The results of studies that try to quantify the effects of climate change on biodiversity loss which include damage to the micro scale level of subspecies and genetic variation are perhaps most shocking.

When however you focus on the response to climate change at the macro level, the ecosystem level, you get a better understanding of what is one of the major drivers of that biodiversity loss: forced migrations. And even here, the numbers may be larger than one would expect, as a new assessment by NASA and Caltech published in the journal Climatic Change shows that by 2100 some 40 percent of ´major ecological community types´ – that is biomes like forest, grassland, tundra – will have switched to a different such state.

According to the same study most of the land on Earth that is not currently desert or under an icecap will undergo at least a 30 percent change in vegetation cover.

Ecological damage is the real climate problem

Based on IPCC temperature projections for 2100 [which are probably on the conservative side] of 2-4 degrees Celsius warming scientists of NASA’s Jet Propulsion Laboratory and the California Institute of Technology ran special computer models to calculate the most probable ecosystem responses across the planet. This average temperature rise is of similar magnitude to the warming that occurred between the Last Glacial Maximum and the onset of the (milder) Holocene – with the big exception that the current warming is happening about 100 times faster – and for ecology that makes a huge difference, the authors stress.

“While warnings of melting glaciers, rising sea levels and other environmental changes are illustrative and important, ultimately, it’s the ecological consequences that matter most,” says John Bergengren from Caltech, who led the study.

It is not just species that have slowly evolved around specific climatic values, the same goes for ecosystems. As another study, recently published in Science, shows tropical biomes like rainforest, savanna and desert are tied to specific climate tipping points. When certain climatic thresholds are crossed the one ecosystem can suddenly switch to the other, as intermediate states somehow prove to be non-existent.

Migrations will be crisscross

As ecosystems shift on a timescale of centuries or less, species cannot adapt [because the required structural evolution takes millions of years] so they have to start moving to find other suited habitat, resembling their original climate and vegetation zones. For most species this requires migration towards the poles – but of course our planet’s many features, from mountain ranges, rivers and coastlines, to areas with high human population density and anything from agricultural plains to highways, industries and parking lots, greatly increases the extinction risk for individual species.

Perhaps somewhat harder to envision for us is that [as other new research shows] under continued climate change marine species face similar migratory distances – as the complexity of that blue world below the waterline is not limited to the presence of salty water, and finding replacement ecosystems may be equally challenging for a coral fish as it is for an orangutan.

The fact that some species are much better capable of migrating than others will likely only increase ecological imbalances and the risk of dangerous ecosystem plague damage.

Most sensitive climate hotspots

The new study by NASA and Caltech defines as ecologically sensitive hotspots – areas projected to undergo the greatest degree of species turnover – regions in the Himalayas and the Tibetan Plateau [as this ‘third pole’ is in fact to be considered a climatic island], eastern equatorial Africa [which has an unstable drought-sensitive climate], Madagascar, the Mediterranean region, southern South America, and North America’s Great Lakes and Great Plains areas. The largest areas of ecological sensitivity and biome changes predicted for this century are found in areas with the most dramatic climate change: in the Northern Hemisphere high latitudes, particularly along the northern and southern boundaries of taiga or boreal forests.

© Rolf Schuttenhelm | www.bitsofscience.org