「適切な」生態系３割回復で、種の絶滅７割回避　研究

【パリＡＦＰ＝時事】農地など人間の用途のために開発されて久しい土地の生態系を30％回復できれば、絶滅が予測されている動植物種の70％が救われ、産業革命以降の人間活動で排出された二酸化炭素（CO2）量の半分が吸収できる──地球を癒やすための野心的な青写真を描いた論文を、国際専門家チームが14日に発表した。ただし、適切な回復対象を選ばなければ、最大限の効果は望めないとしている。（写真は資料写真）
　筆頭著者でブラジルのリオ・カトリック大学で教える国際持続可能性研究所のベルナルド・シュトラスシュブルグ所長は、「優先度の高い地域で生態系を回復することで、気候と生物多様性の二重の危機の克服に大きく貢献できる」とＡＦＰに語った。
　研究では、かつて湿地だった土地を元の自然状態に戻すことが、種の保全と地球温暖化の抑制の両面で最も費用対効果が高いと分かった。
　２番目の優先分野は熱帯雨林だが、温帯林やサバンナ、低木地などあらゆる種類の生態系に、それぞれ果たすべき役割があるという。生態系の回復を目指すべき面積は合わせて約９００万平方キロで、ブラジルの国土とほぼ同じ広さとなる。
　研究チームはコスト面にも着目。手当たり次第に保全活動を行うよりも、重要な地域に集中的に投資するほうが、費用効率性は少なくとも１０倍向上すると結論付けた。
　シュトラスシュブルグ氏は、国連が２０２０年代を「生態系回復の１０年」と位置付けている点を指摘。自然環境を再生するほうが、工学的・技術的な解決策を開発するよりはるかに安価な「手に届く果実」だと考えている企業も多いとして、「新型コロナウイルス流行による経済危機からの回復に際し、各国が環境にやさしい方法を選択するかどうかに多くが懸かっている」と述べた。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2020/10/19-13:26）

Restoring 30 percent of ecosystems long-since converted to agriculture and other human needs could avoid 70 percent of predicted species extinctions and absorb half the CO2 humanity has released into the atmosphere since the industrial revolution, according to an ambitious blueprint for healing the planet released Wednesday.
But it would have to be the right 30 percent to yield maximum benefits, an international team of experts said in a study positioning itself as the scientific cornerstone for a crucial biodiversity summit in China next year.
Implementing restoration in priority areas would be a major contribution to overcoming the twin climate and biodiversity crises, lead author Bernardo Strassburg, director of the International Institute for Sustainability and an assistant professor at PUC-Rio University, told AFP.
Returning wetlands to their natural state would bring the highest return on investment, both in preventing species loss and slowing the pace of global warming, the study found.
Tropical forests are second-tier priority area, though all types of ecosystems -- including temperate forests, savannahs and scrublands -- have a role to play.
In all, the regions earmarked for restoration under the plan cover nearly nine million square kilometres, roughly the size of Brazil.
The study also looks at cost, concluding that concentrating investment on key areas would be at least 10 times more cost-effective than randomly distributed efforts.
The United Nations has tagged the 2020s as the Decade of Ecosystem Restoration, and many companies see the renewal of natural environments as a low-hanging fruit far cheaper than engineered or technological solutions, said Strassburg.
A lot depends on whether countries will choose a green recovery path from the Covid economic crisis, he said.
Economic recovery packages around the world total many trillion dollars so far, but some are more reliant on carbon-intensive inputs and infrastructure building than others.
- Failed efforts -
So far, efforts to protect and restore Nature on a global scale have failed spectacularly.
The planet is on the cusp of a mass extinction event -- only the sixth in the last half-billion years -- in which species are disappearing at 100 to 1,000 times the normal background rate, most scientists agree.
The UN's science advisory panel for biodiversity warned in a landmark report last year that one million species face extinction, due mostly to habitat loss and over-exploitation.
As climate change kicks in over the coming decades, the pace at which life forms disappear will likely intensify.
This gets harder if climate change goes towards the worst-case scenarios, but our optimistic assumption is that we will stay on less pessimistic pathways in keeping with the 2015 Paris Agreement, which calls for capping global warming at well below two degrees Celsius, Strassburg said.
A score of 2020 targets under 195-nation Convention on Biological Diversity designed to protect and restore Nature -- including a slowdown in habitat loss -- have all been badly missed, according to a UN assessment released last month.
Indeed environmental degradation continues apace across a wide range of measures.
In 2019, a football pitch of primary, old-growth trees was destroyed every six seconds -- about 38,000 square kilometres (14,500 square miles) in all, according to satellite data.
- Still enough food? -
Reverting agricultural land to a wild state in a world still plagued by hunger and anticipating another two billion mouths to feed also raises the spectre of food shortages.
It will not be easy and will require concerted efforts, Strassburg concedes. But it is feasible.
A modest uptick in the pace of increasing agricultural productivity, a 50 percent reduction in food waste, and a shift in human diets away from meat and dairy would render the plan feasible, the study found.
The highest-priority targets for restoration are concentrated in the tropics and sub-tropics, especially in Indonesia, Malaysia, India, The Philippines, Vietnam, the coastal regions of Kenya and Tanzania, Madagascar, east Africa from Gambia to Nigeria, Brazil and central America.
But asking these countries alone to shoulder the burden of rewilding cropland is unfair and politically unfeasible, so the scientists modelled a scenario in which all nations restore 15 percent of the priority areas within their borders.
Compared to the optimal plan, benefits for species and climate change were reduced by about 30 percent, while costs increase by half.
The researchers combined mathematically-based modelling and cutting-edge mapping technologies to assess nearly 30 million square kilometres of ecosystems worldwide that had been transformed into agricultural or pasture land.
More than half were originally forests, while a quarter were grasslands and 14% were shrubland. Only two precent were wetlands.