We investigate interstellar extinction curve variations toward \sim 4 deg ^ { 2 } of the inner Milky Way in VIJK _ { s } photometry from the OGLE-III and VVV surveys , with supporting evidence from diffuse interstellar bands and F 435 W,F 625 W photometry .
We obtain independent measurements toward \sim 2,000 sightlines of A _ { I } , E ( V - I ) , E ( I - J ) , and E ( J - K _ { s } ) , with median precision and accuracy of 2 % .
We find that the variations in the extinction ratios A _ { I } / E ( V - I ) , E ( I - J ) / E ( V - I ) and E ( J - K _ { s } ) / E ( V - I ) are large ( exceeding 20 % ) , significant , and positively correlated , as expected .
However , both the mean values and the trends in these extinction ratios are drastically shifted from the predictions of Cardelli and Fitzpatrick , regardless of how R _ { V } is varied .
Furthermore , we demonstrate that variations in the shape of the extinction curve has at least two degrees of freedom , and not one ( e.g . R _ { V } ) , which we conform with a principal component analysis .
We derive a median value of < A _ { V } / A _ { Ks } > = 13.44 , which is \sim 60 % higher than the ‘ ‘ standard '' value .
We show that the Wesenheit magnitude W _ { I } = I - 1.61 ( I - J ) is relatively impervious to extinction curve variations .

Given that these extinction curves are linchpins of observational cosmology , and that it is generally assumed that R _ { V } variations correctly capture variations in the extinction curve , we argue that systematic errors in the distance ladder from studies of type Ia supernovae and Cepheids may have been underestimated .
Moreover , the reddening maps from the Planck experiment are shown to systematically overestimate dust extinction by \sim 100 % , and lack sensitivity to extinction curve variations .