AGW Observer

Observations of anthropogenic global warming

New research from last week 17/2012

Posted by Ari Jokimäki on April 30, 2012

Is it something that is happening in the Sun,
or are atmospheric GHG’s the smoking gun?

Temperature is rising on the surface of the sea.
Did we do it, or did nature do it for free?

Cryospheric presence in Arctic is very nice.
After mankind’s tricks, does anybody see there any ice?

What causes changes in avalanches of snow,
or in floods, does anyone know?

When wetlands are all gone, rotten and stink,
what can carbon do after that, where does it sink?

Migration is something that trees and butterflies have to face.
I just wonder if they’ll end up in same place?

The move from MWP to LIA is a big change,
but weather can do it with same regime, isn’t that strange?

Subtropical clouds are difficult things to simulate.
Can’t climate models ever do it, or is it their fate?


Impact of anthropogenic climate change is observable in Arctic sea ice already today

Observations reveal external driver for Arctic sea-ice retreat – Notz & Marotzke (2012)

Abstract: “The very low summer extent of Arctic sea ice that has been observed in recent years is often casually interpreted as an early-warning sign of anthropogenic global warming. For examining the validity of this claim, previously IPCC model simulations have been used. Here, we focus on the available observational record to examine if this record allows us to identify either internal variability, self-acceleration, or a specific external forcing as the main driver for the observed sea-ice retreat. We find that the available observations are sufficient to virtually exclude internal variability and self-acceleration as an explanation for the observed long-term trend, clustering, and magnitude of recent sea-ice minima. Instead, the recent retreat is well described by the superposition of an externally forced linear trend and internal variability. For the externally forced trend, we find a physically plausible strong correlation only with increasing atmospheric CO2 concentration. Our results hence show that the observed evolution of Arctic sea-ice extent is consistent with the claim that virtually certainly the impact of an anthropogenic climate change is observable in Arctic sea ice already today.”

Citation: Notz, D. and J. Marotzke (2012), Observations reveal external driver for Arctic sea-ice retreat, Geophys. Res. Lett., 39, L08502, doi:10.1029/2012GL051094.


Coastal vegetated wetlands are rapidly vanishing carbon sinks

Carbon sequestration in wetland dominated coastal systems — a global sink of rapidly diminishing magnitude – Hopkinson et al. (2012)

Abstract: “Coastal vegetated wetlands have recently been identified as very important global C sinks but vulnerable to degradation by direct human alteration of their habitats. While their expanse is small globally, areal rates of C burial, or sequestration, are among the highest of Earth’s ecosystems. There is considerable uncertainty in the magnitude of total global sequestration in these systems for two reasons: poor estimates of their global areas and high variability and uncertainty in areal rates of burial between systems. The magnitude of C burial in vegetated coastal systems has been decreasing rapidly over the past century due primarily to human disturbances such as dredging, filling, eutrophication, and timber harvest. These systems continue to be lost globally at rates ranging from 1% to 7% annually. We find that climate change including global warming, human engineering of river systems, continued agricultural expansion, and sea level rise will also negatively impact C burial of coastal vegetated wetlands. A decrease in global C burial in these systems will ultimately exacerbate CO2 emissions, and further contribute to climate change in the future.”

Citation: Charles S Hopkinson, Wei-Jun Cai, Xinping Hu, Current Opinion in Environmental Sustainability, http://dx.doi.org/10.1016/j.cosust.2012.03.005.


Ranges of British butterflies have been thinning as they have expanded northwards

Temporal variation in responses of species to four decades of climate warming – Mair et al. (2012)

Abstract: “Many species are expanding at their leading-edge range boundaries in response to climate warming. Species are known to respond individualistically to climate change, but there has been little consideration of whether responses are consistent over time. We compared responses of 37 southerly-distributed British butterflies over two study periods, first between 1970-82 and 1995-99 and then between 1995-99 and 2005-09, when mean annual temperature increased regionally by 0.03 ⁰C yr−1 (a significant rate of increase) and 0.01 ⁰C yr−1(a non-significant increase), respectively. Our study species might be expected to benefit from climate warming. We measured three responses to climate to investigate this; changes in range margin, distribution area and abundance. In general, the responses of species were inconsistent over time. Species that increased their distribution areas during the first period tended to do so again during the second period, but the relationship was weak. Change in range margins and abundance were not consistent. In addition, only 5/37 species showed qualitatively similar responses in all three response variables over time (three species increased and two species declined in all variables in both periods). Overall rates of range expansion and distribution area change were significantly greater in the second study period, despite the lower rate of warming, perhaps due to species exploiting climate-distribution lags remaining from the earlier, warmer period. However, there was a significantly greater decline in abundance during the second study period, so range expansions northwards were not necessarily accompanied by increases in distribution area and/or abundance. Hence species ranges have been thinning as they have expanded northwards. The idiosyncratic responses of these species likely reflect the balance of climatic and habitat drivers of species distribution and abundance changes.”

Citation: Louise Mair, Chris D Thomas, Barbara J Anderson, Richard Fox, Marc Botham, Jane K Hill, Global Change Biology, DOI: 10.1111/j.1365-2486.2012.02730.x.


Snow avalanche activity has increased in French Alps with temperature

Snow and weather climatic control on snow avalanche occurrence fluctuations over 50 yr in the French Alps – Castebrunet et al. (2012) [FULL TEXT]

Abstract: “Snow avalanche activity is controlled to a large extent by snow and weather patterns. However, its response to climate fluctuations remains poorly documented. Previous studies have focused on direct extraction of trends in avalanche and winter climate data, and this study employs a time-implicit method to model annual avalanche activity in the French Alps during the 1958–2009 period from its most representative climatic drivers. Modelled snow and weather data for different elevations and aspects are considered as covariates that explain actual observed avalanche counts, modelled instability indexes, and a combination of both avalanche activity indicators. These three series present relatively similar fluctuations over the period and good consistency with historically harsh winters. A stepwise procedure is used to obtain regression models that accurately represent trends as well as high and low peaks with a small number of physically meaningful covariates, showing their climatic relevance. The activity indicators and their regression models seen as time series show, within a high interannual variability, a predominant bell-shaped pattern presumably related to a short period of colder and snowier winters around 1980, as well as a very slight but continuous increase between 1975 and 2000 concomitant with warming. Furthermore, the regression models quantify the respective weight of the different covariates, mostly temperature anomalies and south-facing snowpack characteristics to explain the trends and most of the exceptional winters. Regional differences are discussed as well as seasonal variations between winter and spring activity and confirm rather different snow and weather regimes influencing avalanche activity over the Northern and Southern Alps, depending on the season.”

Citation: Castebrunet, H., Eckert, N., and Giraud, G.: Snow and weather climatic control on snow avalanche occurrence fluctuations over 50 yr in the French Alps, Clim. Past, 8, 855-875, doi:10.5194/cp-8-855-2012, 2012.


Does natural variability dominate global sea surface temperature changes since 1984?

On the Observed Trends and Changes in Global Sea Surface Temperature and Air-Sea Heat Fluxes (1984-2006) – Large & Yeager (2012)

Abstract: “Global satellite observations show the sea surface temperature (SST) increasing since the 1970s in all ocean basins, while the net air-sea heat flux, Q, decreases. Over the period 1984-2006 the global changes are 0.28°C in SST and -9.1 W/m2 in Q, giving an effective air-sea coupling coefficient of -32 W/m2/°C. The global response in Q expected from SST alone is determined to be -12.9 W/m2, and the global distribution of the associated coupling coefficient is shown. Typically, about one-half (6.8 W/m2) of this SST effect on heat flux is compensated by changes in the overlying near surface atmosphere. Slab Ocean Models (SOMs) assume that ocean heating processes do not change from year to year, so that a constant annual heat flux would maintain a linear trend in annual SST. However, the necessary 6.1 W/m2 increase is not found in the downwelling longwave and shortwave fluxes, which combined show a -3 W/m2 decrease. The SOM assumptions are revisited to determine the most likely source of the inconsistency with observations. The indirect inference is that diminished ocean cooling due to vertical ocean processes played an important role in sustaining the observed positive trend in global SST from 1984 through 2006, despite the decrease in global surface heat flux. A similar situation is found in the individual basins, though magnitudes differ. A conclusion is that natural variability, rather than long term climate change, dominates the SST and heat flux changes over this 23 year period. On shorter time scales the relationship between SST and heat flux exhibits a variety of behaviors.”

Citation: W. G. Large and S. G. Yeager, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-11-00148.1.


Climate determines where trees live

How are tree species distributed in climatic space? A simple and general pattern – Boucher Lalonde et al. (2012)

Abstract: “Aim: Although many factors undoubtedly affect species geographic distributions, can a single, simple model nonetheless capture most of the spatial variation in the probability of presence/absence in a large set of species? For 482 North American tree species that occur east of the Rocky Mountains, we investigated the shape(s) of the relationship between the probability of occupancy of a given location and macroclimate, and its consistency among species and regions. Location: North America. Methods: Using Little’s tree range maps, we tested four hypothetical shapes of response relating occupancy to climate: (1) high occupancy of all suitable climates; (2) threshold response (i.e. unsuitable climates exclude species, but within the thresholds, species presence is independent of climate); (3) occupancy is a bivariate normal function of annual temperature and precipitation; and (4) asymmetric limitation (i.e. abiotic factors set abrupt range limits in stressful climates only). Finally, we compared observed climatic niches with the occupancy of similar climates on off-shore islands as well as west of the Rockies. Results: (a) Species’ distributions in climatic space do not have strong thresholds, nor are they systematically skewed towards less stressful climates. (b) Occupancy can generally be described by a bivariate normal function of temperature and precipitation, with little or no interaction between the two variables. This model, averaged over all species, accounts for 82% of the spatial variation in the probability of occupancy of a given area. (c) Occupied geographic ranges are typically ringed by unoccupied, but climatically suitable areas. (d) Observed climatic niche positions are largely conserved between regions. Main conclusions: We conclude that, despite the complexities of species histories and biologies, to a first approximation most of the variation in their geographic distributions relates to climate, in similar ways for nearly all species.”

Citation: Véronique Boucher Lalonde, Antoine Morin, David J. Currie, Global Ecology and Biogeography, DOI: 10.1111/j.1466-8238.2012.00764.x.


Transition from Medieval Warm Period to Little Ice Age in North Atlantic does not imply changes in weather regimes

Stability of weather regimes during the last millennium from climate simulations – Yiou et al. (2012)

Abstract: “The variability of the extra-tropical atmospheric circulation and its potential dependence on external forcings have been debated topics in climate modeling and observation communities. A recent reconstruction of the North Atlantic Oscillation Index has argued that the Medieval Warm Period period yielded a persistent positive phase of this index in contrast with an oscillating mode during the Little Ice Age. This paper tests whether this feature can be obtained, in millennium simulations from three different climate models. We examine the daily atmospheric dynamics that drives the main modes of extra-tropical variability. We find that the transition from a Medieval Warm Period to a Little Ice Age in the North Atlantic does not imply changes in patterns or frequency of weather regimes, although the mean surface temperature change is significant. This implies that the interpretation of proxy records in terms of atmospheric variability should be revised in order to take into account the structure of daily meteorological patterns, and/or climate models are too constrained to infer large changes of atmospheric variability.”

Citation: Yiou, P., J. Servonnat, M. Yoshimori, D. Swingedouw, M. Khodri, and A. Abe-Ouchi (2012), Stability of weather regimes during the last millennium from climate simulations, Geophys. Res. Lett., 39, L08703, doi:10.1029/2012GL051310.


Comparison of climate response to solar and GHG forcings

Robustness of Dynamical Feedbacks from Radiative Forcing: 2% Solar versus 2xCO2 Experiments in an Idealized GCM – Cai & Tung (2012)

Abstract: “Despite the differences in the spatial patterns of the external forcing associated with a doubling CO2 and with a 2% solar variability, the final responses in the troposphere and at the surface in a three-dimensional general circulation model appear remarkably similar. Various feedback processes are diagnosed and compared using the Climate Feedback-Response Analysis Method (CFRAM) to understand the mechanisms responsible. At the surface, solar radiative forcing is stronger in the tropics than at the high latitudes, while greenhouse radiative forcing is stronger at high latitudes compared to the tropics. Also solar forcing is positive everywhere in the troposphere and greenhouse radiative forcing is positive mainly in lower troposphere. The water vapor feedback strengthens the upward decreasing radiative heating profile in the tropics and the poleward decreasing radiative heating profile in the lower troposphere. The “evaporative” and convective feedbacks play an important role only in the tropics where they act to reduce the warming at the surface and lower troposphere in favor of upper troposphere warming. Both water vapor feedback and enhancement of convection in the tropics further strengthen the initial poleward decreasing profile of energy flux convergence perturbations throughout the troposphere. As a result, the large-scale dynamical poleward energy transport, which acts on the negative temperature gradient, is enhanced in both cases, contributing to a polar amplification of warming aloft and a warming reduction in the tropics. The dynamical amplification of polar atmospheric warming also contributes additional warming to the surface below via downward thermal radiation.”

Citation: Ming Cai and Ka-Kit Tung, Journal of the Atmospheric Sciences 2012, doi: http://dx.doi.org/10.1175/JAS-D-11-0117.1.


Queensland 2011 flood as PDO indicator

The 2011 southeast Queensland extreme summer rainfall: A confirmation of a negative Pacific Decadal Oscillation phase? – Cai & Rensch (2012)

Abstract: “The devastating southeast Queensland (SEQ) flood and the associated extreme rainfall in January 2011 were accompanied by an extraordinarily strong La Niña. The regional summer rainfall is affected by the El Niño-Southern Oscillation (ENSO) cycle, but modulated by the Pacific Decadal Oscillation (PDO) or the Interdecadal Pacific Oscillation (IPO). What does the recent flood tell about the status of the PDO-IPO? Using three lines of supporting evidence it is proposed that the SEQ 2011 austral summer rain constitutes a confirmation of a transition to a negative phase of the PDO-IPO. Firstly, the 2011 summer saw large SEQ rainfall and SOI values that historically occur only in a negative PDO-IPO phase; secondly, there was an associated re-establishment of an ENSO-SEQ rainfall teleconnection; and finally, the decadal-circulation state, particularly the tropical convection, has developed toward a state similar to that during other negative PDO-IPO periods. The results imply an increased chance of high summer rainfall events over the region during La Niña in the upcoming decade or so.”

Citation: Cai, W. and P. van Rensch (2012), The 2011 southeast Queensland extreme summer rainfall: A confirmation of a negative Pacific Decadal Oscillation phase?, Geophys. Res. Lett., 39, L08702, doi:10.1029/2011GL050820.


Improvements are needed for climate model simulations of cloud forcing in subtropics

Origins of differences in climate sensitivity, forcing and feedback in climate models – Webb et al. (2012)

Abstract: “We diagnose climate feedback parameters and CO2 forcing including rapid adjustment in twelve atmosphere/mixed-layer-ocean (“slab”) climate models from the CMIP3/CFMIP-1 project (the AR4 ensemble) and fifteen parameter-perturbed versions of the HadSM3 slab model (the PPE). In both ensembles, differences in climate feedbacks can account for approximately twice as much of the range in climate sensitivity as differences in CO2 forcing. In the AR4 ensemble, cloud effects can explain the full range of climate sensitivities, and cloud feedback components contribute four times as much as cloud components of CO2 forcing to the range. Non-cloud feedbacks are required to fully account for the high sensitivities of some models however. The largest contribution to the high sensitivity of HadGEM1 is from a high latitude clear-sky shortwave feedback, and clear-sky longwave feedbacks contribute substantially to the highest sensitivity members of the PPE. Differences in low latitude ocean regions (30°N/S) contribute more to the range than those in mid-latitude oceans (30–55°N/S), low/mid latitude land (55°N/S) or high latitude ocean/land (55–90°N/S), but contributions from these other regions are required to account fully for the higher model sensitivities, for example from land areas in IPSL CM4. Net cloud feedback components over the low latitude oceans sorted into percentile ranges of lower tropospheric stability (LTS) show largest differences among models in stable regions, mainly due to their shortwave components, most of which are positive in spite of increasing LTS. Differences in the mid-stability range are smaller, but cover a larger area, contributing a comparable amount to the range in climate sensitivity. These are strongly anti-correlated with changes in subsidence. Cloud components of CO2 forcing also show the largest differences in stable regions, and are strongly anticorrelated with changes in estimated inversion strength (EIS). This is qualitatively consistent with what would be expected from observed relationships between EIS and low-level cloud fraction. We identify a number of cases where individual models show unusually strong forcings and feedbacks compared to other members of the ensemble. We encourage modelling groups to investigate unusual model behaviours further with sensitivity experiments. Most of the models fail to correctly reproduce the observed relationships between stability and cloud radiative effect in the subtropics, indicating that there remains considerable room for model improvements in the future.”

Citation: Mark J. Webb, F. Hugo Lambert and Jonathan M. Gregory, Climate Dynamics, 2012, DOI: 10.1007/s00382-012-1336-x.


CLASSIC OF THE WEEK: Anders (1882)

Forests-Their Influence Upon Climate and Rainfall – Anders (1882) [FULL TEXT]

Abstract: No abstract. Quote from the beginning of the article: “That there exists some sort of relation betwixt forests and conditions of climate, perhaps most observers would be ready to concede. Many attempts have been made to explain how forests affect atmospheric states, but there is great diversity of opinion on the subject, and, indeed, the question to-day remains somewhat involved in obscurity. As every one knows,…”

Citation: Anders, J. M., The American Naturalist, Vol. 16, No. 1 (Jan., 1882) (pp. 19-30).


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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