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When it comes to sea levels, bad news keeps getting worse

Don Paul

After taking some time to digest the new Intergovernmental Panel on Climate Change (IPCC) report on the state of the oceans, I can outline some of the primary findings coalesced by more than 100 distinguished scientists based on 7,000 papers in multiple disciplines.

The bad news is growing worse. The mean rate of sea level rise exceeds earlier forecasts back in the 1980s and 1990s. Rising sea levels are not a matter of breaking news. The mean rate of rise and the increasingly major impacts are the headline material.

Looking at the data via NASA, coastal tide gauge measurements go back to 1870 and run through 2013. More detailed satellite-derived sea level increases extend back to 1993.

The mean rate of sea level rise globally is 3.3 millimeters annually, with a continuing slow increase in that mean rate. However, it must be noted sea level rise is not uniform around the planet. There are a few regions with deep colder waters in which sea level rise is much less, and there are many more regions in which sea level rise is greater. Moreover, coastal zones in which land subsidence exists in combination with rising seas produce a more rapid onset of negative impacts. Such locations include parts of the Gulf, Atlantic and Florida coasts. Globally, this NASA image captures the differing rates of increase.

Sea levels rise through two primary mechanisms, both related to a mean warming climate. Melt-off from ice caps and glaciers, with the largest single source being the Greenland ice cap, is the water source. The second mechanism is expansion of water volume due to ocean heating (water expands in volume as it heats).

Oceans have been acting as a buffer for atmospheric heating, and have absorbed around 90% of the heat generated by global warming due to the increase in carbon dioxide and other greenhouse gases tied to human activity. Without this giant heat “sink” (a body that absorbs heat), the earth’s land mass would be far hotter and warming more rapidly.

This oceanic heating exacts a steep price. The chemistry of the ocean becomes more acidic due to the ocean being a carbon sink as well, absorbing a great deal of the carbon from carbon dioxide. The acidification is killing many coral reefs and will endanger more shellfish, both of which depend on carbonate ions that are reduced by the increasingly acidic content of the waters. Carbon dioxide levels are currently at around 385 parts per million in the oceans, and are on track to approach 520 ppm by midcentury. The acidity brought on by such levels would be fatal to living coral reefs. This stress in combination with deoxygenation in combination with unrelated stresses such as unsustainable fishing practices and plastic waste will place a crushing burden on much marine life, including fish populations.

The frequency of seldom-publicized marine heat waves has been accelerating since the 1980s. That is, large portions of the fish population-supporting waters are undergoing heat waves of sufficient severity and longevity to both thin populations and force migrations farther north for some species. Some species such as Alaskan cod suffer to the extent that Alaska has to drastically drop catch limits by 80%, as was the case in 2018. Local fishing industries struggle to keep up and make adjustments, and native populations face steep declines in their vital catches.

IPCC also reports the warming waters are increasing populations of pathogens. An example is vibrio, a bacterium that infects oysters and other shellfish.

Sherilee Harper, a University of Alberta expert on this topic, told the New York Times vibrio makes 80,000 Americans ill from eating raw or undercooked shellfish each year.

“That’s a good example of how changes in the ocean can affect even people who live far from the coasts,” Harper said.

IPCC outlines a warming-linked element of global food security under the gun. Fish supplies about 17% of the world’s animal protein, and its proportion has been increasing in the last few decades. Yet projections in warming impacts on fisheries and aquaculture could take the amount of sustainable fish stocks down by 25% later in this century, even as need and demand go up.

These oceanic heat waves are multiplying and are expected to increase anywhere from 20 to as many 50 times by late in the century (depending on how much more our greenhouse gas emissions go up). You probably know about toxic algae blooms in areas such as western Lake Erie, tied to nutrient runoffs from agriculture, shallow water and seasonal warming. This occurs on a far greater scale on the North Pacific coast when there is anomalous warming. In 2013 and 2014, fisheries from British Columbia to California had to temporarily close because of this toxicity. Not all of the warming is due to the warming climate, as there are oceanic conveyor currents and oscillations in the mix as well.

It should be noted there appears to be the makings of another warm “blob” in the region at this time, as tweeted by Alaskan climatologist Brian Brettschneider.

Again, the amplification in the rate of oceanic warming is the real headline. It is a certainty even the best-case oceanic scenarios, which would depend on more successful efforts in reducing humanity’s greenhouse gas emissions, will still leave us with drastic impacts such as increased coastal flooding, more intense hurricanes with more destructive storm surges, and more fish, coral and shellfish kill-offs. Costly adaptation efforts, such as cities building sea walls, will become a must.

If we move toward the worst-case scenarios due to inadequate reductions in greenhouse emissions, many adaptation efforts will become ineffective late this century. Meanwhile, time for meaningful mitigation grows shorter.

On a happier note, fans and players are still good to go for the Game of Games Sunday weather forecast. Early tailgaters will have temperatures in the low to mid-50s, rising to the upper 60s in the afternoon.

It will be partly to mostly sunny. A breeze from the ENE will pick up to 8-16 mph, and may have a minor effect on the kicking and passing game.

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