Assessing “Dangerous Climate Change”: Required Reduction of Carbon Emissions to Prote

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

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.
Introduction

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 human-made 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 long-wall 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].



PLOS ONE: Assessing ?Dangerous Climate Change?: Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature
 
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flacaltenn

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More rehashed James Hansen public policy pyrotechnics...
Don't see any new info here.. Just desperation...

Meanwhile --- US CO2 emissions are lower than they were 20 years ago... THANKS to fracking.
And leftist economic failures to promote growth or jobs or a real energy policy...
ZZZZZZZZZZZsstZZZZZZZZsssssZZZZZZZZZZZ
 
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Discussion
We conclude that an appropriate target is to keep global temperature within or close to the temperature range in the Holocene, the interglacial period in which civilization developed. With warming of 0.8°C in the past century, Earth is just emerging from that range, implying that we need to restore the planet’s energy balance and curb further warming. A limit of approximately 500 GtC on cumulative fossil fuel emissions, accompanied by a net storage of 100 GtC in the biosphere and soil, could keep global temperature close to the Holocene range, assuming that the net future forcing change from other factors is small. The longevity of global warming (Fig. 9) and the implausibility of removing the warming if it is once allowed to penetrate the deep ocean emphasize the urgency of slowing emissions so as to stay close to the 500 GtC target.

Fossil fuel emissions of 1000 GtC, sometimes associated with a 2°C global warming target, would be expected to cause large climate change with disastrous consequences. The eventual warming from 1000 GtC fossil fuel emissions likely would reach well over 2°C, for several reasons. With such emissions and temperature tendency, other trace greenhouse gases including methane and nitrous oxide would be expected to increase, adding to the effect of CO2. The global warming and shifting climate zones would make it less likely that a substantial increase in forest and soil carbon could be achieved. Paleoclimate data indicate that slow feedbacks would substantially amplify the 2°C global warming. It is clear that pushing global climate far outside the Holocene range is inherently dangerous and foolhardy.

The fifth IPCC assessment Summary for Policymakers [14] concludes that to achieve a 50% chance of keeping global warming below 2°C equivalent CO2 emissions should not exceed 1210 GtC, and after accounting for non-CO2 climate forcings this limit on CO2 emissions becomes 840 GtC. The existing drafts of the fifth IPCC assessment are not yet approved for comparison and citation, but the IPCC assessment is consistent with studies of Meinshausen et al. [254] and Allen et al. [13], hereafter M2009 and A2009, with which we can make comparisons. We will also compare our conclusions with those of McKibben [255]. M2009 and A2009 appear together in the same journal with the two lead authors on each paper being co-authors on the other paper. McKibben [255], published in a popular magazine, uses quantitative results of M2009 to conclude that most remaining fossil fuel reserves must be left in the ground, if global warming this century is to be kept below 2°C. McKibben [255] has been very successful in drawing public attention to the urgency of rapidly phasing down fossil fuel emissions.

M2009 use a simplified carbon cycle and climate model to make a large ensemble of simulations in which principal uncertainties in the carbon cycle, radiative forcings, and climate response are allowed to vary, thus yielding a probability distribution for global warming as a function of time throughout the 21st century. M2009 use this distribution to infer a limit on total (fossil fuel+net land use) carbon emissions in the period 2000–2049 if global warming in the 21st century is to be kept below 2°C at some specified probability. For example, they conclude that the limit on total 2000–2049 carbon emissions is 1440 GtCO2 (393 GtC) to achieve a 50% chance that 21st century global warming will not exceed 2°C.

A2009 also use a large ensemble of model runs, varying uncertain parameters, and conclude that total (fossil fuel+net land use) carbon emissions of 1000 GtC would most likely yield a peak CO2-induced warming of 2°C, with 90% confidence that the peak warming would be in the range 1.3–3.9°C. They note that their results are consistent with those of M2009, as the A2009 scenarios that yield 2°C warming have 400–500 GtC emissions during 2000–2049; M2009 find 393 GtC emissions for 2°C warming, but M2009 included a net warming effect of non-CO2 forcings, while A2009 neglected non-CO2 forcings.

McKibben [255] uses results of M2009 to infer allowable fossil fuel emissions up to 2050 if there is to be an 80% chance that maximum warming in the 21st century will not exceed 2°C above the pre-industrial level. M2009 conclude that staying under this 2°C limit with 80% probability requires that 2000–2049 emissions must be limited to 656 GtCO2 (179 GtC) for 2007–2049. McKibben [255] used this M2009 result to determine a remaining carbon budget (at a time not specified exactly) of 565 GtCO2 (154 GtC) if warming is to stay under 2°C. Let us update this analysis to the present: fossil fuel emissions in 2007–2012 were 51 GtC [5], so, assuming no net emissions from land use in these few years, the M2009 study implies that the remaining budget at the beginning of 2013 was 128 GtC.
 
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Safe Limit for Global Warming Is Lowered Dramatically by Experts

Carbon taxes and nuclear power will be necessary to cut CO2 emissions quickly enough to avert disastrous climate change, they say
Unless significant, steady reductions in the emissions of carbon dioxide from burning fossil fuels begin extremely soon, the Earth might be much closer to potentially catastrophic warming than is widely believed. So argues climatologist James Hansen of the Columbia University Earth Institute and an international team of colleagues in a new analysis published today in the journal PLOS One. Their paper further underscores other recent studies showing that even small delays in shrinking the industrial output of carbon dioxide (CO2) could steeply complicate not only attempts to temper climate change but also any attempts by future generations to adapt to it.

Without abrupt action to restrict higher emissions "it will become exceedingly difficult to keep warming below a target smaller than 2° C" they write. Furthermore, they say, the supposedly safe “limit” for warming of 2 degrees Celsius—which has driven global climate negotiations for years—is too high. Anything more than 1 degree C could imperil the Earth's ecosystems and societies. Hansen in particular is concerned about inaction imposing a crushing burden on today's children, as reflected in the paper's title: "Assessing Dangerous Climate Change: Required Reductions of Carbon Emissions to Protect Young People, Future Generations and Nature."

Hansen and his co-authors note that these findings sharpen the need to implement carbon taxes and the expanded use of nuclear power, and also show the likely futility of geoengineering. "What's crucial is that we not put stuff in the atmosphere which is going to stay in the climate system forever," Hansen says. "For all practical purposes, that's what it does."

Whether the paper can have the galvanizing effect on climate policy its authors desire remains to be seen, however. At a minimum, it will encounter skepticism that the authors' 1 degree C target for CO2 reduction is simply unrealistic, given the growing global demand for inexpensive energy now provided by fossil fuels.
Safe Limit for Global Warming Is Lowered Dramatically by Experts: Scientific American

Consequently, even small delays in reducing CO2 emissions can have a profound effect on the extent of eventual warming, sometimes called the warming "in the pipeline." Hansen and his team calculate that had the human race started cutting back on CO2 emissions in 2005, warming could in theory have been kept to 1 degree C by 2100 with annual average reductions of just 2 percent. If those reductions started today, the decrease would have to be 6 percent a year. Putting them off until 2020 pushes that figure up to 15 percent. If reductions do not start within about a decade, temperature increases to 2 degrees C and higher are all but inevitable and would persist for hundreds of years.
 
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And why is Hansen "lowering the safe limits"???? Because his projections of HIGHER LIMITS being inevitable --- just aint gonna occur.. And HE NEEDS to keep the crisis alive..

When your science fails --- you better restate the public policy options to keep your job..
 

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