Let's talk about Climate change –

some details that may be new to you

David MacKay FRS

Department of Engineering
University of Cambridge

Former Chief Scientific Advisor
Department of Energy and Climate Change


 
Radiosondes data showing the Quasi-biennial oscillation of the stratospheric wind direction near the Equator

Data from Free University of Berlin
 

The "Lags or leads" story

 

Milankovitch cycles

 

The Paleocene-Eocene Thermal Maximum

Cumulative emissions

Predictions from Met office model

Shallow core from the Dyer Plateau, Antarctic Peninsula
Robert Mulvaney, British Antarctic Survey

Barlow et al, Stable Isotope Laboratory, University of Colorado, GISP2 "B" core
Lorius, Merlivat, Jouzel, and Pourchet, 1979 - Dome C

EPICA Dome C ice core


     

Temperature lags or leads CO2?



     

Temperature lags or leads CO2?

  • different mechanism on the way up and the way down (and neither mechanism is !)
  • abrupt climate change occurs during destruction of ice sheets, rather than during buildup

The last deglaciation


Average global temperature (blue), Antarctic temperature (red), and atmospheric CO2 concentration (yellow dots). nature/journal/v484/n7392/nature10915.html : Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation Jeremy D. Shakun et al (2012).

["Bipolar seesaw": Melting ice reduces the Atlantic meridional overturning circulation (AMOC), so that Southern Hemisphere gets more heat and North gets less, hence Antarctic temperature anomaly is below the global average temperature anomaly. During most of the deglaciation, CO2 leads temperature.]
[And yes, the initial global temperature rise was not preceded by CO2 rise.]

See also luthi and amoc
 

The "Lags or leads" story

 

Milankovitch cycles

 

The Paleocene-Eocene Thermal Maximum

Precession and the earth's elliptical orbit

(eccentricity is exaggerated - true eccentricity is 0.017 today)

by Greg Benson

Axial precession - 25,700 years
Ellipse precession - slower; combined effect has 21,000-23,000 year period
Obliquity has 41,000 year cycle
Eccentricity changes with 100,000 and 413,000 year period

Milankovitch cycles


"When Fourier analysis was applied to deep-sea records in 1975, it emerged that the oxygen-isotope series contained strong cycles with periods near 100,000 years, 41,000 years, and 23,000 years. These are precisely the periods expected if Earth's orbital elements (eccentricity, obliquity, and precession) govern ice-age climates, as proposed by Milankovitch Theory."
What drives Glacial Cycles, W Broecker and G. Denton, Scientific American, January 1990, pp.43-50

What drives Glacial Cycles, W Broecker and G. Denton, Scientific American, January 1990, pp.43-50

Solid line: astronomy; dotted line: geology (marine 18O/16O, a proxy for global ice volume)
Eccentricity forcing of Pliocene-Early Pleistocene climate revealed in a marine oxygen-isotope record, S. Clemens and R. Tiedemann, Nature vol. 385, 27 February 1997, pp. 801-804
EPICA Dome C ice core
December 2011
August 2013




The climate is a twitchy complex system, full of chaotic natural variability and potential instabilities



wouldn't it be handy if we could look at the results of a mega-carbon-release experiment?

The Paleocene-Eocene Thermal Maximum

Palaeocene/Eocene message:


A release of one or two trillion tonnes of carbon over a few thousand years led to a 6°C global temperature rise.

And mass extinctions.

It took 120,000 years for the carbon to be removed.


Challenged by Carbon - Bryan Lovell
Cambridge University Press (2009)





What's next?


Global-mean surface temperature 1880-2013 (NASA GISS data). Grey line shows annual values, the blue line a LOESS smooth to highlight the long-term evolution.

The size of future climate change depends on cumulative emissions


DECC/Met Office, adapted from IPCC 5th Assessment Report (2013)

Summer of 2003

Act!

Act!

[or, to be explicit... assess uncertainty, assess options, assess costs and damages, then use decision theory and game theory]

 
'Okay - it's agreed; we announce - "to do nothing is not an option!" then we wait and see how things pan out...'
Lowe, Private Eye

What pause?


skepticalscience.com



Temperature data, corrected for the ENSO effects Source: Real Climate

Global warming has not stopped

"The arctic had unusually little ice in 1922 too"


"The arctic had unusually little ice in 1922 too"

High-resolution carbon dioxide concentration record 650,000-800,000 years before present Dieter Lüthi, Martine Le Floch, Bernhard Bereiter, Thomas Blunier, Jean-Marc Barnola, Urs Siegenthaler, Dominique Raynaud, Jean Jouzel, Hubertus Fischer, Kenji Kawamura & Thomas F. Stocker
Nature 453, 379-382 (15 May 2008) doi:10.1038/nature06949

High-resolution carbon dioxide concentration record 650,000-800,000 years before present Dieter Lüthi, Martine Le Floch, Bernhard Bereiter, Thomas Blunier, Jean-Marc Barnola, Urs Siegenthaler, Dominique Raynaud, Jean Jouzel, Hubertus Fischer, Kenji Kawamura & Thomas F. Stocker
Nature 453, 379-382 (15 May 2008) doi:10.1038/nature06949

changes are about 12% of the mean (340 W/m2)

Information theory, inference, and learning algorithms


Cambridge University Press
Also available free online
www.inference.org.uk/mackay/itila/

This book is free online


www.withouthotair.com

This book is free online


www.withouthotair.com

The 2050 Calculator



2050-calculator-tool.decc.gov.uk
globalcalculator.org
source files: cd metapost; source climate.runme

this presentation was written in HTML using: Christian Steinruecken's 'slides.css' and 'slides.js'

manuals, examples, keyboard shortcuts