Why is important to find alternative energy sources?
In addition to the above answers, which are all valid and important points, we can also look at this from a national security and independence viewpoint.
We import 2/3 of the oil we use, and much of that comes from unstable countries (Nigeria, Iraq), or nations under the rule of a dictator (Saudi Arabia, Kuwait) where human rights violations are common. We have had forces in and around Iraq for decades now, in order to secure this resource, which is very expensive, costly in terms of life and limb, and has the side effect of encouraging radical Islam. So one could argue that alternative energy could free us from dependence on these regions, and the foreign policy consequences that come with that dependence.
It is very important to do this for two reasons.
First, and perhaps most important, we are in danger of ruining the planet's climate through carbon dioxide emissions. If we continue to use fossil fuels, we may increase the temperature of the planet in ways that will harm us and our entire ecosystem.
Second, we cannot keep using fossil fuels forever. They will eventually run out, even as the population of Earth grows.
For both these reasons, we need to find other sources of energy that do not emit carbon dioxide when used.
Over the past two hundred years mankind has managed to do more damage to the environment through exorbitant use of fossil fuels. We have caused acid rain which affects our fauna, trees, and water systems, and we have depleted the ozone layer. Some cities have such as dangerous level of pollution in the atmosphere that on certain days people wear masks (usually people who have respiratory illnesses). Incidents of respiratory related illnesses as well as non-smoking related lung cancer have increased with a strong correlation to the polluted atmosphere.
The second concern is the need to find replacement fuels because the people on earth are rapidly using up resources that can not be replaced. Trees are being harvested at a rapid rate leaving topic soil uncovered and causing run off. The fuels like coal and oil are going to run out for future generations if something is not done. The fuels were made by species that no longer exit after millions of years of time to decay and transfer. Time is no longer on mankind's side.
The last primary concern is the condition of the ozone layer. The earth has always had a protective layer in the atmosphere which protected the plant from too much heat entering or exiting our planet. The carbon emissions have caused a hole that is still increasing in the ozone area. This has caused increased warming of our planet.
The damage to our water system has been a result of pollution and the hole in the ozone layer. The hole in the ozone has caused ice burgs to melt. The ice burgs are a source of fresh water supply. Because of the damage of ice in the Polar Regions, species are losing their environment and dying off.
Fossil fuel use has also led to damage for species on the planet. For example; the oil spills that have happened have caused the death of many different species, polluted the water system, and destroyed habitats. Air pollution also affects animals.
It is vital for mankind to find cleaner fuel resources to replace fossil fuels because of the reasons that I listed. Alternative energy possibilities include but are not limited to hydro energy produced by water movement, wind energy harnessed from moving air, thermal energy found in underground heated systems, and plant related fuels.