Climate change mega-post

This week there seems to be a lot of climate news around, some good, some bad, and some that is just ugly. Rather than putting up a plethora of posts and getting accused of being Ars Climactica, we thought we would combine them into a single mega post for your consumption. HangZhou Night Net

The first paper, published in Science1, looks at the prospects for narrowing the range of estimates for the future climate. In doing so, they note that the climate is a system that consists of many physical processes that are coupled together nonlinearly. This has led to climate modelers focusing on physical mechanisms and fundamentals of nonlinear dynamics to understand and improve their models. Notably, the specific inclusion of many physical mechanisms has not led to a significant decrease in the range of climate predictions. Most of the blame for this has fallen on the nature of nonlinear systems. Essentially, to obtain a small increase in predictive ability, one needs a very large increase in the accuracy of the initial conditions. We are stuck because we can’t improve the accuracy of our ancestor’s weather stations and other methods, such as ice core samples, will only ever yield averages. But as our earlier coverage on the nature of climate modeling explains, this isn’t really the heart of the issue. Climate models use a range of initial conditions and measure the probability of certain climatic conditions occurring based on those modeling results.

Instead of focusing on the physics of the climate or the dynamical system, Roe and Baker look at the behavior of a simple linear equilibrium system with positive feedback. All the physics is replaced with a simple gain parameter, which describes how an increase in average temperature leads to a further increase in temperature. Although this does not describe the physics, it does encompass what we measure, so the model is valid for their purposes. They then explore how the uncertainty in the gain parameter changes the rate of temperature increase. The positive feedback system has the effect of amplifying the uncertainties (just like a nonlinear system), meaning that it is practically impossible to improve climate estimates. This is not really derived from the initial conditions (e.g., the starting climatic conditions) but rather focuses on the natural uncertainty in physical mechanisms, which is a major focus of current modeling efforts and includes such things as cloud cover. Basically, the amplifying of the uncertainties, and the timescales involved mean that the smallest uncertainties blow out to give the large range of temperatures predicted by climate researchers.

This news will not call off the search for parts of the environment that influence our climate because, if we are to mitigate global warming, then we must know which bits of the environment are the best to change. This obviously includes human behavior, but that covers a whole gamut from urban lifestyles through to farming practices. Part of this picture is soil erosion, which removes carbon from the soil and deposits it elsewhere. The question isn’t so much as where but what happens to that carbon on route and once it arrives. It was thought that perhaps soil erosion contributed carbon dioxide to the atmosphere by opening up new mechanisms for the decomposition of organic matter. Alternatively, it has been argued that soil erosion deposits organic carbon in places—like the bottom of the sea, for instance— where it is effectively stored. However, testing these hypotheses has been problematic.

Nevertheless, problematic is what a good scientist looks for, so, with fortitude and dedication to the cause, scientists from the EU and US have collaborated to measure the uptake and removal of carbon over ten sites. They report in Science2 this week that, like normal land, eroding land also acts as a carbon sink. They do note that in eroding landscapes, the carbon is likely to more laterally more, but is no more likely to enter the atmosphere as carbon dioxide than on healthy pastureland. Of course the amount of carbon stored is slightly less, so these soils are perhaps not as efficient as normal soils as carbon sinks. Some research is needed to determine if there are differences in the long-term destination of carbon between normal pasture and eroding soils—however, until that research is done, we can cross soil erosion off the list of things to worry about in terms of global warming.

On the bad news, rapid industrialization in the developing world and the lack of action in the developed world is now measurably increasing the rate at which we deposit carbon dioxide into the atmosphere. This is the conclusion of a paper to be published in the Proceedings of the National Academy of Science. Essentially, they have looked at estimates for anthropogenic carbon dioxide emissions and compared that to the measured concentration in the atmosphere and determined from the time series that the natural carbon sinks are either already saturated or are nearing saturated. The conclusion from this is that the concentration of carbon dioxide in the atmosphere is likely to increase faster than predicted in most scenarios. This is especially true since most scenarios assume that we will take some action to keep the rate of increase in atmospheric carbon dioxide (as a percentage) below the rate of economic growth (also as a percentage). Not the best news.