Been thinking about this for a while, now. Why is Climate Science so insistent about the importance of land-use and land cover change in discussions of climate change? And what is the problem other people have with this?
First off, a distinction might be useful. Sometimes, this issue is discussed as a purely climate-related matter, in the sense that debate revolves around the relative forcing and feedback roles of land-use change relative to CO2, and the lack of emphasis placed on this by the IPCC, for example. Other times, CS focuses on the vulnerability/adaptation issue, with emphasis on regional and local scale effects of various changes. Occasionally, such as in the recent discussion of the Amazon, the two overlap.
There’s a pretty good chance of stepping on toes, here, as participants in the often lively debates, such as Roger Pielke Sr., the site’s host, and other bloggers/scientists such as Eli Rabett, Steve Bloom, et. al., go at it hammer and tongs to make their various points. One suspects there is little love lost. One also suspects that much of value is lost in the process. Apologies, then, in advance, to anyone I misrepresent or criticise; it really isn’t personal, in this instance; I like you all.
So, what’s the big deal about land-use change? Two aspects; firstly, at a local and regional level, changes in land use (such as deforestation or irrigation) have a measurable impact on climate in the area. In the case of a large system such as the Amazon Basin, there has been evidence recently that ties changes here to climate impacts in Europe, showing a teleconnection effect of the changes in the region. Roger Pielke has frequently made the important claim that the collective impact on the climate of such changes is greater than that assumed in the IPCC reports. From these, he concludes that the IPCC reports are flawed, and that they are advocacy documents rather than ‘balanced’ ‘scientific’ reports. (There may be other reasons for making this claim, too).
The other point about land-use change is that it has an intimate connection to the vulnerability of both social and environmental systems, in the short-term, a much stronger impact than changes from CO2 forcing, and has feedbacks operating at a local level which are likely to interact with global climate changes to exaggerate the negative effects. An example of this would be the transformation of scrubland to grassland, resulting in changes in albedo, soil moisture retention, atmosphere-soil interactions, precipitation patterns and, possibly, extreme weather events. Any negative effect of such a change will likely be enhanced in most GW climate simulations.
The IPCC AR4 includes land-use change as a forcing in its attribution section, but calculates that the various different effects, positive and negative, tend to balance each other out, so, as a forcing which effects global surface temperature trends, its overall impact is small. The technical papers give more details, but, as Roger Pielke Sr. has pointed out, these do not look especially comprehensive, and can be argued to exhibit some implicit bias in the selection of material (not for me to judge).
Critics argue that emphasising land-use impacts on climate ignores the much-cited ‘elephant in the room’ of CO2. The general argument is that, as CO2 is the largest single forcing element, and as land only represents 30% of the global surface, and land-use change only impacts on a proportion of that, the climate signal from changes must be comparatively insignificant. In itself, this is a dubious argument. If one incorporates all the various elements of land impacts generally, including deforestation and related wildfires, landfill, urbanisation and pollution effects, agricultural use shifts towards higher water-consuming products, increased animal production, irrigation changes, etc., the sum impact of all these approaches 18% of all observed changes in regional temperature over the last 50 years. By comparison, CO2’s direct impact is around 24%. (not my numbers; these come from one of the international environmental websites). This would imply that land-use change is a major player in global climate change but, more significantly, in the impacts of change.
More usefully, if one shifts focus on the causes of climate changes to the causes of vulnerability (for example, see my previous post on the vast projected increases in Displaced Persons), changes in land use have a much greater, more immediate, and more direct impact on human vulnerability than longer-term climate changes. The same is true for ecosystems, which are much more immediately effected by human activity on the ground than by the warming climate. You’ll notice a shift in emphasis here, from discussion of the climate in itself, to consideration of the climate within the context of the entire environmental system. Insofar as it the whole system which should be the object of our concern, we should be careful not to isolate climate too much from the human element; after all, the whole point of climate change research is to help people.
Does this mean that land-use change is more important than CO2 emissions, when discussing future policy to combat the impacts of climate change? The point is arguable, but there is a strong case for claiming that, by all measures, land-use must be considered at least as important in terms of how it effects human vulnerability as CO2 emissions. The latter must be addressed; there is no argument about this; the evidence for the need for serious mitigation is strong enough already. But in the arguments over who gets to emit what, about how much needs to be done, about who pays for the shifts, about cap-and-trade, offsetting and geoengineering, there is a tendency to overlook the importance of what is happening on the ground, and this is almost certainly a mistake.
Just one example here: Emissions problem?: Biofuels. Grown where?: Tropics. Effect?: deforestation and displacement. Consequence?: …
As always, I have left a lot of strings flapping about in the wind, but here I’ll conclude by saying that I believe that the general message promoted by Roger Pielke Sr. is closely associable with messages coming from the likes of Jeffrey Sachs, UNEP, the WHO and many other organisations. I’ll also put my head on the block and say that Roger is right to argue that we are losing sight of far too many important considerations by allowing politicians to create a spectre of CO2 as the ‘clear and present danger’. Obviously, the future energy paths of the world are of key importance, especially when the centennial time scale is considered, and when the impacts are like to be enduring to the extent of semi-permanence. But we are in danger of allowing all other considerations to be swept aside in a search for the solution to the energy problem, when in fact this is only one of several critical problems which need addressing now.
I’m not going to debate the relative role of land-use change on climate, as I’m not scientist enough to do it justice. But it should be clear to anyone that these two issues, along with the issues of water, regional conflict resolution and greed/graft/profiteering, are all interconnected and should be addressed as a package, not as discrete issues. Yes, there is an elephant in the room, and it has a howdah on its back.