AGW Observer

Observations of anthropogenic global warming

New research from last week 35/2012

Posted by Ari Jokimäki on September 3, 2012

Cities are doing experiments and citizens are experiencing it. They deflate Polar cell and see what happens to Siperian High. Then they think about what to do next. Someone says, “I know, let’s inflate Hadley cell”. Everyone thinks it’s a good idea, and so they do it. They watch grassland grow and wonder what happens in Amazon area. They are bored with lab rats so they pour acid to oceans and watch what happens to corals. They change climate and see if spring damage increases enough to have an effect on woody plants. They use heaters on sea surface and watch ocean circulation to stop. They manipulate clouds with their aerosols.

Cool experiments, huh?


Climate change mitigation experiments are going on in cities all over the world

A survey of urban climate change experiments in 100 cities – Broto & Bulkeley (2012)

Abstract: “Cities are key sites where climate change is being addressed. Previous research has largely overlooked the multiplicity of climate change responses emerging outside formal contexts of decision-making and led by actors other than municipal governments. Moreover, existing research has largely focused on case studies of climate change mitigation in developed economies. The objective of this paper is to uncover the heterogeneous mix of actors, settings, governance arrangements and technologies involved in the governance of climate change in cities in different parts of the world. The paper focuses on urban climate change governance as a process of experimentation. Climate change experiments are presented here as interventions to try out new ideas and methods in the context of future uncertainties. They serve to understand how interventions work in practice, in new contexts where they are thought of as innovative. To study experimentation, the paper presents evidence from the analysis of a database of 627 urban climate change experiments in a sample of 100 global cities. The analysis suggests that, since 2005, experimentation is a feature of urban responses to climate change across different world regions and multiple sectors. Although experimentation does not appear to be related to particular kinds of urban economic and social conditions, some of its core features are visible. For example, experimentation tends to focus on energy. Also, both social and technical forms of experimentation are visible, but technical experimentation is more common in urban infrastructure systems. While municipal governments have a critical role in climate change experimentation, they often act alongside other actors and in a variety of forms of partnership. These findings point at experimentation as a key tool to open up new political spaces for governing climate change in the city.”

Citation: Vanesa Castán Broto, Harriet Bulkeley, Global Environmental Change, http://dx.doi.org/10.1016/j.gloenvcha.2012.07.005.


Qinghai-Tibetan grassland net primary production has increased significantly since 1961

Impacts of climate and CO2 changes on the vegetation growth and carbon balance of Qinghai-Tibetan grasslands over the past five decades – Piao et al. (2012)

Abstract: “Climate change has significantly influenced global and regional terrestrial carbon balances. After being systematically calibrated against eddy-covariance measurements, meteorological observation, soil inventory data and satellite observed LAI (Leaf Area Index) in the Qinghai-Tibetan plateau (Tan et al., 2010), the process-based ecosystem model called ORCHIDEE (ORganizing Carbon and Hydrology In Dynamic EcosystEms) was used in this study to investigate climate change and rising atmospheric CO2 concentration driven spatio-temporal changes in vegetation net primary production (NPP) and net ecosystem production (NEP) of Qinghai-Tibetan grasslands from 1961 to 2009. Overall, our simulation suggests that Qinghai-Tibetan grassland NPP significantly increased with a rate of 1.9 Tg C yr- 2 (1 Tg = 1012 g) since 1961. At the regional scale, change in precipitation, temperature, and atmospheric CO2 concentration accounts for 52%, 34%, 39% of the increase in NPP, respectively, but their relative roles are not constant across the study area. Increase in NPP over central and southwestern Qinghai-Tibetan plateau is primarily attributed to precipitation changes, while rising atmospheric CO2 concentration is the main cause of NPP increase in eastern plateau. The model simulation also suggests that Qinghai-Tibetan grassland NEP increased from a net carbon source of − 0.5 Tg C yr- 1 in the 1960s to a net carbon sink of 21.8 Tg C yr- 1 in the 2000s, mainly due to the rising atmospheric CO2 concentration and precipitation change. Although recent climate warming benefited vegetation growth, rising temperature did not significantly accelerate net carbon uptake from Qinghai-Tibetan grassland ecosystems due to enhanced soil carbon decomposition accompanying increase in temperature.”

Citation: Shilong Piao, Kun Tan, Huijuan Nan, Philippe Ciais, Jingyun Fang, Tao Wang, Nicolas Vuichard, Biao Zhue, Global and Planetary Change, http://dx.doi.org/10.1016/j.gloplacha.2012.08.009.


Amazon is more vulnerable to climate change due to actions of mankind

Amazon’s vulnerability to climate change heightened by deforestation and man-made dispersal barriers – Feeley & Rehm (2012)

Abstract: “Species migrations in response to climate change have already been observed in many taxonomic groups worldwide. However, it remains uncertain if species will be able to keep pace with future climate change. Keeping pace will be especially challenging for tropical lowland rainforests due to their high velocities of climate change combined with high rates of deforestation, which may eliminate potential climate analogs and/or increase the effective distances between analogs by blocking species movements. Here we calculate the distances between current and future climate analogs under various climate change and deforestation scenarios. Under even the most sanguine of climate change models (IPSL_CM4, A1b emissions scenario), we find that the median distance between areas in the Amazon rainforest and their closest future (2050) climate analog as predicted based on just temperature changes alone is nearly 300 km. If we include precipitation, the median distance increases by over 50% to >475 km. Since deforestation is generally concentrated in the hottest and driest portions of the Amazon, we predict that habitat loss will have little direct impact on distances between climate analogs. If, however, deforested areas also act as a barrier to species movements, nearly 30 or 55% of the Amazon will effectively have no climate analogs anywhere in tropical South America under projections of reduced or Business-As-Usual deforestation, respectively. These “disappearing climates” will be concentrated primarily in the southeastern Amazon. Consequently, we predict that several Amazonian ecoregions will have no areas with future climate analogs, greatly increasing the vulnerability of any populations or species specialized on these conditions. These results highlight the importance of including multiple climatic factors and human land-use in predicting the effects of climate change, as well as the daunting challenges that Amazonian diversity faces in the near future.”

Citation: Kenneth J. Feeley, Evan M. Rehm, Global Change Biology, DOI: 10.1111/gcb.12012.


Area of Hadley cell has increased and area of Polar cell has decreased

Measurements of the movement of the jet streams at mid-latitudes, in the Northern and Southern Hemispheres, 1979 to 2010 – Hudson (2012) [FULL TEXT]

Abstract: “Previous studies have shown that the mean latitude of the sub-tropical jet streams in both hemispheres have shifted toward the poles over the last few decades. This paper presents a study of the movement of both the subtropical and Polar fronts, the location of the respective jet streams, between 1979 and 2010 at mid-latitudes, using total ozone measurements to identify the sharp horizontal boundary that occurs at the position of the fronts. Previous studies have shown that the two fronts are the boundaries of three distinct regimes in the stratosphere, corresponding to the Hadley, Ferrel, and polar meridionally overturning circulation cells in the troposphere. Over the period of study the horizontal area of the Hadley cell has increased at latitudes between 20 and 60 degrees while the area of the Polar cell has decreased. A linear regression analysis was performed to identify the major factors associated with the movement of the subtropical jet streams. These were: (1) changes in the Tropical land plus ocean temperature, (2) direct radiative forcing from greenhouse gases in the troposphere, (3) changes in the temperature of the lower tropical stratosphere, (4) the Quasi-Biennial Oscillation, and (5) volcanic eruptions. The dominant mechanism was the direct radiative forcing from greenhouse gases. Between 1979 and 2010 the poleward movement of the subtropical jet streams was 3.7 ± 0.3 degrees in the Northern Hemisphere and 6.5 ± 0.2 degrees in the Southern Hemisphere. Previous studies have shown that weather systems tend to follow the jet streams. The observed poleward movement in both hemispheres over the past thirty years represents a significant change in the position of the sub-tropical jet streams, which should lead to significant latitudinal shifts in the global weather patterns and the hydrologic cycle.”

Citation: Hudson, R. D.: Measurements of the movement of the jet streams at mid-latitudes, in the Northern and Southern Hemispheres, 1979 to 2010, Atmos. Chem. Phys., 12, 7797-7808, doi:10.5194/acp-12-7797-2012, 2012.


Ocean acidification reduces induction of coral settlement by crustose coraline algae

Ocean acidification reduces induction of coral settlement by crustose coraline algae – Webster et al. (2012)

Abstract: “Crustose coralline algae (CCA) are a critical component of coral reefs as they accrete carbonate for reef structure and act as settlement substrata for many invertebrates including corals. CCA host a diversity of microorganisms that can also play a role in coral settlement and metamorphosis processes. While the sensitivity of CCA to ocean acidification (OA) is well established, the response of their associated microbial communities to reduced pH and increased CO2 was previously unknown. Here we investigate the sensitivity of CCA-associated microbial biofilms to OA and determine whether OA adversely affects the ability of CCA to induce coral larval metamorphosis. We experimentally exposed the CCA Hydrolithon onkodes to four pH/pCO2 conditions consistent with current IPCC predictions for the next few centuries (pH: 8.1, 7.9, 7.7, 7.5, pCO2: 464, 822, 1187, 1638 μatm). Settlement and metamorphosis of coral larvae was reduced on CCA pre-exposed to pH 7.7 (pCO2 = 1187 μatm) and below over a six week period. Additional experiments demonstrated that low pH treatments did not directly affect the ability of larvae to settle, but instead most likely altered the biochemistry of the CCA or its microbial associates. Detailed microbial community analysis of the CCA revealed diverse bacterial assemblages that altered significantly between pH 8.1 (pCO2 = 464 μatm) and pH 7.9 (pCO2 = 822 μatm) with this trend continuing at lower pH/higher pCO2 treatments. The shift in microbial community composition primarily comprised changes in the abundance of the dominant microbes between the different pH treatments and the appearance of new (but rare) microbes at pH 7.5. Microbial shifts and the concomitant reduced ability of CCA to induce coral settlement under OA conditions projected to occur by 2100 is a significant concern for the development, maintenance and recovery of reefs globally.”

Citation: N.S. Webster, S. Uthicke, E. Botté, F. Flores, A.P. Negri, Global Change Biology, DOI: 10.1111/gcb.12008.


Belief in experiencing global warming significantly predicts local risk perception

Do people “personally experience” global warming, and if so how, and does it matter? – Akerlof et al. (2012)

Abstract: “For most people, the direct and personally observable signals of climate change should be difficult to detect amid the variability of everyday weather. Yet, previous research has shown that some people believe they have personally experienced global warming. Through four related studies, our paper sheds light on what signals of global warming some people believe they are detecting, why, and whether or not it matters. These studies were conducted using population survey and climatic data from a single county in Michigan. Study 1 found that 27% of the county’s adult residents felt that they had personally experienced global warming. Study 2 – based on content analysis of people’s open-ended responses – found that the most frequently described personal experiences of global warming were changes in seasons (36%), weather (25%), lake levels (24%), animals and plants (20%), and snowfall (19%). Study 3 – based on NOAA climatic data – found that most, but not all, of these detected signals are borne out in the climatic record. Study 4 – using the survey data – found that personal experience of global warming matters in that it predicts perceptions of local risk of global warming, controlling for demographics, political affiliation, and cultural beliefs about national policy outcomes. We conclude that perceived personal experience of global warming appears to heighten people’s perception of the risks, likely through some combination of direct experience, vicarious experience (e.g., news media stories), and social construction.”

Citation: Karen Akerlof, Edward W. Maibach, Dennis Fitzgerald, Andrew Y. Cedeno, Amanda Neuman, Global Environmental Change, http://dx.doi.org/10.1016/j.gloenvcha.2012.07.006.


Holocene climate variability in northern Italy was influenced by solar activity and NAO

Holocene climate variability in north-eastern Italy: potential influence of the NAO and solar activity recorded by speleothem data – Scholz et al. (2012) [FULL TEXT]

Abstract: “Here we present high-resolution stable isotope and lamina thickness profiles as well as radiocarbon data for the Holocene stalagmite ER 76 from Grotta di Ernesto (north-eastern Italy), which was dated by combined U-series dating and lamina counting. ER 76 grew between 8 ka (thousands of years before 2000 AD) and today, with a hiatus from 2.6 to 0.4 ka. Data from nine meteorological stations in Trentino show a significant influence of the North Atlantic Oscillation (NAO) on winter temperature and precipitation in the cave region. Spectral analysis of the stable isotope signals of ER 76 reveals significant peaks at periods of 110, 60–70, 40–50, 32–37 and around 25 a. Except for the cycle between 32 and 37 a all periodicities have corresponding peaks in power spectra of solar variability, and the 25-a cycle may correspond to NAO variability. This suggests that climate variability in northern Italy was influenced by both solar activity and the NAO during the Holocene. Six periods of warm winter climate in the cave region were identified. These are centred at 7.9, 7.4, 6.5, 5.5, 4.9 and 3.7 ka, and their duration ranges from 100 to 400 a. The two oldest warm phases coincide with the deposition of sapropel S1 in the Mediterranean Sea indicating that the climate in the cave region was influenced by this prominent pluvial phase in the Mediterranean area. For the younger warm phases it is difficult to establish a supra-regional climate pattern, and some of them may, thus, reflect regional climate variability. This highlights the complexity of regional and supra-regional scale Holocene climate patterns.”

Citation: Scholz, D., Frisia, S., Borsato, A., Spötl, C., Fohlmeister, J., Mudelsee, M., Miorandi, R., and Mangini, A.: Holocene climate variability in north-eastern Italy: potential influence of the NAO and solar activity recorded by speleothem data, Clim. Past, 8, 1367-1383, doi:10.5194/cp-8-1367-2012, 2012.


Sea surface has warmed and upper-layer circulation has weakened during winters in South China Sea

Trends of upper-layer circulation in the South China Sea during 1959–2008 – Yang & Wu (2012)

Abstract: “In this paper, the trend of upper-layer circulation in the South China Sea (SCS) is studied based on the Simple Ocean Data Assimilation product for 1959–2008. It is found that the basin-averaged SST in winter displays a warming rate close to the global mean value while it does not have significant trend in summer. The upper-layer circulation in the SCS has been weakened in winter by 10% over this period, while in summer it tends to be more energetic. Further analyses suggest that the weakening of the winter SCS ocean circulation in winter is associated with weakening of the East Asian monsoon over recent decades. Moreover, an eastward retreat of the anti-cyclonic “Kuroshio loop” from the SCS is found, which may be due to an intensification of the Kuroshio transport in the past 50 years.”

Citation: Yang, H., and L. Wu (2012), Trends of upper-layer circulation in the South China Sea during 1959–2008, J. Geophys. Res., 117, C08037, doi:10.1029/2012JC008068.


Spring damage risk for woody plants is increasing due to climate change in Illinois, USA

Reconstructing patterns of temperature, phenology, and frost damage over 124 years – spring damage risk is increasing – Augspurger (2012)

Abstract: “Climate change with both warmer spring temperatures and greater temperature fluctuations has altered phenologies, possibly leading to greater risk of spring frost damage to temperate deciduous woody plants. Phenological observations of 20 woody species from 1993-2012 in Trelease Woods, Champaign Co., Illinois, USA were used to identify years with frost damage to vegetative and reproductive phases. Local temperature records were used in combination with the phenological observations to determine what combinations of the two were associated with damage. Finally, a long-term temperature record (1889-1992) was evaluated to determine if the frequency of frost damage has risen in recent decades. Frost {less than or equal to} -1.7 ºC occurred after bud-break in 14 of the 20 years of observation. Frost damage occurred in five years in the interior and in three additional years at only the forest edge. The degree of damage varied with species, life stage, tissue (vegetative or reproductive), and phenological phase. Common features associated with the occurrence of damage to interior plants were (1) a period of unusual warm temperatures in March, followed by (2) a frost event in April with a minimum temperature {less than or equal to} -6.1˚C with (3) a period of 16 – 33 days between the extremes. In the long-term record, 10 of 124 years met these conditions, but the yearly probability of frost damage increased significantly, from 0.03 from 1889-1979 to 0.21 from 1980-2012. When the criteria were ‘softened’ to {less than or equal to} -1.7 ˚C in April and an interval of 16 – 37 days, 31 of 124 years met the conditions, and the yearly damage probability increased significantly to 0.19 from 1889-1979 to 0.42 from 1980-2012. In this forest, the combination of warming trends and temperature variability (extremes) associated with climate change is having ecologically important effects, making previously rare frost damage events more common.”

Citation: LiAugspurger, Carol K. Reconstructing patterns of temperature, phenology, and frost damage over 124 years – spring damage risk is increasing. Ecology. http://dx.doi.org/10.1890/12-0200.1.


Siberian High makes temperature of arid region of northwest China rise faster

Why does the temperature rise faster in the arid region of northwest China? – Li et al. (2012)

Abstract: “During 1960–2010, the air temperature in the arid region of northwest China had a significant rising trend (P < 0.001), at a rate of 0.343°C/decade, higher than the average of China (0.25°C/decade) and that of the entire globe (0.13°C/decade) for the same period. Based on the analysis of the data from 74 meteorological stations in the region for 1960–2010, we found that among the four seasons the temperature change of winter has been playing the most important role in the yearly change in this region. We also found that the winter temperature in this region has a strong association with the Siberian High (correlation coefficient: R = −0.715) and the greenhouse gas emission (R = 0.51), and between the two the former is stronger. We thus suggest that the weakening of the Siberian High during the 1980s to 1990s on top of the steady increasing of the greenhouse emission is the main reason for the higher rate of the temperature rise in the arid region of the northwest China.”

Citation: Li, B., Y. Chen, and X. Shi (2012), Why does the temperature rise faster in the arid region of northwest China?, J. Geophys. Res., 117, D16115, doi:10.1029/2012JD017953.


Indirect aerosol forcing – mankind affects climate also through clouds

Anthropogenic radiative forcing of marine stratocumulus clouds under different thermodynamic conditions—An LES model study – Song & Yum (2012)

Abstract: “A LES model with bin microphysics was used to investigate the aerosol indirect effects of marine stratocumulus clouds that develop under different thermodynamic conditions. The diurnal contrasts of cloud development were also examined in detail. Three observed CCN spectra that represent maritime, continental and polluted air masses were used as input CCN spectra. Two observed thermodynamic soundings and two derived ones from the observed soundings to vary the inversion altitude were used as initial thermodynamic conditions. With these initial conditions the model was run for the daytime and nocturnal conditions to make the total number of model runs to be 24. For both daytime and nocturnal conditions, the cloud depth and liquid water path (LWP) varied with the thermodynamic soundings. For a given thermodynamic sounding, LWP tended to be similar or slightly smaller for polluted. However, cloud top radiative cooling is stronger for polluted due to smaller sizes of cloud droplets and therefore turbulent mixing is stronger for polluted. However, there were significant differences in LWP between the daytime and nocturnal clouds. For the daytime condition, the cloud became decoupled from the surface layer and moisture supply was limited for all soundings. In contrast, with the absence of solar radiation, cloud top radiative cooling was much stronger, turbulent mixing was also much stronger and therefore no decoupling occurred and clouds were thicker with greater LWP in the nocturnal runs. To note is the derived thermodynamic sounding (named MH) that produced the thickest clouds: the clouds were too thick to be maintained as a single layer cloud and became multi-layered for the daytime condition while the maritime stratocumulus cloud broke up into a cumuliform cloud due to heavy drizzle for the nocturnal condition. From the daytime run results, the anthropogenic cloud radiative forcing was calculated by subtracting the net cloud radiative forcing for maritime from that for polluted. It amounted to be − 21.6 W m− 2 for MH but was more than a factor of two larger for all three other soundings, − 56.4, − 55.4 and − 55.7 W m− 2. For the MH sounding, the LWP was noticeably smaller for polluted than for maritime, the relative difference of the effective radii between maritime and polluted was small and therefore albedo difference between the two was also small, compared to those for the other three soundings. Notable is the similar magnitude of the anthropogenic cloud radiative forcing for these three soundings despite the significant differences in cloud depths among the clouds produced by these soundings. This may imply that there may be an optimal range of cloud depth that can produce a strong anthropogenic cloud radiative forcing. The cloud depths were smaller than 150 m for the thermodynamic sounding that produced the shallowest clouds but it seemed to be within the optimal range.”

Citation: Keunyong Song, Seong Soo Yum, Atmospheric Research, Volume 118, 15 November 2012, Pages 370–389, http://dx.doi.org/10.1016/j.atmosres.2012.07.018.


Deep Arctic Ocean was warmer than today during the last glacial cycle due to ocean circulation conditions

Deep Arctic Ocean warming during the last glacial cycle – Cronin et al. (2012)

Abstract: “In the Arctic Ocean, the cold and relatively fresh water beneath the sea ice is separated from the underlying warmer and saltier Atlantic Layer by a halocline. Ongoing sea ice loss and warming in the Arctic Ocean have demonstrated the instability of the halocline, with implications for further sea ice loss. The stability of the halocline through past climate variations is unclear. Here we estimate intermediate water temperatures over the past 50,000 years from the Mg/Ca and Sr/Ca values of ostracods from 31 Arctic sediment cores. From about 50 to 11 kyr ago, the central Arctic Basin from 1,000 to 2,500 m was occupied by a water mass we call Glacial Arctic Intermediate Water. This water mass was 1–2 °C warmer than modern Arctic Intermediate Water, with temperatures peaking during or just before millennial-scale Heinrich cold events and the Younger Dryas cold interval. We use numerical modelling to show that the intermediate depth warming could result from the expected decrease in the flux of fresh water to the Arctic Ocean during glacial conditions, which would cause the halocline to deepen and push the warm Atlantic Layer into intermediate depths. Although not modelled, the reduced formation of cold, deep waters due to the exposure of the Arctic continental shelf could also contribute to the intermediate depth warming.”

Citation: T. M. Cronin, G. S. Dwyer, J. Farmer, H. A. Bauch, R. F. Spielhagen, M. Jakobsson, J. Nilsson, W. M. Briggs Jr & A. Stepanova, Nature Geoscience, 2012, doi:10.1038/ngeo1557.


CLASSIC OF THE WEEK: Ångström (1949)

Swedish Meteorological Research 1939–1948 – Ångström (1949) [FULL TEXT]

Abstract: No abstract. Like the name says, paper goes through Swedish meteorological research. Also climate research is included.

Citation: Anders Ångström, Tellus, Volume 1, Issue 1, pages 60–64, February 1949, DOI: 10.1111/j.2153-3490.1949.tb01930.x.


When each paper is published, it is notified in AGW Observer Facebook page and 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.

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