There are several reasons, in addition to growing energy demand, why achieving substantial and rapid GHG emissions reductions will be challenging. Some potentially important lower-carbon technologies – including nuclear energy, carbon capture and storage, and electric vehicles – still face significant technology, logistical, political, infrastructure and cost challenges. And worries about the cost of renewable technologies have led some governments to reduce their levels of support. In the meantime, the GHG intensity of oil and gas extraction and production looks set to increase, with the move towards resources that are harder to access.