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Dangerous Climate Change

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Climate change post-1750 is driven by total radiative forcing tracking toward c.3 Watt/m2, near-half the forcing of 6.5±1.5 Watt/m2 associated with the last glacial termination (c.14.7–11.7 kyr). Given the onset of the Antarctic ice sheet at or below 450 parts per million (ppm) CO2 c. 34 Million years (Ma) ago (late Eocene), and of Arctic Sea ice below 400 ppm c. 2.8 Ma-ago (mid-Pliocene), the projected consequences of CO2 trajectories toward 550 or 650 ppm through the 21st century, now considered inevitable by governments, likely involve a return to Pliocene conditions (+ 2–3oC; +25±12 metres sea level rise; permanent El-Nino) through likely climate tipping points. Depending on the degree of methane (CH4)  release from sediments, permafrost and tropical bogs, developments analogous to the PETM (Paleocene-Eocene Thermal Maximum, 56 Ma; + 6oC) and attendant mass extinction may enuse. The Intergovernmental Panel for Climate Change (IPCC) 2007 projections underestimate ice melt and sea level rise parameters. The Garnaut-2008 Report take limited account of the effects of methane release from permafrost and shallow polar ocean sediments and the synergy of carbon cycle feedbacks and ice melt/water feedbacks, as indicated by the recent climate history of Earth.  Assumption of CO2 and climate 'stabilization' and possible reversal on decadal time scale are difficult to reconcile with the sharp transitions between climate states observed in the recent history of the atmosphere. The opening of an ice-free Arctic ocean and slow-down or abortion of the North Atlantic thermohaline circulation lead to a new climate regime in the Northern Hemisphere, possibly similar to events c. 8.2 kyr when ice-melt currents resulted in several degrees cooling and freezing of Europe. According to Anderson and Bows (2008) it may be too late to arrest climate change by reduced carbon emission alone.  Humanity needs to fast-track development of techniques for atmospheric CO2 down-draw to levels c. 350 ppm and below (Hansen et al., 2008).

"My name is Ozymandias king of kings:
Look on my works, ye Mighty, and despair!'
Nothing beside remains.  Round the decay
Of that colossal wreck, boundless and bare,
The lone and level sands stretch far away."
(Percy B. Shelley).

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The onset of ice age conditions c. 34 million years (Ma) ago (end-Eocene), allowing the growth of the Antarctic ice sheet, depended critically on the decline of atmospheric CO2 levels to below 450 parts per million ppm), culminating with the development of the Arctic Sea Ice from c.2.8 Ma (mid-Pliocene) when CO2 levels declined below c.400 ppm (Hansen et al., 2008; Glikson, 2008). The rise of atmospheric CO2 from about 280 ppm to 387 ppm between 1750 and 2008, the highest level since almost 3 million years ago, proceeding at a rate of 2.2 ppm/year, threatens to return the climate to pre-ice age conditions.  A rise of atmospheric CO2 to levels of 550 and 650 ppm, with corresponding mean temperature increases of 3 to 4oC above pre-industrial levels, threatens the demise of civilization as well as a mass extinction of species.Observations to date indicate that climate change trajectories are at, or exceeding, the higher level estimates of the IPCC (Rahmstorf, 2007).

In a recent paper titled "Reframing the climate change challenge in light of post-2000 emission trends" (http://www.tyndall.ac.uk/publications/journal_papers/fulltext.pdf) Anderson and Bowes (2008) of the Tyndall Centre for Climate Change Research state, among other: "It is increasingly unlikely that an early and explicit global climate change agreement or collective ad hoc national mitigation policies will deliver the urgent and dramatic reversal in emission trends necessary for stabilization at 450 ppmv CO2-e. Similarly, the mainstream climate change agenda is far removed from the rates of mitigation necessary to stabilize at 550 ppmv CO2-e. Given the reluctance, at virtually all levels, to openly engage with the unprecedented scale of both current emissions and their associated growth rates, even an optimistic interpretation of the current framing of climate change implies that stabilization much below 650 ppmv CO2-e is improbable."
And "Ultimately, the latest scientific understanding of climate change allied with current emission trends and a commitment to 'limiting average global temperature increases to below 4 degrees C above pre-industrial levels, demands a radical reframing of both the climate change agenda, and the economic characterization of contemporary society."

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The current climate trend commenced with a sharp accentuation of temperature rise rates from the mid-1970s. Prior to this state the superposed effects of greenhouse gas (GHG), solar forcing, ocean currents, the El-Nino Southern Oscillation (ENSO) cycle and aerosol albedo effects on mean global temperatures were difficult to separate.  Since 1975-76, while solar radiation continues to oscillate according to the 11-year-long sunspot cycle, rapid warming at a rate of 0.018 degrees C/year (10 times the mean 1880-1970 rate) exceeds the rate of the last glacial termination (14,700 – 11,700 years-ago) by an order magnitude (Table 1). Climate change developments to date include:

1.           Late 20th century and early 21st century CO2 rise rate average +1.45 ppm/yr, rising to 2.2 ppm/yr in 2007. The trend exceeds 1850-1970 rates by factors of c.4 to 5 and is two orders of magnitude higher than mean CO2 rise rates of the last glacial termination (c. 0.014 ppm/yr) (Rahmstorf et al., 2007; Global Carbon Project, 2008).

2.           Methane (CH4), which after c. 20 years has 23 times the greenhouse warming effect of CO2, rose by 10 ppb during 2007 (http://web.mit.edu/newsoffice /2008/techtalk53-7.pdf), exceeding the 1850-1970 rise rate (c. 5.4 ppb/yr) and orders of magnitude faster relative to the last glacial termination (Table 1). Methane deposits potentially vulnerable to climate change reside in permafrost (c. 900 Billion ton Carbon - GtC), high latitude peat lands (c. 400 GtC), tropical peat lands (c. 100 GtC), vulnerable vegetation (c. 650 GtC) and methane hydrates and clathrates in the ocean and ocean floor sediments (> 16,000 GtC). These exceed the atmospheric level of carbon (c. 750 GtC), carbon emissions to date (c. 305 GtC) and known economic carbon reserves (>>4000 GtC).  Recently elevated methane release from Arctic Sea sediments and sub-Arctic permafrost were recorded (Walter et al., 2006; Rigby, 2008).

3.           A rise of mean global temperature by more than 0.6 degrees C since 1975-6. Mean temperature rise rates of 0.016 degrees C/year during 1970 - 2007 were about an order of magnitude faster than during 1850-1970 (0.0017C) and during the last glacial termination (Table 1). As indicated by deuterium studies of Greenland ice cores, abrupt tipping points during the last termination (14.7 – 11.7 kyr) resulted in extreme temperature changes on the scale of several degrees C in a few years (Steffensen et al., 2008).

4.           The rise of mean Arctic and sub-Arctic temperatures in 2005-2008 by near +2.4C since 1970.

5.           Arctic Sea ice melt rates of c. 5.4% per-decade since 1980, increasing to >10% per year during 2006-2007 (National Snow and Ice Data Centre [NSIDC], 2008).

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6.           West Antarctica warming and ice melt rates >10% per decade culminating in mid-winter ice shelf breakdown (Wilkins ice shelf; June, 2008, NSIDC, 2008).

7.           Advanced melt of Greenland ice of 0.6% per year between 1979 and 2002 (Steffen and Huff, 2002; Frederick et al., 2006) and see  click here style="font-size: 11pt; font-family: Verdana">

8.           Slow-down of the North Atlantic thermohaline conveyor belt and down-welling water columns (NASA, 2004; Bryden et al., 2005), with attendant danger of its cessation analogous to conditions c.8.2 kyr ago (Alley et al., 1997).

9.           Temperature projections for the North Atlantic Ocean (Keenlyside et al., 2008) may reflect the effect of Greenland ice melt waters, which may lead to transient cooling similar to events recorded in ice cores c.12,900 – 11,700 and 8200 years-ago (Steffensen et al., 2008).

10.      Increased frequency and intensification of categories 4 and 5 hurricanes (Webster et al., 2005).

11.      Mean sea level rise rate of c.0.32 cm/yr during 1988-2007 more than doubled relative to the mean c.0.14 cm/yr rate of 1973-1988 and three times those of 1850-1970 (Rahmstorf, 2006). In so far as doubling of sea level rise rates continues at this rate through the 21st century, they may approach rates similar to those of the last glacial termination (1.3 – 1.6 cm/yr) before mid-century, with sea level rise by several metres toward the end of the century as estimated by Hansen et al (2007).

The last glacial termination, triggered by insolation peaks, involved total radiative forcing rise of about 6.5 Watt/m2, including c.3.0+/-0.5 Watt/m2 induced by rising greenhouse gases (GHG: CO2, CH4, N2O) and 3.5±1.0 Watt/m2 induced by lowered albedo associated with melting of ice sheets and spread of vegetation. Both factors, including their feedback effects, result in mean global temperature rise of c. 5.0±1.0 degrees C (Hansen et al., 2008).

Given the onset of the Antarctic ice sheet at or below 450 ppm CO2 at c. 34 Ma (late Eocene), and of the Arctic Sea ice below 400 ppm at 2.8 Ma (mid-Pliocene) (Haywood and Williams, 2005), the projected consequences of CO2 trajectories toward 550 ppm and higher threaten to trigger serious environmental consequences, including extreme weather events and meters-scale sea level rises.
 The effects of the above processes on the Australian continents follow from projections of temperature and rainfall variation charts by the Australian Bureau of Meteorology from the mid-1970s.  

Major factors include: 

1.           Southward migration of climate zones toward the pole by about 400 km, associated with the contraction of the Antarctic wind vortex, resulting in increase in temperature and decrease in rainfall in much of southern Australia, in particular the southwest and the southeast.

2.           Increased frequency of the El-Nino events of the ENSO cycle, resulting in increased draughts in northeast Australia, India and parts of east Africa.

3.           Increased intensity of northwestern cyclones, penetrating west-central Australia with consequent rise in mean precipitation.

4.           An ovrall increase in the intensity of extreme weather events, i.e. cyclones, floods and fires associated with high summer temperatures.

5.           Sea level rise., threatening coastal regions and cities. 

Inherent in the IPCC-2007 and Garnaut Review-2008 climate change projections are gradual changes including stabilization of CO2 rise trends related to reductions in carbon emissions. However, carbon feedbacks and ice melt/water interaction feedbacks are neglected in the IPCC-2007 report on which the Garnaut report relies to a large extent.

The IPCC-2007 Report states:  "The emission reductions to meet a particular stabilization level reported in the mitigation studies assessed here might be underestimated due to missing carbon cycle feed-backs (see also Topic 2.3) AR4 caption to Table 5.1". 

The concept of stabilization is difficult to reconcile with sharp transition between climate states observed in the last glacial termination 11.7 – 14.7 thousand years ago (Steffensen et al., 2008). The recent history of the atmosphere betrays little evidence for stabilization scenarios. Instead, glacial-interglacial cycles culminate with runaway warming and tipping points preceding sharp or gradual temperature declines (Broecker, 2000; Alley et al., 1997, 2003; Braun et al., 2005; Roe, 2006; Hansen et al., 2007, 2008; Steffensen et al., 2008; Kobashi et al., 2008). 

Climate models, effective in modeling 20th and early 21st century climate change, tend to underestimate the magnitude and pace of global warming (Rahmstorf et al., 2007).  According to Hansen et al. (2008):

"Climate models alone may be unable to define climate sensitivity more precisely, because it is difficult to prove that models realistically incorporate all feedback processes. The Earth's history, however, allows empirical inferences of both fast feedback climate sensitivity and long term sensitivity to specified greenhouse gas change including the slow ice sheet feedback."  

The Earth atmosphere is already tracking toward conditions increasingly similar to the mid-Pliocene c.3.0 Ma, with temperatures higher than mean Holocene temperatures by + 2 to 30C, ice-free Arctic Sea, tens of metres sea level rise and a permanent El-Nino (Dowsett et al., 2005; Haywood and Williams, 2005; Gingerich, 2006).  

Additional anthropogenic GHG forcing and methane emission threaten conditions approaching those of the Paleocene-Eocene Thermal Maximum (PETM) 56 Ma, when the eruption of some 1500 GtC (Sluijis et al., 2007), inferred from low δ13C values (-2 to 3‰ 13C), resulted in global warming of c. 6oC, development of subtropical conditions in the Arctic circle (sea temperatures 18 – 23oC -  Sluijis et al., 2007), ocean acidification and mass extinction of 30-35% of benthic plankton (Panchuk et al., 2008).

The recent history of the atmosphere, and the presence of thousands of GtC in metastable methane hydrates, clathrates and permafrost, suggests a CO2 trajectory toward 550 or 650 ppm, projected by Anderson and Bowes (2008), may lead toward breakdown of global civilization (Stipp, 2004) and mass extinction of species. 

References:   Alley, R.B. et al.,1997.  Holocene climatic instability:  prominent widespread event 8200 yr ago. Geology 25, 483-486.  Alley, R. B. et al., 2003, Abrupt Climate Change. Science, 299, 2005 – 2010; Anderson, K. and Bows, A., 2008. Reframing the climate change challenge in light of post-2000 emission trends. Phi. Trans. R. Soc. A.   A. doi:10.1098/rsta.2008.0138;  Broecker, W.S., 2000. Abrupt climate change: causal constraints provided by the paleoclimate record. Earth Sci. Rev. 51, 137-154. Archer, D., 2005, Fate of fossil fuel CO2 in geologic time. J. Geophy. Res. 110, CO9SO5 Braun, H, et al., 2005, Possible solar origin of the 1,470-year glacial climate cycle demonstrated in a coupled model. Nature 438, 208-211.  Bryden, L. et al., 2005, Slowing of the Atlantic meridional overturning circulation at 25N. Nature 438, 655-657.  Dowsett, H.J. et al., 2005, Middle Pliocene sea surface temperature variability.  Aleoceanography  20, PA2014, doi:10.1029/2005PA001133, 2005.  Frederick, T.R. E., Krabill, S. & Martin, C. 2006. Progressive increase in ice loss from Greenland. Geophysical Research Letters 33, L10503, doi:10.1029/2006GL026075; Keenlyside, N.S. et al., 2008. Advancing decadal-scale climate prediction in the north Atlantic sector. Nature 453, 84-88.  Ganopolski, A. & Rahmstorf, S., 2001. Rapid changes of glacial climate simulated in a coupled climate model. Nature 409, 153–158.  Garnaut Climate Change Review, 2008,   http://www.garnautreview.org.au/domino/Web_Notes /Garnaut/ garnautweb.nsfGingerich, P. D., 2006. Environment and evolution through the Paleocene – Eocene thermal maximum. Trends Ecol. Evolution 21, 246 – 253. Glikson, A.Y., 2008. Milestones in the evolution of the atmosphere with reference to climate change. Aust. J. Earth Sci. 55, 125-140  Global Carbon Project, 2008. http://www.globalcarbonproject.org/  Hansen, J. et al., 2008.  Target CO2: where should humanity aim?  http://www.columbia.edu/~jeh1/ 2008/ TargetCO2_20080407.pdf  Hansen, J.R. et al., 2006, Global temperature change. Proc. Nat. Acad. Sci. 101, 16109 – 16114.   Hansen, J.R., 2007. Climate change and trace gases. Phil. Trans.Roy. Soc. London 365A, 1925–1954.  Haywood, A. and Williams, M., 2005, The climate of the future: clues from three million years ago. Geol. Today 21, 138–143.  Kobashi, T. et al., 2008, 4±1.5 °C abrupt warming 11,270 years ago identified from trapped air in Greenland ice. E arth Planet. Sci. Lett. 268, 397–407  NASA, 2004. http://www.nasa.gov/centers/goddard/news/topstory/2004/0415gyre.html NSIDC, 2008, http://nsidc.org/news/press/20080325_Wilkins.html  Panchuk, K.; et al., 2008. Sedimentary response to Paleocene-Eocene Thermal Maximum carbon release: A model-data comparison". Geology 36, 315–318  Rahmstorf, S.R., 2007. Recent climate observations compared to projections. Science  316, 709-711.  Rahmstorf, S.R., 2006.  A Semi-Empirical Approach to Projecting Future Sea-Level Rise. Science 315, 368-370.  Rigby, M., 2008. Reported in: http://www.newscientist.com/article/dn15079; Geophysical Research Letters, DOI:   0.1029/2008GL036037  Roe, G., 2006. In defence of Milankovitch. Geophys. Res. Lett. 33, L24703.  Sluijs, A.,et al., 2007 Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum. Nature, 441, 610-613.  Steffensen, J.P., et al., 2008, High-resolution Greenland ice core data show abrupt climate change happens in few years. Sci. Express, 19.6.2008; Steffen, K. and Huff, R., 2002. A record maximum melt extent on the Greenland ice sheet in 2002. Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado at Boulder.Stipp, D., 2004, The Pentagon's Weather Nightmare: the climate could change radically, and fast. That would be the mother of all national security issues.   Http://money.cnn.com/magazines/fortune/fortune_archive/2004/02/09/360120/index.htm Walter, K.M. et al., 2005. Methane bubbline from Siberian thaw lakes as a positive feedback to climate warming. Nature 443, 71-75.  Webster, P.J. et al., 2005. Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment, Science 309, 1844-1846.   

Table 1.  Greenhouse gas levels, greenhouse gas rise rates, mean CH4, mean temperatures, temperature rise rates per CO2, sea levels and sea level rise rates per year and per 1 oC for the late Holocene, glacial termination-I, Glacial termination-II and the mid-Pliocene. 

PeriodmeanCO2 ppmCO2 rate ppm/yrMean CH4ppbMean ToC MeanToC/yr ToC / 1 ppm CO2Sea Level(cm, m)aplSLcm/yrSLm/1oC
A.  Anthropocene/Holocene
1970-2006/2008~325-387 Mean  1.452006   1.82007   2.2 2007-810 ppb/yr;1970-2006:1400-1750 ppb; 9.7 ppb/yr13.9-14.5 0.0160.0111970-2006+ 8 cm 1988-2007; 0.321973-19880.140.13
1850-1970280-330 0.42750-1400 5.4 ppb/yr13.7-13.9 0.00170.0041870-1970+ 11 cm 0.110.55
10kyr-1750265-285 0.002~700    7kyr-1750Oscillating to near stable   
B.  Glacial Termination-I
11.5-8.5~265-260DeclineIn CO2~600-570+1.00.00030.2-62 to -12 (+50 m)1.6 50
14–11.5~235-26517-11.5kyr0.014ppm/yr~450-600+4.50.001814-8.5kyr0.00070.15-95 to -62m (+33 m)1.32 7.3
C.  Glacial Termination-II
130-128~190-290139-130kyr0.011ppm/yr130-120kyrdecline~320-720+1.2 oCglobal0.00060.06124-120 kyr +8 m (APLl) 5-6.7
D.  mid-Pliocene
 3.29-2.97 Ma360-400  +2-3oC apl; +5 oC apl   +25±12; 35 m APL [Florida] 5-17


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Earth and paleo-climate scientist Australian National University Canberra, A.C.T. 0200

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