Rates of change in past warm periods, Part 3

Following the publication of the IPCC's Fifth Assessment Report in 2013, there has been mounting evidence indicating that the social and ecological impacts of global warming are increasingly contingent on seasonal extremes, such as peak summer temperatures, rather than trends in annual averages. This phenomenon is especially evident in the tropics, where extreme events have become a major threat to ecosystems. However, there remains a paucity of data concerning the present and future rates of change in means and extremes. This dearth of knowledge can be attributed to two key factors: firstly, the paucity of high-resolution data from bygone warm climates that could serve as analogues; and secondly, the absence of sophisticated data analysis methodologies.

The SEARCH project (Seasonal Extremes and Rates of Change in Past Warm Climates: Insights from Advanced Statistical Estimations on High-Resolution Coral Proxy Records) has been developed to enhance our understanding of past climates through the utilization of a database comprising high-resolution coral proxy records, complemented by the application of sophisticated simulation techniques from the domain of statistical science. The SEARCH database contains approximately 50 existing and newly acquired (bi-)monthly resolved coral proxy records from the following periods: (a) the Anthropocene, (b) the Medieval Climate Anomaly-Medieval Warm Period, (c) the Holocene Thermal Maximum, (d) the Last Interglacial, and (e) the Mid-Pliocene Warm Period.

We explain the methodological foundations of the project: proxy calibration, nonparametric kernel estimation of the first derivative of the climate proxy series and linear regression. It is important to note that these methods take into account the typical peculiarities of palaeoclimate time series, including non-Gaussian distributions, autocorrelation, uneven spacing, and uncertain timescales.

The primary outcome of our analyses indicates that the warming rates during the Anthropocene, which approximate 0.14 ± 0.04 °C per decade, appear to be relatively indistinguishable from the rates documented in other warm periods. We proffer an explanation for this observation and propose refinements to the analytical methodology.

This work has been funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), project number 468589022 (SEARCH), within the SPP 2299, project number 441832482