The global temperature rise however can also be expressed as a geographical shift of isotherms. In that case you could say temperature remains the same, but latitude (equator to poles), longitude (continental influence) and altitude (sea level to mountain snowline) change – and because we have a complicated planet, with continents, mountain ranges, oceans and layered atmospheric patterns, this geographical shift is never perfectly linear with time – and may even require detours.
Climate shifts on land: go north, or upslope during warming
It helps to understand the challenges many species face as they will have to migrate to stay within their respective climate zones. When a climate becomes warmer, North American and Eurasian mammals for instance would try to migrate in the direction of the Arctic – or in some cases may try to go upslope*. Earlier today from a Nature publication we learned the ice age megafauna managed to find tundra refuges during various interglacials – but when at the onset of the Holocene additional environmental stressors were added to their equation, genetic diversity declined and some went extinct.
[*) The opposite could also happen: the woolly rhinoceros is thought to have evolved as a cold-loving animal in the high mountain ranges of Tibet, and then descended during the ice ages to conquer the cold low altitude plains of Eurasia, increased in size, and was no longer capable of returning to the mountains once temperatures increased.]
Current climate migrations, from land to oceans
In August a Science publication stated there is now again a measurable climate-induced migration towards the poles – at a pace of about two kilometres per year.
Now a new Science publication has more on species’ climate migrations, but this time not on land, but in the oceans. An international team of researchers, led by the Scottish Association for Marine Science, Scottish Marine Institute, has looked at required migratory patterns of marine species as a result of climatic changes over the last 50 years.
Slow and easy image of oceans is wrong
One would expect species in the oceans would have to travel at a slower speed than the land species, as ocean warming is delayed compared to land warming, because of the oceans’ high thermic mass. But the new research shows the driving force behind marine species migration is actually higher than on land, as two indicators of climate shift are larger: both the geographic shift of isotherms and the shift in seasonal timing of temperatures.
“These indices give a complex mosaic of predicted range shifts and phenology changes that deviate from simple poleward migration and earlier springs or later falls. They also emphasize potential conservation concerns, because areas of high marine biodiversity often have greater velocities of climate change and seasonal shifts.”
As an example of their second climate shift indicator they show seasonal changes can be large at smaller geographical scale levels. For instance the annual onset of spring is now on average 5 days sooner on the Scottish east coast, whereas it changed little on the west coast.
Ecosystems don’t evolve around temperature alone
With areas of high marine biodiversity the researchers also refer to coral ecosystems like the Asian coral triangle [see coral fish above in handout picture of Scottish Association for Marine Science – credit Hugh Brown], where species may be faced with a relatively large migratory challenge.
The reason for that is simple. For coral fish for instance temperature is not the only requirement. They would like to also find a nicely balanced fresh coral ecosystem waiting for their arrival after their long journey north or south. And that’s of course quite a picky thing to ask for.
© Rolf Schuttenhelm | www.bitsofscience.org