Our world’s oceans have been warming steadily for at least 140 years, historic data shows.
Scientist John Murray, who was born in Canada, contributed much to our understanding of the ocean and climate. And one of his greatest contributions was his meticulous collection of data, which is still used today.
What is shows is that, on average, the surface of the ocean has warmed by 0.59 C; by 0.39 C at a depth of 366 metres; and by 0.12 C at a depth of 914 metres.
Averaging all depths, the ocean has warmed by 0.33 C in the past 135 years.
This might not look like a big number, but it is significant. For the entire ocean to have warmed this much over only 135 years suggests there is something going on. Perhaps this is simply continuing the warming trend since the last Ice Age ended, or perhaps this is reflecting the Industrial Revolution, which had transformed much of the world from agrarian to industrial societies between 1750 to 1850.
Our belief is that there has been a general warming trend since the last Ice Age which has been accelerated in the last 200 years by human activities.
Accelerated by how much is what climate scientists argue about in the climate change debates and we’re not going to wade into that.
But something is definitely happening in the ocean. Imagine a kiddie pool filled with cold water. Imagine how many buckets of hot water it takes to raise the temperature, even a little bit. On a broad scale, something is definitely happening to our oceans.
And it affects all fish, farmed and wild. Could this long-term warming trend be linked to the long-term decline in salmon returns over the past century?
We know that salmon can be dramatically affected by even slight variations in water temperatures, which affects how long they stay out in the ocean, their food supply, when they spawn, their survivability as alevins, parr and juveniles, and probably many other factors we haven’t considered. Ocean temperature is hugely important for salmon.
And if the water continues to get warmer, what will it mean for salmon, which have evolved to survive in generally cold water temperatures?
What will it mean for farmed salmon, which although farmed, are still salmon?
We’re not sure. Perhaps salmon runs will increase in the north. Perhaps farms can move north into cooler water. Maybe it won’t be a problem at all.
We’ll have to wait and see what the science says.