Climate Always Changes: It’s the Rate of Change that Matters

In a new paper published in Science magazine, two researchers take a look at much of the current literature about climate change, past and present.  Although terrestrial temperatures have changed in the last 65 million years (since the disappearance of the dinosaurs) as much as that being predicted for our times, the rate of change now is frighteningly faster.

…although the global cooling that occurred between the early Eocene and the Eocene-Oligocene glaciation of Antarctica (52 to 34 million years ago) was greater than the 21st-century warming projected for RCP8.5 [the highest projected greenhouse effect], the Eocene cooling occurred over ~18 million years, making the rate of change many orders of magnitude slower than those of the  RCPs [current projections](fig. S1) (33, 112). Likewise, the Paleocene-Eocene Thermal Maximum (PETM) encompassed warming of at least 5°C in <10,000 years (113), a rate of change up to 100-fold slower than that projected for RCP8.5 and 10-fold slower than that projected for RCP2.6

[RCP is “Representative Concentration Pathways“- projections over time of estimated greenhouse gas increases. Four of these projections have been accepted as most likely, from lowest (RCP 2.6) to highest (RCP8.5)]

The problem is that plants, insects and animals have to adapt or die; adaptation takes time.  Some may be able to move in order to stay in the zones they need to preserve life; others may be able to adapt in sufficient numbers to become new species, able to live in the changed conditions.  Both movement and adaptation, when successful, in ages past, have taken time.  When time was not available, as during the great die-offs, whole species went extinct, in the thousands.  It is estimated that during the Cretaceous-Paleogene event of 65 mya, between one-half to two-thirds of all plant and animal species went extinct.

Plants and animals essentially would need to move about 1 yard each day farther north or higher in elevation to maintain the conditions they prefer, Field said. While farmers and others can shift where they grow crops, Field said, it’s different for a butterfly or a maple tree.

“Maple trees are not good at moving,” Field said, adding, “You don’t have forests moving over long distances very, very fast.”

 Added to the rate of change difference is that human activity has broken naturally occurring habitats into fragments, so that say, maple tree movement by means of squirrels, is far less likely to occur because the squirrel has less territory to run: highways, housing, corn fields….

 

It’s not a pretty picture.  And we’re not talking about much time.

…substantial warming over all terrestrial regions [is projected] by the 2046–2065 period (Fig. 1) (37). The largest annual warming occurs over the Northern Hemisphere high latitudes, including >4°C above the 1986–2005 baseline (or about 5°C above preindustrial temperatures)…

Summary in Scientific American, Salon and Science Daily.

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