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(Click for frequent words.) 74 Eric Rignot 68 Bindschadler 66 Velicogna 65 Zeebe 65 Konrad Steffen 65 glacial melting 65 Serreze 63 Rahmstorf 63 climate modellers 62 Jay Zwally 62 Jevrejeva 62 Isabella Velicogna 62 Le Quéré 61 Greenland ice 61 glacial melt 61 Amundsen Sea 61 Scambos 61 Romero Lankao 61 Nature Geoscience 61 Abdalati 61 Hamish Pritchard 60 Otto Bliesner 60 hydrological cycle 60 glacial retreat 60 atmospheric circulation 60 NSIDC 60 Willerslev 59 Wieslaw Maslowski 59 Gerald Meehl 59 Jakobshavn Isbrae 59 Gaetano Di Achille 59 Tulaczyk 58 Luann Becker 58 oceanic circulation 58 Schladow 58 glaciers 58 Mark Serreze 58 Antarctic ice 57 subglacial lakes 57 Jeffrey Kargel 57 Corinne Le Quere 57 atmospheric methane 57 Waleed Abdalati 57 Paleoclimate 57 Friis Christensen 57 Nature Geoscience journal 57 Zoback 57 mountain glaciers 57 Schmittner 57 Julienne Stroeve 57 Lunine 57 Marika Holland 57 deglaciation 57 Luterbacher 57 Govindasamy Bala 57 journal Nature Geoscience 57 Greenland glaciers 57 Behrenfeld 56 Caspar Ammann 56 Ravishankara 56 glaciologist 56 outlet glaciers 56 anthropogenic warming 56 icesheet 56 Robert Bindschadler 56 journal Geophysical Research 56 glacier shrinkage 56 cryosphere 56 glaciers melting 56 Aiguo Dai 56 Noah Diffenbaugh 56 Greenland Ice 56 Inez Fung 56 polar ice 56 Son Nghiem 56 Tarduno 56 mid latitudes 56 gigatonnes 56 Canadell 56 interglacial period 56 Wilfried Haeberli 56 Ignatius Rigor 56 Martin Sommerkorn 56 sheet Summerhayes 56 Jonathan Overpeck 55 Geophysical Research 55 Global Biogeochemical Cycles 55 Robert Corell 55 Eric Steig 55 atmospheric CO2 concentration 55 Alexander Goncharov 55 Dorthe Dahl Jensen 55 Gregory Asner 55 Igor Semiletov 55 Bette Otto Bliesner 55 greenhouse warming 55 Kounaves 55 Georg Kaser 55 Mojib Latif 55 Stefan Rahmstorf 55 Jane Ferrigno 55 Weiqing Han 55 satellite altimetry 55 Hegerl 55 Shakhova 55 Schellnhuber 55 Kristin Laidre 55 Svensmark 55 Climate Impact Assessment 55 Gabriel Vecchi 55 glacier melting 55 Kharecha 55 ocean acidity 54 Robock 54 atmospheric CO2 levels 54 Richard Camilli 54 polar oceans 54 journal Geology 54 midlatitudes 54 Corinne Le Quéré 54 Haymet 54 geochemists 54 Glaciology 54 Joan Kleypas 54 CoML 54 icesheets 54 atmospheric CO2 54 atmospheric oceanic 54 cryovolcanism 54 Muller Karger 54 Paal Prestrud 54 Philip Mote 54 Luthcke 54 Atlantic Multidecadal Oscillation AMO 54 Drake Deming 54 Nielsen Gammon 54 Waleed Abdalati director 54 Danovaro 54 subglacial 54 Xiaodong Song 54 phytoplankton biomass 54 von Frese 54 Josefino Comiso 54 Malte Meinshausen 54 Bedritsky 53 Ken Caldeira 53 Ira Leifer 53 Nils Axel Morner 53 Schellart 53 Pierre Friedlingstein 53 poleward 53 climatic variability 53 Michael Studinger 53 glaciological 53 tropospheric temperature 53 Last Glacial Maximum 53 Palaeocene Eocene Thermal Maximum 53 Abdussamatov 53 polar caps 53 Colaprete 53 carbon dioxide concentrations 53 Natalia Shakhova 53 Straneo 53 aerosol concentrations 53 Natalie Mahowald 53 Andrew Derocher 53 Gerald Meehl senior 53 ocean basins 53 geoid 53 Nate Mantua 53 Jonathan T. Overpeck 53 AR4 53 subsurface ocean 53 Tad Pfeffer 53 glacier melt 53 Dikpati 53 Roger Bilham 53 interannual variability 53 paleoclimatology 53 mantle convection 53 hydrologic cycle 53 Amundsen Sea Embayment 53 glacial interglacial 53 Ove Hoegh Guldberg 53 Kashlinsky 53 climate modelers 53 Walt Meier 53 Vladimir Keilis Borok 53 melting glaciers 53 Antarctic Ice 53 isostatic rebound 53 Roger Pielke 53 Wysession 53 Rossby waves 53 paleoclimatic 52 Walter Jetz 52 atmospheric carbon dioxide 52 Ellen Stofan 52 palaeoclimate 52 Georgina Mace 52 Stramma 52 Biogeochemistry 52 glacier retreat 52 cosmic ray flux 52 Tibetan Plateau 52 Chris Rapley 52 iceberg calving 52 sediments deposited 52 Amstrup 52 glacial cycles 52 Planetary Change 52 atmospheric chemistry 52 receding glaciers 52 Biogeography 52 Cryospheric Sciences Branch 52 Dronning Maud Land 52 Von Frese 52 paleoclimate 52 Inter Governmental Panel 52 surface temperatures SSTs 52 Camille Parmesan 52 Professor Hoegh Guldberg 52 Guldberg 52 Eduardo Zorita 52 Qiang Fu 52 Reinhard Genzel 52 Makiko Sato 52 Fred Grassle 52 Thiemens 52 solar irradiance 52 Blair Trewin 52 anthropogenic greenhouse gases 52 Johannes Lehmann 52 Geoffrey Schladow 52 Veerabhadran Ramanathan 52 Sara Seager 52 University Lamont Doherty 52 atmospheric CO 52 Molnia 52 Bruce Jakosky 52 Antarctic glaciers 52 temperature reconstructions 52 Klekociuk 52 Villy Christensen 52 paleomagnetic 52 Jonathan Lunine 52 journal Cerebral Cortex 52 Henrik Svensmark 52 Wingenter 52 Sugata Hazra 52 terrestrial ecosystems 52 British Antarctic Survey 52 Sekercioglu 52 Jenniskens 52 ozone layer depletion 52 Rasik Ravindra 52 Sheldon Drobot 52 Solar Terrestrial Physics 52 Harvati 52 Jakobshavn 51 Eske Willerslev 51 Dr van Ommen 51 ocean salinity 51 CIRES 51 Shad O'Neel 51 ICIMOD 51 glaciologists 51 Laurentide ice sheet 51 Hoeppe 51 Aleklett 51 Landsea 51 NCEAS 51 Michael Blanpied 51 Indian climatologist Rajendra 51 Postberg 51 Claudia Tebaldi 51 Kossin 51 constructal theory 51 decadal 51 supercomputer simulations 51 planetary scientist 51 Vengosh 51 NCAR scientist Synte Peacock 51 Christian Nellemann 51 Roland Holst 51 Greenland icecap 51 Climate Impacts Group 51 Wolf Reik 51 Gaensler 51 Synte Peacock 51 Svante Arrhenius 51 mantle plumes 51 thermal inertia 51 journal Icarus 51 Scott Luthcke 51 paleoclimatologist 51 Syed Hasnain 51 Foing 51 MIT planetary scientist 51 Ryskin 51 Himalayan Glaciers 51 El Nino La Nina 51 Bojowald 51 deep convective clouds 51 Orjan Gustafsson 51 Indian Ocean Dipole 51 Peter Jenniskens 51 Nature Geosciences 51 Benjamin Santer 51 Hoerling 51 Shaviv 51 glacial ice 51 glaciology 51 journal Palaios 51 sediment cores 51 glaciers melt 51 NCAR scientist 51 Trenberth 51 Stockholm Resilience 51 VK Raina 51 Pachauri IPCC 51 El Nino warming 51 Jianjun Yin 51 Glikson 51 Valter Longo 51 Ted Scambos 51 Professor Ove Hoegh 51 IPY 51 NCAR scientist Gerald Meehl 51 Greenland glacier 51 PS Goel 51 Yun Qian 51 journal Climatic Change 51 phytoplankton blooms 51 General Michel Jarraud 51 Rebecca Garten 51 planetary geologist 51 Carl Wieman 51 Carl Wunsch 51 Sasselov 51 Climate Impact 51 Kucharik 51 William Bottke 51 Ian Joughin 51 Russ Hopcroft 51 Lars Prahm 51 Diffenbaugh 51 Bramley Murton 50 Makovicky 50 upwellings 50 Leitzmann 50 teleconnections 50 Kevin Trenberth climate 50 Ross Salawitch 50 Boris Worm 50 aerosol particles 50 WMO 50 Pacific hake whitefish 50 springtime ozone 50 Chasma Boreale 50 Hoegh Guldberg 50 CO2 fluxes 50 CO2 concentrations 50 mid Pliocene 50 greenhouse gas concentrations 50 radar altimetry 50 Jay Famiglietti 50 Lamont Doherty 50 anomalously warm 50 Roger Pielke Sr. 50 Madden Julian Oscillation 50 martian meteorites 50 San Diego Scripps Institution 50 glacial earthquakes 50 Nilton Renno 50 Maria Zuber 50 KT boundary 50 Pielke 50 CReSIS 50 tectonic plate movements 50 scientist Jay Zwally 50 Pääbo 50 Czech Hydrometeorological Institute 50 Jeffrey Plaut 50 Gerta Keller 50 Victor Sardina 50 Margaret Gatz 50 interglacial periods 50 Phil Klotzbach member 50 Farzaneh Far 50 USGS geologist 50 Ketterle 50 Dr Raupach 50 Pachauri 50 ESRL 50 Climate modelers 50 poleward shift 50 Smol 50 Neukum 50 tropical troposphere 50 NASA GISS 50 Puijila 50 Rijsberman 50 Masaru Emoto 50 Auwerx 50 Cynthia Rosenzweig 50 Pedro Martinez Arbizu 50 Anthony Barnosky 50 climatologists 50 ° C warmer 50 Dr. Judy Mikovits 50 eruptive activity 50 Prasad Gogineni 50 atmospheric aerosols 50 ocean acidification 50 Mojzsis 50 Bob Corell 50 Drew Shindell 50 Pep Canadell 50 Roland Burgmann 50 bathymetry 50 Alycia Weinberger 50 Alberto Saal 50 Peter Ewins 50 terrestrial biosphere 50 IPCC AR4 50 icecaps 50 Shripad Tuljapurkar 50 Hik 50 Scripps Oceanography 50 IPCC Intergovernmental Panel 50 Sigmundsson 50 De Pontieu 50 Ron O'Dor 50 journal Chemosphere 50 Samuel Wickline 50 equatorial regions 50 Finnish Meteorological 50 meltwater 50 Snowball Earth 50 Natalia Rybczynski 50 Peter Makovicky 50 Dev Niyogi 50 Bill Chameides 50 Priscu 50 Awschalom 50 storied snows 50 S. Lindzen 50 Cassini flyby 50 Nansen Environmental 50 Dansgaard 50 James Vaupel 50 Climate Experiment GRACE 50 Roger Pielke Jr. 50 Jurgen Rehm 49 Tas van Ommen 49 Petoukhov 49 Crutzen 49 planetary astronomy 49 Le Quere 49 USGS 49 Stephane Udry 49 Ulysses spacecraft 49 Nir Barzilai 49 lithosphere 49 Service WGMS 49 ICESat 49 V. Ramanathan 49 Andrew Dessler 49 Mike Raupach 49 Himalayan glaciers melting 49 Alicja Wolk 49 Fram Strait 49 oceanographers 49 IFM GEOMAR 49 explosive volcanism 49 Baross 49 Patricia Romero Lankao 49 La Nina pattern 49 seabed sediments 49 lunar perigee 49 Cotsarelis 49 amplifying feedbacks 49 hydrothermal activity 49 Jean Pierre Bibring 49 biogeochemist 49 axial tilt 49 Buesseler 49 CryoSat mission 49 acidification 49 Neil Adger 49 Kevin Trenberth 49 sulphate aerosols 49 Ontario Lacus 49 Fendorf 49 volcanism 49 Antarctic icecap 49 substorm 49 basaltic rocks 49 Minik Rosing 49 Sheet WAIS 49 Jarraud 49 ACIA 49 Syun Ichi Akasofu 49 Carolyn Driedger 49 atmospheric sciences 49 equatorial Pacific Ocean 49 Veizer 49 Blaire Van Valkenburgh 49 magnetic reconnection 49 Margaret Leinen 49 Geoff Schladow 49 Jonathan Patz 49 atmospheric concentrations 49 Jacques Laskar 49 anthropogenic climate 49 ocean eddies 49 Cryogenian 49 coccolithophores 49 Niels Bohr Institute 49 coastal upwelling 49 Di Achille 49 Boffetta 49 glaciations 49 degrees Fahrenheit warmer 49 Donald Scavia 49 Elisabeth Cardis 49 oxygen isotopes 49 chlorophyll concentrations 49 J. Klotzbach 49 shrinking glaciers 49 Mandushev 49 constructal law 49 Stephen Palumbi 49 #.#oC [001] 49 sub glacial lakes 49 polar vortex 49 Milankovitch cycles 49 Himalayan river basins 49 Siple Dome 49 Domack 49 geomorphology 49 Thatje 49 GFZ 49 Alfred McEwen 49 Shamay Tsoory 49 Jim Kauahikaua 49 oxygen isotope 49 geoscientist 49 Erik Asphaug 49 Wallace Broecker 49 alpine glaciers 49 Graeme Pearman 49 Vernon Kousky NOAA 49 continental crust 49 Paquay 49 permafrost degradation 49 midlatitude 49 boreal regions 49 Robin Canup 49 geodynamics 49 Jonathan Lunine Cassini 49 Beichman 49 Glaciologists 49 Geophysical Union 49 journal Meteoritics 49 spatial variability 49 Maya Tolstoy 49 atmospheric ozone 49 Paytan 49 BN Goswami 48 Nikku Madhusudhan 48 Volker Liebig 48 storminess 48 Lautenbacher 48 neutrino physics 48 Roger Pielke Jr 48 Dariusz Leszczynski 48 Eemian 48 Syed Iqbal Hasnain 48 Gavin Prideaux 48 glacial shrinkage 48 Emile Okal 48 Bottke 48 Wolszczan 48 Winglee 48 Biological Conservation 48 multi decadal 48 Cliff Frohlich 48 Weddell Sea 48 Anisotropy Probe 48 polar regions 48 Alpine glaciers 48 Mars Squyres 48 Van Mooy 48 Zheng Cui 48 Banerdt 48 Computer simulations 48 La Niña pattern 48 Astrobiology 48 CSIRO Wealth 48 Andreas Muenchow 48 Dr. Nabel 48 Jon Ove Hagen 48 Mark Serreze senior 48 Ken Hudnut 48 Tim Frayling 48 El Niño La Niña 48 Scripps Institution 48 marine phytoplankton 48 Svedhem 48 Roger Revelle 48 Climate Change Impacts 48 Venusian atmosphere 48 Permian extinction 48 Rudolf Grimm 48 Bandfield 48 Planetary Science Institute 48 Hans Joachim Schellnhuber 48 permafrost 48 Dennis Todey 48 Fred Kavalier 48 Planetary Science Letters 48 methane hydrate 48 Wick Haxton 48 Andreas Schild 48 Dauphas 48 journal Astrobiology 48 Frank Bertoldi 48 O'Dor 48 glacier calving 48 altimetry 48 Chow Kok Kee 48 Berkeley Seismological Laboratory 48 Glacial melt 48 Qin Dahe 48 Karnosky 48 Earth Observation Programmes 48 Climate Change IPCC 48 Shanna Swan 48 climate modeler 48 atmospheric chemist 48 paleoclimatologists 48 Ghassem Asrar 48 El Niños 48 biogeochemistry 48 scientist Mark Serreze 48 Krimigis 48 journal PLoS Genetics 48 Jay Melosh 48 Climatic Change 48 Nolan Doesken 48 Törnqvist 48 verified experimentally 48 polar icecap 48 Agronomy Journal 48 O'Lenic 48 monsoon rainfall 48 Himalayan glaciers 48 Lake Yoa 48 tropopause 48 Betsy Weatherhead 48 Dolores Piperno 48 journal BioScience 48 authors Kevin Trenberth 48 Physical Oceanography 48 plate tectonics 48 Meteoritics 48 Hans Dieter Sues 48 anthropogenic CO2 emissions 48 Millennium Ecosystem Assessment 48 Vikhlinin 48 amphibian declines 48 Nankai Trough 48 magma ocean 48 Atmospheric Chemistry 48 Cassini radar 48 Lars Wallentin 48 Rokhsar 48 Frank Rijsberman 48 Ecology Letters 48 NOAA Geophysical Fluid 48 El Nino periodic 48 dustier stormier atmosphere 48 SST anomalies 48 Martin Tomasko 48 Ziurys 48 benthos 48 permafrost thaws 48 Synolakis 48 Julia Slingo 48 Alan Robock 48 equatorial latitudes 48 ozone depletion 48 anthropogenic 48 Brigham Grette 48 ppmv 48 Global Precipitation Climatology 48 Louis Zeidberg 48 Arik Posner 48 Jean Luc Margot 48 Melosh 48 Aquatic Toxicology 48 MARSIS 48 forams 48 heatwaves floods droughts 48 Astrophysical Journal 48 Bonnie Buratti 48 hydrosphere 48 Williams Ryan Divish 48 Copeia 48 IWMI 48 nitrogen deposition 47 Professor Wickramasinghe 47 Guhathakurta 47 Ted Scambos glaciologist 47 C# atmospheric concentrations 47 Min Gu 47 subduction zones 47 tropospheric 47 Brendan Godley 47 Jianli Chen 47 Warmer oceans 47 wetter winters 47 scientist Vassilis Angelopoulos 47 Stellacci 47 Beroza 47 polar 47 Mewaldt 47 Cecilia Ramlau Hansen 47 Werthimer 47 carbon fluxes 47 moon Enceladus 47 Antarctica EPICA 47 Erik Seiffert 47 journal Animal Behaviour 47 Mark Westneat 47 Paul Thornalley 47 Kay Bidle 47 Roger Musson 47 Oliver Pergams 47 Glacier Monitoring 47 AGW theory 47 teragrams 47 David Southwood ESA 47 atmospheric CO2 concentrations 47 Sinervo 47 Schulp 47 journal Science 47 EPOCh 47 Roenneberg 47 Glaciologist 47 Dr Trewin 47 sulfate aerosols 47 Atmospheric Administration Jane Lubchenco 47 matter antimatter asymmetry 47 TrES 4 47 seafloor sediments 47 polynya 47 crustal thickness 47 manmade CO2 emissions 47 Shinji Toda 47 lunar magma 47 peer reviewed journal Nature 47 Earthquake Hazards Project 47 glaciation 47 icecap 47 Rune Graversen 47 journal Behavioral Ecology 47 Tegmark 47 Pete Ewins 47 methane hydrate deposits 47 Hans von Storch 47 USGS scientist 47 sunspot activity 47 Massimo Napolitano 47 sulfur isotope 47 Mary Stampone 47 journal NeuroImage 47 Sciencexpress 47 Gino Casassa 47 Koebnick 47 Quaternary Period 47 Andrew Glikson 47 Reynir Bodvarsson director 47 Priyamvada Natarajan 47 oceans 47 NGRI 47 Overpeck 47 Climatic Research 47 Hongbin Qu chief 47 interglacial 47 Bredella 47 DeWeaver 47 Zarnecki 47 Arctic icecap 47 Andrew Maskrey 47 neutrino detectors 47 Edward Leamer director 47 Pericak Vance 47 glacier 47 Appy Sluijs 47 El Ninos 47 thermohaline circulation 47 Geir Braathen 47 scientific journal Proceedings 47 Loveland Curtze 47 Braathen 47 geologically active 47 Wassertheil Smoller 47 permafrost thaw 47 Carnegie Institution Geophysical 47 ENSO cycle 47 IPCC 47 Grillmair 47 asthenosphere 47 anthropogenic emissions 47 species extinctions 47 Beratan 47 Shepson 47 Hörst 47 #.#C #.#C 47 Michel Jarraud WMO 47 Greenland icesheet 47 Ottmar Edenhofer 47 Review Letters 47 Nogues Bravo 47 Shoukhrat Mitalipov 47 AR Ravishankara 47 Hubble observations 47 Brenda Ekwurzel climate 47 World Meteorological Organization 47 journal Nature 47 Frank Guidone Company 47 author Ken Caldeira 47 substorms 47 Aharonson 47 Guido van Langenhove 47 megafauna extinction 47 Hadow 47 upper troposphere 47 Patricia Ganz 47 climatic variations 47 Dr. Marcia McNutt 47 meridional flow 47 latitudes 47 Synthesis NCEAS 47 Meehl 47 Kutzbach 47 YORP effect 47 Mien Chie Hung 47 journal Ethology 47 Atlantic meridional overturning 47 Intergovernment Panel 47 Chicxulub impact 47 tropical glaciers 47 Camilla Toulmin 47 Greenland Antarctica 47 Brian Baptie 47 USGS hydrologist 47 Helheim glacier 47 retreating glaciers 47 Arctic Oscillation 47 Niiler 47 Hugh Possingham 47 Melting glaciers 47 Solar Radiation 47 volcanic aerosols 47 Fabrycky 47 Rainer Klement 47 Calambokidis 47 Human Mutation 47 geomagnetic activity 47 melting polar 47 Sumatra Andaman earthquake 47 continental drift 47 sedimentary deposits 47 Toba eruption 47 numerical modeling 47 Jakosky 47 mesoscale 47 Kenneth Deffeyes 47 Noaa 47 Qi Dai 47 Biochemical Zoology 47 Microbiologist Cynan Ellis 47 Linda Calabresi 47 decadal variability 47 El Niño winters 47 biogeochemical cycles 47 Patzert 47 International Geosphere Biosphere 47 NASA Isabella Velicogna 47 disappearing glaciers 47 Ny Ålesund 47 Stephen P. Utkus 47 Ken Edgett 47 evapotranspiration 47 Noah Fierer 47 Christophe Lovis 47 Christopher Haiman 47 Zachos 47 Applied Meteorology 47 Raupach 47 Ajit Tyagi 47 Harry Hillaker 47 ESA Envisat satellite 47 Geological Surveys 47 Polar Biology 47 Moetasim Ashfaq 47 Anthony Colaprete LCROSS 47 Optics Letters 47 Spudis 47 Kunches 47 abyssal plains 47 numerical simulations 47 Lindzen 47 Milankovitch 47 Lubchenko 47 Irva Hertz Picciotto 47 sterile neutrino 47 Pakrasi 46 Frank Muller Karger 46 science journal Nature 46 Slawek Tulaczyk 46 journal Langmuir 46 Sergio DellaPergola 46 IODP 46 Tod Strohmayer 46 journal Palaeontology 46 Xiang Zhang 46 Year IPY 46 Hochedlinger 46 Gnedin 46 Pikitch 46 Ewan Birney 46 World Meteorological Organisation 46 Nature.com 46 Muller Landau 46 streamflow 46 Keilis Borok 46 glacial meltwater 46 AMSR E 46 Tropical Meteorology Pune 46 Hsee 46 Lida Pet Soede 46 acidic oceans 46 manmade greenhouse gases 46 Angelika Brandt 46 authoritative Intergovernmental Panel 46 Chris Landsea 46 Gravitational waves 46 Norphel 46 radiative forcing 46 marine geophysicist 46 Limnology 46 Heasler 46 Gangotri glacier 46 Anthony Westerling 46 albedo feedback 46 Simin Nikbin Meydani 46 Melott 46 Tropical Meteorology Project 46 opossum shrimp 46 Margarita Marinova 46 Tropical Meteorology 46 Scarmeas 46 Kangerdlugssuaq 46 GHG concentrations 46 Philosophical Transactions 46 Kilimanjaro glaciers 46 Terry Engelder 46 Manfred Kayser 46 Chepstow Lusty 46 Matt Sponheimer 46 Jamie Elsila 46 Eve Van Cauter 46 Ocean Observing 46 ICESCAPE 46 Manoranjan Mohanty 46 iron fertilization 46 Furnes 46 auroral activity 46 phytoplankton bloom 46 MeT department 46 Antarctic Circumpolar Current 46 Christopher Chyba 46 Tim Coughlin MAusIMM 46 Paul Alivisatos 46 NASA QuikScat satellite 46 Icelandic Meteorological Office 46 Max Planck Institut fur 46 Gerard Kuiper 46 Hal Levison 46 Revkin 46 H. Gleick 46 Svalbard archipelago 46 extinctions 46 Keeling Curve