can CO2 from fuel exhausts be pumped into in the sea. What´s his destiny?

The ocean is one of several banks for CO2, just as are trees. These banks can hold up to so much CO2 as permitted before it will not be able to hold anymore. The ocean is already absorbing less CO2 on its own for several reasons. One would be the stronger winds, allowing the ocean to absorb about 10% vs it before ability of 15%. Also the bank will soon reach its limit on how much CO2 it can hold and begin to release it back into the environment, it can also have a devastating effect on the wildlife in the ocean, such as the coral reefs (which like panda bears; need a very specific set of conditions to thrive).

There are several options that we have before us. One of the best possible solutions is to stop emitting so much CO2! But in the meantime we can use trees as a bank as well. Mangroves, the "super-scruber" of trees, is able to hold more CO2 then the other trees. If we were able to set back up previous Mangrove populations they can also work as an effective bank, as well as any other kind of forest. However as soon as these trees are cut down, the CO2 is released back into the atmosphere, hence deforestation is playing a problem to global warming ( and other reasons...).

CO2 is pumped into water routinely. Every bottle of soda is saturated with CO2. Most of it is released when the pressure is removed. Sea water contains massive amounts of CO2. The amount of CO2 that sea water will hold depends on its temperature, its pressure (at sea level and deeper),and perhaps many other things( e g salinity). The CO2 level in the Oceans always progresses toward equilibrium at all times. If CO2 were added to the sea without changing one of the parameters ( like atmospheric or temperature) controlling its equilibrium concentration, it would just out gas into the atmosphere and nothing ( except frivolous spending) would be the result.

Atmospheric CO2 is in equilibrium with the ocean, so pumping it into the ocean means that some will escape to the atmosphere just as pumping into the atmosphere means that some will be absorbed by the ocean. The best option is to use less fossil fuels rather than trying to find ways to make them less harmful.

That is certainly not an option. To start, fish and sea creatures breath via Oxygen (O2) just like you and I. Also, CO2 is a gaseous compound and would have to be condensed into a liquid.