NAS Congressional Report: Recent Global warming is Human-caused
Submitted by Knightrider on June 22, 2006 - 5:45pm.
climate change | Global Warming | Greenhouse gases | Climate Crisis
As I'm sure many of you are now aware, a NAS committee submitted its assessment on Climate Reconstruction models, as requested by Congress. It's mostly good news for the scientific community, in that it validates the overwhelming concensus of their findings, but it could still be used to politically, imo.
Based on the report, the committee concluded with "high confidence" that the "hockey stick" model, as first proposed by Michael Mann ('98) and subsequently validated by other climatology researchers, accurately depicts global warming and climate trends that has occurred over the past few decades. Generally, these studies do support evidence that "human activities are responsible for much of the recent warming". And specifically, it's been the fossil fuel emissions of CO2 and methane (CH4) into the atmosphere that have contributed to the highest global mean surface temperatures (ie global warming) ever recorded over the last 400 years. Of note, 2005 was the hottest year on record.
Although a more comprehensive report is available for purchase, the NAS press statement is carefully and interestingly worded. For example, the committee concluded that although the models were mostly consistent, they placed "low confidence" on climate reconstruction models from 900 AD - 1600 AD, a period also known as the Medieval Warming Period. This period has been used by GW skeptics and science contrarians as evidence that global warming is part of a natural cycle. For some reason, I sense that they'll still use it to only modify their arguments to call for more studies, even in light of the NAS primary conclusion.
Here's the opening statement from the Chair of the Commitee:
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Read Full Report
Date: June 22, 2006
Contacts: Bill Kearney, Director of Media Relations
Megan Petty, Media Relations Assistant
Office of News and Public Information
202-334-2138; e-mail <news@nas.edu>
FOR IMMEDIATE RELEASE
'High Confidence' That Planet Is Warmest in 400 Years - Less Confidence in Temperature Reconstructions Prior to 1600WASHINGTON -- There is sufficient evidence from tree rings, boreholes, retreating glaciers, and other "proxies" of past surface temperatures to say with a high level of confidence that the last few decades of the 20th century were warmer than any comparable period in the last 400 years, according to a new report from the National Research Council. Less confidence can be placed in proxy-based reconstructions of surface temperatures for A.D. 900 to 1600, said the committee that wrote the report, although the available proxy evidence does indicate that many locations were warmer during the past 25 years than during any other 25-year period since 900. Very little confidence can be placed in statements about average global surface temperatures prior to A.D. 900 because the proxy data for that time frame are sparse, the committee added.
Scientists rely on proxies to reconstruct paleoclimatic surface temperatures because geographically widespread records of temperatures measured with instruments date back only about 150 years. Other proxies include corals, ocean and lake sediments, ice cores, cave deposits, and documentary sources, such as historic drawings of glaciers. The globally averaged warming of about 1 degree Fahrenheit (0.6 degrees Celsius) that instruments have recorded during the last century is also reflected in proxy data for that time period, the committee noted.
The report was requested by Congress after a controversy arose last year over surface temperature reconstructions published by climatologist Michael Mann and his colleagues in the late 1990s. The researchers concluded that the warming of the Northern Hemisphere in the last decades of the 20th century was unprecedented in the past thousand years. In particular, they concluded that the 1990s were the warmest decade, and 1998 the warmest year. Their graph depicting a rise in temperatures at the end of a long era became known as the "hockey stick."
- he Research Council committee found the Mann team's conclusion that warming in the last few decades of the 20th century was unprecedented over the last thousand years to be plausible, but it had less confidence that the warming was unprecedented prior to 1600; fewer proxies -- in fewer locations -- provide temperatures for periods before then. Because of larger uncertainties in temperature reconstructions for decades and individual years, and because not all proxies record temperatures for such short timescales, even less confidence can be placed in the Mann team's conclusions about the 1990s, and 1998 in particular.
- The committee noted that scientists' reconstructions of Northern Hemisphere surface temperatures for the past thousand years are generally consistent. The reconstructions show relatively warm conditions centered around the year 1000, and a relatively cold period, or "Little Ice Age," from roughly 1500 to 1850. The exact timing of warm episodes in the medieval period may have varied by region, and the magnitude and geographical extent of the warmth is uncertain, the committee said. None of the reconstructions indicates that temperatures were warmer during medieval times than during the past few decades, the committee added.
The scarcity of precisely dated proxy evidence for temperatures before 1600, especially in the Southern Hemisphere, is the main reason there is less confidence in global reconstructions dating back further than that. Other factors that limit confidence include the short length of the instrumental record, which is used to calibrate and validate reconstructions, and the possibility that the relationship between proxy data and local surface temperatures may have varied over time. It also is difficult to estimate a mean global temperature using data from a limited number of sites. On the other hand, confidence in large-scale reconstructions is boosted by the fact that the proxies on which they are based generally exhibit strong correlations with local environmental conditions. Confidence increases further when multiple independent lines of evidence point to the same general phenomenon, such as the Little Ice Age.Collecting additional proxy data, especially for years before 1600 and for areas where the current data are relatively sparse, would increase our understanding of temperature variations over the last 2,000 years, the report says. In addition, improving access to data on which published temperature reconstructions are based would boost confidence in the results. The report also notes that new analytical methods, or more careful use of existing methods, might help circumvent some of the current limitations associated with large-scale reconstructions.
The committee pointed out that surface temperature reconstructions for periods before the Industrial Revolution -- when levels of atmospheric greenhouse gases were much lower -- are only one of multiple lines of evidence supporting the conclusion that current warming is occurring in response to human activities, and they are not the primary evidence.
The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides science and technology advice under a congressional charter. A committee roster follows.
Copies of Surface Temperature Reconstructions for the Last 2,000 Years will be available from the National Academies Press; tel. 202-334-3313 or 1-800-624-6242 or on the Internet at http://www.nap.edu. Reporters may obtain a pre-publication copy from the Office of News and Public Information (contacts listed above).
[ This news release and report are available at http://national-academies.org ]
http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=11676
I'm just updating this blog with supporting references from RealClimate.org regarding the NAS committee report to Congress earlier last week on global warming. The Committee panel was tasked to review the scientific evidence supportive of the Mann's "hockey stick" model comparing climate data trends the last 2000 years.
The figures below illustrate the evidence and the Commitees findings. The expert panels' report to Congress are agreement with the concensus of scientific findings, which show that global warming is real and that evidence of "human-caused" activities ("anthropogenic forcing" factors) was sufficient to explain the hockey stick effect over the past few decades.
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An excerpt from RealClimate.org.
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"The simulations all show that it is not possible to explain the anomalous late 20th century warmth without including the contribution from anthropogenic forcing factors (human-caused fossil fuel emissions: "oil, gas, coal"), and, in particular, modern greenhouse gas concentration increases. A healthy, vigorous debate can be found in the legitimate peer-reviewed climate research literature with regard to the precise details of empirically and model-based estimates of climate changes in past centuries, and it remains a challenge to reduce the substantial uncertainties that currently exist.
Despite current uncertainties, it nonetheless remains a widespread view among paleoclimate researchers that late 20th century hemispheric-scale warmth is anomalous in a long-term (at least millennial) context, and that anthropogenic factors (ie. human-caused fossil fuel emissions: "oil, gas, coal") likely play an important role in explaining the anomalous recent warmth.
Reviews of past scientific research in this area can be found in the following peer-reviewed journal articles:
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Jones, P.D., Mann, M.E., .>. lang="en">Climate Over Past Millennia, .>. lang="en"> Reviews of Geophysics, 42, RG2002, doi: 10.1029/2003RG000143, 2004. .
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Mann, M.E., Ammann, C.M., Bradley, R.S., Briffa, K.R., Crowley, T.J., Hughes, M.K., Jones, P.D., Oppenheimer, M., Osborn, T.J., Overpeck, J.T., Rutherford, S., Trenberth, K.E., Wigley, T.M.L., .> On Past Temperatures and Anomalous Late 20th Century Warmth , Eos, 84, 256-258, 2003.
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Jones, P.D., T.J. Osborn, and K.R. Briffa, The evolution of climate over the last millennium, Science, 292, 662-667, 2001.
FIGURE 1 [reprinted from Mann et al, 2003, Eos, (C) American Geophysical Union]. Comparison of proxy-based Northern Hemisphere (NH) temperature reconstructions (Jones et al., 1998; Mann et al., 1999; Crowley and Lowery, 2000) with model simulations of NH mean temperature changes over the past millennium based on estimated radiative forcing histories (Crowley, 2000; Gerber et al., 2002results shown for both a 1.5oC/2xCO2 and 2.5oC/2xCO2 sensitivity; Bauer et al., 2003). Also shown are two independent reconstructions of warm-season extratropical continental NH temperatures (Briffa et al., 2001; Esper et al., 2002) and an extension back through the past two thousand years based on eight long proxy temperature series chosen for their ability to retain long-term trends (Mann and Jones, 2003). All reconstructions have been scaled to the annual, full Northern Hemisphere mean, over an overlapping period (1856-1980), using the NH instrumental record (Jones et al., 1999) for comparison, and have been smoothed on time scales of >40 years to highlight the long-term variations. The smoothed instrumental record (1856-2003) is also shown. The gray/pink shading indicates estimated two-standard error uncertainties in the Mann et al. (1999) and Mann and Jones (2003) econstructions. Also shown are reconstructions of ground surface temperatures (GST) based on appropriately areally-averaged (Briffa and Osborn, 2002; Mann et al., 2003) continental borehole data (Huang et al., 2000), and hemispheric surface air temperature trends, determined by optimal regression (Mann et al., 2003) from the GST estimates. All series are shown with respect to the 1961-90 base period. [added 1/12/05: It should be noted (thanks to S. Huang for pointing this out), that the two borehole curves shown in this plot suffer from a small error in the areal weighting normalization. Further discussion, and corrected versions of the borehole temperature estimates can be found in Rutherford and Mann (2004) (and in the Jones and Mann, 2004 article discussed above)]
FIGURE 2 [reprinted from Jones and Mann, 2004, Reviews of Geophysics, (C) American Geophysical Union]. Model-based estimates of northern hemisphere temperature variations over the past two millennia. Shown are 40 year smoothed series. The simulations are based on varying radiative forcing histories employing a hierarchy of models including one-dimensional energy based models (Crowley, 2000), two-dimensional reduced complexity models (Bauer et al, 2003; Bertrand et al, 2002; Gerber et al, 2003), and full three-dimensional coupled atmosphere-ocean general circulation (GKSS-Gonzalez-Rouco et al, 2003; CSMAm mann et al., submitted). Shown for comparison is the instrumental northern hemisphere record 1856-2003 (Jones et al, 1999), and the proxy-based estimate of Mann and Jones (2003) extended through 1995, with its 95% confidence interval. Models have been aligned vertically to have the same mean over the common 1856-1980 period as the instrumental series (which is assigned zero mean during the 1961-1990 reference period).
References:
Bauer, E., M., Claussen, and V. Brovkin, Assessing climate forcings of the earth system for the past millennium, Geophys. Res. Lett., 30 (6), doi: 10.1029/2002GL016639, 2003.
Bertrand C., M.F. Loutre, M. Crucifix, and A. Berger, Climate of the Last millennium: a sensitivity study, Tellus, 54(A), 221-244, 2002.
Briffa, K.R., and T J. Osborn, Blowing Hot and Cold, Science, 295 2227-2228, 2002.
Briffa, K.R., T.J. Osborn, F.H. Schweingruber, I.C. Harris, P.D. Jones, S.G. Shiyatov and E.A. Vaganov, Low-frequency temperature variations from a northern tree-ring density network. J. Geophys. Res., 106, 2929 2941, 2001.
Cook, E.R., J. Esper, and R.D. D'Arrigo, Extra-tropical Northern Hemisphere land temperature variability over the past 1000 years, Quat. Sci. Rev., 23, 2063-2074, 2004.
Crowley, T.J., Causes of Climate Change over the Past 1000 Years, Science, 289, 270-277, 2000.
Crowley, T.J., and T. Lowery, How Warm Was the Medieval Warm Period?, Ambio, 29, 51-54, 2000.
Esper, J., E.R. Cook and F.H. Schweingruber, Low-frequency signals in long tree-line chronologies for reconstructing past temperature
variability, Science, 295, 2250-2253, 2002.Gerber, S., F. Joos, P. Brügger, T. F. Stocker, M. E. Mann, S. Sitch, and M. Scholze Constraining temperature variations over the last millennium by comparing simulated and observed atmospheric CO2, Climate Dynamics, 20, 281-299, 2003.
Gonzalez-Rouco, F., H. von Storch, and E. Zorita, Deep soil temperature as proxy for surface air-temperature in a coupled model simulation of the last thousand years, Geophys. Res. Lett., 30, 2116, doi:10.1029/2003GL018264, 2003.
Huang, S., H. N.Pollack and P.-Y. Shen, Temperature Trends Over the Past Five Centuries Reconstructed from Borehole Temperature, Nature 403, 756-758, 2000.
Jones, P.D., K.R. Briffa, T.P. Barnett and S.F.B. Tett, High-resolution palaeoclimatic records for the last millennium: Integration, interpretation and comparison with General Circulation Model control run temperatures, Holocene, 8, 455-471, 1998.
Jones, P.D., M. New, D.E. Parker, S. Martin, and I.G. Rigor, Surface air temperature and its changes over the past 150 years, Reviews of Geophysics, 37, 173-199, 1999.
Jones, P.D., T.J. Osborn, and K.R. Briffa, The Evolution of Climate Over the Last Millennium, Science, 292, 662-667, 2001.
Mann, M.E., R.S. Bradley, and M.K. Hughes, Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations, Geophysical Research Letters, 26, 759-762, 1999.
Mann, M.E., Jones, P.D., Global surface temperature over the past two millennia, Geophysical Research Letters, 30 (15), 1820, doi: 10.1029/2003GL017814, 2003..>
Mann, M.E., Rutherford, S., Bradley, R.S., Hughes, M.K., Keimig, F.T., Optimal Surface Temperature Reconstructions Using Terrestrial Borehole Data, Journal of Geophysical Research, 108 (D7), doi: 10.1029/2002JD002532, 2003.
All over the nightly news tonight. We've been so dry this year in Kansas. I'm just happy for the rain we got today:) It's been unseasonably warm to hot all year this year. So far, the new windows and doors are helping with the electric bill. My friends in Dallas said their electric bill was like $380 for May. It came as a real shocker for them.
I bought a Chillow at the Discovery store to sleep with as my bedroom is over the garage and gets quite hot compared to the rest of my house. Everyone else sleeps cooler on the lower levels and we don't want to mess with the thermostat, so the Chillow does help with staying cooler to sleep. It's not perfect, but a fairly inexpensive solution to try.