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Wednesday, January 02, 2019

Life Forms are Moving Polewards..

“The velocity of climate change,” is the speed at which zones of suitable climate move across the landscape.

We depend upon natural ecosystems to purify our air, soils, and water, to control pests, to limit erosion, to break down waste that we dump into the environment, and even to stabilize the climate. In general, when the climate warms, species need to move poleward (towards the north in the northern hemisphere and towards the south in the southern hemisphere) to maintain a constant temperature environment. In flat landscapes, the speed a critter needs to move across the surface to stay in a zone of constant temperature can be relatively high. On the other hand, species that live on the slopes of mountains can move upslope to stay at the right temperature; often the speed they need to travel is much less than those for flat-land species, because in steep terrain temperatures can drop quickly a short distance up hill.

Historically the main focus of conservation has been the establishment of protected areas where negative human impacts are restricted. But with climates on the move, many plant and animal species will be tracking their preferred habitats right out of the very areas designed to protect them. Establishing corridors among existing protected areas to give plants and animals landscapes through which they can move is increasingly recognized as a crucial step in conserving biodiversity.

The projected rate of ecosystem change is large in many cases compared to the ability of species and systems to migrate. For the tropical and subtropical broadleaved forest ecosystems characteristic of much of South and South East Asia, the average velocity is about 0.3 km per year. For some species, however, such shifts may not be possible, putting them at risk of extinction.

The state-of-the-art models of global ecosystems project an increasing risk of severe terrestrial ecosystem change with increasing global mean temperature. The area affected increases rapidly with warming. The affected surface increases almost four-fold between warming levels of 2°C and 3°C. The most extensively affected regions lie in the northern latitudes, where current climate conditions would find no analogue in a warmer world. These changes, resulting in shifts in the variability and mean values of carbon and water stock and fluxes and, in some cases, vegetation composition, would pose a major challenge to the survival of plant and animal species in their current habitat.

Over half the world's population depend on fish as an important food source, or a way of making a living - most of these people living in developing countries. To cope with rising temperatures, marine animals are trying to migrate pole-wards, or die. The impacts on the world population will be profound. By 2050s there will be large losses and local extinctions across tropical regions. Migrating animals also cause havoc to the new e
cosystems they move to.

Species are seen to be moving poleward
in studies around the world. The greater the warming in any given region, the farther its plants and animals have migrated. A 2011 study found that on average, species migrated uphill 36 feet per decade and moved away from the equator — to cooler, higher latitudes — at 16 kms per decade. The rates are two to three times those estimated by the last major migration analysis, published in 2003.

For most of the 20th century, North American rodents called pika moved upslope at an average of 43 feet per decade. But since the late 1990s, the critters scurried upward far faster, climbing 475 feet per decade.

Likewise, on Mount Kinabalu in Borneo, moths are flapping higher and higher to escape the heat, an average of 220 feet in altitude in the last four decades.

Mosquitoes that can carry malaria, dengue fever and other tropical diseases have expanded their ranges in recent decades. In 2009, mosquito-borne dengue fever returned to the United States after an absence of nearly 75 years.

A tally of more than 4,000 species from around the world shows that roughly half are on the move. The ones on land are moving an average of more than 16 kms per decade, while marine species are moving four times faster. This is occurring even though sea surface temperatures are warming three times slower than land temperatures. Phytoplankton, zooplankton, and bony fish showed the largest shifts.

"We're talking about a redistribution of the entire planet's species," says the lead author of a new study in Science.

To compensate for the temperature effects of climate change terrestrial species will have to migrate on average 50-60 kilometers towards the poles for every 0.5 degrees Celsius of warming. In mountains each warming of 0.5 degrees requires species to move 100 meters further uphill, in order for full populations to remain in their respective climatic zones 
and not to lose habitat.

The unprecedented rate of global temperature increase means that species need to migrate at rapid rates. Couple this with the destructive effects of agriculture and urbanisation, leading to the fragmentation and disconnection of natural habitats, and migration to a suitable refuge may no longer be possible for many species.

While evidence for the combined effects of habitat fragmentation and climate change is currently scarce, and the full effects are yet to be realised, the predictions are dire. For example, modelling the twin impact of climate change and habitat fragmentation on drought sensitive butterflies in Britain led to predictions of widespread population extinctions by 2050.

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