Some of the earliest clues scientists had that Earth's climate has changed over time were mismatches between the fossil record and a current ecosystem. How could this palm tree have grown in Wyoming? Why have fossils of the tropical breadfruit tree been found as far north as Greenland? These cold places must have once been warm and wet. The world is not as it has always been.
And somehow, despite the tumult, species adapted, moving thousands of miles to habitats where they could survive. Won't species today just do the same as temperatures rise in the years ahead?
It seems they may not have the chance. A new paper in the journal Science finds that climate change is now set to occur at a pace "orders of magnitude more rapid" than at any other time in the last 65 million years. That breakneck speed may mean extinction for species that cannot keep up.
For example, the paper's authors Noah S. Diffenbaugh and Christopher B. Field of Stanford write, consider the global cooling that took place beginning some 52 million years ago. That change was of a greater magnitude than even the worst-case global-warming projections for the 21st century. But that transition occurred over a period lasting 18 million years, not a matter of decades. Similarly, the Paleocene-Eocene Thermal Maximum, thought one of the more rapid climatic shifts, was 100-fold slower than the most dramatic 21st century scenarios, and 10-fold slower than the best-case ones. "Further," the authors add, "the rates of global change during the Medieval Climate Anomaly (MCA), Little Ice Age (LIA), and early Holocene were all smaller than the observed rates from 1880 to 2005 and than for the committed warming calculated to occur over the 21st century if atmospheric concentrations were capped at year-2000 levels" (emphasis added because haha).
The specifics of how this "unprecedented rate of global warming" will affect terrestrial species are uncertain, and will likely vary region to region, habitat to habitat. For some species, hospitable environments may emerge just kilometers away. For others, the authors put it in words that conceal the turmoil, "the constraint may be no-analog climates." Meaning, simply, that they'll have nowhere to go.