Expected impacts of global warming – would certainly be very harmful and dangerous:
A large body of scientific studies, exhaustively reviewed, has produced a long list of possibilities of impacts of global warming. Nobody can say that any of the items on the list are certain to happen. But most of the climate experts agree that the impacts listed below are more likely to happen. The exact timings, for them, are difficult to predict, but they are in the opinion that, if humanity manages to begin restraining its emissions within the next few decades, so that greenhouse gases do not rise beyond twice the pre-industrial level (we are already 35% above it and rising each year, at an accelerating rate) the consequences would certainly be very dangerous - probably including a radical reorganization and impoverishment of many of the ecosystems that sustain our civilization. Expected impacts are:
(1) Most places will continue to get warmer, especially at night and in winter. The temperature change will benefit some regions, at least for a time, while harming others like, patterns of tourism will shift. The warmer winters will benefit health in some areas, but globally, mortality will rise due to summer heat waves and other effects.
(2) Sea levels will continue to rise for many centuries. The last time the planet was 3°C warmer than now, the sea level was roughly 5 meters higher. That submerged coastlines where many millions of people now live. Also, storm surges will cause emergencies.
(3) Weather patterns will keep changing, probably toward an intensified water cycle with stronger floods and droughts. Most regions that are now subject to droughts are expected to get drier (because of warming as well as less precipitation), and most wet regions will get wetter. Changes in extreme weather events are hard to predict, but in some regions storms with more intense rainfall are liable to bring worse floods. Mountain glaciers and winter snowcap will shrink, jeopardizing many water supply systems. Each of these changes has already begun to happen in some regions.
(4) Ecosystems will be stressed, although some managed agricultural and forestry systems will benefit, at least in the early decades of warming. Uncounted valuable species, especially in the Arctic, mountain areas, and tropical seas, must shift their ranges. Many that cannot will face extinction. A variety of pests and tropical diseases are expected to spread to warmed regions. Each of these problems has already been observed in numerous places.
(5) Increased carbon dioxide levels will affect biological systems independent of climate change. Some crops will be fertilized, as will some invasive weeds (the balance of benefit vs. harm is uncertain). The oceans will continue to become markedly more acidic, gravely endangering coral reefs, and probably harming fisheries and other marine life.
(6) There will be significant unforeseen impacts. Most of these will probably be harmful, since human and natural systems are well adapted to the present climate.