Arguments
Global warming is here to stay, whichever way you look at it
Posted on 30 May 2013 by Kevin Trenberth
By Kevin Trenberth, University Corporation for Atmospheric Research
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 700m, 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. 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 ten-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 30cm 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.
Is it still the case that we can't really measure the Earth's energy imbalance directly, but have to infer it from the rate of heat accumulation in the oceans?
Cheers...
Icarus, no that hasn't been true for many years now. I think Harries 2001 was one of the first studies using direct measurements to show the imbalance.
Thanks CB. I understand that the change in spectrum of OLR has been observed and that it validates the modelled changes in the greenhouse effect, but I'm not sure that's quite the same thing as directly measuring the energy imbalance.
Icaraus @1,3, there are satellite observations of both the Outgong Longwave Radiation (OLR) from Earth and the incoming shortwave radiation from the Sun. These are very accurate for changes in magnitude of the radiation, but their accuracy for the absolute level of radiation is substantially less. Consequently calculating the energy balance from the satellite data leaves an error margin several times larger than the observed effect.
SFAIK, that does leave changes in surface heat content (including oceans, atmosphere, cryosphere, soil heat contents) along with minor effects such as change wind and wave energy, change in stored chemical energy in the biosphere as the alternative direct measure of the top of atmosphere energy imbalance. These are not completely measured, but using a scaled 0-2000 m OHC will result in relatively small error bars.
As an aside, I suspect that the well measured changes in OHC from Argos could be used to calibrate the satellite data and gain accurate measurements of the energy imbalance over the satellite period.
I and others have been inserting the word "surface" to identify the 2-3% of heating that goes into the global surface atmospheric temperature record which allows us to reserve global warming, or heating for the whole 100% of energy trapped by the global energy imbalance. The continued use of "Global mean temperature" and the like without explicit reference to surface temperature leaves the onlooker free to misunderstand the situation, and denialists with an avenue for misrepresentation as we all witness.
Has anyone actually genearted a graph of global heat content? Admittedly the instrumental record is a lot shorter than the atmospheric surface temperature record but there must still be a useful amount of data to infer it. I expect the curve will be fairly smooth and will match the smoothed keeling curve.
Thank you for the article, Dr. Trenberth. I would like to use it to help me counter the deniers' hyperfocus on surface atmospheric temperatures. But frustratingly, the article undermines its own point by having the diagram labeled "Global Mean Temperature" instead of "Global Surface Atmospheric Temperature." Likewise, the paragraph after the diagram does not specify "surface atmospheric." Will you change those, please?
Actually, "atmospheric temperature" is preferable to surface temperature. The latter term is used to differentiate from tropospheric temperature. Atmospheric temperature is less ambiguous. So: "global mean atmospheric temperature"
I think it should be mentioned that of the three 'hiatus' decades mentioned in the post, only the present one doesn't include a large cooling volcanic eruption (El Chi'chon 1983, Pinatuba 1991).
But do we need a volcano for a 'hiatus' decade? My back-of-fag-packet calculations of what has been happening within the last decade puts the drop in solar energy at about equal to the rise in GHG forcing over the period, and the increase in ice melt from ice caps and sea ice also about equal energy-wise to the absent surface warming.
Dr. Trenberth writes: There are three ten-year periods with a hiatus warming: 1977 to 1986; 1987 to 1996; 2001 to 2012. Remarkably, because there is not a year between 1986 and 1987. Was there a warming hiatus between 1977 and 1996?
No, in fact (looking at the graph) there was a strong rise in temperature in that period. Dr Trenberth is apparently wrong.
Wallenburg... You can clearly see the three 10 year hiatus periods identified in the graph.
Wallenburg,
Look at the lines on the graph. The flat areas you question run to the start of 1986 and from the end of 1987. The temperature rose rapidly during the start of 1987. You look like you are just arguing to argue when you question Dr. Trenberth in this way, expecially since the graph clearly shows the hiatus periods that he is referring to.
Dr. Trenberth: thank you for your contribution. It helps us to keep our discussions on track when scientists tell us what they think.
I think the next few years are likely to be pivotal with regards to the whole climate issue. My takeaway from this article from Dr Trenberth suggests that we're likely at the end of a 15 year hiatus, and should anticipate another rapid rise in global surface temps.
noelfuller:
I believe Skeptical Science has produced one or two versions of just such a graph over the years.
I think one very interesting point Dr. Trenberth makes is that scientists are documenting new developments in the Pacific, which are connected to the El Nino/La Nina/ENSO cycle. My sense is that the extra energy makes models of cyclical events like the ENSO cycle, which are developed based on data gathered at earlier, lower-energy times, at least potentially suspect. It may be that we are headed for a significant old-fashioned El Nino event in the near future, but on the other hand it may be that the increase in heat content will result in a change to the way the ocean gives up its extra heat that might not fit the way we have come to define the El Nino phase of ENSO.
If the wind patterns have changed and have pushed energy into deeper waters, it seems completely plausible to me that the location/duration/intensity of any future warm water upwelling might also change, which would in turn make further significant changes in the climate likely.
I just read John Cook's update of "It's Cooling" and most of the associated discussion over 2009-2011. I was struck in that discussion by the unsettled business of how OHC below 700m was measured. I was particularly confused by the discussion around how good the Argo data are and the different ways the data is massaged. Is there a good place I can do to get the latest on how the deep sea heat content science is going?
Let me mention that I have also read Balmesda, Trenberth, and Kallen in their accepted for publication article "Distinctive climate signals in reanalysis of global ocean heat content." They make a point of comparing the OHC record with and without Argo data, and they get slightly less warming without Argo. I can't tell if the Argo data are synonymus with "data below 700m". Please help.
[DB] See here for a discussion of BTK13.
tcflood @16, details on the operaton of Argo floats can be found here. As you will note, the Argo floats measure temperature from 0-2000 meters in depth. Other systems are used for temperature (and hence OHC) measurements below that depth. Some continue to be used above 2000 m, but they are nowhere near as numerous as the Argo floats.
For actual OHC data, the NOAA National Oceanographic Data Center (NODC) is the best first stop.
noelfuller and Composer99: There is also an updated heat content graph. You might also like the Global Warming Components infographic.
For readers who haven't visited the SkS Climate Graphics page in awhile, they have been updated by adding informative captions, and links to SkS material that references each graphic. So, browsing the Climate Graphics page provides an informative inroad into the wealth of SkS material.
(-snippedy-snip-snip-)
[DB] More Doug Cotton sock puppetry. Privileges revoked, again.
Hrmmm . . . appears to b a copy/paste and sounds awfully familiar. Where have I heard this before . . .
An evident lack of Climate_Science_Research @19 claims that:
In fact the IPCC states any thing so silly as to claim that a column of air in the troposphere would be isothermal were it not for the greenhouse effect. Nor, to my knowledge, does any scientist associated with the IPCC scientist nor Spencer. Certainly no climate physicist would be so silly. Rather, they state the opposite, ie, that without a non-isothermal troposphere there would be no greenhouse effect.
The greenhouse effect does influence the lapse rate in the troposphere, but only in a small way. It would cause it to be much larger (ie, much greater reduction of temperature with altitude) except for convection. If the slope exceeds a certain value, that generates convection which brings it down to that value (the dry adiabatic lapse rate). If the air is moist, the release of latent energy of vaporization as the water vapour condenses further reduces the lapse rate. These factors, then, shift the lapse rate from what it would be in their absence; but the troposphere would cool with altitude even in their absence.
Having given a wrong account of the history and state of knowledge of planetary physics, he says,
But that is absurd. It is equivalent to saying that knowing the slope of one line is sufficient for knowing its intersect with the x-axis.
The lapse rate is indeed a gradient (slope) and would exist without a green house effect. But for any slope there are an infinite number of possible intersects with the x-axis. Only once you specify the co-ordinates of at least one point on the line does the slope tell you the intercept. Thus when the x-axis is temperature and the y-axis is altitude, the lapse rate is represented by any line having the same slope on the graph. But only when we find the temperature at a given point on such a line do we determine the intercept with the x-axis (surface temperature). And, of course, the temperature that determines the surface temperature is governed by radiative physics.
I recommend that the ill named Climate_Science_Research actually read the last link, and take up the subject there (where it is on topic) rather than here (where it is not).
DSL, classic Sky Dragon of course. Invents a greenhouse theory they know to be false, and kill it - then assert without warrant that the theory they have shown to be false is the actual theory used by climate scientists.
Well with so many other sites banning him, he must be getting desparate - just not desparate enough to read a physics textbook.
Yah, but it seems like I saw something almost identical to this over at SoD a year ago or so. About eight comments of interchange between the regulars and this person, and off s/he went in a huff. I guess we'll see if CSR is a drive by.
Suddenly, all the pyrgeometers in the world stop working. Puckrin and Evans are taken out in handcuffs. Watts posts that he knew it all the time . . . he was working on a paper, in fact. It was going to be a blockbuster . . .
Of course! Cottonballs returns!
@19... "(-snippedy-snip-snip-)"
I do believe you enjoyed that, DB.
owenamoe 7
I think we have to have a reference to where the temperature of some part of the atmosphere is measured and because that is generally where we can easily reach to place a thermometer in a stable position we are measuring temperature within a few metres of the soil or sea surface. I understand that we have to get up a wee bit when we want to get air temperature over ice. If we left out the reference to surface we would be in the rather silly position of implying the measured temperature was the average temperature of the entire troposphere say. We know the air gets colder as we gain altitude. By surface atmospheric temperature we are of course not talking about soil temperatures or sea surface temperatures. This measure is in some ways analogous to sea ice extent. Both measures exist because we can measure them with what we have. Sea ice extent is also subject to which way the wind blows, and I suspect to how thin the ice is. By far the best measure is sea ice volume but that is much harder. Similarly surface atmospheric temperature is also a representative measure. the easiest to record with the longest instrumental history, interestingly influenced by all the agencies that shove heat about in the ocean but by far the most telling figure if only we could measure it as readily is heat content.
LarryM (18) and Composer99 (13)
Thanks for the references, I have seen them before and the one somewhere with all the circles, and found them very helpful. However, they apportion heat content rather than indicate total heat content as a line in kilojoules
which is what I am looking for. I would expect the line to be free of internal acean variability, but wobbling a bit with aerosol, cloud and solar variation but overcoming the ocean lag effect relative to surface atmospheric temperatures. Greenhouse gas buildup would be the dominant influence on the curve. However, I suspect that this is rather hard to achieve with precision.
Have you guys seen this paper by Q.-B. Lu at the U of Waterloo?
http://arxiv.org/ftp/arxiv/papers/1210/1210.6844.pdf
He claims to have good statistical evidence that both ozone depletion and global warming come almost exclusively from halogenated compounds.I got it off Curry's site, so even if it is 100% bogus, I suppose we will be hearing about it from now on.
I'd really like to hear what you think.
tcflood #29, it's
I was on a discussion about this (is Lu saying that CFCs lifted earth out of the Ice Ages?) when a "JohnMashey" interjected with the following information:
Lu has been on this kick for years, publishing in increasingly less credible journals and ignoring all refutations. See Gavin Schmidt on Lu:
search RealClimate for 2011 post: from ‘interesting but incorrect’ to just wrong
www.realclimate.org/index.php/archives/2011/07/lu-from-interesting-but-incorrect-to-just-wrong/
Note that Int J. of Modern Physics B (NOT a climate science journal) did not help its reputation by publishing the absurd Gerlich & Tseuschner paper, also analyzed at RC.
True to form, the paper has done the rounds of the usual blogs and the Wall Street Journal.
So, while the fake-skeptics may twitch with fake-excitement, let's not hold our breath that this is the ex-machina solution we have all been waiting for.
There's a silver lining in the Lu fiasco ...
"He claims to have good statistical evidence that both ozone depletion and global warming come almost exclusively from halogenated compounds"
Once upon a time, this lead one Tony Willard Watts to post, with a big splash, that Lu has shown that halogenated compounds, not CFCs, were responsible for ozone depletion, thus the Montreal accords were based on incorrect science, as CFCs have no affect on ozone.
Think about that for a moment ...
Hilarity ensued ...
John Cook covered the Lu argument in 2010. This is the third or fourth iteration of the same fundamentally flawed argument, without acknowledging that other scientists have revealed those fundamental flaws. It's BS (bad science).
Tom Dayton at 6 writes: “But frustratingly, the article undermines its own point by having the diagram labeled ‘Global Mean Temperature’ instead of ‘Global Surface Atmospheric Temperature.’ Likewise, the paragraph after the diagram does not specify ‘surface atmospheric.’ Will you change those, please?”
Tom, I didn’t find a response to your concerns on this thread, so allow me. The dataset Kevin Trenberth is using in his illustration is the NCDC’s monthly global surface (land and ocean combined into an anomaly) temperature anomaly index (degrees C). Refer to the overview here:
http://www.ncdc.noaa.gov/cmb-faq/anomalies.php
It is made up of sea surface temperature and land surface air temperature data, with most of it (about 70%) being sea surface temperature data. Therefore, Kevin Trenberth cannot call it “surface atmospheric” temperature.
Regards.
Three areas which merit close monitoring are: Increased solar activity, Reduced aerosol pollution and, Emission of ocean heat. The take-home message from this article is that all three will occur and contribute to accelerated global warming in the future. The latter will, as Dr Tenberth points out, have “consequences”.
Could those consequences be to speed-up loss of land based ice, including permafrost, increasing the rate of average sea level rise and carbon emissions from the Arctic?
The result? Who can say but a rise in average global temperature of 2ºC above the pre-industrial and of 1 metre in average sea level within the next 50 years seems possible. But not to worry. I am assured we can readily adapt to such outcomes.
Agnostic #34. I'm with you. now my quibble for all, not singling you out. In my opinion the phrase "global warming" S.B. used to mean an increase in ecosystem heat content and reserved for that. To do otherwise will fuel confusion in lay persons. There are other good descriptive phrases for the various surface & atmosphere aspects, and so on. I understand that science disciplines & professions will have internal colloquialisms. I understand that surface & atmosphere has special importance for the flora & fauna that live there (not the deep fishies). Emission of ocean heat cannot possibly contribute to accelerated global warming. In fact, it would temporarily reduce global warming by reducing the radiative imbalance. I understand that should the oceans warm from present ~4.0 to ~7.0 or whatever eventually, it would not be an acceptable situation for the land flora & fauna if oceans jettison some heat into space via our atmosphere, but that does not change what "global warming" is.
Some comments here refer to nomenclature problems - Heat, Warming, Surface temps and so on - and I've had to adapt my own punter-level commenting to address this.
I now discuss climate change in terms of 'energy'. I have found it easier to discuss the potential of climate change in public discourse if I make clear that the climate is a system of energy imbalances continuously trying to achieve equilibrium, and that if there's more energy available to the climate, then all aspects of it (extreme weather, ice melting and the energy required for phase changes, cold snaps, precipitation, fires, floods, sea-level rise, general instability) must be affected, since the extra energy is indiscriminate.
I do think we need to develop our vocabulary, and trust in the intelligence of the public. Global warming is a misnomer that we spend a lot of time qualifying, and with the greatest respect to Trenberth, I'm not sure 'heating' is a better synonym (even though it is, of course, quite accurate).
noelfuller @comment 5 touches upon an important point. Anyone out there fighting in the trenches of the denialosphere, and the comment sections of newspapers etc, knows that the "it hasn't warmed for 15/16/17 years" meme is very powerful these days.
Recently, it has been clear to those who look at the whole picture, that much of the net energy from the radiative imbalance is, at least temporarily, being sequestered in the deeper ocean. But this is a relatively recent explanation and the denialosphere and media commentators tend to dismiss it as being a form of hand waving. As we are honored to have Dr. Trenberth here, perhaps we can get a definitive "admission" from the horse's mouth? Would it be fair to say, Dr. Trenberth, that the predicted trend in mean surface/atmospheric temperature was represented in the original IPCC literature as being expected to be somewhat more linear than it has proved? As you suggest in your post, there is a relatively recent (and presumably unexpected in the literature) change in ocean sequestering due, as you say, to:
"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"
It seems very likely that the 15 to 20 year old science, that the denialosphere hark back to "prove" that the current pause in global surface/atmosphere temperature trends was not predicted by the science, did not explicitly predict this new ocean mechanism would act as such a temporary atmospheric heat sink.
I think most here realise that a long pause in surface temperature trends is in no way a good thing, but to the general public it looks like a) a good thing and b) that climate science got it rather wrong. Both of these sentiments are heavily exploited by the propagandists.
So, to sum up, I think the time is ripe for those climate scientists with a higher media profile, andt the climate science communication websites, to state that Earth has not behaved quite as most would have expected from reading the IPCC literature 20 years ago. From that perspective, the pathological sceptics are right that the pause was not really predicted. As they use that to jump to the unwarrented conclusion that, because the evidence now shows that the 20 year old science was incomplete, they can discount all the science. From a human perspective, the uncertainties and assumptions in the climate models, the known unknowns, and the unknown unknowns, if they exist, could go either way. To publicly counter the "16 year pause", so a sceptical public accepts the science again, it needs to be said that the unexpected has stepped in to complicate the outlook and the full ramifications and the concomitant risk analysis of this needs to be out there in the public arena so the public can judge whether they feel lucky or not...
Nick Palmer #37 I have quibbles (not disagreement). "at least temporarily" I see no logical reason for it to be "temporarily" but understand it takes a full book to define what "temporarily" means for this. Tiny puffs of heat go in and out, they only seem large to us because air=0.09%, land to 6.5m deep=0.085% of ecosystem heat. My logical reasoning with no education on topic is if AST must rise, as example, +2.8C to balance radiation then ocean must rise +2.8C. Does anyone know a reason why it would significantly differ ? That's long-term, decades, centuries...millenia on a "diminishing returns" curve where it takes up last smidgin of heat at a decelerating rate after centuries (thus, mine is hypothetical/approximate because the TOA balance is unlikely to be entirely steady this long). Meantime, ocean will occasionally accelerate a previously-slowed "global warming" (due to AST getting close to the balance point) by taking some heat down, reducing AST and thus increasing radiative imbalance. "temporarily" as I infer you mean it is that some increased puffs of ocean outbound heat might well happen over the coming decades, the ocean being fluid and with increasing energy content, which seems logical. Long-term it all goes into the oceans (ummm, and freshwater 2.5%).
In "From that perspective, the pathological sceptics are right that the pause was not really predicted" suggest you might add "in short-term AST increase" after "pause" because "global warming" has not paused. You initiated surface temperature trends as the topic in the prior paragraph but I think the repetition is important, not pedantic, because most of the audience has limited knowledge (a euphemism) and a significant minority is a teeny tad mischievious regarding the "quotes" of others.
noelfuller @5 "anyone actually genearted a graph of global heat content" if you mean "global heat content anomaly" then 97.5% yes. NOAA "has" a graph of 97.5% global heat content anomaly (I've seen Dr. Trenberth present it also) and it's called the ocean heat content anomaly. The other 2.325% is the ecosystem fresh water (air=0.09%, land to 6.5m deep=0.085%). I've no spare time to search internet for most ecosystem fresh water mass & any information on its heat increase. If you Googlify "great lakes global warming" that's a start. "the LLO study found that summer surface water temperatures on Lake Superior have increased approximately 4.5°F (2.5°C) during the period 1979–2006". It'll need some time from you and others to find >80% of the fresh water mass & temperature anomaly data for a high enough quality assessment. I assume you'll accept 99.5% of global heat content as "all" global heat content (assuming you actually mean the anomaly) given that the final 0.5% of global heat content is only ~42 months of present 0.85wm**-2 warming if final balanced AST is +2.0C (7 yrs if it's +4.0C and so on). Either add your fresh water heat gains to NOAA graph if you can find >=80% of the fresh water data or, if time-stressed like me, simply divide NOAA global heat content graph by 0.975 and you've got global heat content within +/-~1%.
With paper scrap & calculator I have oceans weigh 1.40*10**21 kg so to heat 1K takes 5.82*10**24J and temperature is 277K so heat content is 1.61**27J. Some Wiki entry says oceans weigh 40 times as much as all fresh water so global heat content is 1.65**27J give or take a few trillion nuclear bombs worth. The preceding guesstimate is if you actually do mean the current ecosystem heat content. I expect that's why climate scientists use "anomaly" and only deal with the changes.
Me@39corrections/clarifications. UK NPL table sea water 3985J/Kg/K so 5.58*10**24J to heat oceans 1C. My ocean heat content 1.61<*10>**27J is hugely incorrect because water is ice at <273K and 3985J/Kg/K will not apply at 0-273K. Re Dr. Trenberth and/or Dr. Randall lectures re land ~6.5m deep at ~50% ocean specific heat capacity - I don't recall whether sea bed is included, probably not, complex because it's not warmed by sun. Geothermal heat flux stated as average entering oceans 0.097 +-0.004 Wm**-2 by M. Hofmann & M. A. Morales Maqueda "Geothermal Heat Flux and its Influence on the Oceanic Abyssal Circulation and Radiocarbon Distribution"