Climate & Climate Change

In yesterday’s The Australian science writer Leigh Dayton claims that the northern hemisphere is hotter now than at any time in the past 1500 years. The article qualified her comment with this is “according” to the most comprehensive reconstruction of the earth’s temperature over the last two millenniums.

Dayton is referring to new research soon to be published by Michael Mann – the climate scientist credited with the now infamous 1998 “hockey stick” graph that shows a sharp uptick beginning around 1900 and that featured prominently in the 2001 IPCCs Third Assessment Report.

The graph was contested from the beginning because it did not show the medieval warm period and then
Canadians Stephen McIntyre and Ross McKitrick were unable to replicate Manns’ results and Mann initially refused to provide them with all the input data. The saga is detailed in various publications** and a chapter in Aynsley Kellow’s book ‘Science and public policy: The virtuous corruption of virtual environmental science’

I wonder how his new research by Mann has dealt with the medieval warm period ? Indeed I wonder how, after all the controversy surrounding Mann’s earlier work, Dayton can so uncritically report something so at odd with what is know about the history of Europe over the last 2,000 years.

Update: The paper is available on line
Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia. PNAS, September 9, 2008, vol. 105, no 36.
http://holocene.meteo.psu.edu/shared/articles/MannetalPNAS08.pdf

hat tip to Nexus 6 for the update/link.

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** The following text including citations is from Ross McKitrick’s website:

Hockey Sticks, Principal Components and Spurious Significance Geophysical Research Letters, Vol 32(3), Feb 12 2005, copyright 2005 American Geophysical Union (doi: 2004GL012750). Further reproduction or electronic distribution is not permitted. This is a preprint of the GRL paper that shows Mann’s program mines for hockey sticks and overstates the statistical significance of the final result. There have been 4 technical comments submitted to GRL in response. We submitted replies to all 4, and they were sent out for refereeing. Two of the comments have been rejected by GRL. The two that were published were accompanied by our replies. These exchanges are discussed below.

The M&M Critique of the MBH98 Northern Hemisphere Climate index: Update and Implications Energy and Environment 16(1)69-100. AVAILABLE ON-LINE AT ENERGY AND ENVIRONMENT by kind permission of the publisher. This paper shows how Mann’s results can be reconciled to our results based on handling of the PC algorithm and a Gaspe cedar ring series. We also discuss the bristlecone pines in detail and show why they should not have been included in the original data set.

“Corrigendum” by Mann, Bradley and Hughes. Nature 430, July 1, 2004 p. 105. This arose from our Materials Complaint to Nature in the winter of 2004. The story is detailed on the page about our dealings with Nature (see below–link to Archive).

“Verification of multi-proxy paleoclimate studies: A case study”. Accepted abstract for presentation at American Geophysical Union Meetings in San Francisco, December 2004. Steve travelled to the AGU in December 2004 and presented our research–this was the abstract.

“Corrections to the Mann et al (1998) Proxy Data Base and Northern Hemisphere Average Temperature Series” Energy and Environment 14(6) 751-772.
This is the paper that started the whole ball rolling!

Studies of Pleistocene glacial-interglacial cycles based on sediments and ice cores back to 640 000 years (640 kyr) document abrupt initiation of global warming and cooling events over short time scales of decades to a few years, implying extreme instability of the Earth’s atmosphere, with implications for 21st century climate change projections.

Current rise rates of atmospheric radiative forcing toward ~450 ppm CO2 are tracking toward an ice-free Earth.

Time tables of carbon emission reduction targets which take little account of the rates of ice sheet melt/water feedbacks and carbon cycle feedbacks, including release of methane hydrates from sea bottom sediments and from bogs, are unlikely to be able to prevent runaway global warming on a scale similar to the last glacial terminations.

Extreme climate change events in the recent history of Earth include:

A. Intra-glacial warming cycles, termed Dansgaard-Oeschger (D-O cycles), between 80 kyr and 20 kyr, including 21 ~1470 years-long cycles, each initiated over decades-scale time frames (Figure 1). The D-O cycles are attributed to interactions between weak solar radiation maxima and ocean current systems [1, 2].

Figure 1. An example of a Dansgaard-Oeschger abrupt climate event. 1 of 21 cycles during the alst ice age, 80 000 – 20 000 years-ago. Greenland ice core. From Rahmstorf, 2004.

B. Evidence for the last glacial termination based on deuterium and oxygen isotopes from the Greenland NGRIP ice core indicates sharp 3-years-long warming by 2 to 4oC at 14.7 kyr, sharp 1 year-long cooling at 12.9 kyr, and sharp 3 years-long warming at 11.7 kyr (Figure 2) [3].

Figure 2. deuterium-drived determinations of temperatures from Greenland NGRIP ice core for the period 14 740 – 11 660 years-ago, displaying abrupt warming and cooling changes between the ‘oldest dryas’ cold period, Allerod and Bolling warm periods, youngest dryas cold period and the Holocene. Note transitions occur over periods of 1 – 3 years. From Steffensen et al., 2008.

C. Evidence for the last glacial termination from the Greenland GISP-2 ice core, based on Nitrogen and Argon isotopes, indicates abrupt warming by 10±4oC at 12.8 kyr over a period of ~100 years and abrupt warming by 4±1.5 oC at 11.27 kyr over period of 70 years [4]. Sea level rose by 40 metres following the termination up to about 8500 years-ago [5].

Mean global temperature changes are estimated as about half the polar temperatures.

The origin of the D-O cycles is interpreted in terms of interaction between weak insolation signals and the thermohaline current system [2]. Glacial terminations at intervals of about 100 kyr, 41 kyr and 23 kyr (Milankovich cycles) were triggered by axial tilt toward the poles, elevating mid-June insolation by up to <60 Watt/m2 at latitude 65N [6]. The glacial terminations involved mean global solar radiation anomalies of 4 to 5 Watt/m2, triggering ice melt feedback loops and greenhouse gas release loops [6]. The intertwined synergy of these processes resulted in: (1) Ice sheet and glacier melt, reduced short-wave reflection (albedo) by sea ice and ice sheets, exposure of water surfaces absorbing infrared, further melting of ice by warming water, migration of boreal forest northward causing decrease in albedo. (2) Carbon gases (CO2, CH4) released from warming oceans, drying biosphere and fires; methane released from sea-bottom methane hydrates (clathrates: water-CH4 molecules) in sea bottom sediments and from drying bogs. Rapid release of methane hydrates is invoked as a mechanism for a runaway greenhouse effect and consequent mass extinctions through the history of Earth, specifically the Permian-Triassic (251 Ma) mass extinction and the Paleocene-Eocene (55 Ma) extinction (~ +6oC global warming) [7] The combined radiative synergy of ice melt-feedback and greenhouse gases-feedback triggering rapid polar meltdown affected pole-ward migration of the inter-tropical convergence zone (ITCZ), subtropical arid zone and mid-latitude zones, affecting the ocean thermohaline circulation. The Greenland ice-melt flow result in abortion of the Gulf Stream which warms Europe and northeast America. Warming of the southern oceans weakens the Humboldt current west of South America and the trade winds, indirectly enhancing El-Nino events which result in droughts in the southwestern Pacific, India and Africa [8]. The rise in mean global temperature by several degrees Celsius over time scales of a few years to a century testifies to a high susceptibility of the atmosphere to minor to moderate energy forcings. According to Hansen et al. 2007 [6] the solar energy pulse from orbital variations which triggered the glacial terminations is up to 0.25 Watt/m2. Mean global atmospheric energy rise associated with the glacial terminations of +4 to +5 Watt/m2 (~ +5 to +7oC) are consistent with the upper range of the IPCC projections for the 21st century, +1.1 to +6.4oC. Comparisons between abrupt glacial-interglacial terminations and 21st century projections are complicated by the lower mean global temperatures at which the glacial terminations commenced and the large volumes of ice compared to the Holocene, including the Laurentian and Fennoscandian ice sheets. The fast rise of the greenhouse gas forcing component since the mid-1800s, at rates since 1960 reaching 387 ppm in 2007 at rates of >1.6 ppm/year, are two order of magnitude higher than CO2 rise rates of 0.012 ppm/year at the last termination. Where 1 ppm CO2 induces an atmospheric energy rise of ~0.02 Watt/m2, this equates to an increase of 1.7 Watt/m2 in atmospheric radiative energy since 1750, not counting carbon cycle and ice melt feedbacks.

The non-linear nature of atmospheric CO2 and CH4 rise, from 1.3%/year in 1990-1999 to 3.3%/year in 2000-2006 [9], combined with further ice melt and albedo decline and carbon cycle feedback effects, including release of CH4 hydrates, drying/burning biosphere, reduced CO2 sequestration by the oceans, threatens to move the Earth’s atmosphere into glacial termination-like conditions. Rapid ice melt rates in Greenland, the Arctic Sea and west Antarctica, the latter continuing through the southern winter, are documented from satellite and on the ground. The polar ice sheets, initiated about 34 million years ago, when CO2 levels declined below 450 ppm, are in danger.

The Earth’s climate is tracking into uncharted territory.

Andrew Glikson
Canberra, Australia

Andrew Glikson undertakes earth and paleo-climate research at the Research School of Earth Science, Australian National University.

[1] Broecker, 2000. Earth-Science Reviews 51, 137–154;
[2] Braun et al., 2005. Nature, 438)
[3] Steffensen et al., 2008. Science Express, 19 June, 2008 ;
[4] Kobashi et al., 2008. Earth Planet. Sci. Lett, 268, 397 ;
[5] Siddall et al., 2003. Nature 423, 853.
[6] Hansen et al., 2007. Phil. Trans. Roy. Soc. London 365A, 1925. Hansen et al., 2008. Am. J. Sci (in press;
[7] Zachos et al., 2008. Nature 451 (7176): 279; Ryski, 2003. Geology; 31, 741;
[8] Trenberth et al., 2002). J. Geophys. Re. 107, 4065..
[9] International Carbon Project 2006. Recent Carbon Trends and the Global Carbon
http://www.globalcarbonproject.org/global/ppt/774,1,

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In 1610 Galileo observed dark features on the face of the sun – sunspots. In the preface to a little book Galileo wrote on sunspots that was published in 1613, he was credited with having discovered sunspots but an Englishman, Thomas Harriott, and a Dutchman, Johann Fabricius, probably beat him to that discovery.

What we do know is that since the invention of the telescope, Europeans have been keenly observing sunspot activity and some have been correlating it with global temperatures.*

The US National Oceanic and Atmospheric Administration (NOAA) publishes the mean monthly sunspot number back to January 1749.

There were no sunspots during a period of unusual cold in the northern hemisphere known as the Maunder Minimum which extended some 70 years from 1645 to 1715.

Because the number of sunspots has shown a general trend of decline since March 2006 there has been much chatter amongst global warming skeptics with some suggesting that we are perhaps in for an extended period of cooling

Now there is more excitement, because August 2008 appears to be the first month since June 1913 without a sunspot.

[But perhaps I should wait until there is a zero recorded at the official NOAA site before announcing this?]

David H. Hathaway, Solar Physics Team Leader at the NASA Marshall Space Flight Center in Huntsville, has suggested that this solar cycle 24 is just taking a while to get started.

Habibullo I. Abdussamatov, head of the space research laboratory of the Russian Academies of Sciences’ Pulkovo Observatory and of the International Space Station’s Astrometry project, has predicted for some time that because of low solar activity we may be entering another period similar to the late 17th century and that this may start in 2012-2015 and reach its peak in 2055-2060.**

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* Why few sunspots could correlate with low tempertures by Richard Mackey:

“The Earth’s geomagnetic field provides a buffer against solar radiation, the solar wind and radiation of all types generated elsewhere in the Universe. The field’s strength depends on solar output and the lunisolar tides. A stronger geomagnetic field will deflect more cosmic radiation than a weaker one.

“A highly active Sun can make the geomagnetic field stronger; a relative inactive Sun will make it weaker. Other things being equal, a strong geomagnetic field contributes to a warmer climate; a weaker field to a cooler climate. But the effect may not be uniform across the planet. Currently, the geomagnetic field seems to be weakening, contributing to global cooling.

“The heliosphere, and the termination shock sphere within it, deflects cosmic radiation. The Earth’s geomagnetic field also deflects cosmic radiation. The strength of the heliosphere depends on the Sun’s activity levels. High levels of solar activity reduce the volume of cosmic rays entering the Earth’s atmosphere, contributing to global warming. High levels of solar activity generate more turbulence in the heliosphere scattering galactic cosmic rays before they reach the inner planets. Conversely, a greater volume of cosmic rays enter our atmosphere during times of low solar activity because the Heliospheric magnetic fields are smoother with less scattering of galactic cosmic rays, resulting in global cooling.”

(from ‘Much more to the Earth’s Climate than human activity’, Submission to the Garnaut Climate Change Review by Richard Mackey, February 2008)

** Lawrence Solomon profiled Dr Abdussamtov in a piece entitled Look to Mars for the truth on global warming, The Deniers — Part IX, Financial Post Published: Friday, February 02, 2007.

Published papers by Dr Abudssamotov predicting cooling include: ‘Optimal Prediction of the Peak of the Next 11-Year Activity Cycle and the Peaks of several Succeeding Cycles on the basis of Long-Term Variations in the Solar Radius or Solar Constant’, Kinematics and Physics of Celestial Bodies, 2007, Vol. 23, No. 3, pp 97-100, and ‘Long-Term variations of the Integral radiation Flux and Possible Temperature Changes in the Solar Core’, Kinematics and Physics of Celestial Bodies, Vol. 21, No. 6, pp. 328-332, 2005.

According to a recent paper** published in the journal Nature, only a dramatic fall in atmospheric carbon dioxide levels are able to explain the transition from the mostly ice-free Greenland of three million years ago, to the ice-covered Greenland of today.

I am not convinced, but anyway, the paper begs the question, why did the purported elevated atmospheric carbon dioxide concentrations fall to levels similar to the pre-industrial era?

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** Late Pliocene Greenland glaciation controlled by a decline in atmospheric CO2 levels, Nature 454, 1102-1105 (28 August 2008), by Daniel J. Lunt, Gavin L. Foster, Alan M. Haywood and & Emma J. Stone.

Read the University of Bristol media release here.