Current global mitigation ambition as under the Paris Agreement as reflected in the National Determined Contributions (NDCs) up to 2030 is insufficient to achieve the Agreement's 1.5 °C long term temperature limit. As governments are preparing new and updated NDCs for 2020, the question as to how much collective improvement is achieved is a pivotal one for the credibility of the international climate regime. The recent Special Report of the Intergovernmental Panel of Climate Change on Global Warming of 1.5 °C has assessed a wide range of scenarios that achieve the 1.5 °C limit. Those pathways are characterized by a substantial increase in near-term action and total greenhouse gas (GHG) emission levels about 50 % lower than what is implied by current NDCs. Here we assess the outcomes of different scenarios of NDC updating that fall short of achieving this 1.5 °C benchmark. We find that incremental improvements in reduction targets even if achieved globally, are insufficient to align collective ambition with the goals of the Paris Agreement. We provide estimates for global mean temperature increase by 2100 for different incremental NDC update scenarios and illustrate climate impacts under those scenarios including for extreme temperature, long-term sea level rise and economic damages for the most vulnerable countries. Under the assumption of maintaining ambition as reflected in current NDCs up to 2100 and beyond, we project a reduction in the Gross Domestic Product (GDP) in tropical countries of about 50–60 % compared to a no-climate change scenario and long-term sea-level rise of close to 2 m in 2300. About half of these impacts can be avoided by limiting warming to 1.5 °C, or below. Scenarios of more incremental NDC improvements do not lead to comparable reductions in climate impacts. An increase in 2030 of the aggregated NDC ambition of big emitters by 33 % does not deliver more than about half the potential reduction in climate impacts compared to limiting warming to 1.5 °C. Our results underscore that a transformational increase in 2030 ambition is required to achieve the goals of the Paris Agreement and avoid the worst impacts of climate change.