OK...
First of all,
obliquity is axial tilt. This is what causes the seasons. We currently have something like a 22.4° axial tilt. The Earth's axial tilt varies between 22.1° and 24.5° with a 42,000 year cycle already. If we were to tilt 2 or three degrees more, we would simply have more slightly more changes between the seasons.
As for a vertical axis, I will assume you mean the equator is always in line with the sun. We would then have no seasonal changes as we perceive them today. Winters would be slightly warmer due to the
eccentricity of the earth. You see, in early January, the earth reaches it's closest point to the sun, 147,098,290 km. In early July, the earth is farthest from the sun, 152,098,232 km. The heat we receive from the sun follows the
inverse square law. The earth would then receive 6.9% more heat in the winter than the summer. This is significant and leads to relatively mild season changes in the northern hemisphere, and more dramatic season changes in the southern hemisphere. This is caused by the
axial precession the earth.
Eccentricity plays it's own special feature to Global warming, and I believe it to be the primary trigger for ice ages. The earth currently has an eccentricity of something like 0.0167, but varies from about 0.05 to almost 0. We are approaching zero eccentricity for the next 20some thousand years. The smaller the eccentricity, the warmer the earth will get.