Publications Published in 2006

1. A 20th Century Acceleration in Global Sea-level Rise. Church, John A.; White, Neil J..
   Geophysical Research Letters: 2006
   Notes
   Multi-century sea-level records and climate models indicate an acceleration of sea-level rise, but no 20th century acceleration has previously been detected. A reconstruction of global sea level using tide-gauge data from 1950 to 2000 indicates a larger rate of rise after 1993 and other periods of rapid sea-level rise but no significant acceleration over this period. Here, we extend the reconstruction of global mean sea level back to 1870 and find a sea-level rise from January 1870 to December 2004 of 195 mm, a 20th century rate of sea-level rise of 1.7 ± 0.3 mm yr−1 and a significant acceleration of sea-level rise of 0.013 ± 0.006 mm yr−2. This acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed. If this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm, consistent with projections in the IPCC TAR.
   
   
   
2. Abrupt reversal in ocean overturning during the Palaeocene/Eocene warm period. Nunes, Flavia; Norris, Richard D..
   Nature: 2006
   Notes
   An exceptional analogue for the study of the causes and consequences of global warming occurs at the Palaeocene/Eocene Thermal Maximum, 55 million years ago. A rapid rise of global temperatures during this event accompanied turnovers in both marine and terrestrial biota, as well as significant changes in ocean chemistry and circulation. Here we present evidence for an abrupt shift in deep-ocean circulation using carbon isotope records from fourteen sites. These records indicate that deep-ocean circulation patterns changed from Southern Hemisphere overturning to Northern Hemisphere overturning at the start of the Palaeocene/Eocene Thermal Maximum. This shift in the location of deep-water formation persisted for at least 40,000 years, but eventually recovered to original circulation patterns. These results corroborate climate model inferences that a shift in deep-ocean circulation would deliver relatively warmer waters to the deep sea, thus producing further warming. Greenhouse conditions can thus initiate abrupt deep-ocean circulation changes in less than a few thousand years, but may have lasting effects; in this case taking 100,000 years to revert to background conditions.
   
   
   
3. Abrupt tropical climate change: Past and present. Thompson, Lonnie G.; Mosley-Thompson, Ellen; Brecher, Henry; Davis, Mary; Leon, Blanca; Les, Don; Lin, Ping-Nan; Mashiotta, Tracy; Mountain, Keith.
   PNAS: 2006
   DOI: 10.1073/pnas.0603900103
   Notes
   Three lines of evidence for abrupt tropical climate change, both past and present, are presented. First, annually and decadally averaged {delta}18O and net mass-balance histories for the last 400 and 2,000 yr, respectively, demonstrate that the current warming at high elevations in the mid- to low latitudes is unprecedented for at least the last 2 millennia. Second, the continuing retreat of most mid- to low-latitude glaciers, many having persisted for thousands of years, signals a recent and abrupt change in the Earth's climate system. Finally, rooted, soft-bodied wetland plants, now exposed along the margins as the Quelccaya ice cap (Peru) retreats, have been radiocarbon dated and, when coupled with other widespread proxy evidence, provide strong evidence for an abrupt mid-Holocene climate event that marked the transition from early Holocene (pre-5,000-yr-B.P.) conditions to cooler, late Holocene (post-5,000-yr-B.P.) conditions. This abrupt event, {approx}5,200 yr ago, was widespread and spatially coherent through much of the tropics and was coincident with structural changes in several civilizations. These three lines of evidence argue that the present warming and associated glacier retreat are unprecedented in some areas for at least 5,200 yr. The ongoing global-scale, rapid retreat of mountain glaciers is not only contributing to global sea-level rise but also threatening freshwater supplies in many of the world's most populous regions.
   
   
   
4. Acceleration of Greenland ice mass loss in spring 2004. Velicogna, Isabella; Wahr, John.
   Nature: 2006
   
   
5. A climate-change risk analysis for world ecosystems. Scholze, Marko; Knorr, Wolfgang; Arnell, Nigel W.; Prentice, I. Colin.
   PNAS: 2006
   DOI: 10.1073/pnas.0601816103
   Notes
   We quantify the risks of climate-induced changes in key ecosystem processes during the 21st century by forcing a dynamic global vegetation model with multiple scenarios from 16 climate models and mapping the proportions of model runs showing forest/nonforest shifts or exceedance of natural variability in wildfire frequency and freshwater supply. Our analysis does not assign probabilities to scenarios or weights to models. Instead, we consider distribution of outcomes within three sets of model runs grouped by the amount of global warming they simulate: <2{degrees}C (including simulations in which atmospheric composition is held constant, i.e., in which the only climate change is due to greenhouse gases already emitted), 2-3{degrees}C, and >3{degrees}C. High risk of forest loss is shown for Eurasia, eastern China, Canada, Central America, and Amazonia, with forest extensions into the Arctic and semiarid savannas; more frequent wildfire in Amazonia, the far north, and many semiarid regions; more runoff north of 50{degrees}N and in tropical Africa and northwestern South America; and less runoff in West Africa, Central America, southern Europe, and the eastern U.S. Substantially larger areas are affected for global warming >3{degrees}C than for <2{degrees}C; some features appear only at higher warming levels. A land carbon sink of {approx}1 Pg of C per yr is simulated for the late 20th century, but for >3{degrees}C this sink converts to a carbon source during the 21st century (implying a positive climate feedback) in 44% of cases. The risks continue increasing over the following 200 years, even with atmospheric composition held constant.
   
   
   
6. A climatologically significant aerosol longwave indirect effect in the Arctic. Lubin, Dan; Vogelmann, Andrew M..
   Nature: 2006
   Notes
   The warming of Arctic climate and decreases in sea ice thickness and extent observed over recent decades are believed to result from increased direct greenhouse gas forcing, changes in atmospheric dynamics having anthropogenic origin and important positive reinforcements including ice–albedo and cloud–radiation feedbacks. The importance of cloud–radiation interactions is being investigated through advanced instrumentation deployed in the high Arctic since 1997 (refs 7, 8). These studies have established that clouds, via the dominance of longwave radiation, exert a net warming on the Arctic climate system throughout most of the year, except briefly during the summer. The Arctic region also experiences significant periodic influxes of anthropogenic aerosols, which originate from the industrial regions in lower latitudes. Here we use multisensor radiometric data to show that enhanced aerosol concentrations alter the microphysical properties of Arctic clouds, in a process known as the 'first indirect' effect. Under frequently occurring cloud types we find that this leads to an increase of an average 3.4 watts per square metre in the surface longwave fluxes. This is comparable to a warming effect from established greenhouse gases and implies that the observed longwave enhancement is climatologically significant.
   
   
   
7. A Combined Mitigation/Geoengineering Approach to Climate Stabilization. Wigley, T. M. L..
   Science: 2006
   DOI: 10.1126/science.1131728
   Notes
   Projected anthropogenic warming and CO2 concentration increases present a two-fold threat: both from the climate changes, and from CO2 directly through increasing acidity of the oceans. Future climate change may be reduced through mitigation (greenhouse-gas emissions reductions) or through geoengineering. Most geoengineering approaches, however, do not address the problem of increasing ocean acidity. A combined mitigation/geoengineering strategy could remove this deficiency. We consider here the deliberate injection of sulfate aerosol precursors into the stratosphere. This can significantly offset future warming and provide additional time to reduce dependence on fossil fuels and so stabilize CO2 concentrations cost-effectively at an acceptable level.
   
   
   
8. A Component-Resampling Approach for Estimating Probability Distributions from Small Forecast Ensembles. Dettinger, Michael.
   Climatic Change: 2006
   Notes
   In many meteorological and climatological modeling applications, the availability of ensembles of predictions containing very large numbers of members would substantially ease statistical analyses and validations. This study describes and demonstrates an objective approach for generating large ensembles of “additional” realizations from smaller ensembles, where the additional ensemble members share important first-and second-order statistical characteristics and some dynamic relations within the original ensemble. By decomposing the original ensemble members into assuredly independent time-series components (using a form of principal component decomposition) that can then be resampled randomly and recombined, the component-resampling procedure generates additional time series that follow the large and small scale structures in the original ensemble members, without requiring any tuning by the user. The method is demonstrated by applications to operational medium-range weather forecast ensembles from a single NCEP weather model and application to a multi-model, multi-emission-scenarios ensemble of 21st Century climate-change projections.
   
   
   
9. Addressing Global Warming, Air Pollution Health Damage, and Long-Term Energy Needs Simultaneously . Jacobson, Mark Z..
   Stanford University: 2006
   
   
10. Aerosol Effects on Clouds and Climate. Lohmann, U..
    Space Science Reviews: 2006
    Notes
    Aerosols affect the climate system by changing cloud characteristics in many ways. They act as cloud condensation and ice nuclei, they may inhibit freezing and they could have an influence on the hydrological cycle. While the cloud albedo enhancement (Twomey effect) of warm clouds received most attention so far and traditionally is the only indirect aerosol forcing considered in transient climate simulations, here I discuss the multitude of effects.