Greenhouse Gas Induced Changes in the Seasonal Cycle of the Amazon Basin in Coupled Climate-Vegetation Regional Model

Abstract

Previous work suggests that changes in seasonality could lead to a 70% reduction in the extent of the Amazon rainforest. The primary cause of the dieback of the rainforest is a lengthening of the dry season due to a weakening of the large-scale tropical circulation. Here we examine these changes in the seasonal cycle. Under present day conditions the Amazon climate is characterized by a zonal separation of the dominance of the annual and semi-annual seasonal cycles. This behavior is strongly modified under greenhouse warming conditions, with the annual cycle becoming dominant throughout the Amazon basin, increasing differences between the dry and wet seasons. In particular, there are substantial changes in the annual cycle of temperature due to the increase in the temperature of the warmest month, but the lengthening of the dry season is believed to be particularly important for vegetation-climate feedbacks. Harmonic analysis performed to regional climate model simulations yields results that differ from the global climate model that it is forced from, with the regional model being more sensitive to changes in the seasonal cycle.

A modified seasonal cycle during MIS31 super-interglacial favors stronger interannual ENSO and monsoon variability

“…In all experiments, the CO 2 concentration was set to 325 ppm, which is based on boron isotopes in planktonic foraminifera shells for the MIS31 interval (Honisch et al, 2009). The MIS31 and CTR experiments have been described in further detail elsewhere by Justino et al (2017), but a brief discussion of the global climate differences between these two runs is provided below. Table 1 shows the global and hemispheric surface temperature values for the CTR and MIS31 simulations, and ERA-Interim (ERA-I; Dee et al, 2011) and HadCRUT4 for the 1980-2010 interval.…”

“…The Marine Isotope Stage 31 (MIS31; early Pleistocene 1085-1055 ka) is a key paleoclimate period to simulate and analyze the global environmental response to a significantly modified climate forcing (Lisiecki and Raymo, 2005;Yin and Berger, 2012). This interval was characterized by boreal summer temperatures that were several degrees greater than modern climate (up to 6 • C), with a substantial recession of the Northern Hemisphere (NH) sea ice (Melles et al, 2012;Justino et al, 2017). On long timescales, Earth's climate is primarily controlled by external and internal processes related to the astronomical forcing and the atmospheric concentration of greenhouse gases (IPCC, 2013;Erb et al, 2015).…”

“…Significantly modified periodicity and amplitude of past ENSO regimes, and their global influence, shed light on the potential effect of human-induced climate change on the equatorial Pacific, and consequently on future ENSO-like climate. Furthermore, it should be argued that disagreement in the magnitude of cooling or warming among coupled climate models and paleoreconstructions may be related to the local responses of temperature and precipitation elicited by distinct ENSO in both spatial and temporal variability (Peltier and Solheim, 2004;Jost et al, 2005;Yin and Berger, 2012;Dolan et al, 2015;Justino et al, 2017).…”

“…The ocean component has 31 vertical levels with layer thicknesses ranging from 10 m at the surface to 500 m at the ocean bottom (16 levels in the upper 200 m). Additional details on the ICTP-CGCM coupled model are discussed by Justino et al (2017). Farneti et al (2014) used the ICTP-CGCM to examine the interaction between the tropical and subtropical northern Pacific at decadal timescales, suggesting that extratropical atmospheric responses to tropical forcing feed back onto the ocean dynamics leading to a time-delayed response of the tropical oceans.…”

Response of South American Terrestrial Ecosystems to Future Patterns of Sea Surface Temperature

“…The response of South American vegetation to climate change may be particularly important, since this continent still contains the largest (but rapidly diminishing) continuous area of tropical rainforest [3]. There are several models that simulate the dynamic relationship between climate and vegetation at a macrogeographic scale [4][5][6][7][8][9]. These could be of great utility for climate modelers since, unlike many climate simulations, they consider the atmosphere and terrestrial biosphere as a coupled system with biogeophysical and biogeochemical processes occurring across a range of timescales [10].…”