When Minnesota temperatures can change 30 degrees in a day, how can a change of just a couple degrees be a big deal?

It's important to recognize that weather and climate are related but they are different things. Daily temperature swings of tens of degrees at a given location are common weather-driven events. But when measurements of the daily high and low temperatures in many thousands of locations all over the world—on land and ocean—are examined for an entire year and then averaged together, the Earth's annual average temperatures from year to year are found to be very stable when the climate isn't changing. In a geological context, a 1.5°F (0.85°C) warming over a span of 100 years is an unusually large temperature change in a relatively short span of time and indicates that the climate is changing. This warming is important because it increases the probabilities of extreme weather and climate events.

If global warming were to stop now, its most potentially serious problems would be prevented. However, global warming is expected to continue at an increasing rate. In several decades our world is likely to become warmer than it's been for over a million years, with unpredictable consequences. It's also important to recognize that Earth is not warming uniformly, nor is it expected to. Middle and high latitudes in general change more than the tropics, and land surface temperatures change more than ocean temperatures. Over the long term, land masses at the latitude of the United States are expected to warm much more than the global average.

Reference: NOAA climate.gov