Wikipedia says:
Global warming is the observed increase in the average temperature of the Earth's near-surface air and oceans in recent decades and its projected continuation.
Global average air temperature near Earth's surface rose 0.74 ± 0.18 °Celsius (1.3 ± 0.32 °Fahrenheit) in the last century. The Intergovernmental Panel on Climate Change (IPCC) concludes, "most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations,"[1] which leads to warming of the surface and lower atmosphere by increasing the greenhouse effect. Other phenomena such as solar variation and volcanoes have had smaller but non-negligible effects on global mean temperature since 1950.[2] While this conclusion has been endorsed by numerous scientific societies and academies of science, a few scientists disagree about the primary causes of the observed warming.
An increase in global temperatures can cause other changes in turn, including a rising sea level and changes in the amount and pattern of precipitation. There may also be increases in the frequency and intensity of extreme weather events, though it is difficult to connect specific events to global warming. Other consequences include changes in agricultural yields, glacier retreat, reduced summer streamflows, species extinctions and increases in the ranges of disease vectors.
Larry West writes:
Along with posing serious future threats to human health, global warming currently contributes to more than 150,000 deaths and 5 million illnesses every year, according to the World Health Organization and the University of Wisconsin at Madison. And those numbers could double by 2030 as global warming accelerates the spread of infectious diseases, increases malnutrition, and accounts for more heat waves and floods.
Research data published in the journal Nature show that global warming may affect human health in a surprising number of ways: speeding the spread of infectious diseases such as malaria and dengue fever; creating conditions that lead to potentially fatal malnutrition and diarrhea; and increasing the likelihood of heat waves and floods.
If to think properly, our healthy life depends on our actions. We tend to be careless to it in many ways though.
