In one microprocessor class back in university, a professor once declared “A cpu is a heater that happens to calculate”. The cpu in the computer or handphone you are using is a super duper transistor. Most cpus today consist of billions of transistors and is built around the same fundamental design of logic gates using transistors.
Transistors in an analogue circuit amplify input signals while transistors in a digital circuits make use of the cut-off behaviour of a transistor to act as a switch. In both cases, heat is unwittingly
Newer cpus are more “efficient” in that lesser heat is produced, i.e. lesser energy is required to compute while lesser energy is expended as heat.
All the appliances and devices we use, including the screen you are reading this on, dissipates heat. The heat must go somewhere and it does go somewhere. The environment.
The funny thing is that even the air-conditioners that cools down our rooms also generates heat. Back in August 2006, I wrote about how air-conditioners do not really produce ‘cold’ or that it is really a displacement of heat . This heat from the air-conditioners and all the other appliances must go some where as well. It dissipates to the air around, i.e. the atmosphere.
Now consider earth, with its atmosphere as the ‘Room’. The rooms we are cooling are akin to tiny little fridges in this big Room. Owing to heat loss to space, the whole earth cools off at night. But in the day itself, the reverse is true. Heat from sunlight is warming up the surfaces of earth and air, while these little fridges are doing their part to displace heat, and inevitably adding on ambient heat to the environment. Simply put, air-cons do not just ‘cool’ the rooms, it also heats up the environment.
In recent studies by scientists, simulations are pointing to a similar conclusion.
Human-made waste heat warms climate 
Energy dissipated as heat in cities can cause regional temperature changes, simulations suggest
The waste heat generated by car engines, power plants, home furnaces and other fossil fuel-burning machinery plays an unappreciated role in influencing regional climates, new computer simulations suggest. By altering atmospheric circulation, human-made heat may raise temperatures by as much as 1 degree Celsius during winter in the northernmost parts of the world.
From the air-conditioning to the pc or mobile, from the television in your living room to the car on the street and the plane in the sky, all appliances, equipments and machineries produce heat, and it is adding up.
Proposing to remove all these modern creature comforts (or to some, necessities) is impractical. Energy efficient appliances and cars can definitely help to reduce the amount of energy wasted, in most cases as heat.
Earth Day raises awareness by having people around the world turn off the lights for an hour at 8pm once a year. Perhaps it may be more effective to turn off the air-conditioner as well. After all, air-conditioners consumes much more energy than than lighting and merely displaces heat while producing heat at the same time!
Are we ready to live without or with lesser air-conditioning?
-  Does air-conditioning work?
-  Human-made waste heat warms climate