SST Trend metrics: The historical rate of change provides information on long-term variation in sea surface temperature (SST) year-round and during the warmest period of the year. This indicates how rapidly temperature may be approaching critical coral bleaching thresholds (i.e., Warm Season and Warmest Month Trends). It also indicates the potential for suppressed seasonal variation, and therefore less time for recovery from summertime conditions (Annual Trend), which may be extreme. SST Trend values are determined at coral reef-containing and adjacent satellite pixel locations worldwide, for the period 1985-2023, using the Version 3.1 (v3.1) daily global 5km CoralTemp satellite SST data product.

Warm Season Trend [range: -0.52 to 0.79°C/decade], Annual Trend [-0.21 to 0.47°C/decade] and Warmest Month Trend [-0.57 to 0.75°C/decade]: Trends are calculated as the decadal rate of change in the average daily temperature (in degrees Celsius) for the Warm Season, Year, and Warmest Month, across the entire v3.1 CoralTemp SST dataset (1985-2023). The Warmest Month is identified in a separate metric (see Climatology page), based on the 28-year (1985-2012) climatology of the CoralTemp SST dataset; the Warm Season is defined as the three-month time period centered on the Warmest Month; and the Annual values are calculated for each calendar year. For all three metrics presented here, we determined the average temperature for the stated time period, for each year in the time-series (1985-2023), and then calculated the trend using a linear generalized least squares model with autoregressive residual of order one.