[Vision2020] PLOS: "Assessing ‘‘Dangerous Climate Change’’: Required Reduction of Carbon Emissions..."

Ted Moffett starbliss at gmail.com
Sat Feb 14 19:10:19 PST 2015


Assessing ‘‘Dangerous Climate Change’’: Required Reduction of Carbon
Emissions to Protect Young People, Future Generations and Nature

James Hansen1*, Pushker Kharecha1,2, Makiko Sato1, Valerie Masson-Delmotte3,
Frank Ackerman4 , David J. Beerling5, Paul J. Hearty6, Ove Hoegh-Guldberg7,
Shi-Ling Hsu8, Camille Parmesan9,10, Johan Rockstrom11, Eelco J. Rohling
12,13, Jeffrey Sachs1, Pete Smith14, Konrad Steffen15, Lise Van Susteren16,
Karina von Schuckmann17, James C. Zachos18

Abstract: We assess climate impacts of global warming

using ongoing observations and paleoclimate data. We

use Earth’s measured energy imbalance, paleoclimate

data, and simple representations of the global carbon

cycle and temperature to define emission reductions

needed to stabilize climate and avoid potentially disastrous

impacts on today’s young people, future generations,

and nature. A cumulative industrial-era limit of

,500 GtC fossil fuel emissions and 100 GtC storage in the

biosphere and soil would keep climate close to the

Holocene range to which humanity and other species are

adapted. Cumulative emissions of ,1000 GtC, sometimes

associated with 2uC global warming, would spur ‘‘slow’’

feedbacks and eventual warming of 3–4uC with disastrous

consequences. Rapid emissions reduction is required to

restore Earth’s energy balance and avoid ocean heat

uptake that would practically guarantee irreversible

effects. Continuation of high fossil fuel emissions, given

current knowledge of the consequences, would be an act

of extraordinary witting intergenerational injustice. Responsible

policymaking requires a rising price on carbon

emissions that would preclude emissions from most

remaining coal and unconventional fossil fuels and phase

down emissions from conventional fossil fuels.


Humans are now the main cause of changes of Earth’s

atmospheric composition and thus the drive for future climate

change [1]. The principal climate forcing, defined as an imposed

change of planetary energy balance [1–2], is increasing carbon

dioxide (CO2) from fossil fuel emissions, much of which will

remain in the atmosphere for millennia [1,3]. The climate

response to this forcing and society’s response to climate change

are complicated by the system’s inertia, mainly due to the ocean

and the ice sheets on Greenland and Antarctica together with the

long residence time of fossil fuel carbon in the climate system. The

inertia causes climate to appear

to respond slowly to this humanmade

forcing, but further long-lasting responses can be locked in.

More than 170 nations have agreed on the need to limit fossil

fuel emissions to avoid dangerous human-made climate change, as

formalized in the 1992 Framework Convention on Climate

Change [6]. However, the stark reality is that global emissions

have accelerated (Fig. 1) and new efforts are underway to

massively expand fossil fuel extraction [7–9] by drilling to

increasing ocean depths and into the Arctic, squeezing oil from

tar sands and tar shale, hydro-fracking to expand extraction of

natural gas, developing exploitation of methane hydrates, and

mining of coal via mountaintop removal and mechanized longwall

mining. The growth rate of fossil fuel emissions increased

from 1.5%/year during 1980–2000 to 3%/year in 2000–2012,

mainly because of increased coal use [4–5].
Vision2020 Post: Ted Moffett
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