Contrails are artificial clouds made by the exhaust of the aircraft engines, or the wingtip vortices
(http://en.wikipedia.org/wiki/Contrail). Contrails produced by the heavy air traffic over the US may have noticeable influences on the weather…

• Commercial air traffic were suspended for three days after the Sept. 11, 2001 attack. This provided a rare chance for the climate scientist to test their theory…
• Measurements show that without contrails the local difference of day and night-time temperatures was about 1 degree Celsius higher than immediately before the attack…

If Earth warms up a bit, then

• carbonate minerals form in the oceans at a higher rate.
• The rate at which the oceans dissolve CO₂ gas increases, pulling CO₂ out of the atmosphere.
• The reduced atmospheric CO₂ concentration leads to a weakened greenhouse effect that counteracts the initial warming and cools the planet back down.

If Earth cools a bit,

• carbonate minerals form more slowly in the oceans.
• The rate at which the oceans dissolve CO₂ gas decreases, allowing the CO₂ released by volcanism to build back up in the atmosphere.
• The increased CO₂ concentration strengthens the greenhouse effect and warms the planet back up