Examining the Recent Slow-Down in Global Warming

With upcoming release of IPCC Fifth Assessment Reports beginning late in September, there will be a sharp focus on specific issues like projected sea-level rise but also on broader issues like climate sensitivity and the decade-and-a-half-long slow-down in the rate of overall warming. Let’s begin by examining that slow-down in depth, and just what is involved in taking Earth’s temperature …

Global surface temperatures have warmed more slowly over the past decade than previously expected. Some in the media have seized this warming pause in recent weeks, and the UK’s Met Office has just released a three-part series of white papers looking at the causes and implications.

While there is still no definitive cause identified, the Met Office scientists point to a combination of more heat going into the deep oceans and downturns in multi-decadal cycles in global temperature — natural variability — as the primary drivers of the pause. Others argue that a plethora of recent small volcanoes, changes in stratospheric water vapor, and a downturn in solar energy reaching the Earth may also be contributing to the slow-down. While few expect the pause to persist much longer, it has raised some questions about the growing divergence between observed temperatures and those predicted by climate scientists.

To understand the decline in the rate of warming requires understanding the different ways of measuring global temperature. These include measurements taken from land-based temperature stations (mostly using mercury thermometers), ocean buoys, ships, satellites, and weather balloons.

Land/Ocean Temperatures

The most common estimate of global temperatures comes from a combination of land temperature stations with sea surface temperature data from ships and buoys. There are three main global land/ocean surface temperature series, produced by NOAA’s National Climate Data Center (NCDC), NASA’s Goddard Institute for Space Studies (GISTemp), and the UK’s Hadley Center (HadCRUT).

As shown in the figure above, all three series agree quite well on global temperatures. The short dashed grey line at the upper right shows the trend in temperatures since 2001, while the long dashed black line shows the trend since 1970. Although the rise in global temperatures has slowed in recent years, it is not obviously divergent from the underlying long-term trend. On the other hand, there are no periods with similar temperature stagnation other than ones associated with a major volcano (e.g. Pinatubo in 1992 or El Chichón in 1982).

Land Temperatures Only

Land and ocean temperatures have diverged notably in recent years. Ocean temperatures generally rise more slowly than land temperatures as a result of the large thermal inertia of the oceans. Since 2001, land temperatures have continued to rise, though slightly more slowly than in prior years.

Here again the short dashed grey line at the top right shows the trend since 2001, while the dashed black line shows the trend over the whole period. The major land series used are CRUTEM4 (the land component of HadCRUT4), NCDC, GISTemp, and Berkeley Earth.

Ocean Surface Temperatures Only

Most of the decline in global surface temperatures in recent years has been concentrated in the oceans. The figure below shows two of the major sea surface temperature records: HadSST3 from the Hadley Center, and NCDC’s ERSST series.

Ocean temperatures have cooled slightly in recent years, after a large jump upwards in 2000/2001.

Lower Tropospheric Temperatures

Global temperatures can also be estimated based on data from satellites in orbit. These use instruments to measure radiance from Earth to determine temperature, and they tend to have quite good spatial coverage of the planet (excluding some high-latitude regions). While there is still some uncertainty regarding how to best correct for issues like orbital drift and transitions to different satellites, satellite-based records now fairly closely mirror surface-based records, though with slightly lower trends. Scientists are still trying to resolve the discrepancy between satellite and surface trends.

Satellite records show some stagnation of temperatures in recent years, somewhere between the land and ocean surface records.

Deep Ocean Temperatures

In recent years, a global network of automated buoys has offered a much-improved picture of what is going on below the surface in the ocean. These buoys automatically dive deep down into the ocean every day, taking temperature measurements as they slowly rise, and transmitting that data back to a central database via satellite. The figure below, via Argo, shows the location of buoys currently active in the world’s oceans.

While measurements of deep-ocean temperatures existed further back in the past, they were taken only in limited locations until 1999, when Argo buoys were widely deployed. However, scientists for far longer have been able to use more limited data to reconstruct temperatures down to depths of 2,000 meters, as shown in the figure below.

Total ocean heat content has increased by around 170 Zettajoules since 1970, and about 255 Zettajoules since 1955. This increased temperature has caused the oceans (0-2,000 meters) to warm about 0.09 C over this period. As the UK’s Met Office points out, if the same amount of energy had gone into the lower atmosphere it would of caused about 36 C (nearly 65 degrees F) warming! The oceans are by far the largest heat sink for the Earth, absorbing the vast majority of extra heat trapped in the system by increasing concentrations of greenhouse gases.

It’s important to point out that overall deep-ocean heating (0-2,000 meters) shows no sign of a slow down in recent years, though shallower layers (0-300 meters and 0-700 meters) do. That the slowdown in surface warming has been concentrated in the ocean-surface (and shallow-ocean) temperatures has led a number of scientists (including the Met Office) to posit that the pause in ocean surface warming may be driven in part by increased heat uptake in the deep ocean.

Multi-Decadal Cycles

There are a number of inter-decadal and multi-decadal cyclical patterns observable in the climate system, particularly in ocean surface temperatures. These include the Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO), both operating over a period of a few decades, and the El Niño Southern Oscillation (ENSO), which has a period of three to seven years. While ENSO tends to average-out over periods of more than a decade, the AMO and PDO can both potentially impact the climate over longer periods of time.

The AMO is generally calculated by subtracting out the linear trend from 1880 to present in North Atlantic sea surface temperatures. This approach isn’t perfect, and it may overestimate the magnitude of natural variability in recent years, but there is a clear cycle present in the North Atlantic that can contribute to variations in global temperatures. The Met Office, for example, cites a paper arguing that variations in the AMO can change global temperatures by around 0.1 C. While the AMO has not changed much in the past 10 years, the strong increase in North Atlantic temperatures between 1970 and 2000 may have contributed to the rapid rise in global temperatures over that period, and the leveling-out of the AMO may help make the observed pause in warming more likely.

The Pacific Decadal Oscillation (PDO) is calculated rather differently from the AMO. The PDO is calculated by examining the difference in temperatures of the northern Pacific from global ocean temperatures as a whole in order to isolate changes specific to that region. This approach more effectively removes any anthropogenic signals affecting the whole world than the simple linear detrending used in calculating the AMO.

The PDO transitioned to a cold phase around the year 2000. While there still is quite a bit of uncertainty surrounding the effects of the PDO on Earth’s climate, the U.K. Met Office says that “decadal variability in the Pacific Ocean may have played a substantial role in the recent pause in global surface temperature rise.” It argues that Global Climate Models (GCMs) that show decadal-scale pauses in surface temperature warming tend to exhibit sea surface temperature patterns similar to those of the PDO in a cold phase.

Incoming Solar Radiation

The sun has a well-known roughly 11-year cycle in solar output that can have an influence on global temperatures, though most solar scientists consider the impact to be relatively minor. Estimates of the difference in temperatures between the peak (high point) and trough (low point) of the solar cycle range between about 0.05 C to 0.1 C, holding everything else equal. If solar cycles hold steady, this won’t really impact trends over periods of 11 years, as the peaks and troughs will cancel-out.

However, the most recent solar cycle has been notable for the extended trough and low peak (at least so far). The figure below shows the PMOD compilation of solar irradiance measurements from a number of different satellites.

The most recent trough in solar activity likely plays a role in depressing short-term trends, and the overall decline in total solar irradiance (TSI) in recent years relative to past solar cycles may be a small contributing factor in the current slow-down in the rate of warming. As the Met Office explains, “There is no doubt that the declining phase of the 11-year cycle of total solar irradiance has contributed to a reduction in incoming energy over the first decade of the 21st century, but still not enough to explain the pause in global surface temperature rise.” On the other hand, climate models using up-to-date solar forcings don’t show noticeably lower temperatures in the past decade, and that data runs counter to the idea that longer-term changes in the solar cycle are playing a major role in the pause.

Stratospheric Water Vapor

Water vapor in the upper atmosphere plays an important role in Earth’s climate. The figure below, from a paper in Science by Susan Soloman and her colleagues, shows a notable decline in stratospheric (high-atmosphere) water vapor after the year 2000. They argue that this “very likely made substantial contributions to the flattening of the global warming trend since about 2000″ and that temperatures between 2000-2009 would have warmed about 25 percent had stratospheric water vapor remained constant. The figure below shows various different estimates of stratospheric water vapor content, with the pre- and post-2001 periods highlighted.

Soloman and her co-authors argue that El Niño has been one of the drivers of changes in stratospheric water vapor, noting that “The drop in stratospheric water vapor observed after 2001 has been correlated to sea surface temperature (SST) increases in the vicinity of the tropical ‘warm pool’ which are related to the El Niño Southern Oscillation (ENSO).”

That said, the models that Soloman and her co-authors use still show significant warming over the past decade even when stratospheric water vapor is declining (they give a rise of 0.10 C instead of 0.14 C, a 0.04 degree C difference). Based on these results, declining stratospheric water vapor would account for only about one-fourth of the slow-down in warming. They also point out that an increase in stratospheric water vapor during the 1990s may have led to about 30 percent more warming during that decade than otherwise would have occurred.

Small Volcanic Eruptions

Stratospheric aerosols — small air-borne particles in the upper atmosphere — play an important role in Earth’s climate. By scattering incoming solar radiation, they can significantly cool the planet. Historically, much of the study of stratospheric aerosols has focused on large volcanic eruptions, which inject large amounts of sulfur dioxide into the stratosphere.

A recent paper by Ryan Neely and coauthors argues that multiple small volcanoes also can have a notable impact on stratospheric aerosols. They point out that “recent studies using ground-based lidar and satellite instruments document an increase in stratospheric aerosol of 4–10 percent per year from 2000 to 2010.” The Neely research argues that “as much as 25 percent of the radiative forcing driving global climate change from 2000 to 2010 may have been counterbalanced by the increases in stratospheric aerosol loading over this period.” The authors examine various potential causes of aerosol increases and identify a number of small volcanoes over the last decade as the most plausible source.

The Met Office downplays these results in its report, arguing that the effect would only be around -0.02 C to -0.03 C during the 2008-2012 period and “will not be detectable above climate variability.” This conclusion relies on an analysis that has been submitted for publication but not yet published, so that analysis may still be subject to revision in the course of the peer review process.

Climate Models and Observations

While it is difficult to distinguish between the recent slow-down in global surface temperatures and the underlying long-term trend, the slow-down stands out much more vividly when compared to projections from the latest set of GCMs. These models predict warming of around 0.2 C per decade from 2000 to present on average.

The figure above compares the three major global surface temperature records to 105 unique runs involving 42 different GCMs used in the upcoming IPCC report. It shows the 5th and 95th percentile of model runs in light grey, and the 25th to 75th percentile in dark grey, with a black line representing the average of all models. While surface temperatures have generally remained fairly close to the multi-model mean in the past, the recent pause threatens to cause surface temperatures to fall below the 5th percentile of models in the next year or two if temperatures do not rise.

The current slow-down also stands out sharply if one looks at the full range of model projections, from 1880 to 2100. However, it’s important to remember that all models are not created equal. Some inevitably will have more realistic parameters, better physical models, higher resolutions, etc. Simply averaging all the models together may not provide an accurate picture of variations in individual model performance.

The figure above shows all 105 model runs, and reveals significant differentiation among the models. Generally speaking, models that are more consistent with recent temperatures tend to have slightly lower climate sensitivity than those that predict higher temperatures over the past few decades. A 2013 paper in Environmental Resource Letters used recent observations to argue that some of the highest sensitivity models may be inconsistent with the observational record.

There have been a number of new papers that use recent atmospheric, ocean, and surface temperature observations to argue that climate sensitivity may be lower than previously estimated (e.g. closer to 2 C than 4 C). These studies tend to be rather sensitive to the time period chosen, and a future warm decade could considerably change the picture. As with many things in science, there is still significant uncertainty surrounding climate sensitivity, and different approaches can obtain fairly different results. However, the longer the current slow-down continues, the more questions will arise about whether GCMs are getting either multi-decadal variability or climate sensitivity wrong.

What is clear is that there is still much we don’t understand about the many different factors impacting Earth’s climate system, especially over periods as short as a decade.

Zeke Hausfather

Zeke Hausfather, a data scientist with extensive experience with clean technology interests in Silicon Valley, is currently a Senior Researcher with Berkeley Earth. He is a regular contributor to The Yale Forum (E-mail: zeke@yaleclimatemediaforum.org, Twitter: @hausfath).
Bookmark the permalink.

50 Responses to Examining the Recent Slow-Down in Global Warming

  1. Alexander says:

    I would like to point out that some of the factors indicated in this article as causes of the warming slowdown–solar activity, decadal cycles, volcanic eruptions, water vapor, etc.– are all potential contributing factors that were completely dismissed, with a sense of derision and mockery, by the “AGW alarmist” community when they were raised by critics of the AGW hypothesis to question the more catastrophic climate change predictions and the idea that all of the climate change was the fault of humans only.

    • Hank says:

      The AGWers are so desperate to have their pet project succeed that they will do anything, even adopt parts of the arguments of the ‘heretics’ to make them their own, to prop up their nonsense.

    • John says:

      Where in the article does it say that these (solar activity, volcanos, water vapor) are important contributors to atmospheric and ocean temperature changes?

    • Tom says:

      It is quite depressing that you have immediately leaped to a position that has practically nothing to do with this very well-written article.
      1. Solar activity was never dismissed by the climate community. It simply cannot explain the rise in temperatures since 1976 since solar activity has been periodic since that time (see graph).
      2. Volcanic aerosol was never dismissed by the climate community. There have been a large number of studies since 1970 devoted to understanding this problem and we have a very clear understanding at this point. We have been monitoring volcanic activity during the satellite era (and before) and there is no trend in stratospheric aerosol amount over that period, let alone one that would explain the temperature trend. In fact there has been very little aerosol at all during this period.
      3. As noted below, no one (skeptics, deniers or otherwise) postulated a change in water vapor until that noted skeptic Susan Solomon published it, so it is hard to argue that it was dismissed.
      4. Decadel cycles have been discussed in great detail and given lots of consideration. We unfortunately lack a long enough dataset to apply statistical methods to the data and current models do not simulate internal oscillations of the climate system very well. However, these factors impact everyone (including skeptics) in terms of ascertaining the importance of these cycles.

      The earth has a greenhouse effect. Adding CO2 to the atmosphere increases the greenhouse effect and must therefore warm the surface. The physics is inescapable. The issue we are struggling with is not whether the earth surface temperature will rise due to human CO2 emissions because it must. The question is how fast and how much, which is the climate sensitivity question. It would greatly help our discussions to agree on this point.

      • Lionstorm says:

        “Adding CO2 to the atmosphere increases the greenhouse effect and must therefore warm the surface.”

        This statement may be true if all other factors remain unchanged. The writer of the comment has given no attention at all to the fact that increase in CO2 is almost certainly NOT the only factor changing. It also ignores the possibility, not unknown in complex systems, that feedback mechanisms and the constraints thereon themselves change in response to greater stimulus.

        While I am not arguing for any particular position, I would like to see fewer statements that demand agreement with illogical theses. There are of course offenders on both sides, but I given this one attention because it arises from the too frequently condescending “We’re scientists, while the skeptics are nutcases” side of things.

        I very much appreciate the summation of recent data and litany of the problems and challenges arising from these data, especially in re the common GCMs. As a non-climate-science scientist, I recognize that I quickly step out of my area of expertise when it comes to the details of climate models, but an honest, open expression of “Here’s where the problems seem to lie” is nice, and adds to the credibility of the discussants.

        • Martin Lack says:

          …the fact that increase in CO2 is almost certainly NOT the only factor changing” – Lionstorm.

          Factually correct but potentially misleading. The question is which changes are significant and capable of causing sustained warming over several decades. As with Matthew (below), please see how you get on with this (slightly modified) multiple choice question. Which is the most likely sustained cause for multi-decadal warming following the Industrial Revolution:
          (a) A 0.1% variation in Total Solar Irradiance (TSI) over short-term Solar Cycles.
          (b) A 0.2% increase in TSI over the last 2000 years.
          (c) A 4% rise in avg. atmospheric moisture content.
          (d) A 40% rise in atmospheric CO2 content.
          Don’t take too long to think about it, your initial reaction to the numbers is probably reliable.

    • NHFF says:

      What is an AWG? Please use words, not acronyms

    • toby52 says:

      I note the dearth of evidence concerning where and when the alleged “dismissals” took place.

      More smoke blown by deniers to shore up an untenable position.

  2. Robert says:

    Well said, Alexander.

  3. Nullius in Verba says:

    “While measurements of deep-ocean temperatures existed further back in the past, they were taken only in limited locations until 1999, when Argo buoys were widely deployed. However, scientists for far longer have been able to use more limited data to reconstruct temperatures down to depths of 2,000 meters, as shown in the figure below.”

    Interesting figure. You’ll notice that the three lines track one another up until 1990, indicating that *all* the rise is in the top 300 m, when a gap suddenly opens up between 300 and 700 m. This gap widens fairly uniformly from then on. In 2000, a gap suddenly opens up between 700 and 2000 m, again widening uniformly with time.

    This seems like quite odd behaviour. Why does no heat pass below 300 m until 1990? Why does no heat pass below 700 m until 2000? What happened at those two points in time to suddenly change things?

    There are a couple of interesting animations showing the number and location of ocean temperature samples taken at 500+ m and 1500+ m.
    http://bobtisdale.files.wordpress.com/2013/03/nodc-temp-obs-at-500m.gif
    http://bobtisdale.files.wordpress.com/2013/03/nodc-temp-obs-at-1500m.gif

    Notice how the sample size jumps up to a global coverage around the early 1990s for the 500 m depth and the early 2000s (i.e. the start of Argo) for the 1500 m depth.

    So up until 1990, almost all the data was for the top couple of hundred metres and there was virtually no data below that, and the ocean heat increases was confined to the top few hundred metres, with virtually no warming below. The heat increase spread to the 300-700 m layer at about the same time as the data collection did. And then the heat rise sank into the 700-2000 m layer just as the data collection expanded down there.

    Just a coincidence, possibly. But maybe it would be worth noting?

    Another interesting calculation is to divide the volume of the oceans down to 2000 m by the number of samples taken there per month, say, and work out what volume of water each single thermometer is measuring the temperature of. And to what accuracy.

    Do you think there might be some rather lumpy error bars on those lines? :-)

    But apart from that, an excellent post! The AMO+PDO stuff is a familiar topic. TSI is interesting but probably too small on its own to have much effect – the question is what other correlated solar activity might also have an effect.

    It might also have been worth highlighting the 1940-80 pause, as an illustration of how a pause doesn’t necessarily mean it’s stopped, and another example of the possible magnitude of natural variation. It could also be worth explaining that while the pause might be a problem for those who think the climate models accurately represent natural variation, for people who *don’t* the pause proves nothing. Without a validated statistical model of signal and noise, you can’t test for significance.

    Only the people who believe the models can say ‘the underlying rise seems to have paused’. The people who don’t believe the models can only say ‘we don’t know, because we can’t tell what’s long-term rise and what’s noise’.

    A subtle point, but some people might find it interesting.

    • John says:

      You might be confusing ZERO-2000 m (e.g.) with 700-2000 m? Also remember that in the top layers, there will be a temperature limit. The ocean gets heat from the sun, and this leads to evaporative cooling at the surface, and an increase in salinity, especially in the tropics. This destabilizes the surface layer, and leads to vertical mixing, mixing the heat to deeper depths.

      • Nullius in Verba says:

        “You might be confusing ZERO-2000 m (e.g.) with 700-2000 m?”

        Don’t think so. If you subtract the 0-700 m line from the 0-2000 m line, you get the heat content in the 700-2000 m layer. i.e. the gap between the lines represents the heat in each layer.

        “Also remember that in the top layers, there will be a temperature limit. The ocean gets heat from the sun, and this leads to evaporative cooling at the surface, and an increase in salinity, especially in the tropics. This destabilizes the surface layer, and leads to vertical mixing, mixing the heat to deeper depths.”

        True, but I doubt that the relatively small amount of evaporation has much effect compared to wind-driven currents. Regions of low and high air pressure cause the wind to drive surface water inwards into convergence zones, from where the only place it can go is down. In various areas you do get major localised upwelling and downwelling.

        But as I understand it, most wind-driven mixing is confined to a layer of seasonally variable thickness that averages only a couple hundred metres, with deeper convection being quite localised. As depth increases the mixing slows, as temperature gradients flatten out, and eventually falls below the bulk rate of rise due to the global thermohaline circulation. The main case of deep downwelling is in polnyas in the Southern Ocean as part of the thermohaline circulation.

        But my point was not to express scepticism that deep downwelling happens, but that the graph *says* that deep downwelling didn’t happen until 1990, when it suddenly started in the 300-700 m layer, and again in 2000 when it extended to the 700-2000 m layer. This is indicated by the width of the gaps between the lines.

        Are you suggesting that your evaporation-driven mixing mechanism only started in 1990? Or any of the other mechanisms you might propose?

        On the contrary, I think that deep downwelling *does* happen, and continues today much as it always has, but that our instrumentation is as yet too sparse and inaccurate to detect it. The wiggly lines we are looking at are mostly measurement noise, systematic drifts are more likely caused by systematic changes in error as the instrumentation evolves, and the period for which we have even arguably global data is far too short to detect any changes.

        If you think you can persuade me that around three thousand thermometers (today) in seven hundred million cubic kilometres of ocean water, i.e. over two hundred thousand cubic kilometres of water per thermometer, each thermometer reading to the nearest degree C, can measure the total ocean heat content increase to an accuracy equivalent to a hundredth of a degree (as implied by quoting two decimal places), then I would be most interested to hear your argument.

        • John says:

          I take your point about the change on or about 1990, but would have to look at the original data to see what’s going on. The only way the ocean can mix vertically over these depth ranges is through the combined effects of changing buoyancy (convective processes) and deep ocean mixing. 0-2000 m is about half the average ocean depth, and the ocean mixes deeper than that. Salinity is important to these convective mixing, and occurs in all regions of the ocean. A salinity effect may be the reason the 0-300m data does not increase like the deeper data.

          Oceanographers quit using thermometers a long time ago, I’m told. Routinely, temperature is measured to the thousandth’s of a degree. The lines are noisy, yes, but still increasing. The problems of sampling the variability in the ocean is helped by the fact that ocean variables typically vary much greater vertically than horizontally.

  4. Matthew says:

    I would also like to point out that solar irradiance is just one measure of the sun’s effect on our planet and climate scientists have generally only looked at that one variable to say “it isn’t enough”. There are many other changes associated with a reduction in the sun’s output including an increase in cosmic ray activity, which has been linked in some research to an increase in cloud cover and cooling global temperatures. We do not fully know the ramifications because this has not happened during our modern times of measurement. http://physicsworld.com/cws/article/news/2013/sep/09/physicists-claim-further-evidence-of-link-between-cosmic-rays-and-cloud-formation

    • John says:

      This is a red herring. Even the link indicates that the cosmic ray-cloud connection is tenuous at best.

    • Martin Lack says:

      Matthew, see how you get on with this multiple choice question. Which is the most likely sustained cause for multi-decadal warming following the Industrial Revolution:
      (a) A 1% increase in Total Solar Irradiance.
      (b) A 4% increase in average moisture content.
      (c) A 40% increase in CO2 content.

      Don’t take too long to think about it, your first impression is probably reliable.

  5. Alexander,

    While there are certainly some who have underplayed the impact of multidecadal climate variability, there are others more dismissive of anthropogenic warming who have argued that natural forcings or variability have played a larger role in modern warming than warranted.

    Its useful to go back to the IPCC’s more general statement that more than 50% of warming over the past 50 years is due to anthropogenic factors. If the actual number is 60% or 80% or something else is still a very open question.

  6. rabbit says:

    “What is clear is that there is still much we don’t understand about the many different factors impacting Earth’s climate system, especially over periods as short as a decade.”

    This is my greatest beef with climatologists in general. When Al Gore stated “the science is settled”, there should have been a chorus of scientists saying “We think we know what is happening, but there is still a enormous amount of uncertainty. The science is not completely settled.”

    Perhaps they were hesitant because they might be called a “denier”, or it might jeopardize their funding, or because they thought a little white lie was okay in support of a good cause.

    But in the long term it has harmed the reputation of climatologists, so that even if the more cataclysmic projections are true, people are now hesitant to act.

    • Adam R. says:

      Perhaps they were hesitant because they might be called a “denier”, or it might jeopardize their funding, or because they thought a little white lie was okay in support of a good cause.

      Faux-reasonable deniers always give themselves away with charges of corruption and conspiracy like this. They know their position is defensible only on the basis that the world of science is conniving to lie to them.

      • Ledg says:

        The word deniers always bothered me. That word has emotional overtones which don’t belong in a rational discussion. What also bothers many skeptics is the fact that we were told that the science was settled. ‘Just believe us’ was the message. Dissenting views are not allowed. ‘You obviously don’t care about the earth’, they said. Sorry, but this is more about politics than it is about the truth.

  7. RC says:

    It seems like we, as humans, have much to learn about earth’s climate — apparently CO2 is not quite THE climate lever that we’ve been told.

    • Adam R. says:

      Nope, RC, science has not changed its mind on this, despite your hopeful but skewed reading of the article above.

      Assuming you did read it, that is.

  8. Ian P Craig says:

    Excellent work – very interesting !

    Is there a graphic for the world’s ice ?

  9. barry says:

    The slowdown had been speculated as being caused by Enso variation, and more recently as heat transport into the deep ocean by due to that interannual oscillation. The other main, if short-lived speculated candidate was aerosols.

    Multi-decadal oscillations (PDO, AMO etc) were played down, but that was usually in response to critics positing that these were the cause of centennial warming, rather than oscillations around a mean. Tamino (statistics expert) discerned a lag of AMO to surface temps, and posited that AMO was largely a reflection of surface temps rather than a driver. Solar influence has been considered negligible, but this again has usually been over the long-term, not in response to short-term effects.

    I don’t remember anyone amongst the critics pointing out stratospheric water vapour as a cause of the slow-down. The fact that large volcanic eruptions can cause a temporary dimming of the sun and cooler temps for a year or two has long been acknowledged by all.

    By and large, the ‘skeptic’ community has not made much effort to describe the recent slow-down as the result of short-term patterns, but as indicative of a longer-term trend, attempting to argue that most climate change in the recent decades has been driven by natural variation. This is what “alarmists” (so-called) have taken issue with.

    Until recently (recent data) it was not clear that these factors had conspired to reduce long-term warming for a few years. It still isn’t, and speculation continues. The leading theory is that heat transport to the deep oceans is responsible (ie, “global” warming hasn’t slowed down, just surface warming). This idea has regularly been scorned by “skeptics”, with some exceptions.

    • Lionstorm says:

      I’m not sure that the hypothesis that the recent lull in surface warming is due to increased heat transport to deep oceans has earned anywhere near enough evidentiary support to be called a theory. Given the alarming paucity of data about the thermal history of the deep oceans prior to a couple decades ago, and absent a plausible, tested explanation of how/why this might be happening, I think it likely best to say we simply don’t know, but this sort of thing might be an explanation. Don’t overextend claims into areas of great uncertainty. In arguments so emotion-laden, such will be greeted with scorn by opponents.

      • Martin Lack says:

        How does global dimming caused by industrial aerosol and particulate pollution grab you. There is plenty of anecdotal evidence for it (but sadly no satellite data) and evidence that the worst periods for it having been a problem correlating with previous plateaus in an overall, multi-decadal warming trend that cannot be explained by ABC (anything but CO2) factors. See my comment at 10:37 am , below.

  10. Nullius in Verba says:

    “Its useful to go back to the IPCC’s more general statement that more than 50% of warming over the past 50 years is due to anthropogenic factors. If the actual number is 60% or 80% or something else is still a very open question.”

    Or 40%, or 150%. If you don’t know the magnitude of the background variation, and you don’t know the magnitude of the feedbacks, it is very difficult to see how the question can be answered scientifically.

    The obvious question to ask is how was the IPCC’s 90% confidence in its general statement (that it is more than 50%) calculated? What happens if you apply the same calculation to the pause?

  11. Willis Eschenbach says:

    Zeke, I find it highly doubtful that somehow, since 1955, there is a TOA imbalance enough to produce 36° of global warming … where is that energy supposed to have come from? I don’t know of even the most extreme alarmists who have made the claim that the change from GHGs is enough to produce 0.75°C of warming each and every year if there were no oceanic absorption, but perhaps I missed it.

    Do you have some kind of explanation?

    (For the record, my explanation is that the ocean data is at least an order of magnitude too uncertain to make any such claim … see my post on “Decimals of Precision“, which to my knowledge no one has falsified, for further details.)

    Many thanks,

    w.

    • Adam R. says:

      Shorter Willis:

      “The numbers lie! Except the ones I like.”

      • Willis Eschenbach says:

        Say what? I said nothing about a lie, Adam R. I asked for an explanation of the numbers. I have also provided a link to a larger explanation of my question. Not sure why that pushes your buttons … but it doesn’t leave you looking good.

        w.

  12. Larry Duncan says:

    What caused the slowdown between 1944 and 1980?
    Could we be experiencing a similar occurrence now?

    • Martin Lack says:

      Well spotted, Larry. The answers are:
      1. Industrial aerosol (nitrate/sulphate) and particulate (carbon) pollution, which prevents solar radiation from reaching ground/sea level.
      2. Yes we are.
      See my comment at 10:37 am, below.

  13. nvw says:

    Zeke,
    In your apologia for “the growing divergence between observed temperatures and those predicted by climate scientists” you list deep ocean heat storage, natural variability, volcanoes, water vapor and solar energy reduction as explanations for the pause. Only at the very end of your article do you mention an overestimate of climate sensitivity to CO2. A cynic would point out that this follows a pattern of failing to list the important causes at the start of the article and burying the bad news in the last paragraphs of the article – you wouldn’t be doing something like this would you?

    You cite the Met Office as preferring the deep ocean heat storage and natural variability as primary causes. Back in the days of AR4 official climate scientists were confident to release certainty numbers of 95% of warming being caused by humans, yet now the Met Office explains the pause as including natural variability – exactly how do you propose to explain to an increasingly skeptical public that climate scientists can properly separate natural variability with human-caused climate?

    As other commentators have mentioned , the ocean heat argument has some reasonable questions being asked of it, including why the divergence occurs with the implementation of a new measuring system (Argo floats) and some explanation of how heat can be transferred from a surface layer that is not warming down to a deeper layer that apparently is. Recognize that you not only need to find a means for transferring atmospheric heat to the deep ocean, but you need to find a method attributable to bad, bad humans since 1990 when this trend appears. Good luck with that. Collectively this blog post reads less like a scientific discussion of the data but more of an advocacy piece designed to provide talking points to defend an increasingly indefensible position.

  14. Jerry Doerr says:

    I’m an “AGW believer”, but I can’t make sense out of the graph titled “Ocean Temperatures at Depth”. First, the title says “Temperatures”, but the y-axis is calibrated in units of energy. If the y-axis should be temperature, then the graph doesn’t make sense (to me) because there is no way that all 3 lines could have the same temperature (see 1991-1992, for instance), and no way that 0-2000 could have a higher temperature than 0-300 (from 1992 onwards). If the y-axis should be energy, then the graph doesn’t make sense because there is again no way that all 3 lines could have the same energy content. (Thinking …) Ahhh, could it be that the zero-line on the y-axis represents a different absolute value for each of the 3 ranges? — so that in 1992, each of the 3 ranges had 25 zettajoules more than whatever its “zero value” is? Not sure that makes sense either, unless the 3 “zero values” were picked from different times. Also, the description for the graph says “Total ocean heat content has increased by around 170 Zettajoules since 1970″. Assuming “Total ocean” means 0-2000), the blue line goes from about -35 to +180, which is 215 rather than 170. (And to really be a whiner, how did “would of caused” get past the proofreader?)

    • Nullius in Verba says:

      You’re right, the graph is mislabeled – arguably for clarity.

      What it should have read was something like: “Evidence of an increase in ocean temperatures at depth indicated by the pentadally-smoothed estimated total ocean heat content anomaly with respect to a 1955-2013 baseline, for dates between 1970-2013.”

      The problem is that seawater specific heat capacity depends on its salinity, which is variable, so plotting average temperature anomaly, as they do for other climate variables, is potentially misleading about how much heating has been going on. So they combine temperature change and salinity measurements to get the change in specific heat content. This is then weighted by the volume of water each thermometer is observing (as I noted above, somewhat in excess of 200,000 cubic kilometres of water per thermometer today, even bigger in the past) to get a total ocean heat content anomaly. I expect the average is also inversely weighted by the uncertainty – less weight for older, less certain data at depth. That’s probably why the lines look identical up until we get global data. The total ocean heat content itself is a slightly ambiguous and fairly pointless concept (the total heat needed to heat ice from absolute zero?), only the change in heat content is of interest. So all values are offset so that (arbitrarily) the 1955-2013 mean of each is zero. Finally, since the early data is so sparse and uncertain, they apply a certain smoothing procedure that lumps together 5 years of readings in order to get a slightly less indecent sample size for each point. I gather it’s not quite as simple as a 5-year moving average, but I’m not quite sure of the details.

      I agree with you on the 170/215 point, except that given the massive uncertainties elsewhere I wouldn’t consider the difference significant.

      But never mind what it really means, just look at the graph going up!!

  15. Jerry Doerr,

    My error on the graph; the title should be Ocean Heat Content and the y-axis should refer to change in heat content (in zetajoules) relative to a 1961-1990 baseline period. The 170 number was an unfortunate relic of an older version of the graph that didn’t go as far back, and I erred in not correcting it.

    Willis,

    About 93% of the imbalance in incoming vs. outgoing solar energy ends up in the oceans per the IPCC: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch5s5-2-2-3.html. The 36 C number is from the MET Office’s report, as I mention in the article.

    Nullius in Verba,

    Levitus et al 2012 specifically separate out the 700-2000m layer in a graph in their 2012 paper (and assign error bars to both that and the 0-2000m layers). You can find a non-paywalled version here: ftp://kakapo.ucsd.edu/pub/sio_220/e03%20-%20Global%20warming/Levitus_et_al.GRL12.pdf

    • Nullius in Verba says:

      Why 1961-1990? I thought the standard for an anomaly was to use the entire period, unless you specifically want to compare with other data that uses a different baseline?

      The IPCC only say that the ocean heat estimate is more than 90% of the total observed increase in heat. I think Willis is asking how that is reconciled with the incoming/outgoing heat balance, which is far smaller.

      Thanks for the link to Levitus. But how does Levitus calculate those standard errors? He doesn’t say, and they seem unreasonably small to me, considering what is being calculated.

      Also, the 700-2000 m curve is a different shape in Levitus’s graph to yours. Levitus shows a steady rise in heat content over the entire period – about 20 ZJ between 1970 and 1990. Your only shows a gap opening up post 2000. Why the discrepancy?

    • Willis Eschenbach says:

      Thanks, Zeke. I took a look at the IPCC page you cited, but I can’t find anything about 93% of the imbalance between 1970 and the present. Near as I can tell, the page says nothing about the period 1970-present.

      More to the point, I see that you accept the claimed accuracy of the Levitus figures … I’ve shown that to be very doubtful. Perhaps you could comment on the idea that we know the average temperature of the global ocean to a depth of 2 kilometers to an accuracy of ± four thousands of a degree.

      This is greater accuracy than is claimed for the surface temperature measurements, and greater than that claimed for your BEST land temperature measurements … and since this claimed accuracy provides the core and basis of your claims, you should at least provide a mathematical explanation of that claim of such fantastic accuracy. Four thousandths of a degree … really?

      w.

    • Jerry Doerr says:

      Thanks so much to Zeke and Nullius for the clarifications. In general, since there is so much more water in 0-2000 than in 0-300, I presume that the same temperature change in the 2 would mean much more heat change in 0-2000. As for specifics, in 1991, where all 3 lines are close to the same value, can we say that 300-700 and 300-2000 were therefore at the 0-700 and 0-2000 baselines? Or can we at least compare 2 years, as from 1991 to 1992 where the lines stay together, and say that there was therefore no change over that time for 300-700 and 300-2000?

      “Pentadally” — interesting word! What is the proper pronunciation? And does it really carry any more meaning that the shorter (and more easily understood) “5-year”?

  16. Miner49er says:

    It has now become known that many of these charts were fudged by “adjustments” made by grant-seeking researchers. See http://stevengoddard.wordpress.com/data-tampering-at-ushcngiss/ .

    The truly unfortunate outcome is that the carbon controls imposed by warming alarmists will (or already have) done more damage to our energy infrastructure than several nuclear wars.

    • toby52 says:

      All the charts show identical trends, even the satellite charts of the lower troposphere temperature maintained by the AGW denier Dr Roy Spencer. Only someone of a particularly paranoid mentality could believe in a worldwide conspiracy of thousands of climate scientists.

  17. Burton Rothberg says:

    In the graphs that compare the models to actual temperature, the fit is quite good until the 1990s. Is that because the models were developed at that time? What time period on the graphs is truly an ex post forecast?

  18. Arno Arrak says:

    First I have to say that this paper is worthless because it is based upon use of faked temperature curves and incorrect theory. Those beautiful straight lines you fit to these data are entirely wrong. The eighties and nineties have been shown in ground-based temperature curves as a so-called “late twentieth century warming” with a warming rate of 0.1 degrees Celsius per decade. This warming does not exist. Those satellite temperatures of yours are incorrect too because your treatment destroys data. You must use monthly resolution and apply a semi-transparent overlay to avoid this. With correct treatment the period from 1979 to early 1997 becomes an 18 year horizontal linear section of the global temperature curve. That is longer than the current 15 year pause in temperature. Between these two linear sections is just enough room to accommodate the super El Nino of 1998 and its accompanying step warming. The step warming was caused by the unusually large amount of warm water carried across the ocean by the super El Nino. It raised global temperature by a third of a degree Celsius and then stopped. It is the only warming during the entire satellite era but most people don’t even know of its existence because it has been covered up by the fake warming of the eighties and nineties. Combined with the linear section of the eighties and nineties we now have experienced 34 years without any greenhouse warming. I discovered that fake warming while doing research for my book “What Warming?” I said so when my book came out in 2010 but nothing happened for two years. Then, suddenly, GISTEMP, HadCRUT, and NCDC in unison decided to stop showing it. This was done secretly and no explanation was given. I suggest that as a starter you discard your warming curves for the eighties and nineties and get hold of the current version of these temperatures. Better yet, use satellite values. Also discard all your graphics and start over. Your new temperature graph will have two horizontal sections, separated by the super El Nino: one in the eighties and nineties and one in the twenty-first century. You should have no trouble interpreting it. The observation of Solomon et al that water vapor has dropped has nothing to do with ENSO. Water vapor is required to drop by the Miskolczi theory of saturated greenhouse warming. Some data I have seen record a steady drop since 1948. Miskolczi theory explains the warming pause as caused by absence of the greenhouse effect. He used NOAA database of weather balloon observations that goes back to 1948 to study the absorption of infrared radiation by the atmosphere over time and found that absorption had been constant for 61 years while carbon dioxide at the same time went up by 21.6 percent. This means that the addition of this substantial amount of CO2 had no influence whatever on the absorption of IR by the atmosphere. And no absorption means no greenhouse effect, case closed. The standstill in the eighties, nineties, and the twenty-first century is thereby explained. And predictions of warming that use the greenhouse effect are invalidated. You have various miscellaneous data in addition to this that you don’t need and can discard when you come out with a revised version of your article. And, yes, it is clear that any earlier warming claimed to be greenhouse warming is misidentified by over-eager scientists trying to prove global warming.

  19. Outstanding article on Global Warming. While Global Warming is the cause,Climate Change is the Effect. As such all measures to contain Global Warming are the need of the hour at the global level.
    Dr.A.Jagadeesh Nellore(AP),India

  20. NoFreeWind says:

    You can learn more about climate by looking at this one picture and caption than by reading the 1,000 word essay above.
    http://juneauempire.com/outdoors/2013-09-13/ancient-trees-emerge-frozen-forest-tomb#.UjrGFcZOOSp

  21. Skip says:

    Did it ever occur to people that the apparent slowing in warming is due to an increase in rate of ice melting. That would happen with an increase in surface area, which would happen with an exposure of the under side of ice sheets, as would occur when they no longer extend down to ocean floor.

    We ain’t seen nothing. Look at a water heat of fusion for water curve. What we are in is just the melting plateau phase. Wait the the ice is gone. Get a clue.

  22. deon geldenhuys says:

    As yet no one has mentioned the effect that the Earths core temperature has on ocean warming . Although it may be negligible it does have an effect . Removal of gas and fossil fuels that absorb heat released by the Earths molten core will lead to a increased rate of heat diffusion towards the surface .

  23. Martin Lack says:

    Sorry to be so late coming to this particular party. But here is what I take away from this article:
    1. Depending upon which dataset you use, (GST, LST, or OST) average warming over the last 40 years has been between 0.1C/decade (OST) and 0.25C/decade (GST).
    2. This cannot be explained by random events (such as volcanic eruptions) or by those operating on shorter timescales (ocean circulation changes and sunspot/solar cycles).
    3. GCM models have failed to predict this hiatus in warming but do not appear to take into account the global dimming effect of industrial aerosols (i.e. sulphate and nitrate pollution) – because we have not been monitoring them.
    4. Given that the warming trend of the last 150 years has included other plateaus, which can be explained by periods of rapid industrial growth in the absence of pollution controls (such as that post-WW2), it would seem almost inevitable that this current hiatus will end if and when industrial pollution comes under similar control in those countries were it has been growing most recently.
    5. If and when this happens, warming is likely to be re-established faster than it was before (so we have absolutely nothing to be complacent about).
    6. In order to buy ourselves more time to reduce CO2 emissions we may have to strike a Faustian bargain and accept that our atmosphere must remain polluted by industrial aerosols in order to retain their global dimming effect.