A leading climate scientist gave an alarming warning that limiting global warming to two degrees Celsius may not prevent a catastrophic sea level rise that would leave major coastal cities from Miami to Mumbai at risk of drowning.

“I think that the major implication of that will be that we hand young people a climate system where it’s not possible to avoid a large sea level rise,” said Hansen, who went on to slam the two-degree target agreed upon at the 2009 Copenhagen talks as being “pulled out of a hat.”

Dr. James Hansen said at a July 20 press conference that average global temperatures today are less than a degree cooler than they were during the last major interglacial or ‘Eemian’ period 120,000 years ago, when global temperatures were just 2°C above the pre-industrial climate and sea levels stood at five to nine metres higher than they are today.

In other words, the earth today is dangerously close to the temperature levels during that period when the sea levels were up to two stories higher than they are today, making a comprehensive climate agreement at the COP-21 talks in Paris all the more urgent.

“It is unlikely that coastal cities or low-lying areas such as Bangladesh, European lowlands, and large portions of the United States eastern coast and northeast China plains could be protected against such large sea level rise,” states a report co-authored by Hansen, titled ‘Ice Melt, Sea Level Rise and Superstorms: Evidence from Paleoclimate Data, Climate Modeling, and Modern Observations that 2°C Global Warming is Highly Dangerous’.

The report warns that continued burning of fossil fuels to increase living standards while expecting humanity to adapt to climate change and mitigate its effects through better technologies “fails to appreciate the nature of the threat posed by ice sheet instability and sea level rise.

“If the ocean continues to accumulate heat and increase melting of marine-terminating ice shelves of Antarctica and Greenland, a point will be reached at which it is impossible to avoid large-scale ice sheet disintegration with sea level rise of at least several meters," the report states. "The economic and social cost of losing functionality of all coastal cities is practically incalculable.

"We suggest that a strategic approach relying on adaptation to such consequences is unacceptable to most of humanity, so it is important to understand this threat as soon as possible.”

Hansen said that the only way to avoid catastrophic flooding of global areas was to cut greenhouse gas emissions ideally by six per cent a year and make fossil fuels more expensive by imposing a “simple, honest, price on carbon emissions.”

This, combined with a rapid transition to renewable energy and more efficient forestry and agriculture practices to sequester carbon, would reduce atmospheric carbon dioxide levels down to a safer level 350 parts per million by 2100, helping to restore the Earth’s energy balance.

But the agreement of major powers such as China and America are vital to an effective climate deal that slashes greenhouse gas emissions as the COP-21 talks loom. China especially is key, owing to its continued use of coal power plants, according to Hansen.

“I think [countries] need to understand that the issue is most urgent and the required rate of reduction of emissions is much greater than that which has been achieved,” said Hansen.

According to the report, the southern ocean near Antarctica is a “tight control knob on global climate."

“If the southern ocean forcing (subsurface warming) of the Antarctic ice sheets continues to grow, it likely will become impossible to avoid sea level rise of several meters, with the largest uncertainty being how rapidly it will occur,” the report states.

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