AGW Observer

Observations of anthropogenic global warming

New research from last week 15/2011

Posted by Ari Jokimäki on April 18, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Forests stabilize temperature

Extreme temperature analysis under forest cover compared to an open field – Ferrez et al. (2011) “We analyse air temperature data from 14 sites in Switzerland, each with two weather stations in close proximity, one under a forest canopy and the other in the open. We use the statistics of extremes to investigate how extremely high maximum and extremely low minimum temperatures depend on the effect of forest cover. Our analysis shows that temperature maxima at two nearby stations are less dependent than are temperature minima. Maxima under the canopy are influenced by altitude: for higher sites, the maxima are less variable and depend less on the open-field data. Southerly orientations increase the dependence of minimum temperatures and so reduce the sheltering effect during cold periods. Extreme maximum and minimum temperatures occur less within conifer forests, indicating that the insulation provided by conifers all over the year is more efficient than that provided by deciduous species. Steepness of slopes has a complex impact on distributions of extremes and on their dependence.” J. Ferrez, A.C. Davison and M. Rebetez, Agricultural and Forest Meteorology, doi:10.1016/j.agrformet.2011.03.005.

Downward IR decreasing due to clouds in one measurement site

Long-Term Trends in Downwelling Spectral Infrared Radiance over the U.S. Southern Great Plains – Gero & Turner (2011) “A trend analysis was applied to a 14-year time series of downwelling spectral infrared radiance observations from the Atmospheric Emitted Radiance Interferometer (AERI) located at the Atmospheric Radiation Measurement (ARM) site in the U.S. Southern Great Plains. The highly accurate calibration of the AERI instrument, performed every 10 minutes, ensures that any statistically significant trend in the observed data over this time can be attributed to changes in the atmospheric properties and composition, and not to changes in the sensitivity or responsivity of the instrument. The measured infrared spectra, numbering over 800,000, were classified as clear-sky, thin cloud, and thick cloud scenes using a neural network method. The AERI data record demonstrates that the downwelling infrared radiance is decreasing over this 14-year time period in the winter, summer, and autumn seasons but is increasing in the spring; these trends are statistically significant and are primarily due to long-term change in the cloudiness above the site. The AERI data also show many statistically significant trends on annual, seasonal, and diurnal time scales, with different trend signatures identified in the separate scene classifications. Given the decadal time span of the dataset, effects from natural variability should be considered in drawing broader conclusions. Nevertheless, this data set has high value due to the ability to infer possible mechanisms for any trends from the observations themselves, and to test the performance of climate models.” P. Jonathan Gero, David D. Turner, Journal of Climate 2011, doi: 10.1175/2011JCLI4210.1.

Warming and acidification bad for shelled pteropod

Impact of ocean acidification and elevated temperatures on early juveniles of the polar shelled pteropod Limacina helicina: mortality, shell degradation, and shell growth – Lischka et al. (2011) “Due to their aragonitic shell, thecosome pteropods may be particularly vulnerable to ocean acidification driven by anthropogenic CO2 emissions. This applies specifically to species inhabiting Arctic surface waters that are projected to become temporarily and locally undersaturated with respect to aragonite as early as 2016. This study investigated the effects of rising partial pressure of CO2 (pCO2) and elevated temperature on pre-winter juveniles of the polar pteropod Limacina helicina. After a 29 day experiment in September/October 2009 at three different temperatures and under pCO2 scenarios projected for this century, mortality, shell degradation, shell diameter and shell increment were investigated. Temperature and pCO2 had a significant effect on mortality, but temperature was the overriding factor. Shell diameter, shell increment and shell degradation were significantly impacted by pCO2 but not by temperature. Mortality was 46% higher at 8 °C than at in situ temperature (3 °C), and 14% higher at 1100 μatm than at 230 μatm. Shell diameter and increment were reduced by 10 and 12% at 1100 μatm and 230 μatm, respectively, and shell degradation was 41% higher at elevated compared to ambient pCO2. We conclude that pre-winter juveniles will be negatively affected by both rising temperature and pCO2 which may result in a possible decline in abundance of the overwintering population, the basis for next year’s reproduction.” Lischka, S., Büdenbender, J., Boxhammer, T., and Riebesell, U., Biogeosciences, 8, 919-932, doi:10.5194/bg-8-919-2011, 2011. [Full text]

Complexity of black carbon climatic effects

Dependence of climate forcing and response on the altitude of black carbon aerosols – Ban-Weiss et al. (2011) “Black carbon aerosols absorb solar radiation and decrease planetary albedo, and thus can contribute to climate warming. In this paper, the dependence of equilibrium climate response on the altitude of black carbon is explored using an atmospheric general circulation model coupled to a mixed layer ocean model. The simulations model aerosol direct and semi-direct effects, but not indirect effects. Aerosol concentrations are prescribed and not interactive. It is shown that climate response of black carbon is highly dependent on the altitude of the aerosol. As the altitude of black carbon increases, surface temperatures decrease; black carbon near the surface causes surface warming, whereas black carbon near the tropopause and in the stratosphere causes surface cooling. This cooling occurs despite increasing planetary absorption of sunlight (i.e. decreasing planetary albedo). We find that the trend in surface air temperature response versus the altitude of black carbon is consistent with our calculations of radiative forcing after the troposphere, stratosphere, and land surface have undergone rapid adjustment, calculated as “regressed” radiative forcing. The variation in climate response from black carbon at different altitudes occurs largely from different fast climate responses; temperature dependent feedbacks are not statistically distinguishable. Impacts of black carbon at various altitudes on the hydrological cycle are also discussed; black carbon in the lowest atmospheric layer increases precipitation despite reductions in solar radiation reaching the surface, whereas black carbon at higher altitudes decreases precipitation.” George A. Ban-Weiss, Long Cao, G. Bala and Ken Caldeira, Climate Dynamics, DOI: 10.1007/s00382-011-1052-y.

Future climate does not treat Greece very well

An integrated assessment of climate change impacts for Greece in the near future – Giannakopoulos et al. (2011) “Climate changes in the Mediterranean region, related to a significant increase in temperature and changes in precipitation patterns, can potentially affect local economies. Agriculture and tourism are undoubtedly the most important economic sources for Greece and these may be more strongly affected by changing future climate conditions. Climate change and their various negative impacts on human life are also detected in their environment; hence this study deals with implications, caused by changing climate, in urban and forest areas. Potential changes for the mid-twenty-first century (2021–2050) are analysed using a high-resolution regional climate model. This paper presents relevant climatic indices, indicative for potential implications which may jeopardise vital economic/environmental sectors of the country. The results provide insights into particular regions of the Greek territory that may undergo substantial impacts due to climate change. It is concluded that the duration of dry days is expected to increase in most of the studied agricultural regions. Winter precipitation generally decreases, whereas an increase in autumn precipitation is projected in most areas. Changing climate conditions associated with increased minimum temperatures (approximately 1.3°C) and decreased winter precipitation by 15% on average suggest that the risk for forest fires is intensified in the future. In urban areas, unpleasantly high temperatures during day and night will increase the feeling of discomfort in the citizens, while flash floods events are expected to occur more frequently. Another impact of climate change in urban regions is the increasing energy demand for cooling in summer. Finally, it was found that continental tourist areas of the Greek mainland will more often face heatwave episodes. In coastal regions, increased temperatures especially at night in combination with high levels of relative humidity can lead to conditions that are nothing less than uncomfortable for foreigners and the local population. In general, projected changes associated with temperature have a higher degree of confidence than those associated with precipitation.” Christos Giannakopoulos, Effie Kostopoulou, Konstantinos V. Varotsos, Kostas Tziotziou and Achilleas Plitharas, Regional Environmental Change, DOI: 10.1007/s10113-011-0219-8. [Full text]

More evidence for upwelling intensification in oceans

Coastal cooling and increased productivity in the main upwelling zone off Peru since the mid-twentieth century – Gutiérrez et al. (2011) “We reconstructed a high-resolution, alkenone-based sea surface temperature (SST) record spanning the last ca. 150 years, from a sediment core retrieved within the main upwelling zone off Peru. A conspicuous SST decline is evidenced since the 1950s despite interdecadal SST variability. Instrumental SST data and reanalysis of ECMWF ERA 40 winds suggest that the recent coastal cooling corresponds mainly to an intensification of alongshore winds and associated increase of upwelling in spring. Consistently, both proxy and instrumental data evidence increased productivity in phase with the SST cooling. Our data expand on previous reports on recent SST cooling in other Eastern Boundary upwelling systems and support scenarios that relate coastal upwelling intensification to global warming. Yet, further investigations are needed to assess the role of different mechanisms and forcings (enhanced local winds vs. spin-up of the South Pacific High Pressure cell).” Gutiérrez, D., et al. (2011), Geophys. Res. Lett., 38, L07603, doi:10.1029/2010GL046324.

Human fingerprint shows also in short satellite records

Atmospheric Climate Change Detection by Radio Occultation Data Using a Fingerprinting Method – Lackner et al. (2011) “The detection of climate change signals in rather short satellite datasets is a challenging task in climate research and requires high quality data with good error characterization. Global Navigation Satellite System (GNSS) radio occultation (RO) provides a novel record of high quality measurements of atmospheric parameters of the upper troposphere-lower stratosphere (UTLS) region. Due to characteristics such as long-term stability, self-calibration, and a very good height-resolution, RO data are well suited to investigate atmospheric climate change. This study describes the signals of ENSO and the QBO in the data and investigates whether the data already show evidence of a forced climate change signal, using an optimal-fingerprint technique. RO refractivity, geopotential height, and temperature within two trend periods (1995–2010 intermittently and 2001–2010 continuously) are investigated. The data show that an emerging climate change signal consistent with the projections of three global climate models from the Coupled Model Intercomparison Project cycle 3 (CMPI3) archive is detected for geopotential height of pressure levels at a 90 % confidence level both for the intermittent and continuous period, for the latter so far in a broad 50°S to 50°N band only. Such UTLS geopotential height changes reflect an overall tropospheric warming. 90 % confidence is not achieved for the temperature record when only large-scale aspects of the pattern are resolved. When resolving smaller-scale aspects, RO temperature trends appear stronger than GCM projected trends, the difference stemming mainly from the tropical lower-stratosphere, allowing for climate change detection at a 95 % confidence level. Overall an emerging trend signal is thus detected in the RO climate record, which is expected to increase further in significance as the record grows over the coming years. Small natural changes during the period suggest that the detected change is mainly caused by anthropogenic influence on climate.” Bettina C. Lackner and Andrea K. Steiner and Gottfried Kirchengast, Journal of Climate 2011, doi: 10.1175/2011JCLI3966.1.

Antarctic surface temperature record 50 to 25 million years ago

A record of Antarctic surface temperature between 25 and 50 m.y. ago – Dallai & Burgess (2011) “We present the first Antarctic terrestrial record of climate variations through the Cenozoic, based on the hydrogen isotope composition of hydrothermally altered minerals of intrusive rocks. This new record provides an independent geochemical proxy for continental climatic conditions; whereas, most land surface temperature proxies are biological. The temperature record is consistent with the range predicted by global climate models and proxy records for glacial and pre-glacial conditions in the Ross Sea region of Antarctica. The combined stable isotope (O and H) and age (40Ar-39Ar) determinations of hydrous mineral from Cenozoic igneous plutons and dikes show that the protracted time scale of magmatic activity and extensive hydrothermal exchange with local meteoric waters has preserved a semiquantitative climate signal of intervals in which atmospheric temperatures significantly fluctuated. These data also reveal that glacial episodes comparable with current polar conditions occurred repeatedly prior to geographical and thermal isolation of the Antarctic continent.” Luigi Dallai and Ray Burgess, Geology, v. 39 no. 5 p. 423-426, doi: 10.1130/G31569.1.

West Antarctic winter warming originates from tropics

Winter warming in West Antarctica caused by central tropical Pacific warming – Ding et al. (2011) “The Pacific sector of Antarctica, including both the Antarctic Peninsula and continental West Antarctica, has experienced substantial warming in the past 30 years. An increase in the circumpolar westerlies, owing in part to the decline in stratospheric ozone concentrations since the late 1970s, may account for warming trends in the peninsula region in austral summer and autumn. The more widespread warming in continental West Antarctica (Ellsworth Land and Marie Byrd Land) occurs primarily in austral winter and spring, and remains unexplained. Here we use observations of Antarctic surface temperature and global sea surface temperature, and atmospheric circulation data to show that recent warming in continental West Antarctica is linked to sea surface temperature changes in the tropical Pacific. Over the past 30 years, anomalous sea surface temperatures in the central tropical Pacific have generated an atmospheric Rossby wave response that influences atmospheric circulation over the Amundsen Sea, causing increased advection of warm air to the Antarctic continent. General circulation model experiments show that the central tropical Pacific is a critical region for producing the observed high latitude response. We conclude that, by affecting the atmospheric circulation at high southern latitudes, increasing tropical sea surface temperatures may account for West Antarctic warming through most of the twentieth century.” Qinghua Ding, Eric J. Steig, David S. Battisti & Marcel Küttel, Nature Geoscience, 2011, DOI: doi:10.1038/ngeo1129.

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