What would happen if Earth lost it's tilt and just stood vertical?
We must be assume that this change in the earth's orbital axis is a thought experiment. The earth can be thought of as a gigantic gyroscope, spinning at over 1000 miles per hour at its equator. If its axis were to be suddenly shifted from its normal inclination, inertial forces produced in such a change would literally tear the earth apart.
That aside, if the rotational axis of the earth were perpendicular to the plane of the ecliptic (the plane that passes through the earth's orbit), several dramatic differences would appear. First would be that the length of day and night would be exactly equal, over the whole planet. There would be no seasons, just one average of the current four. Weather patterns would be very different; much more uniform.
These and other changes in the oceans and atmosphere would result in tremendous and unpredictable changes in conditions on the earth's surface including shifts in the oceans' levels and changes in the location and extent of arid as well as tropical areas.
Scott Wilber, President, ComScire - Quantum World Corporation