How much would 275 ZJ warm average ocean temperature?
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Re: https://sealevel.info/how_fast_are_the_oceans_warming_sciencemag_2019-01-11_perspective_measured_excerpt01.png

If that graph is correct then over 29 years the oceans gained
about 275 ZJ (zetajoules) of energy. So, what do you think that
means in terms that normal people can comprehend, like average
ocean temperature?

Volume of water in the oceans:
1,338,000,000 cubic-km = 1.338 × 10^9 km³ = = 1.338E9 km³

Seawater has an average density of about 1.029 (a bit less near
the surface) so 1.338E9 km³ of seawater weighs:
(1.029 × 1.338) × 10^9 Gt = 1.377E9 Gt

1 Gt = 10^12 kg = 1E12 kg, so the world's seawater masses:
1.377 × 1E9 Gt × (1E12 kg/Gt) = 1.377E21 kg

So, let's calculate how much energy it would take to heat that
amount of water by 1°C?

You probably know that one calorie of energy will raise one gram
of water by one degree Celsius.

So 1000 cal will raise one kg of water by 1°C.

1 cal = 4.184 J, so 4.184 × 10^3 J = 4.184E3 J will raise 1 kg
of water by 1°C.

So it would take 1.377E21 kg × 4.184E3 J/kg = 5.761E24 Joules
to raise the temperature of the oceans by an average of 1°C

1 ZJ = 10^21 = 1E21 joules, so 275 ZJ = 2.75E23 joules

So 275 ZJ of energy should raise the ocean temperature by an
average of (2.75E23 / 5.761E24) = 0.0477 °C, or about
1/20-th of a degree.

That's right, one-twentieth of a degree, in 29 years.

Is that supposed to be frightening?