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Review
. 2013 Dec 3;8(12):e81648.
doi: 10.1371/journal.pone.0081648. eCollection 2013.

Assessing "dangerous climate change": required reduction of carbon emissions to protect young people, future generations and nature

James Hansen  1 , Pushker Kharecha, Makiko Sato, Valerie Masson-Delmotte, Frank Ackerman, David J Beerling, Paul J Hearty, Ove Hoegh-Guldberg, Shi-Ling Hsu, Camille Parmesan, Johan Rockstrom, Eelco J Rohling, Jeffrey Sachs, Pete Smith, Konrad Steffen, Lise Van Susteren, Karina von Schuckmann, James C Zachos
Affiliations
Review

Assessing "dangerous climate change": required reduction of carbon emissions to protect young people, future generations and nature

James Hansen et al. PLoS One. .

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 2°C global warming, would spur "slow" feedbacks and eventual warming of 3-4°C 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.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. CO2 annual emissions from fossil fuel use and cement manufacture, based on data of British Petroleum concatenated with data of Boden et al. .
(A) is log scale and (B) is linear.
Figure 2
Figure 2. Fossil fuel CO2 emissions and carbon content (1 ppm atmospheric CO2 ∼ 2.12 GtC).
Estimates of reserves (profitable to extract at current prices) and resources (potentially recoverable with advanced technology and/or at higher prices) are the mean of estimates of Energy Information Administration (EIA) , German Advisory Council (GAC) , and Global Energy Assessment (GEA) . GEA suggests the possibility of >15,000 GtC unconventional gas. Error estimates (vertical lines) are from GEA and probably underestimate the total uncertainty. We convert energy content to carbon content using emission factors of Table 4.2 of for coal, gas and conventional oil, and, also following , emission factor of unconventional oil is approximated as being the same as for coal. Total emissions through 2012, including gas flaring and cement manufacture, are 384 GtC; fossil fuel emissions alone are ∼370 GtC.
Figure 3
Figure 3. Global surface temperature relative to 1880–1920 mean.
B shows the 5 and 11 year means. Figures are updates of using data through August 2013.
Figure 4
Figure 4. Decay of atmospheric CO2 perturbations.
(A) Instantaneous injection or extraction of CO2 with initial conditions at equilibrium. (B) Fossil fuel emissions terminate at the end of 2015, 2030, or 2050 and land use emissions terminate after 2015 in all three cases, i.e., thereafter there is no net deforestation.
Figure 5
Figure 5. Atmospheric CO2 if fossil fuel emissions reduced.
(A) 6% or 2% annual cut begins in 2013 and 100 GtC reforestation drawdown occurs in 2031–2080, (B) effect of delaying onset of emission reduction.
Figure 6
Figure 6. Annual increase of CO2 based on data from the NOAA Earth System Research Laboratory .
Prior to 1981 the CO2 change is based on only Mauna Loa, Hawaii. Temperature changes in lower diagram are 12-month running means for the globe and Niño3.4 area .
Figure 7
Figure 7. Solar irradiance and sunspot number in the era of satellite data (see text).
Left scale is the energy passing through an area perpendicular to Sun-Earth line. Averaged over Earth’s surface the absorbed solar energy is ∼240 W/m2, so the full amplitude of measured solar variability is ∼0.25 W/m2.
Figure 8
Figure 8. Climate forcings employed in our six main scenarios.
Forcings through 2010 are as in .
Figure 9
Figure 9. Simulated global temperature relative to 1880–1920 mean for CO2 scenarios of Figure 5.
Figure 10
Figure 10. Annual Greenland and West Antarctic ice mass changes as estimated via alternative methods.
Data were read from Figure 4 of Shepherd et al. and averaged over the available records.
Figure 11
Figure 11. Fossil fuel CO2 emissions.
(A) 2012 emissions by source region, and (B) cumulative 1751–2012 emissions. Results are an update of Fig. 10 of using data from .
Figure 12
Figure 12. Per capita fossil fuel CO2 emissions.
Countries, regions and data sources are the same as in Fig. 11. Horizontal lines are the global mean and multiples of the global mean.
Figure 13
Figure 13. United States energy consumption .
Figure 14
Figure 14. World energy consumption for indicated fuels, which excludes wood .
See this image and copyright information in PMC

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Grants and funding

Funding came from: NASA Climate Research Funding, Gifts to Columbia University from H.F. (“Gerry”) Lenfest, private philanthropist (no web site, but see http://en.wikipedia.org/wiki/H._F._Lenfest), Jim Miller, Lee Wasserman (Rockefeller Family Fund) (http://www.rffund.org/), Flora Family Foundation (http://www.florafamily.org/), Jeremy Grantham, ClimateWorks and the Energy Foundation provided support for Hansen's Climate Science, Awareness and Solutions program at Columbia University to complete this research and publication. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.