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Observations of anthropogenic global warming

Archive for March, 2012

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:

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,

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,

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.


Posted in Climate science | 4 Comments »

New research from last week 11/2012

Posted by Ari Jokimäki on March 19, 2012

One aspect of Arctic sea ice decrease is that ice-free season gets longer, as shown in one of this week’s studies. Another study suggests that when sea ice decreases, cloud cover increases. To continue with the Arctic theme, yet another study in this week’s batch discusses links between arctic amplification and extreme weather events.

In non-Arctic studies this week we have biases & tree rings, GHG’s & mass extinctions, hurricanes & volcanos, monsoon & global warming, United States & sea level, cities & weather, CRUTEM & update, Lake Ontario & temperature, soil & acidification, South Africa & temperature extremes, deforestation & droughts, and atmospheric nitrous oxide & fertilizers. In other words, lots of fun & science.

Slow growth and big tree biases in tree ring studies

Detecting evidence for CO2 fertilization from tree ring studies: The potential role of sampling biases – Brienen et al. (2012) [FULL TEXT]

Abstract: “Tree ring analysis allows reconstructing historical growth rates over long periods. Several studies have reported an increasing trend in ring widths, often attributed to growth stimulation by increasing atmospheric CO2 concentration. However, these trends may also have been caused by sampling biases. Here we describe two biases and evaluate their magnitude. (1) The slow-grower survivorship bias is caused by differences in tree longevity of fast- and slow-growing trees within a population. If fast-growing trees live shorter, they are underrepresented in the ancient portion of the tree ring data set. As a result, reconstructed growth rates in the distant past are biased toward slower growth. (2) The big-tree selection bias is caused by sampling only the biggest trees in a population. As a result, slow-growing small trees are underrepresented in recent times as they did not reach the minimum sample diameter. We constructed stochastic models to simulate growth trajectories based on a hypothetical species with lifetime constant growth rates and on observed tree ring data from the tropical tree Cedrela odorata. Tree growth rates used as input in our models were kept constant over time. By mimicking a standard tree ring sampling approach and selecting only big living trees, we show that both biases lead to apparent increases in historical growth rates. Increases for the slow-grower survivorship bias were relatively small and depended strongly on assumptions about tree mortality. The big-tree selection bias resulted in strong historical increases, with a doubling in growth rates over recent decades. A literature review suggests that historical growth increases reported in many tree ring studies may have been partially due to the big-tree sampling bias. We call for great caution in the interpretation of historical growth trends from tree ring analyses and recommend that such studies include individuals of all sizes.”

Citation: Brienen, R. J. W., E. Gloor, and P. A. Zuidema (2012), Detecting evidence for CO2 fertilization from tree ring studies: The potential role of sampling biases, Global Biogeochem. Cycles, 26, GB1025, doi:10.1029/2011GB004143.

Arctic amplification may be linked to extreme weather events

Evidence linking Arctic amplification to extreme weather in mid-latitudes – Francis & Vavrus (2012)

Abstract: “Arctic amplification (AA) – the observed enhanced warming in high northern latitudes relative to the northern hemisphere – is evident in lower-tropospheric temperatures and in 1000-to-500 hPa thicknesses. Daily fields of 500 hPa heights from the National Centers for Environmental Prediction Reanalysis are analyzed over N. America and the N. Atlantic to assess changes in north-south (Rossby) wave characteristics associated with AA and the relaxation of poleward thickness gradients. Two effects are identified that each contribute to a slower eastward progression of Rossby waves in the upper-level flow: 1) weakened zonal winds, and 2) increased wave amplitude. These effects are particularly evident in autumn and winter consistent with sea-ice loss, but are also apparent in summer, possibly related to earlier snow melt on high-latitude land. Slower progression of upper-level waves would cause associated weather patterns in mid-latitudes to be more persistent, which may lead to an increased probability of extreme weather events that result from prolonged conditions, such as drought, flooding, cold spells, and heat waves.”

Citation: Francis, J. A. and S. J. Vavrus (2012), Evidence linking Arctic amplification to extreme weather in mid-latitudes, Geophys. Res. Lett., 39, L06801, doi:10.1029/2012GL051000.

Decreased greenhouse effect might have contributed to Frasnian-Famennian mass extinction

Carbon isotopic evidence for the associations of decreasing atmospheric CO2 level with the Frasnian-Famennian mass extinction – Xu et al. (2012)

Abstract: “A perturbation of the global carbon cycle has often been used for interpreting the Frasnian-Famennian (F-F) mass extinction. However, the changes of atmospheric CO2 level (pCO2) during this interval are much debatable. To illustrate the carbon cycle during F-F transition, paired inorganic (δ13Ccarb) and organic (δ13Corg) carbon isotope analyses were carried out on two late Devonian carbonate sequences (Dongcun and Yangdi) from south China. The larger amplitude shift of δ13Corg compared to δ13Ccarb and its resultant Δ13C (Δ13C = δ13Ccarbδ13Corg) decrease indicate decreased atmospheric CO2 level around the F-F boundary. The onset of pCO2 level decrease predates that of marine regressions, which coincide with the beginning of conodont extinctions, suggesting that temperature decrease induced by decreased greenhouse effect of atmospheric CO2 might have contributed to the F-F mass extinction.”

Citation: Xu, B., Z. Gu, C. Wang, Q. Hao, J. Han, Q. Liu, L. Wang, and Y. Lu (2012), Carbon isotopic evidence for the associations of decreasing atmospheric CO2 level with the Frasnian-Famennian mass extinction, J. Geophys. Res., 117, G01032, doi:10.1029/2011JG001847.

Hurricane activity might decrease in the years following major volcanic eruptions

Atlantic hurricane activity following two major volcanic eruptions – Evan (2012)

Abstract: “In 1982 and 1991, two major volcanic eruptions loaded the stratosphere with long-lived sulfate aerosols, altering the global climate by redistributing longwave and shortwave radiation at the surface and throughout the atmosphere, cooling the surface and subsurface waters of the tropical oceans. Theory and observations demonstrate, through direct and indirect mechanisms, a causal relationship between tropical North Atlantic sea surface temperatures and seasonal Atlantic hurricane frequency, duration, and intensity. Therefore, it is plausible that hurricane activity in the seasons immediately following these eruptions is diminished. However, to date, such a theory remains untested. Here I use observations, reanalysis data, and output from a numerical model to suggest that the number, duration, and intensity of hurricanes in the years following the eruptions of El Chichón (1982) and Mount Pinatubo (1991) decreased via the aerosol direct effect. Determining the effects of each eruption on seasonal cyclone activity is complicated by simultaneous positive ENSO events; thus further study of the relationship between Atlantic tropical cyclones and major volcanic eruptions is warranted.”

Citation: Evan, A. T. (2012), Atlantic hurricane activity following two major volcanic eruptions, J. Geophys. Res., 117, D06101, doi:10.1029/2011JD016716.

Global monsoon area increases with global warming

Increase of global monsoon area and precipitation under global warming: A robust signal? – Hsu et al. (2012)

Abstract: “Monsoons, the most energetic tropical climate system, exert a great social and economic impact upon billions of people around the world. The global monsoon precipitation had an increasing trend over the past three decades. Whether or not this increasing trend will continue in the 21st century is investigated, based on simulations of three high-resolution atmospheric general circulation models that were forced by different future sea surface temperature (SST) warming patterns. The results show that the global monsoon area, precipitation and intensity all increase consistently among the model projections. This indicates that the strengthened global monsoon is a robust signal across the models and SST patterns explored here. The increase of the global monsoon precipitation is attributed to the increases of moisture convergence and surface evaporation. The former is caused by the increase of atmospheric water vapor and the latter is due to the increase of SST. The effect of the moisture and evaporation increase is offset to a certain extent by the weakening of the monsoon circulation.”

Citation: Hsu, P., T. Li, J.-J. Luo, H. Murakami, A. Kitoh, and M. Zhao (2012), Increase of global monsoon area and precipitation under global warming: A robust signal?, Geophys. Res. Lett., 39, L06701, doi:10.1029/2012GL051037.

In fastest Arctic sea ice decrease regions ice-free season is now 3 months longer

Regions of rapid sea ice change: An inter-hemispheric seasonal comparison – Stammerjohn et al. (2012)

Abstract: “This bi-polar analysis resolves ice edge changes on space/time scales relevant for investigating seasonal ice-ocean feedbacks and focuses on spatio-temporal changes in the timing of annual sea ice retreat and advance over 1979/80 to 2010/11. Where Arctic sea ice decrease is fastest, the sea ice retreat is now nearly 2 months earlier and subsequent advance more than 1 month later (compared to 1979/80), resulting in a 3-month longer summer ice-free season. In the Antarctic Peninsula and Bellingshausen Sea region, sea ice retreat is more than 1 month earlier and advance 2 months later, resulting in a more than 3-month longer summer ice-free season. In contrast, in the western Ross Sea (Antarctica) region, sea ice retreat and advance are more than 1 month later and earlier respectively, resulting in a more than 2 month shorter summer ice-free season. Regardless of trend magnitude or direction, and at latitudes mostly poleward of 70° (N/S), there is strong correspondence between anomalies in the timings of sea ice retreat and subsequent advance, but little correspondence between advance and subsequent retreat. These results support a strong ocean thermal feedback in autumn in response to changes in spring sea ice retreat. Further, model calculations suggest different net ocean heat changes in the Arctic versus Antarctic where autumn sea ice advance is 1 versus 2 months later. Ocean-atmosphere changes, particularly in boreal spring and austral autumn (i.e., during ∼March-May), are discussed and compared, as well as possible inter-hemispheric climate connections.”

Citation: Stammerjohn, S., R. Massom, D. Rind, and D. Martinson (2012), Regions of rapid sea ice change: An inter-hemispheric seasonal comparison, Geophys. Res. Lett., 39, L06501, doi:10.1029/2012GL050874.

In United States 10% of population lives below future sea level risk line

Tidally adjusted estimates of topographic vulnerability to sea level rise and flooding for the contiguous United States – Strauss et al. (2012) [FULL TEXT]

Abstract: “Because sea level could rise 1 m or more during the next century, it is important to understand what land, communities and assets may be most at risk from increased flooding and eventual submersion. Employing a recent high-resolution edition of the National Elevation Dataset and using VDatum, a newly available tidal model covering the contiguous US, together with data from the 2010 Census, we quantify low-lying coastal land, housing and population relative to local mean high tide levels, which range from ~0 to 3 m in elevation (North American Vertical Datum of 1988). Previous work at regional to national scales has sometimes equated elevation with the amount of sea level rise, leading to underestimated risk anywhere where the mean high tide elevation exceeds 0 m, and compromising comparisons across regions with different tidal levels. Using our tidally adjusted approach, we estimate the contiguous US population living on land within 1 m of high tide to be 3.7 million. In 544 municipalities and 38 counties, we find that over 10% of the population lives below this line; all told, some 2150 towns and cities have some degree of exposure. At the state level, Florida, Louisiana, California, New York and New Jersey have the largest sub-meter populations. We assess topographic susceptibility of land, housing and population to sea level rise for all coastal states, counties and municipalities, from 0 to 6 m above mean high tide, and find important threat levels for widely distributed communities of every size. We estimate that over 22.9 million Americans live on land within 6 m of local mean high tide.”

Citation: Benjamin H Strauss et al 2012 Environ. Res. Lett. 7 014033 doi:10.1088/1748-9326/7/1/014033.

Review of urban meteorology

Hidden climate change – urban meteorology and the scales of real weather – Janković & Hebbert (2012)

Abstract: “This paper discusses the scale at which the weather is experienced and modified by human activities in urban environment. The climates of built-up areas differ from their non-urban counterparts in many aspect: wind-flows, radiation, humidity, precipitation and air quality all change in the presence of human settlement, transforming each city into a singularity within its regional weather system. Yet this pervasive category of anthropogenic climate change has always tended to be hidden and difficult to discern. The paper first describes the sequence of discovery of the urban heat island since the early nineteenth century, and the emergence and consolidation of a scientific field devoted to the climatology of cities. This is followed by a discussion of various attempts to apply knowledge of climatic factors to the design and management of settlement. We find that real-world application of urban climatology has met with limited success. However, the conclusion suggests that global climate change gives a new visibility and practical relevance to urban-scale climate science.”

Citation: Vladimir Janković and Michael Hebbert, Climatic Change, DOI: 10.1007/s10584-012-0429-1.

Official paper for the new CRUTEM version

Hemispheric and large-scale land-surface air temperature variations: An extensive revision and an update to 2010 – Jones et al. (2012)

Abstract: “This study is an extensive revision of the Climatic Research Unit (CRU) land station temperature database that has been used to produce a grid-box data set of 5° latitude × 5° longitude temperature anomalies. The new database (CRUTEM4) comprises 5583 station records of which 4842 have enough data for the 1961–1990 period to calculate or estimate the average temperatures for this period. Many station records have had their data replaced by newly homogenized series that have been produced by a number of studies, particularly from National Meteorological Services (NMSs). Hemispheric temperature averages for land areas developed with the new CRUTEM4 data set differ slightly from their CRUTEM3 equivalent. The inclusion of much additional data from the Arctic (particularly the Russian Arctic) has led to estimates for the Northern Hemisphere (NH) being warmer by about 0.1°C for the years since 2001. The NH/Southern Hemisphere (SH) warms by 1.12°C/0.84°C over the period 1901–2010. The robustness of the hemispheric averages is assessed by producing five different analyses, each including a different subset of 20% of the station time series and by omitting some large countries. CRUTEM4 is also compared with hemispheric averages produced by reanalyses undertaken by the European Centre for Medium-Range Weather Forecasts (ECMWF): ERA-40 (1958–2001) and ERA-Interim (1979–2010) data sets. For the NH, agreement is good back to 1958 and excellent from 1979 at monthly, annual, and decadal time scales. For the SH, agreement is poorer, but if the area is restricted to the SH north of 60°S, the agreement is dramatically improved from the mid-1970s.”

Citation: Jones, P. D., D. H. Lister, T. J. Osborn, C. Harpham, M. Salmon, and C. P. Morice (2012), Hemispheric and large-scale land-surface air temperature variations: An extensive revision and an update to 2010, J. Geophys. Res., 117, D05127, doi:10.1029/2011JD017139.

Lake Ontario has warmed during last 40 years

On Recent Trends in Atmospheric and Limnological Variables in Lake Ontario – Huang et al. (2012)

Abstract: “The surface air and water temperatures increased at all seasonal and annual time scales during the last 40 years in Lake Ontario. The annual mean air and surface water temperatures have increased by 1.43±0.39°C and 1.26±0.32°C over 1970-2009, respectively. The air temperature increased at a faster rate than surface water temperature in winter and autumn, whereas in spring and summer the surface water temperature warmed faster than air temperature. The length of summer stratified season has increased by 12±2 days since early 1970s due to the increase in water temperature. The decline of surface wind speed over Lake Ontario resulted in shallower surface mixed layer and enhanced the summer thermal stratification, which increased summer surface water temperature more rapidly than air temperature.”

Citation: Anning Huang, Yerubandi R. Rao, and Weitao Zhang, Journal of Climate 2012, doi:

Decrease in Arctic sea ice concentration leads to increase in cloud cover

A cloudier Arctic expected with diminishing sea ice – Liu et al. (2012)

Abstract: “Arctic sea ice cover has decreased dramatically over the last three decades. Global climate models under-predicted this decline, most likely a result of the misrepresentation of one or more processes that influence sea ice. The cloud feedback is the primary source of uncertainty in model simulations, especially in the polar regions. A better understanding of the interaction between sea ice and clouds, and specifically the impact of decreased sea ice on cloud cover, will provide valuable insight into the Arctic climate system and may ultimately help in improving climate model parameterizations. In this study, an equilibrium feedback assessment is employed to quantify the relationship between changes in sea ice and clouds, using satellite-derived sea ice concentration and cloud cover over the period 2000–2010. Results show that a 1% decrease in sea ice concentration leads to a 0.36–0.47% increase in cloud cover, suggesting that a further decline in sea ice cover will result in an even cloudier Arctic.”

Citation: Liu, Y., J. R. Key, Z. Liu, X. Wang, and S. J. Vavrus (2012), A cloudier Arctic expected with diminishing sea ice, Geophys. Res. Lett., 39, L05705, doi:10.1029/2012GL051251.

Soils have been acidifying in northern China

Trends Significant soil acidification across northern China’s grasslands during 1980s-2000s – Yang et al. (2012)

Abstract: “Anthropogenic acid deposition may lead to soil acidification, with soil buffering capacity regulating the magnitude of any soil pH change. However, little evidence is available from large-scale or long-term observations. Here we evaluated changes in soil pH across northern China’s grasslands over a 20 year period using soil profiles obtained from China’s Second National Soil Inventory during the 1980s and a more recent regional soil survey in 2001-2005. A transect from the central-southern Tibetan Plateau to the eastern Inner Mongolian Plateau, where Kriging interpolation provided robust predictions of the spatial distribution of soil pH, was then selected to examine pH changes during the survey period. Our results showed that soil pH in the surface layer had declined significantly over the last two decades, with an overall decrease of 0.63 units (95% confidence interval = 0.54-0.73 units). The decline of soil pH was observed in both alpine grasslands on the Tibetan Plateau and temperate grasslands on the Inner Mongolian Plateau. Soil pH decreased more intensively in low soil carbonate regions, while changes of soil pH showed no significant associations with soil cation exchange capacity. These results suggest that grassland soils across northern China have experienced significant acidification from the 1980s to the 2000s, with soil carbonates buffering the increase of soil acidity. The buffering process may induce a large loss of carbon from soil carbonates and thus alter the carbon balance in these globally important ecosystems.”

Citation: Yuanhe Yang, Chengjun Ji, Wenhong Ma, Shifeng Wang, Shaopeng Wang, Wenxuan Han, Anwar Mohammat, David Robinson, Pete Smith, Global Change Biology, DOI: 10.1111/j.1365-2486.2012.02694.x.

Warm extremes have increased and cold extremes have decreased in South Africa

Trends in extreme temperature indices in South Africa: 1962–2009 – Kruger & Sekele (2012)

Abstract: “Trends in daily maximum and minimum extreme temperature indices were investigated for 28 weather stations in South Africa, not only for the common period of 1962–2009, but also for longer periods which the individual record lengths of the stations would allow. The utilized weather stations had limited gaps in their time series, did not undergo major moves, or had their exposure compromised during the study period, as to influence the homogeneity of their time series. The indices calculated were forthcoming from those developed by the WMO/CLIVAR Expert Team on Climate Change Detection and Indices (ETCCDI), but only those applicable to the South African climate were selected. The general result is that warm extremes increased and cold extremes decreased for all of the weather stations. The trends however vary on a regional basis, both in magnitude and statistical significance, broadly indicating that the western half, as well as parts of the northeast and east of South Africa, show relatively stronger increases in warm extremes and decreases in cold extremes than elsewhere in the country. These regions coincide to a large degree with the thermal regimes in South Africa which are susceptible to extreme temperatures. The annual absolute maximum and minimum temperatures do not reflect the general trends displayed by the other indices, showing that individual extreme events cannot always be associated with observed long-term climatic trends. The analyses of longer time series than the common period indicate that it is highly likely that warming accelerated since the mid-1960s in South Africa.”

Citation: A. C. Kruger, S. S. Sekele, International Journal of Climatology, DOI: 10.1002/joc.3455.

In eastern Australia they cut down forests and got droughts in return

A review and modelling results of the simulated response of deforestation on climate extremes in eastern Australia – Deo (2012)

Abstract: “The native vegetation cover in Australia has been modified extensively since the advent of European population. This was paralleled by increases in mean surface temperatures, decreases in mean rainfall and persistence of long-lasting and severe droughts, especially in eastern Australia. The purpose of this article is twofold: (1) to review the simulated response of deforestation on Australian droughts in light of the physics of land-surface processes, (2) to provide further analysis of the modelling results from the CSIRO Mark 3 Atmospheric Global Climate Model (AGCM) to quantify the changes in Australian droughts from the pre-European to modern-day land cover conditions. The simulated response for the austral summer for the modern-day period showed (1) a shift in the tails of the probability distribution functions of rainfall and temperature towards drier and warmer conditions, (2) a decrease in average rainfall between ~ 4–12%, (3) a reduction in average soil moisture by ~ 40%, (4) an increase dry spells by ~ 3–4 days, (5) a decrease in cumulative wet day rainfall between 10 and 25 mm day−1, (6) an increases in drought duration by ~ 6–12 consecutive days and an increase in drought severity by ~ 4–8%, (7) an average warming of ~ 0.4–3.6 °C, and an increase in dry spells by ~ 6–9 days for the 1982/83 El Niño event. These changes were statistically significant at the 95% confidence level using the non-parametric bootstrapping procedure. The simulated changes in atmospheric variables indicate that deforestation has been a contributing factor to the observed increases in drought severity and duration in eastern Australia.”

Citation: Ravinesh C. Deo, Atmospheric Research, Volume 108, May 2012, Pages 19–38,

Atmospheric nitrous oxide increase since 1940 is largely from nitrogen-based fertilizers

Trends and seasonal cycles in the isotopic composition of nitrous oxide since 1940 – Park et al. (2012)

Abstract: “The atmospheric nitrous oxide mixing ratio has increased by 20% since 1750 (ref. 1). Given that nitrous oxide is both a long-lived greenhouse gas and a stratospheric ozone-depleting substance, this increase is of global concern. However, the magnitude and geographic distribution of nitrous oxide sources, and how they have changed over time, is uncertain. A key unknown is the influence of the stratospheric circulation, which brings air depleted in nitrous oxide to the surface. Here, we report the oxygen and intramolecular nitrogen isotopic compositions of nitrous oxide in firn air samples from Antarctica and archived air samples from Cape Grim, Tasmania, spanning 1940–2005. We detect seasonal cycles in the isotopic composition of nitrous oxide at Cape Grim. The phases and amplitudes of these seasonal cycles allow us to distinguish between the influence of the stratospheric sink and the oceanic source at this site, demonstrating that isotope measurements can help in the attribution and quantification of surface sources in general. Large interannual variations and long-term decreasing trends in isotope composition are also apparent. These long-term trends allow us to distinguish between natural and anthropogenic sources of nitrous oxide, and confirm that the rise in atmospheric nitrous oxide levels is largely the result of an increased reliance on nitrogen-based fertilizers.”

Citation: S. Park, P. Croteau, K. A. Boering, D. M. Etheridge, D. Ferretti, P. J. Fraser, K-R. Kim, P. B. Krummel, R. L. Langenfelds, T. D. van Ommen, L. P. Steele & C. M. Trudinger, Nature Geoscience, 2012, doi:10.1038/ngeo1421.

CLASSIC OF THE WEEK: Unknown author (1895)

The Carbonic Acid Gas in the Atmosphere (1895) [FULL TEXT]

Abstract: No abstract.

Citation: Mon. Wea. Rev., 23, 300–301. doi:;2.

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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New research from last week 10/2012

Posted by Ari Jokimäki on March 12, 2012

This week we wonder if there’s a monsoon in Europe and if data archiving practices of ecologists could be improved. We also have a paper on skating in Canada. Doesn’t sound much like a batch of climate papers, right? We do have studies also on maize in United States, double cropping in China, and soil microbial communities. Still not about climate, you say? Ok, there are also studies on Twentieth Century Reanalysis, hurricane classifications over time, Saudi Arabia temperature trends, and carbon dioxide transport in upper atmosphere. Does that satisfy your hunger for climate papers?

United States maize yields are projected to decrease and become more variable

Projected temperature changes indicate significant increase in interannual variability of U.S. maize yields – Urban et al. (2012)

Abstract: “Climate change has the potential to be a source of increased variability if crops are more frequently exposed to damaging weather conditions. Yield variability could respond to a shift in the frequency of extreme events to which crops are susceptible, or if weather becomes more variable. Here we focus on the United States, which produces about 40% of the world’s maize, much of it in areas that are expected to see increased interannual variability in temperature. We combine a statistical crop model based on historical climate and yield data for 1950–2005 with temperature and precipitation projections from 15 different global circulation models. Holding current growing area constant, aggregate yields are projected to decrease by an average of 18% by 2030–2050 relative to 1980–2000 while the coefficient of variation of yield increases by an average of 47%. Projections from 13 out of 15 climate models result in an aggregate increase in national yield coefficient of variation, indicating that maize yields are likely to become more volatile in this key growing region without effective adaptation responses. Rising CO2 could partially dampen this increase in variability through improved water use efficiency in dry years, but we expect any interactions between CO2 and temperature or precipitation to have little effect on mean yield changes.”

Citation: Daniel Urban, Michael J. Roberts, Wolfram Schlenker and David B. Lobell, Climatic Change, DOI: 10.1007/s10584-012-0428-2.

New paper urges ecologists to archive and share their data

Advances in global change research require open science by individual researchers – Wolkovich et al. (2012)

Abstract: “Understanding how species and ecosystems respond to climate change requires spatially and temporally rich data for a diverse set of species and habitats, combined with models that test and predict responses. Yet current work is hampered by the long-known problems of inadequate management of data and insufficient description of analytical procedures, especially in the field of ecology. Despite recent institutional incentives to share data and new data archiving infrastructure, many ecologists do not archive and publish their data and code. Given current rapid rates of global change, the consequences of this are extreme: because an ecological dataset collected at a certain place and time represents an irreproducible set of observations, ecologists doing local, independent research possess, in their file cabinets and spreadsheets, a wealth of information about the natural world and how it is changing. Although large-scale initiatives will increasingly enable and reward open science, we believe that change demands action and personal commitment by individuals—from students and PIs. Here, we outline the major benefits of sharing data and analytical procedures in the context of global change ecology, and provide guidelines for overcoming common obstacles and concerns. If individual scientists and labs can embrace a culture of archiving and sharing we can accelerate the pace of the scientific method and redefine how local science can most robustly scale up to globally-relevant questions.”

Citation: Elizabeth M. Wolkovich, James Regetz, Mary I. O’Connor, Global Change Biology, DOI: 10.1111/j.1365-2486.2012.02693.x.

Possibly artificial shift in Twentieth Century Reanalysis over central United States

Detecting inhomogeneities in the Twentieth Century Reanalysis over the central United States – Ferguson & Villarini et al. (2012)

Abstract: “The Twentieth Century Reanalysis (20CR), which spans the 138 year period from 1871 to 2008, was intended for a variety of climate applications, including long-term trend assessment. Because over land 20CR only assimilates surface pressure observations and their count increases by an order of magnitude over the course of the record, a key question is whether the 20CR is homogenous and hence suitable for detecting climate-related changes. We use three statistical methods (Pettitt and Bai-Perron tests and segmented regression) to detect abrupt shifts in multiple hydrometeorological variable mean and uncertainty fields over the central United States. For surface air temperature and precipitation, we use the Climate Research Unit (CRU) time series data set for comparison. We find that for warm-season months, there is a consensus change point among all variables between 1940 and 1950, which is not substantiated by the CRU record. While we cannot say with certainty that these shifts in the 20CR analysis fields are artificial, our statistical analyses, coupled with a visual inspection of the underlying assimilated observational count time series, strongly point to this conclusion. Our recommendation is therefore for users to restrict climate trend applications over the central United States to the second half century of the 20CR record, after observational density has stabilized.”

Citation: Ferguson, C. R., and G. Villarini (2012), Detecting inhomogeneities in the Twentieth Century Reanalysis over the central United States, J. Geophys. Res., 117, D05123, doi:10.1029/2011JD016988.

Analysis of the effect of classification method changes to hurricane categories

On the Classification of Extreme Atlantic Hurricanes Utilizing Mid-20th Century Monitoring Capabilities – Hagen & Landsea et al. (2012)

Abstract: “An investigation is conducted to determine how improvements in observing capabilities and technology may have affected our ability to detect and monitor Saffir-Simpson Hurricane Wind Scale Category 5 hurricanes in the Atlantic basin during the mid-20th century. Previous studies state that there has been an increase in the number of intense hurricanes and attribute this increase to anthropogenic global warming. Other studies claim that the apparent increased hurricane activity is an artifact of better observational capabilities and improved technology for detecting these intense hurricanes. The present study focuses on the ten most recent Category 5 hurricanes recorded in the Atlantic from Hurricane Andrew (1992) through Hurricane Felix (2007). These ten hurricanes are placed into the context of the technology available in the period of 1944-1953, the first decade of aircraft reconnaissance. A methodology is created to determine how many of these ten recent Category 5s likely would have been recorded as Category 5s if they had occurred during this period using only the observations that likely would have been available with existing technology and observational networks. Late 1940s and early 1950s best track intensities are determined for the entire lifetime of these ten recent Category 5s. It is found that likely only two of these ten – both Category 5 landfalling hurricanes – would have been recorded as Category 5 hurricanes if they had occurred during the late 1940s period. The results suggest that intensity estimates for extreme tropical cyclones prior to the satellite era are unreliable for trend and variability analysis.”

Citation: Andrew B. Hagen, Christopher W. Landsea, Journal of Climate 2012, doi:

Double cropping may amplify regional warming in northern China

Observational evidences of double cropping impacts on the climate in the northern China plains – Ho et al. (2012)

Abstract: “The impacts of harvested cropland in the double cropping region (DCR) of the northern China plains (NCP) on the regional climate are examined using surface meteorological data and satellite-derived normalized difference vegetation index (NDVI) and land surface temperature (LST). The NDVI data are used to distinguish DCR from single cropping region (SCR) in the NCP. Notable increases in LST in the period May-June are found in the area identified as DCR on the basis of the NDVI data. The difference between the mean daily maximum temperature averaged over the DCR and SCR stations peaks at 1.27°C in June. The specific humidity in DCR is significantly smaller than in SCR. These results suggest that the enhanced agricultural production by multiple cropping may amplify regional warming and aridity to further modify the regional climate in addition to the global climate change. Results in this study may also be used as a quantitative observed reference state of the crop/vegetation effects for future climate modeling studies.”

Citation: C.-H. Ho, S.-J. Park, S.-J. Jeong, J. Kim, and J.-G. Jhun, Journal of Climate 2012, doi:

In Saudi Arabia temperatures have increased and precipitation has decreased significantly

Recent climate change in the Arabian Peninsula: annual rainfall and temperature analysis of Saudi Arabia for 1978–2009 – Almazroui et al. (2012) [FULL TEXT]

Abstract: “The rainfall and temperature climatology over the Arabian Peninsula are analysed on an annual basis using various gridded datasets. For Saudi Arabia, the area of which represents almost 80% of the Peninsula, the climatic datasets from its 27 ground observations are analysed for the period 1978–2009, with additional gridded datasets used to describe the observed state and change of the present climate. The gridded datasets represent well the very dry (40–80 mm) area over the world’s largest sand desert (Rub Al-Khali), the dry (80–150 mm) area over middle-to-north of Saudi Arabia, and the wettest (>150 mm) region in the southwest of the Peninsula. The annual temperature is relatively high (24–27 °C) in the middle-to-south of the Peninsula and low (27 °C) is obtained over the Rub Al-Khali. Over Saudi Arabia, the observed annual rainfall showed a significant decreasing trend (47.8 mm per decade) in the last half of the analysis period, with a relatively large interannual variability, while the maximum, mean and minimum temperatures have increased significantly at a rate of 0.71, 0.60, and 0.48 °C per decade, respectively. This information is invaluable to consider in any climate impact assessment studies in Saudi Arabia.”

Citation: Mansour Almazroui, M. Nazrul Islam, H. Athar, P. D. Jones, M. Ashfaqur Rahman, International Journal of Climatology, DOI: 10.1002/joc.3446.

Aircraft observations show the interhemispheric transport of CO2 in the upper atmosphere

Aircraft observation of the seasonal variation in the transport of CO2 in the upper atmosphere – Sawa et al. (2012)

Abstract: “A large number of in situ carbon dioxide (CO2) measurements from 5224 flights were taken by commercial airliners from 2005 to 2010. We analyzed the seasonal cycles in tropospheric CO2 in wide areas of the world over the Eurasian continent, the North Pacific, Southeast Asia, and Oceania. In the Northern Hemisphere, large seasonal changes of CO2 in the upper troposphere are found from spring through summer at northern midlatitudes to high latitudes with significant longitudinal differences; seasonally low CO2 mixing ratios are vertically transported from the surface over the Eurasian continent and then transported eastward to the North Pacific. In the Southern Hemisphere, the CO2 in the upper troposphere increases rapidly from April to June, indicating clearly the interhemispheric transport of high CO2 from the Northern Hemisphere winter. The rapid increase in the upper southern lower latitudes is equivalent to about 0.2 Pg increase in carbon. This interhemispheric transport should be adequately represented in general circulation models for source/sink estimates by inverse methods, because it is comparable to the seasonal or net fluxes estimated for a current inversion area size or a typical subcontinental domain. Estimation for transport of CO2 through the high altitudes will be more important than ever with increasing data from aircraft observations.”

Citation: Sawa, Y., T. Machida, and H. Matsueda (2012), Aircraft observation of the seasonal variation in the transport of CO2 in the upper atmosphere, J. Geophys. Res., 117, D05305, doi:10.1029/2011JD016933.

Soil microbial communities might react more to nitrogen deposition than to climate

Microbial communities and their responses to simulated global change fluctuate greatly over multiple years – Gutknecht et al. (2012)

Abstract: “We used microbial lipid analysis to analyze microbial biomass and community structure during six years of experimental treatment at the Jasper Ridge Global Change Experiment (JRGCE), a long-term multi-factor global change experiment in a California annual grassland. The microbial community fingerprint and specific biomarkers varied substantially from year to year, in both control and experimental treatment plots. Possible drivers of the variability included plant growth, soil moisture, and temperature. Surprisingly, background variation in the microbial community was of a larger magnitude than even very significant treatment effects, and this variation appeared to constrain responses to treatment. Microbial communities were mostly not responsive or not consistently responsive to the experimental treatments. Both AMF biomarker abundance (16:1 ω5c) and the fungal to bacterial ratio were lower under nitrogen addition in most years. Bacterial lipid biomarker abundances (15:0 iso and 16:1 ω7c) were higher under nitrogen addition in 2002, the year of largest microbial biomass, suggesting that bacteria could respond more to nitrogen addition in years of better growth conditions. Nitrogen addition and warming led to an interactive effect on the Gram-positive bacterial biomarker and the fungal to bacterial ratio. These patterns indicate that in California grassland ecosystems, microbial communities may not respond substantially to future changes in climate and that nitrogen deposition may be a determinant of the soil response to global change. Further, year-to-year variation in microbial growth or community composition may be important determinants of ecosystem response to global change.”

Citation: Jessica LM Gutknecht, Christopher B Field, Teri C Balser, 2012, Global Change Biology, DOI: 10.1111/j.1365-2486.2012.02686.x.

Canadian outdoor skating season has gotten shorter

Observed decreases in the Canadian outdoor skating season due to recent winter warming – Damyanov et al. (2012) [FULL TEXT]

Abstract: “Global warming has the potential to negatively affect one of Canada’s primary sources of winter recreation: hockey and ice skating on outdoor rinks. Observed changes in winter temperatures in Canada suggest changes in the meteorological conditions required to support the creation and maintenance of outdoor skating rinks; while there have been observed increases in the ice-free period of several natural water bodies, there has been no study of potential trends in the duration of the season supporting the construction of outdoor skating rinks. Here we show that the outdoor skating season (OSS) in Canada has significantly shortened in many regions of the country as a result of changing climate conditions. We first established a meteorological criterion for the beginning, and a proxy for the length of the OSS. We extracted this information from daily maximum temperature observations from 1951 to 2005, and tested it for significant changes over time due to global warming as well as due to changes in patterns of large-scale natural climate variability. We found that many locations have seen a statistically significant decrease in the OSS length, particularly in Southwest and Central Canada. This suggests that future global warming has the potential to significantly compromise the viability of outdoor skating in Canada.”

Citation: Nikolay N Damyanov et al 2012 Environ. Res. Lett. 7 014028 doi:10.1088/1748-9326/7/1/014028.

There might be a monsoon in Europe too

Some evidence on European monsoon existence – Radinović & Ćurić (2012)

Abstract: “Large-scale European atmospheric circulation induced by temperature differences between the continent and the North Atlantic Ocean causes thermodynamic and climatic conditions that initiate a European monsoon. In Eastern Europe, the rainy season occurs in early summer, and the dry season occurs in winter. In Western Europe, the rainy season is in the early winter and the dry season is in the spring. This precipitation trend, as well as other climatic features, suggests the existence of a European monsoon.”

Citation: D. Radinović and M. Ćurić, Theoretical and Applied Climatology, DOI: 10.1007/s00704-012-0609-y.

CLASSIC OF THE WEEK: Alexander & Mobley (1976)

Monthly Average Sea–Surface Temperatures and Ice–Pack Limits on a 1° Global Grid – Alexander & Mobley (1976) [FULL TEXT]

Abstract: “Climatological monthly ocean-surface temperatures obtained from the National Center for Atmospheric Research and from Fleet Numerical Weather Central are merged and interpolated onto a 1° global grid. Monthly distributions of the main ice packs of the Arctic and Antarctic are digitized from Fleet Weather Facility ice charts and Navy atlases, and are incorporated into the global arrays. Machine-analyzed maps of the resulting distributions for the months of January, March, May, July, September and November are presented to indicate the seasonal variations of temperature and ice extent.”

Citation: Alexander, Richard C., Robert L. Mobley, 1976: Monthly Average Sea–Surface Temperatures and Ice–Pack Limits on a 1° Global Grid. Mon. Wea. Rev., 104, 143–148.

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.

Posted in Climate science | Leave a Comment »

New research from last week 9/2012

Posted by Ari Jokimäki on March 5, 2012

This week’s scientists are from Estonia, Finland, France, Germany, India, Italy, Netherlands, Portugal, Spain, Switzerland, United Kingdom, and United States. It seems that we have lot of European studies this week. Oh, the studies themselves? Well, they are amazingly interesting as usual. They have studied cold spells, aerosols, clouds, maximum temperatures, water vapor, meteorological measurements, lake sediments, winter precipitation, trees, and even crop prices. And you should have seen the studies that got away!

Where exactly model simulations of clouds go wrong?

Exposing global cloud biases in the Community Atmosphere Model (CAM) using satellite observations and their corresponding instrument simulators – Kay et al. (2012)

Abstract: “Satellite observations and their corresponding instrument simulators are used to document global cloud biases in the Community Atmosphere Model (CAM) versions 4 and 5. The model-observation comparisons show that despite having nearly identical cloud radiative forcing, CAM5 has a much more realistic representation of cloud properties than CAM4. In particular, CAM5 exhibits substantial improvement in three long-standing climate model cloud biases: 1) the underestimation of total cloud, 2) the overestimation of optically thick cloud, and 3) the underestimation of mid-level cloud. While the increased total cloud and decreased optically thick cloud in CAM5 result from improved physical process representation, the increased mid-level cloud in CAM5 results from the addition of radiatively active snow. Despite these improvements, both CAM versions have cloud deficiencies. Of particular concern, both models exhibit large but differing biases in the subtropical marine boundary layer cloud regimes that are known to explain inter-model differences in cloud feedbacks and climate sensitivity. More generally, this study demonstrates that simulator-facilitated evaluation of cloud properties, such as amount by vertical level and optical depth, can robustly expose large and at times radiatively compensating climate model cloud biases.”

Citation: J. E. Kay, B. R. Hillman, S. A. Klein, Y. Zhang, B. Medeiros, R. Pincus, A. Gettelman, B. Eaton, J. Boyle, R. Marchand, and T. P. Ackerman, Journal of Climate 2012.

Possibly positive feedback from cirrostratus and cirrus clouds in warmer climate

Convection-climate feedbacks in the ECHAM5 general circulation model: Evaluation of cirrus cloud life cycles with ISCCP satellite data from a Lagrangian trajectory perspective – Gehlot & Quaas (2012)

Abstract: “A process-oriented climate model evaluation is presented, applying the International Satellite Cloud Climatology Project (ISCCP) simulator to pinpoint deficiencies related to the cloud processes in the ECHAM5 general circulation model. A Lagrangian trajectory analysis is performed to track the transitions of anvil cirrus originating from deep-convective detrainment to cirrostratus and thin cirrus, comparing ISCCP observations and the ECHAM5 model. Trajectories of cloudy air parcels originating from deep convection are computed for both, the ISCCP observations and the model, over which the ISCCP joint histograms are used for analyzing the cirrus life cycle over 5 days. The clouds originating from detrainment from deep-convection decay and gradually thin-out after the convective event over 3 to 4 days. The effect of the convection-cirrus transitions in a warmer climate is analyzed, in order to understand the climate feedbacks due to deep-convective cloud transitions. An idealized climate change simulation is performed using a +2K Sea Surface Temperature (SST) perturbation. The Lagrangian trajectory analysis over perturbed climate suggests that more and thicker cirrostratus and cirrus clouds occur in the warmer climate compared to the present day climate. Stronger convection is noticed in the perturbed climate which leads to an increased precipitation, especially on day-2 and -3 after the individual convective events. The shortwave and the longwave cloud forcings both increase in the warmer climate, with an increase of net cloud radiative forcing (NCRF), leading to an overall positive feedback of the increased cirrostratus and cirrus clouds from a Lagrangian transition perspective.”

Citation: Swati Gehlot and Johannes Quaas, Journal of Climate 2012.

Temperature was related to crop prices in 19th century Sweden

Climatic signatures in crops and grain prices in 19th-century Sweden – Holopainen et al. (2012)

Abstract: “Climate and weather variation affect agricultural productivity, with consequences for both overall food availability and the wider economy. Knowledge of these processes has implications for understanding historical demography and predicting effects of climate change on societies. We studied the relationships between ambient temperature and the yields and prices of principle grains (wheat, rye, barley oats) in Sweden from 1803 to 1914. We found that the annual general crop index (a measure of overall crop yield) correlated negatively with the annual average price of the four grains. Overall temperature during the period of crop growth was related positively to general crop index and negatively to average crop price. At the level of month of crop growth, when the relationship between temperature and general crop index was most positive, that between temperature and average crop price was most negative. This strong structured relationship was found to be consistent when yields of each crop were considered separately, and indicates that the relationships between crop yield and crop price were to a large extent due to the influence of ambient temperature. Price correlations between pairs of crop species were in all cases greater than the correlation of yields. Within individual crops, correlations between price and yield were stronger for those crops for which imports were not available, and which were therefore subject to the weakest influence from rising globalisation. Our analyses demonstrate the sensitivity of historical agriculture to climatic factors, and the extent to which this affected the wider economy. It is likely that the susceptibility of agriculture to climatic risks was ascended by the concomitant climate regime, the ‘Little Ice Age’. Moreover, our study period spans the period of rising globalisation, and suggests a weakening influence of prevailing weather on crop prices.”

Citation: Jari Holopainen, Ian J Rickard, Samuli Helama, The Holocene March 1, 2012 0959683611434220, doi: 10.1177/0959683611434220.

The trees that grow on glaciers

The influence of glacier surface processes on the short-term evolution of supraglacial tree vegetation: A case study of the Miage Glacier, Italian Alps – Pelfini et al. (2012)

Abstract: “Supraglacial debris cover allows vegetation to colonize glacier surface, and whenever it is enough stable and thick, also shrubs and trees can germinate and grow. Supraglacial tree growth and distribution patterns on the glacier are closely connected with the debris-covered glacier dynamics and evolution. The aim of the research reported here was to evaluate the tree age and tree distribution patterns on the glacier tongue and the influence of ice-cliff backwasting, close to glacier terminus, on tree loss. We analysed the fragile and fast-changing environment that is present on the lower ablation sector of the Miage Glacier (Mont Blanc Massif, Italian Alps) where some ice cliffs are present and backwasting and downwasting phenomena occur. Tree features and short-term evolution were analysed with respect to glacier variations (mainly surface displacements and ice ablation) and geometry changes of the two most representative ice cliffs. The supraglacial trees’ life time resulted to be mainly controlled by glacier surface displacements and by the occurrence of backwasting and downwasting processes, whereas tree germination was associated with fine debris presence. These factors, controlling plants’ life and growth on the glacier, are an actual limit when supraglacial trees are analysed to reconstruct past environmental changes occurred on the glacier tongue. Moreover, we found that a large number of trees die under conditions of dominating backwasting inducing the loss of debris substrate (condition met especially on the northern glacier lobe). Instead, in the case of prevalence of downwasting (condition mainly observed on the southern glacier lobe), trees more easily survive and flow downvalley transported by the glacier flux.”

Citation: Manuela Pelfini, Guglielmina Diolaiuti, Giovanni Leonelli, Mauro Bozzoni, Nicoletta Bressan, Daniele Brioschi, Anna Riccardi, The Holocene March 2, 2012 0959683611434222, doi: 10.1177/0959683611434222.

Extreme winter precipitation events projected to increase significantly in western United States

Changes in winter precipitation extremes for the Western United States under a warmer climate as simulated by regional climate models – Dominguez et al. (2012)

Abstract: “We find a consistent and statistically significant increase in the intensity of future extreme winter precipitation events over the western United States, as simulated by an ensemble of regional climate models (RCMs) driven by IPCC AR4 global climate models (GCMs). All eight simulations analyzed in this work consistently show an increase in the intensity of extreme winter precipitation with the multi-model mean projecting an area-averaged 12.6% increase in 20-year return period and 14.4% increase in 50-year return period daily precipitation. In contrast with extreme precipitation, the multi-model ensemble shows a decrease in mean winter precipitation of approximately 7.5% in the southwestern US, while the interior west shows less statistically robust increases.”

Citation: Dominguez, F., E. R. Rivera, D. P. Lettenmaier, and C. L. Castro (2012), Changes in winter precipitation extremes for the Western United States under a warmer climate as simulated by regional climate models, Geophys. Res. Lett., doi:10.1029/2011GL050762, in press.

Greenland lake sediments show Norse agriculture only weakly but modern agriculture markedly

A paleoecological perspective on 1450 years of human impacts from a lake in southern Greenland – Perren et al. (2012)

Abstract: “A multiproxy sedimentary record from Lake Igaliku in southern Greenland documents 1450 years of human impacts on the landscape. Diatoms, scaled chrysophytes, and C and N geochemistry show perturbations consistent with recent agricultural activities (post-AD 1980), superimposed upon long-term environmental variability. While the response to Norse agriculture (~AD 986–1450) is weak, the biological response to the last 30 years of modern sheep farming is marked, with drastic changes in diatom taxa, δ13C and δ15N isotopic ratios, and a sharp increase in scaled chrysophytes. Indeed, current conditions in the lake during the last 30 years are unprecedented in the context of the last 1450 years. The dominant driver for recent changes is likely an intensification of agricultural practices combined with warming summer temperatures. Warm temperatures and agricultural disturbance together during Norse Landnám did not lead to the marked changes seen in the modern lake environment over the last 30 years. The synergistic response between increased climate warming and agriculture will likely have unanticipated effects. These findings confirm the sensitivity of Arctic lakes to external anthropogenic forcing and are the first analyses of their kind for the effects of agriculture in Greenland.”

Citation: Bianca B Perren, Charly Massa, Vincent Bichet, Émilie Gauthier, Olivier Mathieu, Christophe Petit, Hervé Richard, The Holocene March 1, 2012 0959683612437865, doi: 10.1177/0959683612437865.

Calibrating lake sediment records with meteorological data

Calibrating biogeochemical and physical climate proxies from non-varved lake sediments with meteorological data: methods and case studies – von Gunten et al. (2012)

Abstract: “Lake sediment records are underrepresented in comprehensive, quantitative, high-resolution (sub-decadal), multi-proxy climate reconstructions for the past millennium. This is largely a consequence of the difficulty of calibrating biogeochemical lake sediment proxies to meteorological time series (calibration-in-time). Thanks to recent methodological advances, it is now possible. This paper outlines a step-by-step, specifically tailored methodology, with practical suggestions for calibrating and validating biogeochemical proxies from lake sediments to meteorological data. This approach includes: (1) regional climate data; (2) site selection; (3) coring and core selection; (4) core chronology; (5) data acquisition; and (6) data analysis and statistical methods. We present three case studies that used non-varved lake sediments from remote areas in the Central Chilean Andes, where little a priori information was available on the local climate and lakes, or their responses to climate variability. These case studies illustrate the potential value and application of a calibration-in-time approach to non-varved lake sediments for developing quantitative, high-resolution climate reconstructions.”

Citation: Lucien von Gunten, Martin Grosjean, Christian Kamenik, Marian Fujak and Roberto Urrutia, Journal of Paleolimnology, DOI: 10.1007/s10933-012-9582-9.

Portuguese meteorological measurements from 18th century

Early Portuguese meteorological measurements (18th century) – Alcoforado et al. (2012) [FULL TEXT]

Abstract: “Natural proxies, documentary evidence and instrumental data are the only sources used to reconstruct past climates. In this paper, we present the 18th century meteorologists (either Portuguese or foreigners) who made the first observations at several sites in Continental Portugal, Madeira Island and Rio de Janeiro (Brazil), from 1749 until 1802. Information is given concerning observation site, variables observed, measurement period, methods of measurements and sources (both manuscript and printed). Some examples from the data usefulness are given: rainfall variability in Madeira (1749–1753) and in continental Portugal (1781–1793) was reconstructed, allowing to extend towards the late 18th century the well known negative correlation between the NAO index and seasonal rainfall. Furthermore, previously unpublished data for 1783–1784 have allowed analysing the consequences of the Lakagígar eruption in Portugal: foggy and haze days are referred to in summer 1783, but unlike the hot summer observed in northern and central Europe, temperatures in Portugal were lower than average. Additionally, observations from Rio de Janeiro in Brazil show that the Lakagígar consequences may well have spread to sectors of the Southern Hemisphere. Although the series are short, the data have been used for climate reconstruction studies and may also be useful to improve the quality of large scale reconstruction datasets.”

Citation: Alcoforado, M. J., Vaquero, J. M., Trigo, R. M., and Taborda, J. P.: Early Portuguese meteorological measurements (18th century), Clim. Past, 8, 353-371, doi:10.5194/cp-8-353-2012, 2012.

High altitude water vapor feedback analysis

Using satellites to investigate the sensitivity of longwave downward radiation to water vapor at high elevations – Naud et al. (2012)

Abstract: “Many studies suggest that high-elevation regions may be among the most sensitive to future climate change. However, in situ observations in these often remote locations are too sparse to determine the feedbacks responsible for enhanced warming rates. One of these feedbacks is associated with the sensitivity of longwave downward radiation (LDR) to changes in water vapor, with the sensitivity being particularly large in many high-elevation regions where the average water vapor is often low. We show that satellite retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth’s Radiant Energy System (CERES) can be used to expand the current ground-based observational database and that the monthly averaged clear-sky satellite estimates of humidity and LDR are in good agreement with the well-instrumented Center for Snow and Avalanche Studies ground-based site in the southwestern Colorado Rocky Mountains. The relationship between MODIS-retrieved precipitable water vapor and surface specific humidity across the contiguous United States was found to be similar to that previously found for the Alps. More important, we show that satellites capture the nonlinear relationship between LDR and water vapor and confirm that LDR is especially sensitive to changes in water vapor at high elevations in several midlatitude mountain ranges. Because the global population depends on adequate fresh water, much of which has its source in high mountains, it is critically important to understand how climate will change there. We demonstrate that satellites can be used to investigate these feedbacks in high-elevation regions where the coverage of surface-based observations is insufficient to do so.”

Citation: Naud, C. M., J. R. Miller, and C. Landry (2012), Using satellites to investigate the sensitivity of longwave downward radiation to water vapor at high elevations, J. Geophys. Res., 117, D05101, doi:10.1029/2011JD016917.

Maximum temperatures have increased faster than minimum temperatures in Spain

Recent trends in mean maximum and minimum air temperatures over Spain (1961–2006) – del Río et al. (2012)

Abstract: “This study analyzes the mean maximum and minimum temperature trends on a monthly, seasonal, and annual timescale by applying various statistical tools to data from 476 Spanish weather stations during the period between 1961 and 2006. The magnitude of the trends was derived from the slopes of the regression lines using the least squares method, and the nonparametric Mann–Kendall test was used to determine the statistical significance of the trends. Temperature significantly increased in over 60% of the country in March, June, spring, and summer in the case of maximum temperatures and in March, May, June, August, spring, and summer for minimum temperatures. At the annual resolution, temperatures significantly increased in over 90% of Spain with a rise of around 0.3°C/decade. The maximum temperature increased at a higher rate than the minimum temperature from midsummer to early winter as well as in winter, spring, and summer and also on an annual basis.”

Citation: S. del Río, A. Cano-Ortiz, L. Herrero and A. Penas, Theoretical and Applied Climatology, DOI: 10.1007/s00704-012-0593-2.

Analysis of aerosol and cloud forcing over India

Aerosol and cloud feedbacks on surface energy balance over selected regions of the Indian subcontinent – Urankar et al. (2012)

Abstract: “We investigate aerosol and cloud forcing on the surface energy balance over selected regions in India. Four regions were selected with different surface characteristics and have considerable differences in the long-term trends and seasonal distribution of clouds and aerosols. These regions are described as (1) northern semiarid, (2) humid subtropical, (3) populated central peninsula, and (4) northeast monsoon impacted. Modern Era Retrospective-analysis for Research and Applications (MERRA) data and Climate Forecast System Reanalysis version 2 (CFSR) data are used in this study. An intercomparison of cloud fractions from both data sets shows that CFSR systematically underestimates high-cloud fraction during premonsoon and monsoon seasons. However, there are fewer low-cloud fraction biases. The positive temporal trend over 31 years (1979–2009) from MERRA in high clouds is greater than that of low clouds. This is due to positive anomalies in the cloud ice and supercooled liquid water content in MERRA. Biases in the radiative fluxes and surface fluxes show a strong relationship (correlations exceeding 0.8) with cloud fraction biases, more so for the high clouds. During the premonsoon season, aerosol forcing causes a change in surface shortwave radiation of −24.5, −25, −19, and −16 W m−2 over regions 1 −4, respectively. The corresponding longwave radiation decrease is −9.8, −6.8, −4.5, and −1.9 W m−2 over these same regions, respectively. The maximum surface shortwave reduction due to clouds, which is observed during the monsoon season, is −86, −113, −101, and −97 W m−2 for these same regions, respectively. A decreasing trend in the boundary layer height is noticed both in MERRA and CFSR. The variation in the Bowen ratio and its relation to aerosol and cloud effect anomalies are also discussed.”

Citation: Urankar, G., T. V. Prabha, G. Pandithurai, P. Pallavi, D. Achuthavarier, and B. N. Goswami (2012), Aerosol and cloud feedbacks on surface energy balance over selected regions of the Indian subcontinent, J. Geophys. Res., 117, D04210, doi:10.1029/2011JD016363.

Western European cold spells are projected to become warmer

Western European cold spells in current and future climate – de Vries et al. (2012)

Abstract: “This paper discusses western European cold spells (where temperature falls below the 10% quantile of the winter temperature distribution) in current and future climate. It is demonstrated that many of the projected future changes in cold-spell statistics (duration, return period, intensity) can be explained by changes in the mean (increase) and variance (decrease) of the winter temperature distribution. After correcting for these changes (by subtracting the mean temperature and by dividing by the standard deviation), future cold-spell statistics display no major changes outside estimated error bounds. In absolute terms however, the future cold spells are projected to become ∼5°C warmer (and remain above freezing point), thus having a significant climatic impact. An important contributor to the projected future decrease of temperature variance is shown to be the reduction of the mean zonal temperature gradient (land-sea contrast). These results have been obtained using a 17-member ensemble of climate-model simulations with current and future concentration of greenhouse gases.”

Citation: de Vries, H., R. J. Haarsma, and W. Hazeleger (2012), Western European cold spells in current and future climate, Geophys. Res. Lett., 39, L04706, doi:10.1029/2011GL050665.


Change of climate in the northern hemisphere – Kirde (1938) [FULL TEXT]

Abstract: No abstract. Opening sentences: “An attempt is made in this paper to analyze the variations of climate in the Northern Hemisphere. For this purpose we have used the temperature observations of meteorological stations whose period of observation extends at least from 45 to 50 years beginning with 1860 – 1870.”

Citation: Kirde, Kaarel, Äratrükk: Acta et commentationes Universitatis Tartuensis (Dorpatensis), A XXXIII. 5.

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