by Judith Curry
Juoakola spotted an interesting paper, that I missed when it was originally published:
NONLINEARITIES, FEEDBACKS AND CRITICAL THRESHOLDS WITHIN THE EARTH’S CLIMATE SYSTEM
JOSÉ A. RIAL , ROGER A. PIELKE SR., MARTIN BENISTON , MARTIN CLAUSSEN, JOSEP CANADELL , PETER COX, HERMANN HELD , NATHALIE DE NOBLET-DUCOUDRÉ , RONALD PRINN, JAMES F. REYNOLDS and JOSÉ D. SALAS
Abstract. The Earth’s climate system is highly nonlinear: inputs and outputs are not proportional, change is often episodic and abrupt, rather than slow and gradual, and multiple equilibria are the norm. While this is widely accepted, there is a relatively poor understanding of the different types of nonlinearities, how they manifest under various conditions, and whether they reflect a climate system driven by astronomical forcings, by internal feedbacks, or by a combination of both. In this paper, af- ter a brief tutorial on the basics of climate nonlinearity, we provide a number of illustrative examples and highlight key mechanisms that give rise to nonlinear behavior, address scale and methodological issues, suggest a robust alternative to prediction that is based on using integrated assessments within the framework of vulnerability studies and, lastly, recommend a number of research priorities and the establishment of education programs in Earth Systems Science. It is imperative that the Earth’s climate system research community embraces this nonlinear paradigm if we are to move forward in the assessment of the human influence on climate.
This is a really provocative paper, that deals with many topics that have been discussed on previous threads, including chaos and complexity, prediction of emergent behavior, feedbacks and thresholds, natural internal modes and multidecadal ocean oscillations. Numerous examples are given of past abrupt climate changes.
The paper concludes with:
Therefore, we have agreed on a list of desirable research strategies – some of which are specific, employing integrated assessments within the framework of a vulnerability approach, and some of which are general. The list is not intended to be exhaustive but hopefully illustrative of the many challenges (and opportunities) fac- ing the Earth’s climate system research community. Accordingly, we recommend to
• Explore the limits to climate predictability and search for switches and choke points (or hot spots) of environmental change and variability.
• Construct models to explain the nonlinear response of the climate system to changes in insolation forcing due to orbital parameter changes, an objective best approached from the paleoclimate perspective.
• Improve our vision of the climate’s future through a better understanding of its history. Paleoclimate and hydroclimate records exhibit abrupt changes in the form of rapid warming events, the irregular oscillations of ENSO, catastrophic floods, sustained droughts, and many other nonlinear response characteristics. Extracting, identifying, categorizing, modeling and understanding these non- linearities will greatly help our ability to understand the present and future state of the climate.
• Develop GCMs coupled to low-dimensional energy balance ice sheet/litho- sphere hybrid models (e.g., Deconto and Pollard, 2003) that can simulate the interaction between hydrosphere, atmosphere and land over a wide range of spatial (continental to global) and temporal (centennial, millennia) scales.
• Understand the global connectivity and variability of ocean-atmosphere cou- pled phenomena, such as the North Pacific Oscillation (NPO), the Pacific Decadal Oscillation (PDO), the Arctic Oscillation (AO), the North Atlantic Oscillation (NAO), and the El Niño/Southern Oscillation (ENSO).
• Promote research to improve techniques that measure directly or indirectly the spectral variability of the Sun’s irradiance output at decadal and millennial scales.
• Understand the physics of the ocean thermohaline circulation (THC), whose collapse may be one important cause of major climatic change in Western Europe and North America (Rahmstorf, 2000).
• Perform sensitivity experiments with global climate models to evaluate the response of the climate system to biospheric interactions (including vegetation dynamics, and the effect associated with the anthropogenic input of carbon dioxide and nitrogen compounds), the microphysical effects on clouds and precipitation due to anthropogenic aerosol emissions, and land-use change including fragmentation of ecosystems. Existing experiments to explore these effects include Cox et al. (2000), Eastman et al. (2001b), and Pielke (2001a,b).
• Investigate the benefits and risks of large-scale deliberate human intervention in the climate system. For example, carbon sequestration, associated with land-management practices could be a strategy to remove CO2 from the at- mosphere. This should include the concurrent effect on water vapor fluxes into the atmosphere and the net irradiance received at the Earth’s surface (e.g., Betts, 2000, Claussen, 2001). Another example is the effect of the construc- tion of large-scale water systems and the control of large lakes such as Lake Victoria and the Great Lakes on regional climate systems.
• Identify locations or regions that are particularly sensitive to or easily im- pacted by the planetary climate system. The Amazon rain forest and its fluvial regime (Cox et al., 2000), Southeast Asia (Chase et al., 2000), the North Atlantic Ocean (Rahmstorf, 2000), the Arctic Ocean (Foley et al., 1994), the boreal forest (Bonan et al., 1992), and the Nile River system are examples of such sensitive locations.
• Investigate in increasing detail nonlinear interactions involving changes in biospheric emissions of chemically and radiatively important trace gases, changes in atmospheric chemistry affecting the lifetimes of these gases, and resultant changes in radiative forcing. Examples of such investigations using simplified models include Homes and Ellis (1999) and Prinn et al. (1999).
To conclude, we recommend the development of new educational initiatives on environmental/climate science. The complexity of the climate system, its myr- iad of parts, interactions, feedbacks and unsolved mysteries needs researchers able to transcend their own specialties, jump over and build bridges across ar- tificial disciplinary boundaries. Hence, a fundamental requirement for the future environmentalist/climatologist is a firm grasp of the mathematics and physics of nonlinearity and of the methods and goals of interdisciplinary climate science. We enthusiastically endorse John Lawton’s (2001) call for establishing specific programs on ‘Earth System Science’ (ESS) at various institutions and universi- ties, in order to provide upcoming generations of scientists with insight into the complexity, the interdisciplinary nature and the crucial importance of these themes for the future of humanity. The greatest challenge is to build a strong research infrastructure that defines ESS, and as Lawton notes, the greatest barrier at present is the lack of organizations ready to nurture this new discipline.
Sounds really really good to me.
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