Research ArticleCLIMATOLOGY

Human-induced changes in the distribution of rainfall

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Science Advances  31 May 2017:
Vol. 3, no. 5, e1600871
DOI: 10.1126/sciadv.1600871

Figures

  • Fig. 1 Dependence of tropical focusing of rainfall on Earth temperature as determined using an ensemble of general circulation models.

    Map depicts regions that will get wetter (green and blue shades) and drier (brown shades) as the planet warms. The figure is reproduced with permissions from Figure SPM.7 in the Intergovernmental Panel on Climate Change AR5 Report [Summary for Policy Makers, pg. 12 (95)] and is based on the approach of Held and Soden (1). Data are from the ensemble average of the Coupled Model Intercomparison Project Phase 5 (CMIP5)/Intergovernmental Panel on Climate Change (IPCC) RCP 8.5 modeling results (95).

  • Fig. 2 Globally distributed temperature trends for the period CE 1951 to CE 2015.

    Left: Global map of temperature trends calculated for the period CE 1951 to CE 2015. Right: Zonally averaged temperature trends. The northern middle and high latitudes have warmed roughly twice as much as corresponding southern latitudes over the past half-century or so. Plots are based on the GISTEMP (Goddard Institute for Space Studies Surface Temperature Analysis) Reanalysis data set (96, 97).

  • Fig. 3 Seasonal shift of Earth’s rain belts.

    (A) Map illustrates the global seasonal precipitation anomaly [June-July-August (JJA) precipitation minus December-January-February (DJF) precipitation]. Red shades depict the position of the rain belts in the boreal summer, and blue shades indicate the position in the austral summer. (B) Plot of zonally averaged precipitation for JJA (red curve) and DJF (blue curve). Note the southward shift of the precipitation maximum that occurs between boreal summer and winter. Plots are based on data averaged over the period CE 1979 to CE 2015 from NASA Modern Era Retrospective Analysis for Research and Applications (MERRA) (98).

  • Fig. 4 Composite showing LGM (blue) and Late Holocene (red) extents of Lakes Lahontan, Lake Bonneville, the Dead Sea, and Lago Cari-Laufquen.

    These four closed-basin lakes (two in the Great Basin of the western United States, one in Israel-Jordan, and one in Argentina’s Patagonian drylands) were much larger during the LGM compared with the late Holocene (red) (46). This difference reflects generally wetter conditions in the subtropics and middle latitudes during planetary cold episodes, partially at the expense of the drier tropics (1).

  • Fig. 5 Pattern of global warming predicted for the decade 2040 to 2050.

    Map shows the temperature anomaly calculated from subtracting the average temperature of the past decade (that is, CE 2006 to CE 2016) from that predicted for CE 2040 to CE 2050. By this analysis, the differential heating of the hemispheres is predicted to continue for at least the next half-century. Plots are based on results for the ensemble average of the CMIP5/IPCC RCP 8.5 modeling results (99, 100).

  • Fig. 6 Evidence in support of a northward shift in the location of the Amazonian rain belt 14.6 ky ago.

    (A) Drop in reflectance of sediments in the Cariaco Basin caused by an increase in rainfall in Venezuela (34). B-A, Bølling-Allerød. (B) A drop in the ratio of soil debris to marine calcite in a sediment core suggests a decrease in rainfall in eastern Brazil (35). (C) A lake in the southern portion of Bolivia’s Altiplano three times the size of today’s Titicaca dried up at about this time (17, 36). (D) The cessation of a brief episode of stalagmite growth in eastern Brazil indicates a switch to dry conditions (19). It is interesting to note that at the time of this drop in Brazilian rainfall, the Chinese monsoons were becoming stronger (51).

  • Fig. 7 Chinese Cave 18O record.

    Composite oxygen isotope record for Chinese stalagmites for the last 200 ky (above) and for the period 10 to 18 ky ago (below) (49). On the long term, the record follows Northern Hemisphere summer insolation; the higher the insolation, the greater the 18O deficiency. On the short term, 18O follows jumps in the latitude of the thermal equator. Note that 14.7 ky ago [the beginning of the Mystery Interval (MI)], the 18O-to-16O ratio began a steep rise, marking a strengthening of the monsoons. YD, Younger Dryas.

  • Fig. 8 Atmospheric 18O of O2 record.

    Shown in blue is the deconvolved record of the oxygen isotope composition of the O2 contained in polar ice, also considered the change in land fractionation (57). This deconvolution takes into account the residence time of O2 in the atmosphere (~1000 years). This reconstruction of the globally averaged isotopic composition of O2 is markedly similar to that for Chinese stalagmites shown above in purple [a composite record compiled from multiple caves (49, 51, 101)].

  • Fig. 9 Schematic map depicting seasonal shift of tropical rain belts and mid-latitude storm tracks.

    Evidence from the paleoclimate record teaches us that these rain belts shifted toward the north during the Bølling warming, in which the Northern Hemisphere warmed faster than the Southern Hemisphere, and to the south during the LIA, when the Northern Hemisphere experienced a greater magnitude of cooling than the Southern Hemisphere. Red, JJA rainfall; blue, DJF rainfall. Sites discussed in the text are plotted as blue-filled (wet) and tan-filled (dry) circles (Bølling) and triangles (LIA). SPCZ, South Pacific convergence zone; T.E., thermal equator.

  • Fig. 10 LIA isotopic records for the past 1300 years from Chinese stalagmites [33°N (102)] and from Peruvian lacustrine carbonate sediments [11°S (103, 104)].

    Note that the scales are in the opposite sense (that is, more negative is up for China and down for Peru). During the LIA, 18O ratios recorded in China became less negative and those in Peru became more negative. This is consistent with a southward shift in the latitude of the thermal equator. The figure is adapted with permissions from Broecker and Putnam (33). VPDB, Vienna Pee Dee belemnite; AM, Australian monsoon; SASM, South Asian summer monsoon.

  • Fig. 11 The seasonal expression of global warming trends since CE 1951.

    Gridded temperature trends (left) and zonally averaged temperature trends (right) for the boreal winter (December-January-February) (A) and summer (June-July-August) (B) seasons, calculated for the period spanning CE 1951 to CE 2015. Plots are based on GISTEMP Reanalysis data set (96, 97). The interhemispheric temperature contrast appears to be a December-January-February phenomenon.

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