Q&A On Two Climate Science Questions – A Contribution By Ben Herman

As part of my weblog posts, I am inviting internationally well-respected climate science colleagues to answer two questions that I have posted to them.  Today’s scientist is Ben Herman. As written at the University of Arizona website

Dr. Herman is primarily concerned with the optics of atmospheric aerosols, polarization and scattering, and the application of inversion techniques to analyze remote sensing data obtained from aircraft and satellites. Currently, he is working on several satellite based remote sensing projects to monitor ozone, temperature, water vapor and aerosols from space.

The Q&A with Ben follows:

1.  Is global warming (and cooling) a subset of climate change or does it dominate climate change?

Ben’s Answer

In my opinion, “global warming” should be considered a subset of climate change, but in most peoples minds, I believe they immediately associate climate change with global warming. This is probably due, in part at least, to the gradual change on the part of the climate community to use the words “climate change” in place of global warming, and then resort to discussions relating primarily to “global warming”. This then merges the two terms into one in the minds of most lay people.

2. What evidence exists that the multi-decadal global climate models can skillfully predict i) the real-world observed behavior of large-scale atmospheric-ocean circulation features such as ENSO, the NAO, the PDO, ect. and ii) CHANGES in the statistics (patterning and in time) of these circulation features?

Ben’s Answer

I’m not sure that there exist any strong evidence that the models are able to accurately predict either changes in large scale ocean and atmospheric circulation  patterns, or changes in statistics of these patterns.  The variations of the global temperature data during the past 10-15 years as compared to the predicted change is one example of a non-accurate forecast of temperature. I have seen little evidence that large scale circulation patterns such as ENSO, PDO, etc can be predicted over short time periods, let alone 50-100 year periods. I also think there are serious questions as to the accuracy of feed back processes and errors here could cause major errors in long term predictions. Finally, the ability to predict precipitation changes, even over short time periods, is very questionable. So, while overall it is clear that the introduction of “greenhouse gases” into the atmosphere must result in a warming of the troposphere, I can make that prediction without a model. The question as to how much warming will result, and how this will effect overall circulation patterns, precipitation, etc. are questions that I believe have not, to date, been answered with any confidence.

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