The researchers simulated an Earth on which, after 1,800 billion tons of carbon entered the atmosphere, all carbon dioxide emissions suddenly stopped. Scientists commonly use the scenario of emissions screeching to a stop to gauge the heat-trapping staying power of carbon dioxide. Within a millennium of this simulated shutoff, the carbon itself faded steadily with 40 percent absorbed by Earth’s oceans and landmasses within 20 years and 80 percent soaked up at the end of the 1,000 years.

By itself, such a decrease of atmospheric carbon dioxide should lead to cooling. But the heat trapped by the carbon dioxide took a divergent track.

After a century of cooling, the planet warmed by 0.37 degrees Celsius (0.66 Fahrenheit) during the next 400 years as the ocean absorbed less and less heat. While the resulting temperature spike seems slight, a little heat goes a long way here. Earth has warmed by only 0.85 degrees Celsius (1.5 degrees Fahrenheit) since pre-industrial times.

The Intergovernmental Panel on Climate Change estimates that global temperatures a mere 2 degrees Celsius (3.6 degrees Fahrenheit) higher than pre-industrial levels would dangerously interfere with the climate system. To avoid that point would mean humans have to keep cumulative carbon dioxide emissions below 1,000 billion tons of carbon, about half of which has already been put into the atmosphere since the dawn of industry.

The lingering warming effect the researchers found, however, suggests that the 2-degree point may be reached with much less carbon, said first author Thomas Frölicher, who conducted the work as a postdoctoral researcher in Princeton’s Program in Atmospheric and Oceanic Sciences under co-author Jorge Sarmiento, the George J. Magee Professor of Geoscience and Geological Engineering.

“If our results are correct, the total carbon emissions required to stay below 2 degrees of warming would have to be three-quarters of previous estimates, only 750 billion tons instead of 1,000 billion tons of carbon,” said Frölicher, now a researcher at the Swiss Federal Institute of Technology in Zurich. “Thus, limiting the warming to 2 degrees would require keeping future cumulative carbon emissions below 250 billion tons, only half of the already emitted amount of 500 billion tons.”

The researchers’ work contradicts a scientific consensus that the global temperature would remain constant or decline if emissions were suddenly cut to zero. But previous research did not account for a gradual reduction in the oceans’ ability to absorb heat from the atmosphere, particularly the polar oceans, Frölicher said. Although carbon dioxide steadily dissipates, Frölicher and his co-authors were able to see that the oceans that remove heat from the atmosphere gradually take up less. Eventually, the residual heat offsets the cooling that occurred due to dwindling amounts of carbon dioxide.

Frölicher and his co-authors showed that the change in ocean heat uptake in the polar regions has a larger effect on global mean temperature than a change in low-latitude oceans, a mechanism known as “ocean-heat uptake efficacy.” This mechanism was first explored in a 2010 paper by Frölicher’s co-author, Michael Winton, a researcher at the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory (GFDL) on Princeton’s Forrestal Campus.

“The regional uptake of heat plays a central role. Previous models have not really represented that very well,” Frölicher said.

“Scientists have thought that the temperature stays constant or declines once emissions stop, but now we show that the possibility of a temperature increase can not be excluded,” Frölicher said. “This is illustrative of how difficult it may be to reverse climate change — we stop the emissions, but still get an increase in the global mean temperature.”

Melbourne Planning Debacle

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One of the world’s leading climate scientists has outlined a radical plan to hold temperatures to a 2C rise, the threshold that governments have agreed to limit rises to – but he accepts it may cause consternation among the very rich.

Kevin Anderson, professor of energy and climate change at the University of Manchester and deputy head of the Tyndall Centre, has argued previously that industrialised countries may need to go into recession to reduce emissions enough to ensure temperatures do not rise over 2C.

But as a 4C rise, which is looking increasingly realistic, would be “catastrophic” and must be avoided at all costs, he now says that political and personal efforts should be concentrated on changing the consumption patterns of the very few who emit the most – and that includes most of the people at the climate talks currently underway in Warsaw.

“We think it is still possible to avoid 2C rise. It’s feasible, but only just. We think that there are economic but not financial benefits,” he told a side meeting at the UN talks.

“Annex 1 [industrialised] countries need a 70% reduction in emissions consumption in 10 years to give us an outside chance of holding temperatures to a 2C rise. They need to cut emissions by 10% annually. We need to be fully de-carbonised in the 2020-30s, and that means planes, fridges, everything [must emit far less] to give a bit of an opportunity for poorer parts of the world to develop.

“If we had started in the 1992 it might have been different. But now it needs a complete shift in mindsets,” he said.

Anderson argues that governments have become obsessed by growth but should abandon this and concentrate on the things that matter to people like health and food and shelter. “We have to think differently, look at the things that matter and make them better.

“The financial world has failed completely to cut emissions. The self-regulated market hasn’t regulated. We’re awash with capital [but] finance has failed in its own backyard. It cannot deliver the cuts needed. Carbon pricing will not work because it cannot drive prices fast enough.”

The problem is consumption, not supply, he says. “Only a very small percentage of people is responsible for most of the emissions. It’s about the few not the many. Mitigation to 2C is a consumption issue. There are things you can do on the demand side, [yet] we spend all our efforts on the supply side.

“It’s not about 2030, 2040 or later. It’s about what we can do now. How many people really need to reduce emissions? The Pareto’s 80:20 rule [a principle named after the economist Vilfredo Pareto] implies that 80% of emissions come from 20% of the global population. That means that 50% of emissions come from 1% per cent of the population.” This 1%, says Anderson, includes climate scientists and nearly everyone at the UN talks and just about all the rich.

The same 80:20 rule applies to technology, too, he suggests. “An A-rated fridge uses over 80% more than a an AAA-rated machine. The best available [of everything] is usually far, far better than what we usually buy.

“On average cars emit around 150gm of CO2 per kilometre. But the best, already available, are 85-110. If you put in a standard of 85g/km by 2015 and tightened it by 10% a year you would get a 40-50% reduction [in transport emissions] in just 10 years.

“We cannot rely on technologies like nuclear or wind power to reduce emissions in years to come. We start now. We must escape the shackles of the 20th-century mindset.”