AGW Observer

Observations of anthropogenic global warming

New research from last week 48/2010

Posted by Ari Jokimäki on December 6, 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:

South Africa apple and pear trees bloom earlier

Advance of apple and pear tree full bloom dates in response to climate change in the southwestern Cape, South Africa: 1973–2009 – Grab & Craparo (2010) “Studies from throughout the world have demonstrated that tree phenophases are becoming earlier in spring and are closely associated with rising temperatures. Despite many such studies from the Northern Hemisphere, similar comparative work has not been forthcoming from the Southern Hemisphere or from Africa. In addition, few studies have demonstrated the possible role of changes in precipitation and associated soil moisture to driving fruit tree phenophases. Here we provide changes of mean full bloom dates for three apple Malus domestica (Golden Delicious, Sayaka, Granny Smith) and one pear Pyrus communis (Bon Chrétien) cultivars in the southwestern Cape of South Africa. These phenological changes are correlated with temperature and precipitation changes in the same region between 1973 and 2009. Significant early spring (August/September) temperature increases of +0.45 °C/decade are associated with a mean full bloom advance of 1.6 d/decade over the last 37 years. Golden Delicious apple trees have the strongest sensitivity (+4.2 d/°C) to climate change in the region, whilst Granny Smith apple trees have the lowest (+2.4 d/°C). Although winter and early spring rainfall has also decreased over this time, such decreases are not significant. However, significant correlations are found for both temperature and rainfall when comparing with the mean full bloom dates, and it is proposed that both variables operate synergistically to influence mean full bloom dates in the southwestern Cape.” Stefan Grab and Alessandro Craparo, Agricultural and Forest Meteorology, doi:10.1016/j.agrformet.2010.11.001.

Urban cool islands within urban heat island

Derivation of Birmingham’s summer surface urban heat island from MODIS satellite images – Tomlinson et al. (2010) “This study investigates the summer (June, July, August) night urban heat island (UHI) of Birmingham, the UK’s second most populous city. Land surface temperature remote sensing data is used from the MODIS sensor on NASA’s Aqua satellite, combined with UK Met Office station data to map the average variation in heat island intensity over the Birmingham conurbation. Results are presented of average UHI events over four Pasquill-Gifford stability classes D, E, F, and G between 2003 and 2009, as well as a specific heatwave event in July 2006. The results quantify the magnitude of the Birmingham surface UHI as well as the impact of atmospheric stability on UHI development. During periods of high atmospheric stability, a UHI of the order of 5 °C is evident with a clear peak in the central business district. Also identified, are significant cold spots in the conurbation. In one city park, recorded surface temperatures are up to 7 °C lower than the city centre.” C. J. Tomlinson, L. Chapman, J. E. Thornes, C. J. Baker, International Journal of Climatology, DOI: 10.1002/joc.2261.

Sound wave climate science

The Sound of Climate Change – Munk (2010) “It came as a great shock in the 1960s that the oceans, like the atmosphere, have an active weather (i.e. ocean storms are called eddies). The traditional expedition mode of individual research vessels making independent measurements was no longer adequate. Ocean Acoustic Tomography was developed in direct response to the “eddie revolution”. Sound travels faster in warmer water; acoustic waves transmitted from ship to ship give information about the temperature and currents in the intervening waters. The transmission scale has widened over the years from 100 to 1000 to 10,000 km, approaching the antipodal scale of Ewing’s 1960 transmission from Perth (Australia) to Bermuda. In 1991 we successfully transmitted from a source ship on Heard Island in the Indian Ocean to receiver ships in the north and south Atlantic and Pacific Oceans. Brian Dushaw (personal communication, 2010) is planning to repeat Ewing’s experiment; he expects a reduction in travel time of approximately 10 s as confirmation of global ocean warming over the last fifty years. Sea level rose 15cm in the 20th century. The rate has since doubled; values up to 2m by 2100 are now being quoted. To make accurate predictions we must understand the melting processes of continental ice sheets. Floating ice sheets from Antarctic and Greenland glaciers cover huge ocean caverns that have not to date been accessible to observation. We propose probing these caverns with sound waves to study the ocean dynamics at the underside of the floating ice sheets: a daring venture.” Walter Munk, Tellus A, 2010, DOI: 10.1111/j.1600-0870.2010.00494.x.

Fish sperm not bothered by ocean acidification

Effect of ocean acidification on marine fish sperm (Baltic cod: Gadus morhua) – Frommel et al. (2010) “Ocean acidification, as a consequence of increasing marine pCO2, may have severe effects on the physiology of marine organisms. However, experimental studies remain scarce, in particular concerning fish. While adults will most likely remain relatively unaffected by changes in seawater pH, early life-history stages are potentially more sensitive – particularly the critical stage of fertilization, in which sperm motility plays a central role. In this study, the effects of ocean acidification (decrease of pHT to 7.55) on sperm motility of Baltic cod, Gadus morhua, were assessed. We found no significant effect of decreased pH on sperm speed, rate of change of direction or percent motility for the population of cod analyzed. We predict that future ocean acidification will probably not pose a problem for sperm behavior, and hence fertilization success, of Baltic cod.” Frommel, A. Y., Stiebens, V., Clemmesen, C., and Havenhand, J., Biogeosciences, 7, 3915-3919, doi:10.5194/bg-7-3915-2010, 2010. [full text]

Only rapid sea level rise will sink coastal marshes

Limits on the adaptability of coastal marshes to rising sea level – Kirwan et al. (2010) “Assumptions of a static landscape inspire predictions that about half of the world’s coastal wetlands will submerge during this century in response to sea-level acceleration. In contrast, we use simulations from five numerical models to quantify the conditions under which ecogeomorphic feedbacks allow coastal wetlands to adapt to projected changes in sea level. In contrast to previous sea-level assessments, we find that non-linear feedbacks among inundation, plant growth, organic matter accretion, and sediment deposition, allow marshes to survive conservative projections of sea-level rise where suspended sediment concentrations are greater than ∼20 mg/L. Under scenarios of more rapid sea-level rise (e.g., those that include ice sheet melting), marshes will likely submerge near the end of the 21st century. Our results emphasize that in areas of rapid geomorphic change, predicting the response of ecosystems to climate change requires consideration of the ability of biological processes to modify their physical environment.” Kirwan, M. L., G. R. Guntenspergen, A. D’Alpaos, J. T. Morris, S. M. Mudd, and S. Temmerman (2010), Limits on the adaptability of coastal marshes to rising sea level, Geophys. Res. Lett., 37, L23401, doi:10.1029/2010GL045489. [full text]

Regional sea ice decline in Antarctica contrasts overall increase

Ice core evidence for a 20th century decline of sea ice in the Bellingshausen Sea, Antarctica – Abram et al. (2010) “This study uses ice core methanesulphonic acid (MSA) records from the Antarctic Peninsula, where temperatures have been warming faster than anywhere else in the Southern Hemisphere, to reconstruct the 20th century history of sea ice change in the adjacent Bellingshausen Sea. Using satellite-derived sea ice and meteorological data, we show that ice core MSA records from this region are a reliable proxy for regional sea ice change, with years of increased winter sea ice extent recorded by increased ice core MSA concentrations. Our reconstruction suggests that the satellite-observed sea ice decline in the Bellingshausen Sea during recent decades is part of a long-term regional trend that has occurred throughout the 20th century. The long-term perspective on sea ice in the Bellingshausen Sea is consistent with evidence of 20th century warming on the Antarctic Peninsula and may reflect a progressive deepening of the Amundsen Sea Low due to increasing greenhouse gas concentrations and, more recently, stratospheric ozone depletion. As a first-order estimate, our MSA-based reconstruction suggests that sea ice in the Bellingshausen Sea has retreated southward by ∼0.7° during the 20th century. Comparison with other 20th century sea ice observations, reconstructions, and model simulations provides a coherent picture of Antarctic sea ice decline during the 20th century, although with regional-scale differences evident in the timing and magnitude of this sea ice decline. This longer-term perspective contrasts with the small overall increase in Antarctic sea ice that is observed in post-1979 satellite data.” Abram, N. J., E. R. Thomas, J. R. McConnell, R. Mulvaney, T. J. Bracegirdle, L. C. Sime, and A. J. Aristarain (2010), J. Geophys. Res., 115, D23101, doi:10.1029/2010JD014644.

70% chance for climate-carbon feedbacks being positive

Paleoclimatic warming increased carbon dioxide concentrations – Lemoine (2010) “If climate-carbon feedbacks are positive, then warming causes changes in carbon dioxide (CO2) sources and sinks that increase CO2 concentrations and create further warming. Previous work using paleoclimatic reconstructions has not disentangled the causal effect of interest from the effects of reverse causality and autocorrelation. The response of CO2 to variations in orbital forcing over the past 800,000 years suggests that millennial-scale climate-carbon feedbacks are significantly positive and significantly greater than century-scale feedbacks. Feedbacks are also significantly greater on 100 year time scales than on 50 year time scales over the past 1500 years. Posterior probability distributions implied by coupled models’ predictions and by these paleoclimatic results give a mean of 0.03 for the nondimensional climate-carbon feedback factor and a 90% chance of its being between −0.04 and 0.09. The 70% chance that climate-carbon feedbacks are positive implies that temperature change projections tend to underestimate an emission path’s consequences if they do not allow the carbon cycle to respond to changing temperatures.” Lemoine, D. M. (2010), J. Geophys. Res., 115, D22122, doi:10.1029/2010JD014725.

Detecting anthropogenic CO2 changes in Atlantic Ocean

Detecting anthropogenic CO2 changes in the interior Atlantic Ocean between 1989 and 2005 – Wanninkhof et al. (2010) “Repeat observations along the meridional Atlantic section A16 from Iceland to 56°S show substantial changes in the total dissolved inorganic carbon (DIC) concentrations in the ocean between occupations from 1989 through 2005. The changes correspond to the expected increase in DIC driven by the uptake of anthropogenic CO2 from the atmosphere, but the ΔDIC is more varied and larger, in some locations, than can be explained solely by this process. Concomitant large changes in oxygen (O2) suggest that processes acting on the natural carbon cycle also contribute to ΔDIC. Precise partial pressure of CO2 measurements suggest small but systematic increases in the bottom waters. To isolate the anthropogenic CO2 component (ΔCanthro) from ΔDIC, an extended multilinear regression approach is applied along isopycnal surfaces. This yields an average depth-integrated ΔCanthro of 0.53 ± 0.05 mol m−2 yr−1 with maximum values in the temperate zones of both hemispheres and a minimum in the tropical Atlantic. A higher decadal increase in the anthropogenic CO2 inventory is found for the South Atlantic compared to the North Atlantic. This anthropogenic CO2 accumulation pattern is opposite to that seen for the entire Anthropocene up to the 1990s. This change could perhaps be a consequence of the reduced downward transport of anthropogenic CO2 in the North Atlantic due to recent climate variability. Extrapolating the results for this section to the entire Atlantic basin (63°N to 56°S) yields an uptake of 5 ± 1 Pg C decade−1, which corresponds to about 25% of the annual global ocean uptake of anthropogenic CO2 during this period.” Wanninkhof, R., S. C. Doney, J. L. Bullister, N. M. Levine, M. Warner, and N. Gruber (2010), J. Geophys. Res., 115, C11028, doi:10.1029/2010JC006251.

Much of the dissolved organic carbon in ocean is from microbial methane hydrate consumption

Methane hydrate-bearing seeps as a source of aged dissolved organic carbon to the oceans – Pohlman et al. (2010) “Marine sediments contain about 500–10,000 Gt of methane carbon, primarily in gas hydrate. This reservoir is comparable in size to the amount of organic carbon in land biota, terrestrial soils, the atmosphere and sea water combined, but it releases relatively little methane to the ocean and atmosphere. Sedimentary microbes convert most of the dissolved methane to carbon dioxide. Here we show that a significant additional product associated with microbial methane consumption is methane-derived dissolved organic carbon. We use Δ14C and δ13C measurements and isotopic mass-balance calculations to evaluate the contribution of methane-derived carbon to seawater dissolved organic carbon overlying gas hydrate-bearing seeps in the northeastern Pacific Ocean. We show that carbon derived from fossil methane accounts for up to 28% of the dissolved organic carbon. This methane-derived material is much older, and more depleted in 13C, than background dissolved organic carbon. We suggest that fossil methane-derived carbon may contribute significantly to the estimated 4,000–6,000 year age of dissolved organic carbon in the deep ocean, and provide reduced organic matter and energy to deep-ocean microbial communities.” John W. Pohlman, James E. Bauer, William F. Waite, Christopher L. Osburn & N. Ross Chapman, Nature Geoscience, Published online: 28 November 2010, doi:10.1038/ngeo1016.

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