We present a combined tomographic weak gravitational lensing analysis of the
Kilo Degree Survey (KV450) and the Dark Energy Survey (DES-Y1). We homogenize
the analysis of these two public cosmic shear datasets by adopting consistent
priors and modeling of nonlinear scales, and determine new redshift
distributions for DES-Y1 based on deep public spectroscopic surveys. Adopting
these revised redshifts results in a 0.8σ reduction in the DES-inferred
value for S8​, which decreases to a 0.5σ reduction when including a
systematic redshift calibration error model from mock DES data based on the
MICE2 simulation. The combined KV450 + DES-Y1 constraint on S8​=0.762−0.024+0.025​ is in tension with the Planck 2018 constraint from the
cosmic microwave background at the level of 2.5σ. This result highlights
the importance of developing methods to provide accurate redshift calibration
for current and future weak lensing surveys.Comment: 8 pages, 4 figures, new appendix added including a simulated
analysis, version accepted for publication by A&A Letters, chains can be
found at https://github.com/sjoudaki/kidsde