2. * Why change the Earth's climate?
Climate change is complex, there are several dynamics at play.
One important factor may be the relationship between the Earth
and the Sun
If the Earth were not tilted, there would be no seasons and day
and night would be the same length all year. The amount of
solar energy reaching a particular place on Earth would be
constant throughout the year. But Earth is inclined at an angle
of 23.5 °. When it is summer in the Northern Hemisphere, which
begins in June, latitudes receive more sunlight than the
Southern Hemisphere. The days are longer and the sun angle
is higher. Meanwhile, in the Southern Hemisphere's winter. The
days are shorter and the sun angle is lower.

3. The second factor is the Milankovitch studied Earth's orbit
around the sun is not quite circular. The Earth is a bit closer to
the sun at certain times of the year than others. It receives a
little more solar energy when the Earth and Sun are closest
(perihelion) than when they are further away (aphelion).
But the shape of Earth's orbit also changes in cycles of between
90,000 and 100,000 years. There are times when it is more
elliptical than now, so that the difference of solar radiation
received at perihelion and aphelion is greater.
Perihelion presently occurs in January to aphelion in July. This
allows the Northern Hemisphere stations are slightly less
intense because the additional heating effect is in winter. In the
Southern Hemisphere, the seasons are a little more intense
than if the Earth's orbit around the Sun were circular.

4. Aún cuando los inviernos puedan ser menos crudos, seguirán
siendo lo suficientemente fríos como para que nieve en áreas
lejanas al ecuador. Y si los veranos son más frescos, es posible
que la nieve del invierno en esas latitudes elevadas no se
derrita tan fácilmente. La nieve se acumulará año tras año
formando glaciares.
Comparada con el agua y la tierra, la nieve refleja más energía
solar en el espacio, causando un enfriamiento adicional. En
este punto, se pone en juego un mecanismo de re-
alimentación positiva. El descenso de temperatura provoca
mayor acumulación de nieve y crecimiento de los glaciares.
Esto aumenta aún más la reflexión, de modo que la
temperatura disminuye más y así sucesivamente. Es posible
que las edades de hielo hayan comenzado de esta manera.