High-stakes and large uncertainties characterize the science, policy and reality of climate change. A simple analysis of what appears to be most likely for the immediate future of Earth's climate system, including some probable human vulnerabilities, is presented below. In short, climate change is real. Further, numerous observations suggest the onset of a rapid phase transition between the familiar Holocene climatic mode and some future quasi-stable steady state. Such a climatic phase transition may extend from years to decades, presenting dramatic and unfamiliar challenges to ecological and societal organizations at all scales. Potential human hazards--particularly grave for food production--may catalyze dramatic societal changes. The profound uncertainty of abrupt climate change warrants careful reflection and prudent preparation, including assessment and enhancement of household, local and bioregional adaptive capacities. C'est l'importance des enjeux et des risques qui caracterise les efforts scientifiques, politiques ainsi que la realite des changements climatiques. On trouvera ci-dessous la description d'une simple analyse de ce qui semble etre le plus probable des scenarios sur l'avenir a court terme du systeme climatique de la Terre, dont certains aspects de la vulnerabilites pour les humains. En clair, le changement climatique est une realite. De plus, de nombreuses observations indiquent qu'une phase transitoire rapide serait en cours et que celle-ci nous menerait du mode climatique holocene qui nous est familier vers un autre etat d'equilibre quasi stable. Une telle phase transitoire peut s'etaler sur plusieurs annees, voire des decennies, et s'accompagner de defis inedits de diverses echelles, tant sur le plan ecologique que sur celui des organisations sociales humaines. Les risques humains potentiels, specialement ceux lies a la production de nourriture, pourraient entrainer des changements sociaux dramatiques. La gravite de l'incertitude liee au changement climatique abrupt appelle une reflexion minutieuse et des preparatifs consciencieux, dont l'evaluation et le renforcement de mecanismes d'adaptation, tant sur le plan domestique, local que regional.
INTRODUCTION
The cataclysm of Hurricane Katrina brought climate vulnerabilities to the North American forefront. Fast on the heels of Katrina, Hurricane Wilma spun the barometer way down low, setting a new record as the most powerful Atlantic hurricane ever recorded. Although scarcely noted, Catarina came to Brazilian shores in March 2004, as the first South Atlantic hurricane on record. In light of numerous purported climate anomalies in recent years (droughts, floods, heat waves and other extremes) and extensive media attention, Jane and Joe Mainstreet may reach a simple conclusion: the weather outside is frightful!
Is this simple statement accurate? Are recent climatic events the tip of an apocalyptic iceberg or are they manifesting ordinary climate variability? What can we anticipate in the future and how might we respond? These questions and others demand a simple synthesis of what is known--or at least what most environmental Earth scientists believe is most likely--about our climate system and what this may mean for each, and all, of us. This essay summarizes these themes for a broad spectrum of professional scientists, as well as students and others interested in the subject of climate change. The short list of references (including online resources listed herein) delivers a thin wedge into a very extensive literature.
CLIMATE HISTORY AND COMPLEXITY
Oceanic sediments, glacial ice cores and other natural archives can be read as a rich, yet imperfect, record of Earth's climate history. Researching the dynamics of palaeoclimate helps one understand what is possible--including what is most likely--for our planetary and regional future. Computational climate models are employed to generate and test hypotheses about past, present and future climate dynamics. Modern studies of Earth's climate system are illuminating the interdependence of geological, oceanic, ecological and atmospheric processes. Accelerated fossil fuel burning and land-use changes (particularly deforestation) have accompanied the expanding ecofootprint of industrial-powered humanity on local, regional and global scales. It is abundantly clear that the human species has become a profound planetary force (Rees 1997; Vitousek et al. 2002).
To understand climate (and Life itself), we must distinguish between complex and complicated systems. Bureaucracies and technology are complicated; the climate system is authentically complex. Complex and complicated systems may each present behaviour that is perplexing to interpret or predict. However, complicated systems are comparable to mechanisms or machines; they are top-down organized from a preexisting template; they commonly possess an intricate internal structure, and are less than, or equal to, the sum of their parts. Complex systems transform energy flux into a dynamically ordered pattern (Chaisson 2001). These systems are self-organizing; they involve a dynamic process that creates and perpetuates a dynamic pattern and vice versa (Lewin 1992)! They commonly display emergent properties, such as self-regulation, robustness and resilience [www.resalliance.org]. Particularly characteristic are non-linear responses to forcing, including critical-point behaviour, manifested by large abrupt changes when forcing exceeds particular (and often unknown) thresholds (Alley et al. 2003). Self-perpetuation of dynamic pattern, spontaneous novelty, and surprise are intrinsic and characteristic of many complex systems.
