New research from last week 52/2011
Posted by Ari Jokimäki on January 2, 2012
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.
Multiyear ice turning to seasonal ice in Arctic Ocean
On the Arctic Ocean ice thickness response to changes in the external forcing – Stranne & Björk (2011) “Submarine and satellite observations show that the Arctic Ocean ice cover has undergone a large thickness reduction and a decrease in the areal extent during the last decades. Here the response of the Arctic Ocean ice cover to changes in the poleward atmospheric energy transport, F wall, is investigated using coupled atmosphere-ice-ocean column models. Two models with highly different complexity are used in order to illustrate the importance of different internal processes and the results highlight the dramatic effects of the negative ice thickness—ice volume export feedback and the positive surface albedo feedback. The steady state ice thickness as a function of F wall is determined for various model setups and defines what we call ice thickness response curves. When a variable surface albedo and snow precipitation is included, a complex response curve appears with two distinct regimes: a perennial ice cover regime with a fairly linear response and a less responsive seasonal ice cover regime. The two regimes are separated by a steep transition associated with surface albedo feedback. The associated hysteresis is however small, indicating that the Arctic climate system does not have an irreversible tipping point behaviour related to the surface albedo feedback. The results are discussed in the context of the recent reduction of the Arctic sea ice cover. A new mechanism related to regional and temporal variations of the ice divergence within the Arctic Ocean is presented as an explanation for the observed regional variation of the ice thickness reduction. Our results further suggest that the recent reduction in areal ice extent and loss of multiyear ice is related to the albedo dependent transition between seasonal and perennial ice i.e. large areas of the Arctic Ocean that has previously been dominated by multiyear ice might have been pushed below a critical mean ice thickness, corresponding to the above mentioned transition, and into a state dominated by seasonal ice.” Christian Stranne and Göran Björk, Climate Dynamics, DOI: 10.1007/s00382-011-1275-y.
Cold Arctic winters might come with ozone holes
Arctic winter 2010/2011 at the brink of an ozone hole – Sinnhuber et al. (2011) “The Arctic stratospheric winter of 2010/2011 was one of the coldest on record with a large loss of stratospheric ozone. Observations of temperature, ozone, nitric acid, water vapor, nitrous oxide, chlorine nitrate and chlorine monoxide from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) onboard ENVISAT are compared to calculations with a chemical transport model (CTM). There is overall excellent agreement between the model calculations and MIPAS observations, indicating that the processes of denitrification, chlorine activation and catalytic ozone depletion are sufficiently well represented. Polar vortex integrated ozone loss reaches 120 Dobson Units (DU) by early April 2011. Sensitivity calculations with the CTM give an additional ozone loss of about 25 DU at the end of the winter for a further cooling of the stratosphere by 1 K, showing locally near-complete ozone depletion (remaining ozone <200 ppbv) over a large vertical extent from 16 to 19 km altitude. In the CTM a 1 K cooling approximately counteracts a 10% reduction in stratospheric halogen loading, a halogen reduction that is expected to occur in about 13 years from now. These results indicate that severe ozone depletion like in 2010/2011 or even worse could appear for cold Arctic winters over the next decades if the observed tendency for cold Arctic winters to become colder continues into the future." Sinnhuber, B.-M., G. Stiller, R. Ruhnke, T. von Clarmann, S. Kellmann, and J. Aschmann (2011), Geophys. Res. Lett., 38, L24814, doi:10.1029/2011GL049784.
Some clouds go undetected by some cloud-detecting satellites
Cloud features detected by MODIS but not by CloudSat and CALIOP – Chan & Comiso (2011) “The ability to characterize the global cloud cover from space has been greatly enhanced by the availability of MODIS, CloudSat, and CALIOP data. The three sensors provide good complementary information about clouds. In this study, we investigated unexpected observations of certain types of clouds apparent in the MODIS data but not detected by CloudSat and CALIOP. Several examples are presented and generally these undetected clouds are geometrically thin, low-level clouds. In particular, they are located in the Arctic region and have optical thicknesses of less than 14, top height altitudes of below 2.5 km, and layer thickness of less than 1 km. CloudSat may miss such low-level clouds because of its coarse vertical resolution of about 500 m and it has limited sensitivity near the surface. Unexpectedly, CALIOP with a much higher vertical resolution of 30 m also misses these clouds and this is due to the cloud’s geometrically thin nature and surface proximity.” Chan, M. A. and J. C. Comiso (2011), Geophys. Res. Lett., 38, L24813, doi:10.1029/2011GL050063.
Global warming is projected to increase hydroclimate variability
Does global warming cause intensified interannual hydroclimate variability? – Seager et al. (2011) “The idea that global warming leads to more droughts and floods has become commonplace without clear indication of what is meant by this statement. Here we examine one aspect of this problem and assess whether interannual variability of precipitation (P) minus evaporation (E) becomes stronger in the 21st Century compared to the 20th Century, as deduced from an ensemble of models participating in Coupled Model Intercomparison Project 3. It is shown that indeed interannual variability of P-E does increase almost everywhere across the planet with a few notable exceptions such as southwestern North America and some subtropical regions. The variability increases most at the Equator and the high latitudes and least in the subtropics. While most interannual P-E variability arises from internal atmosphere variability the primary potentially predictable component is related to the El Niño-Southern Oscillation (ENSO). ENSO-driven interannual P-E variability clearly increases in amplitude in the tropical Pacific but elsewhere the changes are more complex. This is not surprising in that ENSO-driven P-E anomalies are primarily caused by circulation anomalies combining with the climatological humidity field. As climate warms and the specific humidity increases this term leads to an intensification of ENSO-driven P-E variability. However, ENSO-driven circulation anomalies also change, in some regions amplifying, but in others opposing and even overwhelming, the impact of rising specific humidity. Consequently there is sound scientific basis for anticipating a general increase in interannual P-E variability but the predictable component will depend in a more complex way on both thermodynamic responses to global warming and on how tropically-forced circulation anomalies alter.” Richard Seager, Naomi Naik, Laura Vogel, Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-11-00363.1. [Full text]
No evidence for robust link between cloud cover and solar activity/cosmic rays
Solar irradiance, cosmic rays and cloudiness over daily timescales – Laken & Čalogović (2011) “Although over centennial and greater timescales solar variability may be one of the most influential climate forcing agents, the extent to which solar activity influences climate over shorter time periods is poorly understood. If a link exists between solar activity and climate, it is likely via a mechanism connected to one (or a combination) of the following parameters: total solar irradiance (TSI), ultraviolet (UV) spectral irradiance, or the galactic cosmic ray (GCR) flux. We present an analysis based around a superposed epoch (composite) approach focusing on the largest TSI increases and decreases (the latter occurring in both the presence and absence of appreciable GCR reductions) over daily timescales. Using these composites we test for the presence of a robust link between solar activity and cloud cover over large areas of the globe using rigorous statistical techniques. We find no evidence that widespread variations in cloud cover at any tropospheric level are significantly associated with changes in the TSI, GCR or UV flux, and further conclude that TSI or UV changes occurring during reductions in the GCR flux are not masking a solar-cloud response. However, we note the detectability of any potential links is strongly constrained by cloud variability.” Laken, B. A. and J. Čalogović(2011), Geophys. Res. Lett., 38, L24811, doi:10.1029/2011GL049764.
Hypoxic and anoxic areas will very likely increase in Baltic Sea with warming climate
Hypoxia in future climates: A model ensemble study for the Baltic Sea – Meier et al. (2011) “Using an ensemble of coupled physical-biogeochemical models driven with regionalized data from global climate simulations we are able to quantify the influence of changing climate upon oxygen conditions in one of the numerous coastal seas (the Baltic Sea) that suffers worldwide from eutrophication and from expanding hypoxic zones. Applying various nutrient load scenarios we show that under the impact of warming climate hypoxic and anoxic areas will very likely increase or at best only slightly decrease (in case of optimistic nutrient load reductions) compared to present conditions, regardless of the used global model and climate scenario. The projected decreased oxygen concentrations are caused by (1) enlarged nutrient loads due to increased runoff, (2) reduced oxygen flux from the atmosphere to the ocean due to increased temperature, and (3) intensified internal nutrient cycling. In future climate a similar expansion of hypoxia as projected for the Baltic Sea can be expected also for other coastal oceans worldwide.” Meier, H. E. M., H. C. Andersson, K. Eilola, B. G. Gustafsson, I. Kuznetsov, B. Müller-Karulis, T. Neumann, and O. P. Savchuk (2011), Geophys. Res. Lett., 38, L24608, doi:10.1029/2011GL049929.
Global monsoon precipitation has intensified
Recent change of the global monsoon precipitation (1979–2008) – Wang et al. (2011) “The global monsoon (GM) is a defining feature of the annual variation of Earth’s climate system. Quantifying and understanding the present-day monsoon precipitation change are crucial for prediction of its future and reflection of its past. Here we show that regional monsoons are coordinated not only by external solar forcing but also by internal feedback processes such as El Niño-Southern Oscillation (ENSO). From one monsoon year (May to the next April) to the next, most continental monsoon regions, separated by vast areas of arid trade winds and deserts, vary in a cohesive manner driven by ENSO. The ENSO has tighter regulation on the northern hemisphere summer monsoon (NHSM) than on the southern hemisphere summer monsoon (SHSM). More notably, the GM precipitation (GMP) has intensified over the past three decades mainly due to the significant upward trend in NHSM. The intensification of the GMP originates primarily from an enhanced east–west thermal contrast in the Pacific Ocean, which is coupled with a rising pressure in the subtropical eastern Pacific and decreasing pressure over the Indo-Pacific warm pool. While this mechanism tends to amplify both the NHSM and SHSM, the stronger (weaker) warming trend in the NH (SH) creates a hemispheric thermal contrast, which favors intensification of the NHSM but weakens the SHSM. The enhanced Pacific zonal thermal contrast is largely a result of natural variability, whilst the enhanced hemispherical thermal contrast is likely due to anthropogenic forcing. We found that the enhanced global summer monsoon not only amplifies the annual cycle of tropical climate but also promotes directly a “wet-gets-wetter” trend pattern and indirectly a “dry-gets-drier” trend pattern through coupling with deserts and trade winds. The mechanisms recognized in this study suggest a way forward for understanding past and future changes of the GM in terms of its driven mechanisms.” Bin Wang, Jian Liu, Hyung-Jin Kim, Peter J. Webster and So-Young Yim, Climate Dynamics, DOI: 10.1007/s00382-011-1266-z. [Full text]
Greenland glacier has 3 positive melt feedbacks active
Three positive feedback mechanisms for ice-sheet melting in a warming climate – Ren & Leslie (2011) “Three positive feedback mechanisms that accelerate ice-sheet melting are assessed in a warming climate, using a numerical ice model driven by atmospheric climate models. The Greenland ice sheet (GrIS) is the modeling test-bed under accelerated melting conditions. The first feedback is the interaction of sea water with ice. It is positive because fresh water melts ice faster than salty water, owing primarily to the reduction in water heat capacity by solutes. It is shown to be limited for the GrIS, which has only a small ocean interface, and the grounding line of some fast glaciers becomes land-terminating during the 21st century. The second positive feedback, strain heating, is positive because it produces further ice heating inside the ice sheet. The third positive feedback, granular basal sliding, applies to all ice sheets and becomes the dominant feedback during the 21st century. A numerical simulation of Jakobshavn Isbrae over the 21st century reveals that all three feedback processes are active for this glacier. Compared with the year 2000 level, annual ice discharge into the ocean could increase by ∼1.4 km3 a-1 (∼5% of the present annual rate) by 2100. Granular basal sliding contributes ∼40% of this increase.” Ren, Diandong; Leslie, Lance M., Journal of Glaciology, Volume 57, Number 206, December 2011 , pp. 1057-1066(10), DOI: http://dx.doi.org/10.3189/002214311798843250.
Tree ring based winter temperature reconstruction from China
Tree ring-based winter temperature reconstruction for Changting, Fujian, subtropical region of Southeast China, since 1850: linkages to the Pacific Ocean – Chen et al. (2011) “Until recently, there have been very few tree-ring studies in southeast China due largely to the scarcity of old trees and the complexity of relationships between tree growth and climate in subtropical regions of China. Recent studies on the conifers in southeast China revealed that tree ring-based climate reconstructions are feasible. Here, we describe a reconstruction (AD 1850–2009) of November–February maximum temperatures for Changting, Fujian, southeast China based on tree ring width data of Pinus massiniana which considerably extends the available climatic information. Calibration and verification statistics for the period 1956–2009 show a high level of skill and account for a significant portion of the observed variance (32.9%) irrespective of which period is used to develop or verify the regression model. Split sample validation supports our use of a reconstruction model based on the full period of reliable observational data (1956–2009). Warm periods occurred during 1854–1859, 1868–1880, 1885–1899, 1906–1914, 1920–1943, 1964–1975 and 1994–present; while the periods of AD 1850–1853, 1860–1867, 1881–1884, 1900–1907, 1915–1919, 1944–1963 and 1976–1993 were relatively cold. The climate correlation analyses with gridded temperature dataset and SST revealed that our season temperature reconstruction contains the strong large-scale climate signals. Our results suggest that some warm winters of Changting are coincident with El Niño events over the past 150 years. In addition, several severely cold winters coincide with major volcanic eruptions.” Feng Chen, Yu-jiang Yuan, Wen-shou Wei, Shu-long Yu and Tong-wen Zhang, Theoretical and Applied Climatology, DOI: 10.1007/s00704-011-0563-0.
Reduced vertical mixing might cause Arctic amplification
Boundary layer stability and Arctic climate change: a feedback study using EC-Earth – Bintanja et al. (2011)“Amplified Arctic warming is one of the key features of climate change. It is evident in observations as well as in climate model simulations. Usually referred to as Arctic amplification, it is generally recognized that the surface albedo feedback governs the response. However, a number of feedback mechanisms play a role in AA, of which those related to the prevalent near-surface inversion have received relatively little attention. Here we investigate the role of the near-surface thermal inversion, which is caused by radiative surface cooling in autumn and winter, on Arctic warming. We employ idealized climate change experiments using the climate model EC-Earth together with ERA-Interim reanalysis data to show that boundary-layer mixing governs the efficiency by which the surface warming signal is ‘diluted’ to higher levels. Reduced vertical mixing, as in the stably stratified inversion layer in Arctic winter, thus amplifies surface warming. Modelling results suggest that both shortwave—through the (seasonal) interaction with the sea ice feedback—and longwave feedbacks are affected by boundary-layer mixing, both in the Arctic and globally, with the effect on the shortwave feedback dominating. The amplifying effect will decrease, however, with climate warming because the surface inversion becomes progressively weaker. We estimate that the reduced Arctic inversion has slowed down global warming by about 5% over the past 2 decades, and we anticipate that it will continue to do so with ongoing Arctic warming.” R. Bintanja, E. C. van der Linden and W. Hazeleger, Climate Dynamics, DOI: 10.1007/s00382-011-1272-1.