E. Trenberth, Current Opinion In Environmental Sustainability, October 2009 — Commendable clear statement of the question.  Opening:

The global mean temperature in 2008 was the lowest since about 2000. Given that there is continual heating of the planet, referred to as radiative forcing, by accelerating increases of carbon dioxide and other greenhouses due to human activities, why isn’t the temperature continuing to go up? The stock answer is that natural variability plays a key role and there was a major La Niña event early in 2008 that led to the month of January having the lowest anomaly in global temperature since 2000. While this is true, it is an incomplete explanation. In particular, what are the physical processes? From an energy standpoint, there should be an explanation that accounts for where the radiative forcing has gone.

• Was it compensated for temporarily by changes in clouds or aerosols, or other changes in atmospheric circulation that allowed more radiation to escape to space?
• Was it because a lot of heat went into melting Arctic sea ice or parts of Greenland and Antarctica, and other glaciers?
• Was it because the heat was buried in the ocean and sequestered, perhaps well below the surface?
• Was it because the La Niña led to a change in tropical ocean currents and rearranged the configuration of ocean heat?
• Perhaps all of these things are going on?

But surely we have an adequate system to track whether this is the case or not, don’t we? Well, it seems that the answer is no, we do not. But we should!

(e)  “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.

(f)  “Contributions of Stratospheric Water Vapor to Decadal Changes in the Rate of Global Warming“, Susan Solomon et al, Science, 5 March 2010 — Gated. Open copy here. Opening:

Over the past century, global average surface temperatures have warmed by about 0.75°C. Much of the warming occurred in the past half-century, over which the average decadal rate of change was about 0.13°C, largely due to anthropogenic increases in well-mixed greenhouse gases. However, the trend in global surface temperatures has been nearly flat since the late 1990s despite continuing increases in the forcing due to the sum of the well-mixed greenhouse gases (CO2,CH4, halocarbons, and N2O), raising questions regarding the understanding of forced climate change, its drivers, the parameters that define natural internal variability, and how fully these terms are represented in climate models. Here we use a combination of data and models to show that stratospheric water vapor very likely made substantial contributions to the flattening of the global warming trend since about 2000.

(g)  “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.

(h)  “The role of natural climatic variation in perturbing the observed global mean temperature trend“, Barrie G Hunt, Climate Dynamics, February 2011 — Gated. Abstract:

Controversy continues to prevail concerning the reality of anthropogenically-induced climatic warming. One of the principal issues is the cause of the hiatus in the current global warming trend. There appears to be a widely held view that climatic change warming should exhibit an inexorable upwards trend, a view that implies there is no longer any input by climatic variability in the existing climatic system.

The relative roles of climatic change and climatic variability are examined here using the same coupled global climatic model. For the former, the model is run using a specified CO2 growth scenario, while the latter consisted of a multi-millennial simulation where any climatic variability was attributable solely to internal processes within the climatic system. It is shown that internal climatic variability can produce global mean surface temperature anomalies of ±0.25 K and sustained positive and negative anomalies sufficient to account for the anomalous warming of the 1940s as well as the present hiatus in the observed global warming.

The characteristics of the internally-induced negative temperature anomalies are such that if this internal natural variability is the cause of the observed hiatus, then a resumption of the observed global warming trend is to be expected within the next few years.

(i)  “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.

(j) “Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods“, Gerald A. Meehl et al, Nature Climate Change, October 2011 –Examines 10-year long pauses. Abstract:

There have been decades, such as 2000–2009, when the observed globally averaged surface-temperature time series shows little positive or even slightly negative trend (a hiatus period). However, the observed energy imbalance at the top-of-atmosphere for this recent decade indicates that a net energy flux into the climate system of about 1W m-2 should be producing warming somewhere in the system.

Here we analyse 21st-century climate-model simulations that maintain a consistent radiative imbalance at the top-of-atmosphere of about 1W m-2 as observed for the past decade. Eight decades with a slightly negative global mean surface-temperature trend show that the ocean above 300m takes up significantly less heat where as the ocean below 300m takes up significantly more compared with non-hiatus decades. The model provides a plausible depiction of processes in the climate system causing the hiatus periods, and indicates that a hiatus period is a relatively common climate phenomenon and may be linked to La Niña-like conditions.

(k)  “Global warming, human-induced carbon emissions, and their uncertainties“, Jing Yun 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.

(l)  “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.

(m)  “Deducing Multi-decadal Anthropogenic Global Warming Trends Using Multiple Regression Analysis“, Jiansong Zhou and Ka-Kit Tung, Journal of the Atmospheric Sciences, January 2013 — Free abstract; article is gated.  Potentially important conclusion:

When the AMO is included, in addition to the other explanatory variables such as ENSO, volcano and solar influences commonly included in the multiple linear regression analysis, the recent 50-year and 32-year anthropogenic warming trends are reduced by a factor of at least two. There is no statistical evidence of a recent slow-down of global warming, nor is there evidence of accelerated warming since the mid-20th century.

Abstract:

In order to unmask the anthropogenic global warming trend imbedded in the climate data, multiple linear regression analysis is often employed to filter out short-term fluctuations caused by El Nino-Southern Oscillation (ENSO), volcano aerosols and solar forcing. These fluctuations are unimportant as far as their impact on the deduced multidecadal anthropogenic trends is concerned: ENSO and volcano aerosols have very little multi-decadal trend. Solar variations do have a secular trend, but it is very small and uncertain. What is important, but is left out of all multiple regression analysis of global warming so far, is a long-perioded oscillation called the Atlantic Multi-decadal Oscillation (AMO). When the AMO Index is included as a regressor (i.e. explanatory variable), the deduced multi-decadal anthropogenic global warming trend is so impacted that previously deduced anthropogenic warming rates need to be substantially revised.

The deduced net anthropogenic global warming trend has been remarkably steady and statistically significant for the past 100 years.

(n) “Global Temperature Update Through 2012“, James Hansen, M. Sato, R. Ruedy, 15 January 2013

An update through 2012 of our global analysis 1 reveals 2012 as having practically the same temperature as 2011 , significantly lower th an the maximum reached in 2010 . These short-term global fluctuations are associated principally with natural oscillations of tropical Pacific sea surface temperatures summarized in the Nino index in the lower part of the figure

(o)  “Retrospective prediction of the global warming slowdown in the past decade“. By Virginie Guemas, Francisco J. Doblas-Reyes, Isabel Andreu-Burillo, and Muhammad Asif, Nature Climate Change, 7 April 2013 — Abstract:

Despite a sustained production of anthropogenic greenhouse gases, the Earth’s mean near-surface temperature paused its rise during the 2000–2010 period.

To explain such a pause, an increase in ocean heat uptake below the superficial ocean layer has been proposed to overcompensate for the Earth’s heat storage. Contributions have also been suggested from the deep prolonged solar minimum, the stratospheric water vapour, the stratospheric and tropospheric aerosols. However, a robust attribution of this warming slowdown has not been achievable up to now.

Here we show successful retrospective predictions of this warming slowdown up to 5 years ahead, the analysis of which allows us to attribute the onset of this slowdown to an increase in ocean heat uptake. Sensitivity experiments accounting only for the external radiative forcings do not reproduce the slowdown. The top-of-atmosphere net energy input remained in the [0.5–1] W m−2 interval during the past decade, which is successfully captured by our predictions. Most of this excess energy was absorbed in the top 700 m of the ocean at the onset of the warming pause, 65% of it in the tropical Pacific and Atlantic oceans. Our results hence point at the key role of the ocean heat uptake in the recent warming slowdown.

The ability to predict retrospectively this slowdown not only strengthens our confidence in the robustness of our climate models, but also enhances the socio-economic relevance of operational decadal climate predictions.

(p)  “Strengthening of ocean heat uptake efficiency associated with the recent climate hiatus“, Masahiro Watanabe et al, Geophysical Research Letters, 28 June 2013 — Abstract:

 The rate of increase of global-mean surface air temperature (SATg) has apparently slowed during the last decade. We investigated the extent to which state-of-the-art general circulation models (GCMs) can capture this hiatus period by using multimodel ensembles of historical climate simulations. While the SATg linear trend for the last decade is not captured by their ensemble means regardless of differences in model generation and external forcing, it is barely represented by an 11-member ensemble of a GCM, suggesting an internal origin of the hiatus associated with active heat uptake by the oceans. Besides, we found opposite changes in ocean heat uptake efficiency (κ), weakening in models and strengthening in nature, which explain why the models tend to overestimate the SATg trend. The weakening of κ commonly found in GCMs seems to be an inevitable response of the climate system to global warming, suggesting the recovery from hiatus in coming decades.

(q)  “Climate change: The forecast for 2018 is cloudy with record heat“, Jeff Tollefson, Nature, 10 July 2013 — “Efforts to predict the near-term climate are taking off, but their record so far has been patchy.”  Excerpt:

Lost heat: why has the warming slowed?

It is one of the biggest mysteries in climate science: humans are pumping more greenhouse gases into the atmosphere today than ever before, yet global temperatures have not risen much in more than a decade. That trend does not undermine the idea that greenhouse gases will eventually push global temperatures into uncharted territory, but it does have scientists puzzled.

… with the stalled warming now approaching its 15th year, researchers are seeking some deeper explanation. “The heat must be going somewhere,” says Ed Hawkins, a climate scientist at the University of Reading, UK. “The question is where.” … scientists cannot yet fully explain the recent trends, and the larger question is whether the lack of warming today portends less warming in the future.

(r)  The UK Met Office discusses the pause (these are large pdf’s): July 2013

• Part One:  The recent pause in global warming: What do observations of the climate system tell us?
• Part Two: The recent pause in global warming: What are the potential causes?

Excerpt:

The recent pause in glocurrybal surface warming is shown in Figure 1 in the context of historical observations. Following a period of rapid warming since the 1970s, there has been little further warming of the surface, particularly over the ocean in the most recent 10 to 15 years. … It is clear that there have been other periods with little or no surface warming in the relatively recent past, a good example being the period between the 1940s and the 1970s. … The start of the current pause is difficult to determine precisely. Although 1998 is often quoted as the star t of the current pause, this was an exceptionally warm year because of the largest El Niño in the instrumental record. This was followed by a strong La Niña event and a fall in global surface temperature of around 0.2 o C, equivalent in magnitude to the average decadal warming trend in recent decades. It is only really since 2000 that the rise in global surface temperatures has paused.

(s)  “Recent global warming hiatus tied to equatorial Pacific surface cooling“, Yu Kosaka and Shang-Ping Xie, Nature, 29 August 2013 — Gated. See this analysis by Judith Curry (Prof climate science, GA Inst Tech). Abstract:

Despite the continued increase in atmospheric greenhouse gas concentrations, the annual-mean global temperature has not risen in the twenty-first century, challenging the prevailing view that anthropogenic forcing causes climate warming.

Various mechanisms have been proposed for this hiatus in global warming, but their relative importance has not been quantified, hampering observational estimates of climate sensitivity. Here we show that accounting for recent cooling in the eastern equatorial Pacific reconciles climate simulations and observations. We present a novel method of uncovering mechanisms for global temperature change by prescribing, in addition to radiative forcing, the observed history of sea surface temperature over the central to eastern tropical Pacific in a climate model.

Although the surface temperature prescription is limited to only 8.2% of the global surface, our model reproduces the annual-mean global temperature remarkably well with correlation coefficient r = 0.97 for 1970–2012 (which includes the current hiatus and a period of accelerated global warming). Moreover, our simulation captures major seasonal and regional characteristics of the hiatus, including the intensified Walker circulation, the winter cooling in northwestern North America and the prolonged drought in the southern USA. Our results show that the current hiatus is part of natural climate variability, tied specifically to a La-Niña-like decadal cooling. Although similar decadal hiatus events may occur in the future, the multi-decadal warming trend is very likely to continue with greenhouse gas increase.

(t)  “Climate science: The cause of the pause“, Isaac M. Held, Nature, 19 September 2013 —

After a rise of 0.5C in the 25 years starting in the mid-1970s, the change in Earth’s global mean surface temperture has been close to zero since the turn of the century. This hiatus in global warming has occurred despite retreating Artic sea ice and raising sea levels.

(u)  From chapter 9 of the final draft of the IPCC’s Fifth Assessment Synthesis Report

This is based on the Working Group Reports and Special Reports produced during the 5th or previous Assessment Cycles. Written in a “non-technical style suitable for policymakers”, addresses “a broad range of policy-relevant, but policy-neutral questions.”

Page 5:

Most simulations of the historical period do not reproduce the observed reduc tion in global-mean surface warming trend over the last 10–15 years. There is medium confidence that the trend difference between models and observations during 1998–2 012 is to a substantial degree cause d by internal variability, with possible contributions from forcing error and some models overestimating the response to increasing greenhouse-gas forcing.

A more detailed discussion appears on pp 28-32 in Box 9-2: “Climate Models and the Hiatus in Global-Mean Surface Warming of the Past 15 Years.” They put the pause in a larger context:

Even with this “hiatus” in GMST trend, the decade of the 2000s has been the warmest in the instrumental record of GMST. Nevertheless, the occurrence of the hiatus in GMST trend during the past 15 years raises the two related questions of what has caused it and whether climate models are able to reproduce it.

… This difference between simulated and observed trends could be caused by some combination of

• internal climate variability,
• missing or incorrect radiative forcing, and
• model response error.

These potential sources of the difference, which are not mutually exclusive, are assessed below, as is the cause of the observed GMST trend hiatus.

… In summary, the observed recent warming hiatus, defi ned as the reduction in GM ST trend during 1998–2012 as compared to the trend during 1951–2012, is attributable in roughly equal measure to a cooling contribution from internal variability and a reduced trend in external forcing (expert judgment, medium confidence).

The forcing trend reduction is primarily due to a negative forcing trend from both volcanic eruptions and the downward phase of the solar cycle. However, there is low confidence in quantifying the role of forcing trend in causing the hiatus, because of uncertainty in the magnitude of the volcanic forcing trend and low confidence in the aerosol forcing trend.

Almost all CMIP5 historical simulations do not reproduce the observed recent warming hiatus.

(v)  “An apparent hiatus in global warming?“, Kevin E. Trenberth and John T. Fasullo, Earth’s Future, 5 December 2013 — Abstract:

Global warming first became evident beyond the bounds of natural variability in the 1970s, but increases in global mean surface temperatures have stalled in the 2000s.

(w)  “Sixteen years into the mysterious ‘global-warming hiatus’, scientists are piecing together an explanation.“, Jeff Tollefson, Nature, 15 January 2014 — Well-written news feature, not peer-reviewed research.

The biggest mystery in climate science today may have begun, unbeknownst to anybody at the time, with a subtle weakening of the tropical trade winds blowing across the Pacific Ocean in late 1997. These winds normally push sun-baked water towards Indonesia. When they slackened, the warm water sloshed back towards South America, resulting in a spectacular example of a phenomenon known as El Niño. Average global temperatures hit a record high in 1998 — and then the warming stalled.

… Now, as the global-warming hiatus enters its 16th year, scientists are at last making headway in the case of the missing heat.

(x)  “Reduced Solar Activity Disguises Global Temperature Rise“, Peter Stauning, Atmosphere and Climate Sciences, January 2014 – Abstract:

However, the most recent climate data, show global temperature development levelling off or even turning negative since 2001 in contrast to the anticipated course related to the steady increases in the concentration in the atmosphere of green-house gasses, primarily carbon dioxide and methane.

(Z)  Other articles

Articles in the March 2014 issue of Nature Geoscience on “Recent slowdown in global warming”. Esp note the editorial: Hiatus in context

Climate science: Uncertain temperature trend“, Judith Curry, Nature Geoscience, February 2014 — “Global mean surface temperatures have not risen much over the past 15 years, despite continuing greenhouse gas emissions. An attempt to explain the warming slow-down with Arctic data gaps is only a small step towards reconciling observed and expected warming.”

“Overestimated global warming over the past 20 years“, John C. Fyfe et al, Nature Climate Change, September 2013 — “Recent observed global warming is significantly less than that simulated by climate models. This difference might be explained by some combination of errors in external forcing, model response and internal climate variability.”

“Oceanography: Has global warming stalled?“, Doug Smith, Nature Climate Change, 25 June 2013 — “Following a period of rapid warming from the 1970s, global temperatures seem to have stalled. New analysis of the uptake of heat by the upper ocean sheds light on the cause and suggests that the slowdown could have been predicted.”

(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. Still good news: global temperatures remain stable, at least for now
8. Kevin Drum talks about global warming, illustrating the collapse of the Left’s credibility
9. When did anthropogenic CO2 become the major driver of modern warming?

(11) For More Information

If you liked this post, like us on Facebook and follow us on Twitter. For more information see The keys to understanding climate change, My posts about climate change, and especially these…

• Scientists explore causes of the pause in warming, perhaps the most important research of the decade, 17 January 2014.
• One of the most important questions we face: when will the pause in global warming end?, 25 August 2013.

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