The global ruling classes refuse to give up the system which lays their golden eggs--capitalism. Thus, if we, the people, allow them to keep fouling our atmosphere with their polluting gases, the result as determined by scientific research will be an increase of 4 degrees Celsius in global warming by 2100. This assumes that gas emissions do not increase, a very dubious assumption.
But let's look at what the effects look like if only 4 degrees occur. David Spratt has summarized the findings from the Climate Action Centre:
* The world would be warmer than during any part of the period in which modern humans evolved, and the rate of climate change would be faster than any previously experienced by humans. The world's sixth mass extinction would be in full swing. In the oceans, acidification would have rendered many calcium-shelled organisms such as coral and many at the base of the ocean food chain artefacts of history. Ocean ecosystems and food chains would collapse.
* Half of the world would be uninhabitable. Likely population capacity: under one billion people. Whilst the loss will be exponential and bunch towards the end of the century, on average that is a million human global warming deaths every week, every year for the next 90 years. The security implications need no discussion
* Paleoclimatology tells us that the last time temperatures were 4C above pre-industrial (during the Oligocene 30 million years ago), there were no large ice-sheets on the planet and sea levels were 65–70 metres higher than today. Whilst ice sheets take time to lose mass, and the rise to 2100 may be only 1–2 metres (or possibly a couple more according to James Hansen), the world would be on the way to 65–70 metres.
* 3C may be the “tipping point” where global warming could be driven by positive feedbacks, leaving us powerless to intervene as planetary temperatures soared. James Hansen says warming has brought us to the "precipice of a great tipping point”. If we go over the edge, it will be a transition to “a different planet”, an environment far outside the range that has been experienced by humanity. There will be "no return within the lifetime of any generation that can be imagined, and the trip will exterminate a large fraction of species on the planet".