Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.

Settings

Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup

Settings


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Support

Bluesky Facebook LinkedIn Mastodon MeWe

Twitter YouTube RSS Posts RSS Comments Email Subscribe


Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...



Username
Password
New? Register here
Forgot your password?

Latest Posts

Archives

Can you make a hockey stick without tree rings?

Posted on 2 December 2009 by John Cook

When "Climategate" first broke, I noted the skeptic preoccupation with one tiny piece of climate science while neglecting the full weight of direct observations of current global warming. That tiny piece is paleoclimatology: the reconstruction of past temperature. However, upon reflection, I may have oversold the skeptic position. The focus is on one particular method of that tiny piece: tree ring proxies. In the field of paleoclimatology, there are a variety of independent methods to determine past temperature changes: tree rings, ice cores, lake sediments, boreholes, stalagmites, etc. What do these independent methods find?

Surface temperature changes send thermal waves underground, cooling or warming the subterranean rock.  Boreholes can be used to measure these changes. In Huang 2000, underground temperature measurements were examined from over 350 bore holes in North America, Europe, Southern Africa and Australia. Borehole reconstructions aren't able to give annual or even decadal variation, yielding only century-scale trends. What they find is that the 20th century is the warmest of the past five centuries. This provides independent confirmation that the Earth is warming dramatically (the blue line is the instrumental record). 
 


Figure 1: Global surface temperature change over the last five centuries from boreholes (thick red line). Shading represents uncertainty. Blue line is a five year running average of HadCRUT global surface air temperature (Huang 2000).

Stalagmites (or speleothems) are formed from groundwater within underground caverns. As they're annually banded, the thickness of the layers are used as climate proxies. Figure 2 shows a Northern Hemisphere temperature reconstruction from stalagmites. While the uncertainty band (grey area) is significant, the temperature in the latter 20th Century exceeds the maximum estimate over the past 500 years.


Figure 2: Northern Hemisphere annual temperature reconstruction from speleothem reconstructions shown with 2 standard error (shaded area) (Smith 2006).

Oerlemans 2005 used historical records of glacier length as a proxy for temperature. As the number of monitored glaciers diminishes in the past, the uncertainty grows accordingly. Nevertheless, temperatures in recent decades exceed the uncertainty range over the past 400 years.


Figure 3: Global mean temperature calculated form glaciers. The red vertical lines indicate uncertainty.

Of course, these examples only go back as far as 500 years - this doesn't even cover the Medieval Warm Period. When you combine all the various proxies, including ice cores, coral, lake sediments, glaciers, boreholes & stalagmites, it's possible to reconstruct Northern Hemisphere temperatures without tree-ring proxies going back 1,300 years (Mann 2008). The result is that temperatures in recent decades exceed the maximum proxy estimate (including uncertainty) for the past 1,300 years. When you include tree-ring data, you find the same result for the past 1,700 years.


Figure 4: Composite Northern Hemisphere land and land plus ocean temperature reconstructions and estimated 95% confidence intervals. Shown for comparison are published Northern Hemisphere reconstructions (Mann 2008).

Paleoclimatology draws upon a range of proxies and methodologies to calculate past temperatures. This allows independent confirmation of the basic hockey stick result: that the past few decades are the hottest in the past 1,300 years.

0 0

Printable Version  |  Link to this page

Comments

Prev  1  2  

Comments 51 to 51 out of 51:

  1. Although regional in context, Aono's data documenting the start of the Kyoto Cherry Blossom Festival also describes a hockey stick: The Ljungqvist and the Loehle reconstructions are present on this graph because I originally collated the data in response to one of Tim Lambert's Deltoid posts.
    0 0
    Moderator Response: [mc] Please restrict image width to 500 or less.

Prev  1  2  

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.



The Consensus Project Website

THE ESCALATOR

(free to republish)


© Copyright 2024 John Cook
Home | Translations | About Us | Privacy | Contact Us