Past to future: Towards fully paleo-informed future climate projections

We are transitioning towards a climate state on Earth featuring rapid changes in response to anthropogenic greenhouse gas emissions and land-use change, with severe observable and projected impacts on the occurrence of extreme weather events and increasing risk of crossing large-scale tipping points. Neither the transition nor the long-term climate state has been observed by (human-made) measurements before, making information on past climatic states increasingly more important to help anticipate future Earth System change. Paleoclimate records have enormously expanded over the past decades, and provide extremely rich information about physical, cryospheric, biological, and ecological processes on many spatial and temporal scales. Yet, it has been difficult so far to directly transform this knowledge on past processes into a more confident evaluation of future projections for the Earth system. In this contribution, I will summarise lessons learned from past climate change on our understanding of climate variability, abrupt changes and climate response to greenhouse gas changes and other forcing. For example, generalizations of classical measures such as equilibrium climate sensitivity can be useful in the palaeoclimate and future context for understanding the response of a climate state to radiative forcing beyond the linear regime, i.e. when (part of) the climate system is close to a tipping point. Finally, this contribution will present the ambition and programme of the starting EU-HORIZON project Past-to-Future (P2F) aiming at developing, expanding and using the wealth of paleoclimate data to improve existing Earth System Models in terms of their ability to describe possibly exotic, out of sample, climate states and the transition pathways towards them from current conditions.