Rewilding by Paul Jepson

Rewilding by Paul Jepson

Author:Paul Jepson
Language: eng
Format: epub
Publisher: Icon Books Ltd
Published: 2020-06-08T16:00:00+00:00


The first human-induced global warming

This is the sub-title of another provocative paper by Chris Doughty. He and his co-authors showed that the historic extinction of mammoths in Alaska and the Yukon removed grazing from the system, leading to an increase in birch trees and the shift from boreal (sub-Arctic) grasslands to forests. This would have changed surface albedo, causing warming in Siberia and Beringia by 0.2–1°C.

The albedo effect is an important variable in models of global warming. It refers to the proportion of sunlight and radiation that is reflected by the Earth’s surface. Put simply, snow reflects winter sunlight which makes the planet cooler; darker forests absorb more of the winter sunlight, making it relatively warmer. Arctic researchers are paying increased attention to the effects of defaunation and trophic downgrading on Arctic ecosystems in part because the new dating techniques described in Chapter 2 enable them to do so, but also because climate models predict that global warming will be faster and more pronounced in the Arctic. Models predict that some regions of the Arctic could increase by 4°C compared to the global 2°C average. Understanding how today’s Arctic ecosystems have formed and may react and contribute to global warming is an urgent research priority. Unfortunately, the news does not look good. Thawing permafrost will release huge amounts of carbon and methane at a time when countries are trying to cut emissions and decarbonise economies. Arctic rewilding could offer a natural climate solution to reduce permafrost thawing and Arctic greenhouse emissions.

In Chapter 4, we briefly introduced Sergey Zimov’s research on the implications of the historic collapse of the mammoth steppe for contemporary climate policy, and the Pleistocene Park experiment he and his son Nikita have underway to test whether a grassland system could be recreated. Scientific support of Zimov’s proposition that large areas of the Arctic were open steppe systems is growing. In 2014, an international group of 52 scientists published a very well-evidenced article showing that in the late Holocene, herbaceous flowering plants and grasses dominated the vegetation of the Arctic, which became wetter with bog and tree vegetation when the megafauna disappeared. Their study deployed eDNA‡ techniques to analyse permafrost soil samples. Animals and plants leave fragments of their DNA in soil which can be reassembled and compared to reference collections using modern computational techniques. The technique works particularly well in permafrost because freezing reduces movement of eDNA between strata. The authors suggested that the dominance of herbaceous plants, which are richer in nutrients than grasses, could explain why these cold systems could support such large numbers of herbivores. However, this aspect needs further research because just as the pollen record is biased towards woody species, eDNA is better at picking up herbaceous plants than grasses.

With regard to the Earth’s climate system and the albedo effect, what matters is the build-up of waterlogged peaty soils after the extinction of megafauna. In the absence of herbivores, the cycle of summer vegetation dying and becoming waterlogged with winter snow leads to an accumulation of organic-rich soils which freeze to create permafrost.



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