Seventeen high-profile academics with expertise across the climate research spectrum, from atmospheric science, earth science and environmental science, to economics, global change and public health led by James Hansen, now at Columbia University’s Earth Institute, have published a paper Assessing “Dangerous Climate Change”: Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature which demands attention.
The bottom line is that “aiming for the 2°C pathway would be foolhardy” because it “would have consequences that can be described as disastrous”. The authors believe that humanity and nature, the modern world as we know it, is adapted to the Holocene climate that has existed more than 10,000 years. Departing from this climate by more than 1°C would have intrinsically harmful effects. At 2°C these effects become unacceptably severe. Moreover we enter a zone where further feedbacks, such as ice sheet response, methane release and vegetation change, are likely to push the climate towards further warming, of probably at least 3°C.
James Hansen and Pushker Kharecha have done a summary with discussion here, then there’s Joe Romm at Climate Progress, Tim Radford at Climate Code Red, Damian Pattinson, Editorial Director, PLOS ONE, at Huff Post and John Rennie with links to further material at PLOS Blogs. My partial summary is below.
I won’t recount the arguments as to why we need to stick to 1°C here. Historically the notion of a 2°C guardrail was devised by the Germans back in the 1990s. David Spratt and Philip Sutton did an online piece entitled The big melt in 2007 in response to the dramatic melting of Arctic ice that year wherein they proposed a return to CO2 levels of 320 ppm in order to limit the temperature rise as close as possible to 1°C.
This material was incorporated into the book Climate Code Red which highlighted the notion of a safe climate.
At the same time Bill McKibben had asked James Hansen what the desirable limit of atmospheric CO2 should be. At the time 550ppm was common, with brave souls suggesting 450ppm. In December 2007 at the meeting of the American Geophysical Union Hansen gave his answer – 350 ppm in the first instance, for a safe climate. Little attention was paid to Hansen apart from McKibben who ran with 350 and has been running ever since.
Meanwhile the goal of 2°C was accepted internationally at the UNFCCC meeting at Copenhagen in December 2009. Bolivia made a brave attempt at 1.5°C the following year at Cancun but received no support.
Hansen has never deviated and now argues his case in more detail. The important question is, can 350 ppm and roughly 1°C be achieved. Hansen and Kharecha:
human-made warming could be held to about 1°C (1.8°F) if cumulative industrial-era fossil fuel emissions are limited to 500 GtC (gigatons of carbon, where a gigaton is one billion metric tons) and if policies are pursued to restore 100 GtC into the biosphere, including the soil. This scenario leads to reduction of atmospheric CO2 to 350 ppm by 2100, as needed to restore Earth’s energy balance and approximately stabilize climate.
The current emissions rate for fossil fuels is about 10GtC per year. The authors calculate that cumulative emissions from 2013 to 2050 should not exceed 130GtC. This will require a 6% reduction each year, starting now.
If emissions continue to grow until 2020, as seems likely, emissions will need to reduce by 20% pa thereafter.
In addition, we will need to remove 100GtC from the atmosphere and hold other greenhouse gases to net zero.
Removing 100GtC from the atmosphere will only result in a net reduction of about 50Gt. In simple terms atmospheric carbon is in dynamic balance with carbon sinks. Take CO2 out of the air and it will be partially replaced by CO2 outgassing from the ocean, for example.
Direct removal does not come cheap. The American Physical Union estimates a cost for air capture of 1GtC as about $2 trillion, so the total bill could be $200 trillion. I could be wrong but I make that $545 per tonne of CO2. The paper says that the cost of carbon is uncertain to a factor of 10 or more, but could be as high as $1000/tCO2.
I gather the authors think 100GtC could be removed for less than that via reforestation and improved agricultural and forestry practices. The practicalities of direct capture are significant. One GtC turned into carbonate bricks would yield a pile equivalent to 3000 Empire State buildings or 1200 Great Pyramids of Giza.
Nevertheless it raises the question as to what atmospheric dumping fees should be imposed on carbon emitters.
Given the uncertainty over real costs and political realities, the paper recommends an initial carbon tax of $15/tCO2 with a rise of $10 each year to change behaviour. Border taxes for embedded carbon imports are suggested.
Of course, most fossil fuel reserves will need to be left in the ground. The paper charts the fork in the road in the energy system which began with the industrial era when coal increasingly took over from wood. The size of the task confronting us now is illustrated in this graph:
The paper sees a role for nuclear, which is elaborated in more detail in Hansen and Kharecha. They emphasise new generation technology.
The paper also has some interesting graphs as to who is doing the emitting currently and who has been most responsible in the past. First the current emitters:
This is what that looks like on a per capita basis:
Here we have the cumulative emissions by country since the beginning of the industrial age:
And cumulative emissions on a per capita basis:
In this case China virtually disappears, yielding prominence to the likes of the UK, Germany and Canada.
This information will no doubt be taken into account during negotiations in what has been referred to as “common but differentiated responsibility”.
The big message out of this is that notions of a 2°C guardrail are dangerously wrong-headed. We need to be thinking 1°C if we want to pass on to future generations a safe climate.
Secondly, the time for concerted action to commence is now. Leaving it for a few years makes it harder, much harder.
Third, everyone in the world has to act. The matter is so finely balanced that there can be no free riders.