New research from last week 44/2012
Posted on 6 November 2012 by Ari Jokimäki
In this week's edition we see that mankind has warmed climate in Tibet, Greenland west coast, upper troposphere, and in oceans. Sea levels have been rising since 1920's, and the rise seems to continue into the future. Climate warming melts sea ice which fools ocean life temporally. Also Chinese vegetation has got fooled by warming. We continue emitting greenhouse gases such as nitrous oxide. We also find out that scientists are not alarmists, but why do I always feel like an alarmist when I just report what their studies say?
When did modern rates of sea-level rise start?
Abstract: "Accelerations and inflexions in recent sea-level records are known from instrumental (tidegauge) datasets, but such records are generally too short to shed light on the question when modern rapid rates of sea-level rise commenced. Proxy sea-level records should therefore also be considered. In this review we compare recent proxy and instrumental sea-level records from the North Atlantic, Australia and New Zealand with the long-term (linear) rate of relative sea-level change that prevailed in the centuries and millennia before the 19th century. We re-evaluate dating models that underpin many of the proxy records and only consider published sea-level index points for which a reliable age can be firmly established. For seven coastal sites we determine the start of recent rapid sea-level rise by identifying the time when sea-level rise first departed from the long-term background rate. We find that within a 40 year period, centred around 1925, sea-level rise in all sites started to exceed the late Holocene background rate. This is consistent with local tide-gauge records and also with global and regional tide-gauge compilations. We conclude that proxy and instrumental sea-level datasets record a similar 20th century inflexion. Possible mismatches identified in published literature are therefore reconciled. We suggest that northern hemisphere ice melt, primarily from the Greenland Ice Sheet and small Arctic glaciers, is the main driving mechanism of early 20th century sea-level rise."
Citation: W. Roland Gehrels, Philip L. Woodworth, Global and Planetary Change, http://dx.doi.org/10.1016/j.gloplacha.2012.10.020.
Spring vegetation green-up onset date has advanced in China
Abstract: "The change in spring phenology is recognized to exert a major influence on carbon balance dynamics in temperate ecosystems. Over the past several decades, several studies focused on shifts in spring phenology; however, large uncertainties still exist, and one under-studied source could be the method implemented in retrieving satellite-derived spring phenology. To account for this potential uncertainty, we conducted a multi-method investigation to quantify changes in vegetation green-up date from 1982 to 2010 over temperate China, and to characterize climatic controls on spring phenology. Over temperate China, the five methods estimated that the vegetation green-up onset date advanced, on average, at a rate of 1.3 ± 0.6 days per decade (ranging from 0.4 to 1.9 days per decade) over the last 29 years. Moreover, the sign of the trends in vegetation green-up date derived from the five methods were broadly consistent spatially and for different vegetation types, but with large differences in the magnitude of the trend. The large inter-method variance was notably observed in arid and semi-arid vegetation types. Our results also showed that change in vegetation green-up date is more closely correlated with temperature than with precipitation. However, the temperature sensitivity of spring vegetation green-up date became higher as precipitation increased, implying that precipitation is an important regulator of the response of vegetation spring phenology to change in temperature. This intricate linkage between spring phenology and precipitation must be taken into account in current phenological models which are mostly driven by temperature."
Citation: Nan Cong, Tao Wang, Huijuan Nan, Yuecun Ma, Xuhui Wang, Ranga B. Myneni, Shilong Piao, Global Change Biology, DOI: 10.1111/gcb.12077.
Sea ice phenology affects biological phenology in the ocean
Abstract: "Arctic organisms are adapted to the strong seasonality of environmental forcing. A small timing mismatch between biological processes and the environment could potentially have significant consequences for the entire food web. Climate warming causes shrinking ice coverage and earlier ice retreat in the Arctic, which is likely to change the timing of primary production. In this study, we test predictions on the interactions among sea ice phenology and production timing of ice algae and pelagic phytoplankton. We do so using 1) a synthesis of available satellite observation data; and 2) the application of a coupled ice-ocean ecosystem model. The data and model results suggest that, over a large portion of the Arctic marginal seas, the timing variability of ice retreat at a specific location has a strong impact on the timing variability of pelagic phytoplankton peaks but weak or no impact on the timing of ice-algae blooms in those regions. The model predicts latitudinal and regional differences in the timing of ice algae biomass peak (varying from April to May) and the time lags between ice algae and pelagic phytoplankton peaks (varying from 45 to 90 days). The correlation between the time lag and ice retreat is significant in areas where ice retreat has no significant impact on ice-algae peak timing, suggesting that changes in pelagic phytoplankton peak timing control the variability of time lags. Phenological variability of primary production is likely to have consequences for higher trophic levels, particularly for the zooplankton grazers, whose main food source is composed of the dually pulsed algae production of the Arctic."
Citation: Rubao Ji, Meibing Jin, Øystein Varpe, Global Change Biology, DOI: 10.1111/gcb.12074.
There is a human fingerprint in ocean's salinity and temperature fields
Highlights: •Climate change has altered the salinity field of the world's oceans. •Changes match model predictions over the top 125 m. •The signal is even stronger when salinity is taken jointly with temperature.
Abstract: "The ocean's salinity field is driven primarily by evaporation, precipitation, and river discharge, all key elements of the Earth's hydrological cycle. Observations show the salinity field has been changing in recent decades. We perform a formal fingerprint-based detection and attribution analysis of these changes between 1955–2004, 60°S and 60°N, and in the top 700 m of the water column. We find that observed changes are inconsistent with the effects of natural climate variability, either internal to the climate system (such as El Niño and the Pacific Decadal Oscillation) or external (solar fluctuations and volcanic eruptions). However, the observed changes are consistent with the changes expected due to human forcing of the climate system. Joint changes in salinity and temperature yield a stronger signal of human effects on climate than either salinity or temperature alone. When examining individual depth levels, observed salinity changes are unlikely (p < 0.05) to have arisen from natural causes over the top 125 m of the water column, while temperature changes (and joint salinity/temperature changes) are distinct from natural variability over the top 250 m."
Citation: Pierce, D. W., P. J. Gleckler, T. P. Barnett, B. D. Santer, and P. J. Durack (2012), The fingerprint of human-induced changes in the ocean's salinity and temperature fields, Geophys. Res. Lett., 39, L21704, doi:10.1029/2012GL053389.
A half-million-year record of paleoclimate from Lake Manix, California
Highlights: ► We obtained a 45-m core from Lake Manix, former terminus of the Mojave River ~ 475–25 ka. ► Lake Manix persisted from OIS 12 through early OIS 2, except during interglacial OIS 11. ► Ostracode faunas record a surprising summer-dominated hydrology only during OIS 12. ► Highly variable stable isotopes buffered by evaporation persist in interglacials and glacials. ► Internal drainage-basin changes also affected the isotopic record.
Abstract: "Pluvial lakes in the southwestern U.S. responded sensitively to past climate through effects on rainfall, runoff, and evaporation. Although most studies agree that pluvial lakes in the southwestern U.S. reached their highest levels coeval with glacial stages, the specific timing of increased effective moisture and lake-level rise is debated, particularly for the southwesternmost lakes. We obtained a 45-m core of lacustrine sediment from Lake Manix, the former terminus of the Mojave River prior to about 25 ka, and supplemented data from the core with outcrop studies. These sediments provide a robust record of Mojave River discharge over the last half-million years. Lake Manix persisted from OIS 12 through early OIS 2, including during interstadial OIS 3 and interglacials OIS 5, 7, and 9. The ostracode faunal record displays a shift from an unexpectedly warm, summer-dominated lake hydrology during OIS 12 to predominantly colder, winter-dominated conditions afterwards. The ostracode-based stable isotope record displays a large degree of intra-sample variability and does not mimic other well-known isotopic records of climate change. Evaporation likely buffered the Manix δ18O record from most of the expected isotopic differences between interglacial and glacial-interval discharge. Isotopically depleted and stable lakes occurred only four to six times, most notably during OIS 7 and OIS 9. Internal drainage-basin changes also affected the isotopic record. Persistence of lakes in the Manix basin during interglacials requires atmospheric or oceanic circulation controls on the mean position of the Pacific storm track other than large ice sheets. We propose that the relative strength and sign of the Northern Annular Mode (NAM) and its influence on atmospheric river-derived precipitation is a potential explanation."
Citation: Marith C. Reheis, Jordon Bright, Steve P. Lund, David M. Miller, Gary Skipp, Robert J. Fleck, Palaeogeography, Palaeoclimatology, Palaeoecology, Volumes 365–366, 1 December 2012, Pages 11–37, http://dx.doi.org/10.1016/j.palaeo.2012.09.002.
Climate scientists are not alarmists but have underestimated recent climate changes
Highlights: ► Climate scientists are not alarmists but have underestimated recent climate changes. ► We identify a directional bias toward erring on the side of least drama (ESLD). ► ESLD is an internal pressure arising from norms of objectivity, restraint, etc. ► ESLD may cause scientists to underpredict or downplay future climate changes.
Abstract: "Over the past two decades, skeptics of the reality and significance of anthropogenic climate change have frequently accused climate scientists of “alarmism”: of over-interpreting or overreacting to evidence of human impacts on the climate system. However, the available evidence suggests that scientists have in fact been conservative in their projections of the impacts of climate change. In particular, we discuss recent studies showing that at least some of the key attributes of global warming from increased atmospheric greenhouse gases have been under-predicted, particularly in IPCC assessments of the physical science, by Working Group I. We also note the less frequent manifestation of over-prediction of key characteristics of climate in such assessments. We suggest, therefore, that scientists are biased not toward alarmism but rather the reverse: toward cautious estimates, where we define caution as erring on the side of less rather than more alarming predictions. We call this tendency “erring on the side of least drama (ESLD).” We explore some cases of ESLD at work, including predictions of Arctic ozone depletion and the possible disintegration of the West Antarctic ice sheet, and suggest some possible causes of this directional bias, including adherence to the scientific norms of restraint, objectivity, skepticism, rationality, dispassion, and moderation. We conclude with suggestions for further work to identify and explore ESLD."
Citation: Keynyn Brysse, Naomi Oreskes, Jessica O’Reilly, Michael Oppenheimer, Global Environmental Change, http://dx.doi.org/10.1016/j.gloenvcha.2012.10.008.
Late 20th century temperatures highest of last 2000 years in Tibetan Plateau
Abstract: "Using 1,981 pieces of temperature records extracted from a selection of tree rings, ice cores, sediments, and other materials with high-resolution historical temperature proxy data, a temperature series of the past 2,000 years on the Tibetan Plateau (TP) with 10-year intervals was reconstructed by the method of single sample correction—multi-sample average integration equations. This series shows that the warm periods mainly appeared before 235 A.D., 775–1275 A.D. and 1845–2000 A.D., while the cold periods occurred 245–765 A.D., 1045–1145 A.D., and 1285–1835 A.D. The Little Ice Age left clear evidence on the TP and its coldest period was between 1635 and 1675 A.D. The Medieval Warm Period on the TP was not as warm as that in the late twentieth century. During the nineteenth century, overall temperature tends to be warmer with a clear rising trend, and in the late twentieth century new highs broke the record of the past 2,000 years. Power spectrum analysis shows that temperature on the TP changes consistently and evidently in a 150-year cycle. This integrated series also shows clear correlations with sunspot activity and solar radiation, as high sunspot activities generally led to warmer periods, and vice versa. Solar activities and intense radiation of recent years are naturally conducive to the global warming since the nineteenth century. The combination of greenhouse gases and natural fluctuations in climate has been the main culprit behind the global warming in the twentieth century."
Citation: Hou Guangliang, E Chongyi, Liu Xiangjun, Zeng Fangming, Theoretical and Applied Climatology, October 2012, DOI: 10.1007/s00704-012-0783-y.
Model-observational difference for tropical upper tropospheric warming - biases in GCMs, observational datasets, or both?
Abstract: "Recent studies have examined tropical upper tropospheric warming by comparing coupled atmosphere–ocean global circulation model (GCM) simulations from Phase 3 of the Coupled Model Intercomparison Project (CMIP3) with satellite and radiosonde observations of warming in the tropical upper troposphere relative to the lower-middle troposphere. These studies showed that models tended to overestimate increases in static stability between the upper and lower-middle troposphere. We revisit this issue using atmospheric GCMs with prescribed historical sea surface temperatures (SSTs) and coupled atmosphere–ocean GCMs that participated in the latest model intercomparison project, CMIP5. It is demonstrated that even with historical SSTs as a boundary condition, most atmospheric models exhibit excessive tropical upper tropospheric warming relative to the lower-middle troposphere as compared with satellite-borne microwave sounding unit measurements. It is also shown that the results from CMIP5 coupled atmosphere–ocean GCMs are similar to findings from CMIP3 coupled GCMs. The apparent model-observational difference for tropical upper tropospheric warming represents an important problem, but it is not clear whether the difference is a result of common biases in GCMs, biases in observational datasets, or both."
Citation: Stephen Po-Chedley and Qiang Fu 2012 Environ. Res. Lett. 7 044018 doi:10.1088/1748-9326/7/4/044018.
Nitrous oxide emissions from the global agricultural nitrogen cycle
Abstract: "Reactive nitrogen (Nr) is not only an important nutrient for plant growth, thereby safeguarding human alimentation, but it also heavily disturbs natural systems. To mitigate air, land, aquatic, and atmospheric pollution caused by the excessive availability of Nr, it is crucial to understand the long-term development of the global agricultural Nr cycle. For our analysis, we combine a material flow model with a land-use optimization model. In a first step we estimate the state of the Nrcycle in 1995. In a second step we create four scenarios for the 21st century in line with the SRES storylines. Our results indicate that in 1995 only half of the Nr applied to croplands was incorporated into plant biomass. Moreover, less than 10 per cent of all Nr in cropland plant biomass and grazed pasture was consumed by humans. In our scenarios a strong surge of the Nr cycle occurs in the first half of the 21st century, even in the environmentally oriented scenarios. Nitrous oxide (N2O) emissions rise from 3 Tg N2O-N in 1995 to 7–9 in 2045 and 5–12 Tg in 2095. Reinforced Nr pollution mitigation efforts are therefore required."
Citation: Bodirsky, B. L., Popp, A., Weindl, I., Dietrich, J. P., Rolinski, S., Scheiffele, L., Schmitz, C., and Lotze-Campen, H.: N2O emissions from the global agricultural nitrogen cycle – current state and future scenarios, Biogeosciences, 9, 4169-4197, doi:10.5194/bg-9-4169-2012, 2012.
Study finds very strong recent warming along the west coast of Greenland
Abstract: "We present an updated analysis of monthly means of daily mean, minimum and maximum surface air temperature (SAT) data from Greenland coastal weather stations and from a long-running site on the Greenland ice sheet, and analyse these data for evidence of climate change, especially focusing on the last 20 years but using the whole periods of available records (some since 1873). We demonstrate very strong recent warming along the west coast of Greenland, especially during winter (locally >10 °C since 1991), and rather weaker warming on the east Greenland coast, which is influenced by different oceanographic/sea-ice and meteorological synoptic forcing conditions to the rest of Greenland. Coastal Greenland seasonal mean SAT trends were generally 2–6 °C, strongest in winter (5.7 °C) and least in summer and autumn (both 2.2 °C), during 1981–2011/12. Since 2001 Greenland mean coastal SAT increased significantly by 2.9 °C in winter and 0.8 °C in summer but decreased insignificantly by 1.1 °C in autumn and 0.2 °C in spring, during a period when there was little net change (≤ ± 0.1 °C) in northern hemisphere temperatures. SAT means for the latest 2001–11/12 decade were significantly in excess of those for peak decadal periods during the Early Twentieth Century Warm Period only in summer and winter, and not significantly greater in spring and autumn. Summer SAT increases in southern Greenland for the last 20 years were generally greater for maximum than minimum temperatures. By contrast, in winter, the recent warming was greater for minimum than maximum temperatures. The greatest SAT changes in all seasons are seen on Greenland's west coast. SAT changes on the ice sheet and a key marginal glacier closely followed nearby coastal temperatures over the last 20 years."
Citation: Edward Hanna et al 2012 Environ. Res. Lett. 7 045404 doi:10.1088/1748-9326/7/4/045404.
New projections: higher sea level and more melting from glaciers by 2100 than in previous projections
Abstract: "We examine the limitations of a semiempirical model characterized by a sea level projection of 73 cm with RCP4.5 scenario by 2100. Calibrating the model with data to 1990 and then simulating the period 1993–2009 produces sea level in close agreement with acceleration in sea level rise observed by satellite altimetry. Nonradiative forcing contributors, such as long-term adjustment of Greenland and Antarctica ice sheets since Last Glacial Maximum, abyssal ocean warming, and terrestrial water storage, may bias model calibration which, if corrected for, tend to reduce median sea level projections at 2100 by 2–10 cm, though this is within the confidence interval. We apply the semiempirical approach to simulate individual contributions from thermal expansion and small glacier melting. Steric sea level projections agree within 3 cm of output from process-based climate models. In contrast, semiempirical simulation of melting from glaciers is 26 cm, which is twice large as estimates from some process-based models; however, all process models lack simulation of calving, which likely accounts for 50% of small glacier mass loss worldwide. Furthermore, we suggest that changes in surface mass balance and dynamics of Greenland ice sheet made contributions to the sea level rise in the early 20th century and therefore are included within the semiempirical model calibration period and hence are included in semiempirical sea level projections by 2100. Antarctic response is probably absent from semiempirical models, which will lead to a underestimate in sea level rise if, as is probable, Antarctica loses mass by 2100."
Citation: Jevrejeva, S., J. C. Moore, and A. Grinsted (2012), Potential for bias in 21st century semiempirical sea level projections, J. Geophys. Res., 117, D20116, doi:10.1029/2012JD017704.
Improving sea level reconstructions using non-sea level measurements
Abstract: "We present a new method for reconstructing sea level involving cyclostationary empirical orthogonal functions (CSEOFs). While we show results from a CSEOF reconstruction using basis functions computed from satellite altimetry and subsequently fit to tide gauge data, our focus is on how other ocean observations such as sea surface temperature can be leveraged to create an improved reconstructed sea level data set spanning the time period from 1900 to present. Basis functions are computed using satellite measurements of sea surface temperature, and using a simple regression technique, these basis functions are transformed to represent a similar temporal evolution to corresponding satellite altimeter-derived sea level basis functions. The resulting sea level and sea surface temperature basis functions are fit to tide gauge data and historical sea surface temperature data, respectively, to produce a reconstructed sea level data set spanning the period from 1900 to present. We demonstrate the use of this reconstructed data set for climate monitoring, focusing primarily on climate signals in the Pacific Ocean. The CSEOF reconstruction technique can be used to create indices computed solely from sea level measurements for monitoring signals such as the eastern Pacific (EP) El Niño–Southern Oscillation (ENSO), central Pacific (CP) ENSO, and Pacific Decadal Oscillation (PDO). The EP ENSO, CP ENSO, and PDO signals are all well represented in the CSEOF reconstruction relying solely on sea level measurements from 1950 to present; however, significant improvement can be made in reconstructing these signals during the first half of the twentieth century by including sea surface temperature measurements in the sea level reconstruction procedure."
Citation: Hamlington, B. D., R. R. Leben, and K.-Y. Kim (2012), Improving sea level reconstructions using non-sea level measurements, J. Geophys. Res., 117, C10025, doi:10.1029/2012JC008277.
Other studies from last week
CLASSIC OF THE WEEK: Crowe (1963)
Abstract: "Five-year running averages of mean annual temperature and total annual precipitation are shown for selected British Columbia coast stations. Similar averages of mean seasonal and annual temperature and total seasonal and annual precipitation are also shown for Agassiz, British Columbia. A general rising trend in mean annual temperature of not more than 2F over the 50-year period beginning about 1900 is found for the British Columbia coast. This rising trend is most pronounced in autumn and winter and least evident in spring and summer. There is some evidence that the trend may recently have begun to level off or way have ended. No significant decrease or increase in total annual precipitation has occurred over the British Columbia coast during the past half-century, although summer precipitation along the southern section seems to have been somewhat lower during the second quarter of this century than it was during the first."
Citation: Crowe, R. B., 1963: Recent Temperature and Precipitation Fluctuations along the British Columbia Coast. J. Appl. Meteor., 2, 114–118. doi: http://dx.doi.org/10.1175/1520-0450(1963)0022.0.CO;2.
This is a cross-post from AGW Observer. When each paper is published, it is notified in AGW Observer Facebook page and Twitter page. At least some of these are also retweeted in Skeptical Science Twitter page. Here's the archive for the research papers of previous weeks. If this sort of thing interests you, be sure to check out A Few Things Illconsidered. They also have a weekly posting containing lots of links to new research and other climate related news.