Over the past 100 years human activity has led to an increase in earth's average surface temperature. Scientists have measured the increase to be three-quarters of a degree celsius.
The global warming is caused by an increase in greenhouse gases like carbon dioxide. The extra CO2 enters the atmosphere. Then the CO2 acts like glass in a greenhouse. The suns rays pass through the atmosphere then when reflected heat energy tries to escape it gets trapped making earth warmer. This process is called the greenhouse effect.
Where is all of the extra CO2 coming from? Ever since the industrial revolution people have been using machines to produce goods. These machines burn fossil fuels like coal and oil. Burning fossil fuels produces greenhouse gases. Also, humans have been clearing forests using the wood to build homes. Trees naturally remove CO2 in the process of photosynthesis.
What could happen if humans don't change? Coral reefs could die leading to a change in the food chain. The polar ice caps could start to melt. The massive amounts of water could make the sea level rise. The coastlines would flood and affect the lives of many.
There are things you can do to help our planet. Use less electricity by turning off your lights. Setting the thermostat a few degrees cooler in the winter will save energy. Realize that the things you buy take energy to make and transport. Reuse shopping bags and look for products and packaging made of recycled mat.