Global Warming Made Visible — Some Broods of Mountain Pine Beetles Are Now Breeding Twice a Year, with a Presumably Much Worsened Effect on Western U.S. Forests

© 2012 Peter Free

 

01 May 2012

 

 

I suspect that most people are best convinced about climate warming, when they see its results for themselves

 

Those who live in the Rocky Mountain region have seen the devastation that mountain pine beetles (Dendroctonus ponderosae) have been causing for more than a decade.  Now it appears that some beetle broods are breeding twice a year, apparently due to warming high altitude temperatures.

 

From the abstract:

 

Here we show that after 2 decades of air-temperature increases in the Colorado Front Range, the MPB [mountain pine beetle] flight season begins more than 1 month earlier than and is approximately twice as long as the historically reported season.

 

We also report, for the first time, that the life cycle in some broods has increased from one to two generations per year.

 

The expansion of the MPB into previously inhospitable environments, combined with the measured ability to increase reproductive output in such locations, indicates that the MPB is tracking climate change, exacerbating the current epidemic.

 

© 2012 Jeffry B. Mitton and Scott M. Ferrenberg, Mountain Pine Beetle Develops an Unprecedented Summer Generation in Response to Climate Warming, American Naturalist 179(5): E163-E171 (May 2012) (abstract) (paragraph split)

 

 

Not so trivial effects

 

According to the authors, mountain pine beetles are responsible for forest destruction that is several orders of magnitude (meaning thousands of times or more) worse than forest fires.

 

Climate warming has allowed the beetle to expand its range higher and northward, with today’s range running from the Yukon to southern California and New Mexico.

 

Beetle-killed trees in British Columbia (alone) are expected to release 990 million tons of carbon dioxide into the atmosphere.  That amount is “five times the annual emissions from all forms of transportation in the country.”

 

For more on this, see:

 

W. A. Kurz, C. C. Dymond, G. Stinson, G. J. Rampley, E. T. Neilson, A. L. Carroll, T. Ebata, and L. Safranyik, Mountain pine beetle and forest carbon feedback to climate change, Nature 452(7190): 987-990 (24 April 2008)

 

More subtly, the damaged forests alter hydrology (water flow and cycle) and biogeochemical cycles (biological influences interacting with geology and chemical processes):

 

Thus, extensive beetle kill is altering forest ecology and tipping conifer forests from regional carbon sinks to carbon sources, thereby creating positive feedback for climate-change factors.

 

© 2012 Jeffry B. Mitton and Scott M. Ferrenberg, Mountain Pine Beetle Develops an Unprecedented Summer Generation in Response to Climate Warming, American Naturalist 179(5): E163-E171 (May 2012) (from “Introduction”) (paragraph split)

 

 

Link to a picture of what beetle-killed forest looks like

 

This aerial photograph of beetle-killed forest in Yellowstone National Park on 14 July 2007 was taken by Flickr.com member, EcoFlight.

 

 

“Pete, isn’t this just another alarmist study from a bunch of attention-grabbers?”

 

Probably not.

 

A possible criticism might be that the “summer generation” portion of the beetle data comes from only a two-year analysis.

 

But, when you think about it, this criticism is a bit less persuasive than it appears to be.  The core finding is that some of these beetles are now breeding twice a year, apparently for the first observed time.  The twice-per-year discovery does not need to be based on a statistically deep sample taken over many years.  Previous research on the beetles, which extended over many years, indicated that they had been reproducing only once a year.  Seeing two generations in two succeeding years is reasonably persuasive that something has changed.

 

That said, it is indeed statistically possible that the team’s two-generation finding is a fluke.  Obviously, the observation needs to be confirmed over the coming years.

 

 

Noticeable warming

 

The study’s authors indicated that the mean annual temperature at the University of Colorado’s Niwot Ridge research station has been 1.5° degrees Celsius (2.7° F) higher over the last two decades than the previous two.  That’s a significant rise.

 

 

The moral? — Climatic change has effects, some are obvious

 

Beetle-killed forests are one of the more visible signs of what is going on at altitude in parts of the northern hemisphere.