DOI: 10.1126/science.1120529, 1625 (2005);310 Science

Roger A. Pielke Sr.Land Use and Climate Change

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patients with large lesions that incorporateone of these areas (the orbitofrontal cortex)treat ambiguous and risky choices differ-ently from normal subjects.

Twenty-four different areas in the brainare more active under conditions of ambi-guity than risk. Among these regions, Hsuet al . focused on those that previousresearchers have, with some controversy,associated with the emotional side of deci-sion-making. However, a large number ofthese areas (located in the temporal, pari-etal, and prefrontal lobes of the brain) dealwith the estimation of the values of theoptions, which suggests that the decisionprocess integrates emotional and computa-tional components. The results confirmearlier findings that not only are ambiguityand risk treated differently by the brain (8),but so are related situations such as whenone considers sure and risky outcomes, or

monetary gains and losses (9). Takentogether, these findings support the theoryof ambiguity aversion that economistshave described.

What is next? Elucidating the neuralprocesses underlying decision-making mayhelp us understand important economic dif-ferences between ambiguity and risk.Human attitude to risk fuels the substantialprofits of two large business sectors of oureconomy—gambling and insurance. In con-trast, there is no sector served specificallyby our aversion to ambiguity. This differ-ence between risk and ambiguity is relatedto an experimental fact: If I ask you tochoose repeatedly among risky options,your risk premium remains stable. Butrecent experimental evidence (10) suggeststhat the ambiguity premium declines assubjects repeat their choices: People slowlyadjust to ambiguity; they do not adjust to

risk. Just as we learn to act optimally giventhe actions of others (the Nash equilibriumof game theory), by choosing repeatedly,one may be learning, slowly, to deal withambiguity in our choices.

References and Notes1. D. Ellsberg, Q. J. Econ. 75, 643 (1961).2. I. Gilboa, D. Schmeidler, J. Math. Econ. 18, 141 (1989).3. L. G. Epstein, Am. Econ. Rev. 91, 45 (May 2001).4. C.A. Sims, Am. Econ. Rev. 91, 51 (May 2001).5. G. Chamberlain, Am. Econ. Rev. 91, 55 (May 2001).6. L.P.Hansen,T.J.Sargent, Am.Econ.Rev.91,60 (May 2001).7. M. Hsu, M. Bhatt, R. Adolphs, D. Trane, C. F. Camerer,

Science 310, 1680 (2005).8. J. Dickhaut et al., Proc. Natl.Acad. Sci. U.S.A. 100, 3536

(2003).9. A. Rustichini, J. Dickhaut, P. Ghiradato, K. Smith,

J. Pardo, Games Econ. Behav. 52, 257 (2005).10. J. Snell, I. Levy, A. Rustichini, P. W. Glimcher, paper pre-

sented at the Society for Neuroscience meeting,Washington, DC, 12 to 16 November 2005.

11. Supported by NSF grant SES-0452477.

10.1126/science.1122179

Change and variability in land use byhumans and the resulting alterationsin surface features are major but

poorly recognized drivers of long-termglobal climate patterns (1, 2). Along withthe diverse influences of aerosols on cli-mate (1, 3, 4), these spatially heterogeneousland use effects may be at least as importantin altering the weather as changes in cli-mate patterns associated with greenhousegases. On page 1674 of this issue, Feddemaet al. report modeling results indicating thatfuture land use and land cover will continueto be an important influence on climate forthe next century (5). One implication of thiswork is that the Intergovernmental Panel onClimate Change (IPCC), which has yet toappreciate the significance of the full rangeof phenomena that drive climate change,risks rapidly falling behind the evolvingscience if this effect is not included.Although the impact of land use and landcover on the atmospheric concentration ofcarbon dioxide and methane, and on theglobal average surface albedo, have beenincluded in international climate changeassessments (6), the role of land use andland cover change and variability in alteringregional temperatures, precipitation, vege-tation, and other climate variables has beenmostly ignored.

The importance of land use and land

cover change and variability should not be asurprise. On the basis of research by Avissarand co-workers at Duke University, NASAreports that “scientists estimate thatbetween one-third and one-half of ourplanet’s land surfaces have been trans-formed by human development” (7). A largebody of research has documented the majorrole of land use and land cover change andvariability in the climate system (8–12).

One example of how land use and landcover affects global climate is the changingspatial and temporal pattern of thunder-storms. Land use and land cover change and

variability modify the surface fluxes of heatand water vapor. This alteration in thefluxes affects the atmospheric boundarylayer, and hence the energy available forthunderstorms. As shown in the pioneeringwork of Riehl and Malkus (13) and Riehland Simpson (14), at any time there are1500 to 5000 thunderstorms globally(referred to as “hot towers”) that transportheat, moisture, and wind energy to higherlatitudes. Because thunderstorms occurover a relatively small percentage of Earth’ssurface, a change in their spatial patternswould be expected to have global climateconsequences. The changes in the spatialpatterning of thunderstorms result inregional alterations in tropospheric heatingthat directly change atmospheric and oceancirculation patterns, including the move-ment and intensity of large-scale high- and

AT M O S P H E R I C S C I E N C E

Land Use and Climate ChangeRoger A. Pielke Sr.

Open water

Evergreen needle leaf tree

Deciduous broad leaf tree

Evergreen broad leaf tree

Grasses

Shrubs

Mixed woodland

Crop/mixed farming

Slough, bog, or marsh

Urban/roads, rock, sand

Saw grass/other marshes

Evergreen shrub wetland

Mangroves

Deciduous needle leaf/swamp (cypress)

Wet prairie marsh

Mixed residential

Woody wetlands

Saltwater marshPre-1900s 1993

Changing surface patterns. Vegetation classification of the Florida peninsula before 1900 (left) andin the 1990s (right), which shows the dramatic conversion of the region’s landscape during the 20thcentury. [Reprinted from (21) with permission]

The author is in the Department of AtmosphericScience, Colorado State University, Fort Collins, CO80523, USA. E-mail: pielke@atmos.colostate.edu

www.sciencemag.org SCIENCE VOL 310 9 DECEMBER 2005Published by AAAS

9 DECEMBER 2005 VOL 310 SCIENCE www.sciencemag.org1626

low-pressure weather systems (15). Mostthunderstorms (by a ratio of about 10 to 1)occur over land (16), and so land use andland cover have a greater impact on the cli-mate system than is represented by the frac-tion of area that the land covers.

To understand how these changes areimportant, consider the analogy of theglobal effects of the El Niño–SouthernOscillation (ENSO), a regional phenome-non of the Pacific Ocean. ENSO events haveglobal effects because they are of large mag-nitude, have long persistence, and are spa-tially coherent (17). Land use and land coverchange and variability have spatial scalessimilar to those associated with the sea sur-face temperature anomalies of an ENSO(18, 19). This climate phenomenon also is oflarge magnitude, has long persistence, and isspatially coherent. Thus, land use and landcover have a first-order role as a climate-forcing effect, as Feddema et al. furtherdemonstrate (1). Feddema et al. used theU.S. Department of Energy Parallel ClimateModel (DOE-PCM) to perform climatechange simulations with different scenariosof landscape change during the current cen-tury. Their study shows that future land usedecisions can alter IPCC climate changesimulations from those based solely onatmospheric composition change.

To keep up with evolving science, theIPCC assessment currently under wayshould include land use and land cover

change and variability as a first-order cli-mate forcing, along with the other spatiallyheterogeneous climate forcings as identi-f ied in a recent report of the NationalResearch Council on radiative forcing (1).To fully consider the effects of land use andland cover on climate, the IPCC also shouldmove beyond globally and zonally averagedtemperatures as the primary climate metric.Although the globally averaged surfacetemperature change over time may in fact beclose to zero in response to land use andland cover change and variability, theregional changes in surface temperature,precipitation, and other climate metrics canbe as large as or larger than those that resultfrom the anthropogenic increase of well-mixed greenhouse gases. Moreover, peopleand ecosystems experience the effects ofenvironmental change regionally, and not asglobal averaged values.

The issue of a “discernable humaninfluence on global climate” (20) missesthe obvious, in that we have been alteringclimate by land use and land cover changesince humans began large-scale alterationsof the land surface. The Feddema et al.study shows that we will continue to alterthe regional and global climate system inthe 21st century, and these changes will actas a climate-forcing effect. Such changesare bound to complicate any efforts to sta-bilize the climate system that focus only ona subset of first-order climate forcings.

References

1. Committee on Radiative Forcing Effects on Climate,Climate Research Committee, National ResearchCouncil , Radiati ve Forcing of Climate Change:Expanding the Concept and Addressing Uncertainties(National Academies Press,Washington, DC, 2005).

2. NASA Earth Observatory news feature (http://earthobservatory.nasa.gov/Study/DeepFreeze/deep_freeze5.html).

3. C. E. Chung,V. Ramanathan, J. Clim. 16, 1791 (2003).4. T. Matsui et al., Geophys. Res. Lett. 31, L06109 (2004).5. J. J. Feddema et al., Science 310, 1674 (2005).6. J. T. Houghton et al., Eds., Climate Change 2001: The

Scientific Basis. Contribution of Working Group I to theThird Assessment Report of the IntergovernmentalPanel on Climate Change (Cambridge Univ. Press,Cambridge, 2001).

7. NASA news feature, “Tropical Deforestation Affects Rainfall in the U.S. and Around the Globe”(www.nasa.gov/centers/goddard/news/topstory/2005/deforest_rainfall.html).

8. T. N. Chase et al., Clim. Dyn. 16, 93 (2000).9. M. Zhao et al., Clim. Dyn. 17, 467 (2001).

10. G. Marland et al., Clim. Policy 3, 149 (2003).11. R.Avissar, D.Werth, J. Hydrometeorol. 6, 134 (2005).12. J.A. Foley et al., Science 309, 570 (2005).13. H. Riehl, J. S. Malkus, Geophysica 6, 503 (1958).14. H.Riehl,J.M.Simpson,Contrib.Atmos.Phys.52,287 (1979).15. R.A. Pielke Sr., Rev. Geophys. 39, 151 (2001).16. Global Distribution of Lightning, April 1995–February

2003 (http://thunder.nsstc .nasa.gov/images/HRFC_AnnualFlashRate_cap.jpg).

17. Z.-X.Wu, R. E. Newell, Clim. Dyn. 14, 275 (1998).18. Australian Conservation Foundation, “Australian Land

Clearing, a Global Perspective: Latest Facts & Figures”(www.acfonline.org.au/uploads/res_land_clearing.pdf).

19. K. Klein Goldewijk, Global Biogeochem. Cycles 15, 417(2001).

20. Quoted from “Summary for Policymakers: TheScience of Climate Change,” IPCC Working Group I(www.ipcc.ch/pub/sarsum1.htm).

21. C. H. Marshall Jr., R. A. Pielke Sr., L. T. Steyaert, D. A.Willard, Mon. Weather Rev. 132, 28 (2004).

10.1126/science.1120529

Discovery in neurobiology is repletewith examples of scientists usingtoxins that bind, neutralize, or cleave

physiologically important cellular pro-teins. The inhibitory binding of saxitoxinand tetrodotoxin to the sodium channel,

conotoxin and spi-der toxins to thecalcium channel,α-bungarotoxin tothe acetylcholine

receptor, and clostridial toxins to SNAREproteins that facilitate high-fidelity mem-brane fusion—these toxins were not only

instrumental in their respective isolationand investigation but enabled the dissectionof basic cellular and physiological mecha-nisms. On page 1678 in this issue, Rigoni et

al. (1) report how the action of phospholi-pase A2, a neurotoxic component of snakevenom that paralyzes the neuromuscularjunction, reveals a new regulatory mecha-nism for neurotransmitter release at thesynapse. Lysophospholipids and free fattyacids, the hydrolytic products of this lipase,alter the energetics of the presynaptic mem-brane, thus affecting its disposition to bendand fuse with synaptic vesicles. This findingmay not only explain the long-standing mys-tery of the molecular mechanism of action ofpresynaptic neurotoxins that have phospho-lipase A2 activity, but it also demonstratesthe critical importance of membrane lipidcomposition for synaptic activity.

Phospholipase A2 hydrolyzes stablemembrane lipids into lipids that cannotform bilayers. Rather, the lipid productsform micelles (lysophospholipids) andinverted micelle-like structures (fattyacids) that reveal a positive and negativespontaneous monolayer curvature, respec-tively (2, 3) (see the figure). Our currentunderstanding of the molecular pathway ofbiological membrane fusion began withexperiments in which these curvature-pro-moting lipids revealed curvature-sensitiveintermediates during calcium-dependentexocytosis, intracellular vesicle trafficking,and virus–host cell membrane fusion (4, 5).In a “hemifusion intermediate” (6–9), thecontacting leaflets of two apposing mem-brane bilayers merge. Negative-curvaturelipids such as unsaturated fatty acids pro-mote hemifusion, but positive-curvaturelysophospholipids inhibit this process (6).In contrast, the opening of a fusion porewithin the hemifusion structure (the poreconnects the two aqueous environmentsdelineated by the two apposing mem-branes) depends on the lipid composition ofthe distal monolayers of the membranebilayers. Opening of a fusion pore is inhib-ited by unsaturated fatty acids but promoted

N E U R O S C I E N C E

Synaptic Membranes Bend

to the Will of a Neurotoxin Joshua Zimmerberg and Leonid V. Chernomordik

The authors are in the Laboratory of Cellular andMolecular Biophysics, National Institute of ChildHealth and Human Development, National Institutesof Health, Bethesda, MD 20892–1855, USA. E-mail:joshz@helix.nih.gov, chernoml@mail.nih.gov

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