Once upon a time Mars had liquid water oceans and a thicker atmosphere.  As the years go on we are unlocking the many secrets of Mars.  Could we thicken the Martian atmosphere again and melt the water ice that is locked in the poles and under ground to make Mars more like Earth?  

Present Day Similarities

There are several things that occur on Mars that almost seem Earth like.  

Clouds On Mars

Frost On Mars

Water On Mars

Dust Devil On Mars

Another similarity that can't really be shown visually is that the interior is molten, based on how easily the Sun's gravity distorts the planet's shape, but no one knew whether it is completely liquid, or whether there is a solid inner core like Earth's. In a lot of respects it seems like Mars is a lot like an Earth desert environment.  In reality there are still a lot of differences that would be extremely hard to overcome in trying to make Mars enough like Earth to walk around on the surface without spacesuits and grow plants outside on the surface of Mars.  

What Would Need To Happen 

The main things that need to happen is for the planet to warm up so a large amount of the water ice melts and more carbon dioxide is released into the atmosphere so it would thicken up.  This would theoretically cause the greenhouse effect and continue to warm the surface even more.  

The Problems

1. There is no magnetic field on Mars. This is believed to be one of the main reasons that the atmosphere was largely stripped away in the past.  Here on Earth our magnetic field forms the Van Allen Radiation belt which protects us from solar radiation. Even if the atmosphere started to thicken up on Mars it might be hard to keep it from being stripped away again without a magnetic field.
2. Time is not on our side. Even if you can start this process going it could take a thousand years or more for it to get to the point where people could walk around on the surface without space suits.  
3. The energy required to set this plan in motion would be unreal. Once you see the proposed methods to try to execute on this plan it will make more sense but just think about how much energy would be required to change an entire planet.  It wouldn't be as simple as doing a few things and starting a process in motion and waiting.  
4. Mars only has 38% of the gravity as Earth.  As far as the atmosphere is concerned that still should be enough for it to hold it in place.  Venus is basically the same mass as Earth and the atmosphere is 90 times that of Earths.  Mars' current atmosphere is less than 1% that of Earths. Where the gravity becomes a problem is with humans being on the surface for extended amounts of time.  We aren't sure of the effects of this. 

Proposed Methods of Transformation

1. Detonate thermonuclear weapons over the poles.  The amount of nuclear weapons required to do this I'm sure would be mind boggling.  You could probably set off all of the United States and Russia's nuclear weapons and it might not put a dent in the situation on a Martian global scale.  
2. Crash a planetoid from the outer solar system into Mars that has a lot of Ammonia.  Again Energy doesn't come from no where so our propulsion methods would have to be far more advanced than our current methods.  Can you imagine dislodging a small planet from the outer solar system and then flying it to Mars and smashing it into it.  Ammonia accelerates the greenhouse gas effect so that is the premise of that proposed method.  
3. Use orbital mirrors to heat up the surface.  This is an interesting concept to harness the power of the sun to warm the planet enough to melt the polar ice caps.  Again that is an enormous amount of energy that would need to be directed at the planet for an extended amount of time.  
4. Make the surface darker by spreading dark dust to collect more light.  This is interesting but it is hard to imagine being able to spread enough dark dust to make an impact on a global scale.  Possibly if the dark dust was only spread out over the poles and then the orbital mirrors were directed on the poles that would speed up the process.  Taking volcanic ash or dust from
   Earth seems like a tall order.  It could possibly be collected from the Martian moons Phobos and Deimos.  Those moons aren't that big though.  Phobos is only 14 miles in diameter and part of it is hollow.  So even if you crashed it into the planet and spread it out.  I don't see how it would be enough.  
5. Crash comets into the surface.  This would be a tall order to produce enough energy to move comments out of their orbital paths and direct them to Mars.  There is evidence that a comet crashed into Earth 28 Million years ago above Egypt and they predict that the heat produced at the surface was 3,632 degrees Fahrenheit. With this method you could get more water as well.  A major issue I see is that even if you had the technology to capture one comet that was on a near pass by Mars and steer it over to Mars I don't know if it would be enough to set the green house effect in motion.  

The Most Plausible Method In My Opinion 

With our current technology detonating thermonuclear weapons over the poles would be the quick and dirty way of at least testing the theory.  If they did that they could then test temperature levels and compare that with previous data.  It could take a lot of them to even give any effect what so ever though.  

Even testing this method could be damaging if at that point we already have a Martian colony on the surface.  Imagine the nuclear fallout blowing all over the planet in the large dust storms that Mars has.  

Is The Planet To Much of A Fixer Upper?  

It seems like Mars used to be awesome!  Just like this house.  Are we going to try to repair it?  

The planet doesn't have a magnet field at this current time which I see as a major issue for keeping an atmosphere and for even having people on the surface without getting heavy doses of radiation each day.  

The energy required to do any of the proposed plans is astronomical.  

Personally I feel like the biggest limiting factor is the time constraint.  

If it is going to take 1000+ years for this process to take place and the methods of accomplishing it would be so advanced I would assume that we would have the ability to travel to the nearest star systems in a generation or less. 

Final Thoughts  

A lot of things will become possible in the future.  It is hard telling what we will be capable of so I can't rule out the possiblity that it could become feasible to terraform Mars.  As of right now it is hard for me to imagine because how bad does Earth have to get to want to change an entire planet that has very little signs of liquid water, no magnetic field, no plants, and no known biology? 

I personally can imagine Martian colonies surviving there under the surface but to actually transform the entire planet to where humans could walk around and plant crops on the surface is hard for me to imagine.  The energy that it would require and the precise situation that would have to be achieved seems hard to imagine.  

I feel like we would be better off concentrating on interstellar travel rather than terraforming Mars.  Mars is a good place for a human colony but it isn't Earth 2.0.  

If you want to read my post on utilizing lasers for Interstellar travel here is the link.  

https://steemit.com/space/@brianphobos/lasers-could-get-us-to-the-nearest-star-systems-20-years-and-mars-3-days

If you want to read an amazingly good article by @alexbeyman about interstellar travel utilizing nuclear bombs here is the link.

https://steemit.com/space/@alexbeyman/project-orion-the-starship-propelled-by-nuclear-bombs