Insightful Interview In EOS Of Dr. De-Zheng Sun “Climate Dynamics: Why Does Climate Vary?”

There is an a very important interview by C. Schultz of  De-Zheng Sun of CIRES at the University of Colorado in Boulder in the August 12 2011 issue of EOS. It is titled

Climate Dynamics: Why Does Climate Vary?

The abstact of the interview reads [highlight added]

In recent years, climate change has become a major focus of public and political discussion. Ongoing scientific inquiry, revolving predominantly around understanding the anthropogenic effects of rising greenhouse gas levels, coupled with how successfully findings are communicated to the public, has made climate science both contentious and exigent. In the AGU monograph Climate Dynamics: Why Does Climate Vary?, editors De- Zheng Sun and Frank Bryan reinforce the importance of investigating the complex dynamics that underlie the natural variability of the climate system. Understanding this complexity—particularly how the natural variability of climate may enhance or mask anthropogenic warming—could have important consequences for the future. In this interview, Eos talks to De- Zheng Sun.

Examples, of the insightful comments from De-Zheng  include

“….even without any external forcing from human activity, the state of the climate system varies substantially.

“….one thing this book emphasizes is that, at least for interannual and decadal time scales, the climate is capable of varying in a substantial way in the complete absence of any external forces.”

“the anthropogenic effect was initially studied in a way that gave focus to its effect on the globally averaged energy balance. One- dimensional models were the early tools used to study the anthropogenic effect. While these models illustrated the importance of various radiative feedbacks in the context of global energy balance perturbed by an increase in CO2, they did not have the MJO, monsoons, ENSO, or the Pacific Decadal Oscillation, all of which may change in behavior as more greenhouse gases are released. All you can get from these one- dimensional models is a monotonic increase in global mean temperature as you increase CO2 in the atmosphere. Although three- dimensional models have now been developed, the conceptual picture about the effect of an increase in CO2 is still largely underpinned by the results from those one-dimensional models, as is evident in the notion that a significant linear trend in temperature will be the defining feature of global warming caused by anthropogenic enhancement of the greenhouse effect. The continuing influence from these early models over the way people conceptualize the anthropogenic effect is also because the state-of- the- art three- dimensional models still do not properly simulate natural variability such as MJO and ENSO. As a result, models are not yet able to capture the anthropogenic effect that takes place in the form of climate variability. In other words, our models may be underestimating the effect from anthropogenic forcing on natural variability.It is time to look seriously at an alternative hypothesis, which is that the defining feature of global warming will be changes in the magnitude of climate variability…”

I also wanted to use this book to urge caution with regard to another traditional idea: that even if we don’t simulate natural variability very well, we may still get anthropogenic global warming right. Such an assertion is probably too optimistic. One of the key questions is whether the simulated climate system is in the correct dynamic regime, because a system near a critical point can respond very differently than a system that is in a very stable regime. A poor simulation of a natural mode of variability such as MJO or ENSO suggests that the involved system is not in the correct dynamic regime. Also, those feedbacks that affect global energy balance, such as cloud and water vapor feedbacks, may depend on the natural variability—MJO, ENSO, etc. However successful state-of-the- art climate models may be in simulating some key features of the climate system, the question of whether these models capture fully the complexity of the dynamics—in particular, whether or not these models are in the same dynamic regime as the observed climate— has yet to be answered.”

“The prevailing conceptual framework that has been used to quantify climate changes stemming from anthropogenic forcing is that increasing CO2 concentration will create a linear trend in temperature and other state variables that define the mean climate. I would suggest that the focus may need to shift from looking for trends in mean temperature to statistical changes in the magnitude and other attributes of natural variability. The effect of anthropogenic forcing is likely to manifest in climate phenomena at all time scales so long as these climate phenomena derive energy from differential heating. This shift in paradigm may further highlight the need for a better understanding of the mechanisms behind natural variability, in particular, their thermal and nonlinear aspects.”

“…the complexity of the dynamic processes seems to be either overlooked or oversimplified in many communications to the public. I suspect that could cause problems down the road, because we know climate can vary strongly on a range of time scales in the complete absence of any external forcing. If you overlook the complex dynamics of the climate system, and you don’t explain those processes up-front to the public, then you can cause confusion down the road.”

Some climate scientists and the media, who have been more inclined to equate climate change to a monotonic warming, appeared to experience some trouble in explaining this harsh winter to the public. If one feels difficulty and potential embarrassment in explaining away a cold winter, what happens if we witness that the coming decade is cooler than the decade we have just lived through, something we know is possible within the realm of natural variability? If what is conveyed to the public is essentially a monotonic warming, how do we explain a halting or a reversal in the global temperature trend? “

This interview, and the AGU book that was the reason for the interview, should be read. It further shows that the IPCC 2007 reports ignored the broader view of the climate system which is what is needed if we are going to robustly interpret how humans are altering it.

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