A climate change tipping point: Plant growth, once boosted by warming and increased CO2, may now be declining
Satellite measurements of plant productivity in 2003. Green shows increased productivity, red decreased. (NASA)
Global climate change, as many have observed, is a story that does not break; it oozes. Yet in today’s Science comes a climate change story that does, in a sense, break. To wit: the increased plant productivity caused by warming temperature, increased carbon dioxide and shifting rainfall pattterns has run out and the curve has reversed slope. Whereas plant productivity–the amount of atmospheric carbon taken up by plants–increased by about 6 percent during the 1980s and ’90s, it has since fallen by about 1 percent.
The implications for food production are obvious. If the small decline grows and population increases, malnutrition and outright starvation are likely to get worse.
And yet, as of mid-day on Friday, hardly any news organizations had picked up the story. The only major U.S. source to have it was AP‘s Randolph E. Schmid. International Business Times in the UK also has a story by Balasubramanyam Seshan.
Tracker trackers who spot other stories are invited to post comments with links to them. A more detailed account, with historical perspective, is on the SolveClimate Web site, by Matthew Berger. The Tracker is not familiar with SolveClimate, but it appears to be an environmentalist outfit doing something like real journalism, though with a clear agenda.
Grist for the mill:
A news release from NASA, whose satellites supplied much of the data.
-Boyce Rensberger
August 20th, 2010 at 1:34 pm
The reverse in CO2 uptake trends isn’t really a tipping point — that’s a term reserved for when a slow rate of change suddenly accelerates, and a system jumps from one state to another. Might still happen, with plant respiration playing a part, but not quite yet.
August 20th, 2010 at 3:05 pm
You’re right, at least insofar as Malcolm Gladwell has popularized the phrase. In climatology, the term can refer to the transition from one stable state to another, or from one equilibrium to another. I thought it could also refer to a phenomenon that changes sign–i.e., from plus to minus, growth to decline, up to down. But I could be wrong.
Anyway, thanks for your comment.
August 20th, 2010 at 3:31 pm
Brandon’s right. The (possibly temporary, as the paper makes clear) reversal in CO2 uptake is certainly not likely to push the climate into a new equilibrium state. There are plenty of other feedbacks that are likely to much more powerful.
August 20th, 2010 at 4:24 pm
Nature News covered it:
http://www.nature.com/news/2010/100819/full/news.2010.418.html
and Scientific American via Climatewire:
http://www.scientificamerican.com/article.cfm?id=higher-temperatures-lessen-plants-ability-to-store-co2
August 20th, 2010 at 4:37 pm
The downtrend may well be temporary. But those other feedbacks are almost all in the direction of enhanced warming.
August 20th, 2010 at 6:05 pm
Our article on Universe Today is based on the NASA press release: http://www.universetoday.com/71575/satellite-data-show-plant-growth-is-declining-on-earth/
August 20th, 2010 at 6:53 pm
Thank you Elsa and Nancy.
August 22nd, 2010 at 6:27 pm
I love a good critical transition/regime shift/alternative stable state discussion!
Metaphors for this sort of thing are always tough and easy to mix, but I’ll toss my hat into the ring and imagine a pair of bowls, side-by-side. Each one represents a stable climate state: say, modern temperate bliss, or a hellish hot future. Inside our bowl is a marble, rolling back and forth, up one side and then returning to the bottom, not quite yet jumping to the other bowl.
Natural phenomena — some cyclical, some one-offs — will tilt our bowl. As it rolls, the marble will venture higher up the side, and it won’t roll so far back down as it would have before. The marble is still in the current bowl, but the chances of another tilt tipping it into the other bowl have gone up.
That’s how I think of the CO2 respiration change: tilting the bowl. Maybe we could all put a new term into the vernacular — a “tilting point”?
August 23rd, 2010 at 6:29 pm
Good suggestion, tilting point. Maybe we can plant the meme.
The bowl metaphor is good. So are erosion channels, including rivercourses. Of course, these are rather simplistic because, as you note, there are more factors at work. One could imagine each having its own set of bowls or channels, although that’s a bit like trying to imagine a number of alternative universes all interpenetrating one another.