Paleoscience questions for socially relevant understanding of climate change

Abstract:

Paleoscience research with broad societal interest is featured in national and international reports that assess the scientific understanding of climate change. These reports inform governments in their negotiations to reduce human-caused climate change, and they generate community engagement. Their content is extensively reviewed through a transparent and open procedure. Some of the longstanding and emerging questions that are of relevance to such reports include:

(1) How unusual are recent changes in the Earth system, including climate forcings and rates of change? Past climate states provide the long-term context of climate change to quantify what is normal or extreme.

(2) What are the prominent large-scale, recurrent spatial patterns associated with past global changes (eg, land-sea contrast, polar amplification)? Past climate states reveal large-scale regional patterns that are quantitatively robust and therefore provide predictive capacity.

(3) How well do models with paleoclimate forcings simulate large-scale Earth system changes (eg, global temperature, ice-sheet volume, carbon cycling)? Past climates help to evaluate model performance under forcings that span the range of projected future climate, which is beyond what has been observed by humans.

(4) What is the role of (forced and unforced) natural climate variability, including low-probability events, abrupt changes, climate modes, and volcanic eruptions? Accurate projections must account for internal variability and thresholds in the climate system. Detecting and attributing the human impact requires quantification of natural variability.

(5) What are the long-term effects of sustained warming across the Earth system and what do they indicate about irreversibility and equilibrium climate sensitivity? Paleoclimate provides empirical evidence for how slow-responding components of the climate system (cryosphere, deep ocean, carbon cycle) operate over centuries and millennia.

High-confidence assessments of major conclusions that address some of these key questions are currently limited by a paucity of robust quantitative evidence. However, the continued development of new data resources, analytical tools and community efforts are advancing the response to these prominent social geoscience questions.