Salmon are in trouble. Ask anyone involved and they’ll tell you how bad it is and who’s to blame (it’s always someone else).

It’s so bad that the Atlantic Salmon is now officially an IUCN Red List Endangered Species in the UK. In Ireland, the population has collapsed by 80% in 20 years. Other places and other salmon species are not far behind, and the word extinction really has entered the debate.

We can see this decline by watching the way the money flows. Just about everywhere the value is slowly ebbing out of salmon fishing, almost no matter how or where we do it, and from mega-trawler to rod & line.

Sure, we can remove dams and nets, replant catchments and clean up pollution to help mitigate the decline, but they’re not enough.

This crisis is universal, which is of note, because not everywhere has nets or fish farms or pollution or management corruption. Indeed, some have none of the above, yet their salmon are in trouble.

One of Scotland’s most exclusive rivers, the Helmsdale, used to be a place where fishing was accessed via dead men’s shoes. Royalty graced its banks and the management was so discrete as to be almost uncontactable. A rod on the Helmsdale was a mark of status. Now the Helmsdale has gaps to fill and is promoting itself in upmarket magazines. It has no pollution and no fish farms to blame. Something else is going wrong.

What salmon everywhere have in common is rising water temperatures. This is happening both at sea and in rivers. High temps impact badly on salmon at every stage of their lifecycle, from squeezed and collapsing ocean food chains to overheated redds and undernourished smolts failing to make the journey back to sea. The salmon lifecycle makes them especially vulnerable to warming water.

This is real and it’s happening everywhere. Check out the Missing Salmon Alliance for a thorough breakdown of these combined threats. Their rallying call is Cold, Clean Water – which is as succinct a summary of the salmon’s plight as you can find anywhere.

And it’s not just salmon: Entire food chains are wobbling. In recent years 10 billion snow crabs have gone missing from Alaskan waters and the most plausible explanation is starvation in warming seas. A few years ago 100m Alaskan cod went AWOL for the same reason: Warmth increases fish and crustacean metabolic rates, so they have to eat more just to maintain body weight. At the same time the warm water suppresses growth in their food supply. So they need more, get less and starve. It’s becoming a regular feature of ocean life.

Worse, the increase in metabolic rate may also increase salmon’s need for oxygen beyond the ability of their gills to fully deliver. If so, that too would inhibit growth and reproduction.

To understand why, we need to do some time travelling because today’s benign weather wasn’t always a given. Our ancestors had a much tougher time than us.

About 17,000 years ago the world was in the depths of the last Ice Age. We humans scraped a marginal existence as hunter-gatherers. Life was freezing and the world was a whopping 5c colder than nowadays.

We hit our stride about 10k years ago when the climate warmed and delivered a sweet spot that stuck. We could sow crops, expect to harvest them and feed our expanding population. Great civilisations formed. We could also hunt and fish for nature’s seemingly boundless resources such as the herbivores that roamed the plains and the fish and whales in our seas. The post-glacial world was rich in opportunity.

This is the Holocene Era: The time when the Earth and its climate came good for humans. There were blips along the way: a few major volcanic eruptions that caused cooling and short-term global famines, for example. But since the end of the Ice Age, Planet Earth’s climate has been stable and very hospitable.

Then came the Industrial Revolution and the arrival of the fossil fuel era. We are about 250 years into it now – the red zone below.

Current predictions are that temperatures will likely peak at about +2-3C, with growing confidence that it will be a lot closer to 2C than 3C. The hoped-for 1.5C target is surely a lost cause.

We have understood the basic science behind this since the mid-1800s. It’s not difficult – excess CO2 is pollution that traps heat in the atmosphere. We can measure it very accurately. We know the science is good and that what’s happening now is unfolding as scientists predicted it would (my first TV report saying the Holocene could unwind was nearly 30 years ago, and I was in Antarctica reporting established science, not breaking new ground). The scientists even got the speed of change about right, although as a layman I’m shocked by what we’re seeing now:

NASA animation of global temperature change since 1880:

We’re hitting temperatures not seen for 125,000 years and it’s going to get worse. When we finally stop pumping out CO2, we will revert to a long, slow cooling trajectory (business as usual). It will take thousands of years to get back to where we were just 250 years ago ( NASA ). That’s one heck of a hangover from our CO2 party that we’re giving to future generations.

It’s not all bad news (below). Climate scepticism is fading, clearing the way for better political engagement. The graphic below shows that only the 10% or so on the margin are still drinking neat Clorox. This group are mostly hard-core conspiracy theorists and have bucket lists of competing dire consequences they expect to suffer. You’d think climate doomsterism would be right up their victim-centric street, but I don’t think they will ever shift their position by much. I suppose they believe that one day they’ll be proved right and they won’t be the only ones dying of vaccine-preventable diseases or in G3/4/5 radio mast attacks.

The remaining 90% of us are increasingly concerned about climate change. The dial is shifting.

So where does this leave the salmon?

The answer is worrying: We can do a great deal to adapt to and mitigate the impacts, but the bottom line is that we’re stuck in a pattern of decline that won’t end until we tackle the root problem. The Earth is getting too warm and it’s happening too fast for the fish to adapt.

Ask an Atlantic Salmon. If you can find one …