AGW Observer

Observations of anthropogenic global warming

New research from last week 28/2011

Posted by Ari Jokimäki on July 18, 2011

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:

Medici Network temperature record from 1654-1670 recovered

The earliest temperature observations in the world: the Medici Network (1654–1670) – Camuffo & Bertolin (2011) “This paper presents the earliest temperature observations, scheduled every 3–4 h in the 1654–1670 period, which have been recovered and analysed for the first time. The observations belong to the Medici Network, the first international network of meteorological observations, based on eleven stations, the two main ones being Florence and Vallombrosa, Italy. All observations were made with identical thermometers and operational methodology, including outdoor exposure in the shade and in the sunshine to evaluate solar heating, state of the sky, wind direction and precipitation frequency. This paper will consider only the regular temperature series taken in the shade. The observations were made with the newly invented spirit-in-glass thermometer, also known as Little Florentine Thermometer (LFT). The readings have been transformed into modern units of temperature (°C) and time (TMEC). The LFT has been analysed in detail: how it was made, its linearity, calibration and performances. Since the middle of the LIA, the climate in Florence has shown less than 0.18°C warming. However, although the yearly average showed little change, the seasonal departures are greater, i.e. warmer summers, colder winters and unstable mid seasons. The temperature in the Vallombrosa mountain station, 1,000 m a.m.s.l, apparently rose more, i.e. 1.41°C. A discussion is made on the interpretation of this finding: how much it is affected by climate change or bias. A continuous swinging of the temperature was observed in the Mediterranean area, as documented by the long instrumental observations over the 1654–2009 period. However, changes in vegetation, or exposure bias might have contributed to reduce the homogeneity of the series over the centuries.” Dario Camuffo and Chiara Bertolin, Climatic Change, DOI: 10.1007/s10584-011-0142-5.

Why is northern Tibetan Plateau warming up so rapidly?

The significant climate warming in the northern Tibetan Plateau and its possible causes – Guo & Wang (2011) “We have identified the northern Tibetan Plateau as having experienced the most significant warming of any region in the entire plateau domain since 1961. Warming in the northern plateau violates the previously suggested elevation dependency of warming trends. Further analysis shows that the increase in surface air temperature in summer has played a primary role in the rapid increase of the annual mean air temperature in the northern Tibetan Plateau since the mid-1980s. In addition, the summer air temperature is correlated with ozone in the region, a result which is statistically significant. This correlation seems to have a relationship with solar radiation and ozone depletion ratios. Further discussion shows that the most significant warming in the northern plateau may be related to radiative and dynamical heating that are results of pronounced stratospheric ozone depletion.” Donglin Guo and Huijun Wang, International Journal of Climatology, DOI: 10.1002/joc.2388. [Full text]

Determining forcings over the last 2009 years

Response of Earth’s surface temperature to radiative forcing over A.D. 1–2009 – Friend (2011) “An energy balance model (EBM) of the annual global mean surface temperature is described and calibrated to the sensitivity and temporal dynamics of the Goddard Institute for Space Studies modelE global climate model (GCM). The effective radiative forcings of 10 agents are estimated over the past 2009 years and used as inputs to the model. Temperatures are relatively stable from around A.D. 300 until a “Medieval Climate Anomaly” starting around A.D. 1050. This is ended by a massive volcanic eruption in A.D. 1258, which initiates a multicentury era of low and relatively variable global mean temperatures, including a “Little Ice Age” A.D. 1588–1720. This era only ends at the beginning of the 20th century. The model estimate of forced centennial variability is smaller than the observed variability in reconstructions over the past two millennia. Also, the default parameterization results in less warming than observed over A.D. 1910–1944. Prediction uncertainty in the pre-industrial era is dominated by solar forcing, with the climate feedback factor and volcanic aerosols also playing important roles. In contrast, prediction uncertainty post–A.D. 1750 is much higher and dominated by uncertainties in direct and indirect aerosol and land use forcings. Improving estimates of these will greatly increase our ability to attribute observed temperature variability to contemporary forcings.” Friend, A. D. (2011), J. Geophys. Res., 116, D13112, doi:10.1029/2010JD015143.

AMO might be a statistical artifact

Is the Atlantic Multidecadal Oscillation (AMO) a statistical phantom? – Vincze & Jánosi (2011) “In this work we critically compare the consequences of two assumptions on the physical nature of the AMO index signal. First, we show that the widely used approach based on red noise statistics cannot fully reproduce the empirical correlation properties of the record. Second, we consider a process of long range power-law correlations and demonstrate its better fit to the AMO signal. We show that in the latter case, the multidecadal oscillatory mode of the smoothed AMO index with an assigned period length of 50–70 years can be a simple statistical artifact, a consequence of limited record length. In this respect, a better term to describe the observed fluctuations of a smooth power-law spectrum is Atlantic Multidecadal Variability (AMV).” Vincze, M. and Jánosi, I. M., Nonlin. Processes Geophys., 18, 469-475, doi:10.5194/npg-18-469-2011, 2011. [Full text]

Deep ocean is important for Earth’s radiation balance

Importance of the deep ocean for estimating decadal changes in Earth’s radiation balance – Palmer et al. (2011) “We use control run data from three Met Office Hadley Centre climate models to investigate the relationship between: net top-of-atmosphere radiation balance (TOA), globally averaged sea surface temperature (SST); and globally averaged ocean heat content (OHC) on decadal timescales. All three models show substantial decadal variability in SST, which could easily mask the long-term warming associated with anthropogenic climate change over a decade. Regression analyses are used to estimate the uncertainty of TOA, given the trend in SST or OHC over the same period. We show that decadal trends in SST are only weakly indicative of changes in TOA. Trends in total OHC strongly constrain TOA, since the ocean is the primary heat store in the Earth System. Integrating OHC over increasing model levels, provides an increasingly good indication of TOA changes. To achieve a given accuracy in TOA estimated from OHC we find that there is a trade-off between measuring for longer or deeper. Our model results suggest that there is potential for substantial improvement in our ability to monitor Earth’s radiation balance by more comprehensive observation of the global ocean.” Palmer, M. D., D. J. McNeall, and N. J. Dunstone (2011), Geophys. Res. Lett., 38, L13707, doi:10.1029/2011GL047835.

Melting of Greenland and Antarctica shows in Earth’s oblateness

Recent changes in the Earth’s oblateness driven by Greenland and Antarctic ice mass loss – Nerem & Wahr (2011) “We use temporal gravity variations from GRACE to investigate changes in a 34-year time series of Earth’s oblateness (J2) observed by satellite laser ranging (SLR). We use 2002–2010 GRACE data to compute the effects of Greenland and Antarctic ice mass variations on J2 (2.0 and 1.7 × 10−11/year respectively). Their combined effect on the J2 trend during the GRACE mission is 3.7 × 10−11/year, which agrees well with the GIA-corrected SLR J2 trend over the same time period. The results suggest that at least since 2002, ice loss from Greenland and Antarctica has been the dominant contributor to the current GIA-corrected J2 trend, which apparently began sometime in the 1990s.” Nerem, R. S., and J. Wahr (2011), Geophys. Res. Lett., 38, L13501, doi:10.1029/2011GL047879.

Up to 1/3 of late 20th century warming could have been natural variability

On the time-varying trend in global-mean surface temperature – Wu et al. (2011) “The Earth has warmed at an unprecedented pace in the decades of the 1980s and 1990s (IPCC in Climate change 2007: the scientific basis, Cambridge University Press, Cambridge, 2007). In Wu et al. (Proc Natl Acad Sci USA 104:14889–14894, 2007) we showed that the rapidity of the warming in the late twentieth century was a result of concurrence of a secular warming trend and the warming phase of a multidecadal (~65-year period) oscillatory variation and we estimated the contribution of the former to be about 0.08°C per decade since ~1980. Here we demonstrate the robustness of those results and discuss their physical links, considering in particular the shape of the secular trend and the spatial patterns associated with the secular trend and the multidecadal variability. The shape of the secular trend and rather globally-uniform spatial pattern associated with it are both suggestive of a response to the buildup of well-mixed greenhouse gases. In contrast, the multidecadal variability tends to be concentrated over the extratropical Northern Hemisphere and particularly over the North Atlantic, suggestive of a possible link to low frequency variations in the strength of the thermohaline circulation. Depending upon the assumed importance of the contributions of ocean dynamics and the time-varying aerosol emissions to the observed trends in global-mean surface temperature, we estimate that up to one third of the late twentieth century warming could have been a consequence of natural variability.” Zhaohua Wu, Norden E. Huang, John M. Wallace, Brian V. Smoliak and Xianyao Chen, Climate Dynamics, DOI: 10.1007/s00382-011-1128-8.


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