Global Warming and Animals | 299 understood, and the findings are surprisingly grim The pH of the oceans has dropped around 0.3 over the last 100 years, with the steepest drop beginning around the mid-1970s Carbonic acid, which is causing the lowering of pH, is not only hindering species from laying down needed calcareous structures, but this lower pH is eroding calcareous structures that have already been generated, such as the shells of clams and snails Indeed, by the year 2100 ocean pH is very likely to be lower than during the last 20 million years Changes in Timing Species on every continent are already shifting in the timing (i.e., phenology) of various events primarily occurring in spring, but also to some extent in the autumn Frogs are breeding earlier, cherry blossoms bloom earlier, and leaves turn color later Over the last 30 years, around 115 species (plants and animals together) from locations around the globe were found to be altering the timing of a spring event earlier by around five days per decade Only of the 115 species (~five percent) showed a later change in timing of their spring events Rapid phenological changes of species are of concern, because for over tens of thousands of years or more, animals have been adjusting to the timing of other species around them For example, as the planet warms, farmers may have to change the timing of their planting and might even change the type of crop grown Either of these changes could provide an insect with a food resource that was previously limited, thereby allowing the population size to grow If the insect feeds on the nectar from the flowers of the crop, then the farmer could experience a benefit owing to the plants being pollinated If, however, the insect feeds on the tissue of the crop plant, then the increasing size of the insect population could be seen as a detriment that must be countered in some manner, for example, with pesticides In wild communities, changes in timing could mean that a food source of a species is not available at the time it is needed This in turn could cause the species stress, either in time and energy looking for food, or in competitive interactions with others over the little food available Such stress may lead to lower fecundity rates which, if not rectified, could lead to extinction Changes in Genetics, Behavior, and Other Traits The third type of change is of traits that are reported relatively infrequently: genetics, behavior, and other species’ traits An example of a behavioral change is the foraging habits of polar bears Now, instead of hunting seals, they are by necessity increasingly foraging in garbage dumps Some species that rely on seal kills, the Ross and Ivory gulls, may not be getting the food they need to sustain their population numbers Extirpation and Extinction The escalating rise in average global temperatures over the past century has put numerous species in danger of extinction Functionally extinct species, or species we can anticipate as likely to go extinct unless humans come to their aid, include those that cannot move to a different location by themselves as the temperature increases, due to either lack of available habitat or the inability to access it For example, in Australia the Mallee emu-wren is quite sedentary (rarely moving farther than or km), with a small fragmented range that is frequently threatened by fires This