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Is the climate already dangerous?

Is the climate already dangerous?

David Spratt | September 2013

… the (climate) disruption and its impacts are now growing much more rapidly thanalmost anybody expected even a few years ago. The result of that, in my view, is that theworld is already experiencing ‘dangerous anthropogenic interference in the climatesystem’… The question now is whether we can avoid catastrophic human interference inthe climate system.–

John Holdren (2008), senior advisor to President Barack Obamaon science and technology issues

The stated purpose of international climate negotiations is to avoid “dangerous” climatechange or, more formally, to prevent “dangerous anthropogenic interference with theclimate system”. Most of the climate action movement and most NGOs identify with thisgoal
But if climate change is already “dangerous”, what then is our purpose?

To return the planet to a safe climate (Holocene conditions)?

To accept that climate change is already irretrievably dangerous state of affairs? Inwhich case the purpose instead becomes …

To prevent a plunge into an even worse “catastrophic” breakdown of human society andplanetary and climate system elements?And if conditions existing
for some elements of the climate system and the existinggreenhouse gas levels and radiative forcing are
already sufficient
to push more climatesystem elements past their tipping points and create “catastrophic” breakdown without anyfurther emissions, what then is our purpose?This paper sets out the evidence that dangerous climate change has already occurred andcanvasses possible responses.

1a. Safe boundary
A landmark research paper by Rockstrom, Steffen et al. (2009) established that “humanactivities have reached a level that could damage the systems that keep Earth in the desirableHolocene state… The result could be irreversible and, in some cases, abrupt environmentalchange, leading to a state less conducive to human development…” They observed that“a new era has arisen, the Anthropocene, in which human actions have become the maindriver of global environmental change”.To meet the challenge of maintaining the Holocene state, the authors proposed a framework based on “planetary boundaries” which “define the safe operating space for humanity withrespect to the Earth system and are associated with the planet’s biophysical subsystems orprocesses”. The boundaries are “values for control variables that are either at a ‘safe’distance from thresholds — for processes with evidence of threshold behaviour — or atdangerous levels — for processes without evidence of thresholds”.The authors proposed nine boundaries, including a climate boundary that “humanchanges to atmospheric carbon dioxide (CO
) concentrations should not exceed 350 parts per

million (ppm) by volume, and that radiative forcing should not exceed 1 watt per squaremetre (W/m
) above preindustrial levels”.But CO
concentrations now exceed 400 ppm by volume, and IPCC (2007) estimatedgreenhouse gas forcings of 3 (2.5–3.5) W/m
above pre-industrial levels (Ramanathan and Feng,2008). By this metric, climate change is now clearly dangerous, exceeding the safe boundary by wide margins: more than 50 ppm CO
(equivalent to +0.5ºC of warming) and by morethan 1-2 W/m
Figure 1: The updated “reasons for concern”
1b. “Burning embers”: five concerns
The “burning embers” diagram of IPCC AR3 (2001) was revised and updated by Smith,Schneider et al. (2009), and will be updated again in the new 2014 IPCC report to includethe colour purple to indicate worsening climate risks. It provides five “reasons for concern”:

Risk to unique and threatened systems;


Risk of extreme weather events;


Distribution of impacts;


Aggregate (total economic and ecological) impacts; and


Risk of large-scale discontinuities (abrupt transitions, “tipping points”).

A tipping point is a step change, or passing of a critical threshold, in a major earth-climatesystem component, where a small push or change unleashes a bigger change in thecomponent through positive feedbacks, which amplify the change. The classic case inglobal warming is the ice–albedo feedback, where decreases in the ice cover area changesurface reflectivity, trapping more heat and producing a temperature rise and further ice loss.A discussion of tipping points and the limitations of current tipping point science may befound in the Appendix.

This overview focuses on Arctic tipping points (concern ‘e’ above). It is beyond this paper’sscope to provide comprehensive and robust evidence for all five concerns, but one can note inpassing that recent climate-change impacted extreme weather events, such as SuperstormSandy, would reasonably fall within the definitions of concerns ‘b’ and ‘d’. Thedisproportionate and sizeable impacts of climate change on poor and developing nations,which have already been documented by UN agencies and aid organisations, constitutereasonable evidence for concern ‘c’. The imminent loss of most of the world’s coral reef systems clearly qualifies under ‘a’, and so on.
2a. Arctic sea ice
On 16 September 2012, Arctic sea-ice reached its minimum extent for the 2012 northernsummer of 3.41 million square kilometres, the lowest seasonal minimum extent in thesatellite record since 1979, and just half of the average area for the 1979–2000 period.There was a loss of 11.83 million square kilometres of ice from the maximum extent on 20March 2012. This was the largest summer ice extent loss in the satellite record, more thanone million square kilometres greater than in any previous year.Two-thirds of the loss of sea-ice extent has happened in the 12 years since 2000, and the processappears to be accelerating. From 1979 to 1983 in the Arctic, the sea ice summer minimumcovered an average of just over 51 per cent of the ocean. It fell to just 24 per cent of theArctic ocean surface in 2012.
Figure 2: Arctic sea-ice volume loss (based on PIOMAS)

Not only does the sea ice cover a smaller area of ocean in summer, it is also thinning rapidly.The sea-ice volume is now down to just one-fifth of what it was in 1979. The PIOMASproject (Zhang, Rothrock et al.), which captures the process of sea-ice retreat far better thanany other general climate models, finds a September 2012 minimum of 3,263 cubic kms of ice. Contrasted with the figure of 16,855 cubic kms in 1979, more than 80 per cent of
has been lost (Figure 2).

It is now clear that the Arctic is heading quickly for summer periods free of sea ice. Alinear extrapolation of sea-ice mass loss suggests it may occur within a decade or so. Anexponential fit, which is a better fit for the current data, suggests it might occur within a fewyears (see Figure 3). At time of publication, the minimum volume figure for 2013 was notavailable, but it may be a little higher than the record low of 2012, and similar to 2011.Because climate models generally have been poor at dealing with Arctic sea-ice retreat (seeAppendix), expert elicitations play a key role in considering whether the Arctic has passed avery significant and “dangerous” tipping point. Here’s what leading figures in the researchfield say:

Dr Tim Lenton of the University of Exeter told the March 2012 Planet Under Pressureconference that sea ice since 2007 had departed from model predictions, and thatdisappearance of Arctic sea ice has crossed a “tipping point” that could soon make ice-freesummers a regular feature across most of the Arctic Ocean (Pearce, 2012). This conclusionwas drawn from a subsequently published paper (Livina and Lenton, 2013) which findsthat “an abrupt and persistent increase in the amplitude of the seasonal Arctic sea-ice coverin 2007 which we describe as a (non-bifurcation) ‘tipping point’”.
If 2007 is the crucial point on the Arctic sea-ice decline timeline, it is also important to note that global warming above pre-industrial was 0.76ºC at that time. At equilibrium, a 0.76ºC rise is equivalent to CO
levels of 335 ppm, so the “safe boundary” of 350 ppm already looks too optimistic from this perspective.

The Australian Climate Commissioner, Professor Will Steffen, told
The Age
in Septemberlast year: “I’m pretty certain that we have now passed the tipping point for Arctic sea ice”(Cubby, 2012).

Figure 3: PIOMAS Arctic sea ice annual minimum volume (black) plus “best fit” trend (red)

Dr Seymour Laxon, of the Centre for Polar Observation and Modelling at UniversityCollege London, says: “Preliminary analysis of our data indicates that the rate of loss of sea-ice volume in summer in the Arctic may be far larger than we had previouslysuspected… Very soon we may experience the iconic moment when, one day in the summer, we look at satellite images and see no sea-ice coverage in the Arctic, just openwater” (McKie, 2012).

Professor Carlos Duarte, Director of University of WA’s Oceans Institute, says an Arctic“snowballing” situation would prove as hard to slow down as a runaway train. Hesays melting of the ice is accelerating faster than any of the models could predict and theprospect of an Arctic Ocean free of ice had been brought forward to 2015, comparedwith a prediction in 2007 that at least one-third of the normal extent of sea ice wouldremain in summer in 2100. Duarte says that the Arctic region is fast approaching aseries of imminent “tipping points” which could trigger a domino effect of large-scaleclimate change across the entire planet with “major consequences for the future of humankind as climate change progresses” (UWA, 2012).

US National Snow and Ice Data Centre Director Dr Mark Serreze told Climate Progress in2010: “I stand by my previous statements that the Arctic summer sea-ice cover is in a deathspiral. It’s not going to recover.” (Romm, 2010) Without human intervention to driverecovery, the evidence is very clear that Serreze is right.

Professor Peter Wadhams, of Cambridge University and the Catlin Arctic Survey, and aleading authority on the polar regions, concludes in a research paper: “Has Arctic sea icereached a tipping point? I believe that it has...” (Wadhams, 2012).Wadhams explains:
I have been predicting [the collapse of sea ice in summer months] for many years. The main causeis simply global warming: as the climate has warmed there has been less ice growth during thewinter and more ice melt during the summer… in the end the summer melt overtook the wintergrowth such that the entire ice sheet melts or breaks up during the summer months. This collapse, Ipredicted would occur in 2015–16 at which time the summer Arctic (August to September) would become ice-free. The final collapse towards that state is now happening and will probably becompleted by those dates. As the sea ice retreats in summer the ocean warms up (to +7ºC in 2011)and this warms the seabed too. The continental shelves of the Arctic are composed of offshorepermafrost, frozen sediment left over from the last ice age. As the water warms, the permafrostmelts and releases huge quantities of trapped methane, a very powerful greenhouse gas so this willgive a big boost to global warming. (Vidal, 2012)
Wadhams’ analysis relies in part on a new, more specialised regional climate model,acronym NAME, developed by Dr Wieslaw Maslowski and colleagues. NAME is head andshoulders above other models so far in projecting and replicating sea-ice losses (seeAppendix A). “The future of Arctic sea ice” (Maslowski, Kinney et al., 2012) found that:“Given the estimated trend and the volume estimate for October–November of 2007 at lessthan 9,000 cubic kms,
one can project that at this rate it would take only 9 more years or until 2016 +/-3 years to reach a nearly ice-free Arctic Ocean in summer
” (emphasis added).The impacts of lengthening periods of sea-ice-free Arctic summers are significant and will,together with warming already “in the system”, push more climate elements past theirtipping points. Our knowledge is limited because “a system-level understanding of criticalArctic processes and feedbacks is still lacking” (Maslowski, Kinney et al., 2012) and “noserious efforts have been made so far to identify and qualify the interactions betweenvarious tipping points” (Schellnhuber, 2009).However, we do know that the Arctic is warming quicker than the global average. Duarte,Lenton et al. (2012) find that: “Warming of the Arctic region is proceeding at three times theglobal average, and a new ‘Arctic rapid change’ climate pattern has been observed in the pastdecade.” Reductions in the sea-ice cover are believed to be the largest contributor toward Arctic amplification. Maslowski, Kinney et al. (2012) note that: “a warming Arctic climateappears to affect the rate of melt of the Greenland ice sheet, Northern Hemispherepermafrost sea-level rise, and global climate change”.

The sea-ice cover in June is about two per cent of the earth’s surface. Replacing that duringsummer in the Arctic with darker, more heat-absorbing ocean waters is equivalent to about 20years of human greenhouse emissions, or about +0.5ºC of warming, according to PeterWadhams. This is consistent with a study by Stephen Hudson (2011), which found that, if the Arctic were ice-free for one month a year plus associated ice-extent decreases in othermonths, then, without taking cloud changes into account, the global impact would be about+0.2ºC of warming. If there were no ice at all during the main three months of sunlight, theincrease would be +0.5ºC.

The consequences of the Arctic big melt and the subsequent regional amplification and globaltemperature increase will include:

Accelerated melting of the Greenland ice sheet, very likely pushing it past its tippingpoint (see 2b. below and Appendix);

Pushing Arctic temperatures into a range that will trigger large-scale Arctic carbon storereleases of methane and CO2, a positive feedback which will drive further warming (see4d. below);

Further destabilisation of the Jet Stream and hence more northern hemisphere extremeweather; and

The destruction of the Arctic ecosystem, which is already well under way. This has beenchronicled by many researchers and organisations, including the Center for BiologicalDiversity and Care for the Wild International (Wolf, 2010). In the Arctic,
the rate of climate change is now faster than ecosystems can adapt to naturally
, and the fate of many Arctic marine ecosystems is clearly connected to that of the sea ice (Duarte, Lentonet al., 2012). I remember well attending an Academy of Science conference in Canberra inMay 2008 where the international guest speaker was Dr Neil Hamilton, then head of theWWF Arctic Programme. He told a somewhat stunned audience that the WWF was nottrying to preserve the Arctic ecosystem because “it was no longer possible to do so”.Whilst the campaign to stop the development of an oil and gas industry in the Arctic isnecessary (if only to prevent more global warming emissions), the claim that in so doingwe can thereby “save the Arctic” seems wide of the mark.
2b. Greenland
Complex, non-linear systems typically shift between alternative states in an abrupt, ratherthan a smooth manner (Duarte, Lenton et al., 2012), so it is often difficult to identify tippingpoints in advance. Only a few Arctic specialists, including Ted Scambos, Mark Serreze andRon Lindsay, said prior to 2007 that the sea ice was close to a phase change.If it is sometimes hard to see tipping points coming,
it is also too late to be wise after the fact
.And that is precisely the case with the Greenland Ice Sheet (GIS).Current-generation climate models are not yet all that helpful on GIS. They have a poorunderstanding of the processes involved, and acceleration, retreat and thinning of outletglaciers are not represented.Recent research (see 3a. below) puts a lower boundary of 0.8ºC on GIS’s tipping point, awarming level we have already reached. In July 2013, a new study found that stretches of ice on the coasts of Antarctica and Greenland are at risk of rapidly cracking apart and falling into the ocean: “rapid iceberg discharge is possible in regions where highly crevassedglaciers are grounded deep beneath sea level, indicating portions of Greenland andAntarctica that may be vulnerable to rapid ice loss through catastrophic disintegration”(Bassis and Jacobs, 2013).

In 2012, GIS melting shattered the seasonal record; the duration of GIS melting was thelongest yet observed; a rare, nearly ice sheet-wide melt event (covering as much as 97% of the ice sheet’s surface on a single day) occurred in July; and the reflectivity of GIS,particularly at the high elevations that were involved in the mid-July melt event, declined torecord lows. Unfortunately, data from the GRACE satellite observation of GIS is not yet of sufficient duration to robustly describe the melt trend, but observations are that the rate of melting is increasing, and many glaciers are picking up speed. Since 2001, the JakoshavnGlacier, the world’s fastest flowing glacier, has more than doubled its flow rate, and total GISmass loss in 2011 was 70% larger than the 2003–2009 average annual loss rate.Previously, studies have estimated that it would take centuries to millennia for new climatesto increase the temperature deep within ice sheets such as GIS. But a new study finds thatwhen the influence of meltwater (which drains through cracks in an ice sheet and can warmthe sheet from the inside, softening the ice and letting it flow faster) is considered, warmingcan occur within decades and produce rapid accelerations. Lead author Thomas Phillipssays this research “could imply that ice sheets can discharge ice into the ocean far morerapidly than currently estimated,” thus requiring a re-assessment of the rate of both futuresea-level rises and the rate of mass loss of GIS (Phillips, Rajaram et al., 2013; University of Colorado Boulder, 2013).Has Greenland passed its tipping point? What would be the impact of a sea-ice-free Arcticsummer and the consequent amplified regional warming on the stability of the Greenlandice sheet? Research does not yet provide a robust framework for considering suchquestions, yet most scientists if asked for their expert elicitation would probably say that it ishard to imagine the GIS doing anything other than actively de-glaciating at an acceleratingrate and passing a critical tipping point in such circumstances.NASA climate research chief Dr James Hansen answered this question in the affirmative, ina peer-reviewed paper in 2007:
Could the Greenland ice sheet survive if the Arctic were ice-free in summer and fall? It has beenargued that not only is ice sheet survival unlikely, but its disintegration would be a wet processthat can proceed rapidly. Thus an ice-free Arctic Ocean, because it may hasten melting of Greenland, may have implications for global sea level, as well as the regional environment,making Arctic climate change centrally relevant to definition of dangerous humaninterference.” (Hansen and Sato, 2007)
In the same year, Hansen said that today’s level of CO2 was enough to cause Arctic sea-icecover and massive ice sheets such as in Greenland to eventually melt away: “I think in mostof these cases,
we have already reached the tipping point
” (emphasis added) (Inman, 2007).And last year, Hansen told Bloomberg that: “Our greatest concern is that loss of Arctic seaice creates a
grave threat of passing two other tipping points
– the potential instability of theGreenland ice sheet and methane hydrates… These latter two tipping points would haveconsequences that are practically irreversible on time scales of relevance to humanity”(emphasis added) (Morales, 2012).Glaciologist Jason Box told reporters at the annual conference of the American GeophysicalUnion last December: “In 2012 Greenland crossed a threshold where for the first time wesaw complete surface melting at the highest elevations in what we used to call the dry snow zone… As Greenland crosses the threshold and starts really melting in the upper elevationsit really won’t recover from that unless the climate cools significantly for an extended periodof time which doesn’t seem very likely” (Goldenberg, 2012).
The current level of atmospheric CO

is sufficient to increase the global temperature atequilibrium by +1.5°C, based on the standard assumption of near-term climate sensitivity of 3°C for doubled CO
current greenhouse gases are taken into account, then:
The observed increase in the concentration of greenhouse gases (GHGs) since the pre-industrialera has most likely committed the world to a warming of 2.4°C (within a range of +1.4°C to+4.3°C) above the pre-industrial surface temperatures. (Ramanthan and Feng, 2008)
And the IPCC (2007) Synthesis report (Table 5.1 on emission scenarios) also shows that forlevels of greenhouse gases that have already been achieved (CO
in the range of 350–400 ppm,CO
e in the range 445–490 ppm) and peaking by 2015, the likely temperature rise is in therange of 2–2.4°C.These scenarios include short-lived gases such as methane, which degrades out of theatmosphere in a decade, and also nitrous oxide, which has an atmospheric lifetime of around a century. On the other hand, the fact that temperatures are not already much higherthan they are today is due principally to the large-scale emission of very short-lived (10days) aerosols such as soot and exhausts from burning fossil fuels, industrial pollution anddust storms, which are providing temporary cooling. The effect is known popularly as“global dimming”, because the overall aerosol impact is to reduce, or dim, the sun’sradiation, thus masking some of the heating effect of greenhouse gases. The aerosol impactis not precisely known, but Ramanthan and Feng (2008) estimate it as high as ~1°C. As theworld moves to low-emission technologies, most of the aerosols and their temporary coolingwill be lost. Recent research finds that quickly eliminating all greenhouse gas emissions (andnecessarily the associated aerosols) would produce warming of between 0.25 and 0.5

°Cover the decade immediately following (Matthews and Zickfield, 2012; Hansen, Sato et al.,2011).A practical consideration of “dangerous” can include the question as to whether there aretipping points or “concerns” activated for the elevated temperatures that we are generallyconsidered to be already committed to: conservatively in the range say +1.5 to 2°C and,more pragmatically, in the range of 2 to 2.4°C if all current greenhouse gases areconsidered. A related question is whether the +1.5°C goal advocated by the small islandstates and surveyed recently by Climate Action Network Europe and Climate Analytics(Schaeffer, Hare et al., 2013) would avoid “dangerous” climate change and significanttipping points.This is a broad topic, but four recent important research findings on impacts for the currentcommitted warming are arresting:

Greenland Ice Sheet tipping point
The tipping point for GIS has been revised down by Robinson, Calov et al. (2012) to +1.6ºC(uncertainty range of +0.8-+3.2ºC) above pre-industrial, just as regional temperatures areincreasing at three-to-four times faster than the global average, and the increased heat trapped in the Arctic due to the loss of reflective sea ice ensures an acceleration in theGreenland melt rate. If the
Greenland boundary in the uncertainty range turned outto be right, then with current warming of +0.8ºC over pre-industrial we have alreadyreached Greenland’s tipping point. And, with temperature rises in the pipeline, theupward trajectory of annual greenhouse gas emissions, the projected future increases infossil fuel use, and the continuing political impasse in international climate negotiations,we are very likely to hit the best estimate of +1.6ºC within a decade or two at most.

Coral reefs
Frieler, Meinshausen et al. (2013) show that “preserving more than 10 per cent of coral reefsworldwide would require limiting warming to below +1.5°C (atmosphere–ocean generalcirculation models (AOGCMs) range: 1.3–1.8°C) relative to pre-industrial levels”. Obviouslyat less than 10 per cent, the reefs would be remnant, and reef systems as we know themtoday would be a historical footnote. Already, the data suggests that the global area of reef systems has already been reduced by half. A sober discussion of coral reef prospects can befound in Roger Bradbury’s “A World Without Coral Reefs” (2012) and Gary Pearce’s“Zombie reefs as a harbinger for catastrophic future” (2012). The opening of Bradbury’sarticle is to the point:
It’s past time to tell the truth about the state of the world’s coral reefs, the nurseries of tropicalcoastal fish stocks. They have become zombie ecosystems, neither dead nor truly alive in anyfunctional sense, and on a trajectory to collapse within a human generation. There will beremnants here and there, but the global coral reef ecosystem — with its storehouse of biodiversity and fisheries supporting millions of the world’s poor — will cease to be.

Arctic carbon stores
As Climate Progress recently noted (Romm, 2013): “We’ve known for a while that‘permafrost’ was a misnomer” because thawing permafrost feedback will turn the Arcticfrom a net carbon sink to a net source in the 2020s and defrosting permafrost will likely addup to 1ºC to total global warming by 2100. A 2012 UNEP report on
Policy implications of warming permafrost
says the recent observations “indicate that large-scale thawing of permafrost may have already started.” In February 2013, scientists using radiometric datingtechniques on Russian cave formations to measure historic melting rates warned that a+1.5ºC global rise in temperature compared to pre-industrial was enough to start a generalpermafrost melt. Vaks, Gutareva et al. (2013) found that “global climates only slightlywarmer than today are sufficient to thaw extensive regions of permafrost.”

Vaks says that:
“1.5ºC appears to be something of a tipping point”
(emphasis added).Previously a study of East Siberian permafrost by Khvorostyanov, Ciais et al. (2008) foundthat once mobilised, the process would be self-maintaining due to “deep respiration andmethanogenesis” (formation of methane by microbes). In other words, the microbial actionthat produces methane as the carbon stores melt would produce sufficient heat to maintainthe process: “once active layer deepening in response to atmospheric warming is enough totrigger deep-soil respiration, and soil microorganisms are activated to produce enough heat,the mobilization of soil carbon can be very strong and self-sustainable”.A sharp scientific debate has started on the stability of large methane clathrate stores just below the ocean floor on the shallow East Siberian Sea, following the publication in July2013 of research by Whiteman, Hope and Wadhams which said that the release of a singlegiant “pulse” of methane from thawing Arctic permafrost beneath the East Siberian seacould come with a $60 trillion global price tag (Whiteman, Hope and Wadhams, 2013).Wadhams says “the loss of sea ice leads to seabed warming, which leads to offshore permafrost melt , which leads to methane release, which leads to enhanced warming, whichleads to even more rapid uncovering of seabed”, and this is not “a low probability event”(Ahmed, 2013)

3d. Multiple targets reduce allowable warming
Steinacher, Joos et al. (2013) explore the interaction of targets in emissions reductions,focussing on the 2ºC temperature goal. They find that when
multiple climate targets are set
(such as food production capacity, ocean acidity, atmospheric temperature), “
allowablecumulative emissions are greatly reduced from those inferred from the temperature target alone”.In fact,
“When we consider all targets jointly, CO2 emissions
have to be cut twice as much
as if we only want to meet the 2ºC target.”
Another fruitful line of inquiry on whether climate change is already “dangerous” is to look atthe paleo-climate (climate history) record for circumstances analogous to present conditionsto learn what planetary and climate conditions were like at that time. With current CO
levels at400 ppm, a useful comparison is the Pliocene (3–5 million years ago). The research body islarge and growing in this area, but here are some examples:

Rohling, Grant et al. (2009) find that during the mid-Pliocene, when greenhouse gaseswere similar to today, sea levels were more than 20 metres higher than today “we estimatesea level for the Middle Pliocene epoch (3.0–3.5 Myr ago) – a period with near-modern CO
levels – at 25±5 metres above present, which is validated by independent sea-level data”.Likewise Hansen, Sato et al. (2013) find that “during the middle-Pliocene… we find sea levelfluctuations of 20-40 metres associated with global temperature variations between today’stemperature and +3°C”.

Speed of sea-level rise
The speed of sea-level rise may far exceed the current, rather reticent estimates that are usedfor policy purposes. Blancon, Eisenhauer et al. (2009) examined the paleo-climate recordand showed a sea-level rises of 3 metres in 50 years due to the rapid melting of ice sheets123,000 years ago in the Eemian, when the energy imbalance in the climate system was
thanat present.

Polar feedbacks
Hansen, Sato et al. (2013) find that current temperatures are at least as high as the HoloceneMaximum (i.e., as high as they have been over the last 10,000 years). They sum up:
Earth at peak Holocene temperature is poised such that additional warming instigates largeamplifying high-latitude feedbacks. Mechanisms on the verge of being instigated include loss of Arctic sea ice, shrinkage of the Greenland ice sheet, loss of Antarctic ice shelves, andshrinkage of the Antarctic ice sheets. These are not runaway feedbacks, but together theystrongly amplify the impacts in polar regions of a positive (warming) climate forcing…Augmentation of peak Holocene temperature by even +1ºC would be sufficient to triggerpowerful amplifying polar feedbacks, leading to a planet at least as warm as in the Eemian andHolsteinian periods, making ice sheet disintegration and large sea level rise inevitable.
[It is relevant here to note that warming in the pipeline due to thermal inertia, pluswarming associated with the loss of aerosols, is greater than +1ºC.]And during the Pliocene, with atmospheric greenhouse levels similar to today, the northern hemisphere was free of glaciers and ice sheets and beech trees grew in the TransantarcticMountains. There are also strong indications that permanent El Nino conditions prevailed.

4d. Arctic carbon stores
As discussed in 3c. above, scientists using radiometric dating techniques on Russian caveformations to measure historic melting rates going back 500,000 years conclude that a +1.5ºCglobal rise in temperature compared to pre-industrial is enough to initiate widespreadpermafrost melt.In May this year, Brigham-Grette, Melles et al., (2013) published evidence from LakeEl’gygytgyn, in north-east Arctic Russia, showing that 3.6–3.4 million years ago, summermid-Pliocene temperatures locally were ~8°C warmer than today, when CO
was ~400ppm. This is highly significant because researchers including Celia Bitz (Bitz, Ridley et al,2009) and Philippe Ciais have previously found that the tipping point for the large-scale loss of permafrost carbon is around +8ºC to 10ºC regional temperature increase. Caias told theMarch 2009 Copenhagen climate science conference that: “A global average increase in airtemperatures of +2ºC and a few unusually hot years could see permafrost soil temperaturesreach the +8ºC threshold for releasing
of tonnes of carbon dioxide and methane”(emphasis added) (Adam, 2009). So, if the
current level of greenhouse gases
is enough toproduce Arctic regional warming of ~+8°C and that is a likely tipping point for large-scalepermafrost loss, we have reached a disturbing milestone.Even more disturbing is new research from Ballantyne, Axford et al. (2013) which says thatduring the Pliocene epoch, when CO
levels were ~400 ppm, Arctic surface temperatureswere 15-20°C warmer than today’s surface temperatures. They suggest that much of thesurface warming likely was due to ice-free conditions in the Arctic. Compared to theestimated tipping point for the large-scale loss of permafrost carbon of +8º– 10ºC regionalwarming, this research confirms both that the current level of greenhouse gases is sufficientto both create a sea-ice free Arctic, and Arctic warming more than sufficient to trigger large-scale loss of permafrost carbon.

5a. Climate safety
The research evidence and expert elicitations demonstrate that climate conditions are“dangerous” now – according to the generally accepted “safe boundary”, “five concerns” and“tipping point” metrics:

The 350 ppm “safe boundary” for atmospheric CO
has already been exceeded by 50ppm.

In 2007, at around +0.76ºC warming (equivalent to ~335 ppm CO
at equilibrium),Arctic sea-ice passed its tipping point. The Greenland Ice Sheet may not be far behind,as the Arctic moves to sea-ice-free conditions in summer, triggering further tippingelements.

Around +1.5ºC warming may be the tipping point for the Greenland Ice Sheet and forthe large-scale release of Arctic carbon permafrost stores. At +1.5ºC, coral reefs would be reduced to remnant systems.

The paleo-climate record shows that the current level of atmospheric CO
at 400 ppmis enough to produce sea-level rises of 20–40 metres; is around the tipping point for large-scale release of Arctic carbon permafrost; and is sufficient to trigger powerfulamplifying polar feedbacks.To restore and preserve year-round Arctic sea-ice and prevent triggering powerfulamplifying polar feedbacks, atmospheric CO
would need to be reduced to a safe distance below 335 ppm. Five years ago, James Hansen suggested CO
in the range 300–325 ppmwould be required to restore late Holocene sea-ice conditions.Holocene CO
levels have varied between 270 and 330 ppm. The higher figure occurred inthe early Holocene around 10,000 years ago when temperatures were around

warmer(known as the
Holocene maximum)
than pre-industrial levels, when the CO
level wasaround 280 ppm.A safe climate would not exceed the Holocene maximum. The notion that +1.5ºC is a safetarget is contradicted by the evidence, and even +1ºC degree is not safe given what we nowknow about the Arctic.
5b. Emission reduction challenges
The dominant climate policy frame I have observed is: “Let’s hope it’s not as bad as yousay… Even if you are right about the Arctic… holding the system to +2ºC will be verydifficult… and a huge political and economic challenge… but it’s the best we can hopefor… and while it might be dangerous…that’s a hell of a lot better than +3 or 4ºC … whichwould be catastrophic.”The discussion on “doing the maths” for the carbon budget is about the total emissionsavailable without exceeding 2ºC of warming.This task is very much more challenging than policy-makers accept, as Anderson and Bowsdemonstrate in their 2008 and 2011 papers on emission reduction scenarios. They makesome optimistic assumptions about de-afforestation and food-related emissions for the restof the century, and then ask what emission reduction scenarios would be compatible withholding warming to +2ºC, and find that:

Of the 18 scenarios tested,
ten cannot be reconciled with ~450 ppm CO

If emissions to do not peak till 2025,
no scenarios are available

450 ppm CO2e requires energy emissions to be stabilised by 2015, then declineannually by 6-8 per cent for 2020–2040, with full de-carbonisation by 2050.

A five per cent annual reduction in emissions from a 2020 peak (and a 6–7 per centannual reduction in energy and process emissions) correlates near 550 ppm CO
e, or+3ºC of warming.
If the emissions reduction after a 2020 peak is three per cent, thiscorrelates near 650 ppm CO
e, or +4ºC of warming

And looking at equity issues: if non-Annex 1 (developing) nation emissions growthree per cent a year to 2020 and then peak in 2025, there is
no carbon budget available for Annex 1 (developed nations) after 2015
, for the IPCC’s low-emissionscarbon budget.Research published in August 2013 finds that terrestrial ecosystems absorb approximately11 billion tons less CO
every year as the result of the extreme climate events than they couldif the events did not occur. That is equivalent to approximately a third of global CO
emissions per year (Reichstein, Bahn et al., 2013). As extreme events increase in scale andfrequency with more warming, this may negatively affect the amount of emissionsavailable for the carbon budgets discussed above

5c. Two degrees, or four?
In June 2013, a German research institute which advises Angela Merkel’s governmentconcluded that “policy makers must come up with a new global target to cap temperaturegains because the current goal… limiting the increase in temperature to 2°C sinceindustrialization is unrealistic”. It recommended that “world leaders either allow the 2°Cgoal to become a benchmark that can be temporarily overshot, accept a higher target, orgive up on such an objective altogether” (Nicola and Morales, 2013).International Energy Agency Chief Economist Fatih Birol calls the 2°C goal “a nice Utopia”:“It is becoming extremely challenging to remain below 2°C. The prospect is getting bleaker.That is what the numbers say” (Harvey, 2011).The prevailing climate policy-making framework now poses a choice between a“dangerous but liveable” 2ºC of warming and the “catastrophe” of 4ºC or more, as reflectedin the statement by John Holdren that opens this paper.The World Bank (2012) and PriceWaterhouseCoopers (2012) have recently publishedreports which complement a wide range of scientific research which concludes that theworld is presently heading for 4ºC or more of warming this century, and as soon as 2060.Reuters correspondent Michael Rose (2012) quotes IEA Chief Economist, Fatih Birol assaying that emission trends are “perfectly in line with a temperature increase of 6°C, whichwould have devastating consequences for the planet”.Anderson (2011) says there is a widespread view amongst scientists that “a 4°C future isincompatible with an organised global community, is likely to be beyond ‘adaptation’, isdevastating to the majority of eco-systems and has a high probability of not being stable”.Yet the 2ºC goal is not an option either, because, with climate and carbon cycle positivefeedbacks in full swing, it is less a stable destination than a signpost on a highway to amuch hotter place. The real choice now is to try and keep the planet under a series of bigtipping points by getting it back to a Holocene-like state, or accept that a 3-6ºC“catastrophe” is at hand.
5d. Radical choices
Policy-makers officially focus on the 2ºC goal, without admitting the ambition entailed:
…while the rhetoric of policy is to reduce emissions in line with avoiding dangerous climatechange, most policy advice is to accept a high probability of extremely dangerous climate changerather than propose radical and immediate emission reductions. (Anderson and Bows, 2011)
As Anderson and Bows show, if global emissions don’t peak till 2020, then the carbon budget for the developed world is… zero (5b. above). Even the 2ºC target requires actionsthat are completely outside the current climate policy-making framework, and thereforeconsidered impossible.In “A new paradigm for climate change”, Anderson and Bows (2012) call for academicrigour in elaborating the scientific and economic choices:

… academics may again have contributed to a misguided belief that commitments to avoidwarming of 2°C can still be realized with incremental adjustments to economic incentives… asthe remaining cumulative budget is consumed, so any contextual interpretation of the sciencedemonstrates that the threshold of 2°C is no longer viable, at least within orthodox politicaland economic constraints…At the same time as climate change analyses are being subverted to reconcile them with theorthodoxy of economic growth, neoclassical economics has evidently failed to keep even itsown house in order. This failure is not peripheral. It is prolonged, deep-rooted and disregards national boundaries, raising profound issues about the structures, values and framing of contemporary society… This catastrophic and ongoing failure of market economics and thelaissez-faire rhetoric accompanying it (unfettered choice, deregulation and so on) couldprovide an opportunity to think differently about climate change…It is in this rapidly evolving context that the science underpinning climate change is beingconducted and its findings communicated. This is an opportunity that should and must begrasped. Liberate the science from the economics, finance and astrology, stand by theconclusions however uncomfortable. But this is still not enough. In an increasinglyinterconnected world where the whole — the system — is often far removed from the sum of its parts, we need to be less afraid of making academic judgements. Not unsubstantiatedopinions and prejudice, but applying a mix of academic rigour, courage and humility to bringnew and interdisciplinary insights into the emerging era. Leave the market economists to fightamong themselves over the right price of carbon — let them relive their groundhog day if theywish. The world is moving on and we need to have the audacity to think differently andconceive of alternative futures.”
Anderson is the Deputy Director of the Tyndall Centre for Climate Change Research, whichin late 2013 is hosting a Radical Emission Reduction Conference, whose purpose isdescribed as:
Today, in 2013, we face an unavoidably radical future. We either continue with risingemissions and reap the radical repercussions of severe climate change, or we acknowledge thatwe have a choice and pursue radical emission reductions: No longer is there a non-radicaloption. Moreover, low-carbon supply technologies cannot deliver the necessary rate of emission reductions – they need to be complemented with rapid, deep and early reductions inenergy consumption – the rationale for this conference.
To repeat: “…we face an unavoidably radical future… no longer is there a non-radicaloption.” Can this phrase help liberate us from the prevailing climate policy-makingparadigm, from which no further hope can be wrung?In 2008, in a statement for the book
Climate Code Red
I authored with Philip Sutton, JamesHansen wrote:
We must begin to move rapidly to the post-fossil fuel clean energy system. Moreover, we mustremove some carbon that has collected in the atmosphere since the Industrial Revolution. Thisis the story that ‘Climate Code Red’ tells with conviction. It is a compelling case for recognising,as the UN secretary-general has said, that we face a climate emergency.
And what would a radical, emergency-action option look like, and why it is absolutelynecessary as the last, best hope we have? We described some of its features in
Climate CodeRed
, as has Paul Gilding in his 2011 book,
The Great Disruption
. And this year, Delina andDiesendorf (2013) published research from the University of NSW on the question: “Iswartime mobilisation a suitable policy model for rapid national climate mitigation?”In addition to stopping fossil fuel emissions, very large-scale carbon dioxide removal (CDR)would be a critical task, to reduce the level of atmospheric greenhouse. Can CDR beachieved at the size and scale required to help get us back to safety? A recent and very goodsurvey of CDR options and technologies, their costs, effectiveness and environmentalconsequences has been just published by Caldeira, Bala et al. (2013). As well, it now seemsclear that if we are to prevent the world tripping past a number of critical tipping points,some forms of geo-engineering such as solar radiation management (SRM) will benecessary in the short term. This would be an adjunct to a zero-emissions program andCDR, especially as the “global dimming” effect of aerosols is reduced as emissions fall.Here, too, Caldeira, Bala et al (2013) provide a useful survey, including the pitfalls, thechallenging governance issues and the many “known unknowns”.

All of this may seem like a lot of “ifs” and “buts” and “maybes”. We are now in a world of making the least-worst choices. There is no simple answer, and we do not yet know all thequestions in detail, let alone all of the answers. Nobody ever does at the beginning of anemergency response. That’s what makes it an emergency. But we do now know, with clearevidence that climate change is already “dangerous”, that we are heading towards a“catastrophe”, that we are in an emergency and, yes, we do face “…an unavoidably radicalfuture”. And we do know from past experience that once societies are in emergency mode,they are capable of facing up to and solving seemingly impossible problems.
David Spratt
14 September 2013

A tipping point may be understood as a step change, or passing of a critical threshold, in amajor earth-climate system component, where a small perturbation (a small push orchange) unleashes a bigger change in the component. Potsdam Institute Director, Prof. Hans Joachim Schellnhuber, says that tipping points “identify the most vulnerable components(tipping elements) of the Earth System, the critical warming thresholds where therespective Earth System elements flip into a qualitatively new state”(Schellnhuber, 2009).These elements include ecosystems, major ocean and atmospheric circulation patterns, thepolar ice sheets, and the land- and ocean-based carbon stores.This process is often tied to positive feedbacks, where a change in a component leads toother changes that eventually “feed back” onto the original change to amplify it. Theclassic case in global warming (or, in reverse, cooling) is the ice-albedo feedback, wheredecreases (increases) in the ice cover area change surface reflectivity (albedo), trapping more(less) heat and producing further ice loss (gain).In some cases, passing one threshold will trigger further threshold events, for example wheresubstantial releases from permafrost carbon stores increase warming, releasing morepermafrost carbon but also pushing other systems, for example parts of the Antarctic icesheet, past a threshold point.Once a tipping point is crossed, it is irreversible (under natural conditions) within certaintime frames, so the consequence is to significantly affect the earth’s climate and ecosystems,for example by raising temperatures or greenhouse gas levels, or changing the efficiency of the land and ocean carbon sinks. Given enough time and the right conditions, mostprocesses (but not extinctions, for example) can be reversed.In a period of rapid warming, most major tipping points once crossed (ice sheet loss, large-scale land carbon store releases such as permafrost) are irreversible on human time framesrunning to a few generations, principally due to the longevity of atmospheric CO
(severalthousand years).Large-scale human interventions in slow-moving earth system tipping points might allow atipping point to be reversed (for example, a large-scale atmospheric CO
drawdownprogram, or solar radiation management).There is discussion, for example, that Arctic sea-ice loss is “easily reversible” in a coolingworld, but that is easier said than done. That would require greenhouse gas levels to bereduced significantly, below the level equivalent to the temperature at which the sea-icesystem tipped in 2007, to produce a sufficiently cooler world. This would be around 300–325 ppm CO
, compared to the present level of 400 ppm, so it is not so “easy” in the realworld.The scientific literature on tipping points is relatively recent, with a significant contribution by Lenton, Held et al (2008) on “Tipping elements in the Earth’s climate system” in an issueof the journal
Proceedings of the National Academy of Sciences
devoted to the subject. However,our knowledge is limited because “a system-level understanding of critical Arctic processesand feedbacks is still lacking”
(Maslowski, Kinney et al. 2012) and “
no serious efforts have beenmade so far to identify and qualify the interactions between various tipping points”(Schellnhuber, 2009).Climate models are not yet good at dealing with tipping points. This is partly in the nature of

Is the climate already dangerous? | David Spratt | September 2013 | page 17
tipping points, where a particular and complex confluence of factors suddenly change aclimate system characteristic and drives it to a different state. To model this, all the contributingfactors and their forces have to well identified, as well as their particular interactions, plus theinteractions between tipping points. Duarte, Lenton et al. (2012) conclude that “complex,nonlinear systems typically shift between alternative states in an abrupt, rather than a smoothmanner, which is a challenge that climate models have not yet been able to adequatelymeet”.The classic case was the Arctic sea ice “big melt” in 2007. Many models, including those onwhich the 2007 IPCC report had relied to conclude that Arctic sea-ice was pretty much likely toremain till the end of the century, did not fully capture the dynamics of sea-ice loss. Thus whenin 2007 the summer sea-ice extent dropped radically compared to previous years, some model-oriented researchers exclaimed that the Arctic was melting “a hundred years ahead of schedule”. Even today, papers are still being published with modelling that suggests a sea-ice free Arctic will not occur till mid-century. Given the observations, it’s difficult not toconclude that given a choice between their models and real-world observations, somemodellers will always choose the former.In an overview of the current state of Arctic climate research, Maslowski, Kinney et al. (2012)conclude that: “Model limitations are hindering our ability to predict the future state of Arctic sea ice”, and that the majority of general climate models (GCMs) including those usedin IPCC (2007) “have not been able to adequately reproduce observed multi-decadal sea-icevariability and trends in the pan-Arctic region”, and their ensemble mean trend inSeptember Arctic sea-ice extent “is approximately 30 years behind the observed trend”.For example, what would be the impact of a sea-ice-free Arctic summer and the consequentamplified regional warming on the stability of the Greenland Ice Sheet (GIS)? Researchdoes not yet provide a robust framework for considering such questions, yet mostscientists if asked for their expert elicitation would probably say that it is hard to imagine theGIS doing anything other than melting at an accelerating rate and passing a critical tippingpoint in such circumstances.The sea-ice model that has performed best (acronym NAME), is one of a new range of morespecialised regional climate models developed by Dr Wieslaw Maslowski and colleagues.Maslowski is highly regarded, in part because his position at the American NavalPostgraduate School has given him unique access to half a century of Arctic sea-ice thicknessscans from polar US military submarines. Maslowski told BBC News:
In the past… we were just extrapolating into the future assuming that trends might persist aswe’ve seen in recent times. Now we’re trying to be more systematic, and we’ve developed aregional Arctic climate model that’s very similar to the global climate models participating inIPCC assessments. We can run a fully coupled model for the past and present and see what ourmodel will predict for the future in terms of the sea ice and the Arctic climate. (Black, 2011)
He emphasizes “the need for detailed analyses of changes in sea ice thickness and volume todetermine the actual rate of melt of Arctic sea ice”, and concludes that:
The modeled evolution of Arctic sea ice volume appears to be much stronger correlated withchanges in ice thickness than with ice extent as it shows a similar negative trend beginningaround the mid-1990s. When considering this part of the sea ice–volume time series, one canestimate a negative trend of
1,120 km
with a standard deviation of +/-2,353 km
from combined model and observational estimates for October–November 1996–2007. Giventhe estimated trend and the volume estimate for October–November of 2007 at less than 9000km
, one can project that at this rate it would take only 9 more years or until 2016 +/-3 years toreach a nearly ice-free Arctic Ocean in summer. Regardless of high uncertainty associated with

Is the climate already dangerous? | David Spratt | September 2013 | page 18
such an estimate, it does provide a lower bound of the time range for projections of seasonal seaice cover.
The point cannot be emphasised enough that the best-performing Arctic sea-ice modelprojects 2016 +/-3 years to reach a nearly ice-free Arctic Ocean.The non-linear problem still plagues many Arctic GCMs, and indeed parts of the IPCCprocess which largely excludes tipping points and carbon cycle feedbacks fromconsideration, exemplified by the 2007 IPCC’s reticence on sea level rises.
Severalfundamental projections found in IPCC reports have consistently underestimated real-worldobservations in at least eight key areas (Scherer, 2012). In its February 2007 report on thephysical basis of climate science, the IPCC said that Arctic sea-ice was responding sensitivelyto global warming: ‘While changes in winter sea-ice cover are moderate, late summer sea-iceis projected to disappear almost completely towards the end of the twenty first century.’
Andapparently the forthcoming 2013 IPPC AR5 has omitted consideration of permafrostfeedbacks – another glaring example of that body’s scientific reticence (Romm, 2012).

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“Dangerous” metrics 1Case studies 3Climate system elements in danger fromimplied temperature increases 8Paleo-climate comparisons 10Conclusions 11Appendix: Tipping points and climatemodelling 16References 19
Is climate change already dangerous?Copyright: David Spratt 2013Published byClimate Code Red305/85 Rathdowne StreetCarlton 3053 AustraliaContact: climatecr@gmail.comFirst publishedSeptember 2013