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One of the most important questions we face: when will the pause in global warming end?

25 August 2013

Summary:  Global warming has paused since roughly 1998 (see links in section 10). Today we examine climate scientists’ forecasts of when it will end (spoiler: now, or a decade-plus from now).

The duration of the pause in global warming will make no difference to the long-term history of the planet, and probably little difference to 21st century climate trends. But it might have large political impact, determining the magnitude of our preparations for our changing climate. That’s bad, since both climate research and preparations are absurdly underfunded — inadequate for even normal weather (NYT is at sea level; Sandy revealed it had near-zero flood preparations). The next in this series will discuss the politics of the pause.

Statue of Liberty, National Geographic, September 2013

Slightly more likely than Planet of the Apes

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Contents: forecasts for the pause

  1. One of the first to see the pause, in Nature
  2. Professor Mojib Latif
  3. Barrie G. Hunt (CSIRO)
  4. James Hansen (NASA)
  5. Kevin Trenberth (NOAA)
  6. Professor Judith Curry
  7. UK Met Office Decadal Forecast
  8. UK Met Office analysis of the pause
  9. Research
  10. About the ability of current models to accurately forecast global warming
  11. Basics about climate change
  12. For More Information

See the September 2013 National Geographic story here.

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(1) A so-far successful prediction

One of the first papers reporting the pause:  “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.

See the BBC’s article about it here. See the authors’ slides here.

(2)  Four years later, their prediction has already been proven false

How will Earth’s surface temperature change in future decades?“, Judith L. Lean and David H. Rind, Geophysical Research Letters, August 2009 — Abstract (red emphasis added):

Reliable forecasts of climate change in the immediate future are difficult, especially on regional scales, where natural climate variations may amplify or mitigate anthropogenic warming in ways that numerical models capture poorly. By decomposing recent observed surface temperatures into components associated with ENSO, volcanic and solar activity, and anthropogenic influences, we anticipate global and regional changes in the next two decades.

  1. From 2009 to 2014, projected rises in anthropogenic influences and solar irradiance will increase global surface temperature 0.15 ± 0.03°C, at a rate 50% greater than predicted by IPCC.
  2. But as a result of declining solar activity in the subsequent five years, average temperature in 2019 is only 0.03 ± 0.01°C warmer than in 2014.

This lack of overall warming is analogous to the period from 2002 to 2008 when decreasing solar irradiance also countered much of the anthropogenic warming. We further illustrate how a major volcanic eruption and a super ENSO would modify our global and regional temperature projections.

Other excerpts:

Yet as Figure 1 shows, global surface temperatures warmed little, if at all, from 2002 to 2008, even as green- house gas concentrations have increased, causing some to question the reality of anthropogenic global warming.

… n time scales of 10 to 50 years (and longer) decadal climate forecasts are difficult to make with general circulation climate models due to their many uncertainties [IPCC , 2007].

(3)  Presentation by Mojib Latif (Prof Climate Physics, Kiel University) at the World Climate Conference #3, 1 September 2009 — Slides here; recording here. Note the graph does not distinguish between actual past data and forecastes.

“it may well happen that you enter a decade, or maybe even two, when the temperature cools relative to the present level.”

Latif: Climate Surprises

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(4) The role of natural climatic variation in perturbing the observed global mean temperature trend“, Barrie G Hunt (Australia’s Commonwealth Scientific and Industrial Research Organisation), Climate Dynamics, February 2011 — Gated. Abstract:

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.

(5) Global Temperature Update Through 2012“, James Hansen (NASA), M. Sato, R. Ruedy, 15 January 2013 — Excerpt:

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… the continuing planetary energy imbalance and the rapid increase of CO 2 emissions from fossil fuel use assure that global warming will continue on decadal time scales. Moreover, our interpretation of the larger role of unforced variability in temperature change of the past decade, suggests that global temperature will rise significantly in the next few years as the tropics moves inevitably into the next El Nino phase.

The one major wild card in projections of fut ure climate change is the unmeasured climate forcing due to aerosol changes and their effects on clouds. Anecdotal information indicates that particulate air pollution has increased in regions with increasing coal burning, but assessment of the climate forcing requires global measurement of detailed physical properties of the aerosols. The one satellite mission that was capable of making measurements with the required detail and accuracy was lost via a launch failure, and as yet there are no plans for a replacement mission with the needed capabilities.

(6)  Transcript of interview with Kevin Trenberth (Senior Scientist, National Center for Atmospheric Research; bio here), All Things Considered, NPR, 23 August 2013

HARRIS: Trenberth says the planet has been heating up during that time, it’s just that the heat has been flowing into the oceans, which have a vast capacity to absorb it. Will the oceans come to our rescue, essentially?

TRENBERTH: That’s a good question, and the answer is maybe partly yes, but maybe partly no.

HARRIS: The oceans can, at times, soak up a lot of heat. Some of it goes into the deep oceans, where it can stay for centuries. But heat absorbed closer to the surface can easily flow back into the air. That happened in 1998, which made it one of the hottest years on record. Trenberth says since then, the ocean has mostly been back in one of its soaking-up phases.

TRENBERTH: They probably can’t go on much for much longer than maybe 20 years, and what happens at the end of these hiatus periods is that suddenly there’s a big jump to a whole new level and you never go back down to that previous level again.

(7)  Statement of Judith Curry (Prof climate science, GA Institute of Technology; bio here) to the Subcommittee on Environment on 25 April 2013 — Excerpt:

In light of these uncertainties, what can we say about the future climate of the 21st century? Most scientists anticipate a decrease in solar forcing in the coming decades, but noting the absence of understanding the solar indirect effects on climate, this is not expected to dominate climate change in the 21st century. If the climate shifts hypothesis is correct, then the current flat trend in global surface temperatures may continue for another decade or two, with a resumption of warming at some point during mid-century. The amount of warming from greenhouse gases depends both on the amount of greenhouse gases that are emitted as well as the climate sensitivity to the greenhouse gases, both of which are associated with substantial uncertainties.

(8)  Decadal Forecast, UK Met Office, December 2012 — Forecast of flat, carefully phrased.

… we will continue to see temperatures like those which resulted in 2000-2009 being the warmest decade in the instrumental record dating back to 1850. (Update, 8 January 2013)

UK Met Office: global temperature forecast

Observed (black, from Hadley Centre, GISS and NCDC) and predicted global average annual surface temperature difference relative to 1971-2000. Retrospective predictions starting from June 1960, 1965, …, 2005 are shown as white curves, with red shading representing their probable range, such that the observations are expected to lie within the shading 90% of the time. The most recent forecast (thick blue curve with thin blue curves showing range) starts from November 2012. All data are rolling annual mean values. The gap between the black and blue curves arises because the last observed value represents the period November 2011 to October 2012 whereas the first forecast period is November 2012 to October 2013.

(9) The recent pause in global warming, part 3: What are the implications for projections of future warming?“, UK Met Office, July 2013 — TCR: transient climate response. ECS: equilibrium climate sensitivity. Excerpt:

When projections from the newer climate models are combined with observations, including those from the last 10 years, the uncertainty range for warming out to 2050 is reduced. The very highest values of projected warming are eliminated, but the lower bound is largely unchanged. The most likely warming is reduced by only 10%, indicating that the warming that we might previously have expected by 2050 would be delayed by only a few years.

… ECS can be estimated from a range of methods: directly from observations, from comprehensive climate models or by combining models with observations. ECS can also be estimated using palaeoclimate reconstructions of periods in the distant past, such as the last glacial maximum. Again there are questions of accuracy and the comprehensiveness of palaeoclimate records.

Each approach has its own limitations. As for TCR, the observationally constrained results are sensitive to the specification of radiative forcing, which need to be modelled. The ECS also requires knowledge of the heat storage in the Earth system, particularly the oceans. As discussed at length in the second report, our knowledge of the ocean heat content and the processes through which the oceans take up heat is very limited. So, estimating the gain in energy by the current Earth system is very uncertain. This means that observational estimates of the ECS are prone to even greater uncertainty than for the TCR.

The uncertainty in the estimates of ECS from comprehensive climate models stems largely from the incomplete understanding and representation of cloud and other processes. The accuracy of palaeoclimate reconstructions is limited by the uncertainty in the reconstructed temperature, our understanding of the causes of the changes from present climate, and the degree of relevance of past climate change to a warming driven by increases in greenhouse gases.

… Observationally based approaches span a wider range than these model estimates, reflecting the difficulties in estimating radiative forcing and the change in energy content of the Earth system .

… Finally, much of the interest in ECS relates to the amount of warming that would result if the radiative forcing were stabilised. In reality, other Earth system feedbacks, associated for example with the cycling of carbon through natural systems and releases of carbon from permafrost melt, will change, and are likely to increase the actual expected warming (see e.g. Knutti et al 2013).

What is evident is that, even for the more conservative estimates derived from observations, the prospects of substantial global warming by the end of the century are not materially altered by the recent pause in global surface warming.

(10)  Research — will be updated

(a)  “Overestimated global warming over the past 20 years”, John C. Fyfe, Nathan P. Gillett, Francis W. Zwiers, Nature Climate Change, 28 August 2013 — Gated. Abstract:

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.

Excerpt:

Global mean surface temperature over the past 20 years (1993–2012) rose at a rate of 0.14 ± 0.06 °C per decade (95% confidence interval). This rate of warming is significantly slower than that simulated by the climate models participating in Phase 5 of the Coupled Model Intercomparison Project (CMIP5).

… The evidence, therefore, indicates that the current generation of climate models (when run as a group, with the CMIP5 prescribed forcings) do not reproduce the observed global warming over the past 20 years, or the slowdown in global warming over the past fifteen years. [S]uch an inconsistency is only expected to occur by chance once in 500 years, if 20-year periods are considered statistically independent. Similar results apply to trends for 1998–2012. In conclusion, we reject the null hypothesis that the observed and model mean trends are equal at the 10% level.

One possible explanation for the discrepancy is that forced and internal variation might combine differently in observations than in models. … Another possible driver of the difference between observed and simulated global warming is increasing stratospheric aerosol concentrations. Other factors that contribute to the discrepancy could include a missing decrease in stratospheric water vapour, errors in aerosol forcing in the CMIP5 models, a bias in the prescribed solar irradiance trend, the possibility that the transient climate sensitivity of the CMIP5 models could be on average too high or a possible unusual episode of internal climate variability not considered above.

Ultimately the causes of this inconsistency will only be understood after careful comparison of simulated internal climate variability and climate model forcings with observations from the past two decades, and by waiting to see how global temperature responds over the coming decades.

(b) Recent global warming hiatus tied to equatorial Pacific surface cooling“, Yu Kosaka and Shang-Ping Xie, Nature, 29 August 2013 — Gated. See this analysis of the paper 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.

(c) Role for Eurasian Arctic shelf sea ice in a secularly varying hemispheric climate signal during the 20th century“, Marcia Glaze Wyatt and Judith A. Curry, Climate Dynamics, September 2013 — Ungated copy here.  From the Georgia Tech press research:

“The stadium wave signal predicts that the current pause in global warming could extend into the 2030s,” said Wyatt …

Curry added, “This prediction is in contrast to the recently released IPCC AR5 Report that projects an imminent resumption of the warming, likely to be in the range of a 0.3 to 0.7 degree Celsius rise in global mean surface temperature from 2016 to 2035.” Curry is the chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology.

The University announcement gives a clear summary. Excerpt:

“The stadium wave signal predicts that the current pause in global warming could extend into the 2030s,” said Wyatt …  Curry added, “This prediction is in contrast to the recently released IPCC AR5 Report that projects an imminent resumption of the warming, likely to be in the range of a 0.3 to 0.7 degree Celsius rise in global mean surface temperature from 2016 to 2035.” Curry is the chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology. … “Current climate models are overly damped and deterministic, focusing on the impacts of external forcing rather than simulating the natural internal variability associated with nonlinear interactions of the coupled atmosphere-ocean system,” Curry said.

(e) NAO implicated as a predictor of Northern Hemisphere mean temperature multidecadal variability“, Jianping Li1, Geophysical Research Letters, 28 October 2013 — From the abstract:

NHT {Northern Hemisphere mean surface temperature} in 2012–2027 is predicted to fall slightly over the next decades, due to the recent NAO weakening that temporarily offsets the anthropogenically induced warming.

(f)  Global Temperature Update Through 2013, James Hansen, Makiko Sato and Reto Ruedy, 21 January 2014

The recent slowdown of global warming is a consequence of both a slowdown in the growth rate of climate forcings and recent ENSO history. Given that the tropical Pacific seems to be moving toward the next El Niño, record global temperature is likely in the near term. However, the rate of future warming will depend upon changes of the tropospheric aerosol forcing, which is highly uncertain and unmeasured.

… Assuming that an El Niño begins in summer 2014, 2014 is likely to be warmer than 2013 and perhaps the warmest year in the instrumental record. However, given the lag between El Niño initiation and global temperature, 2015 is likely to have a temperature even higher than in 2014.

(g) Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus“, Matthew H. England et al, Nature Climate Change, in press.

Remarks by Professor England in the University of New South Wales press release:

The winds lead to extra ocean heat uptake, which stalled warming of the atmosphere. Accounting for this wind intensification in model projections produces a hiatus in global warming that is in striking agreement with observations. … Unfortunately, however, when the hiatus ends, global warming looks set to be rapid. … This pumping of heat into the ocean is not very deep, however, and once the winds abate, heat is returned rapidly to the atmosphere.

Abstract:

Despite ongoing increases in atmospheric greenhouse gases, the Earth’s global average surface air temperature has remained more or less steady since 2001. A variety of mechanisms have been proposed to account for this slowdown in surface warming. A key component of the global hiatus that has been identified is cool eastern Pacific sea surface temperature, but it is unclear how the ocean has remained relatively cool there in spite of ongoing increases in radiative forcing.

Here we show that a pronounced strengthening in Pacific trade winds over the past two decades — unprecedented in observations/reanalysis data and not captured by climate models — is sufficient to account for the cooling of the tropical Pacific and a substantial slowdown in surface warming through increased subsurface ocean heat uptake. The extra uptake has come about through increased subduction in the Pacific shallow overturning cells, enhancing heat convergence in the equatorial thermocline.

At the same time, the accelerated trade winds have increased equatorial upwelling in the central and eastern Pacific, lowering sea surface temperature there, which drives further cooling in other regions.

The net effect of these anomalous winds is a cooling in the 2012 global average surface air temperature of 0.1–0.2 °C, which can account for much of the hiatus in surface warming observed since 2001. This hiatus could persist for much of the present decade if the trade wind trends continue, however rapid warming is expected to resume once the anomalous wind trends abate.

(11) Some important things to know about global warming

Truth Will Make You Free

While cheering for their faction of scientists, laypeople often lose sight of the big picture — the key elements for making public policy about this important issue.

(a)  The work of the IPCC and the major science institutes are the best guides for information about these issues.

(b)  The world has been warming during the past two centuries, in a succession of warming, cooling, and pauses. As for our influence:

“It is extremely likely (95 – 100% certain) that human activities caused more than half of the observed increase in global mean surface temperature from 1951 to 2010.”
— conclusion of the IPCC’s AR5 Working Group I

For research about the 1951 date see When did we start global warming? See the surprising answer., 18 October 2012

(c)  There is a debate about the attribution (causes) of past warming — which probably varied over time — between natural drivers (e.g., rebound from the Little Ice Age, solar influences) and anthropogenic drivers (eg, CO2, aerosols, land use changes). Other that that stated in (b), the IPCC’s reports make few claims about attribution of climate activity. This remains actively debated in the literature:  Scientists explore causes of the pause in warming, perhaps the most important research of the decade, 17 January 2014

(d)  Warming of the surface atmosphere paused sometime during 1998-2000:  Still good news: global temperatures remain stable, at least for now., 14 October 2012.

(e)  There is also debate about climate forecasts, both the extent of future CO2 emissions and the net effects of the various natural and anthropogenic drivers.

(f)  For the past five years my recommendations have been the same:

  1. More funding for climate sciences. Many key aspects (e.g., global temperature data collection and analysis) are grossly underfunded.
  2. Wider involvement of relevant experts in this debate. For example, geologists, statisticians and software engineers have been largely excluded — although their fields of knowledge are deeply involved.
  3. Start today a well-funded conversion to non-carbon-based energy sources by the second half of the 21st century; for both environmental and economic reasons (see these posts for details).

(g)  Posts about preparing for climate change:

Day After Tomorrow

From The Day After Tomorrow. I’m staying home.

(12)  For More Information

Reference Pages about climate on the FM sites:

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6 Comments leave one →
  1. 25 August 2013 2:13 pm

    The only thing stopping CO2 mitigation and denial is the uncertainty and the room for doubt that science itself provides by NEVER agreeing it WILL be a crisis, just could be a deadly crisis and might be and potentially………………….

    If science agreed instead that this 28 year old danger to the planet WILL happen instead of just could happen it would shut down the denier machine as the consensus of “could be” instead of “will be” an inevitable crisis feeds denial more than all of oil’s money.

    But it’s too late now as Occupywallstreet does not even mention CO2 in its list of demands anymore because of the bank-funded and corporate run carbon trading stock markets ruled by politicians.

    Like

    • 25 August 2013 2:43 pm

      Nutzuki,

      You raise important points — which are the subject of tomorrow’s post, so I will not say much here. Today we look at what scientists say. However…

      “The only thing stopping CO2 mitigation is … the uncertainty and the room for doubt that science itself provides by NEVER agreeing it WILL be a crisis,”

      The reports of the IPCC and major climate agencies are quite clear — appropriately so — that we know what we know. That is why the IPCC writes in terms of probabilities, not certainties.

      Given the current state of climate science, a wide range of statements can be made about the past — although many important questions remain unclear or even unknown. And, as shown in this post, there are far more uncertainties and even unknowns about the future.

      Lies will not help, and might have horrific consequences. As discussed tomorrow.

      “The only thing stopping CO2 mitigation and denial is the uncertainty”

      I do not understand what this means. “Uncertainty” of scientists about the future stops “denial” of what?

      Like

  2. Mikyo permalink
    25 August 2013 4:46 pm

    Uncertainty and doubt are what science is made of :)

    Like

  3. gerald zuckier permalink
    5 March 2014 7:22 am

    That figure 1 shows that the current “slowdown” is primarily due to the temp just before and after 2000 being quite a big warmer than the prediction. Thus the current “cooling” has nothing to do with “the end of AGW”, and everything to do with “1998 was one damn hot year, even by current standards!”

    Like

    • 5 March 2014 2:24 pm

      Gerald,

      (a) What is this “current ‘cooling'” you refer to?

      (b) There are at least nine well-known theories about the cause(s) of the pause in surface temperature warming (see abstracts and links here). None of the dozens of papers I’ve cited mention your theory.

      This is one of the great questions in climate science research. I suggest writing it up and submitting it to a science journal. Or perhaps you should leave making climate science theory to climate scientists.

      Like

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