James Hansen & Climate Danger in the ‘Hyper-Anthropocene’ Age

SealevelchangeHere the two concluding sections of J. Hansen et alii‘s paper: Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 ◦C global warming is highly dangerous. You can find the whole paper, footnotes, bibliography & figures here.

7 The Anthropocene

The Anthropocene (Crutzen and Stoermer, 2000), the era in which humans have contributed to global climate change, is usually assumed to have begun in the past few 25 centuries. Ruddiman (2003) suggested that it began earlier, with deforestation affecting CO2 about 8000 years ago. Southern Ocean feedbacks considered in our present paper are relevant to that discussion.

Ruddiman (2003) assumed that 40 ppm of human-made CO2 was needed to explain a 20 ppm CO2 increase in the Holocene (Fig. 24c), because CO2 decreased ∼ 20 ppm, on average, during several prior interglacials. Such a large human source should have left an imprint on δ 13CO2 that is not observed in ice core CO2 (Elsig et al., 2009). Ruddiman (2013) suggests that 13 5 C was taken up in peat formation, but the required peat formation would be large and no persuasive evidence has been presented to support such a dominant role for peat in the glacial carbon cycle.

We suggest that Ruddiman overestimated the anthropogenic CO2 needed to prevent decline of Antarctic temperature. The CO2 decline in interglacial periods is a climate 10 feedback: declining Southern Ocean temperature slows the ventilation of the deep ocean, thus sequestering CO2 . Avoidance of the cooling and CO2 decline requires only human-made CO2 forcing large enough to counteract the weak natural forcing trend, not the larger feedback-driven CO2 changes in prior interglacials, because, if the natural forcings are counteracted, the feedback does not occur. The required human- 15 made contribution to atmospheric CO2 would seem to be at most ∼ 20 ppm, but less if human-made CO2 increased deep ocean ventilation. The smaller requirement on the human source and the low δ 13C content of deep-ocean CO2 make the Ruddiman hypothesis more plausible, but recent carbon cycle models (Kleinen et al., 2015) have been able to capture CO2 changes in the Holocene and earlier interglacials without an 20 anthropogenic source.

Even if the Anthropocene began millennia ago, a fundamentally different phase, a Hyper-Anthropocene, was initiated by explosive 20th century growth of fossil fuel use. Human-made climate forcings now overwhelm natural forcings. CO2 , at 400 ppm in 2015, is off the scale in Fig. 24c. CO2 climate forcing is a reasonable approximation 25 of the net human forcing, because forcing by other GHGs tends to offset negative human forcings, mainly aerosols (IPCC, 2013). Most of the forcing growth occurred in the past several decades, and two-thirds of the 0.9 ◦C global warming (since 1850) has occurred since 1975 (update of Hansen et al., 2010, available at http://www.columbia. edu/~mhs119/Temperature/).

Our analysis paints a different picture than IPCC (2013) for how this HyperAnthropocene phase is likely to proceed if GHG emissions grow at a rate that continues to pump energy at a high rate into the ocean. We conclude that multi-meter sea level rise would become practically unavoidable. Social disruption and economic con- 5 sequences of such large sea level rise could be devastating. It is not difficult to imagine that conflicts arising from forced migrations and economic collapse might make the planet ungovernable, threatening the fabric of civilization.

This image of our planet with accelerating meltwater includes growing climate chaos and storminess, as meltwater causes cooling around Antarctica and in the North At- 10 lantic while the tropics and subtropics continue to warm. Rising seas and more powerful storms together are especially threatening, providing strong incentive to phase down CO2 emissions rapidly.

8 Summary implications

Humanity faces near certainty of eventual sea level rise of at least Eemian proportions, 15 5–9 m, if fossil fuel emissions continue on a business-as-usual course, e.g., IPCC scenario A1B that has CO2 ∼ 700 ppm in 2100 (Fig. S21). It is unlikely that coastal cities or low-lying areas such as Bangladesh, European lowlands, and large portions of the United States eastern coast and northeast China plains (Fig. S22) could be protected against such large sea level rise.

Rapid large sea level rise may begin sooner than generally assumed. Amplifying feedbacks, including slowdown of SMOC and cooling of the near-Antarctic ocean surface with increasing sea ice, may spur nonlinear growth of Antarctic ice sheet mass loss. Deep submarine valleys in West Antarctica and the Wilkes Basin of East Antarctica, each with access to ice amounting to several meters of sea level, provide gateways 25 to the ocean. If the Southern Ocean forcing (subsurface warming) of the Antarctic ice sheets continues to grow, it likely will become impossible to avoid sea level rise of several meters, with the largest uncertainty being how rapidly it will occur.

The Greenland ice sheet does not have as much ice subject to rapid nonlinear disintegration, so the speed at which it adds to 21st century sea level rise may be limited. However, even a slower Greenland ice sheet response is expected to be faster than carbon cycle or ocean thermal recovery times. Therefore, if climate forcing continues 5 to grow rapidly, amplifying feedbacks will assure large eventual mass loss. Also with present growth of freshwater injection from Greenland, in combination with increasing North Atlantic precipitation, we already may be on the verge of substantial North Atlantic climate disruption.

Storms conjoin with sea level rise to cause the most devastating coastal damage. 10 End-Eemian and projected 21st century conditions are similar in having warm tropics and increased freshwater injection. Our simulations imply increasing storm strengths for such situations, as a stronger temperature gradient caused by ice melt increases baroclinicity and provides energy for more severe weather events. A strengthened Bermuda High in the warm season increases prevailing northeasterlies that can help 15 account for stronger end-Eemian storms. Weakened cold season sea level pressure south of Greenland favors occurrence of atmospheric blocking that can increase wintertime Arctic cold air intrusions into northern midlatitudes.

Effects of freshwater injection and resulting ocean stratification are occurring sooner in the real world than in our model. We suggest that this is an effect of excessive small 20 scale mixing in our model that limits stratification, a problem that may exist in other models (Hansen et al., 2011). We encourage similar simulations with other models, with special attention to the model’s ability to maintain realistic stratification and perturbations. This issue may be addressed in our model with increased vertical resolution, more accurate finite differencing method in ocean dynamics that reduces noise, and 25 use of a smaller background diffusivity.

There are many other practical impacts of continued high fossil fuel emissions via climate change and ocean acidification, including irreplaceable loss of many species, as reviewed elsewhere (IPCC, 2013, 2014; Hansen et al., 2013a). However, sea level rise sets the lowest limit on allowable human-made climate forcing and CO2 , because of the extreme sensitivity of sea level to ocean warming and the devastating economic and humanitarian impacts of a multi-meter sea level rise. Ice sheet response time is shorter than the time for natural geologic processes to remove CO2 from the climate system, so there is no morally defensible excuse to delay phase-out of fossil fuel emissions as 5 rapidly as possible.

We conclude that the 2 ◦C global warming “guardrail”, affirmed in the Copenhagen Accord (2009), does not provide safety, as such warming would likely yield sea level rise of several meters along with numerous other severely disruptive consequences for human society and ecosystems. The Eemian, less than 2 ◦C warmer than pre-industrial 10 Earth, itself provides a clear indication of the danger, even though the orbital drive for Eemian warming differed from today’s human-made climate forcing. Ongoing changes in the Southern Ocean, while global warming is less than 1 ◦C, provide a strong warning, as observed changes tend to confirm the mechanisms amplifying change. Predicted effects, such as cooling of the surface ocean around Antarctica, are occurring 15 even faster than modeled.

Our finding of global cooling from ice melt calls into question whether global temperature is the most fundamental metric for global climate in the 21st century. The first order requirement to stabilize climate is to remove Earth’s energy imbalance, which is now about +0.6 W m−2 , more energy coming in than going out. If other forcings are unchanged, removing this imbalance requires reducing atmospheric CO2 20 from ∼ 400 to ∼ 350 ppm (Hansen et al., 2008, 2013a).

The message that the climate science delivers to policymakers, instead of defining a safe “guardrail”, is that fossil fuel CO2 emissions must be reduced as rapidly as practical. Hansen et al. (2013a) conclude that this implies a need for a rising carbon 25 fee or tax, an approach that has the potential to be near-global, as opposed to national caps or goals for emission reductions. Although a carbon fee is the sine qua non for phasing out emissions, the urgency of slowing emissions also implies other needs including widespread technical cooperation in clean energy technologies (Hansen et al., 2013a).

The task of achieving a reduction of atmospheric CO2 is formidable, but not impossible. Rapid transition to abundant affordable carbon-free electricity is the core requirement, as that would also permit production of net-zero-carbon liquid fuels from electricity. The rate at which CO2 emissions must be reduced is about 6 % yr−1 to reach 5 350 ppm atmospheric CO2 by about 2100, under the assumption that improved agricultural and forestry practices could sequester 100 GtC (Hansen et al., 2013a). The amount of CO2 fossil fuel emissions taken up by the ocean, soil and biosphere has continued to increase (Fig. S23), thus providing hope that it may be possible to sequester more than 100 GtC. Improved understanding of the carbon cycle and non-CO2 10 forcings are needed, but it is clear that the essential requirement is to begin to phase down fossil fuel CO2 emissions rapidly. It is also clear that continued high emissions are likely to lock-in continued global energy imbalance, ocean warming, ice sheet disintegration, and large sea level rise, which young people and future generations would not be able to avoid. Given the inertia of the climate and energy systems, and the grave 15 threat posed by continued high emissions, the matter is urgent and calls for emergency cooperation among nations.

(Visited 388 times, 1 visits today)

You may also like...

2 Responses

  1. Poo says:

    Part I
    Quick. Run and tell the King. The Prince of panic and doom has just released yet another paper, not peer reviewed mind you, as real scientists do, but straight to the media as PR types do. How scientific. Small wonder NASA no longer needs him. He has become a professional activist and like them, his grasp of the facts gives way to sloganeering and skewed ‘facts.’ As usual, his models are flawed. That is the only way they work. Mind you, he had ‘help’ from associates skilled in the art of the fudge and the blur. They can dance around most anything troublesome to their narrative. Small wonder the grandfather of global warming alarmism is getting the cold shoulder from scientists and the well informed.

    “Their climate model scenario wherein Greenland and Antarctic meltwater caused by warming poles, leads to a near total shutdown of ocean heat transport to higher latitudes, cooling most of the globe (particularly the extra-tropics), seems rather far-fetched to me.”…Michael Mann

    Kevin Trenberth, called the paper “provocative and intriguing but rife with speculation and ‘what if’ scenarios.” He objected particularly to the climate modeling scenarios used to study freshwater injection as ice sheets melt. “These experiments introduce a lot of very cold fresh water in various places, and then they see what happens.”

    It is always the ‘modeling.’ You can prove whatever you choose providing you control the inputs. “The question is how relevant these are to the real world and what is happening as global warming progresses? They do not seem at all realistic to me.” Unrealistic? Hansen? If he is consistent about anything it would be his lack of realism. “There are way too many assumptions and extrapolations for anything here to be taken seriously other than to promote further studies.”

    Or how about Richard Alley who simply says, “This new paper is not ‘the answer’.” Indeed, it is not. “Particularly, replacing the simple assumptions about doubling times of ice loss with physically based insights is a major focus of our field, but is not yet done and not likely to be ready really quickly.”

    When will rapid rates of sea level rise happen, is it decades or centuries? It makes all the difference. Hansen is the master of the ‘what if’, but science matters. It is not mere speculation. Hansen has become a climate activist. That is a long distance from a scientist.

    Ian Joughin believes it will be “a few centuries” before Hansen’s sea rise scenario could occur as there are a number of significant events that must precede it, unlikely events at that. Firstly, a couple of big ice shelves in the Antarctic ice sheet must be removed. That in itself requires a few centuries. A few centuries may be but a finger snap in time but it makes all the difference in the world to a policy maker, a planner or even an incompetent UN bureaucrat. Hansen ignores this. Even a rough ‘When’ matters. A lot can happen in a few centuries. Hansen et al are much more extreme than even the IPCC who were talking AD 2100 to AD 2300. Both are great for classroom discussions on whether they are plausible, possible, or essentially impossible. But realistic?

    Hansen et al. have proposed a catastrophic 5 m plus sea level rise in the 21st century caused primarily by the collapse of the West Antarctic ice sheet (WAIS). But, truth be told, the WAIS has collapsed before during previous inter-glacials. It will undoubtedly collapse again, with or without any climate change. The sea level will also rise again, plus or minus 5m. The question is whether the WAIS can collapse on Hansen’s vastly shorter timescale. Based on current and reliable studies, the plain answer is ‘no’. For such a process to even occur would take centuries. Why? Sea level has been rising for millennia. Recent Scripps research shows that the Greenland ice sheet did not melt as much as formerly thought during the Eemian interglacial period which began about 130,000 years ago and ended about 115,000 years ago. A new paper summarized by Cato also found that the size of the Greenland ice sheet during the mid-Holocene was smaller than it is today.

    Greenland is not the problem, if one even exists. Natural climate change and geothermal processes have caused large sea level changes in the past during interglacial periods. They will continue to cause changes in sea level in the future. They just won’t be “rapid” about it. The contribution of humans to the rise in sea level is insignificant. The rate of sea level rise a century ago is about the same as the current rate.

    Hansen’s futuristic predictions are in a word, crude. Dart board speculation is not a science. The danger posed by sea level rise is more a function of the rate of change far more than the actual sea level itself. When and if necessary, man adjusts. He always has.

    Hansen et al. articulate the worst possible case scenario. Such a case can be informative to the decision making process but hardly decisive. But it does alarm some folks and that is the point. Fudge, blur even lie but alarm and try to build political will on emissions reductions for the forthcoming Paris Wine and Dine. That is the purpose of Hansen’s latest P.R. effort. Nearly every country in the world has provisionally agreed to the 2°C target. That seems like a victory to Hansen and Co.

    24 academic and professional institutions in the United Kingdom have issued a joint communiqué calling on the international community to take immediate action. They suggest that to reaching that goal the Earth must become a zero-carbon world by the second half of the century. It is too comical for commentary. Hey I’m retired. I don’t have to work but what about those that do. Say wait a minute. I need them to work to have my pension. Ooh. I got thinking like Greece there for a minute.

    Hansen believes “there is a danger in excessive caution.” The new paper is, therefore, “significantly more persuasive than anything previously published about just how dangerous 2°C warming would be.” Persuasive? Sounds like a carnival sales pitch. His political agenda is evident. The new paper was rushed into public view with the hope of influencing negotiations in Paris this coming December. He’s out promoting his paper now. I’ve seen him on TV. Haven’t you? If not, blame his PR agents (Grover Park) who have no expertise in the scientific field. Could this be why they were chosen? Glover Park provides strategic communications campaigns for corporations, non-profit organizations and industry associations. The Group is also involved in lobbying but it is open to pretty much all paying customers. So how much did Hansen pay and where did the money came from? It is clear that NASA or Columbia could have issued a press release but no doubt recoiled, as they have in the past, from Hansen’s most alarming statements.

    The most note-worthy and scaremongering passage in the Hansen and Co. paper is this:

    “We conclude that continued high emissions will make multi-meter sea level rise practically unavoidable and likely to occur this century. Social disruption and economic consequences of such large sea level rise could be devastating. It is not difficult to imagine that conflicts arising from forced migrations and economic collapse might make the planet ungovernable, threatening the fabric of civilization.
    This image of our planet with accelerating meltwater includes growing climate chaos and storminess, as meltwater causes cooling around Antarctica and in the North Atlantic while the tropics and subtropics continue to warm. Rising seas and more powerful storms together are especially threatening, providing strong incentive to phase down CO2 emissions rapidly.”

    He got all the buzz phrases but forgot to say, “Boo!”

    Part II tomorrow.

  2. Poo says:

    Part II

    A great deal of the criticism of this paper is due to its integrative, interdisciplinary assessment style as well as the lack of peer review.

    “One of the things that troubles me most is that the rapid-fire publication of unsettled results in highly visible venues creates the impression that the scientific community has no idea what’s going on.”…Tad Pfeffer

    Questions have arisen not only about the manner of release but also the quality, or lack thereof, of its analysis. Despite the publicity push, the Associated Press, The New York Times, the BBC and The Guardian were among those who initially steered clear of the study. The only part of the paper that is news centers on the “likely” inundation of most coastal cities in this century. This is news of the ‘What If’ category. Most science journalists are well trained re the ‘sanctity’ of peer reviewed papers. Hansen’s explicit policy advocacy wrapped in the blanket of a scientific research paper has contributed to the distrust of his research.

    Hansen and Co. have offered up weak and speculative science, more speculative than convincing. The associates should be ashamed of themselves. Hansen has no shame. It is doubtful this paper will have any serious influence on the Paris deliberations which are doomed to fail in any case. Whatever is negotiated and signed will never be enacted in India, China, the U.S. or Canada just to name a few. The Narcissist in Chief will make it all sound good but he will do nothing, as usual.

    The media narrative is that Obama is a climate change champion. It has been a free ride. A new study, however, by the University of California, the University of Maryland and the International Institute for Applied Systems Analysis, published in the journal Nature Communications this month showed this to be a myth.

    It concluded the 11% drop in U.S. greenhouse gas (GHG) emissions between 2007 and 2013 was mainly caused by the 2008 financial recession not by declining coal use. The drop in U.S. emissions was temporary in any case as they are again rising. The replacement of coal by natural gas produces half the carbon dioxide emissions but only because fracking freed up huge reserves of natural gas in the U.S. It is hardly a “green” solution to lowering emissions and predates Obama by decades.

    The study also discredits another myth promoted by Obama’s media and environmental sycophants and cheerleaders; that it is a simple matter to separate economic growth from emissions. In fact, economic growth and decline have been the main causes, respectively, of increases and decreases in global emissions throughout the modern era. Decreases in GHG emissions are mainly the unintended consequence of recessions. Politicians do nothing to reduce them; not by carbon pricing, not by a carbon tax or even by a cap-and-trade system. Europe’s decade old Emissions Trading Scheme (cap-and-trade) is an expensive, corrupt, bureaucratic mess. Carbon taxes levied in Norway since 1991 have proven no better at reducing emissions effectively. What they inefficiently achieve, more by accident than design, is because they raise the cost of living. People therefore have less discretionary income, buy fewer consumer goods and services, most of which are produced using fossil fuel energy. Some plan.

    Obama predicted at the start of his presidency that it would mark the moment, “when the rise of the oceans began to slow and our planet began to heal.” Delusional? Ego-maniacal? Pick one.

    Let’s really look at Obama’s climate/environmental record. He never even tried to ratify the now-defunct Kyoto accord. He took one shot at putting a price on U.S. emissions, failed, and gave up. Under Obama, the U.S. has become the world’s largest producer of oil and natural gas thanks to pre-approvals by Bush. He has, however, approved enough new oil and gas pipelines in the U.S. to more than encircle the Earth. Hypocritically, he refuses to approve Keystone XL, which somehow plays up his non-existent green credentials to a gullible media. He has approved drilling for oil in the Arctic Ocean seemingly forgetting the Deepwater Horizon blowout in the Gulf of Mexico that led only to the worst oil spill in U.S. history. Go Mr. Green, under whom, U.S. coal exports, hardly the clean fossil fuel, hit record levels to Asia and Europe in 2012.

    The so-called “historic” deal on emissions with China turns out to be a non-binding, unenforceable wish list the two countries might do someday, way in the unknown future. Obama’s domestic commitments to reduce U.S. GHG emissions are no more believable, or doable.

    In Paris Obama will be treated as an Environmental God. It will be more proof of the media’s unwillingness to correct the false narratives they create. Paris will be yet another eat, drink and be merry funfest for the already over-bloated on the taxpayers’ dime. But Obama will sound good and isn’t that the whole point?

    As for Hansen, his wild extrapolation of present rates of sea rise is simply irresponsible, a poor piece of research, nothing more than scaremongering. The implications of 4-5 meters sea-level rise by 2100 isn’t really the “catastrophe” it’s made out to be. It has happened before and we’re still here. It by no means justifies the world-wide bureaucratic empire the alarmists are trying to impose given the tiny probability it will ever even happen.

    The warming hiatus has clearly caused panic among the so called “climate scientists.” But, in order to regain the confidence of the public, they must stop tailoring their research and models to their political preferences. Maybe if Hansen did so, others would follow. Maybe. He is the grandfather after all.

Leave a Reply

Your email address will not be published. Required fields are marked *