Answer:
Global warming has been identified as a major issue for the global community. More properly this is called "Global Climate Change" as some areas may be warmer, some cooler, some wetter, some drier...
Background:
The contention of the larger number of climatologists is that human activities since the industrial revolution have increased the content of CO2, methane and other gases in the atmosphere that trap solar heat. At the same time human activities have reduced the forest cover that had traditionally absorbed these same materials. They state that an increasing level of these atmospheric constituents has lead to a chain of chemical and physical changes that have increased the world's average temperature.
Observations of atmospheric gas composition, average sea water temperatures, atmospheric temperatures etc. confirm the trends and support the proposition.
Potential Impacts:
1. The sea levels may rise. Technically this may be caused by melting ice from the polar ice caps or an increase in sea height as the less dense water is less compressed. Low lying land like many Pacific Islands and Miami will be under water.
2. Serious climate changes may result from diverted ocean currents. As an example, the Gulf Stream keeps Europe warm. If the Stream is not running Europe may be much cooler and drier. Crops may not grow.
3. Ecology changes on the land could include species of animals and plants extending their range to the polar regions. Local flora and fauna may become extinct. A good example is the spread of Africanized bees and Fire Ants. Sea life may also be impacted both through the introduction of competitive species presently kept in other areas by water temperature changes, and by failure to adapt to less saline water.
4. Human society may be disrupted if changes in rainfall and temperature cause crop failure. Famine refugees may require significant humanitarian attention by the "lucky" nations.
Conflicting opinions?
Yes indeed, some people don't agree!
However, the problem breaks down into two potential scenarios. Either there is a basis for fear about climate change, or, there isn't.
If Climate Change isn't real and we do nothing - good! Except of course many of the problems that science has identified and blamed as causing Climate Change are just plain wastes of resources, and inefficient and uneconomical practices that should be addressed anyway. A polluted, climatically steady world with no fish and no oil will be no fun at all.
If Climate Change is not real and we do all the things that we should - reduce emissions, cut fuel use, re-establish forests - we're out money (maybe) but in general the world is a better and more sustainable place.
If Climate Change is real and we do nothing - we are dead or at least very miserable.
If Climate Change is real and we work to correct all our bad habits we might still be in trouble ... if it's too little and too late, but we'll go down fighting. If we succeed we live.
An afterthought:
Comments to this original post stated:
If these writers are right ... Wahoo!
However, no case in the summary of potential future scenarios which is based on us sitting around doing nothing at all has a cheery outcome.