Is the earth getting heavier or lighter

[hd_2005]

While reading the column “Is the earth getting heavier or lighter”
<http://www.straightdope.com/classics/a3_355.html&gt;
I was thinking about the relativistic mass increase due to sun light being absorbed
by the earth. A quick calculation using Einsteins relation E=mc^2 yields
for the mass equivalent of the annual solar radiation hitting the earth
m = E/(c^2) = q_s * r_e ^ 2 * pi * 3600 * 24 * 365s / c^2
Inserting q_s = 1.37kW/m^2 (solar irradiance), r_e=6378km (earth radius),
c=310^8m/s (velocity of light) I get (please correct me if I am wrong):
m = 61348394kg = 61348.4 t
I am surprised since this is the same order of magnitude as the weight gain
due to meteorites and dust. Of course, most of the light is either reflected or
reemitted, so little weight change will actually occur. However, solar energy being
stored e.g. in plants or solar power stations will increase the mass, while stored
energy being turned into radiation (fires etc) will decrease the mass.
So “Net change pound-wise, nada” is probably wrong, but not by much.

[DSYoungEsq]

@hd_2005

While reading the column “Is the earth getting heavier or lighter”
<http://www.straightdope.com/classics/a3_355.html&gt;
I was thinking about the relativistic mass increase due to sun light being absorbed
by the earth. A quick calculation using Einsteins relation E=mc^2 yields
for the mass equivalent of the annual solar radiation hitting the earth
m = E/(c^2) = q_s * r_e ^ 2 * pi * 3600 * 24 * 365s / c^2
Inserting q_s = 1.37kW/m^2 (solar irradiance), r_e=6378km (earth radius),
c=310^8m/s (velocity of light) I get (please correct me if I am wrong):
m = 61348394kg = 61348.4 t
I am surprised since this is the same order of magnitude as the weight gain
due to meteorites and dust. Of course, most of the light is either reflected or
reemitted, so little weight change will actually occur. However, solar energy being
stored e.g. in plants or solar power stations will increase the mass, while stored
energy being turned into radiation (fires etc) will decrease the mass.
So “Net change pound-wise, nada” is probably wrong, but not by much.

Here is a link that works.. Welcome to the SDMB, and hope you enjoy your stay.

The Earth’s mass wouldn’t be increasins from the input of solar radiation unless there was an ever increasing amount of such radiation being stored. If the Earth is in a steady state, where the radiated energy is equivalent to the absorbed energy, then the net gain at any point would be zero. I’ll let those who know such things better than I do offer expert opinion on the subject (Chronos?), but it seems to me that, if the Earth were retaining a net increase in solar radiation, we’d be getting warmer every year.

Oh, wait…

[Chronos]

I’ll let those who know such things better than I do offer expert opinion on the subject (Chronos?)

No need; you’re correct. Even with global warming, the Earth is approximately in a steady state, with (almost) all of the energy absorbed from the Sun getting eventually re-emitted.

That said, though, the kind of pedantic nitpicker who would raise the point in the first place is exactly the sort who will fit in just fine around here.

[Lewis]

I thought the earth only weighed 146lbs??? I mean it may be different for you guys, but that’s what my calculations show…
you people should know the difference between mass and weight