According to “Global Risk Report(2019)” by the World Economic Forum,

The top threats that humanity will face over the next 10 years are: First, the climate change and Second, the failure to respond to climate change.
Global warming is an ongoing serious problem.

If the earth’s average temperature rises by 1˚C, the melting of Arctic glaciers accelerates, putting polar bears on the verge of extinction.
If it rises by 2˚C, the entire Greenland will melt down, inundating Miami and Manhattan, and hundreds of thousands of people will die from heat stroke.
If it rises by 3˚C, the Amazon forest will disappear.
If it rises by 4˚C, New York submerges from rising sea levels.
If it rises by 5˚C, all jungles will be burnt down and humans will be left with only a few habitable areas due to droughts and floods.
If it rises by 6˚C, 95% of living things will be extinct.

Earth’s temperature has already increased by 1˚C, and the fate of the cities is dependent on the remaining 1˚C.
Even if we can realize Paris Agreement to keep the temperature less than 2˚C compared to pre-industrial level, The above catastrophe is unavoidable.

The root cause of this climate crisis is the emission of carbon dioxide, or greenhouse gas.
To solve global warming, we need to reduce the amount of CO2 emission.