AGW Observer

Observations of anthropogenic global warming

New research from last week 51/2010

Posted by Ari Jokimäki on December 27, 2010

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

Published last week:

History of climate modeling

History of climate modeling – Edwards (2010) “The history of climate modeling begins with conceptual models, followed in the 19th century by mathematical models of energy balance and radiative transfer, as well as simple analog models. Since the 1950s, the principal tools of climate science have been computer simulation models of the global general circulation. From the 1990s to the present, a trend toward increasingly comprehensive coupled models of the entire climate system has dominated the field. Climate model evaluation and intercomparison is changing modeling into a more standardized, modular process, presenting the potential for unifying research and operational aspects of climate science.” Paul N. Edwards, Wiley Interdisciplinary Reviews: Climate Change, DOI: 10.1002/wcc.95.

Winter warming delays spring phenology

Winter and spring warming result in delayed spring phenology on the Tibetan Plateau – Yu et al. (2010) “Climate change has caused advances in spring phases of many plant species. Theoretically, however, strong warming in winter could slow the fulfillment of chilling requirements, which may delay spring phenology. This phenomenon should be particularly pronounced in regions that are experiencing rapid temperature increases and are characterized by highly temperature-responsive vegetation. To test this hypothesis, we used the Normalized Difference Vegetation Index ratio method to determine the beginning, end, and length of the growing season of meadow and steppe vegetation of the Tibetan Plateau in Western China between 1982 and 2006. We then correlated observed phenological dates with monthly temperatures for the entire period on record. For both vegetation types, spring phenology initially advanced, but started retreating in the mid-1990s in spite of continued warming. Together with an advancing end of the growing season for steppe vegetation, this led to a shortening of the growing period. Partial least-squares regression indicated that temperatures in both winter and spring had strong effects on spring phenology. Although warm springs led to an advance of the growing season, warm conditions in winter caused a delay of the spring phases. This delay appeared to be related to later fulfillment of chilling requirements. Because most plants from temperate and cold climates experience a period of dormancy in winter, it seems likely that similar effects occur in other environments. Continued warming may strengthen this effect and attenuate or even reverse the advancing trend in spring phenology that has dominated climate-change responses of plants thus far.” Haiying Yu, Eike Luedeling, and Jianchu Xu, PNAS December 21, 2010 vol. 107 no. 51 22151-22156, doi: 10.1073/pnas.1012490107. [Full text]

Climate change has affected tundra ecosystem

Climate changes and its impact on tundra ecosystem in Qinghai-Tibet Plateau, China – Wang et al. (2010) “Alpine ecosystems in permafrost region are extremely sensitive to climate change. The headwater regions of Yangtze River and Yellow River of the Qinghai-Tibet plateau permafrost area were selected. Spatial-temporal shifts in the extent and distribution of tundra ecosystems were investigated for the period 1967–2000 by landscape ecological method and aerial photographs for 1967, and satellite remote sensing data (the Landsat’s TM) for 1986 and 2000. The relationships were analyzed between climate change and the distribution area variation of tundra ecosystems and between the permafrost change and tundra ecosystems. The responding model of tundra ecosystem to the combined effects of climate and permafrost changes was established by using statistic regression method, and the contribution of climate changes and permafrost variation to the degradation of tundra ecosystems was estimated. The regional climate exhibited a tendency towards significant warming and desiccation with the air temperature increased by 0.4–0.67°C/10a and relative stable precipitation over the last 45 years. Owing to the climate continuous warming, the intensity of surface heat source (HI) increased at the average of 0.45 W/m2 per year, the difference of surface soil temperature and air temperature (DT) increased at the range of 4.1°C–4.5°C, and the 20-cm depth soil temperature within the active layer increased at the range of 1.1°C–1.4°C. The alpine meadow and alpine swamp meadow were more sensitive to permafrost changes than alpine steppe. The area of alpine swamp meadow decreased by 13.6–28.9%, while the alpine meadow area decreased by 13.5–21.3% from 1967 to 2000. The contributions of climate change to the degradation of the alpine meadow and alpine swamp was 58–68% and 59–65% between 1967 and 2000. The synergic effects of climate change and permafrost variation were the major drivers for the observed degradation in tundra ecosystems of the Qinghai-Tibet plateau.” Genxu Wang, Wei Bai, Na Li and Hongchang Hu, Climatic Change, DOI: 10.1007/s10584-010-9952-0.

Complex climate response of the trees in Pakistan

The dendroclimatic potential of conifers from northern Pakistan – Ahmed et al. (2010) “A collection of 28 tree-ring chronologies from six different species located in northern Pakistan were evaluated in terms of their potential for dendroclimatic reconstructions. 15 of the sites are new while the remaining 13 (all Juniperus excelsa M. Bieb.) have been reported earlier. Several species had trees attaining ages of around 700 years (Cedrus deodara (D. Don) G. Don, Pinus gerardiana Wall. ex D. Don., Pinus wallichiana A.B. Jacks and Picea smithiana (Wall.) Boiss.) but the juniper was clearly the oldest with some trees greater than 1000 years. Correlations between the site chronologies declined with increasing separation distance. This was consistently seen both between sites of the same species and between sites composed of different species. This led to a situation where a much stronger correlation occurred between two different species growing at the same site than between sites of the same species but separated by as little as 0.5 km. Such results highlight the obvious strong elevational gradients present in this mountainous region (where some elevations are over 7000 m). They also lend support to the practice of multi-species combinations for better spatial and temporal coverage. The best prospects for this appear to be C. deodara and P. gerardiana and are consistent with studies from neighbouring India. The comparison to 0.5° gridded climate data was strongest from the same two species though P. smithiana at one site was also highly significant. A general climate correlation pattern from all species was evident that starts with a strong negative relationship to temperature in the previous October, then turns towards positive during winter, before again becoming significantly negative by the current May. The previous October signal is thought to be a lag effect where hot temperatures (and low soil-moisture) stress the trees, thereby reducing reserves available for the following spring. Similarly, hot temperatures in late spring (May) lead to greater soil moisture losses and tree transpiration costs. Conversely, there is an extended strong positive precipitation correlation from late winter to spring (January–May). This ends abruptly and there is no evidence of a summer (June–September) monsoon signal seen in the rainfall correlation functions.” Moinuddin Ahmed, Jonathan Palmer, Nasrullah Khan, Muhammad Wahab, Pavla Fenwick, Jan Esper and Ed Cook, Dendrochronologia, 2010, doi:10.1016/j.dendro.2010.08.007.

Poleward energy transport with global warming increases

Increasing atmospheric poleward energy transport with global warming – Hwang & Frierson (2010) “Most state-of-the-art global climate models (GCMs) project an increase in atmospheric poleward energy transport with global warming; however, the amount of increase varies significantly from model to model. Using an energy balance model that diffuses moist static energy, it is shown that: (1) the increase in atmospheric moisture content causes most of the increase in transport, and (2) changes in the radiation budget due to clouds explain most of the spread among GCMs. This work also shows that biases in clouds, surface albedo, ocean heat uptake, and aerosols will not only affect climate locally but will also influence other latitudes through energy transport.” Hwang, Y.-T., and D. M. W. Frierson (2010), Increasing atmospheric poleward energy transport with global warming, Geophys. Res. Lett., 37, L24807, doi:10.1029/2010GL045440. [Full text]

Changes in lake size and amount in China related to climate change?

A half-century of changes in China’s lakes: Global warming or human influence? – Ma et al. (2010) “Lake size is sensitive to both climate change and human activities, and therefore serves as an excellent indicator to assess environmental changes. Using a large volume of various datasets, we provide a first complete picture of changes in China’s lakes between 1960s–1980s and 2005–2006. Dramatic changes are found in both lake number and lake size; of these, 243 lakes vanished mainly in the northern provinces (and autonomous regions) and also in some southern provinces while 60 new lakes appeared mainly on the Tibetan Plateau and neighboring provinces. Limited evidence suggested that these geographically unbalanced changes might be associated primarily with climate change in North China and human activities in South China, yet targeted regional studies are required to confirm this preliminary observation.” Ma, R., H. Duan, C. Hu, X. Feng, A. Li, W. Ju, J. Jiang, and G. Yang (2010), Geophys. Res. Lett., 37, L24106, doi:10.1029/2010GL045514.

A review of methane cycle in the future – lot of uncertainties

Possible role of wetlands, permafrost, and methane hydrates in the methane cycle under future climate change: A review – O’Connor et al. (2010) “We have reviewed the available scientific literature on how natural sources and the atmospheric fate of methane may be affected by future climate change. We discuss how processes governing methane wetland emissions, permafrost thawing, and destabilization of marine hydrates may affect the climate system. It is likely that methane wetland emissions will increase over the next century. Uncertainties arise from the temperature dependence of emissions and changes in the geographical distribution of wetland areas. Another major concern is the possible degradation or thaw of terrestrial permafrost due to climate change. The amount of carbon stored in permafrost, the rate at which it will thaw, and the ratio of methane to carbon dioxide emissions upon decomposition form the main uncertainties. Large amounts of methane are also stored in marine hydrates, and they could be responsible for large emissions in the future. The time scales for destabilization of marine hydrates are not well understood and are likely to be very long for hydrates found in deep sediments but much shorter for hydrates below shallow waters, such as in the Arctic Ocean. Uncertainties are dominated by the sizes and locations of the methane hydrate inventories, the time scales associated with heat penetration in the ocean and sediments, and the fate of methane released in the seawater. Overall, uncertainties are large, and it is difficult to be conclusive about the time scales and magnitudes of methane feedbacks, but significant increases in methane emissions are likely, and catastrophic emissions cannot be ruled out. We also identify gaps in our scientific knowledge and make recommendations for future research and development in the context of Earth system modeling.” O’Connor, F. M., et al. (2010), Rev. Geophys., 48, RG4005, doi:10.1029/2010RG000326.

Ozone layer protective measures are starting to have an effect

Evidence for the effectiveness of the Montreal Protocol to protect the ozone layer – Mäder et al. (2010) “The release of man-made ozone depleting substances (ODS, including chlorofluorocarbons and halons) into the atmosphere has led to a near-linear increase in stratospheric halogen loading since the early 1970s, which levelled off after the mid-1990s and then started to decline, in response to the ban of many ODS by the Montreal Protocol (1987). We developed a multiple linear regression model to test whether this already had a measurable effect on total ozone values observed by the global network of ground-based instruments. The model includes explanatory variables describing the influence of various modes of dynamical variability and of volcanic eruptions. In order to describe the anthropogenic influence a first version of the model contains a linear trend (LT) term, whereas a second version contains a term describing the evolution of Equivalent Effective Stratospheric Chlorine (EESC). By comparing the explained variance of these two model versions we evaluated, which of the two terms better describes the observed ozone evolution. For a significant majority of the stations, the EESC proxy fits the long term ozone evolution better than the linear trend term. Therefore, we conclude that the Montreal Protocol has started to show measurable effects on the ozone layer about twenty years after it became legally binding.” Mäder, J. A., Staehelin, J., Peter, T., Brunner, D., Rieder, H. E., and Stahel, W. A., Atmos. Chem. Phys., 10, 12161-12171, doi:10.5194/acp-10-12161-2010, 2010. [Full text]

Anthropogenic influence shows in China rainfall

Exploring the interplay between natural decadal variability and anthropogenic climate change in summer rainfall over China. Part 1: Observational evidence – Lei et al.(2010) “Summer rainfall over China has experienced substantial variability on longer timescales during the last century, and the question remains whether this is due to natural, internal variability or is part of the emerging signal of anthropogenic climate change. Using the best available observations over China, the decadal variability and recent trends in summer rainfall are investigated with the emphasis on changes in the seasonal evolution and on the temporal characteristics of daily rainfall. The possible relationships with global warming are reassessed. Substantial decadal variability in summer rainfall has been confirmed during the period 1958–2008; this is not unique to this period but is also seen in the earlier decades of the 20th century. Two dominant patterns of decadal variability have been identified, which contributes substantially to the recent trend of southern flooding and northern drought. More detailed analysis has shown that the decadal variability in the total summer rainfall is characterised by large changes in the seasonal cycle, and is composed of more complex changes in the intensity and frequency. Over the latter half of the 20th century increases in rainfall intensity and decreases in light rainfall frequency are seen country-wide and mainly the result of anthropogenic influences on the regional climate, both through warming and increased aerosol loading. The observed change in heavy rainfall frequency is mainly attributed to the decadal variability. Thus, global warming signals are most prominent over the northeast of China where heavy rainfall is lack, and the decadal variability signals are dominant over southern China. The interplay between anthropogenic climate change and natural decadal variability appears to have played an important role in shaping summer rainfall over China.” Yonghui Lei, Brian Hoskins, and Julia Slingo, Journal of Climate 2010.

Anthropogenic CO2 goes deep in Indian Ocean

Decadal increases in anthropogenic CO2 along 20°S in the South Indian Ocean – Murata et al.(2010) “We used high-quality data for dissolved inorganic carbon and related water properties in the Indian Ocean along 20°S (World Ocean Circulation Experiment Hydrographic Program line I3) and 24°S (I4) obtained 8 years apart (1995–2003/2004) to estimate decadal-scale increases of anthropogenic CO2 in the interior of the South Indian Ocean. Significant increases were detected to about 1800 m depth in the longitude range 35–45°E. In the upper thermocline subtropical subsurface water and Indian Central Water, anthropogenic CO2 increased an average of 7.9 ± 1.1 and 7.7 ± 0.5 μmol kg−1, respectively, whereas in the lower thermocline Antarctic Intermediate Water, the increase was 3.8 ± 0.7 μmol kg−1. A significant increase was also detected in Circumpolar Deep Water (2.5 ± 1.0 μmol kg−1). The estimated uptake rate of anthropogenic CO2 along the I3/I4 line over this time interval was 1.0 ± 0.1 mol m−2 a−1. Seasonal variations, which are influential in this ocean because of the Indian monsoon, did not affect detection of the anthropogenic CO2 signals. Comparisons with previous studies showed that increases of anthropogenic CO2 became larger in the most recent decade and that the CO2 uptake rate was similar to that in the South Pacific (1.0 ± 0.4 mol m−2 a−1) but higher than those in the South Atlantic (0.6 ± 0.1 mol m−2 a−1) and North Pacific (0.5 ± 0.1 mol m−2 a−1) Oceans. Deep penetration of anthropogenic CO2 is possibly associated with the higher uptake rate.” Murata, A., Y. Kumamoto, K. Sasaki, S. Watanabe, and M. Fukasawa (2010), J. Geophys. Res., 115, C12055, doi:10.1029/2010JC006250.

Primary controls of a coral bleaching event

Air-sea energy exchanges measured by eddy covariance during a localised coral bleaching event, Heron Reef, Great Barrier Reef, Australia – MacKellar & McGowan (2010) “Despite the widely claimed association between climate change and coral bleaching, a paucity of data exists relating to exchanges of heat, moisture and momentum between the atmosphere and the reef-water surface. We present in situ measurements of reef-water-air energy exchanges made using the eddy covariance method during a summer coral bleaching event at Heron Reef, Australia. Under settled, cloud-free conditions and light winds, daily net radiation exceeded 800 W m−2, with up to 95% of the net radiation during the morning partitioned into heating the water column, substrate and benthic cover including corals. Heating was exacerbated by a mid-afternoon low tide when shallow reef flat water reached 34°C and near-bottom temperatures 33°C, exceeding the thermal tolerance of corals, causing bleaching. Results suggest that local to synoptic scale meteorology, particularly clear skies, solar heating, light winds and the timing of low tide were the primary controls on coral bleaching.” MacKellar, M. C., and H. A. McGowan (2010), Geophys. Res. Lett., 37, L24703, doi:10.1029/2010GL045291. [Conference paper]

New England water table climate response increases flood risks

Heterogeneous water table response to climate revealed by 60 years of ground water data – Weider & Boutt (2010) “Recent findings suggest that climate change will lead to modifications in the timing and nature of precipitation, giving rise to an altered hydrologic cycle. The response of subsurface hydrology to decadal climate and longer-term climate change to date has been investigated via site specific analyses, modeling studies, and proxy analysis. Here we present the first instrumental long-term regional compilation and analysis of the water table response to the last 60 years of climate in New England. Ground water trends are calculated as normalized anomalies and analyzed with respect to regional compiled precipitation, temperature, and streamflow. The time-series display decadal patterns with ground water levels being more variable and lagging that of precipitation and streamflow pointing to site specific and non-linear response to changes in climate. Recent trends (i.e., last 10 years) suggest statistically significant increasing water tables, which could lead to a higher risk for flooding in New England.” Weider, K., and D. F. Boutt (2010), Geophys. Res. Lett., 37, L24405, doi:10.1029/2010GL045561.


2 Responses to “New research from last week 51/2010”

  1. Oh snap, WIRE Climate Change is no longer available in OA.

  2. Ari Jokimäki said

    Oh well, all good things come to an end.

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