Do the math. 0.07 times 17 = 1.2 — not very different to the claims of climate scientists warning about the effect of this amount of warming. If it is “too small to measure” that counters your own argument. Either it is 0.07 per decade (or something else) or it is too small to have been measured (by you or anyone else).
By the way, do you know what causes the el Nino? Could it perhaps be an effect, rather than a cause, of the “too small to measure” temperature change?