What is the scientific reason for the inclination of earth's rotation axis? This titled position of the earths axis is known as inclination of the earths axis.
The earth's rotation axis makes an angle of about 66.5 degrees with the plane of its orbit around the sun, or about 23.5 degrees from the perpendicular to the ecliptic plane
what is the scientific reason for the inclination of earth's rotation axis? 
and what will happen if the inclination angel changed?
 A: The truth is no one is certain why.  However, there seems to be no pattern in our solar system.  Even the sun has a slight tilt at about 7°.  The only planet with a near zero tilt is Mercury.  Compare that to Uranus which almost spins sideways at 97°.  As mentioned in the comments, collisions make a good case for all this randomness of angles, however, there has been no real way to observe this type of event as proof.
On the Internet you can find a variety of ideas from bizarre EM perturbations to the idea they are primordial and/or collision related.  There are some models/ideas that show this angle can be very chaotic and the moon plays a strong role in stabilizing the Earth. (Laskar, J.; Joutel, F.; Robutel, P. (1993). "Stabilization of the Earth's Obliquity by the Moon")
Based on  Berger, A.L. (1976). "Obliquity and Precession for the Last 5000000 Years": For the past 5 million years, Earth's obliquity has only varied between 22° 02' 33" and 24° 30' 16".  So whatever the cause it seems the Earth's angle is quite stable.
Without our 23° we wouldn't have seasons or longer nights and shorter days throughout the years.  The angle of obliquity also is a major driving factor for weather triggering massive releases of energy during times of tropical revolving storms (hurricanes) which effect the planet's heating and cooling cycle world wide.  The world that we have adapted to would be a very different place without our tilt.  In general less tilt would mean colder poles and hotter equator and more tilt would have more extreme seasons of hot and cold.  In either case the shift in growing seasons and belts would probably cause massive shift in food production, most likely in a bad way ... assuming the plants could survive the change too.
A: Some texts indicate that a large hunk of matter crashed into the earth and splashed to its orbit the material composing our moon. They also suggest this event could be one of the mean reasons for earth's axis tilt.
A: I believe it is this variation that affects our climate and this variation changes over time affecting the temperature in the extreme areas ie the poles
this angle varies by 2 to 3 degrees every 41000 years ie between ice ages and the other the extremes ie hotter because of the surface angle to the suns rays
at the moment we are mid way between an ice age and hot weather gradually getting hotter and we can do nothing about it , we have to get use to it , it is going to get hotter for the next 10000 years no matter what the so called academics think , by the way I have a friend who is an academic , he teaches brick laying at melbourne but I wouldn't
dream of asking him for an oplnion on this subject
Ron lee geelong.
A: The axial tilt, or obliquity, of a planet is a constantly (but slowly) changing thing. There is no one particular reason why a planet should have a particular axial tilt, but whatever the initial tilt is, eventually the tidal forces between moons, planets and the central star tend to cause obliquities to oscillate in a damped manner, eventually leading to a stabilized, equilibrium value.
If the angle changed, seasons would have a different character. If the obliquity was reduced, the seasons would become harder to differentiate between each other because winter wouldn't be as cold and summer wouldn't be as warm. The opposite would occur if the angle was larger.
It would be interesting to observe obliquities of extra-solar planets and perform some statistics on them. Unfortunately, this is rather difficult to do.
A: The tilt of the Earth relative to its orbit plane is definitely caused by a force: the evidence is that the tilt oscillates. Space is frictionless and so a force by a collision or a huge volcanic blast pushes the tilt in one direction and then the oscillation starts with the tile going to maximum in one direction and then back in the other direction, like a sinusoid.  Candidates for the force are:


*

*The huge cataclysmic volcanic blast at Mt. Toba in Sumatra 74,000 years ago;

*The break-away (or pull-away) of the moon mass from the Earth mass, perhaps a few billions of years ago

*The collision of a hugs asteroid with the Earth, such as the one that hit the Gulf of Mexico about 65 million years ago;

*Some other force.


So, the mystery remains unless someone can uncover data that supports such an event.
