Season Creep

Season creep – or more formally, shifts in phenology, the timing of seasonal biological events – provides some of the most familiar and convincing evidence of climate change.

In the northern hemisphere, trees and shrubs are leafing out in spring 2-3 earlier days or more each decade, and holding onto their leaves about a day longer in the autumn. The growing season for crops is 10-20 days longer than it was 30 years ago. Snow and ice melt is occurring earlier. Birds and butterflies are migrating earlier. At the same time plants and animals are extending their ranges northward.

Perhaps even the politicians of Washington, D.C. will notice earlier cherry blossoms (

The evidence is strong. The timing of cherry blossom festivals in Korea and Japan date back to the 11th Century, while records of grapevine blooms in Europe extend back about 300 years. Meanwhile, the notes taken by enthused bird watchers everywhere over the past decades are finally useful. The last three decades are different from anything on record.

But what about marine plants, animals and ecosystems? They should be experiencing season creep as well. In fact because the marine environment is less fragmented than the terrestrial, the creep should be even more obvious. Because it is the ocean, though, we have much less baseline information, and far fewer long-term data sets. But now, there too the evidence is accumulating.

The journal Global Change Biology has published many articles on season creep, both terrestrial and marine

For instance, intertidal molluscs including blue mussels and some limpet species are extending northward and breeding earlier. Cod are moving northward in the North Atlantic. Pollock, cod, snow crabs and Grey Whales are all shifting north in the Bering Sea. All of this is correlated with warmer sea surface temperatures.

Many species have moved north into the Bering Sea (

In the Irish Sea, cod are being replaced by haddock and jellyfish. In the North Sea, small fish species are coming in from the south, and the number of larger more northern species is declining. In the North Atlantic, planktonic copepods are shifting north at about 23 km/yr. On the coast of Florida, Loggerhead turtles are laying eggs 10 days earlier – and the newly hatched juveniles are mostly female. In the subtidal grass beds of the northern Gulf of Mexico, southern fish species are moving in, while more northern species are disappearing. Again, all correlated with warmer sea surface temperatures.

In marine ecosystems, season creep is occurring everywhere one takes the time to look. We can’t ignore it and continue with ‘business-as-usual’.

The problem, though, is that this is creeping change, not pouncing change, and we hardly notice it. What difference does a day or two shift in phenology really make anyway? But as the average temperature of the planet continues to increase, decade after decade, think how much every ecosystem is going to change.

And these are just responses to rising temperatures. Add in the effects of shifts of ocean currents, the impact of stronger hurricanes, the disappearance of coral reefs. These are not idle predictions, they are all occurring now.

Ecosystem upheaval is underway, and we have little idea of how things will settle out. In fact, with ever rising temperatures, they will never settle out but continue to change and shift.

Willing to bet we will take action?
Don’t bet the farm. Maybe move it north though.

Season creep has also hit professional baseball, football and hockey (

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