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Flaws of Lüdecke & Weiss

Posted by Ari Jokimäki on January 11, 2018

Once again a paper that looks at solar-climate connection turns out to be deeply flawed. It contains bad methodology, bad result handling, bad conclusions, and a biased reference list.

Data handling process of Lüdecke & Weiss (2018).

A few months ago, a new paper was published by Lüdecke and Weiss (LW17). Both Lüdecke and Weiss are known climate change contrarians. Serious problems have been reported from their previous work, which used some of the same methods that were used in this new one. The new paper has been published by Bentham Open, which has somewhat questionable reputation.

Climate change contrarians are liking this of course and recently I also encountered the paper when it was shown to me as a proof for something. I decided to take a more thorough look at the paper.

The reference list

The first thing that jumps out from LW17 is the papers they cite in their introduction section. You can immediately see that their review of existing research is biased. They cite Scafetta but not his critics. They cite Svensmark but not his critics. They cite Friis-Christensen & Lassen but not their critics (even F-C & L themselves have later agreed that the findings they reported in the paper cited by LW17 were not correct). They cite lots of papers that suggest some kind of influence of the sun on Earth’s climate, but they leave the multitude of papers that state clearly that sun hasn’t caused current climate change almost un-cited.

The reference list of LW17 is quite long which suggests that they have been relatively thorough in trying to find lot of references that support their argumentation. It also hints to the possibility that the biased reference list is by design and not just an accident due to sloppy paper search.

The methods of the study

The methods section (sections “The Data” and “Spectral Analysis”) of LW17 contains some curious issues. Perhaps the worst aspect of the methods section is that they haven’t described all the methods they used. Their later sections contain many steps that haven’t been described with enough detail in the paper, such as making a representation of the temperature reconstruction from the three sine waves and the steps involved in solar variability – temperature comparison.

Moving on to the things they describe in the methods section, here’s a quote describing one step in the LW17 data processing:

For Bün, HADCRUT4 and Pet respectively the most recent years which show unusual deviations from the remaining reconstructions were also omitted.

This is a kind of thing I have seen climate change contrarians using in their fraud accusations. Yet, I have seen climate change contrarians claiming to have read this paper thoroughly and accepting it as truth without a question, and even defending it fiercely.

Another thing is how LW17 have adjusted the satellite data to HadCRUT4 data. They took 1979 values for each and then shifted satellite data so that their 1979 values were the same (I’m not 100% sure that they did it exactly like this – they don’t give the details – but I think that the process I described results in what they did). I think using only one year worth of data to align the two records is a bad idea. It’s especially bad because there was an El Niño in 1979-1980. El Niño generally shows up more in satellite records than in surface temperature records so using an El Niño year as a baseline creates a bias between the two records (the satellite record runs a bit low after this). I would have used several years of data to align the two records, 10 years for example. They also seem to use only one year data to align their source reconstructions together.

LW17 have used temperature reconstructions from all over the world. This is good. They have also adjusted each reconstruction to a common baseline. This is also good. Their method to create a global data set out of them is a bad one, though. They have computed a simple mean of the reconstructions for each year. There is no area averaging or anything but just a simple mean. To illustrate why this is bad, they have only three reconstructions from the Southern Hemisphere (SH) while they have dozens of reconstructions from the Northern Hemisphere (NH) (making their reconstruction practically a NH one instead a global one). This means that the three reconstructions from SH are strongly out-weighted by the NH reconstructions. In a global temperature reconstruction both hemispheres should have an equal weight but in LW17 they don’t have that, not even close.

Making the SH-NH imbalance even worse in LW17, two of the three reconstructions from SH only cover time-period from 1640 to 1987 and from 1640 to 1993 while they describe their reconstruction as “a global temperature mean G7 over the last 2000 years”. Furthermore, the only SH reconstruction covering the full 2000 years is an ice core based temperature reconstruction from Antarctica which has temporal resolution of 17 to 50 years while the NH records have annual resolution. Hence, most of the LW17 temperature reconstruction is lots of NH records + one bad resolution SH record.

In addition, all the proxies are from land areas but LW17 use global instrumental and satellite data which includes also ocean surface area. Yet another thing is that the NH reconstructions in LW17 seem to be somewhat clustered around North Atlantic, which is a region known to show the Medieval Warm Period very clearly. Overall, the LW17 temperature reconstruction is a strange mix of reconstructions patched together with very questionable methods, and it really is just a NH reconstruction with an emphasis on North Atlantic region.

For the solar activity, LW17 use only one reconstruction that has been constructed from different sources. They seem to use the reconstruction as it is without tampering with it, which seems to be a good thing in the light of what was seen above.

The results of the study

In their analysis, LW17 concentrate on cycles only and mainly to past climate, so the study has only little relevance to current climate change. Causes of past climate changes do not mean that greenhouse gases couldn’t cause climate change now, and the presence of cycles in Earth’s climate don’t negate the effects of greenhouse gases, but climatic cycles and greenhouse gas forcing can (and do) co-exist.

LW17 don’t offer much new to sun-climate connection knowledge either because their main result is a possible correlation between the two which doesn’t offer any information other than solar variability might have an effect on Earth’s climate, which we knew already anyway.

But in addition to general insignificance of the study and the problems identified in the previous sections, there are further problems in the results section of the paper.

LW17 perform a Fourier transformation to their temperature reconstruction and then they select three strongest peaks from the Fourier transformation result. However, from their Figure 2 can be seen that one of the selected peaks (the 1000-year peak) is not statistically significant (it doesn’t exceed what they call “false alarm line”) while some of the statistically significant peaks (~65 year and ~50 year peaks) were not selected. LW17 do not discuss the issue. They just state that they have selected the three strongest peaks.

Next, LW17 use the three selected peaks to do an inverse Fourier transform. The result of this is a representation of their original temperature reconstruction. This hasn’t been described in the methods section, and they don’t also describe it in the results section adequately. They only mention that they have done an inverse Fourier transformation.

They compute a correlation between the original temperature reconstruction and the sine wave representation. Resulting correlation is quite good, but it doesn’t mean much because they correlate an original series with a series that has been constructed from the original series. In practice, they just compute a correlation between two representations of a same signal. This would be okay if they would have just used the correlation to check that the temperature reconstruction from the three sine waves is a reasonably good representation of the original reconstruction, and then proceed with the actual analysis, but they seem to treat the correlation value as one of their most important results, and there’s no further analysis with the inverse Fourier representation.

LW17 continue their analysis under the section “Sun’s Activity and Climate”. For many readers, it probably will not be a surprise that this section also contains problems.

In this section, LW17 first discuss the Fourier transformation results of solar activity proxy series they are using. Their discussion is a stub one. Based on the peaks found, they mention that the three peaks selected from the temperature reconstruction can also be seen in solar activity series. Below is an excerpt of their Figure 2.

The Table 2 (T2) of LW17 claims to show “Strongest spectral peaks for the records Chr, Bün, McK, Vill-N, Vill-S, Pet, G7, and Stei for periods > 700 years, from 700 to 300 years, from 300 to 100 years, and < 100 years”. From the figure above it can be seen that this is not the case. Highest peak of series “Pet” (ice core record from Antarctica) is very close to 0 (corresponding roughly to a wavelength of several thousand years) and the mentioned peak in T2 seems to be a double peak of which the weaker one seems to be better match in wavelength with the peak mentioned in T2. The mentioned peak of 499 years in T2 also seems to be a double peak and here better match seems also to be the weaker one. For both of the double peaks, it is of course difficult to estimate the situation from the graph, but it does seem that LW17 have selected the weaker ones of the mentioned double peaks to T2.

The series “Stei” (the solar activity proxy series) also shows stronger peaks than the ones mentioned in T2. Above 700 years there are two peaks clearly stronger than the mentioned 991-year peak. Also from 700 to 300 years there is one higher peak than the mentioned one.

The figure above shows also that it is easy to find matches for peaks when there are plenty of peaks to choose from. Highlighted is the selection of the peak in “Stei” that corresponds to the 188-year peak in “G7” (and in “Pet”). There are weaker peaks that are closer matches to the wavelength of 188-year peak than the highlighted 203-year peak. One of these is also clearly statistically significant at about 197 years.

Moving on past the selection of solar activity peaks, it should be noted that after LW17 have selected the peaks, they don’t do much about them. They don’t construct a representation of temperature and calculate correlations or anything like they did for temperature series but instead they just mention that the solar activity “shows the same periods” as temperature reconstruction based on the values presented in T2.

One further thing about the figure above, the solar activity series “Stei” shows lot of peaks and as discussed above, some of them are more meaningful than the ones LW17 emphasize. Why those peaks do not show up in the temperature reconstruction? This point has not been discussed by LW17.

Next step is a very curious one. They proceed to check the solar-climate connection further, but for some reason they drop their temperature reconstruction G7 and start using “Pet” which is the low-resolution ice core proxy from Antarctica. They don’t justify this at all.

The method they use here is not described in detail. They only mention that they do a “wavelet analysis”. At the end, however, their analysis here doesn’t extend beyond studying “eyesight similarities”.


In their introduction section, LW17 created a false picture of the situation of current research status of the solar activity – climate connection by citing mostly papers that support LW17 argumentation and ignoring most of the papers that show results against their argumentation. They did a not-even-half-baked analysis containing lot of flaws. In their conclusion section LW17 then suggested that their flawed results are a “confirmation” for the false picture created in the introduction section.

We can also wonder what was the point of the Fourier-inverse Fourier exercise LW17 did (with subsequent eyesight “analysis”), because if you want to demonstrate a solar-temperature correlation, then why not just compute a correlation between them directly? It is curious that they didn’t do this at least as a side-note, surely it would (or should?) have been interesting also to them.

In my opinion, LW17 is throughout bad science – biased citing, bad research methods, strange interpretation of results, etc. Having seen and studied the paper, I cannot help wondering what this quote from LW17 acknowledgements section means: “We express our thanks to the referees for valuable comments.” If the referees gave valuable comments and the resulting paper still is as bad as described above, how bad was this paper originally?


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Some curious things about Svensmark et al. reference list

Posted by Ari Jokimäki on December 22, 2017

The hypothesis of significant effect of cosmic-rays to climate has been shown wrong many times. This is a pet hypothesis of Henrik Svensmark, who continues to push papers on the subject to scientific journals. A few days ago, the journal Nature Communications published a paper of Svensmark (& co-workers). I checked out its reference list because I think that some indicators of the quality of a paper can be found simply by checking the reference list, and how references are used.

S17 reference list – first impressions

I immediately noticed a few things about S17 reference list. I made some tweets (@AGWobserver) where I mention them:

The Kulmala et al. paper I mention there is this one: “Atmospheric data over a solar cycle: no connection between galactic cosmic rays and new particle formation”. It shows results against Svensmark’s hypothesis, but it is not cited by S17. The mentioned paper list in my tweets is this one: “Papers on the non-significant role of cosmic rays in climate”.

(Note added December 27, 2017: This paragraph is incorrect – S17 cites two Laakso et al. papers and I somehow got them mixed.) One Kulmala team paper S17 cites is “Detecting charging state of ultra-fine particles: instrumental development and ambient measurements” (Laakso et al. 2007). S17 uses it in this context: “Cosmic rays are the main producers of ions in Earth’s lower atmosphere21.” (21 is the S17 reference list number for the Laakso et al. paper.) This is strange because Laakso et al. don’t say anything about cosmic rays. Cosmic rays are mentioned only in their reference list in the title of Eichkorn et al. (2002) paper, and Laakso et al. refer to it in this context: “Ion mass spectrometers have been used successfully in the studies of new particle formation in the upper atmosphere (Eichkorn et al., 2002).” Furthermore, as Svensmark’s cosmic ray hypothesis relies on ion induced nucleation, it is noteworthy that one of Laakso et al. conclusions is this: “During a large fraction of days considered here, the contribution of ion-induced nucleation to the total nucleation rate was either negligible or relatively small.” To me it seems that either S17 is citing a wrong paper here, or then the cosmic ray ion production thing is implicitly in Laakso et al. results and I just don’t see it.

S17 reference list – comparison with other paper

I decided to look S17 reference list further. I chose a comparison paper, Gordon et al. (2017, “G17”), which is a research paper on the same issue than S17. Both papers have been published and submitted to their journals during 2017, S17 in May 10 and G17 in March 24, so S17 is a bit newer in that sense. S17 was published in December 19 and G17 in August 24, so also in that sense S17 is newer. I emphasize newer here because it suggests that references in S17 reference list should be as new or newer as references in G17 reference list.

The reference list of S17 contains 39 entries while the reference list of G17 contains 85 entries. As the papers are on the same subject, it seems that S17 reference list is a little short. However, scope of G17 seems to be somewhat broader, so reference list length doesn’t necessarily tell anything.

I also compared the temporal distributions of papers in the reference lists of these two papers. Result can be seen in this graph:

It is quite clear from the graph that S17 reference list focuses on older papers than G17 reference list. highest peak of temporal distribution of S17 is 2005-2009, while corresponding highest peak of G17 is 2010-2014. Also, G17 distribution is rather sharply concentrated on the more recent times, while S17 distribution is more spread out in time, and it almost seems as if the most resent research is being avoided in S17 reference list (the share of 2015-2017 papers is very low in S17 compared to G17).

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Papers on the warming hole of the United States

Posted by Ari Jokimäki on February 8, 2017

This is a list of papers on the warming hole of the United States. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

The United States “warming hole”: quantifying the forced aerosol response given large internal variability (Banerjee et al. 2017)
Abstract: “Twenty-five years of large summer cooling over the southeastern United States ending in the mid-1970s coincided with rapidly increasing anthropogenic aerosol emissions. Here, we assess the claim that the cooling in that period was predominantly due to such aerosols. We utilize two 50-member sets of coupled climate model simulations, one with only anthropogenic aerosol forcings and another with all known natural and anthropogenic forcings, together with a long control integration. We show that, in the absence of aerosol forcing, none of the model simulations capture the observed surface cooling rate (∼0.56∘C decade−1), whereas with increasing aerosol emissions two (of fifty) of the simulations do. More importantly, however, we find that the cooling from aerosols (0.20° C decade−1) is insufficient to explain the observation. Our results therefore suggest that, while aerosols may have played a role, the observed cooling was a rare event that contained a large contribution from unforced internal variability.”
Citation: Banerjee A., L.M Polvani, and J.C. Fyfe (2017), The United States “warming hole’: quantifying the forced aerosol response given large internal variability, Geophys. Res. Lett., 44, doi:10.1002/2016GL071567.

Tracking regional temperature projections from the early 1990s in light of variations in regional warming, including ‘warming holes’ (Grose et al. 2017)
Abstract: “The perception of the accuracy of regional climate projections made in the early 1990s about climate change by 2030 may be influenced by how the temperature trend has changed in the 25 years since their publication. However, temperature trends over this period were influenced not only by external forcings such as greenhouse gases but also natural variations. The temperature of Southern Australia, the Sahel, South Asia and Southern Europe are currently within the warming estimates from statements in the early 1990s from the IPCC and CSIRO, assuming a linear trend between 1990 and 2030. However, northern Australia and central North America are currently at the lower limit or below these projections, having featured areas of multi-year regional cooling during global warming, sometimes called ‘warming holes’. Recent climate model simulations suggest that cooling can be expected in the recent past and near future in some regions, including in Australia and the US, and that cooling is less likely over 1990–2030 than in 1990–2015, bringing observations closer to the IPCC and CSIRO warming estimates by 2030. Cooling at the 25-year scale in some regions can be associated with cyclic variability such as the Inter-decadal Pacific Oscillation, or low trend such as in the Southern Ocean. Explicitly communicating the variability in regional warming rates in climate projections, including the possibility of regional warming ‘holes’ (or the opposite of ‘surges’ or ‘peaks’) would help to set more reliable expectations by users of those projections.”
Citation: Grose, M.R., Risbey, J.S. & Whetton, P.H. Climatic Change (2017) 140: 307. doi:10.1007/s10584-016-1840-9.

North Pacific SST Forcing on the Central United States “Warming Hole” as Simulated in CMIP5 Coupled Historical and Uncoupled AMIP Experiments (Pan et al. 2017)
Abstract: “The central United States experienced a cooling trend during the twentieth century, called the “warming hole,” most notably in the last quarter of the century when global warming accelerated. The coupled simulations of the models that participated in the Coupled Model Intercomparison Project, Phases 3 and 5 (CMIP3/5), have been unable to reproduce this abnormal cooling phenomenon satisfactorily. An unrealistic representation of the observed phasing of the Pacific Decadal Oscillation (PDO)—one of the proposed forcing mechanisms for the warming hole—in the models is considered to be one of the main causes of this effect. The CMIP5’s uncoupled Atmospheric Model Intercomparison Project (AMIP) experiment, whose duration approximately coincides with the peak warming hole cooling period, provides an opportunity, when compared with the coupled historical experiment, to examine the role of the variation in Pacific Ocean sea surface temperature (SST) in the warming hole’s formation and also to assess the skill of the models in simulating the teleconnection between Pacific SST and the continental climate in North America. Accordingly, this study compared AMIP and historical runs in the CMIP5 suite thereby isolating the role of SST forcing in the formation of the warming hole and its maintenance mechanisms. It was found that, even when SST forcing in the AMIP run was “perfectly” prescribed in the models, the skill of the models in simulating the warming hole cooling in the central United States showed little improvement over the historical run, in which SST is calculated interactively, even though the AMIP run overestimated the anti-correlation between temperature in the central United States and the PDO index. The fact that better simulation of the PDO phasing in the AMIP run did not translate into an improved summer cooling trend in the central United States suggests that the inability of the coupled CMIP5 models to reproduce the warming hole under the historical run is not mainly a result of the mismatch between simulated and observed PDO phasing, as believed.”
Citation: Zaitao Pan, Chunhua Shi, Sanjiv Kumar, and Zhiqiu Gao (2017) Atmosphere-Ocean, doi: 10.1080/07055900.2016.1261690.

Disappearance of the southeast U.S. “warming hole” with the late 1990s transition of the Interdecadal Pacific Oscillation (Meehl et al. 2015) [FULL TEXT]
Abstract: “Observed surface air temperatures over the contiguous U.S. for the second half of the twentieth century showed a slight cooling over the southeastern part of the country, the so-called “warming hole,” while temperatures over the rest of the country warmed. This pattern reversed after 2000. Climate model simulations show that the disappearance of the warming hole in the early 2000s is likely associated with the transition of the Interdecadal Pacific Oscillation (IPO) phase from positive to negative in the tropical Pacific in the late 1990s, coincident with the early 2000s slowdown of the warming trend in globally averaged surface air temperature. Analysis of a specified convective heating anomaly sensitivity experiment in an atmosphere-only model traces the disappearance of the warming hole to negative sea surface temperature anomalies and consequent negative precipitation and convective heating anomalies in the central equatorial Pacific Ocean associated with the negative phase of the IPO after 2000.”
Citation: Meehl, G. A., J. M. Arblaster, and C. T. Y. Chung (2015), Disappearance of the southeast U.S. “warming hole” with the late 1990s transition of the Interdecadal Pacific Oscillation, Geophys. Res. Lett., 42, 5564–5570, doi:10.1002/2015GL064586.

Sedimentary proxy evidence of a mid-Holocene hypsithermal event in the location of a current warming hole, North Carolina, USA (Tanner et al. 2015) [FULL TEXT]
Abstract: “A wetland deposit from the southern Appalachian mountains of North Carolina, USA, has been radiocarbon dated and shows continuous deposition from the early Holocene to the present. Non-coastal records of Holocene paleoenvironments are rare from the southeastern USA. Increased stable carbon isotope ratios (δ13C) of sedimentary organic matter and pollen percentages indicate warm, dry early- to mid-Holocene conditions. This interpretation is also supported by n-alkane biomarker data and bulk sedimentary C/N ratios. These warm, dry conditions coincide with a mid-Holocene hypsithermal, or altithermal, documented elsewhere in North America. Our data indicate that the southeastern USA warmed concurrently with much of the rest of the continent during the mid-Holocene. If the current “warming hole” in the southeastern USA persists, during a time of greenhouse gas-induced warming elsewhere, it will be anomalous both in space and time.”
Citation: Benjamin R. Tanner, Chad S. Lane, Elizabeth M. Martin, Robert Young, Beverly Collins (2015) Quaternary Research, Volume 83, Issue 2, March 2015, Pages 315–323, doi: 10.1016/j.yqres.2014.11.004.

Attribution of the United States “warming hole”: Aerosol indirect effect and precipitable water vapor (Yu et al. 2014) [FULL TEXT]
Abstract: “Aerosols can influence the climate indirectly by acting as cloud condensation nuclei and/or ice nuclei, thereby modifying cloud optical properties. In contrast to the widespread global warming, the central and south central United States display a noteworthy overall cooling trend during the 20th century, with an especially striking cooling trend in summertime daily maximum temperature (Tmax) (termed the U.S. “warming hole”). Here we used observations of temperature, shortwave cloud forcing (SWCF), longwave cloud forcing (LWCF), aerosol optical depth and precipitable water vapor as well as global coupled climate models to explore the attribution of the “warming hole”. We find that the observed cooling trend in summer Tmax can be attributed mainly to SWCF due to aerosols with offset from the greenhouse effect of precipitable water vapor. A global coupled climate model reveals that the observed “warming hole” can be produced only when the aerosol fields are simulated with a reasonable degree of accuracy as this is necessary for accurate simulation of SWCF over the region. These results provide compelling evidence of the role of the aerosol indirect effect in cooling regional climate on the Earth. Our results reaffirm that LWCF can warm both winter Tmax and Tmin.”
Citation: Shaocai Yu, Kiran Alapaty, Rohit Mathur, Jonathan Pleim, Yuanhang Zhang, Chris Nolte, Brian Eder, Kristen Foley & Tatsuya Nagashima (2014), Scientific Reports, 4, doi:10.1038/srep06929.

Multidecadal Climate Variability and the “Warming Hole” in North America: Results from CMIP5 Twentieth- and Twenty-First-Century Climate Simulations (Kumar et al. 2013) [FULL TEXT]
Abstract: “The ability of phase 5 of the Coupled Model Intercomparison Project (CMIP5) climate models to simulate the twentieth-century “warming hole” over North America is explored, along with the warming hole’s relationship with natural climate variability. Twenty-first-century warming hole projections are also examined for two future emission scenarios, the 8.5 and 4.5 W m−2 representative concentration pathways (RCP8.5 and RCP4.5). Simulations from 22 CMIP5 climate models were analyzed, including all their ensemble members, for a total of 192 climate realizations. A nonparametric trend detection method was employed, and an alternative perspective emphasizing trend variability. Observations show multidecadal variability in the sign and magnitude of the trend, where the twentieth-century temperature trend over the eastern United States appears to be associated with low-frequency (multidecadal) variability in the North Atlantic temperatures. Most CMIP5 climate models simulate significantly lower “relative power” in the North Atlantic multidecadal oscillations than observed. Models that have relatively higher skill in simulating the North Atlantic multidecadal oscillation also are more likely to reproduce the warming hole. It was also found that the trend variability envelope simulated by multiple CMIP5 climate models brackets the observed warming hole. Based on the multimodel analysis, it is found that in the twenty-first-century climate simulations the presence or absence of the warming hole depends on future emission scenarios; the RCP8.5 scenario indicates a disappearance of the warming hole, whereas the RCP4.5 scenario shows some chance (10%–20%) of the warming hole’s reappearance in the latter half of the twenty-first century, consistent with CO2 stabilization.”
Citation: Sanjiv Kumar, James Kinter, Paul A. Dirmeyer, Zaitao Pan, Jennifer Adams (2013), Journal of Climate, 26, 11, 3511-3527, doi: 10.1175/JCLI-D-12-00535.1.

Intermodel Variability and Mechanism Attribution of Central and Southeastern U.S. Anomalous Cooling in the Twentieth Century as Simulated by CMIP5 Models (Pan et al. 2013) [FULL TEXT]
Abstract: “Some parts of the United States, especially the southeastern and central portion, cooled by up to 2°C during the twentieth century, while the global mean temperature rose by 0.6°C (0.76°C from 1901 to 2006). Studies have suggested that the Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation (AMO) may be responsible for this cooling, termed the “warming hole” (WH), while other works reported that regional-scale processes such as the low-level jet and evapotranspiration contribute to the abnormity. In phase 3 of the Coupled Model Intercomparison Project (CMIP3), only a few of the 53 simulations could reproduce the cooling. This study analyzes newly available simulations in experiments from phase 5 of the Coupled Model Intercomparison Project (CMIP5) from 28 models, totaling 175 ensemble members. It was found that 1) only 19 out of 100 all-forcing historical ensemble members simulated negative temperature trend (cooling) over the southeast United States, with 99 members underpredicting the cooling rate in the region; 2) the missing of cooling in the models is likely due to the poor performance in simulating the spatial pattern of the cooling rather than the temporal variation, as indicated by a larger temporal correlation coefficient than spatial one between the observation and simulations; 3) the simulations with greenhouse gas (GHG) forcing only produced strong warming in the central United States that may have compensated the cooling; and 4) the all-forcing historical experiment compared with the natural-forcing-only experiment showed a well-defined WH in the central United States, suggesting that land surface processes, among others, could have contributed to the cooling in the twentieth century.”
Citation: Zaitao Pan, Xiaodong Liu, Sanjiv Kumar, Zhiqiu Gao, James Kinter (2013) Journal of Climate, 26, 17, 6215-6237, doi: 10.1175/JCLI-D-12-00559.1.

Mechanisms Contributing to the Warming Hole and the Consequent U.S. East–West Differential of Heat Extremes (Meehl et al. 2012) [FULL TEXT]
Abstract: “A linear trend calculated for observed annual mean surface air temperatures over the United States for the second-half of the twentieth century shows a slight cooling over the southeastern part of the country, the so-called warming hole, while temperatures over the rest of the country rose significantly. This east–west gradient of average temperature change has contributed to the observed pattern of changes of record temperatures as given by the ratio of daily record high temperatures to record low temperatures with a comparable east–west gradient. Ensemble averages of twentieth-century climate simulations in the Community Climate System Model, version 3 (CCSM3), show a slight west–east warming gradient but no warming hole. A warming hole appears in only several ensemble members in the Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel dataset and in one ensemble member of simulated twentieth-century climate in CCSM3. In this model the warming hole is produced mostly from internal decadal time-scale variability originating mainly from the equatorial central Pacific associated with the Interdecadal Pacific Oscillation (IPO). Analyses of a long control run of the coupled model, and specified convective heating anomaly experiments in the atmosphere-only version of the model, trace the forcing of the warming hole to positive convective heating anomalies in the central equatorial Pacific Ocean near the date line. Cold-air advection into the southeastern United States in winter, and low-level moisture convergence in that region in summer, contribute most to the warming hole in those seasons. Projections show a disappearance of the warming hole, but ongoing greater surface temperature increases in the western United States compared to the eastern United States.”
Citation: Gerald A. Meehl, Julie M. Arblaster, Grant Branstator (2012) Journal of Climate, 25, 18, 6394-6408, doi: 10.1175/JCLI-D-11-00655.1.

Can CGCMs Simulate the Twentieth-Century “Warming Hole” in the Central United States? (Kunkel et al. 2006) [FULL TEXT]
Abstract: “The observed lack of twentieth-century warming in the central United States (CUS), denoted here as the “warming hole,” was examined in 55 simulations driven by external historical forcings and in 19 preindustrial control (unforced) simulations from 18 coupled general circulation models (CGCMs). Twentieth-century CUS trends were positive for the great majority of simulations, but were negative, as observed, for seven simulations. Only a few simulations exhibited the observed rapid rate of warming (cooling) during 1901–40 (1940–79). Those models with multiple runs (identical forcing but different initial conditions) showed considerable intramodel variability with trends varying by up to 1.8°C century−1, suggesting that internal dynamic variability played a major role at the regional scale. The wide range of trend outcomes, particularly for those models with multiple runs, and the small number of simulations similar to observations in both the forced and unforced experiments suggest that the warming hole is not a robust response of contemporary CGCMs to the estimated external forcings. A more likely explanation based on these models is that the observed warming hole involves external forcings combined with internal dynamic variability that is much larger than typically simulated. The observed CUS temperature variations are positively correlated with North Atlantic (NA) sea surface temperatures (SSTs), and both NA SSTs and CUS temperature are negatively correlated with central equatorial Pacific (CEP) SSTs. Most models simulate rather well the connection between CUS temperature and NA SSTs. However, the teleconnections between NA and CEP SSTS and between CEP SSTs and CUS temperature are poorly simulated and the models produce substantially less NA SST variability than observed, perhaps hampering their ability to reproduce the warming hole.”
Citation: Kenneth E. Kunkel, Xin-Zhong Liang, Jinhong Zhu, and Yiruo Lin (2006) Journal of Climate, 19, 17, 4137-4153, doi: 10.1175/JCLI3848.1.

Altered hydrologic feedback in a warming climate introduces a “warming hole” (Pan et al. 2004) [FULL TEXT]
Abstract: “In the last 25 years of the 20th century most major land regions experienced a summer warming trend, but the central U.S. cooled by 0.2–0.8 K. In contrast most climate projections using GCMs show warming for all continental interiors including North America. We examined this discrepancy by using a regional climate model and found a circulation-precipitation coupling under enhanced greenhouse gas concentrations that occurs on scales too small for current GCMs to resolve well. Results show a local minimum of warming in the central U.S. (a “warming hole”) associated with changes in low-level circulations that lead to replenishment of seasonally depleted soil moisture, thereby increasing late-summer evapotranspiration and suppressing daytime maximum temperatures. These regional-scale feedback processes may partly explain the observed late 20th century temperature trend in the central U.S. and potentially could reduce the magnitude of future greenhouse warming in the region.”
Citation: Pan, Z., R. W. Arritt, E. S. Takle, W. J. Gutowski Jr., C. J. Anderson, and M. Segal (2004), Altered hydrologic feedback in a warming climate introduces a “warming hole”, Geophys. Res. Lett., 31, L17109, doi:10.1029/2004GL020528.

General circulation model simulations of recent cooling in the east-central United States (Robinson et al. 2002) [FULL TEXT]
Abstract: “In ensembles of retrospective general circulation model (GCM) simulations, surface temperatures in the east-central United States cool between 1951 and 1997. This cooling, which is broadly consistent with observed surface temperatures, is present in GCM experiments driven by observed time varying sea-surface temperatures (SSTs) in the tropical Pacific, whether or not increasing greenhouse gases and other time varying climate forcings are included. Here we focus on ensembles with fixed radiative forcing and with observed varying SST in different regions. In these experiments the trend and variability in east-central U.S. surface temperatures are tied to tropical Pacific SSTs. Warm tropical Pacific SSTs cool U.S. temperatures by diminishing solar heating through an increase in cloud cover. These associations are embedded within a year-round response to warm tropical Pacific SST that features tropospheric warming throughout the tropics and regions of tropospheric cooling in midlatitudes. Precipitable water vapor over the Gulf of Mexico and the Caribbean and the tropospheric thermal gradient across the Gulf Coast of the United States increase when the tropical Pacific is warm. In observations, recent warming in the tropical Pacific is also associated with increased precipitable water over the southeast United States. The observed cooling in the east-central United States, relative to the rest of the globe, is accompanied by increased cloud cover, though year-to-year variations in cloud cover, U.S. surface temperatures, and tropical Pacific SST are less tightly coupled in observations than in the GCM.”
Citation: Robinson, W. A., R. Reudy, and J. E. Hansen, General circulation model simulations of recent cooling in the east-central United States, J. Geophys. Res., 107(D24), 4748, doi:10.1029/2001JD001577, 2002.

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Global warming hiatus claims prebunked in 1980s and 1990s

Posted by Ari Jokimäki on January 17, 2017

Recent global warming hiatus has been a subject of intensive studies during the last ten years. But it seems that there already was some research on global warming hiatus during 1980s and 1990s (earliest studies on the issue were actually back in 1940s-1970s). This seems to have gone largely unnoticed in the scientific literature of current global warming hiatus, and it certainly seems to have gone unnoticed by climate mitigation opponents who have made claims on global warming hiatus since at least 2006 and still continue to do so.

Some time ago I stumbled on a few old papers which discussed the temperature evolution of 1940s to 1970s. In the early 20th century there had been warming which seemed to have stopped around 1940 until it continued again in the turn of 1970s and 1980s. Here I will use “global warming moratorium” to describe this early hiatus (reason for this can be found below). Below I’ll go through some of the papers in question.

Early studies on the 1940s-1970s global warming moratorium

Global surface temperature increased during the first half of the 20th century. In 1940s, this warming apparently stopped. Possibly the first to notice this was Kincer (1946):

Up to the end of 1945, records for 13 subsequent years have become available, and these are here presented, supplementary to the original data, to determine tendencies since 1932. They show that the general upward temperature trend continued for several years but that the more recent records indicate a leveling off, and even contain currently a suggestion of an impending reversal.

This was confirmed by Mitchell (1961, 1963), as described by Wigley et al. (1985):

Mitchell (1961, 1963) extended Willett’s analysis beyond 1940, improved the method of area averaging, and found that the warming prior to 1940 had subsequently become a cooling trend (as suggested earlier by Kincer [1946]).

Later, Mitchell (1970) studied the effect of anthropogenic forcings (carbon dioxide and aerosols) on the temperature evolution of 20th century. Mitchell noted on the carbon dioxide forcing:

Changes of mean atmospheric temperature due to CO2, calculated by Manabe et al. as 0.3°C per 10% change in CO2, are sufficient to account for only about one third of the observed 0.6°C warming of the earth between 1880 and 1940, but will probably have become a dominant influence on the course of planetary average temperature changes by the end of this century.

And on the global warming moratorium:

Although changes of total atmospheric dust loading may possibly be sufficient to account for the observed 0.3°C-cooling of the earth since 1940, the human-derived contribution to these loading changes is inferred to have played a very minor role in the temperature decline.

Reitan (1974) extended the temperature analysis to 1968 and reported that the global warming moratorium had continued. Brinkmann (1976) extended the analysis to 1973 and saw the first signs of global warming moratorium ending and warming resuming.

Wigley et al. (1985) mention one further point worth mentioning about the global warming moratorium:

All seasons show the same long-term trends, trends that are also common to all other land-based data sets: a warming from the 1880s to around 1940, cooling to the mid-1960s/early-1970s (less obvious in winter), and subsequent warming, beginning later in summer and autumn than in spring and winter.

According to Wigley et al. (1985), the global warming moratorium remained largely unexplained, although there had been some relatively successful attempts to explain the short-term variability in the surface temperature by volcanic aerosols and solar variations, see for example the discussion and analysis in Hansen et al. (1981) and in Gilliland (1982).

Oceans and surface temperature studies in 1980s

Watts (1985) used a simple model to suggest that changes in the rate of the deep water formation can have an effect to surface temperature:

…variations in the rate of formation of deep water can lead to fluctuations in the globally averaged surface temperature similar in magnitude to variations in the earth’s surface-air temperature that have occurred during the last several hundred years.

Gaffin et al. (1986) got similar results:

The largest features of the northern hemispheric surface land temperature record can be simulated with our climate and deep ocean feedback formulation and CO2 forcing alone.

Jones et al. (1987) studied the rapidity of carbon dioxide induced climate change. Within this study, they also looked at how changes in deep water formation affected warming caused by carbon dioxide. They created a simulation, where there was a global warming caused by carbon dioxide, and then they turned off the deep water formation in the Northern Hemisphere (because the global warming moratorium was strongest in Northern Hemisphere). This resulted in surface cooling right after the deep water formation was stopped, and later warming continued again.

In the late 1980s and early 1990s there were some other similar studies also.

The global warming moratorium discussion of early 1990s

So, it seems that at the turn of 1980s and 1990s there had been several studies suggesting that oceans could have considerable effect on the surface temperature. At this point, there was a discussion in the scientific literature on the global warming moratorium, and this discussion has some interesting resemblance to the current global warming hiatus discussion.

Watts and Morantine (1991), in an editorial of Springer’s journal Climatic Change, reviewed the research which I already have discussed above. They noted the possibility of energy transfer between the surface and the deep ocean and concluded:

It is entirely possible that the greenhouse gas climate change signal is alive and well and hiding in the ocean intermediate waters, having reached there because of increased upwelling, or by some other mechanism that could effectively transport heat from the upper layers of the ocean into the huge thermal reservoir of the intermediate and deep ocean.

Kellogg (1993) revisited the issue, also in the same journal, with a letter named as “An Apparent Moratorium on the Greenhouse Warming Due to the Deep Ocean”. Kellogg described some new observational evidence for the ocean’s role in the issue. Based on this he suggested:

…oceans could sequester a significant part of the incremental greenhouse-generated heat over a period of a few decades, a period during which the surface warming would be curtailed.

Kellogg also discussed some issues relating to timing of the global warming moratorium and what would have happened if oceans wouldn’t have had a role in the surface temperature. Relating to the current global warming hiatus discussion, Kellogg made an interesting note:

One of the arguments most frequently advanced by the skeptics is that the observed warming in this century should have been larger, based on climate models that do not take account of ocean circulations, and that there should theoretically have been no such ‘moratorium’ between 1940 and 1975.

Kellogg then notes that if the oceans played a role, there wouldn’t be such a problem.

Watts and Morantine (1993) also revisited the issue (perhaps the journal sent them Kellogg’s letter and asked for their response). There were couple of additional interesting points in their response relating to current discussion on global warming hiatus. They noted on the significance of the moratorium:

In a recent article by Galbraith and Green (1992), a series of statistical tests were performed on the global average temperature time series from 1880 to 1988 (Hansen and Lebedeff, 1987). A statistically significant trend that can be approximated by a linear term was found, and the deviation from this trend during the period between 1940 and 1970 was found to fall within the range of sample fluctuation.


Even though the surface temperature of the Earth is an important piece of information, the distribution of thermal energy is a three-dimensional problem.

What I have shown here is just a sample of all papers that were studying the issue. The research on the issue also continued after the papers presented here.

The significance for current hiatus discussion

It is clear that before 2000s there had been lot of research on the subject of short-term variability of surface temperature in a presence of long-term warming trend. The research back then also pointed to probable causes of the short-term variability.

Apparently, the first claims of global warming hiatus after 1998 were made in 2006 by well-known climate change mitigation opponents. This was obviously far too soon statistically to make those claims, and there was no indication that the claims were made with knowledge of the earlier discussion and research on the subject. It also should be noted, that the claims in question were not made in scientific literature but in popular media (a situation that has continued after that and largely continues even today).

However, lots and lots of papers have been published on the recent global warming hiatus. I have sampled the reference lists of some of them and it seems that also scientific community has largely forgot that the issue has already been studied. This seems a bit unfortunate and makes one wonder if we will have forgotten the current research when the next moratorium or pause or hiatus or whatever happens.


Waltraud A.R. Brinkmann (1976), Surface temperature trend for the Northern Hemisphere-updated, Quaternary Research, Volume 6, Issue 3, September 1976, Pages 355-358, doi:10.1016/0033-5894(67)90002-6.

Gaffin, S. R., M. I. Hoffert, and T. Volk (1986), Nonlinear coupling between surface temperature and ocean upwelling as an agent in historical climate variations, J. Geophys. Res., 91(C3), 3944–3950, doi:10.1029/JC091iC03p03944.

Gilliland, R.L. (1982), Solar, volcanic, and CO2 forcing of recent climatic changes, Climatic Change, 4: 111. doi:10.1007/BF00140585.

J. Hansen, D. Johnson, A. Lacis, S. Lebedeff, P. Lee, D. Rind, G. Russell (1981) Climate Impact of Increasing Atmospheric Carbon Dioxide, Science 28 Aug 1981: Vol. 213, Issue 4511, pp. 957-966, DOI: 10.1126/science.213.4511.957.

P. D. Jones, T. M. L. Wigley, , S. C. B. Raper (1986), The Rapidity of CO2-Induced Climatic Change: Observations, Model Results and Palaeoclimatic Implications, in Abrupt Climatic Change, Volume 216 of the series NATO ASI Series pp 47-55.

Kellogg, W.W. (1993), An apparent moratorium on the greenhouse warming due to the deep ocean, Climatic Change 25: 85. doi:10.1007/BF01094085.

Kincer, J. B. (1946), Our changing climate, Eos Trans. AGU, 27(3), 342–347, doi:10.1029/TR027i003p00342.

Mitchell, J. M. (1961), RECENT SECULAR CHANGES OF GLOBAL TEMPERATURE. Annals of the New York Academy of Sciences, 95: 235–250. doi:10.1111/j.1749-6632.1961.tb50036.x

J. Murray Mitchell Jr. (1970), A Preliminary Evaluation of Atmospheric Pollution as a Cause of the Global Temperature Fluctuation of the Past Century, 139-155. In, S.F. Singer (ed.), Global Effects of Environmental Pollution. Springer Verlag, New York, New York.

Clayton H. Reitan (1974), A climatic model of solar radiation and temperature change, Quaternary Research, Volume 4, Issue 1, March 1974, Pages 25–38,

Watts, R. G. (1985), Global climate variation due to fluctuations in the rate of deep water formation, J. Geophys. Res., 90(D5), 8067–8070, doi:10.1029/JD090iD05p08067.

Watts, R.G. & Morantine, M.C. (1991), Is the greenhouse gas-climate signal hiding in the deep ocean?, Climatic Change 18: iii. doi:10.1007/BF00142966.

Wigley, T.M.L., Angell, J.K. and Jones, P.D., 1985. Analysis of the temperature record. In: M.C. MacCracken and F.M. Luther (Eds.), Detecting the Climatic Effects of Increasing Carbon Dioxide, (DOE/ER-0235), U.S. Department of Energy, Carbon Dioxide Research Division, Washington, D.C., 55-90.

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New research – temperature (October 18, 2016)

Posted by Ari Jokimäki on October 18, 2016

Some of the latest papers on temperature (related to climate) are shown below. First a few highlighted papers with abstracts and then a list of some other papers. If this subject interests you, be sure to check also the other papers – they are by no means less interesting than the highlighted ones.


Comparing tropospheric warming in climate models and satellite data (Santer et al. 2016)

Abstract: We use updated and improved satellite retrievals of the temperature of the mid- to upper troposphere (TMT) to address key questions about the size and significance of TMT trends, agreement with model-derived TMT values, and whether models and satellite data show similar vertical profiles of warming. A recent study claimed that TMT trends over 1979 and 2015 are three times larger in climate models than in satellite data, but did not correct for the contribution TMT trends receive from stratospheric cooling. Here we show that the average ratio of modeled and observed TMT trends is sensitive to both satellite data uncertainties and to model-data differences in stratospheric cooling. When the impact of lower stratospheric cooling on TMT is accounted for, and when the most recent versions of satellite datasets are used, the previously claimed ratio of three between simulated and observed near-global TMT trends is reduced to ≈ 1.7. Next, we assess the validity of the statement that satellite data show no significant tropospheric warming over the last 18 years. This claim is not supported by our analysis: in five out of six corrected satellite TMT records, significant global-scale tropospheric warming has occurred within the last 18 years. Finally, we address long-standing concerns regarding discrepancies in modeled and observed vertical profiles of warming in the tropical atmosphere. We show that amplification of tropical warming between the lower and mid- to upper troposphere is now in close agreement in the average of 37 climate models and in one updated satellite record.

Deep and Abyssal Ocean Warming from 35 years of Repeat Hydrography (Desbruyères et al. 2016)

Abstract: Global and regional ocean warming deeper than 2000 m is investigated using 35 years of sustained repeat hydrographic survey data starting in 1981. The global long-term temperature trend below 2000 m, representing the time period 1991–2010, is equivalent to a mean heat flux of 0.065 ± 0.040 W m−2 applied over the Earth’s surface area. The strongest warming rates are found in the abyssal layer (4000–6000 m), which contributes to one third of the total heat uptake with the largest contribution from the Southern and Pacific Oceans. A similar regional pattern is found in the deep layer (2000–4000 m), which explains the remaining two thirds of the total heat uptake yet with larger uncertainties. The global average warming rate did not change within uncertainties pre-2000 versus post-2000, whereas ocean average warming rates decreased in the Pacific and Indian Oceans and increased in the Atlantic and Southern Oceans.

The contribution of greenhouse gases to the recent slowdown in global-mean temperature trends (Checa-Garcia et al. 2016)

Abstract: The recent slowdown in the rate of increase in global-mean surface temperature (GMST) has generated extensive discussion, but little attention has been given to the contribution of time-varying trends in greenhouse gas concentrations. We use a simple model approach to quantify this contribution. Between 1985 and 2003, greenhouse gases (including well-mixed greenhouse gases, tropospheric and stratospheric ozone, and stratospheric water vapour from methane oxidation) caused a reduction in GMST trend of around 0.03–0.05 K decade−1 which is around 18%–25% of the observed trend over that period. The main contributors to this reduction are the rapid change in the growth rates of ozone-depleting gases (with this contribution slightly opposed by stratospheric ozone depletion itself) and the weakening in growth rates of methane and tropospheric ozone radiative forcing. Although CO2 is the dominant greenhouse gas contributor to GMST trends, the continued increase in CO2 concentrations offsets only about 30% of the simulated trend reduction due to these other contributors. These results emphasize that trends in non-CO2 greenhouse gas concentrations can make significant positive and negative contributions to changes in the rate of warming, and that they need to be considered more closely in analyses of the causes of such variations.

The Stancari air thermometer and the 1715–1737 record in Bologna, Italy (Camuffo et al. 2016)

Abstract: This paper is focused on the closed-tube Stancari air thermometer that was developed at the beginning of the eighteenth century as an improvement of the Amontons thermometer, and used to record the temperature in Bologna, Italy, from 1715 to 1737. The problems met with this instrument, its calibration and the building technology in the eighteenth century are discussed in order to correct the record. The used methodological approach constitutes a useful example for other early series. The analysis of this record shows that the temperature in Bologna was not different from the 1961–1990 reference period. This result is in line with the contemporary record taken in Padua, Italy, confirming that this period of the Little Ice Age was not cold in the Mediterranean area.

Twenty-five winters of unexpected Eurasian cooling unlikely due to Arctic sea-ice loss (McCusker et al. 2016)

Abstract: Surface air temperature over central Eurasia decreased over the past twenty-five winters at a time of strongly increasing anthropogenic forcing and Arctic amplification. It has been suggested that this cooling was related to an increase in cold winters due to sea-ice loss in the Barents–Kara Sea. Here we use over 600 years of atmosphere-only global climate model simulations to isolate the effect of Arctic sea-ice loss, complemented with a 50-member ensemble of atmosphere–ocean global climate model simulations allowing for external forcing changes (anthropogenic and natural) and internal variability. In our atmosphere-only simulations, we find no evidence of Arctic sea-ice loss having impacted Eurasian surface temperature. In our atmosphere–ocean simulations, we find just one simulation with Eurasian cooling of the observed magnitude but Arctic sea-ice loss was not involved, either directly or indirectly. Rather, in this simulation the cooling is due to a persistent circulation pattern combining high pressure over the Barents–Kara Sea and a downstream trough. We conclude that the observed cooling over central Eurasia was probably due to a sea-ice-independent internally generated circulation pattern ensconced over, and nearby, the Barents–Kara Sea since the 1980s. These results improve our knowledge of high-latitude climate variability and change, with implications for our understanding of impacts in high-northern-latitude systems.

Other papers

New method of estimating temperatures near the mesopause region using meteor radar observations (Lee et al. 2016)

Estimated influence of urbanization on surface warming in Eastern China using time-varying land use data (Liao et al. 2016)

The influence of winter and summer atmospheric circulation on the variability of temperature and sea ice around Greenland (Ogi et al. 2016)

A cold and fresh ocean surface in the Nordic Seas during MIS 11: Significance for the future ocean (Kandiano et al. 2016)

Observed and projected sea surface temperature seasonal changes in the Western English Channel from satellite data and CMIP5 multi-model ensemble (L’Hévéder et al. 2016)

Historical ocean reanalyses (1900–2010) using different data assimilation strategies (Yang et al. 2016)

Analysis of the warmest Arctic winter, 2015-2016 (Cullather et al. 2016)

The influence of synoptic circulations and local processes on temperature anomalies at three French observatories (Dione et al. 2016)

Ocean atmosphere thermal decoupling in the eastern equatorial Indian ocean (Joseph et al. 2016)

Changes of the time-varying percentiles of daily extreme temperature in China (Li et al. 2016)

High atmospheric horizontal resolution eliminates the wind-driven coastal warm bias in the southeastern tropical Atlantic (Milinski et al. 2016)

Effects of Natural Variability of Seawater Temperature, Time Series Length, Decadal Trend and Instrument Precision on the Ability to Detect Temperature Trends (Schlegel & Smit, 2016)

Interhemispheric SST gradient trends in the Indian Ocean prior to and during the recent global warming hiatus (Dong & McPhaden, 2016)

Temperature and precipitation extremes in century-long gridded observations, reanalyses, and atmospheric model simulations (Donat et al. 2016)

Atmospheric structure favoring high sea surface temperatures in the western equatorial Pacific (Wirasatriya et al. 2016)

Spatial and temporal changes in daily temperature extremes in China during 1960–2011 (Shen et al. 2016)

Disaggregation of Remotely Sensed Land Surface Temperature: A New Dynamic Methodology (Zhan et al. 2016)

Impact of high-resolution sea surface temperature and urban data on estimations of surface air temperature in a regional climate (Adachi et al. 2016)

Trends of urban surface temperature and heat island characteristics in the Mediterranean (Benas et al. 2016)

Impacts of urbanization on summer climate in China: An assessment with coupled land-atmospheric modeling (Cao et al. 2016)

The impact of climatic and non-climatic factors on land surface temperature in southwestern Romania (Roşca et al. 2016)

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New research – climate sensitivity, forcings, and feedbacks (September 22, 2016)

Posted by Ari Jokimäki on September 22, 2016

Some of the latest papers on climate sensitivity, forcings, and feedbacks are shown below. First a few highlighted papers with abstracts and then a list of some other papers. If this subject interests you, be sure to check also the other papers – they are by no means less interesting than the highlighted ones.


The Effects of Ocean Heat Uptake on Transient Climate Sensitivity (Rose & Rayborn, 2016)

Abstract: Transient climate sensitivity tends to increase on multiple timescales in climate models subject to an abrupt CO2 increase. The interdependence of radiative and ocean heat uptake processes governing this increase are reviewed. Heat uptake tends to be spatially localized to the subpolar oceans, and this pattern emerges rapidly from an initially uniform distribution. Global climatic impact of heat uptake is studied through the lens of the efficacy concept and a linear systems perspective in which responses to individual climate forcing agents are additive. Heat uptake can be treated as a slowly varying forcing on the atmosphere and surface, whose efficacy is strongly determined by its geographical pattern. An illustrative linear model driven by simple prescribed uptake patterns demonstrates the emergence of increasing climate sensitivity as a consequence of the slow decay of high-efficacy subpolar heat uptake. Evidence is reviewed for the key role of shortwave cloud feedbacks in setting the high efficacy of ocean heat uptake and thus in increasing climate sensitivity. A causal physical mechanism is proposed, linking subpolar heat uptake to a global-scale increase in lower-tropospheric stability. It is shown that the rate of increase in estimated inversion strength systematically slows as heat uptake decays. Variations in heat uptake should therefore manifest themselves as differences in low cloud feedbacks.

Understanding Climate Feedbacks and Sensitivity Using Observations of Earth’s Energy Budget (Loeb et al. 2016)

Abstract: While climate models and observations generally agree that climate feedbacks collectively amplify the surface temperature response to radiative forcing, the strength of the feedback estimates varies greatly, resulting in appreciable uncertainty in equilibrium climate sensitivity. Because climate feedbacks respond differently to different spatial variations in temperature, short-term observational records have thus far only provided a weak constraint for climate feedbacks operating under global warming. Further complicating matters is the likelihood of considerable time variation in the effective global climate feedback parameter under transient warming. There is a need to continue to revisit the underlying assumptions used in the traditional forcing-feedback framework, with an emphasis on how climate models and observations can best be utilized to reduce the uncertainties. Model simulations can also guide observational requirements and provide insight on how the observational record can most effectively be analyzed in order to make progress in this critical area of climate research.

Insights from a Refined Decomposition of Cloud Feedbacks (Zelinka et al. 2016)

Abstract: Decomposing cloud feedback into components due to changes in several gross cloud properties provides valuable insights into its physical causes. Here we present a refined decomposition that separately considers changes in free tropospheric and low cloud properties, better connecting feedbacks to individual governing processes and avoiding ambiguities present in a commonly used decomposition. It reveals that three net cloud feedback components are robustly nonzero: positive feedbacks from increasing free tropospheric cloud altitude and decreasing low cloud cover and a negative feedback from increasing low cloud optical depth. Low cloud amount feedback is the dominant contributor to spread in net cloud feedback but its anticorrelation with other components damps overall spread. The ensemble mean free tropospheric cloud altitude feedback is roughly 60% as large as the standard cloud altitude feedback because it avoids aliasing in low cloud reductions. Implications for the “null hypothesis” climate sensitivity from well-understood and robustly simulated feedbacks are discussed.

Rapid systematic assessment of the detection and attribution of regional anthropogenic climate change (Stone & Hansen, 2016)

Abstract: Despite being a well-established research field, the detection and attribution of observed climate change to anthropogenic forcing is not yet provided as a climate service. One reason for this is the lack of a methodology for performing tailored detection and attribution assessments on a rapid time scale. Here we develop such an approach, based on the translation of quantitative analysis into the “confidence” language employed in recent Assessment Reports of the Intergovernmental Panel on Climate Change. While its systematic nature necessarily ignores some nuances examined in detailed expert assessments, the approach nevertheless goes beyond most detection and attribution studies in considering contributors to building confidence such as errors in observational data products arising from sparse monitoring networks. When compared against recent expert assessments, the results of this approach closely match those of the existing assessments. Where there are small discrepancies, these variously reflect ambiguities in the details of what is being assessed, reveal nuances or limitations of the expert assessments, or indicate limitations of the accuracy of the sort of systematic approach employed here. Deployment of the method on 116 regional assessments of recent temperature and precipitation changes indicates that existing rules of thumb concerning the detectability of climate change ignore the full range of sources of uncertainty, most particularly the importance of adequate observational monitoring.

One Year of Downwelling Spectral Radiance Measurements from 100 to 1400 cm−1 at Dome-Concordia: Results in Clear Conditions (Rizzi et al. 2016)

Abstract: The present work examines downwelling radiance spectra measured at the ground during 2013 by a Far Infrared Fourier Transform Spectrometer at Dome-C, Antarctica. A tropospheric backscatter and depolarization Lidar is also deployed at same site and a radiosonde system is routinely operative. The measurements allow characterization of the water vapor and clouds infrared properties in Antarctica under all sky conditions. In this paper we specifically discuss cloud detection and the analysis in clear sky condition, required for the discussion of the results obtained in cloudy conditions. Firstly, the paper discusses the procedures adopted for the quality control of spectra acquired automatically. Then it describes the classification procedure used to discriminate spectra measured in clear-sky from cloudy conditions. Finally a selection is performed and 66 clear cases, spanning the whole year, are compared to simulations. The computation of layer molecular optical depth is performed with line-by-line techniques and a convolution to simulate the REFIR-PAD measurements; the downwelling radiance for selected clear cases is computed with a state-of-the-art adding-doubling code. The mean difference over all selected cases between simulated and measured radiance is within experimental error for all the selected micro-windows except for the negative residuals found for all micro-windows in the range 200 to 400 cm−1, with largest values around 295.1 cm−1. The paper discusses possible reasons for the discrepancy and identifies the incorrect magnitude of the water vapor total absorption coefficient as the cause of such large negative radiance bias below 400 cm−1.

Other papers

Dependence of global radiative feedbacks on evolving patterns of surface heat fluxes (Rugenstein et al. 2016)

Understanding the varied influence of mid-latitude jet position on clouds and cloud-radiative effects in observations and global climate models (Grise & Medeiros, 2016)

Effect of land cover change on snow free surface albedo across the continental United States (Wickham et al. 2016)

Forced response and internal variability of summer climate over western North America (Kamae et al. 2016)

Detection and attribution of climate change at regional scale: case study of Karkheh river basin in the west of Iran (Zohrabi et al. 2016)

Atmospheric lifetimes, infrared absorption spectra, radiative forcings and global warming potentials of NF3 and CF3CF2Cl (CFC-115) (Totterdill et al. 2016)

A long-term study of aerosol–cloud interactions and their radiative effect at the Southern Great Plains using ground-based measurements (Sena et al. 2016)

Detection of dimming/brightening in Italy from homogenized all-sky and clear-sky surface solar radiation records and underlying causes (1959–2013) (Manara et al. 2016)

Effects of 20–100 nm particles on liquid clouds in the clean summertime Arctic (Leaitch et al. 2016)

Assessment of the first indirect radiative effect of ammonium-sulfate-nitrate aerosols in East Asia (Han et al. 2016)

Sensitivity of precipitation extremes to radiative forcing of greenhouse gases and aerosols (Lin et al. 2016)

Global climate forcing of aerosols embodied in international trade (Lin et al. 2016)

Reprocessing of HIRS Satellite Measurements from 1980-2015: Development Towards a Consistent Decadal Cloud Record (Menzel et al. 2016)

Radiative Forcing from Anthropogenic Sulfur and Organic Emissions Reaching the Stratosphere (Yu et al. 2016)

Near miss: the importance of the natural atmospheric CO2 concentration to human historical evolution (Archer, 2016)

Long-Term Variations of Noctilucent Clouds at ALOMAR (Fiedler et al. 2016)

Estimating Arctic sea-ice shortwave albedo from MODIS data (Qu et al. 2016)

Surface albedo raise in the South American Chaco: Combined effects of deforestation and agricultural changes (Houspanossian et al. 2016)

New Observational Evidence for a Positive Cloud Feedback that Amplifies the Atlantic Multidecadal Oscillation (Bellomo et al. 2016)

Surface water and heat exchange comparison between alpine meadow and bare land in a permafrost region of the Tibetan Plateau (You et al. 2016)

foF2 vs Solar Indices for the Rome station: looking for the best general relation which is able to describe the anomalous minimum between cycles 23 and 24 (Perna & Pezzopane, 2016)

Comparison of Methods: Attributing the 2014 record European temperatures to human influences (Uhe et al. 2016)

Relevance of long term time – series of atmospheric parameters at a mountain observatory to models for climate change (Kancírová et al. 2016)

An energy balance perspective on regional CO2-induced temperature changes in CMIP5 models (Räisänen, 2016)

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New research – temperature (September 5, 2016)

Posted by Ari Jokimäki on September 5, 2016

Some of the latest papers on temperature (in a climatic sense) are shown below. First a few highlighted papers with abstracts and then a list of some other papers. If this subject interests you, be sure to check also the other papers – they are by no means less interesting than the highlighted ones.


Observed and simulated full-depth ocean heat-content changes for 1970–2005 (Cheng et al. 2016)

Abstract: Greenhouse-gas emissions have created a planetary energy imbalance that is primarily manifested by increasing ocean heat content (OHC). Updated observational estimates of full-depth OHC change since 1970 are presented that account for recent advancements in reducing observation errors and biases. The full-depth OHC has increased by 0.74 [0.68, 0.80]  ×  1022 J yr-1 (0.46 Wm−2) and 1.22 [1.16–1.29]  ×  1022 J yr-1 (0.75 Wm-2) for 1970–2005 and 1992–2005, respectively, with a 5 to 95 % confidence interval of the median. The CMIP5 models show large spread in OHC changes, suggesting that some models are not state-of-the-art and require further improvements. However, the ensemble median has excellent agreement with our observational estimate: 0.68 [0.54–0.82]  ×  1022 J yr-1 (0.42 Wm-2) from 1970 to 2005 and 1.25 [1.10–1.41]  ×  1022 J yr-1 (0.77 Wm-2) from 1992 to 2005. These results increase confidence in both the observational and model estimates to quantify and study changes in Earth’s energy imbalance over the historical period. We suggest that OHC be a fundamental metric for climate model validation and evaluation, especially for forced changes (decadal timescales).

Pacific sea level rise patterns and global surface temperature variability (Peyser et al. 2016)

Abstract: During 1998–2012, climate change and sea level rise (SLR) exhibit two notable features: a slowdown of global surface warming (hiatus) and a rapid SLR in the tropical western Pacific. To quantify their relationship, we analyze the long-term control simulations of 38 climate models. We find a significant and robust correlation between the east-west contrast of dynamic sea level (DSL) in the Pacific and global mean surface temperature (GST) variability on both interannual and decadal time scales. Based on linear regression of the multimodel ensemble mean, the anomalously fast SLR in the western tropical Pacific observed during 1998–2012 indicates suppression of a potential global surface warming of 0.16° ± 0.06°C. In contrast, the Pacific contributed 0.29° ± 0.10°C to the significant interannual GST increase in 1997/1998. The Pacific DSL anomalies observed in 2015 suggest that the strong El Niño in 2015/2016 could lead to a 0.21° ± 0.07°C GST jump.

Contrasting effects of urbanization and agriculture on surface temperature in eastern China (Zhou et al. 2016)

Abstract: The combined effect of urbanization and agriculture, two most pervasive land use activities, on the surface climate remains poorly understood. Using Moderate Resolution Imaging Spectroradiometer data over 2010–2015 and forests as reference, we showed that urbanization warmed the land surface temperature (LST), especially during the daytime and in growing seasons (maximized at 5.0 ± 2.0°C in May), whereas agriculture (dominated by double-cropping system) cooled the LST in two growing seasons during the daytime and all the months but July during the nighttime in Jiangsu Province, eastern China. Collectively, they had insignificant effects on the LST during the day (−0.01°C) and cooled the LST by −0.6°C at night. We also found large geographic variations associated with their thermal effects, indicated by a warming tendency southward. These spatiotemporal patterns depend strongly on vegetation activity, evapotranspiration, surface albedo, and the background climate. Our results emphasize the great potential of agriculture in offsetting the heating effects caused by rapid urbanization in China.

A summer temperature bias in early alcohol thermometers (Camuffo & Valle, 2016)

Abstract: This paper analyses the response of alcohol thermometers in relation to the departure from linearity and the choice of the calibration points. The result is that alcohol thermometers are affected by large departures that reach a maximum (i.e. −6 °C) at 50 °C ambient temperature. This may have caused a severe bias in early records, when alcohol thermometers were popular, especially during the Little Ice Age. Choosing a lower temperature for the upper point, calibration may substantially reduce this bias. Examples are given with thermometers in use in the 17th and 18th centuries. A careful correction of long series is necessary to avoid misleading climate interpretations.

The phenology of Arctic Ocean Surface warming (Steele & Dickinson, 2016)

Abstract: In this work, we explore the seasonal relationships (i.e., the phenology) between sea ice retreat, sea surface temperature (SST), and atmospheric heat fluxes in the Pacific Sector of the Arctic Ocean, using satellite and reanalysis data. We find that where ice retreats early in most years, maximum summertime SSTs are usually warmer, relative to areas with later retreat. For any particular year, we find that anomalously early ice retreat generally leads to anomalously warm SSTs. However, this relationship is weak in the Chukchi Sea, where ocean advection plays a large role. It is also weak where retreat in a particular year happens earlier than usual, but still relatively late in the season, primarily because atmospheric heat fluxes are weak at that time. This result helps to explain the very different ocean warming responses found in two recent years with extreme ice retreat, 2007 and 2012. We also find that the timing of ice retreat impacts the date of maximum SST, owing to a change in the ocean surface buoyancy and momentum forcing that occurs in early August that we term the Late Summer Transition (LST). After the LST, enhanced mixing of the upper ocean leads to cooling of the ocean surface even while atmospheric heat fluxes are still weakly downward. Our results indicate that in the near-term, earlier ice retreat is likely to cause enhanced ocean surface warming in much of the Arctic Ocean, although not where ice retreat still occurs late in the season.

Other papers

Comparisons of time series of annual mean surface air temperature for China since the 1900s: Observations, model simulations and extended reanalysis (Li et al. 2016)

First ground-based observations of mesopause temperatures above the Eastern-Mediterranean Part I: Multi-day oscillations and tides (Silber et al. 2016)

An enhanced single-channel algorithm for retrieving land surface temperature from Landsat series data (Wang et al. 2016)

Observed changes of temperature extremes in Serbia over the period 1961 − 2010 (Ruml et al. 2016)

The inter-annual variations and the long-term trends of monthly air temperatures in Iraq over the period 1941–2013 (Muslih & Błażejczyk, 2016)

A multiregion model evaluation and attribution study of historical changes in the area affected by temperature and precipitation extremes (Dittus et al. 2016)

Changes in wind speed under heat waves enhance urban heat islands in Beijing metropolitan area (Li et al. 2016)

Regional differential behaviour of maximum temperatures in the Iberian Peninsula regarding the Summer NAO in the second half of the twentieth century (Favà et al. 2016)

Confidence intervals for time averages in the presence of long range correlations, a case study on earth surface temperature anomalies (Massah & Kantz, 2016)

An ensemble of ocean reanalyses for 1815–2013 with sparse observational input (Giese et al. 2016)

Arctic-North Pacific coupled impacts on the late autumn cold in North America (Sung et al. 2016)

Wet-bulb, dew point, and air temperature trends in Spain (Moratiel et al. 2016)

Insights into elevation-dependent warming in the Tibetan Plateau-Himalayas from CMIP5 model simulations (Palazzi et al. 2016)

Spatial variations in temperature in a mountainous region of Jeju Island, South Korea (Um & Kim, 2016)

Gap filling and homogenization of climatological datasets in the headwater region of the Upper Blue Nile Basin, Ethiopia (Woldesenbet et al. 2016)

A homogenized long-term temperature record for the Western Cape Province in South Africa: 1916–2013 (Lakhraj-Govender et al. 2016)

Inter-model diversity of Arctic amplification caused by global warming and its relationship with the Inter-tropical Convergence Zone in CMIP5 climate models (Yim et al. 2016)

Urban–rural differences in near-surface air temperature as resolved by the Central Europe Refined analysis (CER): sensitivity to planetary boundary layer schemes and urban canopy models (Jänicke et al. 2016)

Monotonic Decrease of the Zonal SST Gradient of the Equatorial Pacific as a Function of CO2 Concentration in CCSM3 and CCSM4 (Yang et al. 2016)

Recent seasonal and long-term changes in southern Australian frost occurrence (Crimp et al. 2016)

Surface temperature trends from homogenized time series in South Africa: 1931–2015 (Kruger & Nxumalo, 2016)

Investigations of the middle atmospheric thermal structure and oscillations over sub-tropical regions in the Northern and Southern Hemispheres (Sharma et al. 2016)

Recent amplification of the North American winter temperature dipole (Singh et al. 2016)

Use of remotely-sensed land surface temperature as a proxy for air temperatures at high elevations: Findings from a 5000 metre elevational transect across Kilimanjaro (Pepin et al. 2016)

Spatial distribution of temperature trends and extremes over Maharashtra and Karnataka States of India (Dhorde et al. 2016)

Assessing atmospheric temperature data sets for climate studies (Cederlöf et al. 2016)

Ocean heat uptake and interbasin transport of passive and redistributive surface heating (Garuba & Klinger, 2016)

Temperature and precipitation regional climate series over the central Pyrenees during 1910–2013 (Pérez-Zanón et al. 2016)

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New research – climate models and projections (August 16, 2016)

Posted by Ari Jokimäki on August 16, 2016

Some of the latest papers on climate models and projections are shown below. First a few highlighted papers with abstracts and then a list of some other papers. If this subject interests you, be sure to check also the other papers – they are by no means less interesting than the highlighted ones.


CMIP5 scientific gaps and recommendations for CMIP6 (Stouffer et al. 2016)

Abstract: The Coupled Model Intercomparison Project (CMIP) is an ongoing coordinated international activity of numerical experimentation of unprecedented scope and impact on climate science. Its most recent fifth phase, CMIP5, has created nearly two petabytes of output from dozens of experiments performed by dozens of comprehensive climate models available to the climate science research community. In so doing, it has greatly advanced climate science. While CMIP5 has given answers to important science questions, with the help of a community survey we identify and motivate three broad topics here that guided the scientific framework of the next phase of CMIP, i.e. CMIP6:

1.How does the Earth System respond to changes in forcing?

2.What are the origins and consequences of systematic model biases?

3.How can we assess future climate changes given internal climate variability, predictability and uncertainties in scenarios?

CMIP has demonstrated the power of idealized experiments to better understand how the climate system works. We expect that these idealized approaches will continue to contribute to CMIP6. The quantification of radiative forcings and responses was poor and requires new methods and experiments to address this gap. There are a number of systematic model biases that appear in all phases of CMIP which remain a major climate modeling challenge. These biases need increased attention to better understand their origins and consequences through targeted experiments. Improving understanding of the mechanisms underlying internal climate variability for more skillful decadal climate predictions and long-term projections remains another challenge for CMIP6.

Climate change in the next 30 years: What can a convection-permitting model tell us that we did not already know? (Fosser et al. 2016)

Abstract: To investigate the climate change in the next 30 years over a complex terrain in southwestern Germany, simulations performed with the regional climate model COSMO-CLM at convection-permitting resolution are compared to simulations at 7 km resolution with parameterised convection. An earlier study has shown the main benefits of convection-permitting resolution in the hourly statistics and the diurnal cycle of precipitation intensities. Here, we investigate whether the improved simulation of precipitation in the convection-permitting model is affecting future climate projections in summer. Overall, the future scenario (ECHAM5 with A1B forcing) brings weak changes in mean precipitation, but stronger hourly intensities in the morning and less frequent but more intense daily precipitation. The two model simulations produce similar changes in climate, despite differences in their physical characteristics linked to the formation of convective precipitation. A significant increase in the morning precipitation probably due to large-scale forced convection is found when considering only the most extreme events (above 50 mm/day). In this case, even the diurnal cycles of precipitation and convection-related indices are similar between resolutions, leading to the conclusion that the 7 km model sufficiently resolves the most extreme convective events. In this region and time periods, the 7 km resolution is deemed sufficient for most assessments of near future precipitation change. However, conclusions could be dependent on the characteristics of the region of investigation.

Evaluating Arctic warming mechanisms in CMIP5 models (Franzke et al. 2016)

Abstract: Arctic warming is one of the most striking signals of global warming. The Arctic is one of the fastest warming regions on Earth and constitutes, thus, a good test bed to evaluate the ability of climate models to reproduce the physics and dynamics involved in Arctic warming. Different physical and dynamical mechanisms have been proposed to explain Arctic amplification. These mechanisms include the surface albedo feedback and poleward sensible and latent heat transport processes. During the winter season when Arctic amplification is most pronounced, the first mechanism relies on an enhancement in upward surface heat flux, while the second mechanism does not. In these mechanisms, it has been proposed that downward infrared radiation (IR) plays a role to a varying degree. Here, we show that the current generation of CMIP5 climate models all reproduce Arctic warming and there are high pattern correlations—typically greater than 0.9—between the surface air temperature (SAT) trend and the downward IR trend. However, we find that there are two groups of CMIP5 models: one with small pattern correlations between the Arctic SAT trend and the surface vertical heat flux trend (Group 1), and the other with large correlations (Group 2) between the same two variables. The Group 1 models exhibit higher pattern correlations between Arctic SAT and 500 hPa geopotential height trends, than do the Group 2 models. These findings suggest that Arctic warming in Group 1 models is more closely related to changes in the large-scale atmospheric circulation, whereas in Group 2, the albedo feedback effect plays a more important role. Interestingly, while Group 1 models have a warm or weak bias in their Arctic SAT, Group 2 models show large cold biases. This stark difference in model bias leads us to hypothesize that for a given model, the dominant Arctic warming mechanism and trend may be dependent on the bias of the model mean state.

The Impact of SST Biases on Projections of Anthropogenic Climate Change: A Greater Role for Atmosphere-only Models? (He & Soden, 2016)

Abstract: There is large uncertainty in the model simulation of regional climate change from anthropogenic forcing. Recent studies have tried to link such uncertainty to intermodel differences in the pattern of sea surface temperature (SST) change. On the other hand, coupled climate models also contain systematic biases in their climatology, largely due to drift in SSTs. To the extent that the projected changes depend on the mean state, biases in the present-day climatology also contribute to the intermodel spread in climate change projections. By comparing atmospheric general circulation model (AGCM) simulations using the climatological SSTs from different coupled models, we show that biases in the climatological SST generally have a larger impact on regional projections over land than do intermodel differences in the pattern of SST change. These results advocate for a greater application of AGCM simulations with observed SSTs or flux-adjusted coupled models to improve regional projections of anthropogenic climate change.

The art and science of climate model tuning (Hourdin et al. 2016)

Abstract: We survey the rationale and diversity of approaches for tuning, a fundamental aspect of climate modeling which should be more systematically documented and taken into account in multi-model analysis.

The process of parameter estimation targeting a chosen set of observations is an essential aspect of numerical modeling. This process is usually named tuning in the climate modeling community. In climate models, the variety and complexity of physical processes involved, and their interplay through a wide range of spatial and temporal scales, must be summarized in a series of approximate sub-models. Most sub-models depend on uncertain parameters. Tuning consists of adjusting the values of these parameters to bring the solution as a whole into line with aspects of the observed climate. Tuning is an essential aspect of climate modeling with its own scientific issues, which is probably not advertised enough outside the community of model developers. Optimization of climate models raises important questions about whether tuning methods a priori constrain the model results in unintended ways that would affect our confidence in climate projections. Here we present the definition and rationale behind model tuning, review specific methodological aspects, and survey the diversity of tuning approaches used in current climate models. We also discuss the challenges and opportunities in applying so-called ‘objective‘ methods in climate model tuning. We discuss how tuning methodologies may affect fundamental results of climate models, such as climate sensitivity. The article concludes with a series of recommendations to make the process of climate model tuning more transparent.

Other papers

High-resolution ensemble projections of near-term regional climate over the continental United States (Ashfaq et al. 2016)

Twentieth century temperature trends in CMIP3, CMIP5, and CESM-LE climate simulations – spatial-temporal uncertainties, differences and their potential sources (Kumar et al. 2016)

Assessing the robustness and uncertainties of projected changes in temperature and precipitation in AR4 Global Climate Models over the Arabian Peninsula (Almazroui et al. 2016)

The influence of model resolution on temperature variability (Klavans et al. 2016)

Evaluation of the skill of North-American Multi-Model Ensemble (NMME) Global Climate Models in predicting average and extreme precipitation and temperature over the continental USA (Slater et al. 2016)

Assessing uncertainties in land cover projections (Alexander et al. 2016)

Effects of southeastern Pacific sea surface temperature on the double-ITCZ bias in NCAR CESM1 (Song & Zhang, 2016)

Stochastic Parameterization: Towards a new view of Weather and Climate Models (Berner et al. 2016)

Do convection-permitting regional climate models improve projections of future precipitation change? (Kendon et al. 2016)

MiKlip – a National Research Project on Decadal Climate Prediction (Marotzke et al. 2016)

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New research – composition of atmosphere (August 15, 2016)

Posted by Ari Jokimäki on August 15, 2016

Some of the latest papers on composition of atmosphere are shown below. First a few highlighted papers with abstracts and then a list of some other papers. If this subject interests you, be sure to check also the other papers – they are by no means less interesting than the highlighted ones.


Role of OH variability in the stalling of the global atmospheric CH4 growth rate from 1999 to 2006 (McNorton et al. 2016)

Abstract: The growth in atmospheric methane (CH4) concentrations over the past 2 decades has shown large variability on a timescale of several years. Prior to 1999 the globally averaged CH4 concentration was increasing at a rate of 6.0 ppb yr−1, but during a stagnation period from 1999 to 2006 this growth rate slowed to 0.6 ppb yr−1. From 2007 to 2009 the growth rate again increased to 4.9 ppb yr−1. These changes in growth rate are usually ascribed to variations in CH4 emissions. We have used a 3-D global chemical transport model, driven by meteorological reanalyses and variations in global mean hydroxyl (OH) concentrations derived from CH3CCl3 observations from two independent networks, to investigate these CH4 growth variations. The model shows that between 1999 and 2006 changes in the CH4 atmospheric loss contributed significantly to the suppression in global CH4 concentrations relative to the pre-1999 trend. The largest factor in this is relatively small variations in global mean OH on a timescale of a few years, with minor contributions of atmospheric transport of CH4 to its sink region and of atmospheric temperature. Although changes in emissions may be important during the stagnation period, these results imply a smaller variation is required to explain the observed CH4 trends. The contribution of OH variations to the renewed CH4 growth after 2007 cannot be determined with data currently available.

Diverse policy implications for future ozone and surface UV in a changing climate (Butler et al. 2016)

Abstract: Due to the success of the Montreal Protocol in limiting emissions of ozone-depleting substances, concentrations of atmospheric carbon dioxide, nitrous oxide, and methane will control the evolution of total column and stratospheric ozone by the latter half of the 21st century. As the world proceeds down the path of reducing climate forcing set forth by the 2015 Conference of the Parties to the United Nations Framework Convention on Climate Change (COP 21), a broad range of ozone changes are possible depending on future policies enacted. While decreases in tropical stratospheric ozone will likely persist regardless of the future emissions scenario, extratropical ozone could either remain weakly depleted or even increase well above historical levels, with diverse implication for ultraviolet (UV) radiation. The ozone layer’s dependence on future emissions of these gases creates a complex policy decision space for protecting humans and ecosystems, which includes unexpected options such as accepting nitrous oxide emissions in order to maintain historical column ozone and surface UV levels.

Changes in surface aerosol extinction trends over China during 1980–2013 inferred from quality-controlled visibility data (Li et al. 2016)

Abstract: Pollution in China has been attracting extensive attention both globally and regionally, especially due to the perceptually worsening “smog” condition in recent years. We use routine visibility measurements from 1980 to 2013 at 272 WMO stations in China to assess the temporal changes in the magnitude and the sign of pollution trends. A strict and comprehensive quality control procedure is enforced by considering several issues not typically addressed in previous studies. Two methods are used to independently estimate the trend and its significance level. Results show that in general, a strong increase in Aerosol Extinction Coefficient (AEC) over the majority of China is observed in the 1980s, followed by a moderate decrease in the 1990s, another increase in the 2000s, and a shift to decrease since around 2006 for some regions. Seasonally, winter and fall trends appear to be the strongest, while summer has the lowest trend.

The millennium water vapour drop in chemistry–climate model simulations (Brinkop et al. 2016)

Abstract: This study investigates the abrupt and severe water vapour decline in the stratosphere beginning in the year 2000 (the “millennium water vapour drop”) and other similarly strong stratospheric water vapour reductions by means of various simulations with the state-of-the-art Chemistry-Climate Model (CCM) EMAC (ECHAM/MESSy Atmospheric Chemistry Model). The model simulations differ with respect to the prescribed sea surface temperatures (SSTs) and whether nudging is applied or not. The CCM EMAC is able to most closely reproduce the signature and pattern of the water vapour drop in agreement with those derived from satellite observations if the model is nudged. Model results confirm that this extraordinary water vapour decline is particularly obvious in the tropical lower stratosphere and is related to a large decrease in cold point temperature. The drop signal propagates under dilution to the higher stratosphere and to the poles via the Brewer–Dobson circulation (BDC). We found that the driving forces for this significant decline in water vapour mixing ratios are tropical sea surface temperature (SST) changes due to a coincidence with a preceding strong El Niño–Southern Oscillation event (1997/1998) followed by a strong La Niña event (1999/2000) and supported by the change of the westerly to the easterly phase of the equatorial stratospheric quasi-biennial oscillation (QBO) in 2000. Correct (observed) SSTs are important for triggering the strong decline in water vapour. There are indications that, at least partly, SSTs contribute to the long period of low water vapour values from 2001 to 2006. For this period, the specific dynamical state of the atmosphere (overall atmospheric large-scale wind and temperature distribution) is important as well, as it causes the observed persistent low cold point temperatures. These are induced by a period of increased upwelling, which, however, has no corresponding pronounced signature in SSTs anomalies in the tropics. Our free-running simulations do not capture the drop as observed, because a) the cold point temperature has a low bias and thus the water vapour variability is reduced and b) because they do not simulate the appropriate dynamical state. Large negative water vapour declines are also found in other years and seem to be a feature which can be found after strong combined El Niño/La Niña events if the QBO west phase during La Niña changes to the east phase.

Evaluation of 4 years of continuous δ13C(CO2) data using a moving Keeling plot method (Vardag, Hammer & Levin, 2016)

Abstract: Different carbon dioxide (CO2) emitters can be distinguished by their carbon isotope ratios. Therefore measurements of atmospheric δ13C(CO2) and CO2 concentration contain information on the CO2 source mix in the catchment area of an atmospheric measurement site. This information may be illustratively presented as the mean isotopic source signature. Recently an increasing number of continuous measurements of δ13C(CO2) and CO2 have become available, opening the door to the quantification of CO2 shares from different sources at high temporal resolution. Here, we present a method to compute the CO2 source signature (δS) continuously and evaluate our result using model data from the Stochastic Time-Inverted Lagrangian Transport model. Only when we restrict the analysis to situations which fulfill the basic assumptions of the Keeling plot method does our approach provide correct results with minimal biases in δS. On average, this bias is 0.2 ‰ with an interquartile range of about 1.2 ‰ for hourly model data. As a consequence of applying the required strict filter criteria, 85 % of the data points – mainly daytime values – need to be discarded. Applying the method to a 4-year dataset of CO2 and δ13C(CO2) measured in Heidelberg, Germany, yields a distinct seasonal cycle of δS. Disentangling this seasonal source signature into shares of source components is, however, only possible if the isotopic end members of these sources – i.e., the biosphere, δbio, and the fuel mix, δF – are known. From the mean source signature record in 2012, δbio could be reliably estimated only for summer to (−25.0 ± 1.0) ‰ and δF only for winter to (−32.5 ± 2.5) ‰. As the isotopic end members δbio and δF were shown to change over the season, no year-round estimation of the fossil fuel or biosphere share is possible from the measured mean source signature record without additional information from emission inventories or other tracer measurements.

Other papers

Intercomparison of in situ NDIR and column FTIR measurements of CO2 at Jungfraujoch (Schibig et al. 2016)

Evaluation of 4 years of continuous δ13C(CO2) data using a moving Keeling plot method (Vardag, Hammer & Levin, 2016)

Intra-seasonal variability of atmospheric CO2 concentrations over India during summer monsoons (Kumar et al. 2016)

Impact of ENSO on variability of AIRS retrieved CO2 over India (Kumar et al. 2016)

Large XCH4 anomaly in summer 2013 over northeast Asia observed by GOSAT (Ishizawa et al. 2016)

Can we detect regional methane anomalies? A comparison between three observing systems (Cressot et al. 2016)

Non-homogeneous vertical distribution of methane over Indian region using surface, aircraft and satellite based data (Kavitha & Nair, 2016)

A probabilistic study of the return of stratospheric ozone to 1960 levels (Södergren et al. 2016)

The representation of solar cycle signals in stratospheric ozone – Part 1: A comparison of recently updated satellite observations (Maycock et al. 2016)

Summer ozone concentrations in the vicinity of the Great Salt Lake (Horel et al. 2016)

Impact of emissions and +2 °C climate change upon future ozone and nitrogen dioxide over Europe (Watson et al. 2016)

Natural and Anthropogenic Aerosol Trends from Satellite and Surface Observations and Model Simulations over the North Atlantic Ocean from 2002 to 2012 (Jongeward et al. 2016)

Aerosol Lidar Observations of Atmospheric Mixing in Los Angeles: Climatology and Implications for Greenhouse Gas Observations (Ware et al. 2016)

Future aerosol emissions: a multi-model comparison (Smith et al. 2016)

Multi-Year Study of the Dependence of Sea Salt Aerosol on Wind Speed and Sea Ice Conditions in the Coastal Arctic (May et al. 2016)

Effects of climate changes on dust aerosol over East Asia from RegCM3 (Zhang et al. 2016)

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New research – atmospheric and oceanic circulation (August 10, 2016)

Posted by Ari Jokimäki on August 10, 2016

Some of the latest papers on atmospheric and oceanic circulation are shown below. First a few highlighted papers with abstracts and then a list of some other papers. If this subject interests you, be sure to check also the other papers – they are by no means less interesting than the highlighted ones.


The North Atlantic Oscillation as a driver of rapid climate change in the Northern Hemisphere (Delworth et al. 2016)

Abstract: Pronounced climate changes have occurred since the 1970s, including rapid loss of Arctic sea ice, large-scale warming and increased tropical storm activity in the Atlantic. Anthropogenic radiative forcing is likely to have played a major role in these changes, but the relative influence of anthropogenic forcing and natural variability is not well established. The above changes have also occurred during a period in which the North Atlantic Oscillation has shown marked multidecadal variations. Here we investigate the role of the North Atlantic Oscillation in these rapid changes through its influence on the Atlantic meridional overturning circulation and ocean heat transport. We use climate models to show that observed multidecadal variations of the North Atlantic Oscillation can induce multidecadal variations in the Atlantic meridional overturning circulation and poleward ocean heat transport in the Atlantic, extending to the Arctic. Our results suggest that these variations have contributed to the rapid loss of Arctic sea ice, Northern Hemisphere warming, and changing Atlantic tropical storm activity, especially in the late 1990s and early 2000s. These multidecadal variations are superimposed on long-term anthropogenic forcing trends that are the dominant factor in long-term Arctic sea ice loss and hemispheric warming.

Evidence of global warming impact on the evolution of the Hadley Circulation in ECMWF centennial reanalyses (D’Agostino & Lionello, 2016)

Abstract: This study analyzes the evolution of the Hadley Circulation (HC) during the twentieth century in ERA-20CM (AMIP-experiment) and ERA-20C (reanalysis). These two recent ECMWF products provide the opportunity for a new analysis of the HC trends and of their uncertainties. Further, the effect of sea surface temperature forcing (including its uncertainty) and data assimilation are investigated. Also the ECMWF reanalysis ERA-Interim, for the period 1979–2010, is considered for a complementary analysis. Datasets present important differences in characteristics and trends of the HC. In ERA-20C HC is weaker (especially the Southern Hemisphere HC) and the whole Northern Hemisphere HC is located more southward than in ERA-20CM (especially in the boreal summer). In ERA-Interim HC is stronger and wider than both other simulations. In general, the magnitude of trends is larger and more statistically significant in ERA-20C than in ERA-20CM. The presence of large multidecadal variability across twentieth century raises doubts on the interpretation of recent behavior, such as the onset of sustained long term trends, particularly for the HC strength. In spite of this, the southward shift of the Southern Edge and widening of the Southern Hemisphere HC appear robust features in all datasets, and their trends have accelerated in the last three decades, but actual expansion rates remain affected by considerable uncertainty. Inconsistencies between datasets are attributed to the different reproduction of the links between the HC width and factors affecting it (such as mean global temperature, tropopause height, meridional temperature contrast and planetary waves), which appear more robust in ERA-20CM than in ERA-20C, particularly for the two latter factors. Further, in ERA-Interim these correlations are not statistically significant. These outcomes suggest that data assimilation degrades the links between the HC and features influencing its dynamics.

Impact of slowdown of Atlantic overturning circulation on heat and freshwater transports (Kelly et al. 2016)

Abstract: Recent measurements of the strength of the Atlantic overturning circulation at 26°N show a 1 year drop and partial recovery amid a gradual weakening. To examine the extent and impact of the slowdown on basin wide heat and freshwater transports for 2004–2012, a box model that assimilates hydrographic and satellite observations is used to estimate heat transport and freshwater convergence as residuals of the heat and freshwater budgets. Using an independent transport estimate, convergences are converted to transports, which show a high level of spatial coherence. The similarity between Atlantic heat transport and the Agulhas Leakage suggests that it is the source of the surface heat transport anomalies. The freshwater budget in the North Atlantic is dominated by a decrease in freshwater flux. The increasing salinity during the slowdown supports modeling studies that show that heat, not freshwater, drives trends in the overturning circulation in a warming climate.

The response of high-impact blocking weather systems to climate change (Kennedy et al. 2016)

Abstract: Midlatitude weather and climate are dominated by the jet streams and associated eastward moving storm systems. Occasionally, however, these are blocked by persistent anticyclonic regimes known as blocking. Climate models generally predict a small decline in blocking frequency under anthropogenic climate change. However, confidence in these predictions is undermined by, among other things, a lack of understanding of the physical mechanisms underlying the change. Here we analyze blocking (mostly in the Euro-Atlantic sector) in a set of sensitivity experiments to determine the effect of different parts of the surface global warming pattern. We also analyze projected changes in the impacts of blocking such as temperature extremes. The results show that enhanced warming both in the tropics and over the Arctic act to strengthen the projected decline in blocking. The tropical changes are more important for the uncertainty in projected blocking changes, though the Arctic also affects the temperature anomalies during blocking.

The anomalous change in the QBO in 2015-16 (Newman et al. 2016)

Abstract: The quasi-biennial oscillation (QBO) is a tropical lower stratospheric, downward propagating zonal wind variation, with an average period of ~28 months. The QBO has been constantly documented since 1953. Here we describe the evolution of the QBO during the Northern Hemisphere winter of 2015-16 using radiosonde observations and meteorological reanalyses. Normally, the QBO would show a steady downward propagation of the westerly phase. In 2015-16, there was an anomalous upward displacement of this westerly phase from ~30 hPa to 15 hPa. These westerlies impinge on, or “cut-off” the normal downward propagation of the easterly phase. In addition, easterly winds develop at 40 hPa. Comparisons to tropical wind statistics for the 1953-present record demonstrate that this 2015-16 QBO disruption is unprecedented.

Other papers

Impact of observed North Atlantic multidecadal variations to European summer climate: a linear baroclinic response to surface heating (Ghosh et al. 2016)

Gridded, monthly rainfall and temperature climatology for El Niño Southern Oscillation impacts in the United States (Dourte et al. 2016)

Southern European rainfall reshapes the early-summer circumglobal teleconnection after the late 1970s (Lin et al. 2016)

Moisture and heat budgets of the south American monsoon system: climatological aspects (Garcia et al. 2016)

The Relative Influence of ENSO and SAM on Antarctic Peninsula Climate (Clem et al. 2016)

Sinuosity of mid-latitude atmospheric flow in a warming world (Cattiaux et al. 2016)

ENSO response to high-latitude volcanic eruptions in the Northern Hemisphere: The role of the initial conditions (Pausata et al. 2016)

Remote influence of Interdecadal Pacific Oscillation on the South Atlantic Meridional Overturning Circulation variability (Lopez et al. 2016)

Robust response of the Amundsen Sea Low to stratospheric ozone depletion (England et al. 2016)

The response of winter Pacific North American pattern to strong volcanic eruptions (Liu et al. 2016)

Atlantic Multidecadal Variability in a model with an improved North Atlantic Current (Drews & Greatbatch, 2016)

Sub-decadal North Atlantic Oscillation variability in observations and the Kiel Climate Model (Reintges, Latif & Park, 2016)

Is there a robust effect of anthropogenic aerosols on the Southern Annular Mode? (Steptoe et al. 2016)

Climate Signals in the Mid- to High-Latitude North Atlantic from Altimeter Observations (Li et al. 2016)

Intensification and poleward shift of subtropical western boundary currents in a warming climate (Yang et al. 2016)

Inter-basin effects of the Indian Ocean on Pacific decadal climate change (Mochizuki et al. 2016)

The influence of boreal spring Arctic Oscillation on the subsequent winter ENSO in CMIP5 models (Chen et al. 2016)

Relationship between North American winter temperature and large-scale atmospheric circulation anomalies and its decadal variation (Yu et al. 2016)

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