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Climate change methadone?

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Geoengineering is increasingly being discussed (not so sotto voce any more) in many forums. The current wave of interest has been piqued by Paul Crutzen’s 2005 editorial and a number of workshops (commentary) and high profile advocacy. But most of the discussion has occurred in almost total ignorance of the consequences of embarking on such a course.

A wider range of people have now started to publish relevant studies – showing clearly the value of continued research on the topic – and a key one came out this week in JGR-Atmospheres. Robock et al used a coupled GCM with interactive aerosols to see what would happen if they injected huge amounts of SO2 (the precursor of sulphate aerosols) into the tropical or Arctic stratosphere. This is the most talked about (and most feasible) geoengineering idea, based on the cooling impacts of large tropical volcanic eruptions (like Mt. Pinatubo in 1991). Bottom line? This is no panacea.
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More PR related confusion

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It’s a familiar story: An interesting paper gets published, there is a careless throwaway line in the press release, and a whole series of misleading headlines ensues.

This week, it’s a paper on bromine- and iodine-mediated ozone loss in marine boundary layer environments (see a good commentary here). This is important for the light that it shines on tropospheric ozone chemistry (“bad ozone”) which is a contributing factor to global warming (albeit one which is about only about 20% as important as CO2). So far so good. The paper contains some calculations indicating that chemical transport models without these halogen effects overestimate ozone near the Cape Verde region by about 15% – a difference that certainly could be of some importance if it can be extrapolated across the oceans.

However, the press release contains the line

Large amounts of ozone – around 50% more than predicted by the world’s state-of-the-art climate models – are being destroyed in the lower atmosphere over the tropical Atlantic Ocean.

(my highlights). Which led directly to the headlines like Study highlights need to adjust climate models.

Why is this confusing? Because the term ‘climate models’ is interpreted very differently in the public sphere than it is in the field. For most of the public, it is ‘climate models’ that are used to project global warming into the future, or to estimate the planet’s sensitivity to CO2. Thus a statement like the one above, and the headline that came from it are interpreted to mean that the estimates of sensitivity or of future warming are now in question. Yet this is completely misleading since neither climate sensitivity nor CO2 driven future warming will be at all affected by any revisions in ozone chemistry – mainly for the reason that most climate models don’t consider ozone chemistry at all. Precisely zero of the IPCC AR4 model simulations (discussed here for instance) used an interactive ozone module in doing the projections into the future.

What the paper is discussing, and what was glossed over in the release, is that it is the next generation of models, often called “Earth System Models” (ESMs), that are starting to include atmospheric chemistry, aerosols, ozone and the like. These models may well be significantly affected by increases in marine boundary layer ozone loss, but since they have only just started to be used to simulate 20th and early 21st Century changes, it is very unclear what difference it will make at the large scale. These models are significantly more complicated than standard climate models (having dozens of extra tracers to move around, and a lot of extra coding to work through), are slower to run, and have been used much less extensively.

Climate models today are extremely flexible and configurable tools that can include all these Earth System modules (including those mentioned above, but also full carbon cycles and dynamic vegetation), but depending on the application, often don’t need to. Thus while in theory, a revision in ozone chemistry, or soil respiration or aerosol properties might impact the full ESM, it won’t affect the more basic stuff (like the sensitivity to CO2). But it seems that the “climate models will have to be adjusted” meme is just too good not to use – regardless of the context.

Tropical tropospheric trends again

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Back in December 2007, we quite heavily criticised the paper of Douglass et al (in press at IJoC) which purported to show that models and data were inconsistent when it came to the trends in the tropical troposphere. There were two strands to our critique: i) that the statistical test they used was not appropriate and ii) that they did not acknowledge the true structural uncertainty in the observations. Most subsequent discussion has been related to the statistical issue, but the second point is perhaps more important.

Even when Douglass et al was written, those authors were aware that there were serious biases in the radiosonde data (they had been reported in Sherwood et al, 2005 and elsewhere), and that there were multiple attempts to objectively address the problems and to come up with more homogeneous analyses. We mentioned the RAOBCORE project at the time and noted the big difference using their version 1.4 vs 1.2 made to the comparison (a difference nowhere mentioned in Douglass et al’s original accepted paper which only reported on v1.2 despite them being aware of the issue). However, there are at least three new papers in press that independently tackle the issue, and their results go a long towards addressing the problems.
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How to cook a graph in three easy lessons

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These days, when global warming inactivists need to trot out somebody with some semblance of scientific credentials (from the dwindling supply who have made themselves available for such purposes), it seems that they increasingly turn to Roy Spencer, a Principal Research Scientist at the University of Alabama. Roy does have a handful of peer-reviewed publications, some of which have quite decent and interesting results in them. However, the thing you have to understand is that what he gets through peer-review is far less threatening to the mainstream picture of anthropogenic global warming than you’d think from the spin he puts on it in press releases, presentations and the blogosphere. His recent guest article on Pielke Sr’s site is a case in point, and provides the fodder for our discussion today.

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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.

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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 src=Keenlyside et al ’08” align = “left” width=90%/>
Figure 4 from Keenlyside et al ’08

The authors also make regional predictions, but naturally it was this global prediction that captivated most newspaper stories around the world (e.g. BBC News, Reuters, Bloomberg and so on), because of its seeming contradiction with global warming. The authors emphasise this aspect in their own media release, which was titled: Will Global Warming Take a Short Break?

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.

_______________________
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 src=Keenlyside et al ’08” align = “left” width=90%/>
Figura 4 extraída del artículo de Keenlyside et al, 2008

Los autores también hacen pronósticos regionales, pero fue, naturalmente, el pronóstico global el que cautivó la mayoría de las historias en diarios alrededor del mundo (ej.: BBC Noticias http://www.nytimes.com/2008/05/01/science/earth/01climate.html?_r=1&>New%20York%20Times,%20¿El Calentamiento Global, se Tomará unas Cortas Vacaciones?

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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