Fish have been around for over half a billion years, but the populations of our favorites have been decimated in the last few decades. We know sea life has been contending with overfishing, pollution and plastic mistaken for fish food. But now a new paper suggests that models for the marine food chain underestimated future decline because they neglected to factor in the melting of the great northern ice sheets.
The problem begins with algae not appreciating the new conditions created as the ice sheets collapse and pour freshwater into the sea.
In Geophysical Research Letters, Lester Kwiatkowski of the Sorbonne University and colleagues explain how Greenland’s ice sheets melting could cause decline from the very bottom of the food chain in the Atlantic, and going up.
“Earth system models” seek to simulate all relevant aspects of the Earth system, as the European Union helpfully puts it. Which means, they try to factor in as many parameters as possible.
But the current set of Earth system models of how climate change will impact “net primary production” in the oceans (the net creation of organic compounds by photosynthesizing algae and diatoms) had not factored in ice sheet collapse.
When ice sheet melt is factored in, the decline of net primary production is projected to be exacerbated, say Kwiatkowski and the team.
Why does freshwater influx into the sea matter? Because it would lower salinity, change the currents and increase the stratification in the oceans. Crucially, the team projects a diminishment in nutrients welling up from the depths toward the surface.
If algae populations are diminished, the populations of small animals that eat the algae will be diminished — which means fish that eat the small animals will be diminished, and the animals up the food chain that eat the fish will be in trouble too. Humans can eat alternative resources of protein, but fish ’n’ chips may become quite the luxury.
The great melt
Forecasting is for fools, but humans have been trying to do it anyway since time immemorial. Ancient oracles were possibly inspired by methane gas leaking from the vents, egomania or schizophrenia, while today’s forecasts are more data-reliant. Even so, global warming and climate change have been ramping up faster than most scientists had expected.
Temperatures in Greenland soared to as much as 40 degrees Fahrenheit (or 22 degrees Celsius) above the average this year, leading its ice sheet to melt to a point only expected in the year 2070, for instance.
That doesn’t mean the trajectory is linear and the acceleration will accelerate. We are in uncharted territory and just don’t know.
In any case, under high emissions scenarios, 21st-century global net primary production is now projected to decline by up to 20 percent. The North Atlantic would suffer from impaired productivity much more than the southern part of the Atlantic.
How much net primary production declines will depend on how much meltwater is added to the oceans — and the forecasts for that vary.
Optimists think that by the year 2100, average sea level rise will be about 50 centimeters (about 20 inches). Pessimists are thinking more like 4 meters, assuming what is presently the worst-case temperature trajectory. The truth is, we have no certainty about either the degree or the timing of scenarios, either for temperature rise or sea level rise. (Just to be clear, we are on track for the worst case: emissions are still rising.)
The caveats to the scenario painted by the new paper are many and myriad. There is so much we don’t know yet, including whether we might get breaks from the warming trend. Meaning, you can take specific projected figures for specific points in time like you take your seafood: with a grain of salt.
But we know with absolute certainty that global warming is happening, that the great northern ice sheets are imploding, and that freshwater influxes into the sea hurts marine life. And now we know that the more and faster the ice sheets melt, the more the bottom of the food chain will suffer — and so will we.
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