Reported tree mortality observations are increasing throughout North America, across a mean annual precipitation range of 202–3,928 mm yr−1 and a mean annual temperature range of −5.7–12.0 °C. Graphic: McDowell, et al, 2015 / Nature Climate Change

By Chris Mooney
21 December 2015

(Washington Post) – In a troubling new study just out in Nature Climate Change, a group of researchers says that a warming climate could trigger a “massive” dieoff of coniferous trees, such as junipers and piñon pines, in the U.S. southwest sometime this century.

The study is based on both global and regional simulations — which show “consistent predictions of widespread mortality,” the paper says — and also an experiment on three large tree plots in New Mexico. The work was led by Nate McDowell of the Los Alamos National Laboratory who conducted the research along with 18 other authors from a diverse group of universities and federal agencies, including the U.S. Geological Survey.

“We have fairly consistent predictions of widespread loss of piñon pine and juniper in the southwest, sometime around 2050,” said McDowell. The paper concludes that the consequences could be vast, citing “profound impacts on carbon storage, climate forcing, and ecosystem services.”

The study examined both an extreme warming scenario — which recent climate policies suggest we may be able to avert — and also a more modest scenario that would likely bring temperatures above 2 degrees Celsius above pre-industrial levels by the year 2100, but not necessarily by that much. The more extreme scenario was certainly worse for these trees, but even under the moderate scenario, the negative results were merely “delayed by approximately one decade,” the study found.

The problem is that climate change is expected to not only increase the risk of drought, but will also drive heat up in general. And this could injure trees in two ways — simply drying them out, but also leading to “carbon starvation.” This could occur if, faced with dry conditions, tree leaves or needles close their stomata to keep water in, but therefore cannot bring in more carbon dioxide and thus suffer from reduced or even fully halted photosynthesis.

In the field experiment, conducted over five years, the researchers found that depriving trees of 48 percent of usual rainfall led to 80 percent mortality of piñon pines more than 100 years old – in other words, fully grown trees – and a 25 percent loss for junipers. […]

Most striking, of course, is the study’s suggesting that even a lesser warming scenario, closer to what the world is now shooting for under the Paris agreement — limiting warming well below 2 degrees Celsius — but still likely beyond it, would still trigger these devastating consequences.

“2 C is huge for trees,” says McDowell. [more]

Scientists say climate change could cause a ‘massive’ tree die-off in the U.S. Southwest


ABSTRACT: Global temperature rise and extremes accompanying drought threaten forests1, 2 and their associated climatic feedbacks3, 4. Our ability to accurately simulate drought-induced forest impacts remains highly uncertain5, 6 in part owing to our failure to integrate physiological measurements, regional-scale models, and dynamic global vegetation models (DGVMs). Here we show consistent predictions of widespread mortality of needleleaf evergreen trees (NET) within Southwest USA by 2100 using state-of-the-art models evaluated against empirical data sets. Experimentally, dominant Southwest USA NET species died when they fell below predawn water potential (Ψpd) thresholds (April–August mean) beyond which photosynthesis, hydraulic and stomatal conductance, and carbohydrate availability approached zero. The evaluated regional models accurately predicted NET Ψpd, and 91% of predictions (10 out of 11) exceeded mortality thresholds within the twenty-first century due to temperature rise. The independent DGVMs predicted ≥50% loss of Northern Hemisphere NET by 2100, consistent with the NET findings for Southwest USA. Notably, the global models underestimated future mortality within Southwest USA, highlighting that predictions of future mortality within global models may be underestimates. Taken together, the validated regional predictions and the global simulations predict widespread conifer loss in coming decades under projected global warming.

Multi-scale predictions of massive conifer mortality due to chronic temperature rise

2 comments :

  1. Survival Acres said...

    I take exception to this sort of journalism. The author is following in the footsteps (and some of his own) of disingenuous journalism.

    "The study examined both an extreme warming scenario — which recent climate policies suggest we may be able to avert — and also a more modest scenario that would likely bring temperatures above 2 degrees Celsius above pre-industrial levels by the year 2100, but not necessarily by that much. The more extreme scenario was certainly worse for these trees, but even under the moderate scenario, the negative results were merely “delayed by approximately one decade,” the study found."

    The author is referring to COP21 (ConJob 21) which is NOT policy, it is simply an "agreement" that is NOT enforceable. Claiming that this policy "suggest we may be able to avert" is definitely disingenuous at best. It's totally untrue, but the author inserts this promise into the article. It's a false hope as the past 21 years of these "gatherings" and non-response has shown.

    The rest of the paragraph then seeks to downplay the significance of what this means without revealing the whole scary truth of what a massive tree die-off really signifies (or hot it's really going to get). This is horrible distracted writing being passed off as news.

    Journalist are even worse then scientists (who are getting better) at reporting the unvarnished truth, who often write the "you'll be ok" hokey pokey promises when writing about the unfolding climate disaster.

    The public should know better by now - everything they claim that won't happen is happening and you have to read carefully for what is being unsaid or ignored in these sort of articles.

    This is what the journalist should have written:

    “Averaging all the models together, the study results suggest that 72 percent of the region’s NET forests will die by 2050, with nearly 100 percent mortality of Southwest U.S. forests by 2100.”

    http://www.udel.edu/udaily/2016/dec/southwest-tree-death-122115.html

    The reality is unfolding all around us now - it's going to be LOT hotter then these journalists are publishing in 2100 (more like 6C or higher).

    I suspect there are multiple efforts afoot to avoid panic. But I contend that this is already a dismal failure. Pretending we've got time, and that's not going to be too bad is to open up the door for delay, inaction and even disbelief. The denialist crowd is very guilty of this, but so are nearly all of today's "journalists" who seem to be completely unable to grasp the true meaning of what they're supposed to be writing about.

    We are NOT getting accurate information from these journalists - not even close. You have to go find this information out for yourself by reading what the science is really saying in the published reports.  

  2. Anonymous said...

    Madonna's Confessions tour in May 2006 produced 440 tonnes of CO2.



     

 

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