Read here. Recently, NASA's James Hansen rounded up some exceptionally gullible and dim-witted teenagers to do legal battle for him in court. Hansen speculates that human CO2 increases will raise global temperatures so much that positive feedbacks occur causing a runaway global warming "tipping point."
Unfortunately for the dumb ass teenagers and their legal team, new peer-reviewed research (Barreiro et al.) determines that greater warming invokes a climatic tropical cloud negative feedback, not a positive feedback. This climate model research outcome basically eviscerates not only Hansen's speculative "tipping point" hypothesis, but also the teenagers' anti-science legal case crusade, pushed on them by a group of hysterical, manipulative adults.
"Using an atmospheric general circulation model coupled to a slab ocean we study the effect of ocean heat transport (OHT) on climate...results indicate that the climate warms only if the OHT increase does not exceed more than 10% of the present-day value in the case of a strong cloud-SST feedback and more than 25% when this feedback is weak. Larger OHT increases lead to a cold state where low clouds cover most of the deep tropics increasing the tropical albedo and drying the atmosphere. This suggests that the present-day climate is close to a state where the OHT maximizes its warming effect on climate and pose doubts about the possibility that greater OHT in the past may have induced significantly warmer climates than that of today." [Marcelo Barreiro, Simona Masina 2011: Journal of Climate]
Additional negative-positive feedback, tipping-point, climate-model and peer-reviewed postings.