The phenomenon of coral bleaching is becoming increasingly common along the Great Barrier Reef in Australia. According to the Australian Institute of Marine Science (AIMS), it happened in 2020 and has now occurred again.
When the water is too warm, corals expel zooxanthellae, an algae living in their tissues — reducing themselves to survive the heat better. The coral is not dead, just slimmer and under greater stress, thus more vulnerable.
The US lost half of its coral reefs in the Caribbean in 2005, when warm waters, centered near the Virgin Islands and Puerto Rico, expanded southward. Satellite data confirmed the thermal stress had been greater than the total of the previous 20 years.
Algae is the coral’s primary food source and gives it color while the coral provides a protected environment for the algae. Thus the two enjoy a symbiotic relationship which under temperature stress can cause the algae to leave. Having lost its principal food source, the coral turns very pale and becomes susceptible to disease. It can take as long as a decade to recover from such trauma.
Thus back to back bleaching events as on Australia’s Great Barrier Reef are cause for concern. This is now its fourth mass bleaching event in six years. The heat stress can slow coral growth and limits its spawning abilities, extending the effects to new generations. Seeding the damaged areas with healthy coral often developed in nurseries to withstand such stresses is another technique.
Meanwhile, the Australian government continues its support of fossil fuel industries, particularly coal and natural gas, even though coal is recognized as the worst fossil fuel polluter responsible for 0.3C of the 1C increase in global mean temperatures.
These temperatures are expected to rise 3.2C by the end of the century at the present rate making the lives of our successor generations exceedingly difficult as they cope with frequent adverse weather events like wildfires, hurricanes or typhoons.
The UN Intergovernmental Panel on Climate Change (IPCC) has now presented its guidelines on what we must do to limit temperature rise to 1.5C.
First carbon emissions must peak no later than 2025, then decline to reach the net zero goal by 2050. Put another way, the CO2 emissions of the last decade is the amount that is allowed to us for the next three.
Experts believe that we will have to resort to negative emissions in the second half of this century, to compensate for all that is already there, to limit warming to 1.5C. They also warn us that if emissions are not controlled by 2030 and continue to rise, there will be so much up there we may have difficulty controlling them at all.
On the positive side, CO2 can be extracted and stored, and changes in farming practices plus tree planting can all help. The machines extracting CO2 are new and very expensive. But there is always hope that scientists and technologists can improve that aspect over time.
Perhaps individual consciousness of climate change will affect behavior. A couple of examples: we can all reduce very short automobile trips or their frequency by bunching errands and car sharing; we can substitute pork for beef and lamb because ruminants produce more gas, and so on. Let us continue to hope we humans are up to the challenge.