Better out than in

After the election of President Trump and a two-house Republican majority, many fear for the future of US climate policy. The new administration has indicated that they will abolish Obama's climate legacy through executive orders1. The repeal of domestic measures will likely result in the US missing its first nationally determined contribution (NDC) under the Paris Agreement, which is an inadequate target of reducing emissions by 2628% compared to 2005 levels by 2025. If other countries adopted comparable targets, global warming would likely exceed 2 °C (ref. 2). The US would need to implement the Clean Power Plan and additional measures to reach its NDC3. Preliminary research suggests that the policies of the Trump administration would instead lead to emissions increasing through to 20253. Now the predominant concern for much of the international community is that the US will withdraw either from the Paris Agreement, or the overarching United Nations Framework Convention on Climate Change (UNFCCC)4. The former would take four years and the latter only one. Both are legally possible and within the presidential mandate5. The conventional wisdom is that a US withdrawal would be a worst-case scenario for international climate policy. However, a sober analysis of the political, legal, and financial impacts suggests otherwise. The modified matrix of risks posed by a recalcitrant US administration summarized in Table 1, and explored in detail below, highlights the paradox of US participation: a rogue US can cause more damage inside rather than outside of the agreement.