The climate is changing because human activity — mainly energy use — has put billions of extra pounds of carbon dioxide into the atmosphere. This has been going on for over 150 years, ever since the beginning of the industrial revolution in the 1800s.
The amount of carbon dioxide in our atmosphere is now 150% (one and a half times) of what it was naturally, because of burning of fossil fuels: coal, natural gas, and oil products (gasoline and others).
The problem with too much carbon dioxide in the air is that it traps heat. Carbon dioxide has a physical way of absorbing heat from the ground that would otherwise escape to space. Other chemicals in the air, like natural gas (methane) also do this. The extra carbon dioxide from so much burning of fossil fuels stays in the atmosphere for thousands of years. That is why it is creating such a long-term problem. (Methane is worse for heat trapping, but it leaves the atmosphere in 10 or 20 years.)
Scientists have been measuring the changes on earth that so much carbon dioxide in the atmosphere has been causing. Their many discoveries are explained on other pages here, to help you understand the many ways our climate and oceans are becoming dangerously un-normal.
Click here to find pages that describe damages happening because of global warming. Click here to learn about thing you can do to reduce emissions of carbon dioxide and methane.