Well Yellowtail, sometimes a short question demands a long answer, it comes here ????
I know my answe goes a litte further than your Why
According to scientist at Nasa.org and others. From the moment we stop the high emitting of CO2 into the atmosphere it will take between 300 and 1000 years before it is naturally gone. Yes, I know there are some there claim only between 50 and 300 years. But still a long time.
Why will it take so long? Because CO2 disappear from the atmosphere when some minerals naturally react with CO2, and turning carbon dioxide from a gas into a solid. This process is commonly referred to as “carbon mineralization” and it naturally happens very very slowly.
Also, the oceans will slowly dissolve some of CO2 besides the 25% it already dissolves every year. But here is a risk factor because the Ocean produces about 60 - 70 % og our oxygen from alger and plankton etc,, and is essential for life. It is not only us humans who consume oxygen, so does the animal world, not to forget that burning fossil fuels consumes oxygen, all forms of burning do. (So, when farmers in Thailand, Laos, Myanmar etc. set the countries on fire, they kill our oxygen and even worse, people dies because smoke ruins their lungs.) Our oxygen level in the atmosphere is normally 21%, but according to Forbes.com it’s slowly decreasing. The critical level for humans is 19.5%
Should also mentioned that ice cores from the Greenland ice sheet shows that present CO2 level ppm 420 has not been recorded for the past 800.000 years. However, an ice sample from the Vostok core shows 298.6 ppm and that happens 330.000 years ago.
Every year the world's oceans absorb approximately ¼ of all the CO2 we emit. We know it's on the ocean floor, and we know the average pH of the ocean is about 8.1, but as the ocean continues to absorb more and more CO2, the pH drops and the ocean becomes more acidic, and over time it will harm life in the oceans it has already an effect on our beautiful corals.
Another problem is Plastic pollution in the Oceans. It’s a danger not only to the animals in the oceans but also to the marine bacteria that are vital for the world's oxygen supply, states ARC, the Australian Research Council, in a news article. A research team has proven that plastic leaches several chemical additives into marine environments, which affect, among other things, the bacteria that produce oxygen.
A lot of our CO2 could have been absorbed by rainforests, if it weren't for the fact that money rule the world and deforestation of rainforests, including the Amazon, continues.
Other dangers are
Our entire ecosystem is so finely tuned, but also fragile when we change the balance. Examples of this are The Gulf Stream and the Monsoon. The gulf stream sends water in two directions, warm water is sent on the surface northwards from the Gulf of Mexico, and this gives North America and Northern Europe a milder climate. Cold water is sent back along the bottom. The Gulf Stream also influences our weather system. According to sciencedaily.com, it has already lost 15% of its strength because the sea temperature in the arctic area has risen, and the Greenland ice sheet is melting at a rapid pace. The fresh water no longer sinks all the way to the bottom and thus contributes to destroying the natural pumping function which sends cold water southwards. No one knows how much the Gulf Stream can tolerate losing in strength before it collapses. If that happens it can cause chain reactions that no one has an overview of. We don’t know if it will affect the Monsoon's rain. But we do know India and the whole of Southeast Asia are dependent on the Monsoon.
The understanding of the enormous problems that lie ahead does not seem to be present among the politicians, especially not in the countries that pollute the most.