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What is signal and what is noise?

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The recent warming has been more pronounced in the Arctic Eurasia than in many other regions on our planet, but Franzke (2012) argues that only one out of 109 temperature records from this region exhibits a significant warming trend. I think that his conclusions were based on misguided analyses.

The analysis did not sufficiently distinguish between signal and noise, and mistaking noise for signal will give misguided conclusions.

[Read more…] about What is signal and what is noise?

References

  1. C. Franzke, "On the statistical significance of surface air temperature trends in the Eurasian Arctic region", Geophysical Research Letters, vol. 39, 2012. http://dx.doi.org/10.1029/2012GL054244

A review of cosmic rays and climate: a cluttered story of little success

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A number of blogs were excited after having leaked the second-order draft of IPCC document, which they interpreted as a “game-changing admission of enhanced solar forcing”.

However, little evidence remains for a link between galactic cosmic rays (GCR) and variations in Earth’s cloudiness. Laken et al. (2012) recently provided an extensive review of the study of the GCR and Earth’s climate, from the initial work by Ney (1959) to the latest findings from 2012.

[Read more…] about A review of cosmic rays and climate: a cluttered story of little success

References

  1. B.A. Laken, E. Pallé, J. Čalogović, and E.M. Dunne, "A cosmic ray-climate link and cloud observations", Journal of Space Weather and Space Climate, vol. 2, pp. A18, 2012. http://dx.doi.org/10.1051/swsc/2012018

The heat is on in West Antarctica

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Eric Steig

Regular followers of RealClimate will be aware of our publication in 2009 in Nature, showing that West Antarctica — the part of the Antarctic ice sheet that is currently contributing the most to sea level rise, and which has the potential to become unstable and contribute a lot more (3 meters!) to sea level rise in the future — has been warming up for the last 50 years or so.

Our paper was met with a lot of skepticism, and not just from the usual suspects. A lot of our fellow scientists, it seems, had trouble getting over their long-held view (based only on absence of evidence) that the only place in Antarctica that was warming up was the Antarctica Peninsula. To be fair, our analysis was based on interpolation, using statistics to fill in data where it was absent, so we really hadn’t proven anything; we’d only done an analysis that pointed (strongly!) in a particular direction.

[Read more…] about The heat is on in West Antarctica

Online video lectures on climate change

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For those who’d like to get the basics of climate change explained first-hand by a climate scientist, here are two video lectures.

In the first, I show some of the basic data sets and findings about global warming, including some comments on historic land marks of our science.

The second lecture deals with the impacts of climate change (with a focus on extreme events and sea-level rise) and the possibilities for holding global warming below 2°C.

These lectures form part of a broader lecture course called World in Transition. It includes 11 themes, presented by the members of the German Advisory Council on Global Change (WBGU). This is a body of experts appointed by the German government and advising it on global change issues. The lecture series, for which international students can enrol and earn credit points, is based on the WBGU flagship report World in Transition – A Social Contract for Sustainability. This report describes how the transition to a sustainable, climate-friendly global economy and life style can be achieved.

Improving the Tropical Cyclone Climate Record

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Guest Commentary by Christopher Hennon (UNC Asheville)

Get involved in a new citizen science project at CycloneCenter.org.

The poor quality of the tropical cyclone (TC) data record provides severe constraints on the ability of climate scientists to: a) determine to what degree TCs have responded to shifts in climate, b) evaluate theories on how TCs will respond to climate change in the future. The root cause for the poor data is the severity of the TC conditions (e.g. high wind, rough seas) and the remoteness of these storms – the vast majority of which form and remain well away from most observing networks. Thus, most TCs are not observed directly and those that are (with buoys, aircraft reconnaissance, ships) are often not sampled sufficiently (see the IBTrACS, (Knapp et al., 2010)).

This leaves tropical cyclone forecasters, who are ultimately responsible for recording TC tracks and intensities (i.e. maximum wind speeds), with a challenging problem. Fortunately, there is a tool called the Dvorak Technique which allows forecasters to make a reasonable determination of the TC intensity by simply analyzing a single infrared or visible satellite image, which is almost always available Velden et al., 2006). The technique calls for the analyst to determine the center location of the system, the cloud pattern type, the degree of organization of the pattern, and the intensity trend. A maximum surface wind speed is determined after the application of a number of rules and constraints.

Hurricane Gay (1992)The Dvorak Technique has been used for many years at all global tropical cyclone forecast centers and has been shown in many cases to yield a good estimate of maximum TC wind speed, when applied properly (Knaff et al., 2010). However, there is a level of analyst subjectivity inherent in the procedure; the cloud patterns are not always clear, it is sometimes difficult to accurately determine the storm center and the rules and constraints have been interpreted and applied differently across agencies. This introduces heterogeneity in the global TC record since the Dvorak Technique is usually the only available tool for assessing the maximum wind speed.

There has been recent work to eliminate the human element in the Dvorak Technique by automating the procedure. The Advanced Dvorak Technique (ADT) uses objective storm center and cloud pattern schemes to remove the subjectivity (Olander and Velden, 2007). All other classification rules and constraints are then applied and combined with additional statistical information to produce automated intensity estimates. Although the ADT skill is comparable to experienced human Dvorak analysts, large errors can occur if the scene type is not identified properly.

A new crowd sourcing project, called Cyclone Center, embraces the human element by enabling the public to perform a simplified version of the Dvorak Technique to analyze historical global tropical cyclone (TC) intensities (Hennon, 2012). Cyclone Center’s primary goal is to resolve discrepancies in the recent global TC record arising principally from inconsistent development of tropical cyclone intensity data. The Cyclone Center technique standardizes the classification procedure by condensing the Dvorak Technique to a few simple questions that can be answered by global, nonprofessional users.

One of the main advantages of this approach is the inclusion of thousands of users, instead of the 1-3 who would normally classify a TC image. This allows the computation of measures of uncertainty in addition to a mean intensity. Nearly 300,000 images, encompassing all global TCs that formed from 1978-2009, will be classified 30 times each – a feat that would take a dedicated team of twenty Dvorak-trained experts about 12 years to complete. Citizen scientists have already performed over 100,000 classifications since the project launch in September. Once the project is complete, a new dataset of global TC tracks and intensities will be made available to the community to contribute to our efforts to provide the best possible TC data record.

Interested readers are encouraged to learn more about and participate in the project at the cyclonecenter.org website (there are some FAQ on the project blog). The CycloneCenter project is a collaboration between the Citizen Science Alliance, NOAA National Climatic Data Center (NCDC), University of North Carolina at Asheville, and the Cooperative Institute for Climate and Satellites (CICS) – North Carolina.

References

  1. K.R. Knapp, M.C. Kruk, D.H. Levinson, H.J. Diamond, and C.J. Neumann, "The International Best Track Archive for Climate Stewardship (IBTrACS)", Bulletin of the American Meteorological Society, vol. 91, pp. 363-376, 2010. http://dx.doi.org/10.1175/2009BAMS2755.1
  2. C. Velden, B. Harper, F. Wells, J.L. Beven, R. Zehr, T. Olander, M. Mayfield, C.â. Guard, M. Lander, R. Edson, L. Avila, A. Burton, M. Turk, A. Kikuchi, A. Christian, P. Caroff, and P. McCrone, "The Dvorak Tropical Cyclone Intensity Estimation Technique: A Satellite-Based Method that Has Endured for over 30 Years", Bulletin of the American Meteorological Society, vol. 87, pp. 1195-1210, 2006. http://dx.doi.org/10.1175/BAMS-87-9-1195
  3. J.A. Knaff, D.P. Brown, J. Courtney, G.M. Gallina, and J.L. Beven, "An Evaluation of Dvorak Technique–Based Tropical Cyclone Intensity Estimates", Weather and Forecasting, vol. 25, pp. 1362-1379, 2010. http://dx.doi.org/10.1175/2010WAF2222375.1
  4. T.L. Olander, and C.S. Velden, "The Advanced Dvorak Technique: Continued Development of an Objective Scheme to Estimate Tropical Cyclone Intensity Using Geostationary Infrared Satellite Imagery", Weather and Forecasting, vol. 22, pp. 287-298, 2007. http://dx.doi.org/10.1175/WAF975.1
  5. C.C. Hennon, "Citizen scientists analyzing tropical cyclone intensities", Eos, Transactions American Geophysical Union, vol. 93, pp. 385-387, 2012. http://dx.doi.org/10.1029/2012EO400002

IPCC draft (redux)

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Amid the manufactured spin and excitement of the unofficial release of the IPCC WG1 Second Order Draft, it is worth remembering that this happened last time too:

IPCC draft: No comment

May 4, 2006

As everyone has now realised, the second-order draft of the new IPCC report has become very widely available and many of the contributors to this site, commenters and readers will have seen copies. Part of the strength of the IPCC process are the multiple stages of review – the report is already significantly improved (in clarity and scientific basis) from the first round of reviews, and one can anticipate further improvements from the ongoing round as well. Thus no statements from this draft report can be considered ‘official’. While most of the contents of the report will come as no surprise to frequent visitors here, we have decided that we are not going to discuss the report until it is finalised and released (sometime in February 2007). At that time, we’ll go chapter by chapter hopefully pulling out the interesting bits, but until then, we feel it’s more appropriate to respect the ‘Do not cite or quote’ injunctions that can be found on every page. We trust that our commenters will likewise respect the process. Patience, people, patience!

The only change is that AR5 will be released in September 2013.

AGU time again…

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This week is Fall AGU, the biggest climate-related conference around. Not everything is related to climate – there is a lot of other geophysics and astrophysics, but it is generally the place to go if you want to see and be seen (and incidentally, be crushed, be excited, be friendly and be frustrated that you can’t be in three places at once).

If you are not going, you should check out the improvements in the ‘Virtual meeting‘, which will offer live streaming of some big sessions, and for those and many additional sessions there is video-on-demand (VOD) after the fact. Many posters will also be available via ePoster. The twitter hashtag is #AGU12.

And if you are going to be there, here is a limited selection of sessions that will discuss issues that often come up here (more details in the scientific program).

Monday, Dec 03:

PP11F. The Climate of the Common Era I + II
8:00 AM – 12:30 AM; 2010 (Moscone West) (including Kevin Anchukatis, Philip Brohan, Eric, and many others).

12:30 PM – 01:30 PM: San Francisco Marriott Marquis – Salon 10 Brown Bag Lunch Workshop with Michael Gerrard on “Legal Duties to Preserve and Disclose Scientific Data and Personal Communications” (note that anyone who wants a private one-on-one session with a lawyer related to these or related issues, can email lawyer(at)climatesciencedefensefund.org to set up a meeting).

PA13B. Countering Denial and Manufactured Doubt of 21st Century Science
1:40 PM – 3:40 PM; 302 (Moscone South)

6:30 PM – 8:30PM; Open Mike Night hosted by Richard Alley. Jillian’s, 175 4th Street, Suite 1070.

Tuesday, Dec 04:

PA21B. Communication of Science Through Art: A Raison d’Etre for Interdisciplinary Collaboration
8:00 AM – 10:00 AM; 104 (Moscone South) (VOD)

GC22B. Communicating Climate Science—Seeking the Best of Old and New Paradigms
10:20 AM – 12:20 PM; 3014 (Moscone West) (including Mike, Richard Alley, Dan Kahan, Richard Somerville and Naomi Oreskes)

PA23B. PA23B. Facebook, Twitter, Blogs: Science Communication Gone Social—The Social Media 101
1:40 PM – 3:40 PM; 302 (Moscone South) (Including Mike, Michael Tobis, Peter Sinclair, and Zeke Hausfather)

Bloggers Forum: Science on the Web:
5:00 pm – 6:00 pm: 3000 (Moscone West)

Wednesday, Dec 05:

Session Title: A32D. New Atmospheric Sciences Fellows Presentations I + II
8:00 AM – 12:20PM; 3002 (Moscone West) (including Tony DelGenio, Mike, Ron Stouffer, Dave Neelin… ) (VOD)

PP31D. Continental Archives of Past Climate and Seismic Events II
8:00 AM – 10:00 AM; 2006 (Moscone West) (including Ray B. discussing this)

PP32A. Emiliani Lecture
10:20 AM – 11:20 AM; 103 (Moscone South)
“No future without a past” or “History will teach us nothing”? (Invited) Richard E. Zeebe (VOD)

12:30 PM – 1:30 PM; Brown Bag lunch with Pete Fontaine “An inside look at the Michael Mann case”. 226 (Moscone South)

GC33F. Construing Uncertainty in Climate Science
2:40 PM – 3:40 PM; 3003 (Moscone West) (including Naomi Oreskes, Gerard Roe)

GC44B. Links Between Rapid Arctic Change and Midlatitude Weather Patterns
5:00 PM – 6:00 PM; 3001 (Moscone West) (including Steve Vavrus, Judah Cohen)

Thursday, Dec 06:

GC43I. Tyndall History of Global Environmental Change Lecture:
2:40 PM – 3:40 PM; 2022-2024 (Moscone West): “Successful Predictions” (Invited), Raymond Pierrehumbert (VOD)

U44A. Dissolving Boundaries Between Scientists, Media, and the Public
4:00 PM – 6:00 PM; 102 (Moscone South) (Including Eric as speaker and panelist).

Friday, Dec 07:

C54B. The Ice Core Record of Carbon Cycle History and Processes
4:00 PM – 6:00 PM; 3007 (Moscone West)

Feel free to advertise other sessions/talks that might be of interest in the comments. Hopefully we’ll get some reports of interesting sessions to share with you (and if anyone wants to send us anything, we’ll post it up that evening).

Responses to volcanoes in tree rings and models

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Houston, we have a problem.

Admittedly, not a huge problem and not one that most people, or even most climatologists, are particularly fascinated by, but one which threads together many topics (climate models, tree rings, paleo-climate) which have been highlighted here in the past. The problem is that we have good evidence in the ice core records for very large tropical eruptions over the last 1000 years – in particular the eruptions in 1258/1259, 1452 and 1809 to 1815 – but for which many paleo-reconstructions barely show a blip in temperature. Models, in attempting to simulate this period, show varied but generally larger (and sometimes much larger) responses. The differences are significant enough to have prompted a few people to try and look into why this mismatch is occurring.

Whenever there is a mismatch between model and observation, there are, roughly speaking, at least three (non-exclusive) possibilities: the model is wrong, the observational data are wrong or the comparison is not like-with-like. There have been many examples of resolved mismatches in each category so all possibilities need to be looked at.

As described in a previous post earlier this year, Mann et al., 2012 (pdf), postulated that for extreme volcanoes, the cooling would be sufficient to saturate the growth response, and that some trees might `skip´ a ring for that year leading to a slight slippage in tree-ring dating, a potential smearing of the composite chronologies, and a further underestimate of the cooling in tree-ring based large-scale reconstructions.

This hypothesis has now been challenged by a group of authors in a comment (Anchukaitis et al.) (pdf, SI, code), who focus on the appropriateness of the tree ring growth model and the spatial pattern the volcanic climate responses. The Mann et al. response (pdf, SI) presents some further modeling and 19th century observational data in support of the original hypothesis.

Of course, there are still two other possibilities to consider. First, the models may have an excessive response. This could be due to either models responding excessively to the correct forcing, or could be related to an excessive forcing itself. There are indeed some important uncertainties in estimating the history of volcanic forcing – which involves inferring a stratospheric aerosol load (and effective radius of the particles and their distribution) from a network of sulphate peaks in ice cores in Greenland and Antarctica. For example, the forcing for the big eruption around 1453 differs by a factor of 2 in the inferred forcing (-12 W/m2 and -5.4 W/m2) in the two estimates proposed for the recent model-intercomparison (Schmidt et al., 2012). Note too that the details of how aerosols are implemented in any specific model can also make a difference to the forcing, and there are many (as yet untested) assumptions built into the forcing reconstructions.

It is also conceivable that climate models overreact to volcanic forcing – however, excellent matches to the Pinatubo response in temperature, radiative anomalies, water vapour and dynamic responses, where we know the volcanic aerosol load well, make that tricky to support (Hansen et al, 2007) (pdf, SI). (As an aside, the suggestion in this paper that the response to Krakatoa (1883) was underpredicted by the historical SST fields was partially vindicated by the results from HadSST3 which showed substantially more cooling).

The third possibility is that some tree-ring reconstructions can’t be easily compared to simple temperature averages from the models. As both the original paper and the comment suggests, there are important effects from memory from previous years in ring widths and, potentially, increases in diffuse light post-eruption promoting growth spurts. This needs to be assessed using more sophisticated forward models for tree ring growth applied to the models’ output – a feature in both the Mann et al, and Anchukaitis et al. approaches. More work is likely needed on this, and using the wider variety of model experiments coming out of CMIP5/PMIP3.

There is clearly potential for these competing hypotheses to get sorted out. Information from newly-digitised old instrumental records in the early 19th Century such as shipping records for the East India Company (Brohan et al, 2012), doesn’t support the largest modelled responses to Tambora (1815), but does suggest a response larger and more defined than that seen in some reconstructions. However, other 19th Century temperature compilations such Berkeley Earth show larger responses to Tambora – though there are spatial sampling issues there as well. There is also the potential for non-tree ring based reconstructions to provide independent confirmation of the magnitude of the response.

So while neither of the latest comments and responses provide a definitive answer to the principal problem, there is certainly lots of scope for extended and (hopefully) productive discussions.

References

  1. M.E. Mann, J.D. Fuentes, and S. Rutherford, "Underestimation of volcanic cooling in tree-ring-based reconstructions of hemispheric temperatures", Nature Geoscience, vol. 5, pp. 202-205, 2012. http://dx.doi.org/10.1038/ngeo1394
  2. K.J. Anchukaitis, P. Breitenmoser, K.R. Briffa, A. Buchwal, U. Büntgen, E.R. Cook, R.D. D'Arrigo, J. Esper, M.N. Evans, D. Frank, H. Grudd, B.E. Gunnarson, M.K. Hughes, A.V. Kirdyanov, C. Körner, P.J. Krusic, B. Luckman, T.M. Melvin, M.W. Salzer, A.V. Shashkin, C. Timmreck, E.A. Vaganov, and R.J.S. Wilson, "Tree rings and volcanic cooling", Nature Geoscience, vol. 5, pp. 836-837, 2012. http://dx.doi.org/10.1038/ngeo1645
  3. M.E. Mann, J.D. Fuentes, and S. Rutherford, "Reply to 'Tree rings and volcanic cooling'", Nature Geoscience, vol. 5, pp. 837-838, 2012. http://dx.doi.org/10.1038/ngeo1646
  4. G.A. Schmidt, J.H. Jungclaus, C.M. Ammann, E. Bard, P. Braconnot, T.J. Crowley, G. Delaygue, F. Joos, N.A. Krivova, R. Muscheler, B.L. Otto-Bliesner, J. Pongratz, D.T. Shindell, S.K. Solanki, F. Steinhilber, and L.E.A. Vieira, "Climate forcing reconstructions for use in PMIP simulations of the Last Millennium (v1.1)", Geoscientific Model Development, vol. 5, pp. 185-191, 2012. http://dx.doi.org/10.5194/gmd-5-185-2012
  5. J. Hansen, M. Sato, R. Ruedy, P. Kharecha, A. Lacis, R. Miller, L. Nazarenko, K. Lo, G.A. Schmidt, G. Russell, I. Aleinov, S. Bauer, E. Baum, B. Cairns, V. Canuto, M. Chandler, Y. Cheng, A. Cohen, A. Del Genio, G. Faluvegi, E. Fleming, A. Friend, T. Hall, C. Jackman, J. Jonas, M. Kelley, N.Y. Kiang, D. Koch, G. Labow, J. Lerner, S. Menon, T. Novakov, V. Oinas, J. Perlwitz, J. Perlwitz, D. Rind, A. Romanou, R. Schmunk, D. Shindell, P. Stone, S. Sun, D. Streets, N. Tausnev, D. Thresher, N. Unger, M. Yao, and S. Zhang, "Climate simulations for 1880–2003 with GISS modelE", Climate Dynamics, vol. 29, pp. 661-696, 2007. http://dx.doi.org/10.1007/s00382-007-0255-8
  6. P. Brohan, R. Allan, E. Freeman, D. Wheeler, C. Wilkinson, and F. Williamson, "Constraining the temperature history of the past millennium using early instrumental observations", Climate of the Past, vol. 8, pp. 1551-1563, 2012. http://dx.doi.org/10.5194/cp-8-1551-2012