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It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
It’s warmer now than for the last 1,000years: true or false?
Peter Bloomfield
Department of Statistics, NCSU
October 13, 2006 / PAMS Alumni & Friends Weekend
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Outline
1 Background
2 Congress Gets Involved
3 The ScienceThe StatisticsWegman Panel ConclusionsNAS Panel Conclusions
4 Does It Matter?
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Global temperatures
On average, temperatures have been rising world-wide forthe last century:
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Intergovernmental Panel on Climate Change
1988: World Meteorological Organization (WMO) andthe United Nations Environment Programme (UNEP)establish the Intergovernmental Panel on ClimateChange (IPCC).IPCC publishes Assessments Reports every 5–6 years.
1990: First Assessment Report.1995: Second Assessment Report.2001: Third Assessment Report.Fourth Assessment Report is in preparation.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
The Past 1,000 Years
1990: IPCC publishes an estimate of how temperature haschanged over the past 1,000 years.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
The Past 1,000 Years revisited
2001: IPCC revises the history, based on work by MichaelMann and co-workers.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
The Hockey Stick
The “hockey stick” shape of the new graph suggests:steady cooling in Northern Hemisphere from AD 1000to around 1900;abrupt warming since then.
Becomes the icon of “global warming” :New analyses of proxy data for the NorthernHemisphere indicate that the increase intemperature in the 20th century is likely tohave been the largest of any century duringthe past 1,000 years. It is also likely that, inthe Northern Hemisphere, the 1990s was thewarmest decade and 1998 the warmest year.
Note. The grey shading indicates “statisticaluncertainty”:
Wide band, particularly before AD 1600.Often ignored–sigh. . .
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
The Hockey Stick
The “hockey stick” shape of the new graph suggests:steady cooling in Northern Hemisphere from AD 1000to around 1900;abrupt warming since then.
Becomes the icon of “global warming” :New analyses of proxy data for the NorthernHemisphere indicate that the increase intemperature in the 20th century is likely tohave been the largest of any century duringthe past 1,000 years. It is also likely that, inthe Northern Hemisphere, the 1990s was thewarmest decade and 1998 the warmest year.
Note. The grey shading indicates “statisticaluncertainty”:
Wide band, particularly before AD 1600.Often ignored–sigh. . .
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
The Hockey Stick
The “hockey stick” shape of the new graph suggests:steady cooling in Northern Hemisphere from AD 1000to around 1900;abrupt warming since then.
Becomes the icon of “global warming” :New analyses of proxy data for the NorthernHemisphere indicate that the increase intemperature in the 20th century is likely tohave been the largest of any century duringthe past 1,000 years. It is also likely that, inthe Northern Hemisphere, the 1990s was thewarmest decade and 1998 the warmest year.
Note. The grey shading indicates “statisticaluncertainty”:
Wide band, particularly before AD 1600.Often ignored–sigh. . .
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
The Hockey Stick
The “hockey stick” shape of the new graph suggests:steady cooling in Northern Hemisphere from AD 1000to around 1900;abrupt warming since then.
Becomes the icon of “global warming” :New analyses of proxy data for the NorthernHemisphere indicate that the increase intemperature in the 20th century is likely tohave been the largest of any century duringthe past 1,000 years. It is also likely that, inthe Northern Hemisphere, the 1990s was thewarmest decade and 1998 the warmest year.
Note. The grey shading indicates “statisticaluncertainty”:
Wide band, particularly before AD 1600.Often ignored–sigh. . .
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
The Hockey Stick
The “hockey stick” shape of the new graph suggests:steady cooling in Northern Hemisphere from AD 1000to around 1900;abrupt warming since then.
Becomes the icon of “global warming” :New analyses of proxy data for the NorthernHemisphere indicate that the increase intemperature in the 20th century is likely tohave been the largest of any century duringthe past 1,000 years. It is also likely that, inthe Northern Hemisphere, the 1990s was thewarmest decade and 1998 the warmest year.
Note. The grey shading indicates “statisticaluncertainty”:
Wide band, particularly before AD 1600.Often ignored–sigh. . .
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
The Hockey Stick
The “hockey stick” shape of the new graph suggests:steady cooling in Northern Hemisphere from AD 1000to around 1900;abrupt warming since then.
Becomes the icon of “global warming” :New analyses of proxy data for the NorthernHemisphere indicate that the increase intemperature in the 20th century is likely tohave been the largest of any century duringthe past 1,000 years. It is also likely that, inthe Northern Hemisphere, the 1990s was thewarmest decade and 1998 the warmest year.
Note. The grey shading indicates “statisticaluncertainty”:
Wide band, particularly before AD 1600.Often ignored–sigh. . .
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
What Happened to the Medieval Warm Period?
Major difference between 1990 and 2001 figures: theMedieval Warm Period disappeared.Reasons explored energetically by Stephen McIntyreand Ross McKitrick, despite difficulties in obtainingMann’s data and methods.M&M claim to find statistical flaws in Mann et al.’smethods, which can introduce spurious “hockey stick”trends.Blog wars: climateaudit.org versus realclimate.org.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
What Happened to the Medieval Warm Period?
Major difference between 1990 and 2001 figures: theMedieval Warm Period disappeared.Reasons explored energetically by Stephen McIntyreand Ross McKitrick, despite difficulties in obtainingMann’s data and methods.M&M claim to find statistical flaws in Mann et al.’smethods, which can introduce spurious “hockey stick”trends.Blog wars: climateaudit.org versus realclimate.org.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
What Happened to the Medieval Warm Period?
Major difference between 1990 and 2001 figures: theMedieval Warm Period disappeared.Reasons explored energetically by Stephen McIntyreand Ross McKitrick, despite difficulties in obtainingMann’s data and methods.M&M claim to find statistical flaws in Mann et al.’smethods, which can introduce spurious “hockey stick”trends.Blog wars: climateaudit.org versus realclimate.org.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
What Happened to the Medieval Warm Period?
Major difference between 1990 and 2001 figures: theMedieval Warm Period disappeared.Reasons explored energetically by Stephen McIntyreand Ross McKitrick, despite difficulties in obtainingMann’s data and methods.M&M claim to find statistical flaws in Mann et al.’smethods, which can introduce spurious “hockey stick”trends.Blog wars: climateaudit.org versus realclimate.org.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Outline
1 Background
2 Congress Gets Involved
3 The ScienceThe StatisticsWegman Panel ConclusionsNAS Panel Conclusions
4 Does It Matter?
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Congressional Duel
2005: U.S. House of Representatives Committees becomeinterested.
Representatives Joe Barton (R, Texas), Chair of theHouse Committee on Energy and Commerce, and EdWhitfield (R, Kentucky), Chair of its Subcommittee onOversight and Investigations, ask Mann and others toprovide extensive background on their work.Representative Sherwood Boehlert (R, New York),Chair of the House Committee on Science, has“strenuous objections” to the request, finding it“misguided and illegitimate.”
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Congressional Duel
2005: U.S. House of Representatives Committees becomeinterested.
Representatives Joe Barton (R, Texas), Chair of theHouse Committee on Energy and Commerce, and EdWhitfield (R, Kentucky), Chair of its Subcommittee onOversight and Investigations, ask Mann and others toprovide extensive background on their work.Representative Sherwood Boehlert (R, New York),Chair of the House Committee on Science, has“strenuous objections” to the request, finding it“misguided and illegitimate.”
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Congressional Duel
2005: U.S. House of Representatives Committees becomeinterested.
Representatives Joe Barton (R, Texas), Chair of theHouse Committee on Energy and Commerce, and EdWhitfield (R, Kentucky), Chair of its Subcommittee onOversight and Investigations, ask Mann and others toprovide extensive background on their work.Representative Sherwood Boehlert (R, New York),Chair of the House Committee on Science, has“strenuous objections” to the request, finding it“misguided and illegitimate.”
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Two Reports
2006: Two reports on the controversy are commissioned.Barton and Whitfield ask Ed Wegman (George Mason)to assemble a small group of statisticians to look intoM&M’s claims.
Wegman adds:Yasmin Said (Johns Hopkins);David Scott (Rice).
Boehlert asks the National Academies to form a panelto review the science of climate reconstruction. JerryNorth (Texas A&M) is asked to chair.
Statisticians:Doug Nychka (National Center for AtmosphericResearch–formerly NCSU);Peter Bloomfield (NCSU).
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Two Reports
2006: Two reports on the controversy are commissioned.Barton and Whitfield ask Ed Wegman (George Mason)to assemble a small group of statisticians to look intoM&M’s claims.
Wegman adds:Yasmin Said (Johns Hopkins);David Scott (Rice).
Boehlert asks the National Academies to form a panelto review the science of climate reconstruction. JerryNorth (Texas A&M) is asked to chair.
Statisticians:Doug Nychka (National Center for AtmosphericResearch–formerly NCSU);Peter Bloomfield (NCSU).
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Two Reports
2006: Two reports on the controversy are commissioned.Barton and Whitfield ask Ed Wegman (George Mason)to assemble a small group of statisticians to look intoM&M’s claims.
Wegman adds:Yasmin Said (Johns Hopkins);David Scott (Rice).
Boehlert asks the National Academies to form a panelto review the science of climate reconstruction. JerryNorth (Texas A&M) is asked to chair.
Statisticians:Doug Nychka (National Center for AtmosphericResearch–formerly NCSU);Peter Bloomfield (NCSU).
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Two Reports
2006: Two reports on the controversy are commissioned.Barton and Whitfield ask Ed Wegman (George Mason)to assemble a small group of statisticians to look intoM&M’s claims.
Wegman adds:Yasmin Said (Johns Hopkins);David Scott (Rice).
Boehlert asks the National Academies to form a panelto review the science of climate reconstruction. JerryNorth (Texas A&M) is asked to chair.
Statisticians:Doug Nychka (National Center for AtmosphericResearch–formerly NCSU);Peter Bloomfield (NCSU).
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Two Reports
2006: Two reports on the controversy are commissioned.Barton and Whitfield ask Ed Wegman (George Mason)to assemble a small group of statisticians to look intoM&M’s claims.
Wegman adds:Yasmin Said (Johns Hopkins);David Scott (Rice).
Boehlert asks the National Academies to form a panelto review the science of climate reconstruction. JerryNorth (Texas A&M) is asked to chair.
Statisticians:Doug Nychka (National Center for AtmosphericResearch–formerly NCSU);Peter Bloomfield (NCSU).
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Outline
1 Background
2 Congress Gets Involved
3 The ScienceThe StatisticsWegman Panel ConclusionsNAS Panel Conclusions
4 Does It Matter?
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
What Are Proxy Data?
Hemispheric and global temperature records go backonly to around AD 1850.Prior to that, temperatures must be inferred from proxydata:
tree ring widths and densities;ocean sediments;isotopic concentrations in ice cores;glacier lengths and borehole temperatures (not strictlyproxies);other proxies.
Some studies use more than one source: multiproxyreconstructions.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
What Are Proxy Data?
Hemispheric and global temperature records go backonly to around AD 1850.Prior to that, temperatures must be inferred from proxydata:
tree ring widths and densities;ocean sediments;isotopic concentrations in ice cores;glacier lengths and borehole temperatures (not strictlyproxies);other proxies.
Some studies use more than one source: multiproxyreconstructions.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
What Are Proxy Data?
Hemispheric and global temperature records go backonly to around AD 1850.Prior to that, temperatures must be inferred from proxydata:
tree ring widths and densities;ocean sediments;isotopic concentrations in ice cores;glacier lengths and borehole temperatures (not strictlyproxies);other proxies.
Some studies use more than one source: multiproxyreconstructions.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
What Are Proxy Data?
Hemispheric and global temperature records go backonly to around AD 1850.Prior to that, temperatures must be inferred from proxydata:
tree ring widths and densities;ocean sediments;isotopic concentrations in ice cores;glacier lengths and borehole temperatures (not strictlyproxies);other proxies.
Some studies use more than one source: multiproxyreconstructions.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
What Are Proxy Data?
Hemispheric and global temperature records go backonly to around AD 1850.Prior to that, temperatures must be inferred from proxydata:
tree ring widths and densities;ocean sediments;isotopic concentrations in ice cores;glacier lengths and borehole temperatures (not strictlyproxies);other proxies.
Some studies use more than one source: multiproxyreconstructions.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
What Are Proxy Data?
Hemispheric and global temperature records go backonly to around AD 1850.Prior to that, temperatures must be inferred from proxydata:
tree ring widths and densities;ocean sediments;isotopic concentrations in ice cores;glacier lengths and borehole temperatures (not strictlyproxies);other proxies.
Some studies use more than one source: multiproxyreconstructions.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
What Are Proxy Data?
Hemispheric and global temperature records go backonly to around AD 1850.Prior to that, temperatures must be inferred from proxydata:
tree ring widths and densities;ocean sediments;isotopic concentrations in ice cores;glacier lengths and borehole temperatures (not strictlyproxies);other proxies.
Some studies use more than one source: multiproxyreconstructions.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
What Are Proxy Data?
Hemispheric and global temperature records go backonly to around AD 1850.Prior to that, temperatures must be inferred from proxydata:
tree ring widths and densities;ocean sediments;isotopic concentrations in ice cores;glacier lengths and borehole temperatures (not strictlyproxies);other proxies.
Some studies use more than one source: multiproxyreconstructions.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
A Tree Ring Chronology
Rings from several trees can be linked into a singlechronology:
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
An Ocean Sediment Core
A Southern Ocean (Antarctic) core sample:
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Drilling Ice
Collecting ice cores in Greenland, 2005:
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
A Glacier retreats
The Qori Kalis Glacier, Quelccaya Ice Cap, Peru, in 1978and 2002:
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Difficulties
All proxy methods must be used with care:Tree rings respond to moisture as well as temperature;they work well only at high latitudes or altitudes;Ocean sediments reflect sea surface temperature, notair temperature, and are influenced by circulation.Ice cores are available only where there’s ice (!)And so on. . .
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Difficulties
All proxy methods must be used with care:Tree rings respond to moisture as well as temperature;they work well only at high latitudes or altitudes;Ocean sediments reflect sea surface temperature, notair temperature, and are influenced by circulation.Ice cores are available only where there’s ice (!)And so on. . .
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Difficulties
All proxy methods must be used with care:Tree rings respond to moisture as well as temperature;they work well only at high latitudes or altitudes;Ocean sediments reflect sea surface temperature, notair temperature, and are influenced by circulation.Ice cores are available only where there’s ice (!)And so on. . .
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Difficulties
All proxy methods must be used with care:Tree rings respond to moisture as well as temperature;they work well only at high latitudes or altitudes;Ocean sediments reflect sea surface temperature, notair temperature, and are influenced by circulation.Ice cores are available only where there’s ice (!)And so on. . .
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Difficulties
All proxy methods must be used with care:Tree rings respond to moisture as well as temperature;they work well only at high latitudes or altitudes;Ocean sediments reflect sea surface temperature, notair temperature, and are influenced by circulation.Ice cores are available only where there’s ice (!)And so on. . .
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
A Collection of Reconstructions
NAS panel identifies some key reconstructions:
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Outline
1 Background
2 Congress Gets Involved
3 The ScienceThe StatisticsWegman Panel ConclusionsNAS Panel Conclusions
4 Does It Matter?
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Statistical Issues
Mann et al. developed an unconventional procedure toreconstruct temperatures from proxy data.
Combines inverse regression and least squaresmethods:
difficult to capture all uncertainties;possibly under-estimates error bars.
Uses Principal Components Analysis to combine manyproxies into a few:
unconventional standardization can introduce spurioustrends.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Statistical Issues
Mann et al. developed an unconventional procedure toreconstruct temperatures from proxy data.
Combines inverse regression and least squaresmethods:
difficult to capture all uncertainties;possibly under-estimates error bars.
Uses Principal Components Analysis to combine manyproxies into a few:
unconventional standardization can introduce spurioustrends.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Statistical Issues
Mann et al. developed an unconventional procedure toreconstruct temperatures from proxy data.
Combines inverse regression and least squaresmethods:
difficult to capture all uncertainties;possibly under-estimates error bars.
Uses Principal Components Analysis to combine manyproxies into a few:
unconventional standardization can introduce spurioustrends.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Statistical Issues
Mann et al. developed an unconventional procedure toreconstruct temperatures from proxy data.
Combines inverse regression and least squaresmethods:
difficult to capture all uncertainties;possibly under-estimates error bars.
Uses Principal Components Analysis to combine manyproxies into a few:
unconventional standardization can introduce spurioustrends.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Statistical Issues
Mann et al. developed an unconventional procedure toreconstruct temperatures from proxy data.
Combines inverse regression and least squaresmethods:
difficult to capture all uncertainties;possibly under-estimates error bars.
Uses Principal Components Analysis to combine manyproxies into a few:
unconventional standardization can introduce spurioustrends.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Outline
1 Background
2 Congress Gets Involved
3 The ScienceThe StatisticsWegman Panel ConclusionsNAS Panel Conclusions
4 Does It Matter?
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Wegman Panel Conclusions
The politicization of academic scholarly work leads toconfusing public debates. . . . In the present examplethere was too much reliance on peer review, whichseemed not to be sufficiently independent.Sharing of research materials, data, and results ishaphazard and often grudgingly done. . . . When codeand data are not shared and methodology is not fullydisclosed, peers do not have the ability to replicate thework and thus independent verification is impossible.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Wegman Panel Conclusions
The politicization of academic scholarly work leads toconfusing public debates. . . . In the present examplethere was too much reliance on peer review, whichseemed not to be sufficiently independent.Sharing of research materials, data, and results ishaphazard and often grudgingly done. . . . When codeand data are not shared and methodology is not fullydisclosed, peers do not have the ability to replicate thework and thus independent verification is impossible.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Wegman Panel Conclusions (continued)
. . . The public policy implications of this debate arefinancially staggering and yet apparently noindependent statistical expertise was sought or used.While the paleoclimate reconstruction has gatheredmuch publicity because it reinforces a policy agenda, itdoes not provide insight and understanding of thephysical mechanisms of climate change except to theextent that tree ring, ice cores and such give physicalevidence such as the prevalence of green-housegases. What is needed is deeper understanding of thephysical mechanisms of climate change.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Wegman Panel Conclusions (continued)
. . . The public policy implications of this debate arefinancially staggering and yet apparently noindependent statistical expertise was sought or used.While the paleoclimate reconstruction has gatheredmuch publicity because it reinforces a policy agenda, itdoes not provide insight and understanding of thephysical mechanisms of climate change except to theextent that tree ring, ice cores and such give physicalevidence such as the prevalence of green-housegases. What is needed is deeper understanding of thephysical mechanisms of climate change.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Wegman Panel Commentary
Mann’s assessments that the decade of the 1990s wasthe hottest decade of the millennium and that 1998 wasthe hottest year of the millennium cannot be supportedby his analysis.The Wall Street Journal jumped the gun with aneditorial entitled “Hockey Stick Hokum.”
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Wegman Panel Commentary
Mann’s assessments that the decade of the 1990s wasthe hottest decade of the millennium and that 1998 wasthe hottest year of the millennium cannot be supportedby his analysis.The Wall Street Journal jumped the gun with aneditorial entitled “Hockey Stick Hokum.”
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Outline
1 Background
2 Congress Gets Involved
3 The ScienceThe StatisticsWegman Panel ConclusionsNAS Panel Conclusions
4 Does It Matter?
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Conclusions
Mann et al.’s statistical methods were problematic.More recent work with different statistical methods yieldsimilar results.Reconstructions from AD 1600 to the present arebased on various proxies, which gives them credibility.Prior to AD 1600, reconstructions depend heavily ontree-rings, and are less credible.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Conclusions
Mann et al.’s statistical methods were problematic.More recent work with different statistical methods yieldsimilar results.Reconstructions from AD 1600 to the present arebased on various proxies, which gives them credibility.Prior to AD 1600, reconstructions depend heavily ontree-rings, and are less credible.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Conclusions
Mann et al.’s statistical methods were problematic.More recent work with different statistical methods yieldsimilar results.Reconstructions from AD 1600 to the present arebased on various proxies, which gives them credibility.Prior to AD 1600, reconstructions depend heavily ontree-rings, and are less credible.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Conclusions
Mann et al.’s statistical methods were problematic.More recent work with different statistical methods yieldsimilar results.Reconstructions from AD 1600 to the present arebased on various proxies, which gives them credibility.Prior to AD 1600, reconstructions depend heavily ontree-rings, and are less credible.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Conclusions (continued)
With a high level of confidence:Global mean surface temperature was higher during thelast few decades of the 20th century than during anycomparable period during the preceding four centuries.This statement is justified by the consistency of theevidence from a wide variety of geographically diverseproxies.
With less confidence:Presently available proxy evidence indicates thattemperatures at many, but not all, individual locationswere higher during the past 25 years than during anyperiod of comparable length since A.D. 900.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Conclusions (continued)
With a high level of confidence:Global mean surface temperature was higher during thelast few decades of the 20th century than during anycomparable period during the preceding four centuries.This statement is justified by the consistency of theevidence from a wide variety of geographically diverseproxies.
With less confidence:Presently available proxy evidence indicates thattemperatures at many, but not all, individual locationswere higher during the past 25 years than during anyperiod of comparable length since A.D. 900.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Conclusions (continued)
With a high level of confidence:Global mean surface temperature was higher during thelast few decades of the 20th century than during anycomparable period during the preceding four centuries.This statement is justified by the consistency of theevidence from a wide variety of geographically diverseproxies.
With less confidence:Presently available proxy evidence indicates thattemperatures at many, but not all, individual locationswere higher during the past 25 years than during anyperiod of comparable length since A.D. 900.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Conclusions (continued)
With a high level of confidence:Global mean surface temperature was higher during thelast few decades of the 20th century than during anycomparable period during the preceding four centuries.This statement is justified by the consistency of theevidence from a wide variety of geographically diverseproxies.
With less confidence:Presently available proxy evidence indicates thattemperatures at many, but not all, individual locationswere higher during the past 25 years than during anyperiod of comparable length since A.D. 900.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Conclusions (continued)
With a high level of confidence:Global mean surface temperature was higher during thelast few decades of the 20th century than during anycomparable period during the preceding four centuries.This statement is justified by the consistency of theevidence from a wide variety of geographically diverseproxies.
With less confidence:Presently available proxy evidence indicates thattemperatures at many, but not all, individual locationswere higher during the past 25 years than during anyperiod of comparable length since A.D. 900.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Conclusions (continued)
Plausible:The Northern Hemisphere was warmer during the lastfew decades of the 20th century than during anycomparable period over the preceding millennium.
Even less confidence:The original conclusions by Mann et al. (1999) that “the1990s are likely the warmest decade, and 1998 thewarmest year, in at least a millennium.”
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Conclusions (continued)
Plausible:The Northern Hemisphere was warmer during the lastfew decades of the 20th century than during anycomparable period over the preceding millennium.
Even less confidence:The original conclusions by Mann et al. (1999) that “the1990s are likely the warmest decade, and 1998 thewarmest year, in at least a millennium.”
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Conclusions (continued)
Plausible:The Northern Hemisphere was warmer during the lastfew decades of the 20th century than during anycomparable period over the preceding millennium.
Even less confidence:The original conclusions by Mann et al. (1999) that “the1990s are likely the warmest decade, and 1998 thewarmest year, in at least a millennium.”
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Conclusions (continued)
Plausible:The Northern Hemisphere was warmer during the lastfew decades of the 20th century than during anycomparable period over the preceding millennium.
Even less confidence:The original conclusions by Mann et al. (1999) that “the1990s are likely the warmest decade, and 1998 thewarmest year, in at least a millennium.”
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
Outline
1 Background
2 Congress Gets Involved
3 The ScienceThe StatisticsWegman Panel ConclusionsNAS Panel Conclusions
4 Does It Matter?
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Commentary
Large-scale surface temperature reconstructions for thelast 2,000 years are not the primary evidence for thewidely accepted views that:
global warming is occurring;human activities are contributing, at least in part, to thiswarming;the Earth will continue to warm over the next century.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Commentary
Large-scale surface temperature reconstructions for thelast 2,000 years are not the primary evidence for thewidely accepted views that:
global warming is occurring;human activities are contributing, at least in part, to thiswarming;the Earth will continue to warm over the next century.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Commentary
Large-scale surface temperature reconstructions for thelast 2,000 years are not the primary evidence for thewidely accepted views that:
global warming is occurring;human activities are contributing, at least in part, to thiswarming;the Earth will continue to warm over the next century.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Commentary
Large-scale surface temperature reconstructions for thelast 2,000 years are not the primary evidence for thewidely accepted views that:
global warming is occurring;human activities are contributing, at least in part, to thiswarming;the Earth will continue to warm over the next century.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Commentary (continued)
The primary evidence for these views includes:measurements showing large increases in carbondioxide and other greenhouse gases beginning in themiddle of the 19th century;instrumental measurements of upward temperaturetrends and concomitant changes in a host of proxyindicators over the last century;simple radiative transfer calculations of the forcingassociated with increasing greenhouse gasconcentrations together with reasonable assumptionsabout the sign and magnitude of climate feedbacks;numerical experiments performed with state-of-the artclimate models.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Commentary (continued)
The primary evidence for these views includes:measurements showing large increases in carbondioxide and other greenhouse gases beginning in themiddle of the 19th century;instrumental measurements of upward temperaturetrends and concomitant changes in a host of proxyindicators over the last century;simple radiative transfer calculations of the forcingassociated with increasing greenhouse gasconcentrations together with reasonable assumptionsabout the sign and magnitude of climate feedbacks;numerical experiments performed with state-of-the artclimate models.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Commentary (continued)
The primary evidence for these views includes:measurements showing large increases in carbondioxide and other greenhouse gases beginning in themiddle of the 19th century;instrumental measurements of upward temperaturetrends and concomitant changes in a host of proxyindicators over the last century;simple radiative transfer calculations of the forcingassociated with increasing greenhouse gasconcentrations together with reasonable assumptionsabout the sign and magnitude of climate feedbacks;numerical experiments performed with state-of-the artclimate models.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Commentary (continued)
The primary evidence for these views includes:measurements showing large increases in carbondioxide and other greenhouse gases beginning in themiddle of the 19th century;instrumental measurements of upward temperaturetrends and concomitant changes in a host of proxyindicators over the last century;simple radiative transfer calculations of the forcingassociated with increasing greenhouse gasconcentrations together with reasonable assumptionsabout the sign and magnitude of climate feedbacks;numerical experiments performed with state-of-the artclimate models.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
NAS Panel Commentary (continued)
The primary evidence for these views includes:measurements showing large increases in carbondioxide and other greenhouse gases beginning in themiddle of the 19th century;instrumental measurements of upward temperaturetrends and concomitant changes in a host of proxyindicators over the last century;simple radiative transfer calculations of the forcingassociated with increasing greenhouse gasconcentrations together with reasonable assumptionsabout the sign and magnitude of climate feedbacks;numerical experiments performed with state-of-the artclimate models.
It’s warmernow than forthe last 1,000years: true or
false?
PeterBloomfield
Background
CongressGets Involved
The ScienceThe Statistics
Wegman PanelConclusions
NAS PanelConclusions
Does ItMatter?
