It may sound adorable at first, but if the climate shift is making animals smaller, it changes the foods they can eat and what can prey on them, thus producing "all sorts of unpredictable knock-on effects in the ecosystem."
It is well established that cold-blooded species get smaller as the climate heats up, says Andrew Hirst of Queen Mary, University of London. Experiments show that, on average, 1 °C of warming reduces their adult body mass by 2.5 per cent. The mystery is why. To find out, Hirst pulled together data on 15 species of copepod that swim in the open sea, focusing on how they grew at different temperatures. As temperatures rose, the copepods got heavier faster. Hirst thinks that's because physiological reactions accelerate at warmer temperatures, allowing the copepods to bulk up faster.
But they also matured to adulthood faster, so their rapid growth ground to a halt at a young age. The overall effect was such that the warmer copepods wound up smaller. It's not clear why temperature has such a strong effect on the way these organisms mature, but Hirst suspects evolution favours organisms that are flexible in how fast they mature to adulthood. In a competitive environment, this increases the odds that individuals will reproduce before they are killed.
This means that one day we may find ourselves saying things like "In my day, sharks couldn't fit in fish tanks. Really, it's true! People were actually pretty afraid of them, which seems weird now that they're flushable."
That is, of course, if any of these creatures survive.
Why The Warming Climate Makes Animals Smaller [NewScientist]