The approach to economic ecology is based on a survey of the state of the ecosystem that departs from the state of global warming as summarized by the Intergovernmental Panel on Climate Change (IPCC). The state of alternatives to fossil energy is reviewed, too. Review of measures to establish a circular economy forms the base of a strategy for transition to carbon neutral economy. The most effective economic intervention towards global heating is identified as a Pigovian Tax on CO2-emission (ET). Evidence on the effectiveness and the state of implementation of ET 2020 is reviewed. For complementary evidence, the ET-calculation model of the Danish Climate Law 2020 is described by representatives of the Danish Climate Council in Appendix by Bendtsen and Stewart.