"There is such a thing as a point of no return," he says. If Obama wins the White House and Democrats expand their majorities in the House and Senate, they will intervene in the economy and redistribute wealth. Yet their economic policies "will pale by comparison to what they will do in permitting countries to acquire nuclear weapons and turn them over to terrorists. Once that happens, we're at the point of no return. The next generation will live under that threat as far out as the eye can see."
A mechanical trauma to the spinal cord can be followed by the development of irreversible and progressive neurodegeneration, as opposed to a temporary or partially reversible neurological damage. An increasing body of experimental and clinical evidence from humans and animal models indicates that spinal cord injury may set in motion the development of disabling and at times fatal neuromuscular disorders, whose occurrence is not normally associated with any major environmental event. This outcome appears to be dependent on the co-occurrence of a particular form of mechanical stress and of a genetically-determined vulnerability. This increased vulnerability to spinal cord injury may depend on a change of the nature and of the timing of activation of a number of neuroprotective and neurodestructive molecular signals in the injured cord. Among the main determinants, we could mention an altered homeostasis of lipids and neurofilaments, an earlier inflammatory response and the failure of the damaged tissue to rein in oxidative damage and apoptotic cell death. These changes could force injured tissue beyond a point of no return and precipitate an irreversible neurodegenerative process. A better knowledge of the molecular signals activated in a state of increased vulnerability to trauma can inform future treatment strategies and the prediction of the neurological outcome after spinal cord injury.
Several of the genes mentioned above are likely to modulate tissue vulnerability to mechanical trauma through oxidative stress, an important determinant of SCI-induced secondary injury neuronal loss. X-ALD post mortem brains  and mouse model of X-ALD  show significant levels of oxidative damage. Mice deficient in Bach1, a transcriptional repressor of the heme oxygenase-1 (Hmox1) gene which has a cytoprotective and anti-oxidant effect, showed a better profile of functional recovery following moderate SCI and a significant smaller area of injury [92, 93]. ABCD1 can also give rise to inflammatory-related demyelination . Trauma-induced lipid peroxidation in mutant App animals is also pointing towards oxidative stress as well as a deranged lipid metabolism as important factors in the determination of susceptibility to trauma .
The neurological impairment induced by SCI may gradually subside or, despite comprehensive rehabilitative efforts over a period of time, turn into an irreversible functional deficits. More atypical post-injury clinical pictures include localized, non-progressive as well as diffused and evolving forms of amyotrophy, neurological pictures very close to what observed in MND . In some other cases, protracted and repetitive mechanical stress like the strenuous use of a limb due to particular occupational exposures or professional sports have been linked to the development of recurrent painful brachial plexus neuropathies, with features of muscle weakness and atrophy as well as sensory loss, similarly to what seen in hereditary neuralgic amyotrophies . Whether permanent or progressive, the neurological consequences of trauma reflect a complex interplay of genetic and environmental factors, which condition an individual's susceptibility to withstand injury. This paper has embraced the body of experimental data describing genes which may potentially modulate susceptibility to trauma, in order to dissect those molecular events that may be responsible of the establishment of irreversible neurodegeneration in the post-injury phase, here defined as the "point of no return".
The possibility of points-of-no-return in the climate system has been discussed for two decades1,2,3. A point-of-no-return can be seen as a threshold which, once surpassed, fundamentally changes the dynamics of the climate system. For example, by triggering irreversible processes like thawing of the permafrost, drying of the rainforests, or acidification of surface waters. Recently, Lenton et al.4 summarized the global situation and warned that thresholds may be closer in time than commonly believed.
In this new Washington Institute Policy Focus, Iranian dissident Mohsen Sazegara examines the changes in Iranian society and what they portend for the country's political future. During the past two centuries, he argues, Iran has been wracked by the conflict between modernity and tradition, democracy and despotism. The Islamic revolution was only the latest in a series of failed efforts to resolve that conflict. The regime has failed not only economically and socially, but also in terms of propagating its ideological, revolutionary, maximalist version of Islam. Having unsuccessfully tried to reform itself, the regime now finds itself unable to address the problems of the country and the people. As Sazegara shows, this combination of an illegitimate regime and a defeated reform movement has put Iran on the razor's edge -- a point of no return on the country's path toward democracy.
I agree that it is important to point out that there can be many tipping points depending on your frame of reference. For islanders that have already been forced to relocate 20th century sea-level rise has already passed a tipping point of no return.
What are the chances of natural, negative feedbacks kicking in at some point? An example of a positive feedback is Arctic sea ice melting, which exposes the ocean, which absorbs far more energy than the snow and ice did, causing the ocean to heat (or the air to cool?). Do similar negative feedbacks occur that tend to keep the climate in its current state?
Based in part on carbon emissions, a new study using simulations identified two tipping points for the Greenland Ice Sheet: releasing 1000 gigatons of carbon into the atmosphere will cause the southern portion of the ice sheet to melt; about 2500 gigatons of carbon means permanent loss of nearly the entire ice sheet.
From among those simulations, the researchers derived the 1000-gigaton carbon tipping point for the melting of the southern portion of the ice sheet and the even more perilous 2,500-gigaton carbon tipping point for the disappearance of nearly the entire ice sheet. 781b155fdc