Having seen the website skepticalscience.com recommended by several people as a comprehensive source for all things climate science, I took a look and just for fun did a search for trees - and this is what came up, "Tree-ring proxies and the divergence problem." Probably most people that don't live in a cave have heard about "climategate" and the hacked emails and the "trick" of "hiding the decline" which has supposedly discredited the entire oeuvre of climate science. But linked in the article is a paper from 1998 by Briffa et al, which forthrightly discusses the decline of expected growth in recent decades and speculates...
"Along with climate, relatively large-scale positive growth influences such as hypothesized `fertilization' due to increased levels of atmospheric carbon dioxide or various nitrogenous compounds, or possibly deleterious effects of `acid rain' or increased ultra-violet radiation, might all be expected to exert some influence on recent tree growth rates."
from the discussion:
"K. R. BRIFFA. At this time, we do not know why maximum late-wood density declines in relation to large- scale changes (recent warming) in temperature. Further work needs to be done to investigate the regional and species-specific extent of this phenomenon. However, its widespread and apparently synchronous manifestation, N. America, Europe and Siberia, suggests one or more hemi- spheric-scale factors. Higher UV-B was suggested as an example of one such influence. Some synergistic interaction between different factors is certainly possible, in fact probable.
One could reasonably speculate that CO2 and temperature are implicated, but no more so (given our current knowledge of tree physiology and what experimental work has been done) than, say, higher nitrate levels or perhaps tropospheric ozone. It is salient to note that relative tree-ring width, and basal area increment, also show a relative decline and divergence from the temperature curve(s), arguing against the decline in density being a compensation reaction to increasing ring growth (as is seen in forestry soil fertilizing experiments).
I would imagine that higher temperatures, and possibly some increasing sensitivity to lower summer soil moisture are involved, but some additional growth-limiting factor must also be implicated. Higher CO2 would be expected to increase basal area growth, so I consider it unlikely that this is the factor."
Hmmm...acid rain...higher nitrate levels...tropospheric ozone...UV radiation...
All this from 1998! There is much more, but I'm so disgusted that nobody is paying attention to the catastrophic implications of "widespread and synchronous manifestations" of tree decline that I feel like screaming.
Arctic Sea Ice Belching Tons of Methane couldn't be much nastier news. Here's the graph:
Methane is actually escaping from the permafrost and dissolving in the water, working it's way to the surface. File this under the mushrooming category: "Faster and Worse than Predicted."