AGW Observer

Observations of anthropogenic global warming

New research from last week 43/2011

Posted by Ari Jokimäki on October 31, 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.

Scafetta looks at auroras and claims most of recent warming is of astronomical origin

A shared frequency set between the historical mid-latitude aurora records and the global surface temperature – Scafetta (2011) “Herein we show that the historical records of mid-latitude auroras from 1700 to 1966 present oscillations with periods of about 9, 10-11, 20-21, 30 and 60 years. The same frequencies are found in proxy and instrumental global surface temperature records since 1650 and 1850, respectively and in several planetary and solar records. Thus, the aurora records reveal a physical link between climate change and astronomical oscillations. Likely, there exists a modulation of the cosmic ray flux reaching the Earth and/or of the electric properties of the ionosphere. The latter, in turn, have the potentiality of modulating the global cloud cover that ultimately drives the climate oscillations through albedo oscillations. In particular, a quasi 60-year large cycle is quite evident since 1650 in all climate and astronomical records herein studied, which also include an historical record of meteorite fall in China from 619 to 1943. These findings support the thesis that climate oscillations have an astronomical origin. We show that a harmonic constituent model based on the major astronomical frequencies revealed in the aurora records is able to forecast with a reasonable accuracy the decadal and multidecadal temperature oscillations from 1950 to 2010 using the temperature data before 1950, and vice versa. The existence of a natural 60-year modulation of the global surface temperature induced by astronomical mechanisms, by alone, would imply that at least 60-70% of the warming observed since 1970 has been naturally induced. Moreover, the climate may stay approximately stable during the next decades because the 60-year cycle has entered in its cooling phase.” Nicola Scafetta, Journal of Atmospheric and Solar-Terrestrial Physics, doi:10.1016/j.jastp.2011.10.013.

Greenland ice sheet melted during Pliocene interglacials

Snapshots of the Greenland ice sheet configuration in the Pliocene to early Pleistocene – Solgaard et al. (2011) “The geometry of the ice sheets during the Pliocene to early Pleistocene is not well constrained. Here we apply an ice-flow model in the study of the Greenland ice sheet (GIS) during three extreme intervals of this period constrained by geological observations and climate reconstructions. We study the extent of the GIS during the Mid-Pliocene Warmth (3.3-3.0 Ma), its advance across the continental shelf during the late Pliocene to early Pleistocene glaciations (3.0-2.4 Ma) as implied by offshore geological studies, and the transition from glacial to interglacial conditions around 2.4 Ma as deduced from the deposits of the Kap København Formation, North Greenland. Our experiments show that no coherent ice sheet is likely to have existed in Greenland during the Mid-Pliocene Warmth and that only local ice caps may have been present in the coastal mountains of East Greenland. Our results illustrate the variability of the GIS during the Pliocene to early Pleistocene and underline the importance of including independent estimates of the GIS in studies of climate during this period. We conclude that the GIS did not exist throughout the Pliocene to early Pleistocene, and that it melted during interglacials even during the late Pliocene climate deterioration.” Solgaard, Anne M.; Reeh, Niels; Japsen, Peter; Nielsen, Tove, Journal of Glaciology, Volume 57, Number 205, October 2011 , pp. 871-880(10). [Full text]

Our uncertain datasets of tropospheric and stratospheric temperatures

Uncertainty of the stratospheric/tropospheric temperature trends in 1979–2008: multiple satellite MSU, radiosonde, and reanalysis datasets – Xu & Powell (2011) “The trends and spreads of tropospheric and stratospheric temperature are discussed in terms of three groups of datasets in 1979–2008. These datasets include (a) three satellite observations of Microwave Sounding Units (MSU) measurements, (b) five radiosonde observations and (c) five reanalysis products. The equivalent tropospheric and stratospheric temperature from radiosonde and reanalyses are calculated based on the vertical weighting function of the MSU channel 2 (CH2) and channel 4 (CH4) measurements, respectively. The results show that both cooling in the stratosphere and warming in troposphere significantly depends on the datasets and latitudes.” Xu, J. and A. M. Powell Jr.: Atmos. Chem. Phys., 11, 10727-10732, doi:10.5194/acp-11-10727-2011, 2011. [Full text]

Arctic amplification might relax in the future

Projected regime shift in Arctic cloud and water vapor feedbacks – Chen et al. (2011) “The Arctic climate is changing faster than any other large-scale region on Earth. A variety of positive feedback mechanisms are responsible for the amplification, most of which are linked with changes in snow and ice cover, surface temperature (Ts), atmospheric water vapor (WV), and cloud properties. As greenhouse gases continue to accumulate in the atmosphere, air temperature and water vapor content also increase, leading to a warmer surface and ice loss, which further enhance evaporation and WV. Many details of these interrelated feedbacks are poorly understood, yet are essential for understanding the pace and regional variations in future Arctic change. We use a global climate model (Goddard Institute for Space Studies, Atmosphere–Ocean Model) to examine several components of these feedbacks, how they vary by season, and how they are projected to change through the 21st century. One positive feedback begins with an increase in Ts that produces an increase in WV, which in turn increases the downward longwave flux (DLF) and Ts, leading to further evaporation. Another associates the expected increases in cloud cover and optical thickness with increasing DLF and Ts. We examine the sensitivities between DLF and other climate variables in these feedbacks and find that they are strongest in the non-summer seasons, leading to the largest amplification in Ts during these months. Later in the 21st century, however, DLF becomes less sensitive to changes in WV and cloud optical thickness, as they cause the atmosphere to emit longwave radiation more nearly as a black body. This regime shift in sensitivity implies that the amplified pace of Arctic change relative to the northern hemisphere could relax in the future.” Yonghua Chen et al 2011 Environ. Res. Lett. 6 044007 doi:10.1088/1748-9326/6/4/044007. [Full text]

Miocene: warm climate at low CO2 = tectonic & vegetation changes + positive water vapor & albedo feedbacks

A warm Miocene climate at low atmospheric CO2 levels – Knorr et al. (2011) “Proxy records from the Miocene epoch (∼23-5 Ma) indicate a warmer climate than today in spite of lower atmospheric carbon dioxide (CO2) concentrations in the range of preindustrial levels. As yet the simulation of a warm Miocene climate with these low CO2 values has proven to be a challenge. In this study we present climate simulations of the Late Miocene (11-7 Ma) with a preindustrial CO2 level, using a coupled atmosphere-ocean general circulation model (AOGCM). The simulated global mean surface temperature of ∼17.8 °C represents a significantly warmer climate than today. We have analyzed the relative importance of tectonic and vegetation changes as forcing factors. We find that the strongest temperature increase is due to the Late Miocene vegetation distribution, which is more than three times stronger than the impact induced by tectonic alterations. Furthermore, a combination of both forcing factors results in a global temperature increase which is lower than the sum of the individual forcing effects. Energy balance estimates suggest that a reduction in the planetary albedo and a positive water vapor feedback in a warmer atmosphere are the dominating mechanisms to explain the temperature increase. Each of these factors contributes about one half to the global temperature rise of ∼3 K. Our results suggest that a much warmer climate during the Late Miocene can be reconciled with CO2 concentrations similar to preindustrial values.” Knorr, G., M. Butzin, A. Micheels, and G. Lohmann (2011), Geophys. Res. Lett., 38, L20701, doi:10.1029/2011GL048873.

Lakes of Canada are shrinking

Shrinking lakes of the Arctic: Spatial relationships and trajectory of change – Carroll et al. (2011) “Over the past 3 decades the Arctic has seen substantial warming. Previous local to regional scale studies have shown a considerable reduction in the size of lakes in this region. The subsequent exposure of carbon- and methane-rich sediments and the direct changes in surface albedo feed back into the drivers of regional and global climate change. Understanding and quantifying changes in the Arctic is a critical component of climate modeling due to the cooling effect of the Arctic on the global climate. The current work utilizes global satellite data from the Moderate Resolution Imaging Spectro-radiometer (MODIS) instrument to investigate changes in lakes across Canada between 2000 and 2009. The results show a net reduction of more than 6,700 km2 in the surface area of water in lakes across Canada. Modest gains in the southern regions are offset by larger losses in surface area farther north. Additionally, spatial analysis shows that the lakes showing change are clustered in groups. This suggests that local variability may play a role in the observed changes. Further work is needed to extend the analysis to the circumpolar Arctic.” Carroll, M. L., J. R. G. Townshend, C. M. DiMiceli, T. Loboda, and R. A. Sohlberg (2011), Geophys. Res. Lett., 38, L20406, doi:10.1029/2011GL049427.

Warmer climate will not increase net carbon uptake in northeast Siberian tundra

Longer growing seasons do not increase net carbon uptake in the northeastern Siberian tundra – Parmentier et al. (2011) “With global warming, snowmelt is occurring earlier and growing seasons are becoming longer around the Arctic. It has been suggested that this would lead to more uptake of carbon due to a lengthening of the period in which plants photosynthesize. To investigate this suggestion, 8 consecutive years of eddy covariance measurements at a northeastern Siberian graminoid tundra site were investigated for patterns in net ecosystem exchange, gross primary production (GPP) and ecosystem respiration (Reco). While GPP showed no clear increase with longer growing seasons, it was significantly increased in warmer summers. Due to these warmer temperatures however, the increase in uptake was mostly offset by an increase in Reco. Therefore, overall variability in net carbon uptake was low, and no relationship with growing season length was found. Furthermore, the highest net uptake of carbon occurred with the shortest and the coldest growing season. Low uptake of carbon mostly occurred with longer or warmer growing seasons. We thus conclude that the net carbon uptake of this ecosystem is more likely to decrease rather than to increase under a warmer climate. These results contradict previous research that has showed more net carbon uptake with longer growing seasons. We hypothesize that this difference is due to site-specific differences, such as climate type and soil, and that changes in the carbon cycle with longer growing seasons will not be uniform around the Arctic.” Parmentier, F. J. W., M. K. van der Molen, J. van Huissteden, S. A. Karsanaev, A. V. Kononov, D. A. Suzdalov, T. C. Maximov, and A. J. Dolman (2011), J. Geophys. Res., 116, G04013, doi:10.1029/2011JG001653.

Higher CO2 level makes glacier forefield plants hide underground

No growth stimulation by CO2 enrichment in alpine glacier forefield plants – Inauen et al. (2011) “Since 1850, glaciers in the European Alps have lost around 40% of their originally glaciated area, releasing bare forefields, which are colonized by alpine pioneer species, setting the scene for later successional stages. These expanding pioneer communities are likely less restricted by resources and competition than late successional systems, we thus hypothesized that rising atmospheric CO2 concentration will enhance plant growth in these high-elevation communities. Nine characteristic, perennial glacier forefield species were assembled in microcosms and grown at a nearby experimental site in the Swiss Alps (2440 m a.s.l.). The communities were exposed to an elevated CO2 concentration of 580 ppm by Free Air CO2 Enrichment (FACE) for three seasons. Four study species were additionally grown in isolation in containers, half of which received a low dose of mineral fertilizer in order to explore a potential nutrient limitation of the CO2 response. Responses of growth dynamics and peak season biomass of the two graminoid species, four forbs and three cushion forming species were analysed by repeated non-destructive assessments and a final biomass harvest. After three seasons, none of the species were stimulated by elevated CO2, irrespective of mineral nutrient addition, which by itself enhanced growth in the fertilized plants by +34% on average. Increased CO2 concentration did not affect total (above- plus belowground) biomass but reduced aboveground biomass by –35% across all species, even in the fast growing ones. This reduced aboveground biomass was associated with higher biomass partitioning to roots. Foliar non-structural carbohydrate (NSC) concentration increased and nitrogen concentration in leaves decreased under elevated CO2. We observed downward adjustment of photosynthetic capacity by on average –26% under long-term exposure to 580 ppm CO2 (assessed in graminoids only). Our results indicate that glacier forefield pioneers, growing under harsh climatic conditions are not carbon limited at current atmospheric CO2 concentration.” Nicole Inauen, Christian Körner, Erika Hiltbrunner, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02584.x.


2 Responses to “New research from last week 43/2011”

  1. john byatt said

    Now and then one should say thank you Ari,

    “Thank you Ari”

    john byatt

  2. Ari Jokimäki said

    Hey, every now and then people do thank me. Thank you, John! 🙂

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