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Debate part 5: The planetary atmosphere and climate change

Posted By JoNova On May 26, 2010 @ 1:20 am In AGW socio-political,Global Warming | Comments Disabled


Round 5 of my debate with Andrew Glikson

Dr Andrew Glikson and I have been debating the evidence first through Quadrant, and then here. Kudos to him for following this up in a polite, diligent manner. This kind of open debate is extremely rare, and I am happy to encourage it. I will post a reply in a few days. For the moment I think the many able commenters here can discuss its merits. The only thing I’ll say now is that in each of my four previous replies I ask for evidence that the models are right on the magnitude of the feedbacks. Is it half a degree or 3.5oC?
Part I: AG / JN; Part II: AG / JNPart III: AG / Part III & IV: JN (& AG). (Part IV took place in the comments below Part III). Yes, this is the first time I’ve had a guest post from a scientist who disagrees… My reply is here.
– Jo

Guest Post by Andrew Glikson

Earth and Paleoclimate scientist
Australian National University, 18 May, 2010

Dr Andrew Glikson

Dr Andrew Glikson ANU

Unique among the terrestrial planets, occupying an intermediate position between Venus, with its thick blanket of greenhouse gases (93 bar; 96.5%CO2, 3.5%N2, 0.015%SO2, 0.002%H2O) and Mars with its thin atmosphere (<0.01 bar; 95.3%CO2, 2.7%N, 1.6%Ar, 0.13%O, 0.08%CO, 210 ppm H2O), the Earth’s atmosphere (78.08%N2, 20.95%O, 0.93%Ar, 398 ppm CO2) allows presence of liquid water at the surface and thereby existence of life. Modulation of the atmosphere by trace greenhouse gases (H2O, CO2, CH4, N2O, Ozone), exchanged with the hydrosphere and the biosphere, constrains surface temperatures in the approximate range of -89.4oC to +58oC.

Due to long atmospheric residence time on the scale of centuries to many millennia (Eby et al. 2009) [8], CO2 is capable of accumulation and modulating terrestrial climate, as contrasted with a shorter atmospheric residence time of methane (~8.5 years) and a short residence time of H2O vapour in the troposphere (~9-10 days). As identified by a range of CO2 proxy methods, listed in Table 1 and elaborated by Royer (2001, 2010) [21][22], the build-up and decline of atmospheric concentrations of CO2 has played a profound role in the evolution of climate through geological time (Figure 1), corroborated by observation of glacial deposits and the environmental classification of fossil plants and organisms. Abrupt rises in levels of CO2 associated with volcanic eruptions and asteroid impacts constituted an essential factor underlying extinction of species (Ward, 1994, 2007 [29] [30]; Veron, 2008 [27]).

Figure 1 Figure 1: Atmospheric CO2 and continental glaciation 400 Ma to present. Note the upper limit of glacial periods under atmospheric radiative forcing levels of ~500 ppm CO2. Top. Vertical blue bars mark the timing and palaeolatitudinal extent of ice sheets. Plotted CO2 records represent five-point running averages from each of the four major proxies. Also plotted are the plausible ranges of CO2 from the geochemical carbon cycle model GEOCARB III. All data have been adjusted to the Gradstein time scale. Middle. Global compilation of deep-sea benthic foraminifera 18O isotope records from 40 Deep Sea Drilling Program and Ocean Drilling Program sites updated with high-resolution records for the Eocene through Miocene interval. Most data were derived from analyses of two common and long-lived benthic taxa, Cibicidoides and Nuttallides. Bottom. Detailed record of CO2 for the last 65 Myr. Individual records of CO2 and associated errors are colour-coded by proxy method; when possible, records are based on replicate samples. Dating errors are typically less than ±1 Myr. The range of error for each CO2 proxy varies considerably, with estimates based on soil nodules yielding the greatest uncertainty. However, re-calibration of the soil-carbon proxy method (Breecker et al. 2010, Royer, 2010) See also IPCC AR4 Ch 6)

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Table 1. Principal proxies applied for reconstruction of Cainozoic climate conditions. Principal reference: Royer et al. 2001.

CO2 proxies Stomata pores in fossil plants
Carbon d13C proxy  – paleo-soil carbonate
Carbon d13C proxy – phytoplankton
Alkenone paleo-CO2
Boron/Calcium
Foraminifera d11B
d44C and d11B as pH and CO2 proxies
Organic component of sediments (Sapropel) / N-alkane plant leaf wax / tropical vegetation.
Detrital component of sediments / dust / indicator of mechanical glacial erosion / wind
Boron / salinity / alkalinity
Carbon-sulphur-oxygen mass balance calculations
Temperature proxies Benthic and plankton d18O; 13C-18O bonds in carbonate
Ice cores air bubbles: d18O / deuterium
Mg/Ca ratios in carbonate; pollen
TEX86 paleothermometer based on the relation between number of rings in the membrane lipids of the marine pico-plankton.
ALKENONE  (KETONE)– Paleo-T and CO2 proxy.

Water vapour, which exert peak radiative forcing effects in the tropics, have minor control of temperature in dry desert regions and almost none over polar regions where the atmosphere is of very low to nil water vapour concentrations, yet during glacial terminations and at present, Arctic and Antarctic latitudes have warmed up to 4 times faster than low to mid-latitudes (Figure 2).

Figure 2 Figure 2: Global temperature projections for mean September 1990-2009 relative to NASA’s baseline of 1951-1980, displaying concentration of warming in H2O vapour-low polar and desert regions. NASA GISS

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Lost all too often in the climate debate is an appreciation of the delicate balance between the physical and chemical parameters of the atmosphere/ocean/land system and the evolving biosphere, which controls the emergence, survival and death of species, including humans. Forming a thin breathable veneer only slightly more than one thousandth of the Earth’s diameter, the troposphere acts as the “lungs” of the biosphere, exchanging carbon gases and oxygen with plants and animals, which in turn affect the atmosphere, for example through release of methane and photosynthetic oxygen.

Prior to about 635 million years (Ma) ago, when complex multicellular Ediacra fauna appeared, the atmosphere had a greenhouse gas-rich oxygen-poor composition, arising from accumulation of CO2 from volcanic eruptions and hydrothermal emanations, activity of methane-synthesizing bacteria and excavation of carbon from sediments through asteroid impacts. Excepting glacial periods (~2400-2200 Ma; 850-635 Ma – the “Snowball Earth period”), the dominance of high-temperature oceans on the early Earth placed constraints on CO2 sequestration, which led to atmospheric build-up of CO2 to thousands and tens of thousands ppm. Intermittently through the Phanerozoic (540 Ma to the present) rising atmospheric oxygen levels, proliferation of protein-synthesizing animals and emergence of vegetation (in the Silurian ~420 Ma) enhanced the biological carbon cycle, including burial and maturation of carbon as coal and oil.

Figure 3 Figure 3: Equilibrium global average temperature increase above pre-industrial (oC) vs greenhouse gas concentration stabilization level (ppm CO2-eq). Plot represents Charney’s (1979) climate sensitivity relation of 3±1.5oC and red squares regions of Pagani et al.’s (2010) early and mid-Pliocene climate sensitivity relations. Colored zones I to VI represent various CO2 stabilization targets
IPCC-2007-AR4.

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Resolution of the effects of CO2 on the atmosphere is defined by the climate sensitivity (CS) parameter, formulated as the rise in atmospheric temperature induced by doubling of CO2 concentration. Charney (1979) [5] defines CS at 3±1.5oC (Figure 3). Recent projections from basic physical laws of the infrared absorption/emission resonance effect (Stefan-Bolzmann law, Krischhoff law), validated by laboratory experiments, are complicated by natural amplification of feedbacks from the carbon cycle and from the ice melt/albedo change amplification effect (replacement of high-reflectance ice by thermal radiation-absorbing water). These processes are classified in terms of fast feedbacks and of slow feedbacks (Hansen et al., 2007, 2008 [11][12]), defined as:

Fast feedbacks: changes of the hydrological cycle, water vapour, clouds, climate-driven aerosols, sea ice and snow cover.

Slow Feedbacks: changes in continental ice sheets, regional vegetation cover, accumulation of greenhouse gases, long term ocean current and wind patterns, position of high pressure ridges, migration of climate zones and frequency and amplitude of the ENSO cycle, consequent on changes in cross-latitude thermal gradients.

Estimates of climate sensitivity for Slow feedback processes are near double Charney’s CS value (Hansen et al., 2008 [12]) (Figure 3). Paleoclimate studies by Pagani et al. (2010) define early and mid-Pliocene (5.2 – 3.0 Ma) climate sensitivities at values in the range of 7.1–9.6, classified by Schneider and Schneider (2010) as “Earth system sensitivity”, with implications for 21st century climate projections (Figure 3). As continent-ocean patterns in the Pliocene were similar to the present, projections of such high CS values to the 21st century imply that, at CO2 levels of 389 ppm, atmospheric energy level is consistent with Pliocene levels, when temperatures were about 3 to 4oC higher than at present.

The significance of the Pliocene analogy to current climate change trends is recognized by the US Geological Survey, which has instigated a major research program (PRISM: Pliocene Research, Interpretation, and Synoptic Mapping). Results to date indicate extensive melting of the polar ice caps, sea level 25±12 meters higher than at present, a strong hydrological cycle and a shift of tropical and subtropical climate zones toward the poles (Haywood and Valdes, 2004 [13]; Haywood and Williams, 2005 [13]; Robinson et al., 2008 [20]; Chandler, 1997) [5](Figure 4).

Figure 4 Figure 4: Albedo changes model for the mid-Pliocene (Chandler, 1997) NASA. Note the larger extent of the deserts (Sahara, Gobbi and Mexico) in the Holocene and of vegetated savanna and of boreal forest in the sub-Arctic and Greenland in the Pliocene.

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During the early Pliocene, as rainforests contracted, hominoids bipeds descended from the trees, subsequently migrating through the savanna. Fast track transition of current climate towards similar conditions will increase evaporation and precipitation in some desert areas (cf. the Kimberley-Pilbara-Officer Basin-Nullabor corridor), whereas polar-ward migration of climate zones would result in droughts in the southeast and southwest Australian wheat belts, consistent with current developments. Calibration of Pliocene sea level rise to temperatures indicates 6-8 meters per 1 degree C, commensurate with reduction of the Greenland and west Antarctic ice sheets by approximately 50±25%.

Current climate trends are consistent with lessons from paleo-climate studies, including:

  1. Enhancement of the frequency and amplitude of the El-Nino phase, and decline of the La Nina phase, of the ENSO cycle (Figure 5), i.e. tracking in the opposite direction to the overall cooling trend recorded from the Pliocene to present (Figure 6).
  2. Increase melting of the large continental ice sheets and the rate of sea level rise (Figure 7)
  3. Polar-ward migration of climate zones, expressed by droughts (Figure 8).
  4. Increase in frequency or/and magnitude of extreme weather events (hurricanes, fires, floods) arising from higher atmospheric energy levels and affecting global insurance costs (Figure 9).

Figure 5 Figure 5. Monthly Southern Oscillation Index (SOI) based on standardized sea level pressure (SLP) difference data measured between Tahiti and Darwin, Australia from 1950 to the present. Note the increase in intensity and frequency El-Nino states from about 1983. NOAA SOI

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Figure 6 Figure 6: Pliocene to present sea surface temperature (0C) records in the western equatorial Pacific (red line, ODP site 806) and in the eastern equatorial Pacific (blue line, site 847), both based on Mg/Ca, and for the eastern Pacific based on alkenones (green dots). Pink shading denotes the early Pliocene. Fedorov et al. 2006. [Science]
Note the temporal divergence of west and east Pacific temperatures, indicating increased role of the La Nina – El Nino polarity.

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Figure 7 Figure 7: Rates of observed recent surface elevation change for Greenland (left: 1989–2005) and Antarctica (right: 1992–2005). Red hues indicate a rising surface and blue hues a falling surface, which typically indicate an increase or loss in ice mass at a site, although changes over time in bedrock elevation and in near-surface density can be important.
IPCC AR4 WG1.

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Figure 8 Figure 8: Catastrophic declined in global food production: 2008–09 droughts. Source: Market Skeptics

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Figure 9 Figure 9: Rising disasters and insurance costs between 1950 and 2006: Values in $billion. Source: Draeger-Stiftung.de

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Current climate change is distinct from and originates due to different factors which drove Pleistocene glacial terminations (420, 320, 230, 125, 14 thousand years-ago), when Milankovic cycle insolation peaks at mid-northern latitudes induced extensive melting of the Greenland and Fennoscandian ice sheets. This was followed by warming of the oceans, reduced CO2 solubility and a rise from 180 to 280 ppm CO2 at a lag of about 800 years behind temperature rise. By distinction, the solar factor since 18th century has risen only by 0.12 Watt/m2, while global warming induced by carbon emissions rose by c.2,48 Watt/m2 (CO2+CH4+Halocarbons; Figure 10)

As distinct from insolation-induced warming, the greenhouse effect displays the following fingerprints:

Warming in the lower atmosphere (troposphere) and cooling in the stratosphere (due to the downward component of backscatter).

  1. Greater degree of warming near the poles relative to the tropics, including relatively high winter temperatures, due to elevated atmospheric greenhouse gas all-year round.
  2. More hot days and nights, fewer cold days and nights, i.e. due to lesser loss of heat into the stratosphere overnight. Consequently, a reduction in the difference between daytime and night-time temperatures

Prior to about 1975-1976 the effects of greenhouse gases, solar forcing, ocean currents, the El-Nino Southern Oscillation (ENSO) cycle and aerosol albedo on mean global temperature were difficult to separate (Solanki, 2002 [23]). 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 exceeds the rate of the last glacial termination (14,700 – 11,700 years ago) by an order magnitude. Climate change trends since the 1990s continue the sharp accentuation of temperature rise rates from the mid-1970s, with strong fluctuations related to the El-Nino (e.g. 1998) and La Nina effects (e.g. 2007-2009). Principal climate change developments 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, exceeds 1850-1970 rates by factors of ~4 to 5 and is two orders of magnitudehigher than mean CO2 rise rates of the last glacial termination (~0.014 ppm/yr) (Rahmstorf et al., 2007 [17]; Global Carbon Project, (2008) [9].
  2. Methane (CH4), which after ~20 years has 23 times the greenhouse warming effect of CO2, has been rising during 1850-1970 at a rate of ~ 5.4 ppb/yr, and has risen by 10 ppb during 2007 (http://web.mit.edu/newsoffice /2008/techtalk53-7.pdf). Methane deposits potentially vulnerable to climate change reside in permafrost (~ 900 Billion ton Carbon – GtC), high latitude peat lands (~ 400 GtC), tropical peat lands (~ 100 GtC), vulnerable vegetation (~ 650 GtC) and methane hydrates and clathrates in the ocean and ocean floor sediments (> 16,000 GtC). These deposits exceed the levels of atmospheric carbon (~750 GtC), carbon emissions to date (~ 370 GtC) and known economic carbon reserves (~6000 GtC). Recently elevated methane release was recorded from Arctic Sea sediments and sub-Arctic permafrost (Walter et al., 2006 [28]; Rigby, 2008 [18]).
  3. A rise of mean Arctic and sub-Arctic temperatures in 2005-2008 by near +2.4C since 1970, underlining the critical role the poles have in global warming.
  4. Arctic Sea ice melt rates of ~ 5.4% per-decade since 1980, increasing to >10% per year during 2006-2007 (National Snow and Ice Data Centre [NSIDC], 2008).
  5. Greenland and WestAntarctica warming and ice melting (Figure 7) at rates of >10% per decade culminating in mid-winter ice shelf breakdown (Wilkinsice shelf; June, 2008, NSIDC, 2008).
  6. Slow-down of the North Atlantic thermohaline conveyor belt and down-welling water columns (NASA, 2004; Bryden et al., 2005) [4], with attendant danger of its cessation analogous to conditions ~8.2 kyr ago (Alley et al., 2000, 2003 [1] [2][1,2]).
  7. Temperature projections for the North Atlantic Ocean (Keenlyside et al., 2008 [15]) may be consistent with slowdown of the Gulf Stream, due to potential effects of Greenland ice melt waters.
  8. Increased frequency and intensification of categories 4 and 5 hurricanes (Webster et al., 2005 [31]).

The polar ice sheets serve as the “thermostat” of glacial conditions which commenced at 34 Ma when CO2 levels declined to below 500 ppm (Figure 1), enhancing the flourishing of large mammals, rendering the decline of Greenland and Antarctic ice sheets of particular concern. NASA satellite gravity and microwave measurements indicate a doubling of Greenland ice melt areas per-decade (NASA 2006). Rates of ice loss of the Greenland ice sheet have increased from 0.05±0.12 mm/yr during 1961–2003 to 0.21±0.07 mm/yr during 1993-2004. The measurements indicate an increase in ice sheet melt area by 16% from 1979 to 2002 (Steffen and Huff, 2002 [24]; Steffen et al., 2004 [25]; NASA, 2006; Hanna et al., 2005 [10]; IPCC-2007; Hansen et al., 2007 [11]). Time-variable gravity measurements from the GRACE (Gravity Recovery and Climate Experiment) satellites of mass variations of the Antarctic ice sheet during April 2002–August 2005 detected a decrease in the mass of the ice sheet at a rate of 152±80 cubic kilometres of ice per year. Most of this mass loss came from the west Antarctic Ice Sheet, including a water equivalent decrease in ice thickness of -1 to -4 cm/year for the Antarctic peninsula and the Ross Sea-Amundsen shelf area (Rignot and Thomas, 2002 [18]; Chen et al., 2006 [6]; Velicogna and Wahr, 2006 [19]). GRACE-based estimates by Chen et al. (2006) [7] identify ice loss of 77±14 km3/year in West Antarctica and gain of +80±16 km3/year in Enderby Land of East Antarctica.

Figure 10 Figure 10: Global mean radiative forcings and their 90% confidence intervals in 2005 for various agents and mechanisms. Columns on the right-hand side specify best estimates and confidence intervals; typical geographical extent of the forcing (Spatial scale); and level of scientific understanding (LOSU) indicating the scientific confidence level. The net anthropogenic radiative forcing and its range are also shown.
IPCC AR4 WG1

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Figure 10 summarizes the various global mean radiative forcings operating on the terrestrial atmosphere from 1750AD. Temperature rise due to total positive forcing of +3.16 Watt/m2 (CO2, CH4, N2O, Halocarbons, ozone, stratospheric vapour due to methane, black carbon) is partly masked by negative feedbacks of -1.45 Watt/m2 (depletion in stratospheric ozone, increase in surface albedo due to land use, albedo effects of aerosols and aerosol effects on clouds). The balance of +1.71 Watt/m2 translates to a potential temperature rise of about 1.3oC. Once the masking effects of aerosols are removed, potential temperature rise would approach near 2oC.

A perspective on current carbon emissions arises from factors underlying the big mass extinction of species, including the end-Devonian (359 Ma; 450 – 1275 ppm CO2; 40% extinction of Genera), Permian-Triassic (251 Ma; 3550 ppm CO2; 80% extinction of Genera), end-Triassic (216.5 Ma and 199.6 Ma; 1300-2200 ppm CO2; 18 – 34% extinction of Genera) and Cretaceous-Tertiary boundary (65.5 Ma; 2300 ppm CO2; 46% extinction of Genera) (Keller, 2005 [16]). Consistent lines of evidence, including basic physical laws, multiproxy-based paleo-climate studies and direct measurements from ground stations, balloons and satellites, suggest societies need to pause before proceeding with open-ended emission of carbon gases into the terrestrial atmosphere.

References

Recent comprehensive compilations of climate change evidence include: (A) Global Risks, Challenges and Decisions. Copenhagen 10-12 March, 2009. http://climatecongress.ku.dk/pdf/synthesisreport (B) Steffen, W., 2009. Climate Change 2009. Faster change and more serious risks. Australian Government Department of Climate Change. (C) Oxford Conference “4 Degrees and Beyond”. 28-30 September, 2009. http://www.eci.ox.ac.uk/4degrees/programme.php

[1] Alley, R.B., 2000. Ice-core evidence of abrupt climate changes. Proceedings of the National Academy of Science, 97, 1331-1334.

[2] Alley, R.B. et al., 2003. Abrupt Climate Change, Science, 299, 2005–2010.

[3] Breecker D.O. et al., 2010. Atmospheric CO2 concentrations during ancient greenhouse climates were similar to those predicted for 2100 A.D. Proceedings of the National Academy of Science, 107, 576–580.

[4] Bryden, H.L. et al., 2005. Slowing of the Atlantic meridional overturning circulation at 25N. Nature, 438, 655-657.

[5] Chandler, M., 1997. The Climate of the Pliocene: Simulating Earth’s Last Great Warm Period.

[6] Charney, J., 1979. Carbon Dioxide and Climate: A Scientific Assessment. National Academy of Sciences Press: Washington DC 1979, 33 pp.

[7] Chen, J.L., Wilson, C.R., Blankenship. D.D., Tapley, B.D., 2006. Antarctic mass rates from GRACE. Geophysical Research Letters, 33, L11502.

[8] Eby, M. et al. 2009. Lifetime of Anthropogenic Climate Change: Millennial Time Scales of Potential CO2 and Surface Temperature Perturbations. Journal of Climate, 22, 2501-2511.

[9] Global Carbon Project, 2008. http://www.globalcarbonproject.org/

[10] Hanna, H. Et al., 2005. Runoff and mass balance of the Greenland ice sheet: 1958–2003. Journal Geophysical Research, 110, D13108.

[11] Hansen, J. et al., 2007. Climate change and trace gases. Philosophical Transactions of the Royal Society, A365, 1925-1954.

[12] Hansen, J. et al., 2008. Target atmospheric CO2: Where should humanity aim? Open Atmospheric Science Journal, 2, 217-231.

[13] Haywood, A. M. & Valdes, P. J., 2004. Modelling Pliocene warmth: Contribution of atmosphere, oceans and cryosphere. Earth Planetary Science Letters, 218, 363-377.

[14] Haywood, A. & Williams, M., 2005. The climate of the future: clues from three million years ago. Geology Today, 21, 138-143.

[15] Keenlyside, N.S. et al., 2008. Advancing decadal-scale climate prediction in the north Atlantic sector. Nature, 453, 84-88.

[16] Keller, G., 2005. Impacts, volcanism and mass extinctions: random coincidence or cause and effect. Australian Journal of Earth Science, 52, 725–757.

[17] Rahmstorf S.R. et al. 2007. Recent Climate Observations Compared to Projections. Science Express, 0.1126/ science. 1136843.

[18] Rigby, M., 2008. Geophysical Research Letters. http://www.newscientist.com/article/dn15079

[19] Rignot, E., Thomas, R.H., 2002. Mass balance of polar ice sheets. Science, 297, 1502-1506.

[20] Robinson, M.M. et al., 2008. Pliocene role in assessing future climate impacts. EOS, 89, 501–512.

[21] Royer, D.L. et al. 2001. Phanerozoic atmospheric CO2 change: evaluating geochemical and paleobiological approaches. Earth-Science Reviews, 54, 349–392

[22] Royer, D.L. 2010. Fossil soils constrain ancient climate sensitivity. PNAS, 107, No. 2, 517–518.

[23] Solanki, S.K., 2002. Solar variability and climate. Change: is there a link? Solar physics, 43, 5.9-5.13.

[24] 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.

[25] Steffen, K. Et al., 2004. The melt anomaly of 2002 on the Greenland Ice Sheet from active and passive microwave satellite observations. Geophysical Research Letters, 31 (20).

[26] Velicogna, I., Wahr, J. 2006. Measurements of Time-Variable Gravity Show Mass Loss in Antarctica, Science, 311.

[27] Veron, J.E.N., 2008. Mass extinctions and ocean acidification: biological constraints on geological dilemmas. Coral Reefs, 27, 459-472

[28] Walter, K.M., Smith, L.C., Chapin, F.S., 2005. Methane bubbling from Siberian thaw lakes as a positive feedback to climate warming. Nature, 443, 71-75.

[29] Ward, P.D., 1994. The End of Evolution: On Mass Extinctions and the Preservation of Biodiversity. Bantam, New York.

[30] Ward, P.D., 2007. Under a Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Can Tell Us About Our Future. HarperCollins, NY, 135 pp.

[31] Webster, P.J. et al., 2005. Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment, Science, 309, 1844-1846.

Note for commenters:

Please stick to the evidence and the topic. Comments will be edited or moved if they are off-topic, impolite or relate to people or motivations. As you write, imagine that readers who are undecided are genuinely interested in finding out arguments both for and against the theory of man-made global warming. Ad homs will be deleted. Thanks — JN

Late 20th century and early 21st century CO2 rise rate average 1.45 ppm/yr, rising to 2.2 ppm/yr in 2007, exceeds 1850-1970 rates by factors of ~4 to 5 and is two orders of magnitudehigher than mean CO2 rise rates of the last glacial termination (~0.014 ppm/yr) (Rahmstorf et al., 2007 [17]; Global Carbon Project, (2008) [9].

LATE NOTE: Table 1 was inadvertantly left out, and has been added in 26-5-10. My apologies.

The Full Debate:

Part I: AG / JN;

Part II: AG / JN

Part III: AG / Part III & IV: JN (& AG). (Part IV took place in the comments below Part III).

Part V: AG / JN (this page).

Part VI: Dr Glikson asked to respond again. I said I’d be happy to post another reply from him. That offer remains open.

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