If humanity wishes to preserve a planet similar to that on which civilisation developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO₂ will need to be reduced from its current 385 ppm [parts per million] to at most 350 ppm... If the present overshoot of this target CO₂ is not brief, there is a possibility of seeding irreversible catastrophic effects.
James HansenAs species are exterminated by shifting climate zones, ecosystems can collapse, destroying more species.
James HansenJail threats did not dissuade Martin Luther King - and intergenerational justice is a moral issue of comparable magnitude to civil rights.
James HansenIn view of the immense power of natural weather and climate fluctuations and the great buffering capacity of the Earth, especially the ocean, it is easy to be skeptical about whether small anthropogenic changes of atmospheric composition can have important practical impacts.
James Hansen