James Hansen is perhaps best known for his testimony regarding the human impact on climate change given to congressional committees in the 1980s that helped raise broad awareness of the global warming issue, testimony that government officials initially sought to discredit but which has now been largely accepted. Hansen has warned that a global “tipping point” will be reached in the near future if levels of greenhouse gases like methane and CO2 are not reduced. Human-made forces, especially greenhouse gases, soot, and other small particles, now exceed natural forces, and the world has begun to warm at a rate predicted by climate models.