Global warming

New study suggests global warming decreases storm activity and extreme weather

Posted on January 25, 2014 by Anthony Watts

A paper published January 21st inQuaternary Science Reviewsreconstructs storm activity in Iceland over the past 1,200 years and finds storminess and extreme weather variability was far more common during the Little Ice Age in comparison to the Medieval Warm Period and the 20th century. The paper adds to many other peer-reviewed publications finding global warming decreases storm activity, the opposite of claims by climate alarmists.

The graph below shows storm activity shown in 2nd graph from top was much greater and more variable during the Little Ice Age in comparison to the Medieval Warm Period and the 20th century.  Top graph shows one of Mann’s bogus hockey sticks in red, and another non-hockey-stickreconstruction in grey [Moberg et al 2005].

Fig. 8. Multiple proxies of environmental change in Iceland AD 700–2000. (a) Two multi-proxy temperature reconstructions, North Atlantic sea surface temperatures (SST, Mann et al., 2009) and Moberg et al. (2005). (b) Shows GISP2 Na+ deviations from the mean, a proxy for storminess (Meeker and Mayewski, 2002). Cumulative deviations from the mean show a shift to stormier and windier conditions around AD 1425 (Dugmore et al., 2007). (c) Changes in total organic carbon at Lake Haukadalsvatn, west Iceland used as a proxy for aeolian erosion (Geirsdóttir et al., 2009). Bold horizontal bars show means over periods matching key tephra horizons in study (see Table 1). (d) Woodland cover is represented by Betulapollen percentages from a lake core near Lake Mývatn, north Iceland (Lawson et al., 2007) and charcoal pits present in south Iceland (Church et al., 2007) (e) Mean aggregate SeAR from Skaftártunga for period separated by dated tephra layers, with 1 standard deviation show by grey shading. Mean calculated where n = >10. (f) Mean aggregate SeAR at the scale of the landholding, from two small landholdings (Hrífunes and Flaga, see Fig. 1d). (g) Change in SeAR at the landscape scale, 2 stratigraphic sections which record the onset of increased erosion at AD 1597, but profile 38 shows stability through the entire settlement period prior to AD 1918. (h) Population trends in Iceland. Prior to the first census in AD 1703 estimates are based on medieval populations being similar to or even higher than the population in AD 1703 (90 and 43). Plague reductions of ∼40% in AD 1402–1404 and ∼30% in AD 1496 are shown (Karlsson, 1996).

The paper:

Late-Holocene land surface change in a coupled social–ecological system, southern Iceland: a cross-scale tephrochronology approach

Richard Streeter, Andrew Dugmore

Highlights

• Tephrochronology can be used to produce cross scale-analysis of land surface change.

• Grímsvötn tephras are dated to AD 1432 ± 5 and AD 1457 ± 5.

• High resolution 1200-year record of land surface change from Skaftártunga, south Iceland.

• Increasing spatial heterogeneity in sediment accumulation rates after AD ∼870.

• Relationship between climate, vegetation cover and land surface change contingent on past conditions.

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Abstract

The chronological challenge of cross-scale analysis within coupled socio-ecological systems can be met with tephrochronology based on numerous well-dated tephra layers. We illustrate this with an enhanced chronology from Skaftártunga, south Iceland that is based on 200 stratigraphic profiles and 2635 individual tephra deposits from 23 different eruptions within the last 1140 years. We present new sediment-accumulation rate based dating of tephra layers from Grímsvötn in AD 1432 ± 5 and AD 1457 ± 5. These and other tephras underpin an analysis of land surface stability across multiple scales. The aggregate regional sediment accumulation records suggest a relatively slow rate of land surface change which can be explained by climate and land use change over the period of human occupation of the island (after AD ∼870), but the spatial patterning of change shows that it is more complex, with landscape scale hysteresis and path dependency making the relationship between climate and land surface instability contingent. An alternative steady state of much higher rates of sediment accumulation is seen in areas below 300 m asl after AD ∼870 despite large variations in climate, with two phases of increased erosion, one related to vegetation change (AD 870–1206) and another related to climate (AD 1597–1918). In areas above 300 m asl there is a short lived increase in erosion and related deposition after settlement (AD ∼870–935) and then relatively little additional change to present. Spatial correlation between rates of sediment accumulation at different profiles decreases rapidly after AD ∼935 from ∼4 km to less than 250 m as the landscape becomes more heterogeneous. These new insights are only possible using high-resolution tephrochronology applied spatially across a landscape, an approach that can be applied to the large areas of the Earth’s surface affected by the repeated fallout of cm-scale tephra layers.

This article was originally published on The Hockey Schtick, and presented here with some minor edits for format and clarity.