In this paper, we introduce the concept of climate debt and provide country-level estimatesthrough 2035 under a business-as-usual scenario. These estimates can help inform the debateon climate change by providing a clear view of which countries have (until the present)contributed the most to climate change, as well as the likely path for climate debt by countryover the next 15 years. We then discuss the implications for carbon emissions if the G-20countries and EU were to adopt either of the two policy options proposed in recent months:the first by President Biden for the US and the other by the EU for its member countries.The implications for fiscal policy are that beyond the need to keep public debt at sustainablelevels, countries will also need to allocate funds for expected increases in pension and healthspending associated with aging populations. As a result, there may be little room for newexpenditures (such as green infrastructure or subsidies for clean energy) to reduce the growthof climate debt. Countries could turn to the revenue side, in particular greater taxation ofenergy with carbon taxes. This would have the advantage of reducing emissions while alsohelping countries to fund spending on green infrastructure.