sentences: global warming is when worldwide temperature increases
docs: global_warming is heating. global_warming is temperature_change. worldwide_excess_of_carbon_dioxide has resulted_in_global_warming sunlight has effect_of_heating_earth world's_temperature is rising_unusually_fast. global_warming is weather. global_warming is effecting_weather. global_warming is heating_air. greenhouse_gases is causing_world's_temperature_to_rise. greenhouse_effect is weather.