Claims the Swedish Scandes are unprecedentedly warm and tree-covered today “appear as large and unfounded exaggerations,” as the “climate and arboreal responses” of the last few decades “are still inside the frames of natural historical variation.” – Kullman, 2022 and Kullman, 2022a
Extensive birch forest fossils can be dated to the early- to mid-Holocene in northern Scandinavian regions, indicating these warmth-sensitive trees could exist in climates that are too cold for them to grow in today. This documents a much warmer period, “at least 3°C higher than during the past few decades,” 3000 to 10,000 years ago, or when CO2 was about 265 ppm (Kullman, 2022).
Contrary to modeler opinions, “there is little factual nourishment” to support modern projections that the Swedish Scandes will soon be returning to the subalpine birch forest climates of past millennia. The observed forest advancement in recent decades “is so small” that these modeling claims appear to be “unfounded exaggerations.”
“In the southernmost Swedish Scandes, pine has already “leap-frogged” over receding the birch forest-limit (Kullman 2014, 2019). That scenario would mimic the arboreal landscape during the early Holocene and shift to a landscape unseen for thousands of years (cf. Blűthgen 1942; MacDonald et al. 2008, Macias-Fauria et al. 2012). During that epoch, summer temperatures are inferred to have been at least 3°C higher than during the past few decades.”
“At the landscape level, the obtained changes contribute to a greater and lusher landscape, in contrast to the dire conditions during the Little Ice Age, more than 100 years ago (Kullman 2010, 2015). Currently, there is little factual nourishment to flourishing projections stating that a major part of Swedish alpine areas is on verge of transformation to subalpine birch forest (e.g. Moen et al. 2004). Apparently, climate and arboreal responses are still inside the frames of natural historical variation, as inferred by several authors (e,g. Hammarlund et al. 2004; Bergman et al. 2005; Kullman 2013, 2017a, b; Kullman & Öberg 2018, 2020).”
“Given that the current relatively warm climate phase continues, the subalpine birch forest belt may eventually recede and give way to a subalpine pine belt. The obtained modest forest-limit advancement is so small that flourishing model simulations of extensive birch forest expansion over most of the current alpine tundra appear as large and unfounded exaggerations.”
Tree remnants (trunks, cones, roots, etc.) found at northern Sweden mountain sites 500 to 700 meters atop where the 21st century tree line ends imply the early-Holocene (~13,000 to 7000 years ago) climate was significantly warmer than today in this region (Kullman, 2022a).
The temperature lapse rate for the Swedish Lapland region is 0.6°C/100 m. Accounting for glacio-isostatic uplift, this tree line elevation implies surface air temperatures were 3.6°C higher than today during the Early Holocene.
“A megafossil wood remnant of Norway spruce (Picea abies (L.) Karst.) was retrieved from a high-elevation nunatak in the southern Swedish Scandes. The site was nearly 600 m higher than the present-day treeline.”
“The early Holocene presence of spruce is firmly documented by megafossils at multiple sites in the subalpine/alpine and upper boreal landscapes along the entire Swedish Scandes. In some cases, the finding sites were located 500-700 m above modern treelines and ranging between 13 000 and 7000 years before the present (14, 23). Occasionally, macro and megafossils tree remains have been released from the rim of melting glaciers and ice patches high above modern treelines, indicating glacier-free mountains and relatively warm conditions during the late-glacial and early Holocene epochs (21, 21, 22).”
Image Source: Kullman, 2022a
Northern Europe’s alpine temperatures are presently “well within the frames of natural variability,” as the “forest border is virtually unchanged in position since the early 20th century” (Kullman and Öberg, 2022). Even the Medieval Warm Period had treelines positioned 100 m or more above the present altitudes, indicating the Viking period was warmer than today.
All this evidence supports the conclusion that “alarmist model predictions of a pending major transformation of alpine tundra in the Swedish Scandes to subalpine forest are little supported by the current and other real-world observations.”
“[I]n the early Holocene…temperatures in northern Europe are inferred to have been about 2-3ºC warmer than during the past few decades (Luoto et al. 2014; Väliranta et al. 2015; Paus & Haugland 2017; Kullman 2017a).”
“Irrespective of regeneration mode, treeline advance and population growth in the treeline ecotone represent a return to a more advanced arboreal state, latest prevailing during the Medieval Climate Optimum (cf. Lamb 1982; Ljungqvist 2017) and predating the Little Ice Age and climate cooling and ensuing vegetation retrogression. During the former interval [Medieval Climate Optimum], treelines in the concerned region and elsewhere in the North, were positioned as 100 m or more higher than today (Shiyatov 2003; Mazepa 2005; Kullman 2012, 2013, 2015b; Linderholm, Zhang, Gunnarson et al. 2014). The present-day treelines at the site, are in the lower range of this interval.”
“Like other records, the forest border is virtually unchanged in position since the early 20th century (Kullman, 1979). Obtained aspects of change and stability appear to be well within the frames of natural variability and conforms to modest climate-mediated conversion of the forest-alpine tundra ecotone (Kullman 2019).”
“In the snow rich NE-facing slope, stands of birch forest may evolve, in the case of further climate warming and earlieer seasonal melt-out of the snow cover. However, alarmist model predictions of a pending major transformation of alpine tundra in the Swedish Scandes to subalpine forest (e.g., Moen et al. 2004; Bernes 2007) are little supported by the current and other real-world observations (cf. Willis et al., 2010; Hofgaard et al. 2013; Kullman 2019).”
February 6, 2023 at 04:07PM