We all have frustrations. Near the top of my list is the often-heard question: “Do you believe in climate change?”
Climate change is not a theological question. Many accept that climate change is happening; some dispute it.
In this column, I’ll offer some evidence you can use to decide for yourself whether climate change is real.
And then, I’ll offer some insights on how our climate affects fisheries.
Is climate change happening?
Manifold evidence supports global warming, the conspicuous centerpiece of global climate change.
Some of this evidence is indirect. Some is challenged as random variations or long-term thermal oscillations such as El Niño or La Niña.
The graph appearing with this column depicts a 130-year trend in average temperatures and the reason for the changes.
The average air temperature from 1880 to 2010 was just a little more than 57.5 degrees. The upward trend in air temperature is obvious.
The line labeled CO2 concentration reflects the concentration of carbon dioxide in the air. It has steadily increased, and the rate of change increasedbeginning in the 1970s.
The upward trend in both air temperature and carbon dioxide concentration is what I find compelling evidence for global warming.
Increasing carbon dioxide in the atmosphere creates a greenhouse effect. High-energy solar radiation passes through the high-carbon dioxide atmospheric blanket. When that solar energy strikes the earth, much is converted to heat, which is low-energy radiation bounced back into space.
But the carbon dioxide in the atmosphere reduces the passage of the low-energy radiation to space, so heat is trapped near the earth.
This is exactly how a greenhouse warms on a sunny day and the reason carbon dioxide is called a “greenhouse gas.”
The increasing carbon dioxide is a result of burning fossil fuels — coal and petroleum — and a reduction in the surface area of the planet that is covered in green plants absorbing carbon dioxide.
Climate change and fisheries
Increasing air temperature will drastically reduce the amount of habitat where cold-water fishes like trout and salmon can persist.
Warm-water fishes will be able to survive farther north and in higher elevations, and their annual growth rates could increase.
This would seem to be a good thing for catfish, sunfish, crappie, bass, shad and the other fish with which Mississippians are familiar.
But the biology of global warming is far from simple.
Warming water temperatures will result in earlier spawning for many warm-water fishes. This might be good if food resources needed by young fish are also available earlier, but if the zooplankton and small invertebrates needed by young fish are not available, the young fish will not survive.
How zooplankton and invertebrates will respond to a warmer climate is yet to be determined.
Also related to food for young fish is how fast forage fish grow. For example, young-of-the-year shad are important forage for piscivorous (fish-eating) young bass, crappie and white bass. If shad spawn earlier and grow faster, they will be available to piscivorous fish for a shorter period time, reducing growth and survival of the young sport fish.
Longer periods of warm water can mean a longer growing season and greater growth of sport fish, but food must be available. A longer growing season plus the higher metabolism of fish in warm water will put a greater demand on forage fish for piscivorous sport fish like bass, crappie, white bass and flathead catfish.
Several studies in other parts of the country have demonstrated that overabundant piscivorous fish can decimate their forage supply. A longer growing season has the same effect as more predators: More forage is needed to feed predators and sustain forage fish populations.
Of course, fish need water. And climatologists predict changes in precipitation patterns with global warming.
Most of these adverse changes will occur in drier parts of the United States, but weather is expected to become more extreme throughout the country.
That means wetter wet seasons and prolonged dry periods. Many reservoirs will have greater water-level fluctuations. More frequent and prolonged droughts could mean less water in Mississippi’s flood-control reservoirs and lakes connected to the Mississippi River.
Although not a major problem in Mississippi reservoirs — at least in the next few decades — water for people, industries and irrigation will take precedence to water for fish.
But Mississippi’s lakes will stratify sooner and remain stratified longer. This will concentrate fish in a smaller volume of water and change predator-prey dynamics.
What is clear is that fishery responses to climate change are complex and the net effects will be negative.
Efforts to reduce carbon dioxide emission will slow warming, but short of a yet-to-be-conceived technological solution only increasing the area of the planet covered in vegetation can reverse the atmospheric carbon dioxide and reverse global warming.