Proxy-based indicators of past climate change show that current global climate models systematically underestimate Holocene-epoch climate variability on centennial to multi-millennial timescales, with the mismatch increasing for longer periods. Proposed explanations for the discrepancy include ocean–atmosphere coupling that is too weak in models, insufficient energy cascades from smaller to larger spatial and temporal scales, or that global climate models do not consider slow climate feedbacks related to the carbon cycle or interactions between ice sheets and climate.

Most of the policy debate surrounding the actions needed to mitigate and adapt to anthropogenic climate change has been framed by observations of the past 150 years as well as climate and sea-level projections for the twenty-first century. The focus on this 250-year window, however, obscures some of the most profound problems associated with climate change.

A reconstruction of global surface temperature is used to show that deglacial temperature is correlated with and generally lags carbon dioxide concentration, a result that contributes to the explanation of the temperature change that occurred at the end of the most recent ice age.

Sea levels during the last interglacial stage (about 125 kyr ago) are known to have been higher than today, and may serve as a partial analogue for anthropogenic warming scenarios. However, because local sea levels differ from global sea level, accurately reconstructing past global sea level requires an integrated analysis of globally distributed data sets.