Snow cover in the Rocky Mountains.
Photo: Sean Linehan, NOS/NGS
Changes in the polar regions are ate. Less ice and snow cover also means that less heat will
important to the rest of the world be used for melting, which will contribute to the warming
trend. In these ways, reduced ice and snow cover warms
In addition to receiving less sun radiation than temperate up polar regions and accelerates global warming. This is
and tropical regions, the polar regions are cold because ice an example of what scientists call positive feedback, a self-
and snow reflect most of the solar radiation back to space, reinforcing effect, in the climate system.
while open sea and bare ground absorb most of the solar
radiation as heat. When the ice and snow cover begin to Climate scientists call the changes in the external natu-
shrink because the climate is getting warmer, more solar ral and human-made factors that can explain the global
radiation tends to be absorbed, which in turn accelerates warming over the last 150 years “climate forcings” (see
the melting. This process develops slowly, but as more also Chapter 3). Forcing is measured in watts per square
and more bare ground and open sea are exposed, the metre of the Earth’s surface – in other words, the rate of
warming will increase and the snow melting will acceler- adding (warming) or subtracting (cooling) energy or heat
CHAPTER 2 WHY ARE ICE AND SNOW IMPORTANT TO US? 21