Extreme Temperatures in the Tasman Sea Responsible for the Record Heat Waves in New Zealand and Tasmania

This is the ocean. See how much hotter it looks?

For the first time, New Zealand's NIWA (National Institute of Water and Atmospheric Research) and Australia's Bureau of Meteorology have released a joint special climate statement discussing the extreme weather seen over the Summer of 2017-2018.  Their statement notes that the water temperature in the Tasman Sea in November increased dramatically, reaching 2°C or higher above average temperatures over an extremely large area.  The patch of warmer water reached all the way from Tasmania and southeast mainland Australia to New Zealand.  This level of ocean heating has never been seen before and was a major factor behind the highest November and December temperatures that Tasmania has ever seen as well as New Zealand's hottest Summer on record.  Although ocean temperatures in the Tasman Sea will sometimes rise dramatically during the Summer months, the geographic size of the temperature rises are usually limited in scope.  This year however the ocean temperatures rose quickly and to unprecedented levels over an enormous area.

Unfortunately, extreme Summer temperatures can have an array of consequences other than just discomfort for the humans living in New Zealand and Australia.  For example, the Royal Albatross Centre in Dunedin, the only mainland albatross colony remaining globally, experienced a poor year for raising chicks due to higher rates of embryonic death in their albatross eggs.  In addition, the drought which struck New Zealand early in the Summer may have been caused or exacerbated by the elevated ocean temperatures.  The intense cyclone season with its extreme flooding events in New Zealand was also likely affected by the abnormally high ocean temperatures, as warmer air is able to hold more water and warmer ocean waters will disrupt the normal climatic conditions in an area.

Another issue with higher ocean temperatures which the report did not mention is the impact on marine life.  When ocean temperatures increase, the pH of the water decreases, causing acidification of the seawater.  This is amplified by the increased levels of atmospheric carbon dioxide currently entering the ocean's water, which also causes ocean acidification.  One of the many results of increasing levels of ocean acidity is that it makes it much more difficult for marine organisms to pull carbonate ions from the seawater, which many marine organisms need to form shells, and in some cases carbonate shells may even dissolve in a more acidic ocean.  Scientists have been concerned that this issue would have grave consequences, affecting not just the species that are unable to form shells as easily (which could manifest itself in the form of reduced survival and reproductive success), but also all of the other species which interact ecologically with those species.  This would be very bad for the stability of the oceanic food webs and would not have good consequences for human harvesting of ocean ecosystems, like fisheries or shellfish farming, either.

Global pH levels are estimated to have already dropped by ~0.1, bringing New Zealand's ocean pH to 8.088, with estimates that it will decline to 7.95 by 2050, and 7.75 by 2100.  Should these pH changes happen as expected, it would be both the lowest pH levels and the quickest rate of change of pH in the past 25 million years.  There are indications that ocean acidification and/or increased ocean temperature may/will have damaging effects upon many of the organisms that create the reef environments (corals, molluscs, sponges, and red algae) that the other marine organisms live in.  If there is no habitat left the other species, which may not be directly affected by acidification, will not survive either.  Apart from the shelled invertebrates which have reduced survival or lower reproductive success as a result of issues with carbonate shell deposition, some other organisms also seem to have potential issues with decreased pH levels.  Some larval fish, for example, experience neurological issues under decreased pH levels, leading to decreased sensory perceptions and slower responses, including taking longer to flee from predators.  There are millions of different species in the oceans and we are only now starting to study the effects of ocean acidification upon them, so it is impossible to determine what the effects will be in most cases.  We can assume that the effects upon the ocean ecosystems as a whole will be massive, however.

If we look at the effects of climate change upon New Zealand, it is sobering to realise that 1) this is still only the early stages of what is yet to come, and 2) New Zealand is expected to be one of the places on the globe which will be the least affected by climate change.  The importance of doing everything that we can to reduce the levels of greenhouse gases in the atmosphere can't be overstated.  Life is not going to be much fun for any of us in the future if we don't sort out our mess now.

Here are the references that I used today. They are all excellent sources with far more information about what is happening and I would highly recommend reading them.  Especially the first one.  Clicking on a title will send you to its web address:

Cliff S. Law, James J. Bell, Helen C. Bostock, Chris E. Cornwall, Vonda J. Cummings, Kim Currie, Simon K. Davy, Malindi Gammon, Christopher D. Hepburn, Catriona L. Hurd, Miles Lamare, Sara E. Mikaloff-Fletcher, Wendy A. Nelson, Darren M. Parsons, Norman L. C. Ragg, Mary A. Sewell, Abigail M. Smith & Dianne M. Tracey (2017). Ocean acidification in New Zealand waters: trends and impacts. New Zealand Journal of Marine and Freshwater Research, 52(2), 155-195. DOI: 10.1080/00288330.2017.1374983

Commonwealth of Australia and NIWA, Special Climate Statement--record warmth in the Tasman Sea, New Zealand and Tasmania, 27 March 2018

Tracey E. M. Bates & James J. Bell (2017): Responses of two temperate sponge species to ocean acidification, New Zealand Journal of Marine and Freshwater Research, 52(2), 247-263. DOI: 10.1080/00288330.2017.1369132