If you are a Canadian of a certain vintage you will remember the 1992 cod moratorium in which a 500-year old Newfoundland fishery was brought to a sudden halt as the cod population crashed and the government had to take drastic steps to prevent complete extinction of the species. What was supposed to be a two-year suspension became permanent, although a small cod fishery was reopened in 2024. This being the 1990s, no one thought to blame climate change for the disappearance of the fish, instead pointing to the massive fishing fleets that had been emptying the oceans of everything that moved for decades. But, never ones to pass up a chance, a group of climate scientists published a paper in 2003 based on, of course, climate models not real-world data, and it warned that ocean warming would speed up the decline of North Sea cod which were already almost all gone. Unfortunately for them, though maybe fortunately for the fish, the #HaveItBothWays rule soon kicked into gear.

Two years later a new paper appeared in a different journal, also based on climate modeling, which reached a different conclusion. Whereas the 2003 paper had said “Output from the model suggests that increasing temperatures will lead to an increased rate of decline in the North Sea cod population compared with simulations that ignore environmental change” the 2005 paper, after noting that cod stocks would grow in some places and shrink in others concluded “Individual growth rates for many of the cod stocks will increase, leading to an overall increase in the total production of Atlantic cod in the North Atlantic.”

To be fair, that paper also said:

“These responses of cod to future climate changes are highly uncertain, however, as they will also depend on the changes to climate and oceanographic variables besides temperature, such as plankton production, the prey and predator fields, and industrial fishing.”

Remember the 2005 paper appeared back in the day when scientists noticed other things happening in the world and didn’t assume carbon dioxide was the control knob for everything. Hence while global warming would, in the model world, lead to more cod, the fishing fleets might swing into action and drive them all back to near-extinction.

So will climate change help or harm the cod population? Tell us which answer you prefer and we’ll find a model that gives it to you. Because with climate change you can #HaveItBothWays.