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Climate Change and Tropical Cyclones (Yet Again)

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By Rasmus Benestad & Michael Mann
Hurricane Katerina
Just as Typhoon Nargis has reminded us of the destructive power of tropical cyclones (with its horrible death toll in Burma–around 100,000 according to the UN), a new paper by Knutson et al in the latest issue of the journal Nature Geosciences purports to project a reduction in Atlantic hurricane activity (principally the ‘frequency’ but also integrated measures of powerfulness).

The close timing of the Knutson et al and Typhoon Nargis is of course coincidental. But the study has been accorded the unprecedented privilege (that is, for a climate change article published during the past 7 years) of a NOAA press conference. What’s the difference this time? Well, for one thing, the title of the paper: “Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions” (emphasis added).

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The Global Cooling Bet – Part 2 Apuesta al Enfriamiento Global – Segunda ParteLa scommessa sul raffreddamento globale – II parte

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Last week we proposed a bet against the “pause in global warming” forecast in Nature by Keenlyside et al. and we promised to present our scientific case later – so here it is.

Una traduzione in italiano è disponibile qui
Dieser Beitrag erscheint zeitgleich auf deutsch auf Klimalounge


Traducido por Angela Carosio

La semana pasada propusimos una apuesta contra el pronóstico en un artículo de la revista Nature “pausa en el calentamiento global” por Keenlyside et al. y prometimos presentar nuestro caso científico en otra ocasión, y aquí está.

[Read more…] about The Global Cooling Bet – Part 2 Apuesta al Enfriamiento Global – Segunda ParteLa scommessa sul raffreddamento globale – II parte

What the IPCC models really say Lo que dicen realmente los modelos del IPCCCosa dicono realmente i modelli dell‘IPCC

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Over the last couple of months there has been much blog-viating about what the models used in the IPCC 4th Assessment Report (AR4) do and do not predict about natural variability in the presence of a long-term greenhouse gas related trend. Unfortunately, much of the discussion has been based on graphics, energy-balance models and descriptions of what the forced component is, rather than the full ensemble from the coupled models. That has lead to some rather excitable but ill-informed buzz about very short time scale tendencies. We have already discussed how short term analysis of the data can be misleading, and we have previously commented on the use of the uncertainty in the ensemble mean being confused with the envelope of possible trajectories (here). The actual model outputs have been available for a long time, and it is somewhat surprising that no-one has looked specifically at it given the attention the subject has garnered. So in this post we will examine directly what the individual model simulations actually show.

Una traducción está disponible aquí
Una traduzione in italiano è disponibile qui
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Global Cooling-Wanna Bet? Enfriamiento Global, ¿Quieres apostar?Raffreddamento Globale – scommettiamo?

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By Stefan Rahmstorf, Michael Mann, Ray Bradley, William Connolley, David Archer, and Caspar Ammann
Por Stefan Rahmstorf, Michael Mann, Ray Bradley, William Connolley, David Archer y Caspar Ammann (Traducido por Angela Carosio)

Dieser Beitrag erscheint zeitgleich auf deutsch auf KlimaLounge
Una traduzione in italiano è disponibile qui

Global cooling appears to be the “flavour of the month”. First, a rather misguided media discussion erupted on whether global warming had stopped, based on the observed temperatures of the past 8 years or so (see our post). Now, an entirely new discussion is capturing the imagination, based on a group of scientists from Germany predicting a pause in global warming last week in the journal Nature (Keenlyside et al. 2008).

Specifically, they make two forecasts for global temperature, as discussed in the last paragraphs of their paper and shown in their Figure 4 (see below). The first forecast concerns the time interval 2000-2010, while the second concerns the interval 2005-2015 (*). For these two 10-year averages, the authors make the following prediction:

“… the initialised prediction indicates a slight cooling relative to 1994-2004 conditions”

Their graph shows this: temperatures in the two forecast intervals (green points shown at 2005 and 2010) are almost the same and are both lower than observed in 1994-2004 (the end of the red line in their graph).

Fig. 4 from <em data-lazy-src=

That this cooling would just be a temporary blip and would change nothing about global warming goes without saying and has been amply discussed elsewhere (e.g. here). But another question has been rarely discussed: will this forecast turn out to be correct?

We think not – and we are prepared to bet serious money on this. We have double-checked with the authors: they say they really mean this as a serious forecast, not just as a methodological experiment. If the authors of the paper really believe that their forecast has a greater than 50% chance of being correct, then they should accept our offer of a bet; it should be easy money for them. If they do not accept our bet, then we must question how much faith they really have in their own forecast.

The bet we propose is very simple and concerns the specific global prediction in their Nature article. If the average temperature 2000-2010 (their first forecast) really turns out to be lower or equal to the average temperature 1994-2004 (*), we will pay them € 2500. If it turns out to be warmer, they pay us € 2500. This bet will be decided by the end of 2010. We offer the same for their second forecast: If 2005-2015 (*) turns out to be colder or equal compared to 1994-2004 (*), we will pay them € 2500 – if it turns out to be warmer, they pay us the same. The basis for the temperature comparison will be the HadCRUT3 global mean surface temperature data set used by the authors in their paper.

To be fair, the bet needs an escape clause in case a big volcano erupts or a big meteorite hits the Earth and causes cooling below the 1994-2004 level. In this eventuality, the forecast of Keenlyside et al. could not be verified any more, and the bet is off.

The bet would also need a neutral arbiter – we propose, for example, the director of the Hadley Centre, home of the data used by Keenlyside et al., or a committee of neutral colleagues. This neutral arbiter would also decide whether a volcano or meteorite impact event is large enough as to make the bet obsolete.

We will discuss the scientific reasons for our assessment here another time – first we want to hear from Keenlyside et al. whether they accept our bet. Our friendly challenge is out – we hope they will accept it in good sportsmanship.

(*) We adopt here the definition of the 10-year intervals as in their paper, which is from 1 November of the first year to 31 October of the last year. I.e.: 2000-2010 means 1 November 2000 until 31 October 2010.

Update: We have now published part 2 of this bet with our scientific arguments.

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Update: Andy Revkin has weighed in at “dot earth”.

Update 5/11/08: so has Anna Barnett at Nature’s ‘climate feedback’ blog

El enfriamiento global parece ser el sabor del mes. Primero, ha brotado una discusión descarriada en los medios de comunicación sobre si el calentamiento global se ha detenido, basándose en las temperaturas observadas en los pasados 8 años (ver nuestro correo aquí). Ahora hay una nueva discusión que está capturando la imaginación, basada en un grupo de científicos alemanes que predijeron una pausa en el calentamiento global la semana pasada en un artículo en la revista Nature (Keenlyside et al. 2008).

En dicho artículo se hacen dos pronósticos de temperaturas globales, y se discuten en los últimos párrafos y se muestran en la Figura 4 (ver abajo). El primer pronóstico se refiere a los años 2000-2010, mientras que el segundo se refiere a los años 2005-2015 (*). Los autores hacen las siguientes predicciones para estos dos intervalos promedio de diez años:

“la predicción inicial indica un leve enfriamiento con respecto a las condiciones en los años 1994-2004”

El gráfico muestra lo siguiente: Las temperaturas en los dos intervalos pronosticados (los puntos verdes muestran 2005 y 2010) son casi iguales y son ambas más bajas que las observadas en 1994-2004, correspondiente al final de la línea roja en el gráfico.

Fig. 4 from <em data-lazy-src=

No es siquiera necesario explicar que este enfriamiento es solo un pequeño parpadeo y que no cambiará nada del calentamiento global. El tema ha sido ampliamente discutido en otros sitios (ej. aquí). Pero hay una pregunta que se ha discutido poco: ¿Será correcto el pronóstico?

Nosotros pensamos que no, y estamos dispuestos a apostar una importante suma de dinero por nuestra postura. Hemos verificado dos veces con los autores: ellos insisten en que su artículo es un pronóstico serio y que no se trata de un experimento metodológico. Si los autores realmente piensan que su pronóstico tiene una chance de ser correcta mayor al 50%, entonces deberían aceptar nuestra apuesta; sería una oportunidad de ganar dinero fácil. Si no aceptan nuestra apuesta, deberíamos cuestionar, entonces, cuanta fe realmente tienen en su pronóstico.

La apuesta que proponemos es muy simple y concierne su pronóstico específico en el artículo de la revista Nature. Si la temperatura promedio de 2000-2010 (su primer pronóstico) resulta ser más baja o igual que la temperatura promedio de 1994-2004 (*), les pagaremos € 2500. Si resulta ser más alta, ellos nos pagan € 2500 a nosotros. Esta apuesta será decidida a fines del 2010. Ofrecemos lo mismo para el segundo pronóstico: si la temperatura promedio de 2005-2015(*) resulta ser más baja o igual comparando con la temperatura promedio de 1994-2004(*) les pagaremos € 2500, si resulta ser más alta, ellos nos pagan a nosotros esa cifra. Tomaremos el HADCRUT3, conjunto de datos del promedio de la temperatura de superficie global, como base para comparar las temperaturas, que es la misma base de datos utilizada por los autores en el artículo.

Para ser justos, necesitaríamos una cláusula de salvaguardia, por si un gran volcán hace erupción o si un gran meteorito golpea la tierra y causa un enfriamiento menor al del promedio de 1994-2004. En este caso, el pronóstico de Keenlyside et al. no se podría verificar y por lo tanto la apuesta sería inválida.

La apuesta también tendría que tener un árbitro neutral, proponemos, por ejemplo, el director del Hadley Centre, donde se albergan los datos utilizados por Keenlyside et al., o un comité de colegas neutrales. Dicho árbitro neutral también decidirá si una eventual explosión volcánica o un impacto de meteorito son lo suficientemente grandes para invalidar la apuesta.

Discutiremos pronto las razones científicas de nuestra evaluación, primero queremos ver si Keenlyside et al. acepta nuestra apuesta. Nuestro amigable desafío ha sido propuesto y esperamos que sea aceptado con buen espíritu deportivo.

(*) Adoptamos aquí la misma definición de intervalos de 10 años que en su artículo, que va del 1 de noviembre del primer año al 31 de octubre del último año, ej.:2000-2010 significa 1 de noviembre de 2000 hasta 31 de octubre de 2010.

Actualización: Ya hemos publicado la segunda parte de esta apuesta con nuestros argumentos científicos.

Back to the future Volver al Futuro

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A few weeks ago I was at a meeting in Cambridge that discussed how (or whether) paleo-climate information can reduce the known uncertainties in future climate simulations.

The uncertainties in the impacts of rising greenhouse gases on multiple systems are significant: the potential impact on ENSO or the overturning circulation in the North Atlantic, probable feedbacks on atmospheric composition (CO2, CH4, N2O, aerosols), the predictability of decadal climate change, global climate sensitivity itself, and perhaps most importantly, what will happen to ice sheets and regional rainfall in a warming climate.

The reason why paleo-climate information may be key in these cases is because all of these climate components have changed in the past. If we can understand why and how those changes occurred then, that might inform our projections of changes in the future. Unfortunately, the simplest use of the record – just going back to a point that had similar conditions to what we expect for the future – doesn’t work very well because there are no good analogs for the perturbations we are making. The world has never before seen such a rapid rise in greenhouse gases with the present-day configuration of the continents and with large amounts of polar ice. So more sophisticated approaches must be developed and this meeting was devoted to examining them.

Traducido por Angela Carosio
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Butterflies, tornadoes and climate modelling

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Ed Lorenz hiking Many of you will have seen the obituaries (MIT, NYT) for Ed Lorenz, who died a short time ago. Lorenz is most famous scientifically for discovering the exquisite sensitivity to initial conditions (i.e. chaos) in a simple model of fluid convection, which serves as an archetype for the weather prediction problem. He is most famous outside science for the ‘The Butterfly Effect’ described in his 1972 paper “Predictability: Does the Flap of a Butterfly’s Wings in Brazil Set Off a Tornado in Texas?”. Lorenz’s contributions to both atmospheric science and the mathematics of dynamical systems were wide ranging and seminal. He also directly touched the lives of many of us here at RealClimate, and both his wisdom, and quiet personal charm will be sorely missed.

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Moulins, Calving Fronts and Greenland Outlet Glacier Acceleration Sifones, frentes glaciares y la aceleración de los glaciares exteriores de Groenlandia

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Guest Commentary by Mauri Pelto

The net loss in volume and hence sea level contribution of the Greenland Ice Sheet (GIS) has doubled in recent years from 90 to 220 cubic kilometers/year has been noted recently (Rignot and Kanagaratnam, 2007). The main cause of this increase is the acceleration of several large outlet glaciers. There has also been an alarming increase in the number of photographs of meltwater draining into a moulin somewhere on the GIS, often near Swiss Camp (35 km inland from the calving front). The story goes—warmer temperatures, more surface melting, more meltwater draining through moulins to glacier base, lubricating glacier bed, reducing friction, increasing velocity, and finally raising sea level. Examining this issue two years RealClimate suggested this was likely the correct story. A number of recent results suggest that we need to take another look at this story.

Una traducción está disponible aquí
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Model-data-comparison, Lesson 2

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In January, we presented Lesson 1 in model-data comparison: if you are comparing noisy data to a model trend, make sure you have enough data for them to show a statistically significant trend. This was in response to a graph by Roger Pielke Jr. presented in the New York Times Tierney Lab Blog that compared observations to IPCC projections over an 8-year period. We showed that this period is too short for a meaningful trend comparison.

This week, the story has taken a curious new twist. In a letter published in Nature Geoscience, Pielke presents such a comparison for a longer period, 1990-2007 (see Figure). Lesson 1 learned – 17 years is sufficient. In fact, the very first figure of last year’s IPCC report presents almost the same comparison (see second Figure).
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Target CO2 Objectivo CO2

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What is the long term sensitivity to increasing CO2? What, indeed, does long term sensitivity even mean? Jim Hansen and some colleagues (not including me) have a preprint available that claims that it is around 6ºC based on paleo-climate evidence. Since that is significantly larger than the ‘standard’ climate sensitivity we’ve often talked about, it’s worth looking at in more detail.


Traducido por Angela Carosio

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Blogs and peer-review Blogs y reseña de pares

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Nature Geoscience has two commentaries this month on science blogging – one from me and another from Myles Allen (see also these blog posts on the subject). My piece tries to make the point that most of what scientists know is “tacit” (i.e. not explicitly or often written down in the technical literature) and it is that knowledge that allows them to quickly distinguish (with reasonable accuracy) what new papers are worth looking at in detail and which are not. This context is what provides RC (and other science sites) with the confidence to comment both on new scientific papers and on the media coverage they receive.

Myles’ piece stresses that criticism of papers in the peer-reviewed literature needs to be in the peer-reviewed literature and suggests that informal criticism (such as on a blog) might undermine that.

We actually agree that there is a real tension between a quick and dirty pointing out of obvious problems in a published paper (such as the Douglass et al paper last December) and doing the much more substantial work and extra analysis that would merit a peer-reviewed response. The approaches are not however necessarily opposed (for instance, our response to the Schwartz paper last year, which has also lead to a submitted comment). But given everyone’s limited time (and the journals’ limited space), there are fewer official rebuttals submitted and published than there are actual complaints. Furthermore, it is exceedingly rare to write a formal comment on an particularly exceptional paper, with the results that complaints are more common in the peer reviewed literature than applause. In fact, there is much to applaud in modern science, and we like to think that RC plays a positive role in highlighting some of the more important and exciting results that appear.

Myles’ piece, while ending up on a worthwhile point of discussion, illustrates it (in my opinion) with a rather misplaced example that involves RC – a post and follow-up on the Stainforth et al (2005) paper and the media coverage it got. The original post dealt in part with how the new climateprediction.net model runs affected our existing expectation for what climate sensitivity is and whether they justified a revision of any projections into the future. The second post came in the aftermath of a rather poor piece of journalism on BBC Radio 4 that implied (completely unjustifiably) that the CPDN team were deliberately misleading the public about the importance of their work. We discussed then (as we have in many other cases) whether some of the responsibility for overheated or inaccurate press actually belongs to the press release itself and whether we (as a community) could do better at providing more context in such cases. The reason why this isn’t really germane to Myles’ point is that we didn’t criticise the paper itself at all. We thought then (and think now) that the CPDN effort is extremely worthwhile and that lessons from it will be informing model simulations some time into the future. Our criticisms (such as they were) were mainly associated instead with the perception of the paper in parts of the media and wider community – something that is not at all appropriate for a peer-reviewed comment.

This isn’t the place to rehash the climate sensitivity issue (I promise a new post on that shortly), so that will be deemed off-topic. However, we’d be very interested in any comments on the fundamental issue raised – how do (or should) science blogs and traditional peer-review intersect and whether Myles’ perception that they are in conflict is widely shared.


Traducido por Angela Carosio

Nature Geoscience tiene dos comentarios este mes sobre ciencia y blogging, uno mío y otro de Myles Allen (véase también estos correos de blogs sobre el tema aqui y aqui).

Mi comentario trata de establecer una proposición que es que la gran mayoría de lo que los científicos conocen es “tácito” (por ejemplo, no explícito o escrito en la literatura técnica) y es ese conocimiento que les permite distinguir rápidamente, con precisión razonable, que artículos nuevos valen la pena leer en detalle y cuáles no. Este contexto es lo que provee a RC, y a otros sitios científicos, la seguridad para comentar sobre nuevos artículos científicos y sobre la cobertura que éstos reciben en los medios.

El comentario de Myles destaca que la crítica de artículos y la reseña de pares debe permanecer en la literatura de reseña de pares y que la crítica informal, como la que se encuentra en un blog, podría desmerecer el artículo.

Estamos de acuerdo con que hay una gran diferencia entre rápidamente indicar problemas obvios en un artículo publicado (como el artículo de Douglass et al de diciembre pasado) y hacer un trabajo sustancial y un análisis extra que merece una respuesta reseñada por pares. Los enfoques no son necesariamente opuestos (por ejemplo, nuestra respuesta al artículo de Schwartz el año pasado, que dio lugar a un comentario referido). Pero dada la limitación de tiempo de todos, y la limitación de espacio del periodismo, se presentan y se publican muchas menos refutaciones comparando con la cantidad de quejas. Es más, es extremadamente raro que se escriba un comentario formal sobre un artículo particularmente excepcional, dando como resultado que las quejas son mucho más comunes que los aplausos en la reseña de pares. De hecho, hay mucho que aplaudirle a la ciencia moderna, y nos gustaría pensar que RC juega un rol positivo en resaltar algunos de los resultados más importantes y apasionantes que aparecen.

El comentario de Myles, si bien termina con un interesante punto de discusión, es ilustrado, en mi opinión, con un ejemplo fuera de lugar que involucra a RC, un correo y el posterior seguimiento de un artículo de Stainforth et al (2005) y la gran cobertura que éste tuvo en los medios. El correo original aborda el tema sobre como los modelos ejecutados en el sitio climateprediction.net han afectado nuestra expectativa actual sobre que es la sensibilidad climática y si se justifica una revisión de cualquier proyección a futuro. El segundo correo vino luego de un artículo de periodismo, un tanto inferior, en Radio 4 de la BBC que implicaba, injustificadamente, que el público estaba siendo engañado deliberadamente por el equipo CPDN (Climate Prediction Dot Net, por sus siglas en ingles) sobre la importancia de su trabajo. Hemos discutido entonces, así como le hemos hecho en otras ocasiones, si parte de la responsabilidad de artículos inexactos o exaltados publicados pertenece a la misma prensa o si nosotros como comunidad, podríamos hacer un esfuerzo por proveer un contexto en dichos casos. La razón por la cual esto no es pertinente a lo que Myles opinó es que no hemos criticado en absoluto el artículo en sí. En ese entonces pensábamos, y seguimos pensándolo ahora, que el esfuerzo del equipo CPDN valió la pena y que cualquier lección aprendida será informada a los modelos de simulación en un futuro. Nuestra crítica, tal como era, fue asociada en vez con la percepción del artículo en parte de los medios y en la comunidad en general. Estos medios no son para nada adecuados para comentar una reseña de pares.

Este no es el lugar adecuado para argüir el tema de la sensibilidad climática (prometo un nuevo correo respecto a eso pronto), de modo que se considerará fuera de tema. Sin embargo, estamos muy interesados en comentarios sobre el tema fundamental planteado: como se interceptan, o como debieran interceptarse los blogs sobre ciencia y las tradicionales reseñas de pares, y si la percepción de Myles que estas están en conflicto es ampliamente compartida.