Late 19th-Century Navigational Uncertainties and Their Influence on Sea Surface Temperature Estimates

TL;DR

This paper develops a Bayesian framework to quantify historical ship position errors and their impact on sea surface temperature estimates, revealing significant uncertainties in 19th-century data.

Contribution

It introduces a novel Bayesian inference method to assess and incorporate historical navigational errors into SST uncertainty estimates, improving climate change reconstructions.

Findings

Posterior median celestial correction uncertainty: 33.1 km in longitude, 24.4 km in latitude.

Two-hour dead reckoning uncertainties: 19.2% in speed, 13.2° in heading.

Position errors translate into measurable SST uncertainties using ensemble sampling.

Abstract

Accurate estimates of historical changes in sea surface temperatures (SSTs) and their uncertainties are important for documenting and understanding historical changes in climate. A source of uncertainty that has not previously been quantified in historical SST estimates stems from position errors. A Bayesian inference framework is proposed for quantifying errors in reported positions and their implications on SST estimates. The analysis framework is applied to data from the International Comprehensive Ocean-Atmosphere Data Set (ICOADS3.0) in 1885, a time when astronomical and chronometer estimation of position was common, but predating the use of radio signals. Focus is upon a subset of 943 ship tracks from ICOADS3.0 that report their position every two hours to a precision of 0.01{\deg} longitude and latitude. These data are interpreted as positions determined by dead reckoning that are periodically updated by celestial correction techniques. The posterior medians of uncertainties in celestial correction are 33.1 km (0.30{\deg} on the equator) in longitude and 24.4 km (0.22{\deg}) in latitude, respectively. The posterior medians of two-hourly dead reckoning uncertainties are 19.2% for ship speed and 13.2{\deg} for ship heading, leading to random position uncertainties with median 0.18{\deg} (20 km on the equator) in longitude and 0.15{\deg} (17 km) in latitude. Reported ship tracks also contain systematic position uncertainties relating to precursor dead-reckoning positions not being updated after obtaining celestial position estimates, indicating that more accurate positions can be provided for SST observations. Finally, we translate position errors into SST uncertainties by sampling an ensemble of SSTs from the Multi-scale Ultra-high resolution Sea Surface Temperature (MURSST) data set.