２０１９年の海水温、記録史上最高　国際研究

【パリＡＦＰ＝時事】2019年の世界の海水温度が記録史上最高となった。科学者らが14日、発表した。人為的な温室効果ガス排出による海洋温暖化の進行ペースがますます速くなっており、地球の気候に破滅的な影響が及ぶおそれがあるという。（写真は資料写真）
　海洋は、温室効果ガスの排出で生成される余剰熱の９０％以上を吸収する。そのため、海水温の上昇が数年でどの程度進んだかを定量化することにより、科学者らは地球温暖化の進行速度を正確に読み取ることが可能になる。
　世界中の専門家で構成された研究チームは今回、水深２０００メートルまでの海水温の過去数十年にわたる上昇傾向を明確に把握するため、中国科学院大気物理研究所（ＩＡＰ）が蓄積したデータを詳細に調査した。
　その結果、２０１９年の海洋の海水温が観測史上群を抜いて最も高かったことが明らかになった。この海洋温暖化の影響はすでに異常気象の増加、海水面の上昇、海洋生物への被害などの形で表れていると、研究チームは指摘する。
　学術誌「Ａｄｖａｎｃｅｓ　ｉｎ　Ａｔｍｏｓｐｈｅｒｉｃ　Ｓｃｉｅｎｃｅｓ」に掲載された研究論文によると、２０１９年の海水温は過去（１９８１年～２０１０年）の平均値を０．０７５度上回ったという。
　これは、世界の海洋が最近数十年間で吸収したエネルギー量が２２８ゼタジュール（１０の２１乗ジュール）に上ることを意味する。
　「ゼロのなんと多いことか」と論文の筆頭執筆者でＩＡＰの気候環境科学国際センターに所属するチェン・リジン准教授は述べ、「過去２５年間で世界の海洋に吸収された熱量は、広島型原爆３６億個分に相当する」と説明した。
　論文の執筆者らによると、豪州南東部で数か月間猛威を振るっている森林火災などの気候関連の災害と海洋温暖化の間には明確な関連性が存在するという。
　執筆者の一人、米ペンシルベニア州立大学のマイケル・マン氏は「海水温の上昇は蒸発量の増加を意味する」と説明する。
　マン氏によると、その結果として降雨量が増加し、大気における蒸発の需要も増えるという。
　「これは次に大陸の乾燥を引き起こす。大陸の乾燥は、南米アマゾンから米カリフォルニア州や豪州、北極圏までに及ぶ地域で最近発生している森林火災の背景にある主要な要因の一つだ」【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2020/01/15-12:44）

The world's oceans were the hottest in recorded history in 2019, scientists said on Tuesday, as manmade emissions warmed seas at an ever-increasing rate with potentially disastrous impacts on Earth's climate.
Oceans absorb more than 90 percent of excess heat created by greenhouse gas emissions and quantifying how much they have warmed up in recent years gives scientists an accurate read on the rate of global warming.
A team of experts from around the world looked at data compiled by China's Institute of Atmospheric Physics (IAP) to gain a clear picture of ocean warmth to a depth of 2,000 metres over several decades.
They found that oceans last year were by far the hottest ever recorded and said that the effects of ocean warming were already being felt in the form of more extreme weather, rising sea levels and damage to marine life.
The study, published in the journal Advances in Atmospheric Sciences, said that last year the ocean was 0.075 Celsius hotter than the historical average between 1981-2010.
That means the world's oceans have absorbed 228 Zetta Joules (228 billion trillion Joules) of energy in recent decades.
That's a lot of zeros, said Cheng Lijing, lead paper author and associate professor at the International Centre for Climate and Environmental Sciences at the IAP.
The amount of heat we have put in the world's oceans in the past 25 years equals 3.6 billion Hiroshima atom bomb explosions.
The past five years are the five hottest years for the ocean, the study found.
As well as the mid-term warming trend, the data showed that the ocean had absorbed 25 Zetta Joules of additional energy in 2019 compared with 2018's figure.
That's roughly equivalent to everyone on the planet running a hundred hairdryers or a hundred microwaves continuously for the entire year, Michael Mann, director of Penn State's Earth System Sciences Center, told AFP.
- Centuries of warming -
The 2015 Paris accord aims to limit global temperature rises to well below 2C, and to 1.5C if at all possible.
With just 1C of warming since the pre-industrial period, Earth has experienced a cascade of droughts, superstorms, floods and wildfires made more likely by climate change.
The study authors said there was a clear link between climate-related disasters -- such as the bushfires that have ravaged southeastern Australia for months -- and warming oceans.
Warmer seas mean more evaporation, said Mann.
That means more rainfall but also it means more evaporative demand by the atmosphere, he said.
That in turn leads to drying of the continents, a major factor that is behind the recent wildfires from the Amazon all the way to the Arctic, and including California and Australia.
Hotter oceans also expand, leading to sea level rises.
The United Nations Intergovernmental Panel on Climate Change in a landmark oceans report last year warned that tens of millions of people could be displaced from coastal areas by the end of the century because of encroaching seas.
And given that the ocean has a far higher heat absorption capacity than the atmosphere, scientists believe they will continue to warm even if humanity manages to drag down its emissions in line with the Paris goals.
As long as we continue to warm up the planet with carbon emissions, we expect about 90 percent of the heating to continue to go into the oceans, said Mann.
If we stop warming up the planet, heat will continue to diffuse down into the deep ocean for centuries, until eventually stabilising.