Observed warming over northern South America has an anthropogenic origin
We investigate whether the recently observed trends in daily maximum and minimum near-surface air temperature (Tmax and Tmin, respectively) over South America (SA) are consistent with the simulated response of Tmin and Tmax to anthropogenic forcing. Results indicate that the recently observed warming in the dry seasons is well beyond the range of natural (internal) variability. In the wet season the natural modes of variability explain a substantial portion of Tmin and Tmax variability. We demonstrate that the large-scale component of greenhouse gas (GHG) forcing is detectable in dry-seasonal warming. However, none of the global and regional climate change projections reproduce the observed warming of up to 0.6 K/Decade in Tmax in 1983–2012 over northern SA during the austral spring (SON). Thus, besides the global manifestation of GHG forcing, other external drivers have an imprint. Using aerosols-only forcing simulations, our results provide evidence that anthropogenic aerosols also have a detectable influence in SON and that the indirect effect of aerosols on cloud’s lifetime is more compatible with the observed record. In addition, there is an increasing trend in the observed incoming solar radiation over northern SA in SON, which is larger than expected from natural (internal) variability alone. We further show that in the dry seasons the spread of projected trends based on the RCP4.5 scenario derived from 30 CMIP5 models encompasses the observed area-averaged trends in Tmin and Tmax. This may imply that the observed excessive warming in the dry seasons serve as an illustration of plausible future expected change in the region.
We acknowledge the support provided by the US National Science Foundation AGS-1547899. We further acknowledge the Cluster of Excellence ‘CliSAP’ (EXC177), Universität Hamburg, funded through the German Science Foundation (DFG). Data used in this paper are available from the corresponding author (firstname.lastname@example.org) upon request.
- Blázquez J, Nestor-Nuñez M, Kusunoki S (2012) Climate projections and uncertainties over South America from MRI/JMA global model experiments. Atmos Clim Sci 2:381–400Google Scholar
- Forster P et al (2007) Changes in atmospheric constituents and in radiative forcing. In: Solomon S et al (eds) Climate change 2007: the physical science basis. Contribution to working group I to the fourth assessment report of the intergovernmental panel on climate change. Cambridge University Press, Cambridge, pp 129–234Google Scholar
- IPCC (2013) Climate change 2013: the physical science basis. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change. Cambridge University Press, Cambridge, p 1535Google Scholar
- Marengo JA, Chou SC, Kay G et al (2012) Development of regional future climate change scenarios in South America using the eta CPTEC/HadCM3 climate change projections: climatology and regional analyses for the Amazon, São Francisco and the Paraná river basins. Clim Dyn 38:1829. https://doi.org/10.1007/s00382-011-1155-5 CrossRefGoogle Scholar
- Mariano GL, Mariano EVC, de Oliveira Am (2014) Aerosol optical depth over South America: the influence of biomass burning. In: Wang H (ed) Air pollution and pollutants. http://AcademyPublish.org, pp 74–89 (ISBN 978-1-941249-02-4)
- Meinshausen M, Smith SJ, Calvin KV, Daniel JS, Kainuma MLT, Lamarque J-F, Matsumoto K, Montzka SA, Raper S. C. B., Riahi K, Thomson AM, Velders GJM, van Vuuren D (2011) The RCP greenhouse gas concentrations and their extension from 1765 to 2300. Clim Change (special issue). https://doi.org/10.1007/s10584-011-0156-z Google Scholar
- Nuñez MN, Solman SA, Cabré MF (2009) Regional climate change experiments over Southern South America. II: climate change scenarios in the late twenty-first century. Clim Dyn 32(7–8):1081–1095. https://doi.org/10.1007/s00382-008-0449-8
- van der Werf GR, Randerson JT, Giglio L, Collatz GJ, Mu M, Kasibhatla PS, Morton DC, DeFries RS, Jin Y, van Leeuwen TT (2010) Global fire emissions and the contribution of deforestation, savanna, forest, agricultural, and peat fires (1997–2009). Atmos Chem Phys 10:11707–11735. https://doi.org/10.5194/acp-10-11707-2010 CrossRefGoogle Scholar