Effects of CO2 Physiological Forcing on Amazon Climate

Abstract:

Earth system models provide us with an opportunity to examine the complex interactions and feedbacks between land surface, vegetation and atmosphere. A more thorough understanding of these interactions is essential in reducing uncertainty surrounding the potential impacts of climate and environmental change on the future state and extent of the Amazon rainforest. This forest is a important resource for the region and globally in terms of ecosystem services, hydrology and biodiversity.

We aim to investigate the effect of CO₂ physiological forcing on the Amazon rainforest and its feedback on regional climate by using the CMIP5 idealised 1% CO₂ simulations with a focus on HadGEM2-ES. In these simulations, the atmospheric CO₂ concentration is increased by 1% per year for 140 years, reaching around 1150ppm at the end of the simulation. The use of idealised simulations allows the effect of CO₂ to be separated from other forcings and the sensitivities to be quantified. In particular, it enables non-linear feedbacks to be identified.

In addition to the fully coupled 1% CO₂ simulation, in which all schemes respond to the forcing, we use simulations in which (a) only the biochemistry scheme sees the rising CO₂ concentration, and (b) in which rising CO₂ is only seen by the radiation scheme. With these simulations we examine the degree to which CO₂ effects are additive or non-linear when in combination. We also show regional differences in climate and vegetation response, highlighting areas of increased sensitivity.