Current warming and likely future impacts - Climate Change: Biological and Human Aspects - page 287

USA, respectively, had their synthesis on the effects of climate change on the world's
oceans published in the journal Science . It was arguably the first global assessment
of its kind. They concluded that impacts of anthropogenic climate change so far
include decreased ocean productivity, altered food-web dynamics, reduced abund-
ance of habitat-forming species, shifting species distributions and a greater incidence
of disease. They also noted that although there is considerable uncertainty about the
spatial and temporal details, climate change is clearly and fundamentally altering
ocean ecosystems. They warned that further change will continue to create consid-
erable challenges and costs for societies worldwide, particularly those in developing
countries.
The other place where species' spatial options become constrained with global
warming is the tops of mountains. As noted, with global warming thermally determ-
ined zonation on mountains changes and rises. If the warming becomes too great then
there is nowhere for alpine species to go as species cannot migrate above mountain
summits. This is of some ecological and wildlife concern. The alpine biome is just
3% of the vegetated terrestrial surface and such ecological islands are shrinking.
For instance, in the Ural Mountains, where temperatures rose by as much as 4 ◦ Cin
the 20th century, tree lines have risen between 20 and 80 m upslope, so reducing
the regional alpine zones by 10-20%. Meanwhile, an example of an animal under
severe threat comes from the southern hemisphere and is the mountain pygmy pos-
sum ( Burramys parvus ). It is a marsupial found in montane heathland from 1400
to 2230 m in south-eastern Australia. It is not a possum in the American sense and
is unrelated to true opossums. (The word opossum was taken from the Algonquian
Indian word for the American animal.) At the beginning of the 21st century, with just
some 2600 adults remaining, the mountain pygmy possum is considered to be under
serious threat (and indeed prior to 1970 was thought to be extinct). The species is
further pressured as its habitat is favoured by skiers. Human land use fragments the
landscape and further aggravates the conservation problems posed by current climate
change. Land-use concerns recur in many discussions about current climate change
and wildlife conservation.
Another example of threatened montane species, but this time one that includes
the changing environmental conditions that accompany climate change, comes from
local endemic animal extinctions in the highland forests of Monteverde, Costa Rica.
The situation became apparent following a step-like warming of the tropical ocean in
1976; indeed, 20 of the 50 anuran species (frogs and toads) in a 30 km 2 study area went
extinct, which suggests pressure on the broader population. In conservation terms, one
of the most serious of these local extinctions was that of the locally endemic golden
toad ( Bufo periglenes ) in 1987. The population crashes were all associated with a
decline in dry-season mist frequency (which had been measured) and it is presumed
that this in turn was due to a raising of the cloud-bank base (which unfortunately
was not measured). Furthermore, as noted at the beginning of this section, climate
change causes modifications in the way that populations from different species asso-
ciate. In this instance, along one stream as the habitat became drier harlequin frogs
( Atelopus varius ) gathered near waterfalls, so increasing the probability of their being
attacked by parasitic flies, and this in turn resulted in increased mortality (Pounds
et al., 1999). The researchers concluded that the aforementioned population crashes