“This paper demonstrates that even the complete elimination of state GHG emissions will have no measurable effect on climate change risks unless Cali- fornia-style policies are widely adopted throughout the United States, and particularly in other countries that now generate much larger GHG emissions. As California Governor Jerry Brown, a staunch proponent of climate change policies, recently observed, “We can do things in California, but if others don’t follow, it will be futile.” . . . Nevertheless, the extent to which California’s GHG policies have and may be likely to inspire similar measures in other locations, is rarely, if ever seri- ously evaluated by state lawmakers or the California judiciary. Absent such considerations, imposing much more substantial GHG mandates may not only fail to inspire complementary actions in other locations, but could even result in a net increase in GHG emissions should population and economic activity move to locations with much higher GHG emission rates than California. “