AGW Observer

Observations of anthropogenic global warming

New research from last week 12/2012

Posted by Ari Jokimäki on March 26, 2012

Lot of global warming effects this week – species spreading, cloud cover decreasing, sea ice disappearing, weather events affected, grass growing more, non-frozen season getting longer, and temperatures increasing. We also have studies on tree stump, stratospheric ozone, virtual water, forest cover, and bipolar seesaw.


Can species spread fast enough to keep up with climate change?

Keeping pace with climate change: what can we learn from the spread of Lessepsian migrants? – Hiddink et al. (2012)

Abstract: “Species need to move to keep pace with changing climates, but we do not know if species can move at the required speed. Spread rates of native species may underestimate how fast species can move, we therefore assessed how fast Lessepsian species (marine non-native species that invaded the Mediterranean from the Red Sea through the Suez Canal) can spread to give a ‘best-case’ assessment of the effects of climate change on marine biodiversity. We show that about 20% of Lessepsian species could not spread fast enough to keep pace with climate change in about 20% of the global seas and this suggests that climate change may lead to biodiversity loss. The velocity of climate change on the seabed is much lower than at the sea surface, and as a result of this the proportion of species that keep pace with climate change at the seabed was much larger than at the sea surface. This suggests that locations at depth could act as refuges for slow dispersing species. Our analysis compared different estimates of the spreading abilities of marine species and showed that the estimate of spread rates strongly affects the predicted effect of climate change on biodiversity. Providing more accurate estimates of the spreading ability of marine species should therefore have priority if we want to predict the effect of climate change on marine biodiversity. This study is a first approximation of the potential scale and distribution of global marine biodiversity loss and can provide benchmark estimates of the spread rates that species could achieve in colonizing suitable habitat. Assisted colonization may be required to maintain biodiversity in the most strongly affected areas.”

Citation: J.G. Hiddink, F. Ben Rais Lasram, J. Cantrill, Andrew J. Davies, Global Change Biology, DOI: 10.1111/j.1365-2486.2012.02698.x.


Europe has become less cloudy during 1984-2007 period

European hot summers associated with a reduction of cloudiness – Tang et al. (2012)

Abstract: “A pronounced summer warming is observed in Europe since the 1980s that has been accompanied with an increase in the occurrence of heat waves. Water deficit that strongly reduces surface latent cooling is a widely accepted explanation for the causes of hot summers. We show that the variance of European summer temperature is partly explained by changes in summer cloudiness. Using observation-based products of climate variables, satellite-derived cloud cover and radiation products, we show that during the 1984-2007 period Europe has become less cloudy (except of northeastern Europe) and the regions east of Europe have become cloudier in summer daytime. In response, the summer temperatures increased in the areas of total cloud cover decrease, and stalled or declined in the areas of cloud cover increase. Trends in the surface shortwave radiation are generally positive (negative) in the regions with summer warming (cooling or stalled warming), while the signs of trends in top-of-atmosphere (TOA) reflected shortwave radiation are reversed. Our results suggest that total cloud cover is either the important local factor influencing the summer temperature changes in Europe or a major indicator of these changes.”

Citation: Qiuhong Tang, Guoyong Leng, Pavel Ya. Groisman, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-12-00040.1.


Most likely global warming threshold for September Arctic sea ice to disappear is 2°C

September Arctic sea ice predicted to disappear near 2°C global warming above present – Mahlstein & Knutti (2012)

Abstract: “The decline of Arctic sea ice is one of the most visible signs of climate change over the past several decades. Arctic sea ice area shows large interannual variability due to the numerous factors, but on longer time scales the total sea ice area is approximately linearly related to Arctic surface air temperature in models and observations. Overall, models however strongly underestimate the recent sea ice decline. Here we show that this can be explained with two interlinked biases. Most climate models simulate a smaller sea ice area reduction per degree local surface warming. Arctic polar amplification, the ratio between Arctic and global temperature, is also underestimated but a number of models are within the uncertainty estimated from natural variability. A recalibration of an ensemble of global climate models using observations over 28 years provides a scenario independent relationship and yields about 2°C change in annual mean global surface temperature above present as the most likely global temperature threshold for September sea ice to disappear, but with substantial associated uncertainty. Natural variability in the Arctic is large and needs to be considered both for such recalibrations as well as for model evaluation, in particular when observed trends are relatively short.”

Citation: Mahlstein, I. and R. Knutti (2012), September Arctic sea ice predicted to disappear near 2{degree sign}C global warming above present, J. Geophys. Res., doi:10.1029/2011JD016709.


All weather events are affected by climate change

Framing the way to relate climate extremes to climate change – Trenberth (2012) [FULL TEXT]

Abstract: “The atmospheric and ocean environment has changed from human activities in ways that affect storms and extreme climate events. The main way climate change is perceived is through changes in extremes because those are outside the bounds of previous weather. The average anthropogenic climate change effect is not negligible, but nor is it large, although a small shift in the mean can lead to very large percentage changes in extremes. Anthropogenic global warming inherently has decadal time scales and can be readily masked by natural variability on short time scales. To the extent that interactions are linear, even places that feature below normal temperatures are still warmer than they otherwise would be. It is when natural variability and climate change develop in the same direction that records get broken. For instance, the rapid transition from El Niño prior to May 2010 to La Niña by July 2010 along with global warming contributed to the record high sea surface temperatures in the tropical Indian and Atlantic Oceans and in close proximity to places where record flooding subsequently occurred. A commentary is provided on recent climate extremes. The answer to the oft-asked question of whether an event is caused by climate change is that it is the wrong question. All weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be.”

Citation: Kevin E. Trenberth, Climatic Change, DOI: 10.1007/s10584-012-0441-5.


Future grass yield increases in North Europe but also frost damage risk might increase

Assessing uncertainties in impact of climate change on grass production in Northern Europe using ensembles of global climate models – Höglind et al. (2012)

Abstract: “Forage-based dairy and livestock production is the backbone of agriculture in Northern Europe in economic terms. Changes in growing conditions that affect forage grass yield may have great economic consequences. This study assessed the impact of climate change on two grass species, timothy and ryegrass, at 14 locations in Northern Europe (Iceland, Scandinavia, Baltic countries) in a near-future scenario (2040–2065) compared with the baseline period 1960–1990. Local-scale climate scenarios were based on the CMIP3 multi-model ensembles of 15 global climate models in order to quantify the uncertainty in the impacts relating to highly uncertain projections of future climate. Potential yield of timothy, the most important perennial forage grass in Northern Europe, was simulated under the assumption of optimal overwintering conditions and current CO2 level, in order to obtain an estimate of the effect of changes in summer climate per se. The risk of frost and ice damage during winter was also assessed. The simulation results demonstrated that potential grass yield will increase throughout the study area, mainly as a result of increased growing temperatures. The yield response to climate change was slightly larger in irrigated than non-irrigated conditions (14% and 11%, respectively), due to larger water deficit for the 2050 scenario. However, a geo-climatic gradient was evident, with the largest predicted yield response at western locations. A geo-climatic gradient was also revealed with respect to potential frost damage, which was predicted to increase during winter in some areas east of the Baltic Sea for timothy, and for a larger number of locations both east and west of the Baltic Sea for perennial ryegrass. The risk of frost damage in spring was predicted to increase mainly in western parts of the study area. If frost damage to perennial ryegrass increases during winter, the expected increase in winter temperature due to global warming may not necessarily improve overwintering conditions, so the growing zone may not necessarily expand to the north and east of the study area by 2050. The uncertainty in impacts was frequently, but not consistently, greater in western than eastern locations.”

Citation: Mats Höglind, Stig Morten Thorsen, Mikhail A. Semenov, Agricultural and Forest Meteorology, http://dx.doi.org/10.1016/j.agrformet.2012.02.010.


Weak evidence for bipolar seesaw between Arctic and Antarctic climate

Is a bipolar seesaw consistent with observed Antarctic climate variability and trends? – Schneider & Noone (2012)

Abstract: “A bipolar seesaw of Arctic and Antarctic temperature anomalies has been reported to be evident in instrumental data on decadal timescales during the last century. This finding hinges upon a global temperature data set that for the area polewards of ~60{degree sign}S is derived from only one sub-Antarctic station prior to the mid-1940s, and does not include a substantial number of Antarctic stations until the late 1950s. The timeseries of the single-station record for the early period spliced to the data based on broader coverage for the latter period is an artificial estimate of the Antarctic climate trend and its variability. We estimate the real variability using the original timeseries from the sub-Antarctic station, a reconstruction of the Southern Annular Mode index, and an ice-core based reconstruction of Antarctic temperature. None of these Antarctic timeseries are significantly correlated with Arctic or North Atlantic climate records, nor with the index of the Atlantic Multidecadal Oscillation, which was proposed as the driving mechanism of the seesaw. Instead, each of these records is consistently correlated with tropical Pacific sea surface temperatures. However, neither the seesaw nor the tropics alone can fully capture the complexity of Antarctic climate variability and climate change.”

Citation: Schneider, D. P. and D. C. Noone (2012), Is a bipolar seesaw consistent with observed Antarctic climate variability and trends?, Geophys. Res. Lett., doi:10.1029/2011GL050826.


Non-frozen season has increased in Northern Hemisphere

Satellite detection of increasing Northern Hemisphere non-frozen seasons from 1979 to 2008: Implications for regional vegetation growth – Kim et al. (2012)

Abstract: “The landscape freeze–thaw (FT) signal from satellite microwave remote sensing is closely linked to vegetation phenology and land–atmosphere trace gas exchange where seasonal frozen temperatures are a major constraint to plant growth. We applied a temporal change classification of 37 GHz brightness temperature (Tb) series from the Scanning Multichannel Microwave Radiometer (SMMR) and Special Sensor Microwave Imager (SSM/I) to classify daily FT status over global land areas where seasonal frozen temperatures influence ecosystem processes. A temporally consistent, long-term (30 year) FT record was created, ensuring cross-sensor consistency through pixel-wise adjustment of the SMMR Tb record based on empirical analyses of overlapping SMMR and SSM/I measurements. The resulting FT record showed mean annual spatial classification accuracies of 91 (+/−8.6) and 84 (+/−9.3) percent for PM and AM overpass retrievals relative to in situ air temperature measurements from the global weather station network. The FT results were compared against other measures of biosphere activity including CO2 eddy flux tower measurements and satellite (MODIS) vegetation greenness (NDVI). The FT defined non-frozen season largely bounds the period of active vegetation growth and net ecosystem CO2 uptake for tower sites representing major biomes. Earlier spring thawing and longer non-frozen seasons generally benefit vegetation growth inferred from NDVI spring and summer growth anomalies where the non-frozen season is less than approximately 6 months, with greater benefits at higher (> 45 °N) latitudes. A strong (P < 0.001) increasing (0.189 days yr− 1) trend in the Northern Hemisphere mean annual non-frozen season is largely driven by an earlier (− 0.149 days yr− 1) spring thaw trend and coincides with a 0.033 °C yr− 1 regional warming trend. The FT record also shows a positive (0.199 days yr− 1) trend in the number of transitional (AM frozen and PM non-frozen) frost days, which coincide with reduced vegetation productivity inferred from tower CO2 and MODIS NDVI measurements. The relative benefits of earlier and longer non-frozen seasons for vegetation growth under global warming may be declining due to opposing increases in disturbance, drought and frost damage related impacts.”

Citation: Youngwook Kim, J.S. Kimball, K. Zhang, K.C. McDonald, Remote Sensing of Environment, Volume 121, June 2012, Pages 472–487.


Forest cover has increased in southwest China but biodiversity still declines

Using Landsat imagery to map forest change in southwest China in response to the national logging ban and ecotourism development – Brandt et al. (2012)

Abstract: “Forest cover change is one of the most important land cover change processes globally, and old-growth forests continue to disappear despite many efforts to protect them. At the same time, many countries are on a trajectory of increasing forest cover, and secondary, plantation, and scrub forests are a growing proportion of global forest cover. Remote sensing is a crucial tool for understanding how forests change in response to forest protection strategies and economic development, but most forest monitoring with satellite imagery does not distinguish old-growth forest from other forest types. Our goal was to measure changes in forest types, and especially old-growth forests, in the biodiversity hotspot of northwest Yunnan in southwest China. Northwest Yunnan is one of the poorest regions in China, and since the 1990s, the Chinese government has legislated strong forest protection and fostered the growth of ecotourism-based economic development. We used Landsat TM/ETM+ and MSS images, Support Vector Machines, and a multi-temporal composite classification technique to analyze change in forest types and the loss of old-growth forest in three distinct periods of forestry policy and ecotourism development from 1974 to 2009. Our analysis showed that logging rates decreased substantially from 1974 to 2009, and the proportion of forest cover increased from 62% in 1990 to 64% in 2009. However, clearing of high-diversity old-growth forest accelerated, from approximately 1100 hectares/year before the logging ban (1990 to 1999), to 1550 hectares/year after the logging ban (1999 to 2009). Paradoxically, old-growth forest clearing accelerated most rapidly where ecotourism was most prominent. Despite increasing overall forest cover, the proportion of old-growth forests declined from 26% in 1990, to 20% in 2009. The majority of forests cleared from 1974 to 1990 returned to either a non-forested land cover type (14%) or non-pine scrub forest (66%) in 2009, and our results suggest that most non-pine scrub forest was not on a successional trajectory towards high-diversity forest stands. That means that despite increasing forest cover, biodiversity likely continues to decline, a trend obscured by simple forest versus non-forest accounting. It also means that rapid development may pose inherent risks to biodiversity, since our study area arguably represents a “best-case scenario” for balancing development with maintenance of biodiversity, given strong forest protection policies and an emphasis on ecotourism development.”

Citation: Jodi S. Brandt, Tobias Kuemmerle, c, Haomin Li, Guopeng Ren, Jianguo Zhu, Volker C. Radeloff, Remote Sensing of Environment, Volume 121, June 2012, Pages 358–369.


Less than 10% of global population controls over 50% of virtual water exports

On the temporal variability of the virtual water network – Carr et al. (2012)

Abstract: “Food security strongly depends on how water resources available in a certain region contribute to determine the maximum amount of food that it can produce. Human societies often cope with water scarcity by importing food products from other regions. Thus, the international trade of food commodities is associated with a virtual transfer of water resources from production to consumption regions through a network of trade. Even though global food security increasingly relies on this trade, the spatiotemporal patterns of the virtual water network remain poorly investigated. It is unclear how these patterns are changing over time, whether there is an increase in the interconnectedness of the network, and at what rate the globalization of water resources is occurring. Here we use a rich database of international trade and reconstruct the virtual water network from 1986 through 2008. We find that the total flow has more than doubled, and the number of links has increased by 92% over this time period. The network has become more homogeneous but most of the flow concentrates in few links and hubs, while several countries exhibit only few (and weak) connections. 50% of the global fluxes are carried by 1.1% of the links, and on average 6-8% of the global population controls more than 50% of the net virtual water exports. The network is extremely dynamic and intermittent with only few permanent links, while each year many links are created and dismissed.”

Citation: Carr, J. A., P. D’Odorico, F. Laio, and L. Ridolfi (2012), On the temporal variability of the virtual water network, Geophys. Res. Lett., doi:10.1029/2012GL051247, in press.


New paper claims that stratospheric ozone is most important driver of recent climate

Climate sensitivity to the lower stratospheric ozone variations – Kilifarska (2012)

Abstract: “The strong sensitivity of the Earth’s radiation balance to variations in the lower stratospheric ozone – reported previously – is analyzed here by the use of non-linear statistical methods. Our non-linear model of the land air temperature (T) – driven by the measured Arosa total ozone (TOZ) – explains 75% of total variability of Earth’s T variations during the period 1926–2011. We have analyzed also the factors which could influence the TOZ variability and found that the strongest impact belongs to the multi-decadal variations of galactic cosmic rays. Constructing a statistical model of the ozone variability, we have been able to predict the tendency in the land air T evolution till the end of the current decade. Results show that Earth is facing a weak cooling of the surface T by 0.05–0.25 K (depending on the ozone model) until the end of the current solar cycle. A new mechanism for O3 influence on climate is proposed.”

Citation: N.A. Kilifarska, Journal of Atmospheric and Solar-Terrestrial Physics, http://dx.doi.org/10.1016/j.jastp.2012.03.002.


Minimum temperatures have increased in Libya

Variability of minimum temperature across Libya (1945–2009) – Ageena et al. (2012)

Abstract: “Daily and monthly minimum temperature data from 15 meteorological stations were analysed during the period 1945–2009. The spatial and temporal variability in the daily and monthly temperatures were examined, with daily minimum temperature for eight coastal stations during the period 1956–2009 (only monthly data is available for the coastal station at Nalute) and the monthly minimum temperature for the period 1945–2009 from six inland stations. Five distinct 10 year interval blocks (with the exception of the last 9 years for the eight coastal stations and 7 years for inland stations) are analysed to examine temperature patterns across Libya. The annual minimum temperature over the last 27 years (1983–2009) for the majority of coastal stations identified significant warming in the minimum temperature. The mean annual minimum temperature at all study stations (1945–2009) identified significant increases in the minimum temperature, with significant changes in annual minimum temperature over the last 32 years (1978–2009) for the majority of the coastal and inland stations across Libya. Significant changes in minimum seasonal temperature for 33/32 year intervals (1945–1977 and 1978–2009) are identified in the summer (56%) and autumn (67%) at coastal stations (67%) and inland stations (50%).”

Citation: I. Ageena, N. Macdonald, A. P. Morse, International Journal of Climatology, DOI: 10.1002/joc.3452.


Tree stump in a lake is evidence for medieval megadrought

New evidence for extreme and persistent terminal medieval drought in California’s Sierra Nevada – Morgan & Pomerleau (2012)

Abstract: “The level of Cliff Lake, a small, subalpine, moraine-dammed lake in California’s south central Sierra Nevada, was approximately 5 m lower than present for 50 years or more approximately 600 years ago, this determined by radiocarbon dating of wood recovered from a submerged tree stump found in the lake. This finding corresponds to commensurate data from throughout much of western North America, suggesting the duration and magnitude of terminal medieval megadrought was similar throughout the region. Ultimately this datum helps give credence to the perspective that though late Holocene climate in California was indeed variable, the effects of terminal Medieval megadrought was similar across both time and broad geographic expanse.”

Citation: Christopher Morgan and Monique M. Pomerleau, Journal of Paleolimnology, DOI: 10.1007/s10933-012-9590-9.


CLASSIC OF THE WEEK: A. Ångström (1913)

Studies of the Nocturnal Radiation to Space – A. Ångström (1913) [FULL TEXT]

Abstract: No abstract. Studies how water vapor affects to nocturnal radiation.

Citation: Anders Ångström, 1913, Astrophysical Journal, vol. 37, p.305.


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.

4 Responses to “New research from last week 12/2012”

  1. barry said

    Hey Ari,

    is there any particular topic on the list you’d like updating? Let me know and I’ll go a-hunting.

  2. Ari Jokimäki said

    Well, I see you have brought me something to do over the weekend…🙂

    I’m sure there are such topics but I’ll have to check. There has been couple of cloud feedback papers lately and that is also an important topic so that could be one such topic. There’s also a possibility that you make a whole new list on some topic, if you like. If you wish to discuss that, drop me an e-mail. You can find the address in the “about” page.

  3. barry said

    I’m bombing you with papers, Ari. Hopefully they’re in the right catagories. I’ll think about maybe starting a new category. The list possibilities seem to approach infinity…

  4. barry said

    I guess you could have a whole section on modeling – you tend to favour observational-based studies. Plenty of sub-categories there, including cloud feedbacks – eg:

    https://140.208.31.101/cms-filesystem-action/user_files/gav/publications/SV11_CLOUDFB.pdf

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