Warmist von Storch: No warming consistent with climate models
We have recently uploaded to academia.edu a manuscript, coauthored by us two and two others, with the title 'Can climate models explain the recent stagnation in global warming', in which we compare the magnitude trends in the global mean temperature recently observed - trends in the last 10 years and the trends in the last 15 years (1998-20012) - with the ensemble of trends simulated by climate models participating in the Climate Model Intercomparison Projects CMIP3 and CMIP5. Recent trends as low or lower as those observed in the HadCRUT4 data set, of merely 0.4 C/century, are reproduced by at most 2% of the scenario simulations. Also two other analyses of the development of global mean temperature have been considered, with a higher trend of 0.8 C/century by GISS and 0.4 C/century by NCDC - these other trends show up in the ensemble of scenario simulation at most in 4.7% of all cases and 0.6% of all cases. Obviously, there is some uncertainty in the trends, but our overall conclusion that the present trends are at the margin of the distribution generated by available A1B and RCP4.5 scenarios is robustagainst this uncertainty.
To increase the size of the simulated ensemble of model-suggested trends we analysed not only the recent simulated trends under the regime of A1B and RCP4.5 scenarios, but also alln-time segments in the period up to 2060, in which the assumed external forcing increases linearly as in the emission scenarios A1B and RCP 4.5. These scenarios describe changing emissions of greenhouse gases and aerosols, but do not describe changing solar activity, volcanic activity or any cosmic influences, since scenarios (or even predictions) of these factors for the next decades are very uncertain to construct. We let n vary between 10 and 30 years.
If the slow trend derived from the GISS, HadCRU or NCDC analysis would continue for a total of 20 years, the trend would occur at most in 0.9% of all cases. Of course, this statement is conditioned by the presently available set of scenario calculations (in CMIP3 and CMIP55). The title "Can climate models explain the recent stagnation in global warming" was likely misleading, as we did not examine climate models in general, but merely the output of contemporary climate models, subject to a specific class of scenarios, which are best mimicking the recent development. Maybe a title like "is the on-going warming consistent the developments envisaged by scenarios simulations exposed to realistic increases in GHG forcing" would have been more appropriate.
This manuscript was submitted to Nature, but it was not accepted for publication. Unfortunately, the reviews are subject to copyright-rules by nature, and we are not allowed to reproduce the reviews here. The manuscript has been clicked on more than 3000 times until 22. August 2013, with most clicks from spiegel.de, but also many from bishop-hill.net. We want here to set straight some misinterpretations that may have arisen in the blogosphere, e.g. Bishophill, and may also have been present in the review processes by Nature as well.
The main result is that climate models run under realistic scenarios (for the recent past) have some difficulty in simulating the observed trends of the last 15 years, and that are not able to simulate a continuing trend of the observed magnitude for a total of 20 years or more. This main result does not imply that the anthropogenic greenhouse gases have not been the most important cause for the warming observed during the second half of the 20th century. That greenhouse gases have been responsible for, at least, part or even most of the observed warming, is not only based on the results of climate simulations, but can be derived from basic physical principles, and thus it is not really debated. It is important to stress that there is to date no realistic alternative explanation for the warming observed in the last 50 years. The effect of greenhouse gases is not only in the trend in global mean near-surface temperature, but has been also identified in the spatial pattern of the observed warming and in other variables, such as stratospheric temperature, sea-level pressure and others.
However, climate model projections are not perfect. They are in a constant state of revision and improvement. The comparison between simulations and observations, and the identification of any mismatches between both, is thus a very important, and probably unending, task in climate research. This manuscript should be viewed under this perspective. However, the basic features of man-made climate change have been robustly described by these models in the course of time, even if more detail has been added, and rates of changes have somewhat changed in the course of time.
To understand the present mismatch, we suggest four different explanations; none is pointing to a falsification of the concept that CO2 and other greenhouse gases exert a strong and likely dominant influence on the climate (statistics of weather). None represents a falsification of climate models. But all point to the need for further analysis and improvement of our tools - which are scenario simulations with climate models û for describing possible future developments.
One is an underestimation of the natural climate variability, which could be related to variations in the heat-uptake by the ocean and/or in internal variations of the energy balance itself (such as cloud cover). Another possibility is that the climate sensitivity of models may be too large, but a longer period of mismatch would be required to ascertain this possibility, as 15-years trends are still strongly influenced by internal climate variations. A third possibility is that the set of external forcings prescribed in the CMIP5 simulations lack a component of relevance. In particular, the CMIP ensembles assume a constant solar irradiance, due to the difficulties in predicting solar activity. However, solar irradiance displays a negative trend in the last 15 years, which could be part of the explanation of this mismatch. Finally, although the number of simulations that produce a trend as subdued as observed is small, it is still not zero. The last 15 years may have been an outlier, especially considering that the starting years - 1998 - experienced a strong ENSO event, and therefore was anomalously warm. Thus, further analyses are necessary and we intend to carry them forward.
At present, we cannot disentangle which of the different possible explanations is the best - maybe a combination, but the conclusion is not: GHGs play a minor or no noteworthy role in ongoing and expected future climate change. A conclusion that we draw is that the A1B and RCP4.5 scenarios, which are used in very many impact studies, are suffering from some limitations.
Our paper does not represent a crises of the understanding of the climate system, but a wake-up call that scenarios have to be prepared better, and that all impact studies should expect that details of future scenarios concerning speed of change and intensity of natural variability may be described quite differently.
http://klimazwiebel.blogspot.com/2013/08/hans-von-storch-and-eduardo-zorita-on.html#more
To increase the size of the simulated ensemble of model-suggested trends we analysed not only the recent simulated trends under the regime of A1B and RCP4.5 scenarios, but also alln-time segments in the period up to 2060, in which the assumed external forcing increases linearly as in the emission scenarios A1B and RCP 4.5. These scenarios describe changing emissions of greenhouse gases and aerosols, but do not describe changing solar activity, volcanic activity or any cosmic influences, since scenarios (or even predictions) of these factors for the next decades are very uncertain to construct. We let n vary between 10 and 30 years.
If the slow trend derived from the GISS, HadCRU or NCDC analysis would continue for a total of 20 years, the trend would occur at most in 0.9% of all cases. Of course, this statement is conditioned by the presently available set of scenario calculations (in CMIP3 and CMIP55). The title "Can climate models explain the recent stagnation in global warming" was likely misleading, as we did not examine climate models in general, but merely the output of contemporary climate models, subject to a specific class of scenarios, which are best mimicking the recent development. Maybe a title like "is the on-going warming consistent the developments envisaged by scenarios simulations exposed to realistic increases in GHG forcing" would have been more appropriate.
This manuscript was submitted to Nature, but it was not accepted for publication. Unfortunately, the reviews are subject to copyright-rules by nature, and we are not allowed to reproduce the reviews here. The manuscript has been clicked on more than 3000 times until 22. August 2013, with most clicks from spiegel.de, but also many from bishop-hill.net. We want here to set straight some misinterpretations that may have arisen in the blogosphere, e.g. Bishophill, and may also have been present in the review processes by Nature as well.
The main result is that climate models run under realistic scenarios (for the recent past) have some difficulty in simulating the observed trends of the last 15 years, and that are not able to simulate a continuing trend of the observed magnitude for a total of 20 years or more. This main result does not imply that the anthropogenic greenhouse gases have not been the most important cause for the warming observed during the second half of the 20th century. That greenhouse gases have been responsible for, at least, part or even most of the observed warming, is not only based on the results of climate simulations, but can be derived from basic physical principles, and thus it is not really debated. It is important to stress that there is to date no realistic alternative explanation for the warming observed in the last 50 years. The effect of greenhouse gases is not only in the trend in global mean near-surface temperature, but has been also identified in the spatial pattern of the observed warming and in other variables, such as stratospheric temperature, sea-level pressure and others.
However, climate model projections are not perfect. They are in a constant state of revision and improvement. The comparison between simulations and observations, and the identification of any mismatches between both, is thus a very important, and probably unending, task in climate research. This manuscript should be viewed under this perspective. However, the basic features of man-made climate change have been robustly described by these models in the course of time, even if more detail has been added, and rates of changes have somewhat changed in the course of time.
To understand the present mismatch, we suggest four different explanations; none is pointing to a falsification of the concept that CO2 and other greenhouse gases exert a strong and likely dominant influence on the climate (statistics of weather). None represents a falsification of climate models. But all point to the need for further analysis and improvement of our tools - which are scenario simulations with climate models û for describing possible future developments.
One is an underestimation of the natural climate variability, which could be related to variations in the heat-uptake by the ocean and/or in internal variations of the energy balance itself (such as cloud cover). Another possibility is that the climate sensitivity of models may be too large, but a longer period of mismatch would be required to ascertain this possibility, as 15-years trends are still strongly influenced by internal climate variations. A third possibility is that the set of external forcings prescribed in the CMIP5 simulations lack a component of relevance. In particular, the CMIP ensembles assume a constant solar irradiance, due to the difficulties in predicting solar activity. However, solar irradiance displays a negative trend in the last 15 years, which could be part of the explanation of this mismatch. Finally, although the number of simulations that produce a trend as subdued as observed is small, it is still not zero. The last 15 years may have been an outlier, especially considering that the starting years - 1998 - experienced a strong ENSO event, and therefore was anomalously warm. Thus, further analyses are necessary and we intend to carry them forward.
At present, we cannot disentangle which of the different possible explanations is the best - maybe a combination, but the conclusion is not: GHGs play a minor or no noteworthy role in ongoing and expected future climate change. A conclusion that we draw is that the A1B and RCP4.5 scenarios, which are used in very many impact studies, are suffering from some limitations.
Our paper does not represent a crises of the understanding of the climate system, but a wake-up call that scenarios have to be prepared better, and that all impact studies should expect that details of future scenarios concerning speed of change and intensity of natural variability may be described quite differently.
http://klimazwiebel.blogspot.com/2013/08/hans-von-storch-and-eduardo-zorita-on.html#more
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