Suppose the Orbit of the Earth Were 5% Smaller (a = 0.95 au) than it is today (a = 1.0 au). What would happen??

We can certainly say that the average temp on the planet would be higher... which would in turn create many other differences.

... then we'd suppose tides would be different too. Even if the moon stayed it's current distance from us, then the sun's gravitational pull would be stronger.

These are just what I could come up with off the top of my head. I bet there'd be other changes/differences also.

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Originally Posted by arabgal

Suppose the Orbit of the Earth Were 5% Smaller (a = 0.95 au) than it is today (a = 1.0 au). What would happen????

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The positions of orbits of all planets is fixed by a pattern based on harmonics synchronisation. You can not have one planet only moving 5%.
The observed pattern is :
0.4 AU - Mercury
0.7 AU - Venus
1.0 AU - Earth
1.5 AU - Mars
2.3 to 3.3 AU - Asteroid Belt (position for a never formed planet due to Jupiter influence)
5.2 AU - Jupiter
9.5 AU - Saturn
19.6 AU- Uranus
30.0 AU- Neptune
.
But ASSUMING it would be possible to move the orbit of planet earth 5% nearer to the sun, the results would be an increase of incoming solar energy by about 7%. Deadly for nature as we know it, as it would raise the earth surface temperature with over 7% - on top of the already rising temperature due to pollution effects.
;)

Suppose the Orbit of the Earth were 5% larger (a=1.05au) today than it was yesterday when a=1.0 au. What would be different in life?

If it was 5% larger diameter, I believe the surface of the Earth would be raised over 3700 Miles, Way taller than Everest, Likely much colder, Tides would not be a problem as the water would be frozen.
Also to consider that the Lower Atomsphere would be at the new elevation and may be normal as now.
If I had a Sun and some Planets to experiment with, I could come up with a better answer?
Wonder if someone is able to provide a more accurate guess/answer.

Stratmando - he asked about earth's orbit being 5% larger, not the earth's diameter. The effect of the earth's diameter being 5% larger really depends on whether you assume the earth's density remains the same as today - in which case the earth's gravity at sea level would be greater than it is today - or if you assume the earth's mass remains the same - in which case the density would be less and gravity at the earth's surface would also be less.

Kreck - see RickJ's earlier answer - that should help you think it through what happens if the earth's orbit is changed. One thing I would add is that the length of the year would be longer - for circular orbits the period of orbit squared is proportional to the radius of the orbit cubed. So the year would be about 7.6% longer than the current year, or about 27 days longer. And since the radiative heating of a body is inversely proportional to the square of the distance you can see that average temperatures would be lower as well - by about 10% on the kelvin scale. That equates to average temps worldwide below freezing.