Pacific trade winds have forced heat into the ocean for decades, now set to reverse

by John Upton, Climate Central, December 22, 2014

Chemical clues in skeletons produced by coral growing at Kiribati contain a newly discovered warning. They caution of a global climate system that’s capable of drawing decades’ worth of hoarded heat out of the Pacific Ocean, and belching it back into the atmosphere.

A cryptic chemical weather log kept by Tarawa Atoll’s stony coral in the tropical Pacific archipelago has been cracked, helping scientists explain a century of peaks and troughs in global warming — and inflaming fears that a speedup will follow the recent slowdown.

Added to a growing body of research, the newly published findings indicate that all it would take to trigger what could be a historically unparalleled period of rising global temperatures would be a shift in the winds. And that type of change in the intensity of Pacific trade winds appears to happen every 20 to 30 years or so.

Kiribati. Credit: Luigi Guarino/flickr

The coral-based findings, published Monday in Nature Geoscience, provide new historical data supporting previous modeling results and observations that point to the long-term waxing and waning pattern of the trade winds in affecting worldwide temperatures.

For the past few decades, the Interdecadal Pacific Oscillation, as the influential cycle is known, has been in what’s called a negative phase, meaning trades winds have been strong.

The growing body of scientific evidence indicates that this negative phase has played a heavy role in driving an approximately 15-year old slowdown in worldwide surface warming. It suggests that a speedup in warming may follow the next switch to the oscillation’s positive phase, when trade winds weaken, and the effects of the natural cycle exacerbate those of unnaturally increasing levels of greenhouse gases in the atmosphere.

Diane Thompson, a postdoctoral fellow at the National Center for Atmospheric Research who led the study published Monday, said we’re in a surface warming slowdown right now because the Pacific trade winds are strong. But she says that apparent bout of good fortune won’t last forever.

“When winds weaken, which they inevitably will, warming will once again accelerate,” Thompson said. “The warming caused by greenhouse gases and the warming associated with this natural cycle will compound one another.”

Strong tropical Pacific trade winds serve as an air conditioner for the world, scientists are concluding. They mix warm equatorial surface water into greater depths, and help bring cooler waters to the surface. But, like the window-mounted AC unit that cools your living room during summer, all the while heating the air outside, the strong winds aren’t cooling the planet. They’re just moving heat-wielding energy to where it will bother us less.

And, just like that window-mounted unit, the strong trade winds will eventually break down. When the global air conditioner breaks down, modeling and past experience suggest that the process will start to operate in reverse.

In February 2014, Australian and American researchers who compared ocean and climate modeling results with weather observations published findings in Nature Climate Change advancing earlier studies that explored the oscillation’s global influence. They found that the effects of strong Pacific trade winds during the past two decades were “sufficient to account” for the recent slowdown in global warming.

The slowdown refers to slower-than-expected rates at which temperatures measured on the land and at sea surfaces have been rising since the turn of the century. The amount of energy being trapped on Earth continues to rise at a quickening pace, because of the effects of the thickening cloud of greenhouse gas pollution in the atmosphere, but more of that energy than usual has been ending up in the oceans. That ocean heat — while hard for many of us to notice directly — has been driving record-breaking global temperatures, with 2014 on track to be the hottest on record, and to more vicious tropical storms.

The Australian and American researchers drew a similar comparison in their paper between strong trade winds and a slight cooling in global surface temperatures from 1940 to the 1970s.

Surface air temperature (SAT) has risen fastest during the Interdecadal Pacific Oscillation's positive phases, when trade winds have been weakest. Credit: England, M. H. et al. Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus. Nature Clim. Change 4, 222–227 (2014).

On Monday, a team of American and British scientists led by Thompson reported on their chemical analysis of a sample core bored out of coral on the most populated atoll of Kiribati, a postcard-worthy Pacific Ocean country comprising many small islands. The sample was selected for the coral's location, growing just outside the mouth of a west-facing lagoon.

The scientists measured changes over time in the amount of manganese in the skeletons produced by coral growing since the 1890s. The waters inside the lagoon are sheltered by a ring of land from the trade winds, which blow from the east. When trade winds are weak, the lagoon’s waters are churned more frequently by gusts blowing from the west. When those gusts blow in, they kick up sediment in the lagoon, releasing manganese into the water that corals can use in place of calcium to grow their skeletons.

The team also measured strontium in a coral sample taken from Jarvis Island, an uninhabited speck of land southwest of Kiribati, to gauge historical surface water temperatures. Strontium levels in coral skeletons are affected by ocean temperatures.

The scientists found that winds blowing a century ago had a similar relationship with global weather as the more recent links that have been discovered by other scientists.

“We know that winds flip-flop between periods of strong trade winds and periods of weak trade winds,” Thompson said. “Our study shows that these winds play a role in the rate of global temperature rise.”

Thompson’s team found evidence in its Kiribati coral core of weak trade winds early in the 20th century. Those winds coincided with a period, from 1910 to 1940, when global temperatures rose faster than could have been caused by greenhouse gas pollution alone, given the still-nascent state of mass industrialization.

The group also found evidence that trade winds were stronger and surface temperatures were cooler from 1940 to 1970, providing additional evidence of the relationship between the Pacific trade winds and the rates at which global temperatures have been changing.

Coral coring at Jarvis Island. Credit: Julia Core, University of Arizona

“The paper confirms the idea that tropical Pacific trade winds play a major role in global climate variability,” Matthew England, a professor at the University of New South Wales who was not involved with the coral study, said. He said its findings support those from other recent studies, including February’s Nature Climate Change paper, which was published by a team that England led.

“What’s very much new here is the attribution of the early 20th century warming to weakened Pacific trade winds,” England said.

The use of coral cores in the study was praised by Braddock Linsley, a professor at the Lamont-Doherty Earth Observatory of Columbia University who studies ancient climatic conditions by analyzing coral skeleton samples. He was not involved with the study.

Linsley said the new results were “exciting,” suggesting that the “poorly understood, rapid rise” in surface temperature from 1910 to 1940 was, in part, “related to changes in trade wind strength and heat release from the upper water column” of the Pacific Ocean.

“The mounting evidence is coalescing around the idea that decades of stronger trade winds coincide with decades of stalls or even slight cooling of global surface temperatures, as heat is apparently transferred from the atmosphere into the upper ocean,” Linsley said.

Winds over the Atlantic Ocean also appear to modulate global surface temperatures, albeit to a lesser extent than those over the Pacific Ocean. The science isn't settled on just how much those Atlantic winds, and other potential forces, have contributed to the heaving nature of global warming. "We're still at the beginning" of this field of research, Stefan Brönnimann, a University of Bern professor who investigates climate variability, said. He also wrote a 'news and views' article for Nature Geoscience assessing and describing the new research. "Pacific and Atlantic influences are not mutually exclusive."

The new study’s findings were limited by the fact that just one coral core was analyzed to serve as a proxy wind gauge — a shortcoming that the researchers aim to address. 

“Measurements of manganese in coral skeletons are difficult and time consuming,” Thompson said. “Now that we know how important they can be, we will be making more.”

Evidence of rising temperatures deep in the Pacific Ocean, even as surface temperature rise has slowed, has come in part from measurements of the rise of expanding seas. As global temperatures continue to increase, the hastening rise of those seas as glaciers and ice sheets melt threatens the very existence of the small island nation, Kiribati, whose corals offered up these vital clues from the warming past — and of an even hotter future, shortly after the next change in the winds.

http://www.climatecentral.org/news/corals-secrets-of-warming-18468

Robert Schribbler: July 2014 Shows Hottest Ocean Surface Temperatures on Record as New Warm Kelvin Wave Forms

by Robert Schribbler, from his blog, August 18, 2014

According to NOAA’s Climate Prediction Center, July of 2014 was the 4th hottest in the 135-year global temperature record. Land surface temperatures measured 10th hottest in the global record while ocean surface temperatures remained extraordinarily hot, tying July of 2009 as the hottest on record for all years on measure over the past two centuries.

Overall, land temperatures were 0.74 C above the 1950-1981 average and ocean surface temperatures were 0.59 C above the same average.

These new record or near record highs come after the hottest 2nd quarter year in the global temperature record where combined land and ocean temperatures exceeded all previous global high temperatures in the measure.

Much Hotter Than Normal July

Few regions around the globe showed cooler than average temperatures during July with zones over the east-central US, in the Atlantic just south of Greenland, and off South America in the Southern Ocean as the only regions showing cooler than normal temperatures. Record warmest temperatures ranged from Scandinavia to Iceland to Northeast Siberia, from California to Alaska to the Northeast Pacific, along a broad stretch of Pacific Ocean waters east of the Philippines and New Guinea, in pools in the North and South Atlantic Oceans off the coasts of North and South America, and in spots from Australia through the Indian Ocean to South Africa.

Land and Ocean temperature anomalies for July of 2014. Image source: NOAA’s Climate Prediction Center.

Overall, most of the surface of the Earth featured above average to record warmest conditions, while a minority of the Earth’s surface showed average or below average temperatures.

These new global heat records were reached even as slightly cooler than average waters began to up-well in the critical Eastern Equatorial Pacific region. A powerful Kelvin Wave that initiated during late winter and spring of 2014 failed to set off a summer El Nino and finally faded out, reducing heat transfer from Pacific Ocean waters to atmosphere. Even so, the ocean to atmosphere heat dump was enough to set off two record hot months for May and June and a record hot ocean surface month for July as ocean surface waters remained extraordinarily warm across many regions.

Ocean surface temperatures remained at or near record hot levels during July and August of 2014 despite a failed El Nino development in the Equatorial Pacific. The above graphic shows global water temperatures for August 18, 2014, at an extraordinary +1.13 C above the already hotter than normal 1979-2000 average. Image source: University of Maine.

New Warm Kelvin Wave Begins to Form

Though the atmosphere failed to respond to a powerful Kelvin Wave issuing across the Pacific earlier this year, stifling the development of a predicted El Nino, it appears a new warm Kelvin Wave is now beginning to form. Moderate west wind back bursts near New Guinea initiated warm water down-welling and propagation across the Pacific Ocean during July and early August. The down-welling warmth appeared to link up with warm water upwelling west of New Guinea and began a thrust across the Pacific over the past week.

As of the most recent sub-sea float analysis, anomalies in the new Kelvin wave ranged as warm as 4-5 C above average:

New warm Kelvin wave forming in the Equatorial Pacific. Image source: Climate Prediction Center.

These sub-sea temps are rather warm for an early phase Kelvin wave and may indicate another ocean to atmosphere heat delivery is on its way, despite a broader failure of El Nino to form by this summer.

Typically, strong Kelvin waves provide the energy necessary for El Nino to form. The heating of surface waters due to warm water upwelling in the Equatorial Pacific tends to set off atmospheric feedbacks that perpetuate an El Nino pattern in which waters remain warmer than average in the Central and Eastern Equatorial Pacific for many months. Without these atmospheric responses, El Nino cannot form.

During 2013 and 2014, strong Kelvin waves forming during spring time were not enough to over-ride prevailing and historically strong trade wind patterns thereby allowing El Nino to emerge.

Atmospheric ‘Hiatus’ is No Halt to Global Warming

During recent years, scientific analysis has confirmed that a negative Pacific Decadal Oscillation together with record strength trade winds has suppressed El Nino formation and ocean to atmosphere heat transfer, leading to a temporary slow down in atmospheric temperature increases even as world ocean temperatures spiked.

Global ocean heat content for 0-2000 meters of depth shows inexorable upward trend despite the so-called atmospheric warming hiatus. Image source: NOAA Ocean Heat Content.

This natural variability, which typically lasts for 20-30 years, began around the year 2000 and has continued through 2014. During such periods of negative PDO, we would expect rates of atmospheric warming to cease or even to go slightly negative. Unfortunately, even though PDO has been negative for nearly 15 years (a phase that during the 1940s to 1970s drove 0.35 C of transient atmospheric cooling against an overall larger warming trend), we have still seen atmospheric warming in the range of 0.1 C per decade.

This is bad news. For as ocean heat content is spiking, the transfer from atmosphere to ocean has not been enough to even briefly cut off atmospheric warming. And at some point, the oceans will deliver a portion of their latent heat back to the atmosphere, causing an even more rapid pace of temperature increase than was seen during the 1980s through 2000s period.

In other words, we’ve bent the cycle of natural variability to the point where we see warming, albeit slower warming, during times when we should have seen atmospheric cooling. And all indicators — radiative balance measured by satellite, deep ocean water temperatures, glacial melt, and atmosphere — show ongoing and inexorable warming.

http://robertscribbler.wordpress.com/2014/08/18/july-2014-shows-hottest-ocean-surface-temperatures-on-record-as-new-warm-kelvin-wave-forms/

Dr. Richard Rood talks on the changes outside natural variability wrt ENSO, and other cyclical oscillations

by Peter Sinclair, Climate Crocks, March 8, 2014

Dr. Richard  Rood is a veteran NASA Atmospheric Scientist, currently teaching at the University of Michigan’s College of Atmospheric, Oceanic, and Space Sciences.

Dr. Rood also posts regularly on Dr. Jeff Master’s Weather Underground.

I sat down with Dr. Rood not long ago to talk about developments in climate science. This is a small, but significant piece of the conversation, in light of this week’s announcement of a heightened alert for a developing El Nino event in the Pacific.

http://climatecrocks.com/2014/03/08/dr-richard-rood-on-atmospheric-cycles/

Benjamin Santer et al., “Human and natural influences on the changing thermal structure of the atmosphere”

Fact sheet for “Human and natural influences on the changing thermal structure of the atmosphere” [1] [Sorry, this is screwed up -- had to copy from a pdf file, and some things did not make it.  Anyone wanting the pdf should send an email to me at apaixonada.por.rio@gmail.com ]
 
by Benjamin D. Santer, Jeffrey F. Painter, Céline Bonfils, Carl A. Mears, Susan Solomon, Tom M.L. Wigley, Peter J. Gleckler, Gavin A. Schmidt, Charles Doutriaux, Nathan P. Gillett, Karl E. Taylor, Peter W. Thorne, and Frank J. Wentz

To be published in Proceedings of the U.S. National Academy of Sciences, Online Early Edition,
Embargoed until September 16, 2013, 3:00 p.m., U.S. Eastern Time

Summary: Observational satellite data and the computer model response to human influence have a common pattern of changes in the thermal structure of the atmosphere. The key features of this pattern are global-scale tropospheric warming and stratospheric cooling over the 34-year satellite temperature record. We show that current climate models are highly unlikely to produce this distinctive signal pattern by internal variability alone, or in response to naturally forced changes in solar output and volcanic aerosol loadings. We detect a “human influence” signal in all cases, even if we test against natural variability estimates with much larger fluctuations in solar and volcanic influences than those we have observed since 1979. Our results highlight the very unusual
nature of observed changes in atmospheric temperature. [2]

Signal-to-noise analysis: A brief primer

Our PNAS paper describes results from a climate change detection and attribution study, in which we investigate the causes of temperature changes in Earth’s atmosphere. The focus of our study is on the vertical structure of atmospheric temperature change – in other words, on patterns of change that vary with latitude and with altitude. These patterns provide information about temperature changes in the troposphere and the stratosphere (see below):

Figure 1: This figure is from Synthesis and Assessment Product 1.1 of the U.S. Climate Change Science Program (Karl et al., 2006 1). It shows the approximate pressure and altitude boundaries of the troposphere and the stratosphere. The multi-colored line indicates the average dependence of temperature on altitude.

We rely on estimates of atmospheric temperature change from satellites and from computer models of the climate system (“climate models”). The satellite observations are made available by two different research groups; the simulation output is from as many as 20 of the models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP-5).

In the real world, many factors – both human and natural – are simultaneously acting on the climate system. We do not have a “control Earth,” on which there are no human-caused changes in atmospheric levels of greenhouse gases.

With climate models, however, it is possible to perform such controlled simulations. For example, we run climate models with our best estimates of the purely natural changes in volcanic activity and the Sun’s energy output over the last 1,000 years [2]. We can then ask whether these computer model estimates of the “world without us” produce climate-change patterns similar to the ones we have actually observed since 1979 [3]. The availability of “world without us” results allows us to examine – and to test – persistent claims that observed changes in climate are primarily due to natural causes, like an increase in solar irradiance, or the “recovery” of atmospheric temperature after large volcanic eruptions.

Our paper also considers simulations in which only human influences act on the climate system, and there are no changes in solar or volcanic influences. Examples of human influences include changes in atmospheric levels of greenhouse gases and particulate pollution. Such “human effects only” simulations are used to estimate the climate-change signal (also called the “fingerprint”) that we expect to see as a result of human activities [4].

Finally, the model simulation output gives us estimates of the year-to-year and decade-to-decade “noise” of internal climate variability, arising from such natural phenomena as the El Niño/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). This internal variability (which we refer to as VINT) is unrelated to changes in the Sun, or to changes in volcanic activity.

We use a standard fingerprint method [5] to search for the model “human effects only” signal pattern [6] in the satellite observations. First, we quantify the changing strength of the signal pattern in observations. We then estimate the changes in signal strength that are caused by purely natural changes in climate.

Our signal detection method allows us to calculate so-called signal-to-noise (S/N) ratios. If the observed patterns of atmospheric temperature change are becoming increasingly similar to the model “human influence” fingerprint, and if the natural variability patterns are dissimilar to the fingerprint pattern, the S/N ratios will be large. S/N ratios larger than 3 show that there is highly significant correspondence between the model fingerprint and satellite data, and that natural climate variability is unlikely to explain this pattern match.

Our S/N ratios depend on the length of the temperature record. We focus on S/N ratios calculated over the full, 34-year period of the satellite data (1979 to 2012). Looking at long, multi-decade periods of record helps to reduce the impact of large, year-to-year natural variability, and more clearly reveals any underlying signal of human influences on climate. [4]

Question 1: What’s new about this research?

Two aspects are novel.

First, virtually all detection and attribution studies to date use computer model estimates of VINT (natural internal variability; see definition in the “primer”) to determine whether a human-caused climate change signal can be detected in observations. Here, we look at the signal detection issue in several different ways. We try to detect a human influence signal not only against the background noise of internal climate variability, but also against the natural variability information from the CMIP-5 “world without us” simulations. These simulations [7] give us estimates of the “total” natural variability of the climate system, VTOT, which arises from the combined effects of internal variability, fluctuations in the Sun’s energy output, and changes in the levels of volcanic particulates in the atmosphere. 

Second, most previous detection and attribution studies with temperature changes in a “slice” through the atmosphere [8] used results from only one or two climate models, and from a single observational temperature data set. We consider results from up to 20 climate models, and from two different observational data sets [9]. This enables us to determine whether previous claims of the positive detection of a human fingerprint in satellite temperature records are sensitive to current uncertainties in models and observations. We find that prior “positive detection” claims [10] are robust to the model and observational uncertainties considered here.

Question 2: What are your key findings?

In the satellite data, we’ve observed a pattern of large-scale warming of the lower atmosphere (the troposphere) and cooling of the stratosphere. Computer model estimates of the “human influence” fingerprint are broadly similar to the observed pattern (see Fig. 2). In sharp contrast, model simulations of internal and total natural variability cannot produce the same sustained, large-scale warming of the troposphere and cooling of the stratosphere. So in current climate models, natural causes alone are extremely unlikely to explain the observed changes in the thermal structure of the atmosphere.

This is true even if our signal detection approach uses total natural variability estimates from before the period of satellite temperature observations [11]. The “world without us” simulations sample changes in 5 volcanic and solar activity over the last 150 to 1,000 years. Many of these eruptions and solar irradiance changes are much larger [12] than the volcanic and solar changes we have observed since 1979. A remarkable aspect of our results is that even in this “worst case” signal detection situation, when we make signal identification difficult by using very large estimates of total natural variability, we still obtain consistent detection of a “human influence” fingerprint. [12] Examples include the major eruptions of Krakatoa in 1883 and Kuwae in 1452, and the large estimated changes in solar irradiance around the time of the Maunder Minimum (from roughly 1645 to 1715).
 
Satellite observations (Remote Sensing Systems)

Climate models (average of “human influence” simulations)

Figure 2: The vertical structure of changes in atmospheric temperature in satellite observations (top panel) and in computer model simulations performed as part of phase 5 of the Coupled Model Intercomparison Project (CMIP-5; bottom panel). As described in the PNAS paper, both panels provide a vertically smoothed picture of atmospheric temperature change. Information from only three atmospheric temperature layers – the lower stratosphere (TLS), the mid- to upper troposphere (TMT), and the lower troposphere (TLT) was used in generating the two plots. We show temperature changes in this “vertically smoothed” space because satellite-based estimates of atmospheric temperature change are available for TLS, TMT, and TLT, and because our signal detection study is performed with the zonally-averaged temperature changes for these three layers. All temperature changes are in the form of linear trends (in degrees Celsius) over the 408-month period from

Question 3: Is there evidence that the models you’ve used here systematically underestimate the total natural variability of atmospheric temperature?

If the CMIP-5 models analyzed here systematically underestimated the size of observed “total” natural variability, our S/N ratios would be spuriously inflated. In our previous work [13], we found no evidence that this is the case. To test the fidelity with which models simulate observed total natural variability, we compared modeled and observed temperature fluctuations on decadal timescales [14]. On average, the CMIP-5 models substantially overestimate the size of observed tropospheric temperature variability, suggesting that our S/N ratios are probably too conservative [15]. 

Question 4: Are there remaining problems?

Yes. Although we found a “pattern match” between the modeled and observed vertical structure of atmospheric temperature changes, most models have problems capturing the size of the observed changes. On average, the CMIP-5 models underestimate the observed cooling of the lower stratosphere, and overestimate the warming of the troposphere [16]. Some scientists have claimed that there is only one possible interpretation of such differences – that models are too sensitive to greenhouse gas increases. Such claims are incorrect. There are multiple interpretations of differences between modeled and observed temperature changes. Other possible explanations include: (A) residual errors in the observations; (B) an unusual sequence of natural climate fluctuations in the observations; and (C) the neglect or inaccurate specification of key “forcings” in model simulations of historical climate change. 

Results presented in our PNAS paper and elsewhere suggest that forcing errors make an important
contribution to the biases in model temperature trends [17].

References




1 Karl, T.R., S.J. Hassol, C.D. Miller, and W.L. Murray (eds.), 2006: Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences. A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. National Oceanic and Atmospheric Administration, National Climatic Data Center, Asheville, NC, USA, 164 pp.  

2 Such simulations lack any human-caused changes in greenhouse gases or particulate pollution.

3 The period over which we have been monitoring atmospheric temperature from space.

4 Like the burning of fossil fuels.

5 Our fingerprint method has been successfully employed for the identification of human effects on surface and atmospheric temperature, upper ocean heat content, the height of the tropopause (the boundary between the troposphere and stratosphere), and atmospheric moisture over oceans.

6 As noted above, the signal is the latitude/altitude pattern of atmospheric temperature change.  

6 January 1979 to December 2012. The model results are an average of “human influence” simulations performed with 8 different CMIP-5 models. The y-axis shows atmospheric pressure (in hectoPascals).  

7 Which are referred to as “NAT” and “P1000” in our paper.

8 In other words, at the pattern of temperature change with latitude and altitude.

9 One of the two observational groups (Remote Sensing Systems in Santa Rosa) explored uncertainties in the
processing steps used to create the observations, and developed a set of four hundred plausible estimates of
observed atmospheric temperature change. We used this “ensemble of observations” in our detection study.

10 See, e.g., Santer, B.D., K.E. Taylor, T.M.L. Wigley, T.C. Johns, P.D. Jones, D.J. Karoly, J.F.B. Mitchell, A.H. Oort, J.E. Penner, V. Ramaswamy, M.D. Schwarzkopf, R.J. Stouffer, and S. Tett, 1996: A search for human influences on the thermal structure of the atmosphere. Nature, 382, 39-46.

11 The last 34 years. 

13 Santer, B.D., J.F. Painter, C.A. Mears, C. Doutriaux, P. Caldwell, J.M. Arblaster, P.J. Cameron-Smith, N.P. Gillett, P.J. Gleckler, J. Lanzante, J. Perlwitz, S. Solomon, P.A. Stott, K.E. Taylor, L. Terray, P.W. Thorne, M.F. Wehner, F.J. Wentz, T.M.L. Wigley, L.J. Wilcox, and C.-Z. Zou, 2013: Identifying human influences on atmospheric temperature. Proceedings of the National Academy of Sciences, 110, 26-33, doi: 10.1073/pnas.1210514109.

14 This analysis used digitally-filtered temperature data; the filtering highlighted temperature variability on timescales ranging from 5 to 20 years.

15 In the lower stratosphere, the size of modeled and observed decadal variability is (on average) very similar.

16 Particularly in tropics and Southern Hemisphere (see Fig. 2).

17 Note that these biases have relatively small impact on the S/N results presented here. This is because the searched-for fingerprint patterns are normalized – thus reducing the effect of biases in the size of modeled temperature changes.

Dana Nuccitelli: The Pacific Ocean fills in another piece of the global warming puzzle

Evidence continues to mount that the slowed warming of global surface temperatures is mainly due to changes in the oceans

by Dana Nuccitelli, Climate Consensus - The 97%, The Guardian, September 3, 2013

A new study published in the journal Nature incorporates temperature changes in the tropical Pacific Ocean into an advanced climate model, and finds that the model can reproduce observed global surface temperature changes remarkably well.

 

This graph shows the good match between temperatures in the Nature paper model (in red) and measured temperatures (in black). Just accounting for human and solar climate influences doesn't reproduce the recent surface warming slowdown (in purple). 

  Importantly, as authors Yu Kosaka and Shang-Ping Xie from the Scripps Institution of Oceanography explain, accounting for the changes in the Pacific Ocean allows the model to reproduce the slowed global surface warming over the past 15 years. It also accurately reproduces the regional and seasonal changes in surface temperatures, which adds confidence that their results are meaningful.

Our results show that the current hiatus is part of natural climate variability, tied specifically to La-Niña-like decadal cooling … For the recent decade, the decrease in tropical Pacific sea surface temperature has lowered the global temperature by about 0.15 degrees Celsius compared to the 1990s.

Despite only covering 8.2% of the Earth's surface, these results suggest that the tropical Pacific Ocean plays a major role in short-term changes in the average global surface temperature. And over the past 15 years, it's offset most of the global surface warming from the increased greenhouse effect.

These results are broadly consistent with several other important recent papers investigating the role of the oceans in global warming. For example, the model used in this study finds that the overall heating of the planet has not slowed when the warming of the oceans are taken into account, as studies led by John Abraham, myself, and several others have also concluded.
Research led by Gerald Meehl has similarly focused on the importance of the Pacific Ocean in short-term global surface temperature changes. His climate model predicts that there will be decades when surface temperature changes are relatively flat because more heat is transferred to the deep oceans, precisely as we have observed over the past decade. Meehl discussed the Kosaka & Xie study with Carbon Brief,

This paper basically confirms, with a novel methodology, what we originally documented in our Nature Climate Change paper in 2011 and followed up with in our Journal of Climate paper ... We went beyond [the new paper] to show that when the tropical Pacific was cool for a decade ... more heat is mixed into the deeper ocean, something the new paper doesn't address.

Kevin Trenberth, who co-authored several of these important ocean studies, has likewise pointed to the important role of the Pacific Ocean in transferring more heat to the deep oceans.

The cause of the shift is a particular change in winds, especially in the Pacific Ocean where the subtropical trade winds have become noticeably stronger, changing ocean currents and providing a mechanism for heat to be carried down into the ocean. This is associated with weather patterns in the Pacific, which are in turn related to the La Niña phase of the El Niño phenomenon.

Research by Masahiro Watanabe of the Japanese Atmosphere and Ocean Research Institute has also suggested that the transfer of heat to the deep oceans and corresponding slowed global surface warming is related to changes in the Pacific.
Thus the scientific picture is becoming increasingly clear that the Pacific Ocean has played a large role in the slowed surface warming in recent years, but the warming of the oceans and planet as a whole have continued unabated. Thus the slowed surface warming is very likely to be a temporary effect, similar to the flat global surface temperatures between 1940 and 1970 when the Pacific Ocean was in another cool cycle.

Although it may be a natural reaction to hope that the recent slowed surface warming suggests that climate change isn't an imminent threat, the scientific evidence simply does not support such optimism. Climate scientist Judith Curry, who I recently criticized for failing to grasp the concept of climate risk management, recently articulated this rosy view on her blog. By focusing at the model simulation data specifically from 1975 to 1998, Curry incorrectly argued that the study supports the position that global warming is mostly natural.

There are a few major problems with this argument. Between 1975 and 1998 when the Pacific Ocean was in a warm phase of its cycle, it accounted for some of the observed global surface warming (though less than Curry asserts; about 30%). But the thing about cycles – they're cyclical. Focusing on the warm cycles while ignoring the cool cycles is an example of classic cherry picking.

If we look at the full record, for both 1950–2012 and 1970–2012 (the Pacific Ocean temperature data are most reliable since 1970), according to the model used in this study, the Pacific Ocean has actually had a slight overall cooling effect on global surface temperatures. It's also important to note that this cycle is just moving heat around between oceans and air – the overall warming of the planet has remained steady and rapid.

Thus the body of scientific research consistently shows that global warming continues unabated, and is predominantly human-caused. The Pacific Ocean has likely played a significant role in the slowed global surface warming over the past 15 years by transferring more heat to the deep oceans, but that change appears to be a temporary one. When the Pacific Ocean enters its next warm cycle, we're likely to see a rapid warming of global surface temperatures. If we continue to use the temporary slowed surface warming as an excuse to delay climate action, we'll regret that decision when the surface warming kicks in with a vengeance.

http://www.theguardian.com/environment/climate-consensus-97-per-cent/2013/sep/03/global-warming-pacific-ocean-puzzle-piece

MORE MUST READ TIDBITS: Kevin Trenberth on ocean heat content, changing trade winds, mechanism for heat to be carried down deeper in the ocean

Global warming is here to stay, whichever way you look at it

by Kevin Trenberth, University Corporation for Atmospheric Research, The Conversation, May 22, 2013

Has global warming stalled? This question is increasingly being asked because the local weather seems cool and wet, or because the global mean temperature is not increasing at its earlier rate or the long-term rate expected from climate model projections.

The answer depends a lot on what one means by “global warming.” For some it is equated to the “global mean temperature.” That keeps going up but also has ups and downs from year to year. More on that shortly.

Why should it go up? Well, because the planet is warming as a result of human activities. With increasing carbon dioxide and other heat-trapping greenhouse gases in the atmosphere, there is an imbalance in energy flows in and out of the top of the atmosphere: the greenhouse gases increasingly trap more radiation and hence create warming. “Warming” really means heating, and this can exhibit itself in many ways.

Rising surface temperatures are just one manifestation. Melting Arctic sea ice is another. So is melting of glaciers and other land ice that contribute to rising sea levels. Increasing the water cycle and invigorating storms is yet another. But most (more than 90%) of the energy imbalance goes into the ocean, and several analyses have now shown this. But even there, how much warms the upper layers of the ocean, as opposed to how much penetrates deeper into the ocean where it may not have much immediate influence, is a key issue.

The ups and downs of global temperature

My colleagues and I have just published a new analysis showing that in the past decade about 30% of the heat has been dumped at levels below 700 meters, where most previous analyses stop.

The first point is that this is fairly new; it is not there throughout the record. The cause of the shift is a particular change in winds, especially in the Pacific Ocean where the subtropical trade winds have become noticeably stronger, changing ocean currents and providing a mechanism for heat to be carried down into the ocean. This is associated with weather patterns in the Pacific, which are in turn related to the La Niña phase of the El Niño phenomenon.

The second point is that we have found distinctive variations in global warming with El Niño. A mini global warming, in the sense of a global temperature increase, occurs in the latter stages of an El Niño event, as heat comes out of the ocean and warms the atmosphere. The ocean’s temperature is also affected by volcanic eruptions, which also affect the perceptions of global warming.

Normal weather also interferes by generating clouds that reflect the sunshine, and there are fluctuations in the global energy imbalance from month to month. But these average out over a year or so.

Another prominent source of natural variability in the Earth’s energy imbalance is changes in the sun itself, seen most clearly as the sunspot cycle. From 2005 to 2010 the sun went into a quiet phase and the warming energy imbalance is estimated to have dropped by about 10 to 15%.

Some of the penetration of heat into the depths of the ocean is reversible, as it comes back in the next El Niño [whenever that is -- no signs of one for the rest of this year]. But a lot is not; instead it contributes to the overall warming of the deep ocean. This means less short-term warming at the surface, but at the expense of greater long-term warming, and faster sea level rise. So this has consequences.

Global warming is here to stay

Coming back to the global temperature record, one thing is clear. The past decade is by far the warmest on record. Human-induced global warming really kicked in during the 1970s, and warming has been pretty steady since then.

While the overall warming is about 0.16 °C per decade, there are three 10-year periods where there was a hiatus in warming, as the graph above shows, from 1977 to 1986, from 1987 to 1996, and from 2001 to 2012. But at each end of these periods there were big jumps. We find exactly the same sort of flat periods in climate model projections, lasting easily up to 15 years in length.

Focusing on the wiggles and ignoring the bigger picture of unabated warming is foolhardy, but an approach promoted by climate change deniers. Global sea level keeps marching up at a rate of more than 30 cm per century since 1992 (when global measurements via altimetry on satellites were made possible), and that is perhaps a better indicator that global warming continues unabated. Sea level rise comes from both the melting of land ice, thus adding more water to the ocean, plus the warming and thus expanding ocean itself.

Global warming is manifested in a number of ways, and there is a continuing radiative imbalance at the top of atmosphere. The current hiatus in surface warming is temporary, and global warming has not gone away.

Kevin Trenberth does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.


This article was originally published at The Conversation. Read the original article.

http://theconversation.com/global-warming-is-here-to-stay-whichever-way-you-look-at-it-14532

RealClimate: The answer is blowing in the wind: The warming went into the deep end [of the oceans]

by rasmus, RealClimate, April 26, 2013

 

There has been an unusual surge of interest in the climate sensitivity based on the last decade’s worth of temperature measurements, and a lengthy story in the Economist tries to argue that the climate sensitivity may be lower than previously estimated. I think its conclusion is somewhat misguided because it missed some important pieces of information (also see Skeptical Science’s take on this story here).

The ocean heat content and the global mean sea level height have marched on.

 

While the Economist referred to some unpublished work, it missed a new paper by Balmaseda et al. (2013) which provides a more in-depth insight. Balmaseda et al. suggest that recent years may not have much effect on the climate sensitivity after all, and according to their analysis, it is the winds blowing over the oceans that may be responsible for the ‘slow-down’ presented in the Economist.

It is well-known that changes in temperature on decadal time scales are strongly influenced by natural and internal variations, and should not be confused with a long-term trend (Easterling & Wehner 2009, Foster & Rahmstorf 2011).

An intensification of the trades has affected surface ocean currents called the subtropical gyres, and these changes have resulted in a predominance of the La Nina state. The La Nina phase is associated with a lower global mean temperature than usual.

Balmaseda et al.’s results also suggested that a negative phase of the Pacific Decadal Oscillation (PDO) may have made an imprint on the most recent years. In addition, they found that the deep ocean has warmed over the recent years, while the upper 300 m of the oceans have ‘stabilised.’ 
 
The oceans can be compared to a battery that needs to be recharged after going flat. After the powerful 1997-98 El Nino, heat flowed out of the tropical oceans in order to heat the atmosphere (evaporative cooling) and the higher latitudes. The warming resumed after the ‘deflation,’ but something happened after 1998: since then, the warming has involved the deep ocean to a much greater extent. A weakening of the Atlantic Meridional Overturning Circulation (MOC) may have played a role in the deep ocean warming.

The recent changes in these decade-scale variations appear to have masked the real accumulation of heat on Earth.

The new knowledge from this paper, the way I read it, is the revelation of the role of winds for vertical mixing/diffusion of heat in a new analysis of the world oceans. Their results were derived through a set of different experiments testing the sensitivity to various assumptions and choices made for data inclusion and the ocean model assimilation set-up.

The analysis involved a brand new ocean analysis (ORAS4, Balmaseda et al. 2013) based on an optimal use of observations, data assimilation, and an ocean model forced with state-of-the-art description of the atmosphere (reanalyses).

By running a set of different experiments with the ocean model, including different conditions, such as surface winds and different types of data, they explored which influence the different conditions have on their final conclusion.

The finding that the winds play a role for the state of the warming may not be surprising to oceanographers, although it may not necessarily be the first thing a meteorologist may consider.

http://www.realclimate.org/index.php/archives/2013/04/the-answer-is-blowing-in-the-wind-the-warming-went-into-the-deep-end/#more-15062