April 5, 2013
By: Nick Buhbe, M.S.
Rising sea levels, coastal resiliency, and global climate change are pressing issues with potentially catastrophic effects. Significant work has gone into modeling the effects of global climate change on ecosystems. Just 13 years ago, a model of global climate change, predicted the Amazon would become savannah grassland. A recent paper shows otherwise: the study evaluated the resilience of tropical rain forests to rising atmospheric CO2 levels (C. Huntingford et al., 2013) and, in contrast to previous predictions (from 2000), indicates that the Amazon will not only retain existing biomass as forest, but also that biomass will likely increase relative to pre-industrial levels. This is an important development, as the alternative hypothesis suggested carbon would be released from the Amazon and cause catastrophic global climate change—not to mention the consequences of a major habitat shift.
Modeling large-scale environmental processes requires large amounts of data. Modeling the effects of global climate change on tropical rainforests considers existing conditions and changes in rainfall, temperature, carbon sequestration, and primary production (among other metrics). Each of these components is a highly complex process, difficult to quantify, and involves multifaceted feedback loops.
The previous model focused on a single model and predicted an ecosystem-type change for the Amazon; whereas, the Huntingford study used 22 climate models to simulate biomass retention of tropical rainforest systems not only in the Amazon, but also in the Americas, Africa, and tropical Asia under various land-surface process assumptions. This end result is a comprehensive evaluation of global climate change on the three globally important tropical rain forest systems, rather than a study of a single model for a single system. Remarkably, only one of Huntingford’s 66 model results indicated a loss of biomass under various global climate change conditions (see below figure). The authors concluded that their modeling results provided evidence that tropical rainforest systems are generally resilient with respect to their ability to store carbon.
In the case of the Amazon (and for global rain forests), it is clear that a deeper understanding of the system and a multiple lines of evidence approach are helpful in terms of developing what is hopefully a better understanding of the potential ramifications of global climate change.
Huntingford’s team also evaluated the sources of model uncertainty to better understand the drivers of their conclusions. The factors that most affected the model outcomes were plant physiological responses and future emissions scenarios. The plant physiology component shows that “CO2 fertilization will beat the negative effects of climate change…forests will continue to accumulate carbon throughout the 21st century.” (P. Cox) The variability of climate response to increasing CO2 is less likely to affect models of rainforest resiliency. Rather, an understanding of plant physiology and future CO2 emissions are the key to further refining estimates of the ability of tropical rainforest systems to retain carbon, and should therefore drive global climate change responses. These results illustrate how more complex modeling efforts have the potential to capture additional information, change projected outcomes, and ultimately enable better climate management decisions.
So what does this mean for recent discussions on coastal resiliency? The Amazon study reminds us that when modeling for coastal resiliency, the right data at the right level of detail must be considered to inform the public, regulators and stakeholders of the most desirable options. Most importantly, it demonstrates that a deep understanding of factors contributing to resiliency is key component of any sustainable ecology.
Cox P.M., R.A. Betts, C.D. Jones, S.A. Spall, I.J . Totterdell. 2000 Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model. Nature. 408, 184–187.
C. Huntingford, P. Zelazowski, D. Galbraith, L. M. Mercado, S. Sitch, R. Fisher, M. Lomas, A. P. Walker, C. D. Jones, B. B. B. Booth, Y Malhi, D. Hemming, G. Kay, P. Good, S.L. Lewis, O. L. Phillips, O. K. Atkin, J. Lloyd, E. Gloor, J. Zaragoza-Castells, P. Meir, R. Betts, P. P. Harris, C.Nobre, J. Marengo & P.M. Cox. 2013. Simulated resilience of tropical rainforests to CO2-induced climate change. Nature Geoscience 6:268-273.
Doyle, Alister. Amazon forest more resilient to climate change than feared – study. Reuters. February 6, 2013.