Influence of geoengineered climate on the terrestrial biosphere

Potential climate engineering effectiveness and side effects during a high carbon dioxide-emission scenario

The realization that mitigation efforts to reduce carbon dioxide emissions have, until now, been relatively ineffective has led to an increasing interest in climate engineering as a possible means of preventing the potentially catastrophic consequences of climate change. While many studies have addressed the potential effectiveness of individual methods there have been few attempts to compare them. Here we use an Earth system model to compare the effectiveness and side effects of afforestation, artificial ocean upwelling, ocean iron fertilization, ocean alkalinization and solar radiation management during a high carbon dioxide-emission scenario. We find that even when applied continuously and at scales as large as currently deemed possible, all methods are, individually, either relatively ineffective with limited (<8%) warming reductions, or they have potentially severe side effects and cannot be stopped without causing rapid climate change. Our simulations suggest that the potential for these types of climate engineering to make up for failed mitigation may be very limited.

The effectiveness of climate engineering in averting potentially catastrophic climate change has thus far been poorly evaluated. Keller et al. use an Earth system model to show that five different climate engineering scenarios are likely to have either a limited impact or potentially severe side effects.

Climatic control of tracheid production of black spruce in dense mesic stands of eastern Canada

Inferences on climate change effects are reliable only if they are based on a causal relationship rather than simple statistical predictive capacity. To assess for causal links between climate and mature black spruce (Picea mariana (Mills.) BSP) radial growth, we combined the use of wood anatomy, cambium phenology, climate and soil measurements (air temperature and humidity, precipitations, soil temperature and water content, photosynthetically active radiation), and a model selection approach proceeding backwards from a full model. Results show that the number of tracheids is responsible for 88% of the variation in ring width whereas mean tracheid diameter accounts for the remaining 12%. The number of tracheids produced depends on factors related to photosynthesis during tracheid production, i.e., daily light intensity and maximum temperature between the day of initiation and the day of cessation of tracheid production, plus soil temperature during August of the previous year which is an important period for determining the number of new needles produced. It is also important to consider duration of the period for tracheid production. These results imply that short-term climate change should increase black spruce radial growth. They also suggest that the typical use of post-growth ring width sampling individually linked to air temperature and precipitations is not sufficient to infer climate change effects accurately on radial growth where there is no strong single climatic limitation but multiple limitations instead.