A new thread at bender’s suggestion. Treelines are a climate indicator that I’ve paid attention to in the past as evidence that made sense to me about the relationship of modern and medieval climate. I’ve posted up threads in the past about tree lines in California being higher than at present in the MWP and Holocene Optimum; likewise in the Urals and Fennoscandia – see this Category for some prior posts. Reader Tom has sent in a news report that Swedish tree lines are at levels that are matching the Holocene Optimum.
“The tree line has moved by up to 200 meters (656 feet) in some places. Trees have not grown at such high levels for around 7,000 years,” Leif Kullman, a professor at Umeaa University’s department of ecology and environmental science, told AFP Tuesday.
I’ve read a number of articles by Kullman from about 15 years ago in which he noted that tree lines at that time had not responded to warming; he even wondered whether the local temperature records were accurate. Kullman’s website However the present situation appears to be different. The article goes on to say:
“The number of plants and animals in Swedish forests has grown 100 percent in the last 50 years,” Kullman said.
Usually we hear that climate change has all sorts of adverse results; I wonder if we’ll see about loud headlines about unprecedented increases in plants and animals in Swedish forests.
IPCC 4AR takes a very dismissive position towards treeline changes as a temperature indicator in its criticism of Hubert Lamb. They said that such vegetation change is “difficult to interpret in terms of accurate quantitative temperature influences” ant that it may result “from physical or biological systems that involve complex lags between forcing and response, as is the case for vegetation and glacier changes.” Because IPCC 4AR dismissed this class of evidence, they did not review the state of evidence from tree line change in various parts of the world – a review that is long overdue.
Notwithstanding the casual dismissal of this line of evidence by IPCC 4AR, I regard evidence of tree lines reaching Holocene levels as potentially legitimate evidence of warm climate and will pay close attention to Kullmann’s information as it comes along. If tree lines have reached Holocene Optimum levels in Sweden, but treelines in Siberia and California haven’t even reached MWP levels, it will pose a conundrum – but an interesting one. Let’s hope that people survey the evidence rather than cherry picking, but that may be hoping too much.
I would hasten to say that, if changing treelines demonstrate modern warmth, that would not disprove our criticisms of the Hockey Team reconstructions. They would remain as valid as criticisms of the Piltdown Mann or Enron accounting. Just because I don’t accept bad accounting from the Team doesn’t mean that I’m not open to some other form of evidence in this matter.
Another recent article on Swedish treelines is Jonas Bergman, Dan Hammarlund, Gina Hannon, Lena Barnekow, Barbara Wohlfarth, 2005. Deglacial vegetation succession and Holocene tree-limit dynamics in the Scandes Mountains, west-central Sweden: stratigraphic data compared to megafossil evidence Review of Palaeobotany and Palynology 134 (2005) 129– 151. They discuss Kullmann’s results stating:
The long-term Holocene vegetation development in the central part of the Scandes is known through radiocarbon dating of subfossil wood remains (megafossils) found above the present-day tree-limit (Lundqvist, 1959; Kullman, 1995, 1998b; Kullman and Kjallgren, 2000). …
This megafossil data-set includes almost 250 samples of Pinus sylvestris, Betula pubescens, and Alnus incana collected above the modern altitudinal forest-limit…. the tree-limit in the southern part of the Scandes has ascended by 100–130 m in response to warming during the 20th century (Kullman, 2001), whereas no significant vegetation response has been reported from southern Sweden.
Bergman et al 2005 Figure xx.
The figure of 200 m in the news article is greater than the figure of 100-130 m in the academic article. Above is a graphic from Bergman et al which shows that treelines 100-200 meters above 19th century treelines are not unprecedented since higher levels were achieved in the Holocene Optimum but a sustained 200 meter rise in treeline would indicate warmth exceeding medieval levels in this area.