How do we know the air is getting warmer? The evidence is very strong.
The 2001-2010 decade is the warmest since 1880—the year when enough temperature records became available worldwide to calculate a global average.
Over the last 50 years, the number of cold days and record low temperatures in various locations has declined, while the number of hot days and heat waves has risen most places worldwide.
The best projections show that average global temperatures are likely to increase 3.1-7.2° F (1.8-4.0° C) by the end of the century depending on the amount of carbon emissions.