New Paper “SST And Circulation Trend Biases Cause An Underestimation Of European Precipitation Trends” By Van Haren Et Al 2012

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I was alerted to an important new paper that further documents the significant limitations in multi-decadal regional climate model predictions [h/t Jos de Laat].  The article is

Ronald van Haren, Geert Jan van Oldenborgh, Geert Lenderink, Matthew Collins and Wilco Hazeleger, 2012: SST and circulation trend biases cause an underestimation of European precipitation trends Climate Dynamics 2012, DOI: 10.1007/s00382-012-1401-5

[Note: There is a guest post tomorrow by the authors on this important research also]

The abstract reads [highlight added]

Clear precipitation trends have been observed in Europe over the past century. In winter, precipitation has increased in north-western Europe. In summer, there has been an increase along many coasts in the same area. Over the second half of the past century precipitation also decreased in southern Europe in winter. An investigation of precipitation trends in two multi-model ensembles including both global and regional climate models shows that these models fail to reproduce the observed trends. In many regions the model spread does not cover the trend in the observations. In contrast, regional climate model (RCM) experiments with observed boundary conditions reproduce the observed precipitation trends much better. The observed trends are largely compatible with the range of uncertainties spanned by the ensemble, indicating that the boundary conditions of RCMs are responsible for large parts of the trend biases. We find that the main factor in setting the trend in winter is atmospheric circulation, for summer sea surface temperature (SST) is important in setting precipitation trends along the North Sea and Atlantic coasts. The causes of the large trends in atmospheric circulation and summer SST are not known. For SST there may be a connection with the well-known ocean circulation biases in low-resolution ocean models. A quantitative understanding of the causes of these trends is needed so that climate model based projections of future climate can be corrected for these precipitation trend biases.

The conclusion of the paper includes the summary of the findings

To conclude, modeled atmospheric circulation and SST trends over the past century are significantly different from the observed ones. These mismatches are responsible for a large part of the misrepresentation of precipitation trends in climate models. The causes of the large trends in atmospheric circulation and summer SST are not known. For SST there may be a connection with the well-known ocean circulation biases in low-resolution ocean models. Because it is not clear (yet) whether the trend biases in SST and large scale circulation are due to greenhouse warming, their importance for future climate projections need to be determined. Therefore, a quantitative understanding of the causes of these trends is needed so that climate model based projections of future climate can be corrected for these trend biases.

This paper is yet another example of a peer reviewed paper that supports the conclusion in

Kevin Trenberth Was Correct – “We Do Not Have Reliable Or Regional Predictions Of Climate”

that the presentation of regional climate predictions to the impacts community for the coming decades, which are based on these models is fundamentally flawed.  My only comment on the paper is the statement that “…it is not clear (yet) whether the trend biases in SST and large scale circulation are due to greenhouse warming…..”

The models presumably include the increase of CO2 and other greenhouse gases over time. If they do not, it should be straightforward to run them with this trend in atmospheric composition included to see if it can explain the biases.

I asked Geert Jan (who has presented a guest post in an earlier weblog; see) this question

Hi …Geert Jan

P.S. I am going to set to post early next week, but would like your feedback (which I would like to post) on this statement in your paper

“…it is not clear (yet) whether the trend biases in SST and large scale circulation are due to greenhouse warming…..”

The models presumably include the increase of CO2 and other greenhouse gases over time. If they do not, it should be straightforward to run them with this trend in atmospheric composition included to see if it can explain the biases.

Did the models include this greenhouse gas trend? If not, are you going to run the models to answer this question?

Geert Jan promptly replied

Dear Roger,

Of course the models included increasing greenhouse gas concentrations and (the GCMs at least) semi-realistic aerosol concentrations. What we meant is that the simulated response over the period 1961-2010 locally has significant differences with the observed one. How significant the differences are globally wrt the low-frequency noise inherent in the system remains to be established, I hope I have time to continue working on this RSN, I had a draft paper using CMIP3 but have to update it to CMIP5.  For Europe this paper and its predecessor for temperature (van Oldenborgh et al, 2009, Climate of the Past) established that relative to the observed and modelled variability the discrepancy is quite significant.

With the remark you quoted we just wanted to state that we do not know whether the differences are due to underestimated natural variability (which would imply that we expect it to revert back eventually), due to inaccurately modelled aerosol effects (which means they will become progressively less important than greenhouse warming) or due to wrongly-represented aspects of greenhouse warming (which means the discrepancies will grow over time).

Hope this is clearer,

Geert Jan

Roger

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