There would be no seasons for one. Things like seasonal wind characteristics would change as well as various ocean cycles. The good thing is is that there would be no ozone hole or at least not to the extent it currently exists.
The earth is about 1 million miles closer to the sun in December than it is in July, which results in a 10% change of the amount of solar energy received over a 6 month period, which would result in some type of seasonal variation that would be buffered by the oceans and would be too complicated to predict the seasonal changes. However, Antarctica and Greenland would lose substantial amounts of ice which would result in much higher sea levels, perhaps hundreds of feet.
There would be hardly any seasons. Perhaps a slight warming at perihelion and a slight cooling at aphelion. Temperatures would still get colder towards the poles. I don't think we would see record highs or lows getting as extreme as they have. There would still be wind, although some patterns would be different without the seasonal cooling and warming. On any day at a given location there can be cooling at night and warming by day. The differential from that should decrease towards the poles, since at the poles the sun skims the horizon all day, every day, always the same. Elevation, terrain, presence or absence of water will vary, and so not every spot along a given latitude will warm or cool the same as others along that latitude.
Life can exist without seasons, but the exact development of it would be different.
There would still be seasons but seasonal variation would be much smaller than at present. Currently our seasons are dominated by obliquity but this isn’t the only factor.
If there was perpendicularity between the Equatorial and orbital axes, such that the orbital and rotational axes were the same, then seasonaility would be influenced primarily by the apsides of aphelion and perihelion.
Time wise the peak of summer would move to early January to coincide with perihelion, although the maximum warming would occur later in Jan and Feb due to the warming feedbacks (as happens with climates anyway). Winter would move to early July with Jul and Aug being the coldest months.
The magnitude of cooling in winter would be greater than the warming in summer, this is because at aphelion Earth is farther from the mean than it is at perihelion. This means that the onset of spring would be a slightly slower process than the onset of fall. These differences are small enough that they would go more or less un-noticed, they’d only really be evident in instrumental observations.
The greatest changes would be observed in the higher latitudes with the weather and climate becoming more equable all year round. There is already little seasonal variation in the Tropical regions so the effects here would be very small.
In terms of what it would mean for temps, the seasonal variation would be just over 1°C with mean winter global minima of approx 13.98°C and maxima of 15.09°C.
If obliquity remained at 0°C for thousands of years than the oceans and atmosphere would approach a state of temperature equilibrium, there would be very little in the way of temperature and pressure gradients and the global climates would be very much moderated and very similar.
There would be moderate rainfall all year round, winds would be gentler, there would be an absence of severe storms. The difference between day and night insolation would be the major contributor, this would drive short-term and localised weather. There would be a distinct absence of large weather events such as cyclonic and anti-cyclonic systems.
I agree with Trevor just from the plain fact of a elliptical orbit. That would explain seasons redefined. The shifts in non tilt would just relocate winds, bulging. and isolation.
no seasons
Instead of dark and frigid temperatures in the winter and warmer and constant sun in the summer, the polar areas would have much more uniform temperatures year round and the sun would always be low on the horizon.
There would be no changes in climate for different regions and no seasons.
The poles would be frozen. But whether or not their would be seasons would depend on the eccentricity of Earth's orbit. If Earth's orbit were perfectly circular as well, there would be no seasons. If it were as eccentric as that of Mercury or Pluto, we would get hot summers and cold winters, but such seasons would happen at the same time in both hemispheres.
The magnetic and geographical North Poles would be in the same place.
You could play pinball longer and score more points.
If Earth had zero tilt how would it effect the climate?
No seasons.
