Climate alarmists have long argued that ocean warming will damage the world’s coral reefs. What do the data show? From CO2Science.org: A new study notes that “[El Nino] events are predicted to increase in frequency and intensity, potentially generating recurring thermal stress and mass bleaching events in coral reef ecosystems.” The authors examined coral reefs in the Eastern Tropical Pacific over the 1970-2014 interval, during which there were several powerful El Nino events. They found that instead of showing increased stress, the reefs showed increased resilience to warming events over time.
Paper Reviewed: Romero-Torres, M., Acosta, A., Palacio-Castro, A.M., Treml, E.A., Zapata, F.A., Paz-García, D.A. and Porter, J.W. 2020. Coral reef resilience to thermal stress in the Eastern Tropical Pacific. Global Change Biology DOI: 10.1111/gcb.15126.
Writing by way of introduction to their study, Romero-Torres et al. (2020) say that “ENSO events are predicted to increase in frequency and intensity, potentially generating recurring thermal stress and mass bleaching events in coral reef ecosystems.” And in light of such model-based predictions they add “the most recent climate-change assessment therefore predicts a very high likelihood of irreversible damage to coral reefs worldwide.”
Searching for real-world observations that might support these dire predictions, the seven-member research team focused on studying coral reefs located within the Eastern Tropical Pacific (ETP), which reefs are presently characterized by many as “analogues of future environmental conditions under global warming and ocean acidification scenarios” given their warm temperatures and regions of persistent upwelling. In accomplishing this objective, Romero-Torres et al. performed an exhaustive literature review to collect data that enabled them to analyze coral cover trends from 1970 to 2014 and their relationship with thermal stress caused by repeated El Niño events.
With regard to their findings, the researchers report that over the 45-year period of study “ETP coral cover exhibited temporary reductions following major ENSO events, but no overall decline.” Indeed, as seen by the red trend line in Figure 1, coral cover increased slightly during this time, though the increase was not statistically significant. Of perhaps greater interest to the subject at hand, however, is the apparent increasing resistance of this parameter over time to the thermal stress caused by major El Niño events; whereas coral cover experienced a 25.6% decrease following the 1982/83 El Niño, it rebounded to pre-event levels within a decade and remained at such levels following the subsequent super 1997/98 El Niño event.
Commenting on their work, Romero-Torres et al. say that “after repeated thermal stress disturbances, such as those caused by the 1997-1998 El Niño, ETP coral reefs have demonstrated regional persistence and resiliency.” Consequently, they conclude “ETP coral reefs have adapted to thermal extremes to date, and may have the ability to adapt to near-term future climate-change thermal anomalies,” adding “these findings for ETP reef resilience may provide general insights for the future of coral reef survival and recovery elsewhere.” And those insights do not support the fervent claims of climate alarmists of current and ongoing irreversible damage to coral reefs.
Figure 1. Illustration of the influence of ENSO events on the coral cover in the Eastern Tropical Pacific (ETP). Top panel (a): Positive (red) and negative (blue) sea surface temperature anomalies in the Niño-3 region during 1971-2014. The vertical orange bars indicate the strongest El Niño events. Bottom panel (b): Live coral cover aggregated at the region scale for ETP coral reefs with its fitted linear trend (red dashed line). The fitted smooth line trend in green represents the long-term cycles of loss and recovery (95% confidence level interval in gray). Box plots describe the minimum, maximum, interquartile ranges and median values of live coral cover for each year. Source: Romero-Torres et al. (2020).