Climate Lingo 1: Isotherms. “We’re moving poleward baby!”


What is an “isotherm?” It is a line which represents an average temperature… as these graphs show…   “Isotherms” are important in climate science discussions because…


Isotherms are moving…  and they are all moving exactly the same way, and that’s poleward baby. They are moving at the rate of 100km/decade; or 10km each year. Fast isn’t it?


When isotherms move, so do creatures who like to live at a certain temperature. Since 1975, the majority of marine species (75%) have moved polewards, some up to 1000km.


When it comes to land based critters (terrestrial species), ‘less’ of them have moved – ‘only’ 50%  – and when they move, they tend to move more slowly; they have shifted up to 600km since 1975.


When species move… this can create ripples of disorder and confusion … much like a ‘newcomer’ arriving in a town. Not all ecosystems remain in-tact, some can’t keep pace. For some land species who wish to move so as to stay in their optimum climatic zone, they may find an enormous city or urban sprawl blocks their path. Sadly, for many of these creatures, that can mean ‘game-over’ – you are now just a statistic in the mass extinction event currently under way. Ecologists and others try to help through breeding programs, assisted shifts, or building ‘habitat’ corridors, but its hard yakka. Generally, species are losing the game.

Humans are also impacted of course, as their food supply is also on the move.


Yet complicating this is the rather strictly defined state and territorial borders, which are not moving…


Isotherm movement. Important.




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