You are absolutely right! We do experience large temperature changes not only on a daily basis, but also a yearly basis. These are normal seasonal changes that occur around the world. BUT, what your books are likely referring to is a 3.5° F average temperature increase on a global scale. Each year average temperatures are recorded for different areas around the world. What scientist’s are seeing is that these average temperatures are slowly increasing year by year. For example, say the average temperature of the North Pole recorded last year was 31.3° F, but this year the average temperature recorded was 31.4° F. This means that from last year, the average temperature of the North Pole has increased by 0.1° F. Now, imagine that average temperatures around the globe have increased by 0.1° F. What your books are suggesting is that if these average temperatures increase by not 0.1° F, but 3.5° F then the polar ice caps may be in great danger of melting!

Currently, the average global temperature of our Earth has increased by about 1.4° F since the late 1800’s!

First off, what the books are saying is incorrect. It would take 10+ degrees (Celsius) of warming around the Earth to melt the Antarctic ice sheet. Melting the Greenland ice sheet may be easier, though.

The other reason is that the warming isn't distributed over the Earth evenly. The Earth on average may warm up only three degrees, but it is one degree or less in the tropics, and ten degrees or more at the poles. The reason this happens is because of the heat-dissipating properties of warm water (it evaporates, condenses to form cloud, and then rains back to Earth, thus moving heat from the sea up to the stratosphere, from where it radiates into space).