Today, the planet is warming up faster than ever before since it was created 4.54 billion years ago, and this is because of CO2 emissions produced by humans. Indeed, carbon dioxide has gone up from 280 parts per million (ppm) in 1800, to 415 nowadays. Because of that, the global average temperature in the same period has increased 1.2 °C, reaching 15.5 °C, and it is very likely that the planet will warm up another 2 °C by 2100, as the atmosphere will reach 1000 ppm.
Despite that the US and Europe's greenhouse emissions have diminished since the 90s, the global ones are set to continue climbing for many more decades to come. This, because countries like China, India and the rest of the Global South are catching up with industrialization by using fossil fuels, which are still more accessible for them than renewable energies.
Natural changes in the temperature and CO2 concentrations in the atmosphere take millions of years for getting to the actual levels, and this is one of the many proofs that the current climate change is human-made. Certainly, the last 10 years on the planet have been by far the warmest since records began in late 19th century, and the ice sheet at the poles is at its minimum.
It is important to notice that the warmest epoch since the dinosaurs went extinct has been the Paleocene, between 57 and 55 million years ago. By then, the average temperature of the planet was around 27 °C, and the greenhouse gas carbon dioxide concentration level was 3,000 ppm. Crocodiles were living in the Arctic, Alaska had palm trees, and the average maximum temperature around the equator was 50 °C.
What would the earth look like then if it warms up 3 °C from pre-industrial levels?
Modeling the climate is extremely complicated, but we can say with almost 100% certainty that sea levels will rise 50 cm by 2100, heatwaves will be much more frequent, and the acidification of the oceans will increase.
Then, there are other effects which nobody can tell really how negative they will be:
With a warmer planet, moisture would be greater in the air resulting from the evaporation of the seas, increasing the probability of rainfalls. But with higher temperatures, it is also true that some regions would suffer desertification. So the overall result is very unknown.
Similarly, it is possible that a warmer planet will just diminish the difference of temperatures between seasons, because with a higher humidity, it will be the winters that will experience a bigger temperature change, not the summers.
Moreover, contrary to the mainstream perception, the satellites of NASA have provided the following evidence:
The land surface in the world that has been affected by fires has diminished steadily since the 80s, despite that vegetated area (forests, grass, tundra and shrub) has increased since then. As for the number of hurricanes in the world, their occurrence has been constant since the 70s with a very small increase in intensity.
At the same time, the amount of people that have perished in natural disasters has decreased sharply in the last 100 years, greatly because of improvements in readiness in societies. Additionally, there are 9 times more people that die from cold than from heat in the world, and 650,000 fewer people have died from these temperature exposures in the last 20 years compared to the period 1980-2000.
Taking into account all these facts, it is possible to say the following:
It is much better to have a stable climate resulting from reducing the emissions of greenhouse gasses in the world. Nevertheless, it would be exaggerated to portray a global average temperature of 18 °C by 2100 as "the end of the world". It is true, however, that by leaving behind fossil fuels as a main source of energy, fewer people would die of pollution and the incentives for governments to become more democratic will be high, as the economy will not depend on extractive methods.
Finally, it seems that the world is following a natural transformation on becoming more clean. Without doubt, this will have a big impact on reducing greenhouse emissions without needing to establish radical measures that would hurt the development of societies around the world. But it is also true that this might not be enough, and that stronger measures would be needed to limit the negative impacts of climate change.