Environmental Law Prof Blog

Hansen says Limit Greenhouse Gases Definitively within 10 Years and Hold Increase to 1 degree C

Link: Planet Ark : World Has 10-Year Window to Act on Climate - Expert.

NASA scientist James Hansen, widely considered the doyen of American climate researchers, said governments must adopt an alternative scenario to keep carbon dioxide emission growth in check and limit the increase in global temperatures to 1 degree Celsius (1.8 degrees Fahrenheit).

"I think we have a very brief window of opportunity to deal with climate change ... no longer than a decade, at the most," Hansen said at the Climate Change Research Conference in California's state capital.

If the world continues with a "business as usual" scenario, Hansen said temperatures will rise by 2 to 3 degrees Celsius (3.6 to 7.2 degrees F) and "we will be producing a different planet."

On that warmer planet, ice sheets would melt quickly, causing a rise in sea levels that would put most of Manhattan under water. The world would see more prolonged droughts and heat waves, powerful hurricanes in new areas and the likely extinction of 50 percent of species.

Hansen, who heads NASA's Goddard Institute for Space Studies, has made waves before by saying that President George W. Bush's administration tried to silence him and heavily edited his and other scientists' findings on a warmer world.

He reiterated that the United States "has passed up the opportunity" to influence the world on global warming.

The United States is the largest emitter of greenhouse gases, most notably carbon dioxide. But Bush pulled the country out of the 160-nation Kyoto Protocol in 2001, arguing that the treaty's mandatory curbs on emissions would harm the economy.

Hansen praised California for taking the "courageous" step of passing legislation on global warming last month that will make it the first US state to place caps on greenhouse gas emissions.

He said the alternative scenario he advocates involves promoting energy efficiency and reducing dependence on carbon burning fuels.

"We cannot burn off all the fossil fuels that are readily available without causing dramatic climate change," Hansen said. "This is not something that is a theory. We understand the carbon cycle well enough to say that."

ABA SEER quick conference on Tacoma v. FERC decision

        Section of Environment, Energy, and Resources

 

                                        Hydro Power Committee

City of Tacoma v. FERC: Did the Hydro Industry Get the Number of that Train?

      

       

         

Friday, September 29, 2006
          12:00 p.m. – 1:30 p.m. Eastern / 11:00 a.m. – 12:30 p.m. Central
  10:00 a.m. – 11:30 a.m. Mountain / 9:00 a.m. – 10:30 a.m. Pacific

         

Program Overview:
          On August 22, 2006, the U.S. District Court of Appeals issued a decision in the case of City of Tacoma v. FERC. The decision addressed a number of issues that may significantly change that way that the Federal Energy Regulatory Commission issues licenses for hydropower projects pursuant to the Federal Power Act. The D.C. Circuit Court of Appeals modified in part and granted in part, Petitions for Review of the FERC Order Issuing New License for the Cushman Hydroelectric project on the Skokomish River in the State of Washington. Some of the issues were: (i) whether a relicensing proceeding or a new license proceeding should be undertaken for a project that previously held a minor part license, (ii) whether the mandatory conditioning authority under Federal Power Act Section 4(e) is limited to those areas where the hydro project is located on a federal reservation, (iii) must the federal agencies who submit “mandatory” conditions pursuant to FPA Section 4(e), and presumably Section 18, comply with FERC’s regulatory deadlines for submittal of the conditions, (iv) the degree to which FERC must evaluate a state water quality agency’s compliance with Clean Water Act Section 401, (v) whether a FERC license that makes a project uneconomic to operate constitutes a de facto decommissioning of the project, and (vi) how FERC should treat the state of Washington’s decision not to object to the project under the state’s Coastal Zone Management Act authority.

Faculty:
      Moderator:
      Nino J. Mascolo, Southern California Edison Company, Rosemead, CA

Panelists:
        John Katz, Federal Energy Regulatory Commission, Washington, DC
        Mark Quehrn, Perkins Coie, LLP, Bellevue, WA
        Bella Seawall, U.S. Department of the Interior, Washington, DC

Click Here to Register

Link:Tacoma v. FERC program

The Summer of 2006 - It was HOT!!!

Link: National Climatic Data Center - Climate of Summer 2006

Based on preliminary data, globally averaged combined land and sea surface temperature was fourth warmest on record for August and third warmest on record for boreal summer (June - August 2006).     * June - August temperatures were above average in much of North America, Europe and Asia. There were no notable areas of colder than average conditions.     * Precipitation during June - August was above average in the U.S. Northeast, southern Argentina, and east Asia, with drier than average conditions in the U.S. Pacific Northwest, western Australia, and Scandinavia.     * ENSO conditions remained neutral during August.

Introduction

Temperature anomalies for June - August and August 2006 are shown on the dot maps below. The dot maps, below left, provide a spatial representation of anomalies calculated from the Global Historical Climatology Network (GHCN) data set of land surface stations using a 1961-1990 base period. The maps, below right, are products of a merged land surface and sea surface temperature anomaly analysis, which is based on data from the GHCN of land temperatures and the Comprehensive Ocean-Atmosphere Data Set (COADS) of Sea-Surface Temperature (SST) data. Temperature anomalies with respect to the 1961-1990 mean for land and ocean are analyzed separately and then merged to form the global analysis. Additional information on this product is available. 

During boreal summer, temperatures were above average across the entire globe. There were no notable areas of cooler than average temperatures.

During boreal summer, warmer than average SSTs occurred over the North Atlantic and South Pacific. Cooler than average conditions were observed in the North Pacific and Southern Indian Oceans.Please see the latest  ENSO discussion for further information.

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During August, there were above average temperatures across much of the United States, Brazil, Scandinavia, the Middle East and Asia. Cooler than average temperatures were observed primarily in Russia, Alaska and the U.S. far Northeast. During January-August 2006, there were above average temperatures in the majority of North America, China, western Europe, South America and Africa. Cooler than average temperatures were observed in Alaska and western Australia. In January-August, warmer than average SSTs occurred in the South Pacific, North and South Atlantic and southern Indian Oceans, with cooler than average conditions observed in the North Pacific and off the coast of western Australia. In August, warmer than average SSTs occurred in the North Atlantic and the Niño 1+2 region, with cooler than average conditions observed in the North Pacific and southern Indian Oceans. Please see the latest ENSO discussion for further information.

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The mean position of upper level ridges of high pressure and troughs of low pressure (depicted by positive and negative 500-millibar height anomalies on the June - August 2006 map and the August map) are generally reflected by areas of positive and negative temperature anomalies at the surface, respectively. For other Global products see the Climate Monitoring Global Products page.

Images of sea surface temperature conditions are available for all weeks during 2006 at the weekly SST page.

Temperature Rankings and Graphics

Effective with the January, 2006 report, NCDC transitioned from the use of the Operational Global Surface Temperature Index (Quayle et al. 1999) to the blended land and ocean dataset developed by Smith and Reynolds (2005).  The differences between the two methods are discussed in Smith et al. 2005.

Current Month / Seasonal / Year-to-date

August	Anomaly	Rank	Warmest Year on Record
Global Land Ocean Land and Ocean	+0.73°C (+1.31°F) +0.47°C (+0.85°F) +0.54°C (+0.97°F)	3rd warmest 5th warmest 4th warmest	1998 (+0.92°C/1.66°F) 1998 (+0.54°C/0.97°F) 1998 (+0.64°C/1.15°F)
Northern Hemisphere Land Ocean Land and Ocean	+0.74°C (+1.33°F) +0.59°C (+1.06°F) +0.64°C (+1.15°F)	4th warmest 4th warmest 3rd warmest	1998 (+0.95°C/1.71°F) 2005 (+0.65°C/1.17°F) 2003 (+0.72°C/1.30°F)
Southern Hemisphere Land Ocean Land and Ocean	+0.69°C (+1.24°F) +0.38°C (+0.68°F) +0.43°C (+0.77°F)	13th warmest 7th warmest 7th warmest	1981 (+1.31°C/2.36°F) 1998 (+0.51°C/0.92°F) 1998 (+0.57°C/1.03°F)

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June-August	Anomaly	Rank	Warmest Year on Record
Global Land Ocean Land and Ocean	+0.82°C (+1.48°F) +0.46°C (+0.83°F) +0.56°C (+1.01°F)	3rd warmest 5th warmest 3rd warmest	1998 (+0.90°C/1.62°F) 1998 (+0.54°C/0.97°F) 1998 (+0.64°C/1.15°F)
Northern Hemisphere Land Ocean Land and Ocean	+0.87°C (+1.57°F) +0.54°C (+0.97°F) +0.66°C (+1.19°F)	2nd warmest 5th warmest 3rd warmest	1998 (+0.92°C/1.66°F) 2005 (+0.64°C/1.15°F) 2005 (+0.71°C/1.28°F)
Southern Hemisphere Land Ocean Land and Ocean	+0.68°C (+1.22°F) +0.40°C (+0.72°F) +0.44°C (+0.79°F)	4th warmest 7th warmest 4th warmest	2005 (+0.89°C/1.60°F) 1998 (+0.53°C/0.95°F) 1998 (+0.58°C/1.04°F)

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January-August	Anomaly	Rank	Warmest Year on Record
Global Land Ocean Land and Ocean	+0.72°C (+1.30°F) +0.43°C (+0.77°F) +0.50°C (+0.90°F)	6th warmest 6th warmest 6th warmest	2002 (+1.00°C/1.80°F) 1998 (+0.53°C/0.95°F) 1998 (+0.65°C/1.17°F)
Northern Hemisphere Land Ocean Land and Ocean	+0.80°C (+1.44°F) +0.43°C (+0.77°F) +0.57°C (+1.03°F)	7th warmest 5th warmest 5th warmest	2002 (+1.14°C/2.05°F) 2005 (+0.54°C/0.97°F) 2005 (+0.69°C/1.24°F)
Southern Hemisphere Land Ocean Land and Ocean	+0.46°C (+0.83°F) +0.43°C (+0.77°F) +0.43°C (+0.77°F)	8th warmest 5th warmest 6th warmest	2005 (+0.89°C/1.60°F) 1998 (+0.55°C/0.99°F) 1998 (+0.60°C/1.08°F)

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The most current data may be accessed via the Global Surface Temperature Anomalies page.

Precipitation The maps below represent anomaly values based on the GHCN data set of land surface stations using a base period of 1961-1990. During June - August 2006, above average precipitation fell over areas that include the U.S. Northeast and Gulf Coast, Alaska, southern Argentina, eastern Europe, parts of India and southeast Asia. Heavy rain and flooding occurred in Ethiopia, India, the Phillipines and Thailand. Below average precipitation was observed in areas including the U.S./Canadian border, western Europe, Scandinavia, and western Australia. Additional details on flooding and drought can also be found on the August Global Hazards page.  During August, above average precipitation fell over areas that include the U.S. Great Plains, southern Alaska, eastern Europe and parts of India. Below average precipitation was observed across Scandinavia, parts of the U.S. southern Plains, most of Australia, and much of southeast Asia.

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ENSO SST Analysis Click here for animated loop

Sea Surface Temperatures increased across most of the central and eastern equatorial Pacific Ocean during August, but ENSO remained in a neutral state (shown in the adjacent animation of weekly sea surface temperature anomalies). A comprehensive summary of August 2006 ENSO conditions can be found on the ENSO monitoring page. For the latest advisory on ENSO conditions go to NOAA's Climate Prediction Center (CPC) and the CPC ENSO Diagnostic Discussion Images of sea surface temperature conditions are available for all weeks during 2006 at the weekly SST page

Northern Hemisphere Sea Ice Extent

Northern Hemisphere sea ice extent, which is measured from passive microwave instruments onboard NOAA satellites, was around 6 million square kilometers as of September 5, 2006, (image to the right). According to the National Snow and Ice Data Center, during August the pattern of unusually warm conditions that have been present throughout this year were broken. Temperatures near the pole were 1° to 2°C cooler than average, inhibitng further melting this month. For further information on Northern Hemisphere snow and ice conditions, please see the NSIDC News page, provided by the NOAA's National Snow and Ice Data Center (NSIDC).

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Troposphere Current Month / Seasonal Mid-tropospheric and lower stratospheric temperature data are collected by NOAA's TIROS-N polar-orbiting satellites and adjusted for time-dependent biases by the Global Hydrology and Climate Center at the University of Alabama in Huntsville (UAH).  An independent analysis is also performed by Remote Sensing Systems (RSS) and a third analysis has been performed by Dr. Qiang Fu of the the University of Washington (UW) (Fu et al. 2004)**  to remove the influence of the stratosphere on the mid-troposphere value. The table below summarizes mid-tropospheric conditions for August 2006. These temperatures are for the atmospheric layer centered in the mid-troposphere (approximately 2-6 miles above the Earth's surface) which also includes a portion of the lower stratosphere. (The MSU channel used to measure mid-tropospheric temperatures receives about 25 percent of its signal above 6 miles). For additional information on MSU data used in this report, please see the Microwave Sounding Unit page. All datasets indicate August temperatures were above average. Records began in 1979.

August	Anomaly	Rank	Warmest Year on Record	Trend
UAH mid-trop	+0.07°C/0.13°F	12th warmest	1998 (+0.44°C/0.79°F)	+0.06°C/decade
*RSS mid-trop	+0.29°C/0.52°F	4th warmest	1998 (+0.52°C/0.94°F)	+0.14°C/decade
**UW-UAH mid-trop	+0.19°C/0.34°F	5th warmest	1998 (+0.59°C/1.06°F)	+0.11°C/decade
**UW-*RSS mid-trop	+0.38°C/0.68°F	4th warmest	1998 (+0.65°C/1.17°F)	+0.19°C/decade

*Version 02_1

June- August	Anomaly	Rank	Warmest Year on Record	Trend
UAH mid-trop	+0.07°C/0.13°F	10th warmest	1998 (+0.47°C/0.85°F)	+0.05°C/decade
*RSS mid-trop	+0.28°C/0.50°F	3rd warmest	1998 (+0.55°C/0.99°F)	+0.13°C/decade
**UW-UAH mid-trop	+0.16°C/0.29°F	7th warmest	1998 (+0.60°C/1.08°F)	+0.11°C/decade
**UW-*RSS mid-trop	+0.37°C/0.67°F	3rd warmest	1998 (+0.66°C/1.19°F)	+0.18°C/decade

*Version 02_1

Stratosphere Current Month / Seasonal The table below summarizes stratospheric conditions for August 2006. On average, the stratosphere is located approximately between 10-14 miles above the Earth's surface. Over the last decade, stratospheric temperatures have been below average in large part due to the depletion of ozone. The large increase in temperature in 1982 was caused by the volcanic eruption of El Chichon in Mexico, and the increase in 1991 was a result of the eruption of Mt. Pinatubo in the Philippines. Therefore the base period used is 1984-1990 which was chosen to avoid contamination by these eruptions.

August	Anomaly	Rank	Coolest Year on Record
UAH stratosphere	-0.48°C (-0.86°F)	5th coolest	1996 (-0.70°C/-1.26°F)
*RSS stratosphere	-0.29°C (-0.52°F)	10th coolest	1996 (-0.64°C/-1.15°F)

*Version 02_1

June-August	Anomaly	Rank	Coolest Year on Record
UAH stratosphere	-0.45°C (-0.81°F)	6th coolest	1996 (-0.73°C/-1.31°F)
*RSS stratosphere	-0.27°C (-0.49°F)	9th coolest	1996 (-0.63°C/-1.13°F)

*Version 02_1

For additional details on precipitation and temperatures in August, see the Global Hazards page.

References Christy, John R., R.W. Spencer, and W.D. Braswell, 2000: MSU Tropospheric Temperatures: Dataset Construction and Radiosonde Comparisons.   J. of Atmos. and Oceanic Technology 17  1153-1170. Fu, Q., C.M. Johanson, S.G. Warren, and D.J. Seidel, 2004: Contribution of stratospheric cooling to satellite-inferred tropospheric temperature trends. Nature, 429, 55-58. Mears, Carl A., M.C. Schabel, F.J. Wentz, 2003: A Reanalysis of the MSU Channel 2 Tropospheric Temperature Record.  J. Clim 16, 3650-3664. Peterson, T.C. and R.S. Vose, 1997: An Overview of the Global Historical Climatology Network Database. Bull. Amer. Meteorol. Soc., 78, 2837-2849. Quayle, R. G., T. C. Peterson, A. N. Basist, and C. S. Godfrey, 1999: An operational near-real-time global temperature index. Geophys. Res. Lett., 26, 333-335. Smith, T. M., and R. W. Reynolds (2005), A global merged land air and sea surface temperature reconstruction based on historical observations (1880-1997), J. Clim., 18, 2021-2036.

For all climate questions other than questions concerning this report, please contact the National Climatic Data Center's Climate Services Division:   Climate Services Division NOAA/National Climatic Data Center 151 Patton Avenue, Room 010 Asheville, NC 28801-5001 fax: 828-271-4876 phone: 828-271-4800 email: ncdc.orders@noaa.gov For questions about this report, please contact:   Jay Lawrimore NOAA/National Climatic Data Center 151 Patton Avenue Asheville, NC 28801-5001 fax: 828-271-4328 email: Jay.Lawrimore@noaa.gov -or- David Easterling NOAA/National Climatic Data Center 151 Patton Avenue Asheville, NC 28801-5001 fax: 828-271-4328 email: David.Easterling@noaa.gov

IPCC Narrows Range of Projected Global Warming

It appears that IPCC projects global mean temperatures will likely rise 2 - 4.5 degree C by 2100.  Link: Tiempo Climate Newswatch, Week ending September 17th 2006.  Remember the geographic distribution of global warming: a 3 degree increase on average may translate into an 8 - 10 degree increase in the polar regions.  That sort of increase is not good for ice sheets and other positive feedback mechanisms:

Leaked information from the forthcoming Fourth Assessment of the International Panel on Climate Change suggests that the more extreme forecasts of global warming rates may be revised down. The current draft narrows the range of predictions for the year 2100 from 1.4 to 5.8 degrees Celsius to 2 to 4.5 degrees Celsius, reflecting increasing confidence in the forecasts. Holding greenhouse gas emissions at current levels would limit the rise to two degrees by the end of the century, the draft report concludes. The report will finalized in the first quarter of 2007.

Recovery Plans Critical to Success

GAO's recent report indicates that recovery plans have been important in improving the status of endangered species.  Link: GAO report

Most corals unable to adapt to warming oceans - life - 13 September 2006 - New Scientist

Link: New Scientist.

Three-quarters of the world’s coral reefs may lack the ability to cope with climate change, despite previous optimistic predictions, according to a new review of coral research.

Earlier studies had demonstrated that some corals are able adapt to warmer water temperatures by forming new, additional symbiotic relationships with algae. But a new analysis of more than 400 coral species suggests that only one-quarter of them would be able to adapt in this way.

These latest findings add to already bleak predictions for the world’s coral reefs, which are also threatened by coastal pollution and acidifying oceans. Stressors such as these cause coral to lose the algae that keep it alive by supplying it with nutrients. Even a 1 degree rise in temperature can cause the death of this fragile animal. Some experts have predicted that Australia’s Great Barrier Reef will lose 95% of its living coral by 2050.

However, two studies published in 2004 offered hope that some corals had coped with changing water temperatures by hosting new types of algae. For example, the corals along the Panama coast that were able to switch from one type of Symbiodinium algae, known as clade C, to another one called clade D.

These corals survived the particularly devastating 1997-1998 El Nino event – a recurring climate occurrence that causes elevated sea temperatures of up to 5C on the longitude line that crosses Peru and Ecuador (see Corals adapt to cope with global warming).
One at a time

Tamar Goulet at the University of Mississippi in the US carried out a review of these two research papers and 41 others to try to understand what proportion of all coral species might possess an ability to switch algae.

She found the only corals documented to be able make this swap are those that can host multiple algae. And those that can host only one clade, or type, of algae at a time have no such switching ability.

Only 23% of the 442 coral species included in Goulet's research review were able to host more than one clade of algae. As a result, she suggests that less than one-quarter of coral species may have the ability to adapt to climate change by swapping symbiotic algae. Without adaptation, coral becomes bleached and dies.

However, Goulet says she does not know the division of species among the world’s coral reefs: it is possible that adaptable species of coral are more prevalent. The studies included in Goulet’s review only covered a small fraction of the 93,000 coral species known to exist.

Journal reference: Marine Ecology Progress Series (vol 321, p 1, 2006)

Environmental Law Article Hit Parade

Link: SSRN Top Downloads.

Rank Downloads Paper Title
1     104     Montreal vs. Kyoto: A Tale of Two Protocols
                Cass R. Sunstein, University of Chicago Law School
2     74     Administrative Law in the U.S. Supreme Court, 2004-2006:                     Trends, Cases, and Unexploded Bombshells
                Robin Kundis Craig, Florida State University
3     65     Citizen Participation in Rulemaking: Past, Present, and                       Future
                Cary Coglianese, Harvard University - John F. Kennedy                     School of Government, University of Pennsylvania Law                     School
4     60     Waters of the United States: Legal Theory, Legal Practice                 and Cross Purposes at the Supreme Court
                Jamison E. Colburn, Western New England College
5     58     Regulation of Health, Safety, and Environmental Risks
                W. Kip Viscusi, Vanderbilt University
6     54     The White House and the Kyoto Protocol: Double                             Standards on Uncertainties and their Consequences                         Philippe Tulkens, Henry Tulkens, TERI School of Advanced                 Studies, Catholic University of Louvain - Center for                         Operations Research and Econometrics (CORE)
7     50     Sustainability Reporting Frameworks
                Nigel Finch, Macquarie UniversityGraduate School of                         Management
8     49     The Transatlantic GMO Dispute Against the European
                 Communities: Some Preliminary Thoughts
                David A. Wirth, Boston College Law School
9     37     CO2 Prices, Energy and Weather
                Maria Mansanet Bataller, �ngel Pardo Tornero,
                Enric Valor, University of Valencia - Faculty of Economics,
10    37     Constructing the License to Operate: Internal Factors and                 Their Influence on Corporate Environmental Decisions                     Jennifer Howard-Grenville, Jennifer Nash, Cary                                 Coglianese       
                Boston University School of Management, Harvard                             University - John F. Kennedy School of Government,                         University of Pennsylvania Law School

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The Science of Global Warming: Surface Sea Temperatures -- global warming or natural cycles

Real Climate just posted an assessment of the contribution of the previously posted Santer study to the scientific debate over the link between global warming and hurricane activity.  Real Climate link
The conclusion:

At least four studies, two based entirely on analyses of observations, and the other two based on climate model simulations, independently come to the conclusion that warming tropical Atlantic and Pacific SSTs cannot be purely attributed to any natural oscillation. These studies do not conclusively show a hurricane/global warming link, let alone determine what it's magnitude might be, but they do strengthen one pillar of that linkage.

The full post:

Roughly a year ago, we summarized the state of play in the ongoing scientific debate over the role of anthropogenic climate change in the observed trends in hurricane activity. This debate (as carefully outlined by Curry et al recently) revolves around a number of elements - whether the hurricane (or tropical cyclone) data show any significant variations, what those variations are linked to, and whether our understanding of the physics of tropical storms is sufficient to explain those links.

Several recent studies such as Emanuel (2005 -- previous discussed here) and Hoyos et al (2006 -- previous discussed here) have emphasized the role of increasing tropical sea surface temperatures (SSTs) on recent increases in hurricane intensities, both globally and for the Atlantic. The publication this week of a comprehensive paper by Santer et al provides an opportunity to assess the key middle question - to what can we attribute the relevant changes in tropical SSTs? And in particular, what can we say about Atlantic SSTs where we have the best data?

This role of SST remains pivotal in understanding long-term trends in hurricane activity, regardless of whether the SST increases are natural or anthropogenic in origin. Mann and Emanuel (2006) noted that once SST is accounted for as a factor, there is no apparent multidecadal signal in long-term hurricane numbers, regardless of what that signal might be (i.e., SST, wind sheer, or any other factors that potentially influence activity). Other studies (e.g. Bell and Chelliah, 2006) generally agree that the 'memory' of any multi-decadal osillation (whether forced or natural) lies in the ocean, and atmospheric simulations using observed SST data in the Atlantic reproduce many of the observed correlations (Zhang and Delworth, 2006). So understanding the origin of the warming SSTs is central to understanding changes in hurricane behavior.

The essential question, then, is what has caused the long-term SST changes? This question is sometimes reduced to the 'straw man' of whether tropical SSTs trends (which are very clear in the data) are internal (i.e., due to a natural oscillation of the climate system) or anthropogenic (i.e. forced by some combination of human-related causes)? Of course, this is a over-simplification since there always at least some role for internal variability. So a more useful question is to what extent SST changes can be attributed to various possible causes. 

In the Atlantic, the  proposition advanced by some is that a natural oscillation known as the Atlantic Multidecadal Oscillation (AMO) is responsible for the observed trends in SST (and by extension, North Atlantic hurricane activity). To examine that question requires a clear analysis of the data, and examination of what models suggest regarding the likely amplitude, spatial extent and physical mechanisms underlying this oscillation.

First of all, how is the AMO defined? It is intrinsically quite difficult to detect any multidecadal oscillation in roughly only one century of instrumental data. Simply put, separating an oscillation from trend becomes exceedingly tricky (and increasingly dependent on statistical assumptions) as the timescale of the oscillation approaches the length of the record. Unfortunately, this situation holds for the AMO, which has been attributed periodicities anywhere from 40-100 years, the latter approaching the length of available instrumental climate observations. In some earlier studies, the AMO was defined using multivariate signal detection procedures to tease oscillatory patterns apart from long-term (potentially non-linear) trends (e.g. Mann and Park, 1994) or using climate model-based estimates of forced trends to estimate a possible residual oscillatory component (e.g. Schlesinger and Ramankutty, 1994).

In some more recent studies, however, the AMO has been defined simply as the residual low-frequency pattern after linear detrending of SST observations (e.g. Goldenberg et al, 2001). The linear detrending is intended to remove any potential forced signal, under the assumption that it is linear in time. However, if the forced signal is not linear, then this procedure can produce a false apparent 'oscillation' purely as an artifact of the aliasing of the non-linear secular trend (Trenberth and Shea , 2006). In fact, we have very strong indications for the 20th Century that the forcings over that period have not varied in a smooth, linear fashion.

Because of the procedural difficulties in isolating the AMO signal in the instrumental record, the estimated attributes of the signal are quite sensitive to how it is defined. The earlier studies mentioned above (i.e., Mann and Park, 1994; Schlesinger and Ramankutty, 1994) found an AMO signal with a large projection onto high-latitude North Atlantic SST variations, but little projection onto tropical North Atlantic SST. This contrasts with studies using the linear detrending procedure described above, which indicate a sizeable impact of the AMO on tropical North Atlantic SST.

In a regression analysis using instrumental observations, Emanuel and Mann (2006) find that the estimated temporal history of the anthropogenic climate change signal in tropical North Atlantic SST superficially resembles the temporal pattern often ascribed to the AMO (i.e., early 20th century and 1960s-1980s cool phases, and 1930s-1950s and recent warm phase). However, they identify this irregular warming pattern with a combination of greenhouse gas warming influences and late 20th century sulphate aerosol cooling influences (which are especially large during the late boreal summer in the tropical Atlantic). It is therefore likely that the non-linear temporal history of anthropogenic tropical Atlantic warming has masquaraded as the 'AMO' in some studies.

Does the AMO even exist as a climate phenomenon absent the complications in detecting the signal in actual observations? Here the answer is probably yes. Within coupled models, enhanced multi-decadal variability with an apparent origin in Atlantic ocean-atmosphere dynamics, does occur. This was shown in work published in the early 1990s by Delworth and collaborators using the GFDL coupled ocean-atmosphere model (see the update and review in Delworth and Mann, 2000), and in more recent work by Knight et al (2005 and 2006) with the Hadley Centre coupled model. This AMO signal, in the model simulations, is associated with oscillatory variations in the meridional overturning circulation such that when the overturning is stronger than normal, there is a warming pattern in the North Atlantic (and vice versa). However, the warming in the model simulations is largely confined to the extratropical North Atlantic, with only a small (roughly 0.1 C maximum) projection onto the Main Development Region (MDR) for Atlantic hurricanes. The model simulation results therefore appear consistent with those analyses of observations which find that the AMO signal does not have a substantial projection onto tropical Atlantic SST.  This does not mean that the AMO could not in principle influence tropical Atlantic Hurricane activity. In fact, detailed analyses of both the GFDL and Hadley Centre simulations indicate that the AMO is associated with moderate changes in wind sheer in the tropical Atlantic, which could potentially influence Atlantic hurricane activity. However, as discussed earlier, a number of studies find that it is the SSTs that have played the primary role in the observed increases in hurricane intensities in recent decades.

An alternative approach to the problem is a formal 'detection and attribution' analysis which seeks to establish the role of a potentially forced signal in the midst of climate 'noise'. This is where the new Santer et al paper comes in. Here, the authors examine the model simulations for the 20th Century that were coordinated for the IPCC AR4 and which now form a very valuable database that can be used in addressing issues such as those which concern us here. For each of the models, the trends in key Atlantic and Pacific regions can be compared in the runs with and without forcing. Assuming for the moment that the models produce a reasonable approximation for the naturally occurring decadal variability, it can easily be seen whether a) the trends in the models are similar to those in the real world, and b) to what extent they can be explained by the forcings. In the Santer et al study, they find that the model trends when driven with the 20th Century forcings do match the observations, and moreover, are clearly larger than can be explained by internal variations (see the figure extracted from Figure 2 of their paper). Interestingly, the study also supports the observation-based finding of Emanuel and Mann (2006) that sulphate aerosols are likely to have masked a significant component of the late 20th century tropical Atlantic greenhouse warming.

But do the models produce a reasonable amplitude of internal variability? This is a difficult question to answer because it can't be easily deduced from the climate record (since there are many forcings, some natural, some anthropogenic) that are potentially obscuring the internal signal. However, over the period when we have good data, we can certainly check whether the models amplitude of variability is in the ball park of the observations. Santer et al did this as well, and find that indeed, there is no reason to think that models as a whole are systematically underestimate the internal component. One of the advantages of the IPCC AR4 data is that with so many models participating (22 models here), there will be a range of results - some models have more variability than observed, others less. A robust conclusion can therefore be drawn if the signals are clear regardless of the magnitude of any one models' representation of the internal variability. (Santer et al have posted an illuminating Q&A on their study that discusses this point further.) 

This result (and an associated paper by Knutson  et al who look in more detail at the GFDL simulations) is particularly notable because among the models they look at at precisely the GFDL and HadCM3 models known to generate the 'AMO' in control simulations. Thus even in those models which exhibit oscillatory 'AMO' behavior, the observed tropical SST trends can only be explained when anthropogenic forcing is included.

In total, at least four studies, two based entirely on analyses of observations, and the other two based on climate model simulations, independently come to the conclusion that warming tropical Atlantic and Pacific SSTs cannot be purely attributed to any natural oscillation. These studies do not conclusively show a hurricane/global warming link, let alone determine what it's magnitude might be, but they do strengthen one pillar of that linkage.

 

Bird Flu Blues: Another View of Air Travel Bans

Link: Aches on a Plane -- Enserink 2006 (911): 1 -- ScienceNOW.

By scouring mortality data from 121 cities across the United States, Harvard researchers have found footprints of 9/11 that they say should guide policy during an influenza pandemic. The decline in air travel in the months after the terrorist attacks delayed the annual flu season in the United States by almost 2 weeks, they conclude--a finding that suggests that a flu pandemic, too, could be slowed down, perhaps by months. But researchers who have studied the same question using computer models--and found closing down airports to be less useful--are skeptical.

The 2003 outbreak of SARS drove home the widely held belief that global mobility helps spread infections; indeed, it's almost a clich� among researchers to say that the most important disease vector today is the Boeing 747. But air-travel restriction won't help slow a flu pandemic much, three model studies concluded earlier this year--especially when compared to the judicious use of vaccines, antiviral drugs, isolation, and quarantine (ScienceNOW, 2 May).

But in the real world, the 27% reduction in air-travel volume after 9/11 appears to have caused a 13-day delay in the 2001-02 influenza season--considerably more than the models would predict, say John Brownstein and Kenneth Mandl of Children's Hospital Boston and Harvard Medical School in a paper released on 11 September by PLoS Medicine. And analyzing data from 1996 to 2005, the team found a consistent correlation between higher air-travel volumes in the fall and a slightly earlier flu season. Extrapolations suggest that a full-blown travel ban, as opposed to the post-9/11 slump, might delay a flu pandemic by as much as 2 months, says Brownstein--precious time to activate countermeasures and work on a vaccine.

World Health Organization (WHO) spokesperson Gregory Hartl says the new study is "very interesting" and "opens up the debate again." The modelers aren't convinced, however. One--Neil Ferguson of Imperial College London--says there is no proof that the relation between travel and timing of the flu season is causal. In addition, he questions the team's use of a complex statistical measure to determine the timing of the peak. Although the study is "very nice," the 9/11 effect "is an n of 1; it's intriguing, but you can't draw any conclusions," says Ira Longini of the University of Washington, Seattle, who co-authored a paper in the Proceedings of the National Academy of Sciences in April that also concluded that travel bans had little value.

The Science of Global Warming: Hurricanes

Science reported on Santer's study published in PNAS this week linking hurricane activity to global warming.  Santer's team concluded that there is a very high probability (84%) that two-thirds of the observed temperature changes were caused by human activities. "There is no way of explaining the observed increases without positing a large human impact on these ocean temperatures." ScienceNOW link .  The 3-day average sea surface temperatures as Hurricane Katrina approached the Louisiana coast. Areas in yellow, orange, or red represent SSTs of 82 degrees Fahrenheit or more.

PNAS Abstract : Previous research has identified links between changes in sea surface temperature (SST) and hurricane intensity. We use climate models to study the possible causes of SST changes in Atlantic and Pacific tropical cyclogenesis regions. The observed SST increases in these regions range from 0.32°C to 0.67°C over the 20th century. The 22 climate models examined here suggest that century-timescale SST changes of this magnitude cannot be explained solely by unforced variability of the climate system. We employ model simulations of natural internal variability to make probabilistic estimates of the contribution of external forcing to observed SST changes. For the period 1906-2005, we find an 84% chance that external forcing explains at least 67% of observed SST increases in the two tropical cyclogenesis regions. Model "20th-century" simulations, with external forcing by combined anthropogenic and natural factors, are generally capable of replicating observed SST increases. In experiments in which forcing factors are varied individually rather than jointly, human-caused changes in greenhouse gases are the main driver of the 20th-century SST increases in both tropical cyclogenesis regions.

Since last year's devastating hurricane season, few issues have been more contentious than whether human-driven global warming is responsible for the increased intensity and frequency of these storms. Research reported online this week in the Proceedings of the National Academy of Sciences points the finger pretty directly, showing that human activities have warmed the oceans and thus helped breed stronger hurricanes.

Hurricanes are born in the warm waters of the tropical Atlantic and Pacific oceans, which are both getting warmer. Over the 20th century, ocean surface temperatures increased by between 0.32 degrees Celsius in the Pacific tropical region and 0.67 degrees C in the Atlantic tropical region. This has correlated with a twofold increase in category-4 and -5 hurricanes over the last 30 years (ScienceNOW, 17 August). Some researchers maintain that these changes in sea surface temperature (SST) are within the natural variability of climate. Others say that the human-caused climate change is the culprit.

To figure out just how much people are to blame, atmospheric scientist Ben Santer of Lawrence Livermore National Laboratory in California and colleagues compared observed SSTs with the predictions of 22 global climate models. They ran the different models under various physical scenarios, including changes in solar irradiance, volcanic eruptions, and increased sulfate aerosols and greenhouse gas emissions. Only model simulations that included the known human-caused increases in greenhouse gases replicated the observed rise in SST. In total, the team found an 84% probability that two-thirds of the observed temperature changes were caused by human activities. "There is no way of explaining the observed increases without positing a large human impact on these ocean temperatures," Santer says.

Kerry Emanuel, an atmospheric scientist at the Massachusetts Institute of Technology in Cambridge, agrees that natural variability isn't the culprit. And because warmer seas provide more fuel to the engine of tropical storms, Emanuel says, "it would suggest that there are going to be stronger hurricanes."

But don't expect an enormously bigger wallop. Chris Landsea, a research meteorologist with the National Hurricane Center in Miami, Florida, expects hurricanes to increase their strength only about 1% over the next 100 years. Most researchers agree that the biggest issue with hurricane damage now is not necessarily the strength of the storms but the intense urban development that has emerged along U.S. coasts.