Doomsday scenarios will not come for at least 20 years. "The day after tomorrow" and all that other alarmist crap is decades away. The only way it would become an "endgame" scenario soon is if a workable industrialization model emerged for third world countries and was universally applied, exponentially increasing pollutants, and/or the population expansion keeps up and there is no workable pollution controls or dampeners applied.
In this scenario, especially in light of the current Chinese expansion, the acceleration of the saltiness of water near the equator and freshness of water near the poles would contribute to polar ice cap melting and flooding, making lowland areas in the US such as the water-heavy southern tip of Florida and several island nations unhabitable.
In the best case scenario of the most major report on Warming, 9 percent of land-based plants and animals face extinction by 2050. In the worst case scenario, between 35 to 50 percent of plants and animals could face extinction. Ocean stocks of large fish such as cod are already decreasing, with 1/3 of animals along the California coastline already endangered. This sort of decline in species will contribute to a further loss of diversity among food sources. Already in the ocean, coral life is being depleted, and plankton and kelp beds cover vast areas once full of biodiversity.
Eventually, this "farming out" will lead to a lower supply of food, as minerals consistently used to harvest food will deplete. China could use its diplomatic channels and possibly force to acquire the energy and freshwater resources of Russia, etc. As areas near the equator get hotter than is sustainable for human life, immigrants from Africa will flood Europe, Latin America flood America, etc. The entire Australian outback could expand in Area by 40% through force of climate...leading to unforseeable, inexplainable, and possibly catastrophic outcomes.
