AGW Observer

Observations of anthropogenic global warming

New research from last week 40/2011

Posted by Ari Jokimäki on October 10, 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.

Agriculture is facing difficult times due to crop heat stress

Global hot-spots of heat stress on agricultural crops due to climate change – Teixeira et al. (2011) “The productivity of important agricultural crops is drastically reduced when they experience short episodes of high temperatures during the reproductive period. Crop heat stress was acknowledged in the IPCC 4th Assessment Report as an important threat to global food supply. We produce a first spatial assessment of heat stress risk at a global level for four key crops, wheat, maize, rice and soybean, using the FAO/IIASA Global Agro-Ecological Zones Model (GAEZ). A high risk of yield damage was found for continental lands at high latitudes, particularly in the Northern Hemisphere between 40 and 60°N. Central and Eastern Asia, Central North America and the Northern part of the Indian subcontinent have large suitable cropping areas under heat stress risk. Globally, this ranged from less than 5 Mha of suitable lands for maize for the baseline climate (1971–2000) to more than 120 Mha for wetland rice for a future climate change condition (2071–2100) assuming the A1B emission scenario. For most crops and regions, the intensity, frequency and relative damage due to heat stress increased from the baseline to the A1B scenario. However for wheat and rice crops, GAEZ selection of different crop types and sowing dates in response to A1B seasonal climate caused a reduction in heat stress impacts in some regions, which suggests that adaptive measures considering these management options may partially mitigate heat stress at local level. Our results indicate that temperate and sub-tropical agricultural areas might bear substantial crop yield losses due to extreme temperature episodes and they highlight the need to develop adaptation strategies and agricultural policies able to mitigate heat stress impacts on global food supply.” Edmar I. Teixeira, Guenther Fischer, Harrij van Velthuizen, Christof Walter, Frank Ewert, Agricultural and Forest Meteorology, doi:10.1016/j.agrformet.2011.09.002.

Contrasting calcification responses to ocean acidification

Contrasting calcification responses to ocean acidification between two reef foraminifers harboring different algal symbionts – Hikami et al. (2011) “Ocean acidification, which like global warming is an outcome of anthropogenic CO2 emissions, severely impacts marine calcifying organisms, especially those living in coral reef ecosystems. However, knowledge about the responses of reef calcifiers to ocean acidification is quite limited, although coral responses are known to be generally negative. In a culture experiment with two algal symbiont-bearing, reef-dwelling foraminifers, Amphisorus kudakajimensis and Calcarina gaudichaudii, in seawater under five different pCO2 conditions, 245, 375, 588, 763 and 907 μatm, maintained with a precise pCO2-controlling technique, net calcification of A. kudakajimensis was reduced under higher pCO2, whereas calcification of C. gaudichaudii generally increased with increased pCO2. In another culture experiment conducted in seawater in which bicarbonate ion concentrations were varied under a constant carbonate ion concentration, calcification was not significantly different between treatments in Amphisorus hemprichii, a species closely related to A. kudakajimensis, or in C. gaudichaudii. From these results, we concluded that carbonate ion and CO2 were the carbonate species that most affected growth of Amphisorus and Calcarina, respectively. The opposite responses of these two foraminifer genera probably reflect different sensitivities to these carbonate species, which may be due to their different symbiotic algae.” Hikami, M., H. Ushie, T. Irie, K. Fujita, A. Kuroyanagi, K. Sakai, Y. Nojiri, A. Suzuki, and H. Kawahata (2011), Geophys. Res. Lett., 38, L19601, doi:10.1029/2011GL048501.

Arctic sea ice drifts more with stronger winds and thinning ice

Trends in Arctic sea ice drift and role of wind forcing: 1992–2009 – Spreen et al. (2011) “We examine the spatial trends in Arctic sea ice drift speed from satellite data and the role of wind forcing for the winter months of October through May. Between 1992 and 2009, the spatially averaged trend in drift speed within the Arctic Basin is 10.6% ± 0.9%/decade, and ranges between −4% and 16%/decade depending on the location. The mean trend is dominated by the second half of the period. In fact, for the five years after a clear break point in March 2004, the average trend increased to 46% ± 5%/decade. Over the 1992–2009 period, averaged trends of wind speed from four atmospheric reanalyses are only 1% to 2%/decade. Regionally, positive trends in wind speed (of up to 9%/decade) are seen over a large fraction of the Central Arctic, where the trends in drift speeds are highest. Spatial correlations between the basin-wide trends in wind and drift speeds are moderate (between 0.40 and 0.52). Our results suggest that changes in wind speed explain a fraction of the observed increase in drift speeds in the Central Arctic but not over the entire basin. In other regions thinning of the ice cover is a more likely cause of the increase in ice drift speed.” Spreen, G., R. Kwok, and D. Menemenlis (2011), Geophys. Res. Lett., 38, L19501, doi:10.1029/2011GL048970.

Climate impact of albedo modification by building cool roofs

The radiative forcing benefits of “cool roof” construction in California: quantifying the climate impacts of building albedo modification – VanCuren (2011) “Exploiting surface albedo change has been proposed as a form of geoengineering to reduce the heating effect of anthropogenic increases in greenhouse gases (GHGs). Recent modeling experiments have projected significant negative radiative forcing from large-scale implementation of albedo reduction technologies (“cool” roofs and pavements). This paper complements such model studies with measurement-based calculations of the direct radiation balance impacts of replacement of conventional roofing with “cool” roof materials in California. This analysis uses, as a case study, the required changes to commercial buildings embodied in California’s building energy efficiency regulations, representing a total of 4300 ha of roof area distributed over 16 climate zones. The estimated statewide mean radiative forcing per 0.01 increase in albedo (here labeled RF01) is −1.38 W/m2. The resulting unit-roof-area mean annual radiative forcing impact of this regulation is −44.2 W/m2. This forcing is computed to counteract the positive radiative forcing of ambient atmospheric CO2 at a rate of about 41 kg for each square meter of roof. Aggregated over the 4300 ha of cool roof estimated built in the first decade after adoption of the State regulation, this is comparable to removing about 1.76 million metric tons (MMT) of CO2 from the atmosphere. The point radiation data used in this study also provide perspective on the spatial variability of cool roof radiative forcing in California, with individual climate zone effectiveness ranging from −37 to −59 W/m2 of roof. These “bottom-up” calculations validate the estimates reported for published “top down” modeling, highlight the large spatial diversity of the effects of albedo change within even a limited geographical area, and offer a potential methodology for regulatory agencies to account for the climate effects of “cool” roofing in addition to its well-known energy efficiency benefits.” Richard VanCuren, Climatic Change, DOI: 10.1007/s10584-011-0250-2.

Pollen reconstruction suggests MWP was cooler than present in North America

The climate of North America during the past 2,000 years reconstructed from pollen data – Viau et al. (2011) “The temperature of the warmest month was reconstructed for the past 2000 years using 748 pollen sites from the North American Pollen Database. The modern analogue technique was used to quantify paleoclimate conditions using a modern pollen database with calibration sites from across North America. Across North America, both the Medieval Warm Period (MWP) and Little Ice Age (LIA) were cooler than the present (AD1961-1990). The MWP was warmer than the LIA over at least the boreal and eastern portions of the continent and perhaps across the continent. These reconstructed anomalies during the MWP and LIA are significant anomalies from the long-term neoglacial cooling. The atmospheric circulation was likely dominated by a poleward shift of the summer Subtropical High Pressure system in the North Atlantic during the MWP.” A.E. Viau, M. Ladd, K. Gajewski, Global and Planetary Change, doi:10.1016/j.gloplacha.2011.09.010.

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