如何有道理报警海平面预测

如何有道理报警海平面预测

You may have read recent reports about huge changes in sea level, inspired by 新的研究 from James Hansen, NASA’s former Chief Climate Scientist, at Columbia University. Sea level rise represents one of the most worrying aspects of global warming, potentially displacing millions of people along coasts, low river valleys, deltas and islands.

The Intergovernmental Panel on Climate Change, the UN’s scientific climate body, 预测 rises of approximately 40 to 60 cm by 2100. But other studies have found much greater rises are likely.

Hansen and 16 co-authors found that with warming of 2C sea levels could rise by several metres. Hansen’s study was published in the open-access journal Atmospheric Chemistry and Physics Discussion, and has not as yet been peer-reviewed. It received much media coverage for its “alarmist” findings.

So how should we make sense of these dire forecasts?

What We’re Pretty Sure About

According the to the IPCC sea level rise has accelerated from 0.05 cm each year during 1700-1900 to 0.32 cm each year during 1993-2010. Over the next century the IPCC expects an average rise of 0.2 to 0.8 cm each year.

flooding2 8 10Observed and projected sea level rise. IPCC AR5 Sea level rise has accelerated. IPCC AR5Sea level rise has accelerated. IPCC AR5The collapse of the West Antarctic ice sheet would add several tens of centimetres to the total.

The IPCC report adds that “it is very likely that there will be a significant increase in the occurrence of future sea level extremes” and “it is virtually certain that global mean sea level rise will continue for many centuries beyond 2100, with the amount of rise dependent on future emissions”.

Looking To The Past

The IPCC estimates stand in sharp contrast to projections made by some climate scientists, in particular James Hansen who pointed out 在2007in his and his colleagues' latest study of the effects of ocean warming on the ice sheets.

The IPCC reports did not take into account rates of dynamic ice sheet breakdown, despite satellite gravity measurements reported in the peer-reviewed literature by other scientists.

In Greenland, ice loss reached around 280 gigatonnes of ice each year during 2003-2013, whereas in Antarctica the loss reached around 180 gigatonnes of ice each year during the same period. Both ice sheets appear to be undrgoing accelerated rates of ice melt, as shown in the diagrams.

flooding4 8 10Melting of the Greenland ice sheet recorded by satellites. GRACE

flooding5 8 10Melting of the West Antarctic ice sheet recorded by satellites. GRACE Hansen and his 16 colleagues reach their conclusion by looking at both the present and the past. During the Eemian interglacial, a period between ice ages around 130,000–115,000 years ago, average global temperatures were around 1C warmer than temperatures before the industrial revolution – that is, similar to today’s temperatures. In Greenland temperatures were about 8C warmer (the rise in polar temperatures is generally higher than the rise in tropical and subtropical temperatures, due to the ice-water albedo contrast effect). This led to sea level rise of around 6-7米, to a large extent due to melting of the Antarctic ice sheet.

The study points out that during the Eemian contact between the warming ocean and ice sheets led to abrupt disintegration of the ice, raising sea levels by several metres over period of 50-200 years, an extreme rate exceeding current IPCC estimates. The concern is that similar high rates of warming and of sea level rise may pertain in future.

For these reasons Hansen’s group considers sea level could reach several meters toward the end of the century.

These authors state: “We conclude that 2C global warming above the pre-industrial level, which would spur more ice shelf melt, is highly dangerous. Earth’s energy imbalance, which must be eliminated to stabilize climate, provides a crucial metric.”

flooding6 8 10Earth with a sea level rise of six meters. NASA

Criticisms Of The Study

Extensive criticism of this conclusion followed. Kevin Trenberth, of the US National Centre for Atmospheric Research, stated “there are way too many assumptions and extrapolations for anything here to be taken seriously other than to promote further studies.”

Greg Holland, also from the US National Centre for Atmospheric Research, stated: “There is no doubt that the sea level rise, within the IPCC, is a very conservative number, so the truth lies somewhere between IPCC and [James Hansen].”

迈克尔·曼 Hansen’s estimates are prone to a very large “extrapolation error”.

Media comments range from 积极 to . However, few comments respond in detail to the comprehensive analysis by the authors of Hansen’s 2015 paper.

Could It Be Worse?

先进的冰融化的后果包括: 增加的冰山放电 从崩解冰盖,因为在间冰期的于冰阶阶段发生在过去。 Stadials有以下的最高温度,而造成冷融水排放到海洋中急剧降温阶段。 这类放电构成的负反馈,即冷却。

过去于冰阶阶段,在峰值温度之后,包括新仙女木(12,900 - 11,700年同期)和熔融劳伦冰盖 8,500年同期.

一个于冰阶冻结,预计因的崩溃 北大西洋温盐电流 将遵循大规模融化和格陵兰冰盖的大部分排放之后。 随着大气CO2进一步上升,这将构成对全球变暖的一个短暂阶段。

变暖 2-4C 意味着海平面上升若干很多米。 未来海平面上升,一旦达到约2C的温升比工业化前温度平衡,可以在上新世的(预2.6万年前)左右25 12 +/-米,规模达到的水平。 4C比工业革命前高的温度上升将是高峰中新世(约16万年前)平衡海平面一致的约40米。

我们不知道需要多长时间的海上升与气温上升高。 但是大气温室气体浓度的急剧上升率, 每年高于2 ppm的CO2如果继续下去,威胁着海平面上升的加速率。

如果是这样,它遵循人类文明现在已经开始主持到地球的地图的重大变化。

关于作者谈话

giikson安德鲁安德鲁Glikson是澳大利亚国立大学地球和古气候学家。 他是一个客座研究员考古学和人类学,澳大利亚国立大学的学校,在那里他正在审查气候对史前人类进化的影响。

本文最初发表于 谈话。 阅读 原创文章.

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