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- ItemDiurnal variation of midlatitudinal NO3 column abundance over table mountain facility, California(Göttingen : Copernicus GmbH, 2011) Chen, C.M.; Cageao, R.P.; Lawrence, L.; Stutz, J.; Salawitch, R.J.; Jourdain, L.; Li, Q.; Sander, S.P.The column abundance of NO3 was measured over Table Mountain Facility, CA (34.4° 117.7° W) from May 2003 through September 2004, using lunar occultation near full moon with a grating spectrometer. The NO 3 column retrieval was performed with the differential optical absorption spectroscopy (DOAS) technique using both the 623 and 662 nm NO 3 absorption bands. Other spectral features such as Fraunhofer lines and absorption from water vapor and oxygen were removed using solar spectra obtained at different airmass factors. We observed a seasonal variation, with nocturnally averaged NO3 columns between 5-7 × 1013 molec cm-2 during October through March, and 5-22 × 10 13 molec cm-2 during April through September. A subset of the data, with diurnal variability vastly different from the temporal profile obtained from one-dimensional stratospheric model calculations, clearly has boundary layer contributions; this was confirmed by simultaneous long-path DOAS measurements. However, even the NO3 columns that did follow the modeled time evolution were often much larger than modeled stratospheric partial columns constrained by realistic temperatures and ozone concentrations. This discrepancy is attributed to substantial tropospheric NO3 in the free troposphere, which may have the same time dependence as stratospheric NO 3.
- ItemTracing the Snowball bifurcation of aquaplanets through time reveals a fundamental shift in critical-state dynamics(Göttingen : Copernicus, 2023) Feulner, Georg; Bukenberger, Mona; Petri, StefanThe instability with respect to global glaciation is a fundamental property of the climate system caused by the positive ice-albedo feedback. The atmospheric concentration of carbon dioxide (CO2) at which this Snowball bifurcation occurs changes through Earth's history, most notably because of the slowly increasing solar luminosity. Quantifying this critical CO2 concentration is not only interesting from a climate dynamics perspective but also constitutes an important prerequisite for understanding past Snowball Earth episodes, as well as the conditions for habitability on Earth and other planets. Earlier studies are limited to investigations with very simple climate models for Earth's entire history or studies of individual time slices carried out with a variety of more complex models and for different boundary conditions, making comparisons and the identification of secular changes difficult. Here, we use a coupled climate model of intermediate complexity to trace the Snowball bifurcation of an aquaplanet through Earth's history in one consistent model framework. We find that the critical CO2 concentration decreased more or less logarithmically with increasing solar luminosity until about 1 billion years ago but dropped faster in more recent times. Furthermore, there was a fundamental shift in the dynamics of the critical state about 1.2 billion years ago (unrelated to the downturn in critical CO2 values), driven by the interplay of wind-driven sea-ice dynamics and the surface energy balance: for critical states at low solar luminosities, the ice line lies in the Ferrel cell, stabilised by the poleward winds despite moderate meridional temperature gradients under strong greenhouse warming. For critical states at high solar luminosities, on the other hand, the ice line rests at the Hadley cell boundary, stabilised against the equatorward winds by steep meridional temperature gradients resulting from the increased solar energy input at lower latitudes and stronger Ekman transport in the ocean.
- ItemThe RCP greenhouse gas concentrations and their extensions from 1765 to 2300(Dordrecht [u.a.] : Springer, 2011) Meinshausen, M.; Smith, S.J.; Calvin, K.; Daniel, J.S.; Kainuma, M.L.T.; Lamarque, J.; Matsumoto, K.; Montzka, S.A.; Raper, S.C.B.; Riahi, K.; Thomson, A.; Velders, G.J.M.; van Vuuren, D.P.P.We present the greenhouse gas concentrations for the Representative Concentration Pathways (RCPs) and their extensions beyond 2100, the Extended Concentration Pathways (ECPs). These projections include all major anthropogenic greenhouse gases and are a result of a multi-year effort to produce new scenarios for climate change research. We combine a suite of atmospheric concentration observations and emissions estimates for greenhouse gases (GHGs) through the historical period (1750-2005) with harmonized emissions projected by four different Integrated Assessment Models for 2005-2100. As concentrations are somewhat dependent on the future climate itself (due to climate feedbacks in the carbon and other gas cycles), we emulate median response characteristics of models assessed in the IPCC Fourth Assessment Report using the reduced-complexity carbon cycle climate model MAGICC6. Projected 'best-estimate' global-mean surface temperature increases (using inter alia a climate sensitivity of 3°C) range from 1.5°C by 2100 for the lowest of the four RCPs, called both RCP3-PD and RCP2. 6, to 4.5°C for the highest one, RCP8. 5, relative to pre-industrial levels. Beyond 2100, we present the ECPs that are simple extensions of the RCPs, based on the assumption of either smoothly stabilizing concentrations or constant emissions: For example, the lower RCP2. 6 pathway represents a strong mitigation scenario and is extended by assuming constant emissions after 2100 (including net negative CO2 emissions), leading to CO2 concentrations returning to 360 ppm by 2300. We also present the GHG concentrations for one supplementary extension, which illustrates the stringent emissions implications of attempting to go back to ECP4. 5 concentration levels by 2250 after emissions during the 21st century followed the higher RCP6 scenario. Corresponding radiative forcing values are presented for the RCP and ECPs.
- ItemThe HadGEM2-ES implementation of CMIP5 centennial simulations(Göttingen : Copernicus, 2011) Jones, C.D.; Hughes, J.K.; Bellouin, N.; Hardiman, S.C.; Jones, G.S.; Knight, J.; Liddicoat, S.; O'Connor, F.M.; Andres, R.J.; Bell, C.; Boo, K.-O.; Bozzo, A.; Butchart, N.; Cadule, P.; Corbin, K.D.; Doutriaux-Boucher, M.; Friedlingstein, P.; Gornall, J.; Gray, L.; Halloran, P.R.; Hurtt, G.; Ingram, W.J.; Lamarque, J.-F.; Law, R.M.; Meinshausen, M.; Osprey, S.; Palin, E.J.; Parsons, Chini, L.; Raddatz, T.; Sanderson, M.G.; Sellar, A.A.; Schurer, A.; Valdes, P.; Wood, N.; Woodward, S.; Yoshioka, M.; Zerroukat, M.The scientific understanding of the Earth's climate system, including thecentral question of how the climate system is likely to respond tohuman-induced perturbations, is comprehensively captured in GCMs and EarthSystem Models (ESM). Diagnosing the simulated climate response, andcomparing responses across different models, is crucially dependent ontransparent assumptions of how the GCM/ESM has been driven - especiallybecause the implementation can involve subjective decisions and may differbetween modelling groups performing the same experiment. This paper outlinesthe climate forcings and setup of the Met Office Hadley Centre ESM, HadGEM2-ES for the CMIP5 set of centennial experiments. We document theprescribed greenhouse gas concentrations, aerosol precursors, stratosphericand tropospheric ozone assumptions, as well as implementation of land-usechange and natural forcings for the HadGEM2-ES historical and futureexperiments following the Representative Concentration Pathways. Inaddition, we provide details of how HadGEM2-ES ensemble members wereinitialised from the control run and how the palaeoclimate and AMIPexperiments, as well as the "emission-driven" RCP experiments wereperformed.
- ItemThe PMIP4 contribution to CMIP6 - Part 3: The last millennium, scientific objective, and experimental design for the PMIP4 past1000 simulations(Göttingen : Copernicus GmbH, 2017) Jungclaus, J.H.; Bard, E.; Baroni, M.; Braconnot, P.; Cao, J.; Chini, L.P.; Egorova, T.; Evans, M.; Fidel González-Rouco, J.; Goosse, H.; Hurtt, G.C.; Joos, F.; Kaplan, J.O.; Khodri, M.; Klein Goldewijk, K.; Krivova, N.; Legrande, A.N.; Lorenz, S.J.; Luterbacher, J.; Man, W.; Maycock, A.C.; Meinshausen, M.; Moberg, A.; Muscheler, R.; Nehrbass-Ahles, C.; Otto-Bliesner, B.I.; Phipps, S.J.; Pongratz, J.; Rozanov, E.; Schmidt, G.A.; Schmidt, H.; Schmutz, W.; Schurer, A.; Shapiro, A.I.; Sigl, M.; Smerdon, J.E.; Solanki, S.K.; Timmreck, C.; Toohey, M.; Usoskin, I.G.; Wagner, S.; Wu, C.-J.; Leng Yeo, K.; Zanchettin, D.; Zhang, Q.; Zorita, E.The pre-industrial millennium is among the periods selected by the Paleoclimate Model Intercomparison Project (PMIP) for experiments contributing to the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and the fourth phase of the PMIP (PMIP4). The past1000 transient simulations serve to investigate the response to (mainly) natural forcing under background conditions not too different from today, and to discriminate between forced and internally generated variability on interannual to centennial timescales. This paper describes the motivation and the experimental set-ups for the PMIP4-CMIP6 past1000 simulations, and discusses the forcing agents orbital, solar, volcanic, and land use/land cover changes, and variations in greenhouse gas concentrations. The past1000 simulations covering the pre-industrial millennium from 850 Common Era (CE) to 1849 CE have to be complemented by historical simulations (1850 to 2014 CE) following the CMIP6 protocol. The external forcings for the past1000 experiments have been adapted to provide a seamless transition across these time periods. Protocols for the past1000 simulations have been divided into three tiers. A default forcing data set has been defined for the Tier 1 (the CMIP6 past1000) experiment. However, the PMIP community has maintained the flexibility to conduct coordinated sensitivity experiments to explore uncertainty in forcing reconstructions as well as parameter uncertainty in dedicated Tier 2 simulations. Additional experiments (Tier 3) are defined to foster collaborative model experiments focusing on the early instrumental period and to extend the temporal range and the scope of the simulations. This paper outlines current and future research foci and common analyses for collaborative work between the PMIP and the observational communities (reconstructions, instrumental data).
- ItemInterglacials of the last 800,000 years(Hoboken, NJ : Blackwell Publishing Ltd, 2016) Berger, B.; Crucifix, M.; Hodell, D.A.; Mangili, C.; McManus, J.F.; Otto-Bliesner, B.; Pol, K.; Raynaud, D.; Skinner, L.C.; Tzedakis, P.C.; Wolff, E.W.; Yin, Q.Z.; Abe-Ouchi, A.; Barbante, C.; Brovkin, V.; Cacho, I.; Capron, E.; Ferretti, P.; Ganopolski, A.; Grimalt, J.O.; Hönisch, B.; Kawamura, K.A.; Landais, A.; Margari, V.; Martrat, B.; Masson-Delmotte, V.; Mokeddem, Z.; Parrenin, F.; Prokopenko, A.A.; Rashid, H.; Schulz, M.; Vazquez Riveiros, N.