Russia is one of the main oil and gas producers and one of the biggest emitters of carbon dioxide globally. Its energy policies are still underpinned by the necessity of establishing ‘spheres of influence’ and are not on track to achieve the objectives of the United Nations Framework Convention on Climate Change (UNFCCC) and the Paris Agreement. Politically, war in Ukraine is arguably a consequence of this approach and discloses for the European Union (EU) the possibility of a diversification of its energy sources to achieve security of supply, which unlocks the opportunity of accelerating the green transition envisaged in the European Green Deal. Legally, given that they are not at war with Russia, the EU and its Member States could invoke the energy supply crisis and the political misalignment between the Russian energy policy and the Green Deal, rather than war per se, as a justification to abandon consolidated long-term energy contracts and accelerate the green transition.