Marine Heat Waves

Largely invisible to the public, Marine Heat Waves (MHW) are separate and distinct amplifications of a general trend that has warmed the oceans significantly over the past 50 years. These large scale underwater temperature spikes are impacting entire ecosystems, especially coral reefs and kelp forests. If climate change continues at this pace, there is no reason not to conclude that massive destruction will occur in these critical marine environments, with large scale threats to marine species and food supplies anticipated. It is important to state clearly that this process is well underway.

The oceans have absorbed more than 90% of  excess fossil-fuel-generated greenhouse gas emissions over the past 50 years. To some degree, in the short term, this process has disguised the extent of overall warming by providing what might be called a buffer for the atmosphere. In other words, surface temperatures would be higher than they are if not for this effect. The degree to which this was happening was not fully understood, and this faux hiatus was quickly leveraged by fossil fuel operatives as the end of the global warming hoax. Unfortunately, it is more accurately described as the beginning of a global warming acceleration. The heat absorbed by the oceans has not left the planetary system. The oceans will retain this heat.

A January report from the journal Science (incorporating adjusted data from the  Intergovernmental Panel on Climate Change) indicates that the oceans have actually been warming 40% faster than the previous consensus. 2018 being the warmest ocean temp year ever measured globally followed sequentially backward in time by the years 2017, 2016 and 2015.

One report from National Oceanographic Data Center’s Ocean Climate Lab projects that if the heat absorbed by the oceans over the past 70 years were added back to the atmosphere, air temperatures would climb 65 degrees F. That would be bad.

In addition to the absorption of heat energy, the ocean is absorbing enough excess CO2 that the pH of the water (and the chemical composition) is changing, becoming more acidic. The ocean dissolves about 25% of the CO2 released by burning fossil fuels, currently about 22 millions tons daily.

Here are some of the obvious and less obvious consequences:

Expanding ocean volume: Melting land ice on Greenland and Antarctica are contributing to rapid sea level rise, but the planetary ocean is also expanding as it warms. This is a simple matter of physics. Warmer liquids take up more space.

More extreme hurricanes: This is a much larger topic, but suffice to say the past few years have delivered overwhelming evidence that this process is well underway. Warmer waters contain more energy and directly increase wind speeds. Rapid intensification, which has presented a whole new set of problems for forecasters, is in part due to deeper layers of warm water.


November 2016 photo provided by ARC Center of Excellence for Coral Reef Studies: dead staghorn coral killed by bleaching on the northern Great Barrier Reef, Australia. (Greg Torda/ASSOCIATED PRESS)

Threats to marine life on multiple levels: Temperature increases begin to compromise underwater ecosystems simply by exceeding the range the species can tolerate. Coral reefs are bleaching and dying around the planet, but especially in the Southern Ocean and off the northern coast of Australia in the Great Barrier Reef. The latter, a World Heritage Site, has sustained irreversible damage.

Kelp forest off the California coast.

Kelp forests are an amazing sight generally observed first hand only by scuba divers, but they also comprise another key ocean ecosystem. Underwater “kelp trees” grow to 40 feet or more, and provide shelter and food for a wide range of fish. Kelp forests are dying of heat and invasive species such as purple urchins.

Disruption of commercial fishing supplies: This phenomenon is separate from depletion of species due to over fishing. The combination of industrial over fishing, pollution and rising water temperatures is devastating many commercial species. In general, marine species are migrating to cooler waters in the direction of the poles, which causes the food chain to break down across the board.

Disruption of ocean currents: In 2012, a marine heat wave in the Gulf of Maine ushered in a new era that spells complex change for the iconic lobster fishery in the region. Meanwhile, squid and butterfish species are moving up from the south. This particular marine region is an excellent example of the connectivity of the Earth’s waters, because the changes in the Gulf of Maine is caused in part by the rapidly melting glaciers to the northeast in Greenland. The fresh water is disrupting the water circulation in the North Atlantic, with yet to be anticipated consequences for the future. This is only one example.

Changes in ocean chemistry (pH): The ocean is becoming more acidic, with a slight .1 pH downtick.  But the pH scale is logarithmic, so small changes are significant. The shift in chemistry has already had a negative impact on oysters, mussels, urchins and starfish as shells show a tendency to dissolve when forming. In addition to shellfish, tiny zooplankton are affected by pH, as they build shells of their calcium carbonate. While the overall effect of chemistry and warmer temps on zooplankton is as yet unknown, consider that they are the basis of the marine food web. Their skeletons become a key mechanism for removing CO2 from the atmosphere.

Over geologic eras, species adapt gradually to changing conditions in a variety of ways, especially by migration and to some degree by evolving. Ocean pH has been stable for millions of years. However, in the Anthropocene age, the pace of change is faster than the ability of many species to adapt.

Decreases in oxygen levels: Decline in dissolved oxygen has been observed for some time, but the scale of the condition is increasing significantly. Oxygen levels in various tropical regions have dipped by 40% over 50 years. Elsewhere, the average loss is about 2%.

Toxic algae blooms: Another phenomenon that combines agricultural pollution and warming water temperatures, toxic algae outbreaks now threaten water supplies and marine recreation industries around the globe.