AGW Observer

Observations of anthropogenic global warming

New research from last week 45/2010

Posted by Ari Jokimäki on November 15, 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 I write them. 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:

Atmospheric CO2 leads glacial terminations

A proxy for atmospheric carbon dioxide concentration is described in a new study. The proxy is based on carbon-13 in ocean floor. The carbon-13 based proxy is found to correlate well with atmospheric carbon dioxide concentration. The proxy also gives information about the timing of the events during the glacial periods:

“[The proxy] reproduces characteristic differences between pCO2 and ice volume during Late Pleistocene glaciations and indicates that pCO2 usually leads terminations by 0.2–3.7 kyr but lags by 3–10 kyr during two “failed” terminations at 535 and 745 ka.”

Lowest concentration of carbon dioxide in the atmosphere during the last 1.5 million years is found to be about 155 ppm at about 920,000 years ago.

Citation: Lisiecki, L. E. (2010), A benthic δ13C-based proxy for atmospheric pCO2 over the last 1.5 Myr, Geophys. Res. Lett., 37, L21708, doi:10.1029/2010GL045109. [abstract]

Removing confusion from solar-climate relationships

Legras et al. have looked into the work presented in two recent papers about solar-climate relationships:

“A recent work by Le Mouël et al. (2010) and its companion paper by Kossobokov et al. (2010) show spectacular correlations between solar activity and temperature series from three European weather stations over the last two centuries.”

The result:

“We stress (1) that correlation with solar forcing alone is meaningless unless other forcings are properly accounted for and that sunspot counting is a poor indicator of solar irradiance, (2) that long temperature series require homogenization to remove historical artefacts that affect long term variability, (3) that incorrect application of statistical tests leads to interpret as significant a signal which arises from pure random fluctuations. As a consequence, we reject the results and the conclusions of Le Mouël et al. (2010) and Kossobokov et al. (2010).”

Citation: Legras, B., Mestre, O., Bard, E., and Yiou, P.: A critical look at solar-climate relationships from long temperature series, Clim. Past, 6, 745-758, doi:10.5194/cp-6-745-2010, 2010. [abstract, full text]

Arctic sea ice decrease adds clouds which cause more warming

Satellite measurements spanning 5 “last” years were used to evaluate the effect of Arctic sea ice extent to the polar cloud fraction and vertical distribution:

“We find an anticorrelation between sea ice extent and cloud fraction with maximum cloudiness occurring over areas with little or no sea ice. We also find that over ice-free regions, there is greater low cloud frequency and average optical depth.”

Polar cloud fraction during the five years increased by about 7 % in October and about 10 % in March. Average sea ice decrease was about 5 to 7 %. Here is the surprising conclusion:

“Increasing cloud amount and changes in vertical distribution and optical properties have the potential to affect the radiative balance of the Arctic region by decreasing both the upwelling terrestrial longwave radiation and the downward shortwave solar radiation. Because longwave radiation dominates in the long polar winter, the overall effect of increasing low cloud cover is likely a warming of the Arctic and thus a positive climate feedback, possibly accelerating the melting of Arctic sea ice.”

Citation: Palm, S. P., S. T. Strey, J. Spinhirne, and T. Markus (2010), Influence of Arctic sea ice extent on polar cloud fraction and vertical structure and implications for regional climate, J. Geophys. Res., 115, D21209, doi:10.1029/2010JD013900. [abstract]

Arctic ocean was net carbon dioxide sink between 1998 and 2003

Reduction of sea ice in the Arctic is expected to cause changes in the air-sea carbon dioxide flux because there’s new areas of sea exposed to exchange gases with atmosphere. A new study has evaluated the air-sea exchange of carbon dioxide indirectly:

“The present study utilizes remotely sensed data on distributions of both sea ice and chlorophyll a, together with modeled temperature and salinity fields, to obtain high-resolution basin-scale estimates of the air-sea flux of CO2 (FCO2) in the Arctic Ocean for the years 1998–2003.”

From those it is possible to calculate the FCO2. Some results from that:

“Annual FCO2 was highest in the Atlantic-dominated Greenland and Barents sectors due to their lower sea ice cover, although area-normalized FCO2 in these sectors was low. Only the Siberian sector exhibited a significant increase in annual FCO2 during the time of our study, due to a corresponding increase in ice-free water.”

The end result:

“Overall, the Arctic Ocean was a net atmospheric sink for CO2, with annual FCO2 averaging 118 ± 7 Tg C yr−1 during 1998–2003.”

Citation: Arrigo, K. R., S. Pabi, G. L. van Dijken, and W. Maslowski (2010), Air-sea flux of CO2 in the Arctic Ocean, 1998–2003, J. Geophys. Res., 115, G04024, doi:10.1029/2009JG001224. [abstract]

Maximum estimates of global potential of bio-energy reduced?

A new study has estimated the global potential for bio-energy which has been though to be able to substitute fossil energy. Currently about 10 % of energy humans use comes from bio-energy (about 50 EJ/year). Previous (recent) estimates of the future potential of bio-energy have spanned from 30 to 1000 EJ/year. However, the maximum estimates might be too large:

“In our opinion, the high end of the range is implausible because of (1) overestimation of the area available for bio-energy crops due to insufficient consideration of constraints (e.g., area for food, feed or nature conservation) and (2) too high yield expectations resulting from extrapolation of plot-based studies to large, less productive areas.”

The new improved estimate is:

“According to this review, the global technical primary bio-energy potential in 2050 is in the range of 160–270 EJ/yr if sustainability criteria are considered.”

If that is true, then the potential of bio-energy is only a little over 50 % of current energy demand, and the energy demand is also expected to grow.

Citation: Helmut Haberl, Tim Beringer, Sribas C Bhattacharya, Karl-Heinz Erb and Monique Hoogwijk, 2010, The global technical potential of bio-energy in 2050 considering sustainability constraints, Current Opinion in Environmental Sustainability, doi:10.1016/j.cosust.2010.10.007. [abstract]

Future hot spots of vegetation-climate feedbacks in Europe

Future vegetation-climate feedbacks in Europe were simulated in a new study:

“Simulated variations in leaf area index and in the relative coverage of evergreen forest, deciduous forest, and open land vegetation in response to simulated climate influence atmospheric state via variations in albedo, surface roughness, and the partitioning of the land-atmosphere heat flux into latent and sensible components.”

Three hot spots of vegetation-climate feedbacks were identified:

“In the Scandinavian Mountains, reduced albedo resulting from the snow-masking effect of forest expansion enhanced the winter warming trend. In central Europe, the stimulation of photosynthesis and plant growth by “CO2 fertilization” mitigated warming, through a negative evapotranspiration feedback associated with increased vegetation cover and leaf area index. In southern Europe, increased summer dryness restricted plant growth and survival, causing a positive warming feedback through reduced evapotranspiration.”

Overall conclusion from this is that while Europe as a whole exhibits quite modest vegetation-climate feedbacks, they can be strong regionally.

Citation: Wramneby, A., B. Smith, and P. Samuelsson (2010), Hot spots of vegetation-climate feedbacks under future greenhouse forcing in Europe, J. Geophys. Res., 115, D21119, doi:10.1029/2010JD014307. [abstract]

Methane escape features in ocean floor off New Zealand

A new study has found gas release features from the ocean floor near New Zealand. Features cover a region of at least 20,000 square kilometers and they are thought to be signs of methane hydrate dissociation. Of the features found, 10 were 8-11 km in diameter and about 1000 were 1-5 km in diameter. Also about 10,000 features of about 150 m diameter were observed. The released methane amounts are impressive:

“The amount of methane potentially released from hydrates at each of the largest features is ~7*1012 g. If the methane from a single event at one 8–11 km scale pockmark reached the atmosphere, it would be equivalent to ~3% of the current annual global methane released from natural sources into the atmosphere.”

Citation: Davy, B., I. Pecher, R. Wood, L. Carter, and K. Gohl (2010), Gas escape features off New Zealand: Evidence of massive release of methane from hydrates, Geophys. Res. Lett., 37, L21309, doi:10.1029/2010GL045184. [abstract]

Climate warms, Alaska gets dry -> more wildfires observed

Climate has warmed in Alaska which has resulted in more dry conditions in the summer. 55-year wildfire observation dataset from Alaska has been analysed in a new study. It was found that annual area burned has increased. Furthermore:

“Due to climate change, the last three decades have shown to be warmer than the previous decades. Hence, in the first 28 years of the data, two fires were observed with an area burned greater than 10,000 km2, while there were four in the last 27 years.”

The study also provides a full analysis of the year 2004 which was especially bad wildfire year in Alaska.

Citation: G. Wendler, J. Conner, B. Moore, M. Shulski and M. Stuefer, Climatology of Alaskan wildfires with special emphasis on the extreme year of 2004, Theoretical and Applied Climatology, 2010, DOI: 10.1007/s00704-010-0357-9. [abstract]

Extra water coming to Mediterranean sea from somewhere

Water runoff to Mediterranean sea has been estimated in a new study. The study period was 1980-2000. Their result for long term trends:

“Finally, it was shown through a trend analysis, that the fresh water discharge into the Mediterranean Sea did not exhibit any significant change during the study period in spite of a significant increase in temperature and partial decrease of precipitation. Consequently, awareness should be raised on possible depletion of other water stocks in the Mediterranean river basins, such as mountain glaciers and aquifers.”

Citation: Bouraoui, F., B. Grizzetti, and A. Aloe (2010), Estimation of water fluxes into the Mediterranean Sea, J. Geophys. Res., 115, D21116, doi:10.1029/2009JD013451. [abstract]

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