The Weekly Carboholic: boreal forest moves north, reducing Arctic albedo


When we think about forests and global heating, we generally think about how forests sequester carbon via respiration and storage in their trunks and leaves. For that reason, we’re often told that we should support reforestation efforts, support efforts that reduce deforestation, and even plant trees ourselves. And all of those things will help. But in some cases, forests can also behave as a net carbon source instead of a carbon sink. The Carboholic reported on one such possible instance back on January 9. Last week, ScienceNews reported on the release of a study that shows that expanding forests taking over tundra could also further exacerbate global heating.

The problem is this: as the boreal forest that blankets North America, Europe, and Asia up to the Arctic Circle spread further north into former tundra, the albedo (the amount of light reflected off the ground back into space) of the land goes down, effectively creating yet more Arctic heating in a positive feedback loop.

Ecologists and climatologists are concerned because the emerging forest data suggest that the albedo, or reflectivity, of large regions across the Arctic could change. Most sunlight hitting snow and ice bounces back into space. But convert a white landscape to open sea water or boreal forest, and the surface suddenly becomes a great collector of solar energy.

So, while the expanding boreal forest probably soaks up more carbon via photosynthesis, the probable result is a hotter Arctic. And a hotter Arctic results in less sea ice and more methane emissions from peat and permafrost as well as submarine methane hydrates. As such, there’s a good chance that the net result of a hotter Arctic will be yet another increase in global heating.


Scientists have known for a while now that the atmospheric concentrations of both carbon dioxide (CO2) and methane are significantly higher today than they have been in the last 650,000 years. In fact, the image at right (click for a larger version) shows just how far above the last 650,000 years we actually are for CO2 and methane: CO2 topped out at about 300 ppm in the ice age record used by the IPCC, and methane appears to have stayed at or below 850 ppb. In 2007 (the latest year for which we have complete data) the atmospheric concentrations of CO2 and methane were at 386 ppm CO2 and about 1792 ppb methane. As reported by Reuters India last week, new Antarctic ice core data has now pushed back the earliest data from 650,000 years ago to about 800,000 years ago. And the longer ice core confirms that the present day atmosphere has far more CO2 and methane than at any time over the last 800,000 years.

“We can firmly say that today’s concentrations of carbon dioxide and methane are 28 and 124 percent higher respectively than at any time during the last 800,000 years,” said Thomas Stocker, an author of the report at the University of Berne.

Some of you are certainly wondering why this matters. It’s important because it makes the anthropogenic global heating (AGH) case even stronger. 600,000 years isn’t long enough, according to some AGH deniers, to draw any conclusions. But what about 800,000 years? Or, as the researchers hope to achieve in the next few years, 1.5 million years? How far back do we have to have good data to prove that human civilization is heating up the planet?

Ultimately, scientists will reach a point where it doesn’t make sense to go back any farther. This point is whenever the last major change in the Earth’s orbit, or the last significant solar irradiance change, or even the last major change in the shapes of the continents due to plate tectonics, or some other dramatic change in the Earth. Whatever that dividing line is, after it will be reasonable to compare to present day climate, and before it will be unreasonable for comparison except in very carefully defined circumstances. And every time scientists push back the date of that point, the arguments of the AGH deniers get weaker as the evidence for AGH gets stronger.


In the last week, another major study came out, this one correlating a truly massive number of other studies since 1970 to global heating. According to the BBC story about the study:

The researchers assembled a database including more than 29,500 records that documented changes seen across a wide range of natural phenomena (emphasis mine)

The phenomena listed include animals arriving in cold climates earlier in the year, pack ice breaking up earlier and freezing later, melting ice fields and glaciers, etc. And the researchers, many of whom were associated with the IPCC AR4 WG1 report last year, found that “[a]bout 90% of the changes documented were consistent with rising temperatures at regional scales”.

Now, I won’t go as far as two of Nature’s reviewers did and claim that this study “formally link[s] observed global changes in physical and biological systems to human-induced climate change”, because that language is too strong. The study formally links the observed global changes to increases in regional temperatures. Other studies are required to forge that particular link.

Of course, there are literally thousands of other studies that do precisely that.


Hybrid vehicles are cool, and if I could have afforded one and received mine in a timely manner, I might have purchased a Toyota Prius when my car was totaled in a multi-car collision several years ago. But hybrid cars aren’t as environmentally friendly as they could be. For starters, they’re still made from aluminium, plastic, and steel, and they burn gasoline, just a lot less of it. And manufacturing hybrid batteries is a very, very dirty process. Now, unfortunately but not surprisingly, there is some evidence that the carbon savings of a hybrid car aren’t as significant as claimed by most of the hybrid manufacturers. According to the Independent.ie story, Auto Express magazine did road tests of multiple hybrids and found that most of them didn’t meet their carbon emission claims.

As with most products, marketing writes the specifications, not engineering, and while there are supposedly limits to what you can claim and stay clear of fraud claims, you can still push the envelope or use loopholes. That’s how you can drive a car that gets 36 mpg on a highway at 55 mph and never get more than 30 mpg on a real highway – the difference is that you’re driving at the speed limit of 65 mpg, or you’re carrying a passenger, or that you’ve got some cargo in the trunk, or… you get the idea. The same is true of hybrids. And as with all things, be careful what you buy – not everything that’s green is environmentally friendly.

6 replies »

  1. Forests taking over the tundra exacerbating global warming? That’s wild.

    Damned if you do; damned if you don’t.

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  3. Russ – Yeah, and it’s a great example of the problem of positive feedback vs. negative feedback. As the earth heats up, the boreal forest can expand and thus can store more carbon. But at the same time, a hotter Arctic means more carbon emissions from permafrost, peat bogs, and submarine methane hydrates. In addition, green trees absorb more energy than tundra plants and mosses do. So which force dominates, the positive feedback of more carbon emissions plus a falling albedo, or the negative feedback of more carbon storage in the trunks of growing boreal trees? It’s a complex exercise, and I don’t know the answer personally, but I suspect that scientists with experience in this area (how much carbon a tree can store, how fast boreal forest is expanding, how many trees that is per acre or sq. kilometer, etc.) can make an estimate and attach error bars to it.

    The “good” thing is that, in realty, every positive feedback mechanism has a limiting factor that constrains the instability. In electrical engineering, if I design a circuit that is unstable, it’ll go crazy until it hits the limit of the circuit, usually the power supply. In the Arctic, melting sea ice is a positive feedback element because open water absorbs more sunlight than floating ice does – until there’s no more ice to melt. At that point, the positive feedback term in the Arctic climate equation is negated and other terms take over again.

    Of course, just because there’s a limit doesn’t mean that limit is a good thing. In an electrical circuit, the limit could be a capacitor that overheats, pops, and dumps foul-smelling black carcinogenic smoke into the air. In climate feedbacks, just because the limiting factor of sea ice would be no sea ice doesn’t mean that homo sapiens en toto would like the global climate at that point.